52951390 Pawels Trans A

Manual Part A

Installation, Operation and Maintenance Instructions

Pauwels Power Transformers

PAUWELS TRAFO http://www.pauwels.com/Antwerpsesteenweg 167 Tel: ++ 32 / (0) 15 / 283 333B-2800 Mechelen Fax: ++ 32 / (0) 15 / 283 300

http://www.pauwels.com/

Installation, Operation and Maintenance Instructions 4001158/ dmyra. – Mechelen, (7/10/2009 10:21)


Serial Number: 4001158

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Transformer: 95 MVA Year of manufacture: 2009 Manufacturer: PTB

Manufacturer serial number: 4001158

Customer: SEC WOA


Serial number: 4001158

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General Index

1 General information ...................................................................................................................15 1.1 General information ...........................................................................................................17

1.1.1..IOM-manual structure ..............................................................................................17 1.1.2..Safety instructions and notes ..................................................................................17 1.1.3..Use of most important drawings ..............................................................................17 1.1.4..General figures used in the text...............................................................................18 1.1.5..Use of checklists and forms.....................................................................................18 1.1.6..Special instructions..................................................................................................18 1.1.7..For more information ...............................................................................................18

1.2 Safety practice for transformers and related electrical equipment ....................................19 1.2.1..Basic safety practice................................................................................................19 1.2.2..Transformer specific safety practice........................................................................19 1.2.3..Voltage hazards and temporary grounding (earthing) systems for transformers....20

1.3 Material Safety Data Sheets(MSDS) .................................................................................22 1.4 Warranty period and conditions .........................................................................................22

1.4.1..Actions to be taken at installation and commissioning ............................................23 1.4.2..Actions to be taken in case of severe abnormal conditions ....................................23

1.5 Insurance ...........................................................................................................................23 1.5.1..Transfer of risks .......................................................................................................23 1.5.2..Transportation damage............................................................................................23 1.5.3..Informing Pauwels ...................................................................................................24

1.6 Tables ................................................................................................................................24 1.6.1..Correction factors for megger and power factor tests .............................................24 1.6.2..Torque values for bolt-nut connection .....................................................................24 1.6.3..Torque values for SEFCOR connectors ..................................................................25

1.7 Conversion tables ..............................................................................................................26 2 General transformer description ..............................................................................................33

2.1 General electrical and mechanical data.............................................................................35 2.1.1..Nameplate: ..............................................................................................................35 2.1.2..General Arrangement Drawing................................................................................35 2.1.3..Schematic Control and Schematic Motor drive unit ................................................35 2.1.4..Test Reports ............................................................................................................35 2.1.5..Overload capability ..................................................................................................35



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2.2 Information on mechanical transformer parts.................................................................... 35 2.3 Tank design....................................................................................................................... 36

2.3.1. General tank design ................................................................................................ 36 2.3.2. Tank handling.......................................................................................................... 36 2.3.3. Protective measures in tank design ........................................................................ 36 2.3.4. Tank accessories .................................................................................................... 36

2.4 Non-membrane conservator design.................................................................................. 37 2.5 Transformer grounding (earthing) and equipotential bonding........................................... 37

2.5.1. Introduction ............................................................................................................. 37 2.5.2. Parts to be grounded (earthed)............................................................................... 37

2.6 Transformer Painting......................................................................................................... 39 2.6.1. Painting system....................................................................................................... 39

3 Packing, Transport, Receiving, Storage.................................................................................. 41 3.1 Packing.............................................................................................................................. 43

3.1.1. General.................................................................................................................... 43 3.1.2. Transformer body.................................................................................................... 43 3.1.3. Condenser bushings ............................................................................................... 43 3.1.4. Hygroscopic electrical parts .................................................................................... 43 3.1.5. Radiators................................................................................................................. 43 3.1.6. Conservator, pipes and cable boxes....................................................................... 44 3.1.7. Control cabinets ...................................................................................................... 44

3.2 Transport and handling ..................................................................................................... 44 3.2.1. General transport and handling notes..................................................................... 44 3.2.2. Handling instructions during loading and unloading ............................................... 45 3.2.3. Blocking and securing............................................................................................. 46 3.2.4. Shipping documents................................................................................................ 46

3.3 Receiving........................................................................................................................... 46 3.3.1. Inspection of damage.............................................................................................. 46 3.3.2. Transformer inspection procedure .......................................................................... 47

3.4 Impact recorder ShockLog RD298.................................................................................... 49 3.5 Performing internal inspections ......................................................................................... 49

3.5.1. Reasons to perform an internal inspection ............................................................. 49 3.5.2. Planning the inspection........................................................................................... 50 3.5.3. Procedure of an internal inspection ........................................................................ 50

3.6 Dew point measurement ................................................................................................... 50



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3.7 Storage...............................................................................................................................51 3.7.1..Storage of the transformer.......................................................................................52 3.7.2..Storage of accessories ............................................................................................52 3.7.3..End of storage .........................................................................................................54

4 Assembling and installation .....................................................................................................55 4.1 Locating a transformer .......................................................................................................57

4.1.1..Preparation to move a transformer..........................................................................57 4.1.2..Positioning a transformer on its final destination.....................................................58

4.2 General installation topics..................................................................................................60 4.2.1..Planning of the installation.......................................................................................60 4.2.2..Recommended assembling and energization sequence.........................................60 4.2.3..Collecting and preparing the required equipment ...................................................61

4.3 Installation of the transformer body ...................................................................................62 4.3.1..Grounding the tank ..................................................................................................62 4.3.2..Preparation of the transformer before assembling accessories..............................62

4.4 Installation of accessories..................................................................................................62 4.4.1..Unpacking accessories............................................................................................63 4.4.2..Preparing accessories .............................................................................................63 4.4.3..Equipment safety during installation........................................................................63 4.4.4..General assembling instructions for accessories ....................................................63

4.5 Installation of Conservator and Pipes ................................................................................66 4.6 Installation of radiators.......................................................................................................68

4.6.1..Mounting instructions...............................................................................................68 4.6.2..Different types of gaskets used ...............................................................................69 4.6.3..Filling radiators for (partially) oil-filled transformers.................................................69 4.6.4..Draining oil from a radiator ......................................................................................69 4.6.5..Disassembling a radiator from a filled transformer..................................................70

4.7 Installation of CTs ..............................................................................................................71 4.7.1..Current transformers for bottom–connected bushings (phase / neutral)................71 4.7.2..Current transformers for draw lead bushings (phase / neutral)..............................71

4.8 Wiring on the transformer ..................................................................................................71 4.8.1..Mounting instructions...............................................................................................72

4.9 Oil quality requirements .....................................................................................................72 4.9.1..New transformer oil..................................................................................................72 4.9.2..Oil treatment (degassing, streamlining)...................................................................73



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4.9.3. New treated transformer oil in new equipment ....................................................... 73 4.9.4. Transformer oil for transformers in service ............................................................. 73

4.10 ..Pulling vacuum .................................................................................................................. 73 4.10.1Before pulling vacuum............................................................................................. 74 4.10.2Establishing connections......................................................................................... 74 4.10.3Pulling vacuum........................................................................................................ 75 4.10.4Troubleshooting ...................................................................................................... 75

4.11 ..Oil filling standard.............................................................................................................. 75 4.11.1Oil filling................................................................................................................... 75 4.11.2Filling procedure in the event of process interruption ............................................. 77

4.12 ..Topping up oil after initial vacuum filling ........................................................................... 77 4.13 ..Air venting.......................................................................................................................... 78 4.14 ..Pre-operational tests ......................................................................................................... 78

4.14.1Mechanical tests and checks .................................................................................. 79 4.14.2Oil sampling and testing.......................................................................................... 79 4.14.3Electrical tests ......................................................................................................... 79

4.15 ..Pre-operational tests and checks of accessories.............................................................. 79 4.16 ..Oil sampling and testing .................................................................................................... 81

4.16.1Sampling ................................................................................................................. 81 4.16.2Required oil quality tests ......................................................................................... 81 4.16.3Oil quality requirement ............................................................................................ 81

4.17 ..Megger test (Required) ..................................................................................................... 81 4.17.1Winding insulation megger test............................................................................... 81 4.17.2Core grounding megger test ................................................................................... 82 4.17.3Accessories insulation megger test ........................................................................ 83

4.18 ..Voltage ratio test (Required) ............................................................................................. 83 4.18.1Ratio meter method................................................................................................. 83 4.18.2Voltage ratio test for turns ratio............................................................................... 83

4.19 ..Vector group test (Optional) .............................................................................................. 83 4.20 .. Insulation power factor test or TAN δ (Special)................................................................. 84 4.21 ..Bushing power factor test (Special test)............................................................................ 85 4.22 ..Winding resistance test (Special test) ............................................................................... 85 4.23 ..Continuity impedance check (Special test) ....................................................................... 86 4.24 ..Removal of surface moisture............................................................................................. 87

4.24.1Removal of surface moisture by vacuum................................................................ 87



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4.24.2Removal of surface moisture by dry air recycling....................................................87 5 Commissioning ..........................................................................................................................89

5.1 Repeating pre-operational tests.........................................................................................91 5.1.1..Energization follows within 4 weeks after installation and testing ...........................91 5.1.2..Energization follows 4 weeks to 6 months after installation and testing .................91 5.1.3..Energization follows later than 6 months after installation and testing....................91

5.2 Operational system tests ...................................................................................................91 5.2.1..Alarm circuits and contacts......................................................................................91 5.2.2..Trip circuits and contacts .........................................................................................92 5.2.3..Remote control ........................................................................................................92 5.2.4..Temperature settings...............................................................................................92 5.2.5..Verification of overpressure relief devices...............................................................92 5.2.6..Voltage relation check .............................................................................................92

5.3 Energization .......................................................................................................................92 5.3.1..Minimum oil stabilising period after final oil filling....................................................93 5.3.2..First energizing at no load conditions. .....................................................................93 5.3.3..Loading the transformer...........................................................................................94

6 Maintenance................................................................................................................................95 6.1 Transformer maintenance..................................................................................................97

6.1.1..Safety during maintenance......................................................................................97 6.1.2..General maintenance guidelines .............................................................................97 6.1.3..External cleaning .....................................................................................................97

6.2 Periodic Inspection of transformers in service ...................................................................98 6.2.1..Oil levels and silica gel ............................................................................................98 6.2.2..Oil quality .................................................................................................................98 6.2.3..Venting.....................................................................................................................98 6.2.4..External circuits and control equipment...................................................................98 6.2.5..(On) Load tap changer – (O)LTC ............................................................................98 6.2.6..De-energized tap changer – DTC............................................................................98 6.2.7..Cooling system ........................................................................................................99 6.2.8..Fans.........................................................................................................................99 6.2.9..Temperature ............................................................................................................99 6.2.10Inspection of tank, cover, gaskets and valves...................................................... 100 6.2.11Periodic electrical testing...................................................................................... 100

6.3 Periodic inspection of transformers in storage................................................................ 100



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6.4 Maintenance inspection chart.......................................................................................... 101 6.4.1. Frequency indications ........................................................................................... 101 6.4.2. Maintenance activity to perform ............................................................................ 101

6.5 Troubleshooting............................................................................................................... 104 6.5.1. Electrical malfunction ............................................................................................ 104 6.5.2. Mechanical malfunction or malfunction of accessories......................................... 105

6.6 Oil quality......................................................................................................................... 106 6.7 Oil sampling..................................................................................................................... 106

6.7.1. Taking samples for general oil testing purposes .................................................. 106 6.7.2. Taking samples for DGA tests .............................................................................. 107

6.8 Dielectrical strength......................................................................................................... 107 6.9 Moisture content .............................................................................................................. 108 6.10 ..Particles in oil .................................................................................................................. 108 6.11 ..Dissolved Gas Analysis on transformer oils from the main tank of a transformer .......... 109 6.12 ..Frequency of analysis ..................................................................................................... 109 6.13 ..Evaluation........................................................................................................................ 109

6.13.1Actions................................................................................................................... 111 6.14 ..Replacement of defective parts....................................................................................... 112

6.14.1Ordering replacement or spare parts .................................................................... 112 7 Forms, checklists .................................................................................................................... 113

Receiving inspection report ....................................................................................................... 115 Energization Report ................................................................................................................... 117 Parts ordering form (1) ................................................................................................................ 119 Site commissioning report ......................................................................................................... 121

8 Special instructions................................................................................................................. 137 8.1 Special instructions ......................................................................................................... 139



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Index of tables

Table 1 Minimum recommended (temporary) grounding cable size for copper cable .................. 22 Table 2 Temperature correction factors for megger (K1) and power factor or tan δ tests (K2)........ 24 Table 3 Max. spanner values for bolt – nut connections ............................................................... 24 Table 4 Recommended torque values for SEFCOR connectors................................................... 25 Table 5 International System of units (SI) (Metric practice)........................................................... 26 Table 6 Multiplication factors ......................................................................................................... 26 Table 7 United States System ....................................................................................................... 27 Table 8 SI conversion factors ........................................................................................................ 29 Table 9 Conversion table for pressure and stress ......................................................................... 30 Table 10 Dew point measurement ................................................................................................... 51 Table 11 Minimum number of rods required per set under the transformer .................................... 59 Table 12 Required vacuum pump capacities................................................................................... 61 Table 13 Oil treatment...................................................................................................................... 73 Table 14 Required vacuum for flashing surface moisture ............................................................... 87 Table 15 Vacuum hold times for flashing surface moisture ............................................................. 87 Table 16 Maintenance inspection chart ......................................................................................... 103 Table 17 Electrical malfunction troubleshooting chart ................................................................... 104 Table 18 Mechanical malfunction troubleshooting chart................................................................ 105 Table 19 Water in oil ...................................................................................................................... 108 Table 20 Particles in oil .................................................................................................................. 108 Table 21 Limits for normal values for Pauwels Transformers........................................................ 109



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Table of figures

Figure 1 Example of SEFCOR connector ....................................................................................... 25 Figure 2 Parts to be grounded (earthed)......................................................................................... 38 Figure 3 Outside oil drum storage (method 1) ................................................................................ 53 Figure 4 Outside oil drum storage (method 2) ................................................................................ 53 Figure 5 Sequence of tightening bolt – nut connections (1 -> 2 -> 3 -> 4 -> …)............................. 64 Figure 6 Different types of gaskets ................................................................................................. 65 Figure 7 Gasket joint ....................................................................................................................... 66 Figure 8 Conservator and pipes assembly...................................................................................... 67 Figure 9 Example of radiator No. 92 ............................................................................................... 68 Figure 10 Drain plug No. 95 .............................................................................................................. 70 Figure 11 Vent plug No. 94 ............................................................................................................... 70 Figure 12 Throttle valve No. 93 open................................................................................................ 70 Figure 13 Throttle valve No. 93 closed ............................................................................................. 71 Figure 14 Equalizing pipe connections ............................................................................................. 74 Figure 15 Transformer filling (without conservator) .......................................................................... 76 Figure 16 Transformer filling with conservator .................................................................................. 77 Figure 17 Core grounding assembly ................................................................................................. 83 Figure 18 Vector group test............................................................................................................... 84 Figure 19 Bushing testtap ................................................................................................................. 85 Figure 20 Capacitive bushing representation ................................................................................... 85



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1 General information



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1.1 General information

This transformer Installation, Operation and Maintenance manual (IOM-manual) is your guide to installing and energizing the Pauwels transformer(s). This IOM-manual contains important information for the safe and reliable use of the transformer(s).

Please read this IOM-manual completely before starting installation and commissioning.

NOTE Pauwels cannot be held responsible for any damage due to improper handling, installation, use or maintenance of the equipment. If you have any doubts about how to proceed, we advise you to contact your Pauwels contact person or the nearest Pauwels representative directly. Should you feel unconfident about installing and/or energizing the transformer completely on your own, feel free to contact us. We will be at your service to provide more information on complete installation and commissioning programs or on supervising programs.

1.1.1 IOM-manual structure

This IOM-manual has a logical structure following the sequence of activities from transportation over commissioning to maintenance. A main index listing the available chapters is included in the beginning of the manual.

The IOM-manual consists of 3 parts:

• Part A: Installation, Operation and Maintenance Instructions

• Part B: Documentation of Transformer Accessories

• Part C: Transformer Drawings In the Manufacturing Data Record Book (MDRB) – a separate binder – the test reports of the transformer and its accessories are included.

1.1.2 Safety instructions and notes

All personnel involved in installation, commissioning, operation, maintenance or repair of the equipment must:

• be suitably qualified and • strictly observe these IOM Instructions

Improper operation or misuse can lead to:

• a reduction in the efficiency of the equipment • damage to the equipment and property of the

user • serious or fatal injury

Safety instructions in this manual are presented in three different forms to emphasize important information.

DANGER This kind of information indicates particular danger to life and health. Disregarding such a warning can lead to serious or fatal injury.

CAUTION This kind of information indicates particular danger to the equipment or other property of the user. Serious or fatal injury cannot be excluded.

NOTE Notes provide important information on a certain subject.

1.1.3 Use of most important drawings

The text will often refer to specific drawings [part C]. In many cases part numbers will be given. These numbers refer to the General Arrangement Drawing and the Materials List, e.g.: Drain Plug No. 95.

The most important drawings are the following:



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The General Arrangement Drawing: shows a side, top and front view of the transformer. The dimensions and weight of the fully assembled transformer are given, as well as the weight of the oil. All important components are identified by "item numbers" which relate to the Materials List.

The Materials List: can be printed on the General Arrangement Drawing or on a separate document. The Materials List gives the type and brand of most accessories.

Schematic Drawings (of Control & Protection Circuits and Motor Drive Unit): give information on the connection between the different protective devices mounted on the transformer.

Name Plate (or Rating Plate): gives the main electrical characteristics.

1.1.4 General figures used in the text

The text contains figures that sometimes indicate specific types of equipment and/or specific dimensions. These figures are provided to explain general principles and situations. Neither the type nor the dimensions of these figures necessarily apply to the purchased transformer. Only type and dimensions on the drawings [part C] apply to the purchased transformer.

This IOM-manual includes a list of figures after the general index.

1.1.5 Use of checklists and forms

The text refers to several checklists and forms that can be found in section [7]. Some of them have to be completed and forwarded to your Pauwels contact person as soon as possible.

For your convenience, we would advise you to make additional copies of these checklists in order to keep a complete IOM-manual for future use. The most important checklist is the “Site commissioning report”. This report must be completed and returned before energization of the transformer.

1.1.6 Special instructions

In case the transformer installation, operation or maintenance requires special instructions, these instructions are included in section [8]. The special instructions are specifically written for the transformer.

NOTE Always consult the special instructions section [8] to verify if special procedures have to be followed during installation, operation or maintenance.

1.1.7 For more information

1.1.7.1 Your Pauwels contact person

During production, transportation and installation you have continuously been in contact with the Pauwels Project Manager. He is the one who is responsible for the complete execution of the order until the end of the warranty period. In case of any questions or problems, contact this person and he will help you as soon as possible. Normally, you will have his coordinates at hand.

PAUWELS INTERNATIONAL N.V. Antwerpsesteenweg 167 2800 MECHELEN BELGIUM Tel: ++ 32 / (0) 15 / 283 333 (8 am – 5 pm) Fax: ++ 32 / (0) 15 / 283 300

1.1.7.2 Pauwels Transformer Service

Pauwels Transformer Service (PTS) is the Pauwels service department. They can handle all operation related topics such as:

• installation and commissioning • site testing and inspection • maintenance and repair works • ordering of repair, spare or additional parts • supervision on above activities



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During the complete warranty period PTS receives its instructions from the Pauwels Project Manager for all warranty related topics. However, in very urgent cases you can always contact PTS for advice.

For problems or questions after the warranty period has expired or for additional parts or materials (not included in the scope of the order) you can contact PTS directly.

PAUWELS TRANSFORMER SERVICE Rue Vital Françoisse 220 6000 CHARLEROI BELGIUM Tel: ++32 / (0) 71 / 47 25 25 Fax: ++32 / (0) 71 / 47 01 89

1.2 Safety practice for transformers and related electrical equipment

1.2.1 Basic safety practice

Every employee must have a safety program and he has to know how to use it in the event of an accident.

Ensure that safety equipment and tools are always close at hand.

Keep suitable fire extinguishing equipment and qualified personnel available. Make sure that the equipment used is suitable for fire involving oil filled electrical installations.. Make sure that it is correctly charged and that you know how to use it.

Always be alert to emergencies. If an accident should occur, quickly utilize the safety equipment, emergency tools and equipment at hand. Before you begin a project, ensure that at least two people know first aid procedures and that they have the proper first aid kits at hand.

Ensure that all protective equipment required for the job is available to all workers and ensure that it is used correctly. This equipment may include hard-hats, breathing apparatus, eye protection, gloves, foot protection, …

Ensure that all electrical circuits to be worked on have been traced and de-energized. Ensure that all safety grounds have been correctly applied to protect personnel against the accidental application of power to these circuits (refer to chapter 2 for more information on temporary grounding.) Do NOT assume that someone else has turned off the power, check for yourself.

Use the padlock and key interlock system where available to protect yourself and others.

Do not work under equipment that is raised and insecurely blocked. Do not walk under equipment that is suspended from a crane.

Do not walk holding a ladder or any other long object near a transformer or overhead lines under voltage.

Before lifting any object by any means, ensure that its weight can be handled correctly. Use the appropriate lifting or handling tools.

Do not work on or adjust moving equipment. Do not work on or adjust mechanical equipment unless its motive source has been deactivated.

1.2.2 Transformer specific safety practice

Do not walk on a transformer or its parts unless the unit has been de-energized.

Do not walk on a transformer under vacuum. Never perform any electrical tests on a transformer under vacuum. Do not apply vacuum when it is raining or when the transformer is unsupervised.

When pressure tests are being performed or when vacuum is being applied, the pressure must be equalized between the main tank and the (On) Load Tap Changer compartment if these compartments are separated by terminal panels which might not be able to withstand pressure differences mechanically. Find out which parts will not be able to withstand a complete vacuum.

Before removing any cover plate or transformer fitting, ensure that the overpressure inside the transformer is zero and that the oil level is lower than the opening in question.



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In the event of a sudden change in the weather bringing penetrating rain or snow, provisions must be made for closing the tank quickly and pressurizing it with nitrogen in order to preserve the insulation.

To allow anyone entering a transformer the air has to support life with a sufficient oxygen level (19.5 %).

Extreme precautions are to be taken to protect the insulation of the transformer from any damage and to prevent the ingress of foreign objects and moisture during the checking and erection of the transformer.

Whilst the transformer is open, no one may be allowed on top of it, unless this person has emptied his/her pockets, has checked himself/herself for the presence of objects such as watch, rings etc. and has removed them. These precautions must be taken to prevent objects from falling into the transformer.

Anyone going inside a transformer must wear clean clothes and clean synthetic-rubber boots.

Never stand directly on any part of the insulation.

Clean rags, sheets of paper, etc. are to be used under the working surfaces in the transformer to prevent objects from falling into the windings.

All tools must be listed. For “safety first” reasons they must be attached to the wrists or belt, so that they cannot fall into the windings.

Smoking is not allowed on the transformer, nor is it allowed in the vicinity of an oil-processing plant.

Lamps used for lighting the inside of the transformer must be the shielded type with a maximum voltage of 36 V. Debris from a broken lamp bulb may not be able to drop out.

• If in spite of all preventive measures something does fall into the transformer tank and cannot be retrieved, do not proceed with the energization and do not perform any electrical tests that may cause damage to the transformer. Immediately contact Pauwels instead.

Correct operation of all protective circuits and protective devices for the transformer should be checked on a regular basis. Neglection of these

circuits or devices, or overriding of the functions of these circuits or devices could allow minor problems to develop into a major problems. This may result in a total loss of the transformer, damage to other equipment and injury of personnel.

A pressure relief device incorporates heavy spring in compression, DO NOT DISMANTLE such a device, unless suitable safeguards have been implemented, otherwise personnel injury may occur.

Recommended commissioning checks must be performed before the first energization of the transformer.

1.2.3 Voltage hazards and temporary grounding (earthing) systems for transformers

1.2.3.1 Voltage hazards

The turns ratio between the windings of any power transformer makes them capable of transforming what are normally considered harmless voltages into dangerous and even lethal levels.

Electrical welders, continuity checking instruments and insulation testing apparatus are examples of sources of so-called harmless voltages. Even if these are direct current (DC) devices, they are capable of producing voltages high enough to be hazardous to human life, when the circuits they are connected to are made or interrupted.

Other situations which may present hazardous conditions include the high voltage produced by open circuited current transformers (including these which are used for Winding-Temperature-Indicators, WTIs) which have current flowing in the primary circuits and the electrical charge which may by retained by condenser style bushings after the transformer has been disconnected from the external circuits. The open circuit voltage that is developed depends on the design of the CT, but is nearly always dangerously high. NEVER disconnect a CT secondary while the primary circuit is energized. CTs must be connected to a suitable load or must be shorted by a link that is suitable for carrying the rated secondary current.



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Delta-connected windings that are not connected to any external circuit may also retain a charge after the transformer has been de-energized for a period of time.

DANGER For personnel and equipment safety reasons: ground the transformer tank as soon as possible, ground all bushings whenever possible and connect CT secondary circuits to a suitable load or short-circuit them.

1.2.3.2 Preventive measures

When personnel is working on de-energized transformers, winding terminals should be suitably short-circuited and grounded according to the correct safety practice in order to avoid injury or even death (see section below).

Unused current transformers must always have their secondary windings short-circuited with suitably sized wire to avoid high open circuit voltages.

a) Recommendations concerning temporary grounding (earthing) systems

Temporary groundings, used while personnel are working on de-energized transformers, must always be applied in accordance with the approved safety and operation practices issued by the employer. In addition, they must be in accordance with the instructions for the specific grounding equipment used.

Temporary grounding is required for a number of reasons:

• Induced voltage from adjacent energized lines. • Fault current feed-over from adjacent lines. • Lightning strikes anywhere on the circuit. • Switching equipment malfunction or human

error. • Accident initiated contact with adjacent lines.

It is important to ground ALL terminals of the transformer (not just HV circuit) to protect against back-feed from the low voltage or tertiary voltage circuits.

Only screw type grounding clamps may be used. Clip-on clamps are not acceptable. Clamps must always be securely tightened. Clamps and cable size are to be selected in accordance with the short circuit capability of the power system at the transformer terminals and for the maximum duration of time that the fault current will flow before the protection system de-energizes the circuit. If the actual fault capacities are not known, National Standards provide recommended levels that can be used.

Grounding cables are to be securely lashed to structural members or other fixed objects to prevent violent whipping of the cable due to electromagnetic forces developed by the flow of the fault current (violent whipping may loosen or disconnect the ground clamps). For similar reasons, no slack or loops in the grounding cables may be allowed.

If multiple grounding cables are used in parallel, they must be twisted or lashed together to prevent mechanical reaction between the cables during the flow of fault current. The grounding clamps must be installed touching each other to prevent them from pulling together and from possible loosening during a fault.

Groundings are to be applied from each of the transformer terminals to the station grounding bus. Phase-to-phase jumpering after one phase has been grounded is permissible. This short circuit limits the amount of fault current which circulates through the grounding cable back to the phases. Jumpering is usually not suitable in HV switchyards due to the large inter-phase clearances.

b) Minimum grounding (earthing) cable sizes

The following minimum grounding cable sizes are recommended, in association with suitably sized screw type grounding clamps:



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Min. cable size per phase Max fault

current

Max duration of fault current AWG mm2

<22 kAmps 25 cycles 1x2/0 ~1x70 22-34 kAmps 25 cycles 1x4/0 ~1x110 34-60 kAmps 25 cycles 2x4/0 ~2x110

Table 1 Minimum recommended (temporary) grounding cable size for copper cable

c) Establishing the grounding (earthing) system

DANGER Ensure that at least one person is present who is trained in the correct application of temporary grounding systems.

In order to physically attach temporary groundings in a correct manner, first ensure that the circuits are intentionally de-energized. Use an approved voltage detector to assure yourself that the circuit is dead. Next, clean oxides and contaminants from the conductor to be grounded, whether it is cable or busbar. When attaching the screw type ground (earth) clamp, use the torque recommended in your safety procedures or by the clamp manufacturer.

1.3 Material Safety Data Sheets(MSDS)

Material Safety Data Sheets for the potentially hazardous materials and products are included in the documentation [part B]. The information in the MSDS refers only to new materials and products as manufactured, before their use in/on a transformer or electrical product.

The content of Material Safety Data Sheets may include:

• Identification of the Substance/Preparation and the Company/Undertaking

• Composition/Information of Ingredients • Hazards identification • First aid Measures • Fire-fighting Measures

• Accidental Release Measures • Handling and Storage • Exposure Controls/Persona Protection • Physical and Chemical Properties • Stability and Reactivity • Toxicological Information • Ecological Information • Disposal Considerations • Transport Information • Regulatory Information • Other Information

NOTE The information provided in the Material Safety Data Sheets is correct to the best of our knowledge at the date of its publication. The information given is designed as a guidance for safe handling, use, processing, storage, transportation, disposal, and release and is not to be considered as a warranty or quality specification. The information relates only to the specific material in combination with any other materials or in any other process, unless specified in the MSDS or in this IOM-manual.

1.4 Warranty period and conditions

Although the equipment is under warranty for a certain period, it is advisable to do whatever is necessary to minimize the impact of abnormal conditions.

• Minor problems may cause serious defects in certain cases.

• Never energize a transformer that is not fit for use.

• Always follow the instructions in this IOM-manual.

• In case of doubt, contact Pauwels

The applicable warranty period and conditions are indicated in the contractual terms and conditions.



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1.4.1 Actions to be taken at installation and commissioning

The warranty becomes operational on the condition that following steps have been taken:

1. Before energization: a complete (fax)copy of the “Site commissioning report” has been sent to your Pauwels contact person. Make sure that all tests and inspections have been satisfactory before energization. Especially all securing and protective accessories have to be checked. When not all parameters are according to the requirements, do not energize. We will evaluate the report and advise you how to proceed.

2. After energization: a complete (fax)copy of the “Energization report” has been received by Pauwels latest one week after energization.

Only upon receiving these 2 reports the contractual warranty conditions, concerning operational defects, will be applied.

During operation it is recommended to record all events (readings, inspections, tests, network conditions, …) in a transformer log book. This log book should be available at the time of an intervention.

1.4.2 Actions to be taken in case of severe abnormal conditions

First of all, take all necessary preventive measures to minimize the risks of damage. If the transformer has not yet been switched off by own securing systems, make it manually! A quick response often prevents things from getting worse. Once personnel are safe and equipment conditions are stabilized, contact your Pauwels contact person and provide as much information on the event as possible. Never start neither any corrective measures nor re-energizing without the approval of Pauwels.

1.5 Insurance

1.5.1 Transfer of risks

The transfer of risks is closely related to the delivery terms and conditions stipulated in the contract or order. We refer to the contractual terms and conditions for more information about which delivery term applies. For more information on delivery terms (FOB, CIF, DDU, …) and their implications, we refer to the international literature about this topic.

1.5.2 Transportation damage

NOTE Under no conditions should a damaged shipment or any part of that shipment be unloaded until the damage claim has been resolved with the carrier(s).

NOTE In case of any doubt, file a hidden damage claim. This allows for later filing of additional claims if hidden damage is detected during installation or commissioning.

Upon receiving a transformer and/or its accessories with visual external or potential (hidden) internal damage:

1. Check for visible damage before unloading 2. Check the impact recorder for high readings 3. When assessing the damages sustained by

packing and/or contents: describe your findings in the transport document intended for the carrier and be sure to keep a copy. If need be, write down a joint statement together with the driver.

4. You may subsequently unload.

Further procedure or assessment of damages after receipt:



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a) If you received an insurance certificate and/or in case land carriage was preceded by MARIN TRANSPORT 1. follow the instructions on the flip side of the

insurance certificate conscientiously 2. never sign any clean receipts but formulate

your reserve in these documents. 3. always inform our ”insurance” department

b) If you did not receive an insurance certificate and in case land carriage was not preceded by MARIN TRANSPORT 1. hold the carrier immediately liable by

registered letter 2. inform our transport and insurance

departments immediately 3. always do what is necessary to limit the

present damages and prevent subsequent damages.

c) In case of transport by rail: have the competent authorities make a report at the arrival station.

1.5.3 Informing Pauwels

Inform your Pauwels contact person as soon as possible. We assume all goods have arrived in good condition if one week after customs clearance, we have not received any damage report or statement from the customer. Section [7] contains a “Receiving inspection report” for this purpose. Complete this report and send it to your Pauwels contact person.

1.6 Tables

1.6.1 Correction factors for megger and power factor tests

Multiply the measured insulation resistance by the approximate correction factor, given by the table below, to bring the measured value back to a 200C reference temperature.

TºC 5 10 15 20 25 30K1 0.36 0.50 0.70 1.00 1.40 2.00K2 1.03 1.02 1.00 1.00 1.00 1.00

TºC 35 40 45 50 55 60K1 2.80 4.00 5.60 7.85 11.20 16.00K2 1.01 1.02 1.065 1.10 1.17 1.27

TºC 65 70 75 80 K1 22.00 32.00 45.00 62.00 K2 1.46 1.56 1.75 2.00

Table 2 Temperature correction factors for megger (K1) and power factor or tan δ tests (K2).

Megger test: Resistance at 20 0C = Resistance at mean oil temperature * K1

Power factor (or tan δ) test: Power factor at 20 0C = Power factor at mean oil temperature / K2

1.6.2 Torque values for bolt-nut connection

Maximum Torque values in Nm (a)

Without gasket (b) With gasket (c)

Bolt diameter Steel (8.8) bolts

Stainless steel (70) bolts

All bolt types

M 6 (x 1) 9 6 < 6M 8 (x 1.25) 22 16 < 8M 10 (x 1.5) 45 32 8 - 16M 12 (x 1.75) 77 56 16 - 24M 16 (x 2.0) 193 135 32 - 64M 20 (x 2.5) 369 273 M 24 (x 3.0) 639 471 M 30 (x 3.5) 1260 897 M 36 (x 4.0) 2340 1632

Table 3 Max. spanner values for bolt – nut connections



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Remarks:

This table applies to bolt – nut connections that are not greased (μ = 0.14 steel and 0.20 for stainless steel):

• the given values are in Nm and they are values at 80% of elasticity limit of the material.

• values in lbs-ft can be found by multiplying the Nm values by 0.737

• the simple method of “1/4 turns past tight” to tighten bolts, can be used if an appropriate torque spanner tool is not available. This however is not recommended.

Also considered as joints without gasket are (see also section [4]):

• Gasket systems with gasket grooves or gasket stops

• High density fiber gaskets

For impregnated cork and nitrile rubber the gasket material is the limiting factor. The general rule of 10 N/mm2 maximum pressure and 2N/mm2 minimum applies1.

Torque values for other bolt – nut material combinations can be found in the specific literature.

1.6.3 Torque values for SEFCOR connectors

1 This pressure range can be obtained by reducing

the gasket thickness to 2/3th of its original value.

Hardware

Silicon Bronze Aluminium Galv. Steel Stainless Steel

Bolt Dia (J)2

in-lb ft-lb N-m in-lb ft-lb N-m

5/16” 180 15 20.3 120 10 13.6 3/8” 240 20 27.1 180 15 20.3 1/2” 480 40 54.2 300 25 33.9 5/8” 660 55 74.6 480 40 54.2 3/4” 840 70 94.9 720 60 81.3

Table 4 Recommended torque values for SEFCOR connectors.

Remarks

• Connectors are not necessarily part of PAUWELS scope of supply.

• Recommended torque values do not necessarily apply for other connector brands. Please consult specific documentation.

Figure 1 Example of SEFCOR connector

2 See figure “Example of SEFCOR connector“



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1.7 Conversion tables

Quantity Unit of Symbol Formula Base units Length Meter m Mass Kilogram kg Time Second s Electric current Ampere A Thermodynamic temperature Kelvin K Amount of substance Mole mol Luminous intensity Candela cdSupplementary units Plane angle Radian rad Solid angle Steradian srDerived units (with special names) Force Newton N Kg m/s2 Pressure. Stress Pascal Pa N/m2 Energy. Work. Quantity of heat Joule J Nm Power Watt W J/sDerived units (without special names) Area Square meter m2

Volume Cubic meter m3

Velocity Meter per second m/s Acceleration Meter per second m/s2 Specific volume Cubic meter per kilogram m3/kg Density Kilogram per cubic meter kg/m3

Table 5 International System of units (SI) (Metric practice)

Multiplication factor Prefix SymbolSI Prefixes 1 000 000 000 000 000 000 = 1018 Exa E 1 000 000 000 000 000 = 1015 Peta P 1 000 000 000 000 = 1012 Tera T 1 000 000 000 = 109 Giga G 1 000 000 = 106 Mega M 1 000 = 103 Kilo k 100 = 102 Hecto h 10 = 101 Deca da 0.1 = 10-1 Deci d 0.01 = 10-2 Centi c 0.001 = 10-3 Milli m 0.000 001 = 10-6 Micro µ 0.000 000 001 = 10-9 Nano n 0.000 000 000 001 = 10-12 Pico p 0.000 000 000 000 001 = 10-15 Femto f 0.000 000 000 000 000 001 = 10-18 Atto a

Table 6 Multiplication factors



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Linear measure Inches Feet Yards Rods Furlongs Miles

1.0 .08333 .02778 .0050505 .00012626 .00001578 12.0 1.0 .33333 .0606061 .00151515 .00018939 36.0 3.0 1.0 .1818182 .00454545 .00056818

198.0 16.5 5.5 1.0 .025 .003125 7920.0 660.0 220.0 40.0 1.0 .125

63360.0 5280.0 1760.0 320.0 8.0 1.0 Square and land measure Sq. inches Sq. feet Sq. yards Sq. rods Acres Sq. miles

1.0 .006944 .000772 144.0 1.0 .111111

1296.0 9.0 1.0 .03306 .000207 39204.0 272.25 30.25 1.0 .00625 .0000098

43560.0 4840.0 160.0 1.0 .0015625 3097600.0 102400.0 640.0 1.0

Avoirdupois weights Grains Drams Ounces Pounds Tons

1.0 .03657 .002286 .000143 .0000000714 27.34375 1.0 .0625 .003906 .00000196

437.5 16.0 1.0 .0625 .00003125 7000.0 256.0 16.0 1.0 .0005

14000000.0 512000.0 32000.0 2000.0 1.0 Dry measure Pints Quarts Pecks Cubic feet Bushels

1.0 .5 .0625 .01945 .01563 2.0 1.0 .125 .03891 .03125

16.0 8.0 1.0 .31112 .25 51.42627 25.71314 3.21414 1.0 .80354

64.0 32.0 4.0 1.2445 1.0 Liquid measure Gills Pints Quarts U.S. Gallons Cubic feet

1.0 .25 .125 .03125 .00418 4.0 1.0 .5 .125 .01671 8.0 2.0 1.0 .250 .03342

32.0 8.0 4.0 1.0 .1337 7.48052 1.0

Table 7 United States System



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Quantity Multiply by to obtain

Ounce-force 0.278 014 Newton N Pound-force 4.448 222 Newton N Newton 3.596 942 Ounce-force oz.f

Force

Newton 0.224 809 Pound-force lbf Pound-force-inch 0.112 985 Newton-meter N-m Pound-force-foot 1.355 818 Newton-meter N-m Newton-meter 8.850 748 Pound-force-inch lbf-in

Torque

Newton-meter 0.737 562 Pound-force-foot lbf-ft Pound-force per square inch 6.894 757 Kilopascal kPa

Foot of water (39.2F) 2.988 98 Kilopascal kPa Inch of mercury (32F) 3.386 38 Kilopascal kPa

Kilopascal 0.145 038 Pound-force per square inch (psi) lbf/in2

Kilopascal 0.334 562 Foot of water (39.2F)

Pressure.Stress

Kilopascal 0.295 301 Inch of mercury (32F) in Hg Foot-pound-force 1.355 818 Joule J British thermal unit 1.055 056x103 Joule J Calorie 4.186 800 Joule J Kilowatt hour 3.600 000x106 Joule J Joule 0.737 562 Foot-pound-force ft-lbf Joule 0.947 817x10-3 British thermal unit Btu Joule 0.238 846 Calorie cal

Energy. Work. Heat

Joule 0.277 778x10-6 Kilowatt hour kW-h Foot-pound-force/second 1.355 818 Watt W British thermal unit per hour 0.293 071 Watt W

Horsepower (550ft.lbf/s) 0.745 700 Kilowatt kW

Watt 0.737 562 Foot-pound-force/second ft-lbf/s

Watt 3.412 141 British thermal unit per hour Btu/h

Power

Kilowatt 1.341 022 Horsepower (550ft.lbf/s) hp

Degree 17.453 29x10-3 Radian rad Angle

Radian 57.295 788 Degree Temperature Degree Fahrenheit tºC=( tºF-32)/1.8 Degree Celsius °C Degree Celsius tºF=1.8x tºC+32 Degree Fahrenheit °F Length Inch 25.400 Millimeter mm Foot 0.304 800 Meter m Yard 0.914 400 Meter m



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Quantity Multiply by to obtain

Mile (U.S.Statute) 1.609 347 Kilometer km Millimeter 39.370079x10-3 Inch in Meter 3.280 840 Foot ft Meter 1.093673 Yard yd Kilometer 0.621 370 Mile (U.S.Statute) mi Area Square inch 0.645160x103 Square millimeter mm2 Square foot 0.092 903 Square meter m2 Square yard 0.836 127 Square meter m2 Square mile (U.S.Statute) 2.589 998 Square kilometer km2 Acre 4.046 873x103 Square meter m2 Acre 0.404 687 Hectare ha Square millimeter 1.550 003x10-3 Square inch in2 Square meter 10.763 910 Square foot ft2 Square meter 1.195 990 Square yard yd2

Square kilometer 0.386 101 Square mile (U.S.Statute) mi2

Square meter 0.247 104x10-3 Acre Hectare 2.471 044 Acre Volume Cubic inch 16.387 06x103 Cubic millimeter mm3 Cubic foot 28.316 85x10-3 Cubic meter m3 Cubic yard 0.764 555 Cubic meter m3 Gallon (U.S. liquid) 3.785 412 Liter l Quart (U.S. liquid) 0.946 353 Liter l Cubic millimeter 61.023 759x10-6 Cubic inch in3 Cubic meter 35.314 662 Cubic foot ft3 Cubic meter 1.307 951 Cubic yard yd3 Liter 0.264 172 Gallon (U.S. liquid) gal Liter 1.056 688 Quart (U.S. liquid) qt Mass Ounce (avoirdupois) 28.349 52 Gram g Pound (avoirdupois) 0.453 592 Kilogram kg Short ton 0.907 185x103 Kilogram kg Gram 35.273 966x10-3 Ounce (avoirdupois) oz(avdp) Kilogram 2.204 622 Pound (avoirdupois) lb (avdp) Kilogram 1.102 311x10-3 Short ton

Table 8 SI conversion factors



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unity bar mbar Pa KPa MPa kgf/cm2 mm of mercury (torr)

mm of water psi

1 bar 1 1000 100.000 100 0.1 1.01972 750.062 10197.16 14.5038

1 mbar 0.001 1 100 0.1 0.0001 1.01972x10-3 0.7501 10.1972 0.0145

1 Pa 0.00001 0.01 1 0.001 0.000001 1.01972x10-5 0.0075 0.10197 0.000145

1 kPa 0.01 10 1000 1 0.001 0.010197 7.5006 101.972 0.145

1Mpa 10 10.000 1.000.000 1000 1 10.1972 7500.62 101972 145.038

1 kgf/cm2 0.981 980.7 98066.5 98.0665 0.09807 1 735.56 10.000 14.2233 1mm of mercury (1 Torr)

0.00133 1.333 133.3 0.13332 0.1333x10-3 0.001539 1 13.5951 0.01934

1 mm of water 0.000098 0.098 9.807 0.009807 9.807x10-6 0.0001 0.07356 1 0.00142

1 psi 0.06895 68.95 6895.06 6.895 6.895x10-3 0.07031 52.717 703.012 1

Table 9 Conversion table for pressure and stress



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33

2 General transformer description



34



35

2.1 General electrical and mechanical data

The supplied power transformer has been designed according to specific ratings and characteristics as listed on the drawings [part C]. The factory inspection results are provided in the Manufacturing Data Record Book (MDRB).

2.1.1 Nameplate:

General electrical data and network conditions, e.g.:

• Standard • Transformer type • Vector group • Rated power (MVA) • Voltages • Frequency • Number of phases .. • Tap positions • …

Working conditions

• maximum altitude above sea level • maximum temperature rise of winding and top

oil temperature

Other information

• Dielectric insulation levels • Connections for operation • Short-circuit conditions

2.1.2 General Arrangement Drawing

General mechanical data

• Dimensions: length, width, height of the completely assembled transformer

• Untanking height • Mass core and windings • Tank and fittings

Oil in: main tank, radiators, conservator (at 200C)

• Total liquid • Total mass • Shipping mass of heaviest part

2.1.3 Schematic Control and Schematic Motor drive unit

The schematic drawings provide all information concerning control and protection circuits and the corresponding settings.

2.1.4 Test Reports

All values measured during factory testing (as requested in the order) are listed on the test reports which are included in the MDRB.

• Excitation current • Load and no load losses • Percent impedance voltage • Zero-impedance voltage • Sound level • …

2.1.5 Overload capability

The transformer is designed to permit loading in accordance with the applicable standards. If tested during factory testing, the test results are available in the MDRB.

2.2 Information on mechanical transformer parts

Some mechanical parts and other topics require extra information. This is why the text below provides a short description of some of the major transformer parts. In addition, you will find information about the standard painting system used for the transformer



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2.3 Tank design

2.3.1 General tank design

The tank is a welded steel construction that is designed to operate over a range of top oil temperatures as per specified standard or customer specifications. Furthermore, the tank-cover-conservator combination can sustain the specified pressure and vacuum levels as per specifications.

For more specific details on the tank design, we refer to the General Arrangement Drawing.

The transformer tank, conservator and radiators are most likely designed for full vacuum, but to be sure always check the transformer nameplate.

CAUTION Never apply full vacuum unless the nameplate states that the tank / conservator has been designed for full vacuum.

2.3.2 Tank handling

The tank / cover has certain handling possibilities which are indicated on the General Arrangement Drawing. These might be:

• jacking bosses • lifting lugs • moving facilities (wheels) • Anchor lugs are provided to anchor the

transformer.

DANGER Before jacking, lifting or moving a transformer, always consult the General Arrangement Drawing to make sure that the right devices are used. Do not attempt to jack, lift or move a transformer at any time while it is under a vacuum. This applies even if a partial vacuum is present.

2.3.3 Protective measures in tank design

Although the tank is designed to withstand certain pressures, a pressure relief device (if requested) protects it against splitting under high internal pressures caused by exceptional working conditions. The tank may be supplied with an optional switch. A gas detector type Buchholz relay with alarm and trip contacts is a commonly used accessory for this purpose.

CAUTION Do not close a valve that may isolate a full oil-filled tank, because this can produce a very high internal over- or underpressure due to the thermal expansion of the oil. This can damage the transformer or parts of it. Besides this, humidity or water can penetrate and damage the insulation system.

DANGER Fault gases generated during operation are combustible, keep away from fire if gases release.

2.3.4 Tank accessories

The tank is provided with all necessary accessories according to customer specifications and in accordance with the applicable standard. For more information on specific accessories, please see documentation.



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2.4 Non-membrane conservator design

A non-membrane conservator has been used in order to take into account the rise and fall of the oil level due to changes in transformer loading and ambient temperature. The main tank is connected to the conservator through a pipe equipped with a valve. The air space in the conservator is directly in contact with the oil and it is connected to the atmosphere through a dehydrating breather.

This system requires a small amount of maintenance; ensure that the silica gel is replaced when needed. The period of time between two replacements depends on a number of factors such as relative humidity and rate of change of loading and ambient temperatures. This cannot be predicted in advance, periodic inspection is necessary.

To allow sufficient space for oil expansion, the internal capacity of the conservator is defined by the specified load and ambient temperatures listed in the standard and/or specifications. Furthermore, the conservator is provided with adequate access for cleaning, a shut-off valve to the main tank, and filling / draining devices.

For most load tap changer transformers the conservator contains a separate section for the (O)LTC (completely separate, no liquid or gas intermixing). Some (O)LTC designs may have a small, separate conservator. These will be clearly indicated on the General Arrangement Drawing [part C]

2.5 Transformer grounding (earthing) and equipotential bonding

2.5.1 Introduction

For safety of both personnel and equipment all metal parts and accessories of the transformer should be connected to ground potential.

2.5.2 Parts to be grounded (earthed)

Parts that are not welded to the tank or cover are connected with tank or cover by means of metal-strip in the factory. These connections have to be remade during installations.

Remarks:

• Connections made by bolts are not considered as connected to ground potential.

• Remove paint or rust before (re-)making grounding (earthing) connections.

Client grounding (earthing) connections are always found in accessible positions near the bottom of the tank (a minimum of 2 groundings/earthings diagonally located). For the exact location we refer to the General Arrangement Drawing [part C]:



38

Figure 2 Parts to be grounded (earthed)

1. Drycol breather 2. Conservator and parts 3. Tap changer 4. Bushing 5. Cable box 6. Current transformer 7. Lightning arrester 8. Current transformer 9. Marshalling kiosk Motor drive unit Drycol breather 10. Oil-air cooler 11. Radiator 12 Fan 13. Oil-water cooler 14. Pump 15. Equipotential bonding 25

mm2 (M6) 16. Grounding (earthing)

connection 70 mm2 (M12) 17. Ground connection client

(flat 30x10 / stainless steel)



39

The grounding (earthing) connections on the transformer are made of flexible copper strips of 70 mm2 with M12*20 bolts and washers.

The equipotential bonding is made of flexible copper strips of 25 mm2 with M6 bolts and washers.

The connection is made by means of stainless steel bolts and washers.

2.6 Transformer Painting

The transformer painting is always in accordance with the specifications of the customer.

Remark:

Preparation and painting of metal parts (conservator, pipes, radiators, ...) are equivalent to preparation and painting for the main transformer (unless otherwise specified).

2.6.1 Painting system

2.6.1.1 Preparation

In accordance with ISO 8501-1 : 1988 or SIS 55055900.

Sandblasting to class Sa 2 1/2 i.e. derusting to a clean metal surface. Previous painting, rust and mill scale are completely eliminated and a surface with very good adherence properties is obtained.

Depending on the specified painting system Zinc spraying or Hot-dip-galvanising may also be applied to the outside structures only.

2.6.1.2 Painting system

The different coats of paint are applied by spraying.

The painting system and color is indicated on the General Arrangement drawing. The two component painting system consists of one or more anti corrosive primer paint layers (EP) and a finishing

coat (PUR). The minimum total thickness of the EP layer(s) is 100 μm, the total thickness of the complete system (EP + PUR) is minimum 160 μm.

The painting system resists satisfactorily a salt spray test in accordance with ASTM-B117 specifications, for more than 1000 hours.

2.6.1.3 Qualities of the paint

a) Primer paint (EP)

Two components, polyamine adduct cured epoxy paint. Contains zinc phosphate and mio.

Composition:

Solvents: Xylen, …

Solids (62%): - resin: epoxy - pigments: zinc phosphate, colour pigments - micaceous iron oxide - additives

Adhesion after polymerization: cross cut test in accordance with ISO 2409, class 0

b) Enamel (PUR)

A two components acrylic polyurethane coating with micaceous iron oxid.

Composition:

Solvents: aromatic hydro carbons Solids (54%):

- resin: acrylic - color pigments - micaceous iron oxid - additives

Adhesion after polymerization on primer paint: cross cut test in accordance with ISO 2409, class: 0

Aspect: matt, gloss meter GARDNER 60°: 35% (unless otherwise specified)

Color: see General Arrangement drawing



40

Corrosion resistance: salt spray test following ASTM-B117: 5 % NaCl. After 1000 hours at a thickness of 100 µm rust extension max. 0.5 mm.

2.6.1.4 All inner transformer surfaces

Preparation: identical to outside structures

System: a two component epoxyprimer, 30 µm, white

Qualities of the paint:

- contains zincphosphate and is oil resistant

- after submerging in oil and in combination with high temperatures (120 °C) there might be only a slight discolorisation



41

3 Packing, Transport, Receiving, Storage



42



43

3.1 Packing

3.1.1 General

The packing type, dimensions, weights and degree of protection depend on:

• Allowed dimensions and/or weight for handling and transport

• Means of transportation (railway, road, seatransport, …)

• Legal obligations concerning transportation • Limitations given by roads, railways, … • Limitations due to local handling equipment • Customer specifications

Each package is marked and contains a packing-list. These packing lists will be a usefull tool during installation on site so make sure that they stay with the packages.

3.1.2 Transformer body

The transformer body is not packed (unless otherwise specified), sensitive parts (especially on the top) are protected by wooden barriers or metal caps. Shock recorders are provided if specified. (See further in this section)

All openings of the transformer tank, radiators, cover, oil-filled cable boxes, turrets of the bushings or conservator, etc.., have been sealed by blind flanges. All dismounted parts have been packed separately (see below).

Remarks:

a) Transformers which are partially filled with oil or which are empty of oil during transportation, are equipped with an inert gas pressure system. This to prevent humidity entering the transformer body

b) Smaller transformers can be transported completely assembled and completely filled with oil. In these cases there is no need for an inert gas pressure system. Another advantage is that the installation time is seriously reduced.

c) For details of dismounted parts for transport, see the General Arrangement Drawing and Materials List [part C].

3.1.2.1 Seperately deliverd oil

Separately delivered oil is usually packed in sealed (metal)-drums of 200 liters. The drums are collected on standard pallets (4 drums per pallet).

For bigger quantities also special oil-tanks or containers can be used.

3.1.3 Condenser bushings

Condensor bushings are packed in the original wooden box or crate. Each condenser bushing in an hermetic sealed plastic bag which contains a small quantity of silica gel (for humidity control).

3.1.4 Hygroscopic electrical parts

Parts which are under oil or oil-filled under working condition, and which must be dismantled for transport, are packed under oil or filled with oil. The necessary gas-space for the thermal expansion of the oil during transport is provided.

If packing under oil or oil-filling is not possible, the parts will be pre-impregnated with oil, then packed in hermetic sealed plastic bags whith a quantity of silica gel (for humidity control). The sealed bags are packed in wooden boxes.

3.1.5 Radiators

Radiators are packed on pallets as a standard. Crates or boxes are provided if specified.



44

3.1.6 Conservator, pipes and cable boxes

These parts are packed on pallets and protected with a plastic cover.Crates or boxes are provided if specified.

3.1.7 Control cabinets

Control cabinets are provided with bags of an adequate quantity of silica gel for a storage of some weeks to prevent condensation water damage. The corners of the cabinets are protected by special profiles.

Control cabinets are packed on pallets and protected with a plastic cover. Crates or boxes are provided if specified.

3.2 Transport and handling

In many cases, a transformer has to travel long distances before reaching its final destination. During this journey many handling operations are needed for loading, transportation, unloading and transfer to other carrier types.

It is obvious that during this critical period in the lifetime of the transformer all necessary precautions have to be taken to assure safe arrival in optimal conditions.

3.2.1 General transport and handling notes

First of all, it is very important to have experienced people on board who can handle a power transformer. Problems often arise when people are not familiar with handling transformers. Personal harm and damage to the transformer are to be prevented at all costs.

DANGER Take all necessary safety measures during handling and transportation to prevent personal harm. Especially pay attention during the lifting or jacking of a transformer: Never work under a non-secured lifted or jacked transformer. Never attempt to move a transformer by pushing against the tank itself or any of the accessories. Do not weld other attachments to the tank, nor loop cables around the tank or any of the accessories.

Always handle a transformer as gently as possible. Heavy shocks or impacts can damage the transformer internally without any external sign of damage. That is why the prescribed receiving inspection must be followed without any deviation. [see further in this section]

CAUTION Should the transformer tank be dropped, contact Pauwels immediately. Even dropping a tank 25 mm (1 inch) may cause internal damage or damage the tank.

Please note that the means of transportation are important parameters during the design of a transformer. This information is used to calculate the maximum allowed impacts in all directions. During railway transportation especially the impacts may be higher. As a result, the design has been made accordingly.

CAUTION Railway transport is only allowed if this method was specified in the purchase order and if the design has been made accordingly.

If specified, impact recorders are provided to record the impacts that occurred during transportation.



45

3.2.2 Handling instructions during loading and unloading

3.2.2.1 Lifting a transformer by crane

Usually, the transformer body will be lifted by crane during loading and unloading. The smaller packages can be lifted by crane or forklift.

Lifting points are clearly marked by the red painted surfaces. In case of any doubt, consult the General Arrangement Drawing (or other drawings concerning transportation) before lifting.

DANGER Only use lifting points to lift the complete transformer or assembly. Always use all lifting points together. Consult the General Arrangement Drawing for the location of these lifting points.

Only an experienced crew should be allowed to move and position a transformer by crane. Ensure that the capacity of the lifting equipment is suited to the load being lifted, including the angle from the vertical that the crane boom must provide.

Do not attempt to move a transformer by crane if there is inadequate space in any direction. The crane boom must be able to be swung, raised or lowered safely. Take great care concerning other electrical equipment that may be energized, including overhead lines.

Take care to use spreader bars between the cables, or use a lifting beam appropriate in order to keep the lifting cable roughly vertical. THE LOADED CABLES SHOULD NEVER ANGLE MORE THAN 15 DEGREES FROM THE VERTICAL.

An empty tank or a tank partially stripped of subassemblies may slope slightly when lifted by lifting lugs. Should the tank begin to tilt significantly, immediately put the transformer down and investigate before continuing.

Attach guide ropes to the skidding eyes at the base of the tank to guide the tank into position. Do not allow the transformer to swing freely from the crane. Do not lift the load higher than necessary.

Never attempt to lift the transformer unless the transformer cover is securely fastened to the tank. Ignoring this advice may result in deformation of the tank and damage to the core and windings.

Pauwels transformers are designed with lifting lugs No. 105 that can lift an assembled and fully filled transformer.

3.2.2.2 Jacking a transformer

Also jacking can be a helpful method during loading or unloading, although handling by crane is preferred. Jacking, however, becomes more useful for final positioning of the transformer on its foundation as described in section [4]

Pauwels transformers are always equipped with jacking steps No. 102. These jacking steps are designed in such a way that each step can support half the weight of the transformer (in addition to the required mechanical design safety factors). This is done to ensure the safety of the transformer when unbalanced movements are made.

DANGER • Do not jack the transformer from any other

point than the jacking steps provided. • Never jack the transformer when it is under

vacuum. • Always use all jacking points together. In

exceptional cases jacks can be used two by two at one side of the transformer. In this case, pay attention to the angle of the transformer.

• Do not support the transformer for an extended period of time using the jacks only.

• Add sufficient support blocking under the tank base (if a flat base) or under the skids (if a skid base) as soon as possible.

• Never work under the transformer when it is raised solely on jacks.

1. For maximum safety and stability, the jacks must be placed under the jacking steps as centrally as possible. A steel or wooden block must always be placed under the jack that must be sitting flat and level on the ground.



46

2. The ground must be capable of supporting the weight of the transformer with the area of the ground contact used (defined by the size of the pads under the jacks and the gross weight of the transformer).

3. The full plunger surface of the jack has to be located completely under the jacking step.

4. Jack the transformer evenly in order to distribute the stress evenly.

5. While lowering the transformer, ensure that it is lowered gently and evenly. Release pressure SLOWLY to avoid dropping the transformer.

3.2.3 Blocking and securing

During transportation, make sure that the transformer body is blocked and secured in all directions. This should be done to prevent the transformer body from shifting.

a) TRUCK TRANSPORT: The transformer body has to be chained into position or secured into position by any other means.

b) RAILWAY TRANSPORT: The transformer body is usually secured by tension rods or chains, welded or bolted onto the car body. “DO NOT HUMP” signs should be placed on each end of the rail car loaded with transformers.

c) TRANSPORT BY SHIP: The transformer body is usually blocked by timber sections bolted onto wood decked vessels or by steel blocking, welded onto metal decked vessels.

CAUTION If blocking or other securing equipment is loose, bent or missing on arrival, the possibility for shipping damage exists. See section RECEIVING below for inspection and reporting procedures.

3.2.4 Shipping documents

The contents, routing, destination and the conditions of the carrier's agreement are carefully documented for each shipment. Invoices of shipment, bills of loading, etc.., are transmitted to the carrier's agent. A copy of the packing list accompanies the shipment.

CAUTION In case of an abnormality during shipment, follow the instructions of the Insurance guidelines available in section [1].

3.3 Receiving

The process of receiving a transformer begins when the rail car, the trailer or the vessel is presented for unloading. If possible, ensure that the final site or the unloading point is inspected, so that the rail car or trailer can be positioned to make the unloading as easy and as straightforward as possible.

It is recommended that the inspection be performed in the presence of the representative of the carrier.

Remarks:

In case of different loading, unloading or transfer stages during transportation, the below guidelines have to be followed in each stage. This should be done to make sure that possible damage is detected as early as possible.

3.3.1 Inspection of damage

The process of receiving must include a careful and thorough inspection of the transformer and accessories before unloading is permitted or begins. This inspection aims to uncover any damage that may have occurred during shipment.

The inspection process must include a thorough inspection of the exterior of the transformer, the bracing, the packing of parts and components that



47

are shipped detached from the main unit, as well as the inspection of the impact recorder (if supplied).

It is recommended that the external inspection takes place as soon as possible. If damage is found, an immediate internal inspection of the transformer - on the rail car or on the trailer - is recommended.

Pauwels has a warranty providing protection against defective design and manufacturing, but does not accept responsibility for damage that occurs while the transformer is in transit. Damage that occurs during shipment may be the responsibility of the carrier. The carrier is relieved of responsibility once the shipment has been accepted at the destination. This is why careful inspection is required before you accept the shipment.

Remarks:

A “Receiving inspection report” is included in section [7]. Complete this report and return it to your Pauwels contact person within one week after the arrival inspection.

In case of any damage, a claim procedure has to be started immediately. Follow the instructions in the insurance guidelines available in section [1]

3.3.2 Transformer inspection procedure

The different steps are the following:

1. Preparing for the inspection. 2. Inspection of the external portion of the

transformer and attachments. 3. Inspection of the accessories and all other

components shipped with the main unit. 4. Receiving tests

Internal inspection has to be avoided, except when there might be internal damage.

3.3.2.1 Preparing for the inspection

The inspection should take place with a representative of the carrier present. All the

equipment necessary for the complete inspection should be gathered before the inspection process begins. The list of equipment should include:

• All necessary safety equipment, such as hardhats, gloves, etc..

• Flashlight • Tools (to open manholes, etc.) • Suitable grounds for grounding the

transformer, bushings and tank • Notebook and a camera with flash for

recording purposes • Thermometer for measuring the ambient

temperature • Megger. (nominal voltage of 500 – 5000 V DC) • Dielectric oil-test equipment

In case of internal inspection:

• Clean plastic boots (if there will be personnel entry)

• String or cord for securing tools, flashlight etc.. • Clean rags or other clean wiping material • Material, covering manholes or handholes to

keep out moisture laden ambient during inspection

• Dry air installation for injecting dry air to chase away the inert gas (nitrogen)

CAUTION All tools or equipment that will be used over an open manhole or handhole or that will be taken inside the transformer, have to be secured by a cord or string to a point outside the tank so that they can be pulled out if dropped. Also be aware of the specific weight of the oil, swimming is not possible.

3.3.2.2 The external inspection

a) Preliminary inspection A preliminary inspection of the shipment must include looking for signs of damage to the blocking, guy rods or cables, signs of impact on covers, control boxes, major paint scrapes etc.. Note these observations on the form "Receiving inspection report" in section [7]. Do not attempt to repair any damage to the transformer main body or to any of



48

the components.After the preliminary inspection please proceed with the next steps in the receiving procedure.

b) Inspection of the impact recorder and inert gas pressure system

If specified, an impact recorder (No. 145) has been installed. This will be indicated on the General Arrangement Drawing

See further for more information.

Inspect the nitrogen or dry air pressure system (if applicable). If required, an inert gas pressure system has been installed. This will be indicated on the General Arrangement Drawing.

See further for more information.

c) Detailed external inspection Pauwels has taken all necessary precautions to limit damage during shipping. However, even the most elaborate steps cannot totally eliminate the possibility of damage during transit. The largest component, and the one most seriously affected by potential damage, is the main tank and the core and winding assembly it contains. That is why the external inspection should begin there. Report all observations on the form "Receiving inspection report". If damage is found, photograph the areas of concern to substantiate any claims. Do not remove or open any part of the shipment until the carrier's representatives have made their inspection.

• Examine the tank for signs of oil leakage, paint scrapes, dents or other signs of damage.

• Examine timber bracing, steel blocking, boltdown rods and cables for signs of shifting of the load.

INSPECTION HINTS

• Depressed steel rail cars will usually have steel blocking welded to the car, sitting tightly against the base of the transformer. Shifting of the load can result in dents in the transformer at the location of the blocks and/or of the steel blocking itself. Also look for scratched paint.

• Flat rail cars and trailers will usually have wooden blocking sitting tightly against the base or skid base of the transformer, bolted to the bed of the car or trailer. Movement of the load

may result in broken blocking, pulling out of the bolts or crushing and splintering of the blocks. Tie down rods or cables may stretch and become loose under high impacts. Check that they are straight and tight all around.

• If the transformer was shipped oil-filled, carefully look for signs of leakage on welded joints, bolted and welded flanges and covers. Inspect all valves (drain valves, sampling valves, radiator valves) for damage or leaks. Check whether the oil level is providing the right reading.

• All control cabinets (main control cabinet, LTC motor drive etc..) should be tightly sealed and closed. Inspect for damage by water ingress and for signs of tampering.

• Check that the de-energized tap changer mechanically moves correctly (if applicable). Electrical checks will be performed later during the commissioning process.

• Inspect radiators for dents, scrapped paint, damaged or missing fans (if applicable).

• Check all bushings for cracked or damaged porcelain. Check for oil around gasketted joints. Check the oil level on oil-filled bushings (the bushing must be vertical or nearly vertical to check this).

• Check arresters (if any) for cracked or damaged porcelain.

• Check the conservator tank (if applicable) for dents or scrapes or other signs of damage.

• Check the shipment against the bill of loading and report any shortages.

3.3.2.3 Inspection of accessories

Locate the packing list, so that all accessories can be checked off as they are inspected. Check for damage to each crate or package. Open and inspect the contents of each package while referring to the packing list. If any packing or items are missing, immediately notify the carrier's representative and Pauwels.



49

CAUTION Hygroscopic materials are protected by packing in hermetically sealed plastic bags, including silica gel as indicator for unacceptable moisture penetration. After inspection, store these materials according to the instructions on the package (close bags and store in dry room), or mount them immediately.

3.3.2.4 Standard receiving tests

a) Core grounding megger test The core grounding megger test is to be performed whenever possible. We refer to section [4] for detailed information. On a completely assembled and oil-filled unit one can also perform the winding insulation megger test. Please note however that the unit has to be oil filled for safe measurement.

b) Dew point measurement A dew point measurement is required upon arrival of inert gas filled units when tank pressure is below 0.05 bar. This test gives a good indication of the amount of moisture the insulation is containing. More detailed information is given further in this IOM-manual .

c) Additional receiving tests if damage or water ingress is suspected

Some additional tests have to be performed if internal damage or water contamination of the insulation system is suspected. Strictly follow the guidelines described in the testing sections.

• Insulation power factor test. Section [4] gives complete information on this test.

• Ratio and resistance tests. Section [4] gives complete information on this tests.

In addition, oil tests can be performed to detect moisture contamination. For taking oil samples and for oil testing, please refer to section [6]. The oil tests that are most important in receiving applications are:

• Dielectric strength • Water content • Power factor

3.3.2.5 Internal inspections

If internal damage is suspected it is recommended to perform an internal inspection of the unit. (See further in this section.)

3.4 Impact recorder ShockLog RD298

The electronic impact recorder, ShockLog RD298, is a 3-dimensional, registration type. Before transport, this device will be mounted on the cover of the transformator.After arrival on site, please note the correct date and time during removal of this device and send the registrated data for analysis to:

PAUWELS TRAFO BELGIUM N.V. Division: Quality Control VT Antwerpsesteenweg 167 B-2800 MECHELEN BELGIUM

3.5 Performing internal inspections

3.5.1 Reasons to perform an internal inspection

A full internal inspection is only necessary when there are good reasons to do this. These reasons can be:

• signs of severe damage on the outside of the transformer which indicate that there may also be internal damage

• that the impact recorder indicates that there were excessive forces on the load during shipment [see earlier in this section]

• that the megger test shows far too low readings which cannot be explained by the water content of the oil. In this case, it is appropriate to first test the oil before considering a full internal inspection that requires draining of the oil.



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If it seems that an internal inspection is required, contact Pauwels immediately to inform us about the situation. We will study the observations and give you advice on how to proceed with the internal inspection or we will send a certified technician to perform the inspection.

Please note that an internal inspection exposes the transformer to risks. If any damage occurs due to improper handling (entering, exposure time) of the transformer, we cannot be held responsible. So please be careful and strictly follow the guidelines.

3.5.2 Planning the inspection

It is a good idea to plan the internal inspection in advance if possible. Ensure that all equipment is in proper working order, that all emergency safety equipment is present and operational and that all members of the team know their duties.

3.5.3 Procedure of an internal inspection

Always read and follow the guidelines in the Danger & Safety section [1]

A full internal inspection requires draining all the oil into dry, clean tanks of suitable capacity, while filling the transformer tank with dry air and having a dew point equal to or less than -510C.

DANGER Do not attempt to enter a transformer tank, unless the internal gas has been tested for sufficient oxygen content to support life. Testing should be done with an approved detector. A minimum of 19.5% of oxygen is always required. For security reasons, a second person must be present.

A partial internal inspection is possible if the internal components can be observed through manholes or

handholes or covers in the tank cover. In this case, a minimal quantity of oil has to be drained.

For smaller transformers it will be impossible to physically enter the transformer. This means all inspections will have to be conducted by removing manholes and handholes, one at a time, to prevent the ingress of moisture-laden ambient air by cross breathing.

Remarks:

During the inspection look for:

• parts of the transformer structure that are laying on the tank floor or floating in the residual oil. This includes small pieces of insulation. Look for loose bolts, washers, nuts, etc.

• parts of the transformer and lead structure that appear broken or bent. Look for loose key spacers in the windings, loose clamping and support blocks.

• damage around leads. Winding leads that are disconnected from draw lead bushings for transit are tied into a loop and secured to the lead support structure. If these break loose, the end of the lead can damage other components in the transformer.

• strange murkiness or cloudiness of the oil, especially if water contamination is suspected. Look for liquid water on the tank floor (liquid water sinks in oil). Look for evidence of condensation.

• Look for signs of corrosion on bare metal parts.

Inform Pauwels and the carrier what was discovered. If damage was found, file a damage claim, but do not perform any further work until Pauwels gives approval and guidance.

3.6 Dew point measurement

How to perform the dew point measurement can only be explained in relation to the equipment that is used. That is why we refer to the dew point measurement instrument manual.

Pauwels requires that the moisture level of the insulation be less than or equal to 1% for a



51

transformer installed in the field. This is reflected in the line drawn in the curve in Table 10 (based on Piper∗).

An assumption inherent in using the curve to estimate overall transformer dryness is that the gas is in equilibrium with the insulation. This means that the vapor pressures of gas and insulation are equal. This is true if:

• the solid insulation is reasonably uniformly dry (e.g. no large amount of water vapor has been suddenly and recently introduced by an event such as people breathing and perspiring inside the tank during internal inspection or internal assembly.)

• the gas has been in contact with the solid insulation, in a closed system, for a minimum of 24 hours but preferably for 48 hours

• the temperature of the gas is about equal to the temperature of the solid insulation.

If these three assumptions are approximately met, then use the curve in Table 10. Draw a horizontal line from the insulation temperature on the vertical axis, and read the minimum required dew point from the horizontal axis.

∗ Moisture Equilibrium Between Gas Space and Fibrous materials in Enclosed Electric Equipment / John D. Piper . – AIEE, December 1946, volume 65

Table 10 Dew point measurement

3.7 Storage

Liquid-filled transformers are meant to always have their insulation covered by oil. Without oil they will survive satisfactorily for some period of time, such as during shipping. However, prolonged storage without the insulation immersed may cause future problems, as the insulation will pick up moisture and contaminant. Apart from this, internal voids may form in the insulation as the liquid gradually drains out of the insulation.

When a transformer has to be stored, the procedures below have to be followed for safe storage.

Remarks:

• The higher the voltage and the larger the MVA of a transformer, the more important the storage conditions. However, it is always better to store the transformer correctly.

• If a transformer is fully assembled, oil-filled and pre-tested, the general maintenance instructions can be followed (refer to section [6]).



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DANGER For your personal safety and for the safety of the equipment, always ground all terminals when transformers are in temporary storage.

3.7.1 Storage of the transformer

If possible, the transformer should be stored in its correct position on the prepared foundation. This foundation must be strong enough to support the mass of the complete transformer, accessories and liquid. It must be level and must support the transformer base evenly.

If the permanent foundation is not available, then the transformer must be stored on a solid platform that is suitably prepared to provide proper support for the transformer base. Indoor transformers should be stored indoors.

3.7.1.1 Completely assembled or at least with conservator

If the correct maintenance activities in section [6] are performed, a completely filled transformer with conservator can be stored for unlimited time.

Assemble and fill the transformer completely with oil as soon as possible, at the latest within 30 days after arrival on site (or maximum 90 days after shipment from the factory). In the intermediate storage period the inert gas installation (if applicable) should be checked weekly.

• Mount the silica gel air breather(s) by means of a temporary pipe connection to prevent unnecessary under- or overpressure because of ambient temperature changes.

• Activate and check all gas bleeders (if applicable).

• Connect and supply panel heaters to prevent damage by condensation.

• Ground all bushings and the tank to prevent damage by unexpected lightning (see section [1]).

• Store accessories in a safe place. (oil drums, bushings, radiators, conservator, fans, etc..). For instructions, see below.

• Perform the recommended maintenance as described in the maintenance chapter (section [6]) if longer periods of storage are required.

3.7.1.2 Oil-filled transformer with inert gas cushion

When the conservator cannot be installed, the transformer can be stored with an inert gas cushion. The maximum storage period is limited to 6 months. Always do a weekly check of the inert gas pressure that should be above 0.05 bar.




3.7.1.3 Transformers without any oil and completely filled with an inert gas

Total storage time is limited to 3 months from the time the transformer has left the factory. The inert gas overpressure must be checked weekly.




3.7.2 Storage of accessories

All accessories that are shipped separate from the transformer must also be stored correctly. All shipping crates or boxes that are opened for the



53

receiving inspection must be carefully resealed and stored in a dry clean atmosphere between +50C and +300C. It is recommended that all accessories, boxes or crates that are marked FRAGILE also be stored indoors in a dry, clean room and above +50C. All accessories stored outdoors must be covered and protected from severe weather.

3.7.2.1 Storage of oil shipped in drums

Mineral oil in drums may be stored inside a building that protects them from water accumulation on the cover. In this case, local fire regulations must be followed for storage of flammable materials.

Oil drums that are stored outside must be positioned in such way that water cannot accumulate on the top of the drum. (water can be draw into the drum during temperature cycling, thus contaminating the oil).

Corroded steel drums may start leaking. This condition must be avoided by ongoing inspection of the stored drums.

There are two acceptable methods of outside drum storage, illustrated below in order of preference:

Figure 3 Outside oil drum storage (method 1)

Bungs must be set parallel to the ground so that oil covers them both. This restricts cross breathing.

Figure 4 Outside oil drum storage (method 2)

Cover the drum with a plastic sheet, tied in place to avoid water accumulation on the top.

3.7.2.2 Bushings

Bushings are packed in wooden boxes or crates. All condenser bushings (or other bushings with hygroscopic parts) are packed separately in a hermetically sealed plastic bag to keep moisture out and do contain a bag of desiccant. Prior to storage, check that the bushing upper end terminal and wrap is tight and undamaged. Replace the desiccant if necessary. Ensure that oil-filled bushings are stored with the top of the cap elevated at a minimum of a 200 angle.

Remark:

Bushings packed in their original boxes are always elevated at the right angle

Bushings thus protected from the environment may be stored outdoors, although if indoor facilities are available, it is highly recommended that they be used instead. Regularly verify that the desiccant is dry.

3.7.2.3 Radiators

All radiators and radiator assemblies that are shipped separately have their openings sealed with a shipping gasket covered by a temporary attached cover plate. Ensure that all seals are tight before storage. Storage conditions must ensure that water will not collect and stand around sealed openings. Radiators and radiator assemblies should not sit directly on the ground, but should be on timber supports above the ground.

3.7.2.4 Fans

Fans have weatherproof motors and can be stored outside. However, since their shipping positions are not necessarily the normal working positions it is required that they be stored inside in a dry, clean atmosphere and above +50C.



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3.7.2.5 Pumps, conservator and pipework

It is recommended that they be stored inside in a dry, clean atmosphere and above +50C.

Pumps and connecting pipework are sealed with a shipping gasket and a temporary cover plate. Check all sealed openings prior to storage.

If inside storage is impossible, pumps and pipework may be stored outdoors up to 30 days after the arrival date.

For storage periods exceeding 30 days, it is recommended that bags of fresh, dry silica gel be attached to the inside of the blanking plate (attachment to the blanking plate means it is unlikely the bag will be accidentally left inside during final assembly).

3.7.2.6 Control cabinets

Control cabinets shipped separately from the transformer are usually packed in wooden crates or boxes. Venting openings or breathers may be closed to prevent water ingress. A bag of sufficient silica gel is placed inside the control box to pick up the moisture of the inside air during the normal shipping time.

Unpack all control cabinets immediately after arrival.

• Verify that the silica gel is dry and that there is no corrosion damage.

• Check for loose or broken parts (plug-in relays, wiring channels etc..).

• Verify that all venting openings are open and mount breathers.

• Connect heaters to the appropriate power supply. If heaters cannot be connected to the supply, check the silica gel weekly and replace it if necessary.

• Store the cabinet indoors in a dry, clean room and between +50C and +300C.

3.7.3 End of storage

Check the transformer and all stored components again just before final assembling and testing in accordance with the standard receiving procedures in section [3].



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4 Assembling and installation



56



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4.1 Locating a transformer

The instructions below are meant as a guideline to move a transformer and its accessories safely and with a minimum of risk for damages.

4.1.1 Preparation to move a transformer

A number of items need to be prepared and checked before a transformer is moved to its final position on site:

• The site has to be prepared correctly and must be ready for receipt of the unit

• The transformer itself has to be declared fit to move.

• The transformer has to be prepared to move. • The transportation route has to be prepared for

the move.

4.1.1.1 Inspection of the final location

Before the transformer is moved to its permanent foundation or to a temporary storage area, the site must be carefully inspected.

Inspect the foundation the transformer will be placed on. Ensure that its size and structural properties are correct for the transformer load. You might also confirm with the foundation engineering personnel to be sure. Also ensure that control wiring conduits or channels are in the correct position for the transformer control box(es), especially if supplied from underground (through the foundation surface).

Ensure that there are proper clearances around the transformer for:

• Fire prevention equipment, fire walls, personnel safety.

• Noise barriers, fences, water deluge systems, ladders, etc...

• Cabling to control cabinets and for opening the cabinet doors

• Proper personnel access for construction and maintenance purposes

• Proper transformer ventilation (roughly speaking, transformers with cooling fans under the radiators need a minimum clearance to the ground of approximately the diameter of the fan).

4.1.1.2 Inspection of equipment to move

Equipment that is to be moved to its final position has to be ready.

• Newly received transformers that are to be moved, must first be inspected according to the procedures listed in section [3] before final positioning on its foundation.

• Equipment that has been in temporary storage has to be re-packed or prepared, so that is suitable for the specific movement. ° This refers especially to the disconnection

of all equipment, accessories or power that might have been attached for storage purposes.

° If the transformer is under pressure or vacuum for storage purposes, relieve the pressure (or the vacuum to atmospheric pressure by using dry air or nitrogen with a suitable low dew point less than -510C).

Always:

• Disconnect all power supplies.

DANGER If there is any power to be disconnected, do not take any further steps until this has been properly done.

• Unbolt any bolts, nuts or cables that may be fastening the transformer to its current location (or carrier). Carefully check that all wires, cables and groundings (earthings) have been removed and that there are no parts stopping the free transportation of the transformer.

• Check the transformer for any equipment or accessories that must be removed before moving it to the new location (in order to clear any obstacles along the route). For equipment or accessories which must be removed:



58

° Matchmark the pieces ° Disconnect them ° Store them carefully in a clean dry place

until they are required for re-assembling (see also the storage chapter [3])

° Clean all remaining openings ° Seal the openings carefully, using

blanking plates and gaskets. NEVER re-use shipping gaskets for the final assembly

° Tighten all blanking plates and covers carefully

Remarks:

• Should any equipment be missing or damaged upon arrival, contact Pauwels immediately.

• If any equipment is damaged or lost during (dis-) assembly, order replacement parts through Pauwels.

4.1.1.3 Inspection of the route

Prior to the movement of the transformer a provisional route inspection must be performed. The route is investigated to determine its suitability for the movement of the transformer and to assess whether the removal of street furniture is required. On completion of the route survey, the movement must be communicated to all relevant authorities. Inform the local police if escorts are required.

A number of items must be inspected along the entire route. These items include:

• Overhead obstructions: verify that there is sufficient clearance for the transformer and its moving equipment to pass under all overhead obstructions. Check for clearance to any overhead electrical equipment that may require electrical clearances much larger than just physical ones.

• Side-to-side obstructions: verify that there is sufficient clearance between buildings, gates, fences and other equipment. Ensure that sufficient clearances are available for the moving equipment and any turning circles required. Check for appropriate clearances to energized electrical equipment and carefully mark these for safety.

• The roadway: ensure that the roadway can support the load of the moving equipment and its load. Make sure that it is level enough not to cause interference. Ensure that any slopes, either up grade or down grade are within the limits of the moving equipment to handle. The transformer must never be tilted more than 15 degrees from the vertical, side-to-side or front to back. This rule also applies to skidding a transformer to a pad. For steeper slopes, use a crane.

• Traffic: sometimes transportation routes will cross other routes such as roads, loading docks, railway tracks etc. Make arrangements to block, keep clear or divert other traffic if required.

Finally, expect the unexpected. Bad weather may make an otherwise smooth surface soft or slippery. A change in weather can cause a firm surface to turn to mush. Moving equipment may break down. Expect that some delays will occur.

4.1.2 Positioning a transformer on its final destination

4.1.2.1 General handling notes, lifting a transformer by crane and jacking

Information on general handling notes, lifting a transformer by crane and jacking can be found in the transport section [3].

4.1.2.2 Moving a transformer on wheels or steel rods

a) Moving a transformer on wheels (if available) Transformers supplied with wheels can be moved in directions at right angles to the tank base. Usually these movements are executed on ground level on special tracks.

Assembling the wheels:

• Jack up the transformer using the jacking steps. Raise the transformer the height required just to install the rollers. Block the



59

transformer with suitable timbers or support blocks (for safety purposes) placed near the jacking steps under the lateral skids or stiffeners.

• Attach the wheels to the mounting pads located under the tank using the necessary four bolts (a center bolt may also be provided to easily turn the rollers by 900 on itself). The wheels are quite heavy. Therefore, the smaller the distance they have to be lifted, the easier the installation will be.

• Once the wheels have been attached, use the jacks to raise the transformer just enough to remove the blocking.

• Gently lower the transformer until it is resting on the rollers.

• The transformer may be now rolled into position.

Moving at right angles

• Place a jack under each of the jacking steps, and ensure that the surface under the jacks is solid and suitable for the weight to be lifted. Raise the transformer the height required just to clear the rollers above the ground. Block both ends of the transformer by placing suitable timbers or support blocks (for safety purposes) placed near the jacking steps under the lateral skids or stiffeners.

• Unbolt each roller and turn 900. Bolt each roller into the new position using all available bolts.

• Raise the transformer slightly, and remove the blocking.

• Lower the transformer gently until it is resting on the rollers.

• The transformer may now be moved in the new direction.

To remove the wheels:

• Follow the guidelines to assemble the wheels in opposite order.

b) Moving a transformer on steel rods A transformer is moved by "skidding" whenever lifting and moving by crane is impossible or unpractical. Transformers with a skid base are made to be skidded in directions at right angles to the tank base using steel rods. Transformers with a flat base can be moved in any direction.

Remark: The estimated force to start horizontal movement is 15-20% of the weight to be moved.

Steel rods must all be the same diameter, evenly and closely spaced. Refer to the table below for the minimum required number of rods in relation to the weight being moved.

• Use at least three sets of rods side by side. The rods must be of sufficient width to suit the transformer being moved. Do not use a single row or two rows of rods.

• Rods are preferably iron-pipe profiles, double extra strong IPS pipe.

• If rods are to be used with timbers, the timbers must be steel faced. Each set of rods must have its own set of timbers.

Diameter (mm) Weight to be moved (tons) 25 50 75 100 125 150

45 - 70 52 26 18 70 - 90 70 34 24 18 90 - 115 86 44 30 22 18 115 - 135 52 36 26 20 135 - 160 30 24 20 160 - 180 34 28 24 180 - 210 39 33 30 210 - 240 45 36 33 240 - 270 51 42 36 270 - 300 57 48 39

Table 11 Minimum number of rods required per set under the transformer

Remarks:

• The table above assumes the use of 3 – 300 mm (3 - 12 inch) wide steel faced timbers

• The table above gives the number of rods per set under the transformer.

Different steps in moving a transformer on steel rods:

• The first step is to prepare the route for moving the transformer: ° The truck bed, the railcar deck or the

transfer car bed must be jacked up and blocked so that it is level and firm



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° Ensure that the supporting surfaces are firm enough to support the weight of the transformer

° Assemble the necessary tools (such as jacks, "tow and drag" winches etc..), support blocks, rods, greased turning plates or greased skids etc…, required for all events of the movement.

• Connect appropriately sized cables to the haulage eyes located near the transformer base. Only pull a transformer by the correct attachment points. Haulage eyes are mentioned on the general arrangement drawing. Utilize a spreader bar if required to limit the strain on the haulage eyes.

• Raise the transformer using four hydraulic jacks. Place the rods on the steel faced timber (or on the rails in the event of using a transfer cart with embedded rails) and roll them under the transformer. The longitudinal skid members serve as stops for positioning the rollers. When all of the rollers are in place, carefully lower the transformer onto them.

• Move the transformer into the next position. • Once the transformer is situated on its

foundation: ° Remove the haulage cables ° Jack the transformer to remove timbers

and/or rollers from under the transformer ° Set the transformer onto its foundation.

Remarks:

For flat base type transformers, timbers and rods must be positioned in such a way that they support core and windings during movement. The rollers must therefore be centered at one-third the width and two-thirds the width of the base plate, seen from the movement direction.

If the transformer is to be moved on greased timbers or by machinery movers, the same kind of procedures and/or precautions should be followed.

4.2 General installation topics

Although power transformers are designed and manufactured to National or International Standards, every transformer ends up being

designed for a specific site, as well as a for specific electrical network. Hence they usually are of a completely unique design. For this reason, every transformer installation will to be a unique event as well. People involved in the installation have to study the specific design and have to use their experience and this IOM-manual for the installation. A well-prepared installation is the first condition to make it a successful event. Furthermore the installation of a transformer requires specialized equipment as well as services. These services may be sourced internal in your organization or may be sourced externally (eventually by the service department of Pauwels). Accurate scheduling is required in order to make efficient use of these sources. We assume in below text that the transformer is correctly positioned on its foundation according to the instructions in the previous chapter and that all necessary transformer components and accessories are available for installation.

4.2.1 Planning of the installation

As some equipment or resources are not always readily available it is advised to start some weeks or even months in advance depending on the available experience. A graphical planning tool (e.g. MS-Project) can be useful in accomplishing a good installation program including all necessary steps and resources.

4.2.2 Recommended assembling and energization sequence

Although situations can be different from one case to another, below sequence is recommended during installation and energization of the transformer. This sequence guarantees the best result with the minimum effort, minimum risk for damages and (oil) contamination.

1. Installation and preparation of the transformer tank

2. Inspection of availability of all parts and equipment

3. Installation of main accessories:



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a) metal parts.conservator, radiators, pipes, pumps,...

b) bushing turrets and bushings. When all metal parts have been installed the risk for damaging bushings while installing these parts is minimized.

c) cable boxes 4. Oil treatment (if necessary) 5. Vacuum processing and initial oil filling 6. Topping up the oil 7. Installation of remaining accessories: fans,

measurement devices, control cabinets, wiring on the transformer. When the transformer has been completely filled there is no more risk to spill any oil on electrical accessories.

8. Pre-operational tests and checks

4.2.3 Collecting and preparing the required equipment

4.2.3.1 Assembling tools and equipment

The following equipment is recommended to have on hand during installation. By collecting the following equipment prior to the start of installation, you eliminate many of the possible delays:

• All necessary safety equipment, such as hardhats, flashlights, fire extinghuisers, plastic overboots (for internal inspection), etc,...

• A set of large socket wrenches and optional compressed air tool for the use of the sockets. These will be needed for opening and closing manhole and handhole covers, for removing blanking plates etc..

• Crowbar and claw hammer for opening accessory crates etc..

• A set of large open end wrenches. • Cable cutter(s) • Strong nylon ropes and slings for bushing

installations. • Strong strings for installation of draw leads (to

pull leads through bushings) and for tying tools taken inside of the transformer tank.

• A crane for installation of heavy components and or correctly sized blocks and tackle assemblies.

• Normal tools for an electrician (for – external – wiring and connection).

• CLEAN tarpaulins, plastic sheeting etc..

• Clean rags for cleaning. • Methyl Hydrate (or equivalent) for cleaning

bushings. • Powdered talc and/or gasket-glue for use on

gaskets. • Dry air cylinders, with pressure regulators and

inlet hose if internal work is to perform.

4.2.3.2 Oil filling and processing tools and equipment

Once the transformer accessories are installed, it must be filled. In addition, the following filling and oil treatment equipment will be required:

• Oil processing and pumping equipment, with filters etc. This equipement may include: ° vacuum degassing and drying function ° filtering function ° pumping function

• Vacuum pump (can be a part of the oil treatment equipment) ° Capable to obtain the required vacuum ° (recommended 0,2 mbar or lower) ° Required capacity depends on

transformer oil quantity

Oil quantity Recommended vacuum pump capacity

< 25 m3 ± 250 m3/h < 50 m3 ± 500 m3/h < 100 m3 ± 1000 m3/h

Table 12 Required vacuum pump capacities

• Vacuum gauge • Pipes and valves of suitable size depending on

the capacity • The right quantities of transformer oil • A Megger (500 – 5000 V DC) • Transformer Turns Ratio meter (or use

voltmeter system). • Oil dielectric tester. • Dewpoint tester.

A dielectric test set especially if benchmark tests are to be taken prior to in service



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4.3 Installation of the transformer body

4.3.1 Grounding the tank

Once the transformer has been placed on its foundation, it is important to ground the tank before any more work is done. For positioning of the grounding pads, refer to the General Arrangement Drawing No. 115. The grounding leads must be of suitable dimension to be effective. Refer to section [1]: Danger and safety notes and section [2] for general information on transformer grounding.

CAUTION Correctly ground the transformer tank before doing any assembly or commissioning work.

4.3.2 Preparation of the transformer before assembling accessories

While working on an inert gas-filled transformer, pay attention to the internal overpressure. It could be up to 0.3 bar at any time. This is especially so while opening valves or removing blind flanges. Also bushing turrets are under pressure.

To install certain accessories, the transformer tank will have to be opened. Depending on the specific shipping or storage conditions:

• Oil has to be (partially) drained and the removed oil has to be stored in dry and clean containers

• Inert gas has to be replaced with breathable dry gas

DANGER Do not attempt to enter a transformer or do not put your head inside, until: The tank has to be evacuated using a vacuum pump to 50 mm of mercury (absolute); and then to be filled with dry air; The tank has finally been checked for sufficient oxygen to support life. The check should be performed with an approved gas detector. A minimum of 19.5% of oxygen is required. Failure to comply with this warning can be fatal.

When opening a transformer:

• Try to open only one manhole or handhole at a time to prevent cross breathing of the tank (which lets in moisture).

• Do not open a transformer if bad weather threatens, and try not to open the tank during periods of high humidity. Temporary weather shields may be necessary as a last resort.

• Besides following the above measures, always limit the exposure time of core and windings to 24 hours. This is the total allowable time the active part may be exposed to atmospheric conditions. If exposure time exceeds 24 hours, the vacuum pulling process has to be extended.

In case of any doubt about humidity of the insulation:

• Fill the transformer with dry nitrogen or air (dew point < -51 ºC) and wait for 48 hours.

• Take a sample and perform a dew point measurement. If requirements are not met, perform an extended vacuum processing. [see further in this section]

• Decide whether the insulation is dry or not.

In case of any doubt, contact Pauwels before energization.

4.4 Installation of accessories

There are a lot of different accessories that can be used on power transformers. Some guidelines



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always apply, whatever the type of accessory to install. Other guidelines are more specific. We will start by providing general recommendations concerning installation. Next, we will provide an overview of the most frequently used accessories and their mounting instructions.

Although not all provided information will apply to the scope of delivery of the transformer, it might be useful to have it at hand for other transformers or for future extensions.

Always have a look at the drawings in section [part C] and documentation in section [part B] to learn about the specific accessories used and to apply the correct instructions.

4.4.1 Unpacking accessories

Unpack the shipping boxes or crates (except for oil-filled bushings), identify and inspect the parts. It is important to handle all accessories with care.

NOTES ON OIL-FILLED (CONDENSER) BUSHINGS: Oil-filled bushings may not be immediately unpacked. The reason for this is that the top must remain higher than the bottom so that the air space does not travel into the insulation. At this point, only identify each bushing. During assembly, unpack only one bushing at a time: unpack the bushing when it is needed for assembly.

The bushing porcelain is fragile and must be protected from damage during unpacking and installation. Be careful with the tools used to remove the packing-cover and the clamps used for shipment of the bushing. Bushing deliveries can be quite long and if you damage a bushing, it may take months to replace it.

4.4.2 Preparing accessories

Before finally assembling the accessories, make sure all bolts, nuts, gaskets, etc. are at hand. Put the accessories in the order in which they will be assembled. This will make the installation easier.

4.4.3 Equipment safety during installation

Whatever the equipment or accessories to install always make sure nothing drops into the transformer tank. Especially during installation of bushings one must be careful not to drop any parts into the tank.

Bolts, nuts and washers can easily be dropped and even a small washer can cause a permanent transformer breakdown. Entering a transformer to recover the lost parts is a serious job, especially when the transformer is already oil-filled (draining oil, looking for the part, …). The worst case is when things have been dropped and one doesn’t know what was dropped or how many parts were dropped.

CAUTION Be very careful when handling bolts, nuts and washers inside the tank or on a transformer cover with open manholes. You should be careful so as to avoid dropping these items into the windings or other insulation structures. We strongly advice you to use a drop cloth under the internal bushing terminals to collect dropped parts as well as to count the number of components taken into the tank. If any parts are dropped and cannot be retrieved, contact Pauwels and do not try to energize the transformer.

4.4.4 General assembling instructions for accessories

These general instructions should be used for all accessories, especially when no detailed



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information is available in the documentation [part B] or in other assembly instructions. However, not all possibilities can be addressed in this IOM-manual, therefore general rules for good workmanship should always be taken into account.

4.4.4.1 Tightening bolts

Bolted assemblies are generally used for:

• Mechanical assemblies without gaskets (supports)

• Mechanical assemblies with gaskets (oil pipes, valves, flanged covers, devices in contact with oil, bushings, etc..)

• Electrical assemblies (busbar connections, internal connections to bushings and/or terminal boards, ground connections, etc..)

Every bolted assembly must utilize the following hardware sequence: the bolt with a flat washer under the head, and on the other side a flat washer against the flange and a nut. Lock washers or lock nuts are provided for some of the connections (in certain cases the external paint locks the nut correctly).

Typical bolt tightening sequence: tighten pairs of bolts on diagonal lines and in two steps to avoid overstressing: tighten each of the bolts twice, snugly in the first pass and bring them to the final tightness in the final pass.

9

3 4

7 1 5 11

12 6 2 8 10

1

28

3 4

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5

Figure 5 Sequence of tightening bolt – nut connections (1 -> 2 -> 3 -> 4 -> …)

4.4.4.2 Gasket systems

a) Used gasket systems on transformer



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Figure 6 Different types of gaskets

Non re-usable gasket types (A – B)

System A: This is the system that is normally used for flanged joints on IEC transformers. The gasket material is impregnated cork. Joints are treated with a typical sealing compound. The surface of the gasket material that is exposed to the ambient air and/or sunlight is treated and painted to prevent degradation of the gasket material.

System B: This is the system that is normally used for flanged joints which are mechanically loaded by the weight of (or force to) the mounted component (radiators, etc..). The gasket material is a high-density-fiber plate (IT) (based on aramid fibers). Joints may be treated with a sealing compound to become a safer joint. The gaskets are not re-usable.

Re-usable gasket types (C – D)

System C: This system is used for typical components that have gasket-grooves on the

apparatus or in the flange. The gasket may be an O-ring or a flat gasket. The gasket material is usually high quality nitrile. For some specific components, other base material can be used. The gasket is powdered (with talc) or treated with acid-free Vaseline. The surface of the flanges is treated to prevent corrosion. The gaskets might be considered re-usable after accurate inspection of the used gasket.

System D: This system is used where metal gasket stops must be present (for ANSI and CSA standards). The gasket material is nitrile or impregnated cork. The gasket stops prevent overstressing of the gasket material. Sealing compound may not be used. The gaskets may be considered re-usable after accurate inspection of the used gasket. Depending on the expected lifetime of the gasket system, special gasket material can be provided.

b) Handling re-usable gaskets (C – D) • Dismantling

° Make sure not to damage the gaskets when an element is removed from the main tank.

• Replacement ° Gaskets and metal surfaces have to be

free of dust, oil and other impurities before installation.

° The cleaning can be done with a degreasing product (a solvent based degreaser).

• Additives ° No glue or other additives may be used

between gaskets and metal surface.

NOTE Vaseline is sometimes used for easy mounting of the gaskets. Please note that the use of vaseline is only allowed (however not required and not recommended) on gaskets that are fully located in a chamber or groves. In case vaseline is used on non-groved or non-chambered surfaces, the friction towards the compression surfaces is no longer sufficient and therefore not allowed.

c) Lifetime of gaskets



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The re-usability of the re-usable gaskets is influenced by time and temperature. However, within a period of approximately 10 years, normal re-use of gaskets is allowed. Therefore, we recommend renewing the gaskets when a gasket is removed after 10 years from date of manufacture.

d) Making a gasket joint (A – D) Sometimes, gaskets are made from two or more pieces in order to cover the whole gasket surface. If this is the case, the following instructions have to be taken into consideration.

Replacement or spare gaskets for systems A and D may need to be cut and/or adjusted on site as follows:

Figure 7 Gasket joint

• Nitrile rubber gasket joints ° In case the joint between two pieces is

not broken during dismantling, no special precautions have to be taken.

° In case the joint is broken, then the connections have to be cleaned by peeling–off the sealing compound (e.g. with a knife) and after cleaning, a new sealing compound can be used such as ”Curil K2” or ”AEG Sealing Compound” or equivalent.

• Impregnated cork gasket joints ° Cork gasket joints can be reproduced in

the required shape with sealing compound. When tightening the connection, the cork material will expand and close the joint.

4.5 Installation of Conservator and Pipes



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Figure 8 Conservator and pipes assembly



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1. Unpack all components, check them and clean all gasket surfaces.

2. Mount the conservator support(s). 3. Mount the conservator on its supports (bolts

are not to be tightened at this time). 4. Mount the oil pipes on the cover, including new

gaskets (bolts are not to be tightened at this time):

• The oil connection between tank and conservator.

• The oil connection between bushing turrets and the oil pipe (if any).

• The oil connection between the tap changer head and its conservator.

5. Mount the vertical oil pipes and their components including new gaskets (bolts are not to be tightened at this time):

• The oil drain valve(s) (LTC and main conservator).

• The pipe to the silica gel breather and the breather itself.

• If all components are in place, tighten the bolts on the pipe connections in the same sequence as you have mounted them. Then tighten the bolts on the conservator support(s).

CAUTION Before final tightening of oil connections, check the position of the valves: full oil filled chambers may not be entirely closed by any valve, because thermal oil expansion may produce high internal pressures possibly damaging the transformer or its components.

If the oil (vacuum) filling process cannot follow immediately, insert dry air or nitrogen (dew point < -510C) into the transformer and keep a slight positive pressure (± 0.2 bar) to prevent moisture ingress.

4.6 Installation of radiators

Every transformer uses custom designed radiator assemblies to provide proper cooling for the specific design.

The transformer might be shipped:

• completely assembled including radiators: no special installation or filling is required

• (partially) filled with oil: the radiators have to be filled with oil by the transformer tank one by one. Remarks: As small amounts of oil may leak out of closed throttle valves, make sure that an oil can is placed underneath the throttle valves. Connect the radiators as soon as possible.

• with an inert gas and without any oil: the radiators should be filled during the vacuum-filling process of the main tank.

Figure 9 Example of radiator No. 92

4.6.1 Mounting instructions

Unpack and check each radiator carefully; remove blind flanges (the inside should be dry, clean and free from foreign objects): clean gasket surfaces. For filled transformer tanks, check whether the throttle valve(s) No. 93 is (are) closed.

Remove the blind flanges on the throttle valves: clean the gasket surfaces.

Mount the radiators (one by one) to the tank with the right side up (top-side = lifting lug); use new gaskets. Tighten all bolts. Retighten after 24 hours.



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CAUTION Never lift radiators by the spotwelded side rods. Always use the lifting lugs on top.

Mount stiffener bars (if any) between the radiators.

If necessary, touch up the damaged/scratched radiator surfaces.

Remarks:

The same instructions apply for mounting radiators on a cooler bank. For connecting the cooler bank to the transformer we refer to the General Arrangement drawing.

4.6.2 Different types of gaskets used

4.6.2.1 High-density-fiber gasket (IT):

This gasket type does not use gasket-stops (see also section [3] for different gasket types)

Always mount two new gaskets together (2x2mm) and position them on the valves between the stud-bolts. Using a small amount of a correct sealing compound will help to keep the gaskets in place during installation and will limit the risk for leaks.

4.6.2.2 Impregnated cork gaskets or O-rings:

These types of gaskets need a gasket stop (usually by positioning the gasket in groves at the valve-side, see also earlier in this section for different gasket types).

• Inspect the O-ring for any damage prior to reusing it in the final installation.

• Use fresh cork-gaskets to the radiator valve. A small amount of petroleum jelly will help to keep the gaskets in place during installation.

4.6.3 Filling radiators for (partially) oil-filled transformers

Fill the radiators one by one as follows:

1. Open the air-vent screw No. 94 on the top of the radiator and valve No. 123 between the conservator and the tank.

2. Partially open the lower throttle valve No. 93. 3. When oil escapes from the air-vent screw,

close the air-vent screw. 4. Completely open the upper and the lower

throttle valve.

Remarks:

During this process, the oil level in the transformer tank must be checked regularly; the oil level may never sink under the radiator inlet / highest point of the windings to avoid moisture, air, or gas ingress. For this reason, it could be necessary to fill-up oil immediately (refer to oil filling instructions).

4.6.4 Draining oil from a radiator

1. Close valve No. 123 between the conservator and the main tank and close both throttle valves No. 93 of the radiator No. 92.

2. Unscrew the protection cover of the drain plug No. 95

3. Make sure that the air vent No. 94 is fully closed.

4. Unscrew entirely and make sure that outcoming oil does not drip on the ground.

5. After a while, the oil flow stops due to a vacuum created in the radiator.

6. Connect a flexible hose or another device to the drain plug so that oil spillage is avoided.

7. Open the air vent No. 94 8. Remove the protection cover. 9. Open the air vent by turning the screw in a

counterclockwise direction. 10. Incoming air in radiator results in a rapid oil

draining via the drain plug. 11. After draining :

° close vent plug No. 94 ° remount protection cover of vent plug ° close drain plug No. 95 ° remount protection cover of drain plug



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4.6.5 Disassembling a radiator from a filled transformer

It might be necessary to disassemble one or more oil-filled radiators during installation activities. Follow below guidelines.

1. Remove the fans and fan supports 2. Close valve No. 123 between conservator and

main tank. 3. Close throttle valves No. 93 and drain oil. 4. Unscrew nuts underneath and on top of the

throttle valves. 5. Remove radiators by means of a lifting device. 6. Place a blank flange on the throttle valves of

the transformer when the radiators are removed for longer than 1 hour. If the radiators are to be used again, provide them also with a blank flange.

Figure 10 Drain plug No. 95∗

∗ Part numbers refer to DIN 42558

Figure 11 Vent plug No. 94

Figure 12 Throttle valve No. 93 open



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Figure 13 Throttle valve No. 93 closed

4.7 Installation of CTs

4.7.1 Current transformers for bottom–connected bushings (phase / neutral)

4.7.1.1 Dismounting

1. Disconnect bushing leads from network. 2. Remove HV bushing. 3. Disconnect cables in terminal box No. 32 on

front- and backside of terminal. 4. Unscrew nuts on base plate. 5. Disconnect grounding connection between

base plate and cover. 6. Remove base plate.

Turn base plate over so that current transformer arrangement is on the top side.

7. Unscrew 4 nuts. Remove Bakelite base plate, protecting cork ring, distance tubes and fixing blocks. Disconnect grounding connection between current transformer core and base plate.

8. Remove current transformer from base plate.

4.7.1.2 Mounting

Reverse procedure.

4.7.2 Current transformers for draw lead bushings (phase / neutral)

4.7.2.1 Dismounting

1. Disconnect bushing leads from network. 2. Close valve No. 123 between conservator and

Buchholz. 3. Drain oil in main tank. 4. Disconnect cables in terminal box No. 32 on

front- and backside of terminal 5. Remove HV bushing. 6. Unscrew nuts on base plate. 7. Disconnect grounding connection between

base plate and cover. 8. Remove base plate.

Turn base plate over so that current transformer arrangement is on the top side.

9. Unscrew 4 nuts. Remove Bakelite base plate, protecting cork ring, distance tubes and fixing blocks. Disconnect grounding connection between current transformer core and base plate.

10 Remove current transformer from base plate.

4.7.2.2 Mounting

Reverse procedure.

4.8 Wiring on the transformer

The wiring on the transformer is always completed and checked during assembly in the factory. However, the connection between transformer and remote control cabinets is only made as a temporary base for testing.

During disassembly for shipment of the transformer, some parts with an electrical connection must be disconnected. This will result in free cable-ends (or free plug-ends) that can be situated on the



72

dismantled part or on the transformer. Free cable-ends will be coiled and protected by plastic bags or another protection and tied to the transformer tank or assemblies. The wires of free cable-ends are marked with the same terminal number as the terminal to which they have to be connected during the final wiring on site.

Current transformer circuits have been short-circuited before and during transportation for safety purposes. This short circuit wire has to be removed at the time of final wiring and/or testing.

The following wiring types are used:

• Cabling with a certain cable type. The cables are mounted into stainless steel cable channels (possibly with covers) that are fixed to the transformer tank or assembly. This is the normal standard for IEC transformers.

• Wiring into conduits (galvanized or in aluminum) that are fixed on the transformer tank or assembly. This is the normal standard for ANSI and CSA transformers.

• Plug-in cable connections, used for some typical accessories (Qualitrol apparatus, fans, etc.).

4.8.1 Mounting instructions

After mechanical installation of the parts that are to be electrically connected:

1. Remove the protection on the cable-end and check the wire marking with the wiring diagram.

2. Clean wire ends (and contact-pins of cable-plugs, if any).

3. Fix the cable in the cable channel. 4. Introduce the cable into the cable gland. 5. Check with the wiring diagram. 6. Connect the wires to the right terminal. 7. Tighten the cable gland.

Once again, make sure that the right connection has been established.

4.9 Oil quality requirements

The oil quality is very important for the reliability of the transformer. Oil filling and oil treatment procedures have an enormous impact on the oil quality. This is why the procedures below should be followed strictly.

The specific filling and treatment procedure to follow depends on:

• The transformer design • The oil supply method • The voltage class (Un < 70 kV – Un > 70 kV) • The method of shipment of the transformer

In the explanation below we assume that:

• The transformer has been assembled according to the previous guidelines.

• The transformer is filled with an inert gas and does not contain any oil.

Remarks:

Starting from an empty, inert gas filled transformer, vacuum filling can be performed in one step (commonly used for small transformers and for sealed transformers or for transformers with a positive pressure system) or in two steps (commonly used for large transformers): first filling the tank and then filling up the conservator.

• All necessary oil filling and oil treatment equipment is available.

• New transformer oil of the right quality is available (see below).

NOTE Oil quality and care in handling are extremely important for the proper functioning of the transformer.

4.9.1 New transformer oil

New transformer oil can be available in drums or in containers. Normally, new transformer oil is not degassed and has to be treated (streamlined) according to the processing parameters below.



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Before using any transformer oil to fill (or top up) a transformer, the oil quality should be in accordance with the applicable standards:

• IEC 60296 • ASTM D 3487-88

4.9.2 Oil treatment (degassing, streamlining)

Oil treatment is used to improve the oil quality by filtering and degassing the oil.

Transfer the oil from the barrels into a dry and clean container of suitable size (preferably the same size as the amount of oil to be treated). Connect the treatment installation in a closed loop to the container and circulate the oil volume 3 times. The vacuum should be 1 mbar or less.

Non-inhibited transformer oils: treatment should be performed at a temperature of 60 ºC 2 (maximum 65 ºC).

Inhibited transformer oils: due to the volatile character of the inhibitor one should limit the temperature in order to prevent loss of inhibitor. Conditions that have been found satisfactory for most inhibited mineral oil processing can be found in the table below. In general, one should limit the treatment temperature for inhibited transformer oils to 50 ºC.

Minimum Pressure 3 T (ºC) Pa Mbar Torr 40 5 0.05 0.04 50 10 0.1 0.075 60 20 0.2 0.15 70 40 0.4 0.3 80 100 1.0 0.75 90 400 4.0 3.0 100 1000 10.0 7.5

Table 13 Oil treatment

2 Temperature at the outlet of the degassing installation 3 Reference: ASTM D 3787

See section [5].

Required oil quality after oil treatment:

Dielectric strength: ≥ 75 kV (IEC 60156)

Water content: see section 5

Tangent δ (90 ºC): ≤ 0.5 %

If temporary storage of the oil is required, prevent air and water from entering the container. Test the oil again just before filling.

Remarks:

Some filling installations are equipped with integrated degassing features and do not require separate degassing. In this case, oil samples should be taken at a regular basis before the oil enters the transformer.

4.9.3 New treated transformer oil in new equipment

Oil quality should be in accordance with the applicable standards and Pauwels specifications:

• IEC 60422 • ASTM • Pauwels specifications: see further in this

section and section [5].

4.9.4 Transformer oil for transformers in service

Same as above (4.9.3) applies.

4.10 Pulling vacuum

The purpose of pulling vacuum is to lower the pressure inside the transformer tank below the partial pressure of water vapor at the temperature of the insulation. The more the vacuum is lowered below the partial pressure, the better the removal of the surface moisture will be.



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4.10.1 Before pulling vacuum

Test if there are any leaks. This can easily be done by applying a pressure of 0.15 up to 0.2 bar with dry air or nitrogen. If leaks are detected, close them.

Ensure that all radiator valves are opened.

If the transformer is equipped with non-vacuum/pressure tight accessories (such as a gas detection apparatus, drycol breathers, pressure relief devices, etc.) block these until the vacuum process is completed or remove them.

CAUTION In case a Drycol dehydrating breather is installed on the conservator, or if a gas analyzer and electronic devices such as a “Hydran” is installed on the tank, do NOT allow either a vacuum to be drawn on, or oil to be injected into the apparatus. Ensure that either the valves on this apparatus are closed off on both inlet and outlet sides or that the devices are removed for the period of pulling vacuum and filling.

If the transformer is equipped with a(n) (on) load tap changer, refer to the appropriate (O)LTC documentation included in this IOM. Prior to pulling vacuum or performing a leak test using overpressureing be aware that, an equalizing pipe (A) is installed between the (O)LTC compartment and the tank during transportation. Maintain this connection untill starting to pull vacuum. In case a connection with valve is used, the valve should be open while pulling vacuum and closed when the transformer is energised.

If the conservator is of a membrane type, the membrane is NOT capable of withstanding a vacuum or overpressure. Install the necessary pressure equalizing pipe (B) between the expansion membrane, the conservator compartment of the transformer and the conservator compartment of the (O)LTC.

CAUTION Mount the necessary equalizing pipes between all hydraulic chambers that cannot resist full vacuum by itself before drawing a vacuum or before starting any filling process. Check the General Arrangement drawing, the documentation and nameplate for more details on vacuum resistance. Especially have a look at the tap changer and its conservator, membrane type conservators etc.

B

A

OLTC

Transformercompartment

OLTC-compartment

Expansion tank

vacuum installation

tank

Figure 14 Equalizing pipe connections

DANGER Never perform an electrical test on a transformer under vacuum. Internal flashovers may occur at voltages as low as 200 V, causing severe damage. Do not attempt to climb on a transformer, or walk around on any part of the cover, while the transformer is under vacuum. This is unsafe for personnel and equipment.

4.10.2 Establishing connections

Connect the vacuum connecting point on the conservator No. 125 with the internal part of the atmoseal bag (via dehydrating breather connection flange, on top of conservator). The vacuum connection should be made as short as possible. Ensure that a shut off valve is installed. Please refer to the Figure in "Filling Procedures" included in this IOM.



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• Connect a vacuum proof transparent hose (L3) between the oil sampling device on the bottom filter valve No. 112 and the connecting line of the vacuum pump (L2) on top of the conservator (or tank if no conservator is present) to visualize the oil level during filling. This transparent hose should be at least 50 cm (20”) longer than necessary.

• Connect the oil pump installation (VP, F) to the bottom filter valve (No. 112 - L1). A filter and degassing installation (if non-degassed oil is used) should be part of the installation procedure in order to filter out all the water particles and impurities.

• Open all the cooling systems’ isolation valves No. 93 if this has not been done already.

4.10.3 Pulling vacuum

Start the vacuum pump, open all the vacuum lines to the transformer tank (and other vacuum proof compartments) and then draw a vacuum 6.7 mbar or less, absolute. Hold this vacuum for at least 8 hours (increased with 1 hour per 8 hours exposure time) to assure all gas is removed from the insulation structures.

DANGER Never leave a transformer under vacuum unattended.

4.10.4 Troubleshooting

If the specified vacuum cannot be reached or maintained, one or more of the following may be the case:

• The vacuum pump is too small for the size of the transformer.

• The vacuum pump requires servicing and/or new sealing oil.

• The vacuum connections or the transformer itself are leaking.

• There is significant moisture in the tank and the vapor pressure of the moisture is limiting the vacuum to drop to the specified level.

Try the following procedure to determine the cause of the problem. While the vacuum pump is running, close the valves (for a minimum of 30 min.) between the vacuum pump and the transformer tank.

• Compare the level of vacuum on the tank and on the pump side of the valves that are closed. If the tank pressure increases quite fast, the transformer is leaking.

• If the vacuum pump side of the valves does not drop down quickly, the pump capacity is too small or probably requires servicing.

• If the vacuum pump side of the valves drops down quickly and the transformer tank pressure increases slowly, then there is excess moisture in the tank.

Correct the problem and restart the vacuum procedure. Should repair on the vacuum pump or on the vacuum connections take some time, then refill the transformer with dry gas. Should the transformer require repairing, then the tank MUST be refilled with dry gas before attempting repairs.

If the problem is excessive moisture, an extended vacuum procedure can be applied and special attention should be paid to the oil quality before energization. See end of this section.

4.11 Oil filling standard

4.11.1 Oil filling

A vacuum of minimum 13 mbar must be maintained during the entire filling process. This means the valve of the oil supply pipe has to be throttled to maintain this vacuum. This is necessary because, while entering the tank, the oil will give off dissolved gasses that must be evacuated by the vacuum pump. The oil-filling valve must be adjusted to maintain a positive pressure up to the throttled valve.



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If degassed oil is used to fill the transformer, the quantity of oil flowing into the tank should not exceed 12 mm (0.5 inch) per minute, even if the required vacuum can be held at a higher filling rate. This rule should be followed to ensure all voids are correctly filled with oil.

The use of oil treatment equipment (streamliner) with an integrated vacuum degassing chamber is preferable. In this way residual dissolved gasses are removed while the oil enters the transformer tank. The risk for a process interruption will be limited as well.

Remarks:

Certain transformers with a maximum voltage class of 34 kV may be filled with non-degassed oil. The oil should be entered on the top of the tank using a special spray-nozzle. The rate of oil admitted to the tank should not exceed 33 liters or 12 mm per minute, even if the required vacuum can be held at a higher rate. This rule should be followed to ensure degassing of the oil during filling and to ensure all voids are correctly filled with oil.

Check the dielectric strength of the oil during filling in samples taken from the transformer side of the oil treatment equipment. If a test indicates a lowering of strength, the filters must be replaced before continuing.

Continue to fill under vacuum until the oil level gauge reads the correct level.

Remarks:

In case of first step filling of a transformer equipped with a conservator (refer to Figure 15) fill up to approx. 100 mm below the highest point of the cover. The main insulation must be covered with oil completely.

When the oil level in the transformer main tank (or in the conservator) is correct, stop the oil filling and stop the vacuum pump. Break the vacuum using dry air or nitrogen, whichever is available. The gas supply should be 0.15 bar or less, until a pressure of about 0.15 up to 0.2 bar is obtained in the transformer. Dismantle the vacuum and oil-filling equipment from the transformer. Mount silica gel air breathers (if there are any).

Open the valves on the non-vacuum/pressure tight accessories (such as a gas detection apparatus, drycol breathers, pressure relief devices, etc.).

Unblock items that were blocked for overpressure protection.

If the transformer is equipped with oil pumps, vent these pumps. Furthermore, it is recommended to occasionally run the pumps. The procedure is to run the pumps for an hour or so, then stop the pumps and about 15 to 30 minutes later, bleed all bleeder points on the transformer. Restart the pumps and proceed with a number of cycles.

Ensure that the (O)LTC compartment (and its conservator) is correctly filled.

In the case of a conservator design transformer, bleed air from manholes, bushing turrets, cooling component systems etc., using the bleeder screws or valves on the equipment. Mount the air breather(s).

Recheck the transformer oil level and top up if necessary (see further).

Figure 15 Transformer filling (without

conservator)

V = Oil storage tank F = High vacuum filter (streamliner) VP = Vacuum pump (streamliner) S = Sampling device (drain plug) of installation L1 = Filling line of the transformer tank L2 = Connecting pipe of the vacuum pump L3 = Vacuum proof, transparent hose T = Transformer Tank M = Vacuum measuring device C = Conservator with atmoseal bag



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Figure 16 Transformer filling with conservator

4.11.2 Filling procedure in the event of process interruption

The procedure of pulling vacuum and oil filling is meant to be a smooth and uninterrupted process. Should the process be interrupted for any reason, then:

Stop the flow of oil into the transformer tank. Attempt to return power to the process equipment as soon as possible. Upon the resumption of power, inspect the vacuum gauge.

If the internal tank pressure is below 13 mbar: proceed with the filling process.

If the tank pressure is between 13 and 32 mbar: first pull vacuum below 6.7 mbar, then continue with the filling process.

If the tank pressure is above 32 mbar: drain the oil from the tank and begin the vacuum filling process all over again (from the start).

CAUTION The purpose of vacuum filling is to remove all gas from the insulation structure. The presence of gas in the insulation may cause failures and/or may develop partial discharges that can develop into an internal failure. In addition, the interpretation/analysis of dissolved gasses will be not correct. Therefore, it is very important that the vacuum filling is performed strictly in accordance with these instructions.

4.12 Topping up oil after initial vacuum filling

This procedure can be used after the initial vacuum filling of the main tank (leave filling line L1 connected to the bottom filter valve No. 112) or for transformers that are shipped (partially) oil-filled (connect the filling line L1 to the top oil filter valve No. 111). Please note that initial filling of an empty transformer should always be done following the vacuum filling procedure described above or by using the “oil-spray-system”. In certain circumstances only topping up the oil might be done without following the vacuum filling procedure. However if vacuum filling equipment is available, vacuum filling is to be prefered in any case as this method prevents air bubles to be trapped in the transformer.

• Conservator design type transformers and Un < 70 kV may be topped up with degassed oil, directly pumped through a suitable filter (1 to 5 μm) into the conservator without drawing vacuum.

• Conservator design type transformers and Un > 70 kV must be topped up under vacuum; the same procedure applies as for initial vacuum filling. However, the vacuum hold time before filling may be reduced to 4 hours.

• Non-conservator design type transformers only need correction of the oil level using degassed oil.

• If radiators are not mounted before the initial vacuum filling, mount and fill them according to the mounting and filling instructions for radiators (see earlier in this section).



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Remarks:

If no degassed oil is available, use streamlining equipment and apply the correct processing parameters (depending on the oil type used).

CAUTION Never attempt to top up a transformer with oil that has not first been tested for adequate dielectric strength. Special care should be taken for oil that has been stored outside in drums.

4.13 Air venting

Once the filling process has been completed, all vent plugs should be opened until all air bubbles have been evacuated. The most appropriate venting sequence is first opening the lower vent plugs and then the higher ones.

For example:

• Radiators • Cover • Overpressure valve • (O)LTC • Bushing turrets • Bushings • Buchholz • Conservator

Remarks:

1. If an expansion membrane of the conservator type No. 96 has been used and topping up has been done without applying vacuum: put overpressure on the pipe to the dehydrating breather No. 23 on the membrane, open the vent screws and wait until oil runs out. If required, adjust the oil level by using the lower filter valve No. 112. Install the dehydrating breather (according to the specific installation procedures available in the documentation section[7]).

• When complete filling or topping up has been done following the vacuum procedure, no more

air should be trapped in the conservator or other parts of the transformer.

• Do not re-open the vent plugs No. 99 on the conservator after filling and venting has been done as described above. If you do re-open the vent plugs, air can enter the conservator and the filling or topping up procedure should be repeated.

2. Transformers with forced oil circulation using pumps should be vented a first time after complete oil filling. Have the pumps run for at least two hours. The oil has to stabilize for several hours and a second venting sequence should be performed.

3. After completion of the venting procedure: ° Securely close all vent plugs and replace

protection caps (if present). ° Clean all spilled oil around the vent plugs

so that it cannot be mistaken for oil leaks.

4.14 Pre-operational tests

At this point, the transformer has been installed, completely filled and should be ready for energization. However, in many cases, energization will not directly follow completion of the installation and filling process. This is so because other related equipment (such as circuit breakers, remote control, …) has to be ready first. It can take weeks to complete the entire substation after completion of the transformer installation.

Whatever the time in-between, we recommend proceeding with the installation and filling procedure as soon as possible for the following important reasons:

• Equipment safety: the best practice to store a transformer is completely assembled, filled and well maintained.

• Equipment completeness: during erection activities one can easily check whether all necessary materials are available. Missing and defective parts will be discovered and can be replaced in time.

To ensure Equipment functionality both mechanical and electrical tests on the transformer and its accessories are recommended as soon as installation and filling have been completed. This



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will allow you to perform all necessary tests without exceeding the available time limits. Please use a copy of the “Site commissioning report” in section [9] to register all applicable test results.

If immediate energization is possible after testing this is, of course, to be recommended and will result in the highest efficiency.

Section [4], “Putting into Operation”, provides an overview of the periods a transformer is allowed to wait for energization. Depending on the length of the waiting period, some or all tests should be repeated.

Once the transformer has been fully assembled and oil filled, a number of tests and checks are required to ensure safe energization of the transformer.

4.14.1 Mechanical tests and checks

First of all, a thorough inspection of the transformer and its accessories should be performed to ensure safe electrical tests and reliable test results.

4.14.2 Oil sampling and testing

At the end of the mechanical inspection of the transformer it is required to take the necessary oil samples for oil testing.

4.14.3 Electrical tests

If the oil quality meets the specifications, you can proceed with the electrical tests. Before starting any voltage tests, make sure that the current transformers are correctly short-circuited.

Required tests have to be performed in all cases. Although the optional test, the vector group test, is an often performed field test, it is not necessary. In the “Site commissioning report” section [9] test sheets are available for the required and optional tests.

Special tests are only to be performed if there are indications of potential problems or defects.

If Pauwels is doing the erection and commissioning, contractual specifications concerning site testing have precedence over the sequence below.

Remarks:

Tests and checks related to the specific network or to remote controls, as well as cable tests are not included in this section.

DANGER - Never perform DC tests other than the ones described below. These types of tests may overstress the insulation system and/or disturb the magnetic features and may cause damage to the transformer. - Never perform an electrical test on a transformer under vacuum.

Required tests:

• Megger test ° Winding megger test ° Core grounding megger test

• Voltage ratio test

Optional test:

• Vector group test

Special tests:

• Insulation power factor test • Bushing power factor test • Winding resistance test • Continuity / impedance check

4.15 Pre-operational tests and checks of accessories

General items

• Check for remaining equipment or tools on the transformer cover or other parts

• Check for leaks or other damages • Check for damaged painting



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• Check the presence of the Nameplate (or Ratingplate)

• Check grounding connections

The transformer tank, all external metal parts and accessories should be permanently grounded according to the correct safety and operation practice and in accordance with instructions for the specific equipment being used.

All bushings have to remain grounded until final energization of the unit (except to perform the electrical tests).

• All cables that are connected to the transformer should be adequately grounded.

Valves and associated items

• Check that all bolted joints are correctly tightened and that there are no leaks.

• Make sure that all valves (including radiator valves) are in the operation position.

• Ensure that all venting openings are closed.

(Air) breathers

• Check the color of the silica gel and replace if necessary. Check oil locks.

Gas detector / Buchholz relays

• De-block floaters (if applicable). • Bleed the air from the appropriate device.

Bushings

• Ensure that all bushings and bushing turrets are correctly air bled. Check for leaks, especially on bolted flanges and the bushing top terminals.

• Ensure that capacitive test taps on condenser type bushings are correctly grounded or connected.

• Check for sufficient voltage clearances.

Temperature gauges

• Temperature gauges are set in the factory at the values indicated on the documentation or to customer requested values.

Pressure devices

• Pressure relief devices are set in the factory; check that the device is unblocked. Do not open the device; strong loaded springs inside it may endanger the personnel.

• If pressurized gas equipment is supplied, check the regulator for correct operation.

Current transformers

• All current transformers’ secondary windings must either be connected to a load or be shorted out.

• If it is suspected that the current transformer core has become magnetized, this must be corrected, as it will adversely affect the operation of connected loads, especially protective relays.

• Connect a 100 ohm variable resistor of sufficient wattage based on the secondary output voltage at 150 % secondary current across the secondary winding, then slowly reduce the current to zero. Remove the resistor and connect the current transformer to its load or short it.

Load tap changers

• Check the protective relay. • Check the motor drive after it has been

electrically connected. Check at least the following: ° Overcurrent motor protection. ° Step by step function. ° Mechanical and electrical overrunning

protection. ° Other trip and alarm functions as per

specification. ° Remote control function (if present).

De-energized tap changer

• Check the trip contact (if present). • Check and padlock the tap changer into

position.

Cooling system

• Check oil pumps, fans and their control system. Check for leaks. Observe operation for at least one hour.



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• Check if all condensation release plugs are removed on electrical motors.

• Overcurrent motor protections. • Check and set temperature controllers. • Check the flow indicators for the correct flow

direction. • Other trip and alarm functions as per

specification. • Remote control function (if present).

CAUTION For transformers with OFAF cooling (Oil Forced Air Forced), oil pumps always have to be in operation if the transformer is energized, even at no load: pumps always have to run.

4.16 Oil sampling and testing

4.16.1 Sampling

For the sampling procedure we refer to the maintenance section [5] further on in this IOM Manual.

4.16.2 Required oil quality tests

After oil filling and before performing electrical tests two oil tests are required. Write the test results on a copy of the “Site commissioning report”.

• Dielectric strength • Moisture or water content

More information on these oil tests and additional oil tests is provided in the maintenance section [5]. The additional tests may be necessary if there are indications of potential problems or if specific maintenance procedures require reference values (e.g. DGA analysis).

4.16.3 Oil quality requirement

Minimum dielectric strength of transformer oil must be met: see section [5].

Maximum moisture content as a function of the temperature must be met: see section [5].

More detailed oil specifications are given in the applicable standards IEC 60422 and ASTM.

4.17 Megger test (Required)

The purpose of the megger test is to detect internal movement of parts that may have shorted out some of the insulation on the core and on the windings and leads, as well as to check for excessive moisture contamination.

Remarks: • For all megger tests a good estimate of the

inner transformer temperature is required. For oil-filled transformers the oil temperature gauge can give a good estimation. Be aware of the atmospherical influences.

• Multiply the measured insulation resistance by the correction factors, given by the table in section [0], to bring the measured value back to a 200C reference temperature.

• Insulation resistances measured without oil filling on a nitrogen-filled transformer are not comparable with the measured values in the factory. Below values are given for an oil-filled transformer.

4.17.1 Winding insulation megger test

A megger test on a transformer winding is a single- phase test. When testing the HV winding, ground all LV and TV bushings, connect all HV bushings together, and megger the HV bushings to ground. Wait for one minute and repeat the test. Do this for 10 subsequent measurements. Follow the same way for all megger tests of all windings. The polarization index is the measurement after 10 minutes divided by the one after one minute.

Use a megger voltage of 5000 V DC (1000 V DC for a nitrogen-filled transformer). The bushings



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must be cleaned and dry. Do not use pieces of strings etc.., to hold leads apart, as they may damp and introduce a leakage path sufficient to greatly distort the true readings. High atmospheric humidity will also influence the test results.

In the case of a two-winding transformer, the following winding megger tests should be performed:

• HV windings to ground, with LV windings grounded.

• LV windings to ground, with HV windings grounded.

• Connect all HV and LV windings together and megger to ground.

Complete the “Insulation resistance measurement” part of the site commissioning report for 2-winding transformers .

In the case of a three-winding transformer, the following winding megger tests should be performed:

• HV windings to ground, with LV and TV windings grounded.

• LV windings to ground, with HV and TV windings grounded.

• TV windings to ground, with HV and LV windings grounded.

• Connect all HV, LV and TV windings together and megger to ground.

Complete the “Insulation resistance measurement” part of the site commissioning report for 3-winding transformers.

Required values:

• Megger values: minimum 10 Mohm/kV with a minimum of 400 Mohm.

• Polarization index: minimum 1

4.17.2 Core grounding megger test

The core grounding megger test is used to determine the state of the core clamping structure, core to ground and/or clamp to ground insulation. The core is tested by accessing the core ground bushing located on the cover of the tank No. 137.

The test is conducted by using a megger voltage of 1000 V DC. All windings must be shorted and grounded before starting this test.

Both core grounding and clamp grounding megger values should exceed 100 Mohms corrected to 20°C according to the correction table in the table section [0].

1. Open the access hole towards the terminals No. 137 by unbolting the access cover. The atmosphere in this box is ”air”.

2. Disconnect the core grounding link by unscrewing the bolts on the core bushing and grounding point. The core is now disconnected from ground potential.

3. Perform a megger test between bushing and grounding point.

NOTE Some transformers have more than one core in the main tank.

• Each core grounding is brought out to a separate insulation bushing and the purpose is marked near each bushing.

• The measurement has to be done for each individual core.

After testing:

1. Reconnect the core grounding link between the core bushing and grounding point.

on bushing

stud on grounding point

Maximum torque spanner value

40 Nm (30 lbf.ft)

20 to 30 Nm (14.8 to 21.1 lbf.ft)

2. Put the nitrile rubber gasket back into place on

the box frame. 3. Put the cover back into place and tighten with

bolts/nuts



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4.17.3 Accessories insulation megger test

The insulation of accessories should be meggered with a megger voltage of 500 V DC.

OIL IN MAIN TANK

Nitrile gasket with retainers

AIR

Transformer cover

Core grounding lead TO CORE

Access cover

Bushing

Bolts / nuts

Grounding point

Figure 17 Core grounding assembly

4.18 Voltage ratio test (Required)

DANGER Always use a low voltage power supply (maximum 400 V) and connect it to the HV windings so that ALL OTHER INDUCED VOLTAGES WILL BE STEPPED DOWN. Pay special attention to the bushings during this test.

The voltage ratio test is used to ensure that internal connections have been made correctly. The test can be performed with a transformer turns ratio meter or by using the voltage ratio check. The

measured values should be within the tolerances given in the Test Reports in section [8].

For transformers with tap changing equipment, on load and/or de-energized, it is recommended that the ratio be measured on all taps. Do not change taps whilst the voltage is being applied to the transformer.

4.18.1 Ratio meter method

Follow the instruction that comes with the instrument you will be using. The turns ratio between the transformer windings can be obtained from the transformer nameplate. Remember to take into account the phase relationships of the windings that are being measured. The measured ratio must be within the tolerance as specified in the standards.

The null meter on the ratio instrument should be steady while the test is performed. If the needle on the instrument jumps about or if it is not possible to null the meter, this may indicate incorrect instrument use, incorrect or poor measurement lead connection, open or shorted turns in one or more windings.

4.18.2 Voltage ratio test for turns ratio

Connect the voltage power supply to the HV windings. Two voltmeters must be used; one connected to the HV windings and one to the LV windings. They should be read simultaneously. The ratio of the readings of both voltmeters should correspond with the nameplate ratio. The values must be within the tolerance as specified in the standards (taking into account the accuracy of the used voltmeters).

4.19 Vector group test (Optional)

The vector group test is used to ensure that the internal connections have been made correctly. The



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vector group can be checked by using the alternating voltage method.

Connect one point of the HV windings to one point of the LV windings (see the figure below for example).

Connect a low voltage power supply to the full HV windings. Record readings of the applied voltage and the superposed voltages (as shown on the figure below for example). Compare the measured values with the calculated values applicable for the transformer vector group. Check if all values are correct.

Example: vector group Yd1; Three-phase voltage supply on HV windings.

Figure 18 Vector group test∗

∗ connect these points together

4.20 Insulation power factor test or TAN δ (Special)

The insulation power factor test is also called tangens delta test (tan δ). The test results are used to help determine the dryness of the insulation system in the main transformer and the bushings (see further).

The measuring method depends on the equipment used. We refer to the guidelines of the specific equipment.

Remarks:

1. The bushings have to be clean and dry. Do not use pieces of strings etc. to hold leads apart, as they may damp and introduce a leakage path sufficient to greatly distort the true reading. High atmospheric humidity will also influence the test results.

2. There may be problems to test in the field if power frequency interference is nearby. Some test sets work at a higher frequency to reduce the interference problem.

3. Considering the potential lack of experience, the number of intervening factors and the absence of standards relating to measuring instruments, you have to be careful with the interpretation of insulation power factor tests. Therefore, when site tests are comparably performed, the changes observed from one test result to the next are more important than the absolute values of the individual tests.

Perform the test between:

• HV and LV with TV windings grounded (if present).

• LV and HV with TV windings grounded (if present).

• TV (if present) and HV with LV windings grounded.

Normal values for transformers in service have to be below 1 % (50 Hz and corrected to 20°C); for factory new transformers even below 0.5 % is recommended. Values above 2 % call for immediate examination.



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4.21 Bushing power factor test (Special test)

HV bushings require attention during the whole life of a transformer. The bushing power factor test can be performed using a dissipation/power factor bridge or a Doble test set. The transformer lead must be disconnected from the bushing for this test. It is relatively simple to do this for draw lead bushings, but oil must be drained for bottom connected bushings.

Groundingspring

Tapelectrode

Insulatingbushing

Figure 19 Bushing testtap

Bushingcenterconductor

Test cap

Ground

C1

C2

Figure 20 Capacitive bushing representation

Evaluation of the test results should be based on the bushing test certificates in the documentation section [7].

Some testing notes and suggestions:

• The bushings must be clean and dry. High atmospheric humidity will also influence the test results.

• Remove the test cap with the grounding spring and connect the power factor test equipment.

• The power factor test should be performed at about the same temperature as the factory test to allow correlation of test results. The power factor reading depends on the temperature, and the less correction that has to be applied, the better. Test from the test cap to the top cap, from the test cap to ground and from the top cap to ground. The values of C1 and C2 can be derived. Expect to have a difference between the factory test values and the field test results (commonly ~ 10 %).

CAUTION The bushing test terminal grounding cap MUST be put into place at the end of the test. Operation of the bushing without grounding the tap electrode will very likely cause flashover due to the high open circuit voltage produced at the tap.

4.22 Winding resistance test (Special test)

Measuring of resistances is not required. It may however be a practical test in the field, although a continuity impedance check is a better test (see further).

Please note that resistance measurement results may be influenced by:

• Heating up of the windings during the test. • Contact resistance of all connection points

during the test. • Contact resistance of a tap changer. In case of

important deviations, operate the load tap changer many times with about 10 % current (as described below under "continuity check"): this will clean the surface contacts. De-energized tap changers should be operated only mechanically!

If the measured resistance values change by using another measuring current, this indicates that the measuring system is influenced by one of the above points.



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The resistance of the windings may be measured by using a resistance bridge. There is a large number of bridges on the market, but the two most known are:

• The Kelvin bridge, for the measurement of resistances lower than one ohm.

• The Wheatstone bridge, for the measurement of resistances of one ohm or higher.

Some modern bridges can cover a wider resistance range than these traditional bridges.

The operation of the bridge will be explained in the instructions that come with it. However, there are some points to watch out for when measuring transformer resistance.

All CTs in the transformer must be shorted so that no remanence is introduced into the CT-core. This would adversely affect the operation of the transformer protection system.

DANGER Read the following points concerning the energy stored in the winding during this test.

Although a power supply of only 12 volts is used, the amount of energy stored in the inductive reactance of the windings is quite large. Switching the circuit on is safe, but interrupting the current at the completion of each test can be dangerous. Please pay attention to the following:

• Use a resistance bridge that is specifically suitable for measuring highly inductive loads.

• Break the circuit slowly dissipated in an arc, or shunt the winding through a resistance before opening the circuit.

• Before disconnecting the leads from the transformer, ensure that all stored energy has been dissipated.

Failure to do this may endanger personnel and the transformer.

Temperature conversions can be calculated as follows:

)235235(

++

=TmTsRmRs Where:

Rs = the resistance at desired temperature

Rm = measured resistance Ts = desired reference temperature Tm = temperature at which resistance was

masured. For aluminum windings, change the factor 235 to 225.

4.23 Continuity impedance check (Special test)

The continuity impedance test is meant to check the impedance and all internal connections, including the continuity of the current for the windings and all tap connections. At the same time, the main function of the load tap changer can be checked. The current should be limited to a maximum of 10 % of the rated current.

Use an AC power voltage supply. The needed supply can be defined as follows:

• Supply voltage = 10 % or less of the impedance voltage. (expressed in % of the rated voltage on the Nameplate or Ratingplate).

• Current supply = 10 % or less of the rated current (refer to the Nameplate or Ratingplate).

The power may be supplied to the HV windings or to the LV windings, depending on the available power supply. The not supplied windings are to be shorted with adequately sized shorting leads. Refer to the transformer Nameplate (or Ratingplate).

Once all connections are made, switch the power on and read the supply voltages and currents. Switch off the supply and repeat the test for each position of the de-energized or load tap changer. Do not operate the load tap changer while the supply is switched on.

In the case of unbalanced currents, voltages or discontinuity, something is wrong with the internal connections or there is a malfunction on the load tap changer.



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4.24 Removal of surface moisture

If the dew point test that was performed (at arrival or for exposure times > 24 hours) indicates an unacceptable dew point temperature, an extended vacuum processing can be used to flash off surface moisture. This can be done to see if this improves the situation before attempting more complicated and costly drying out procedures.

4.24.1 Removal of surface moisture by vacuum

The purpose behind the application of vacuum is to lower the pressure inside the transformer tank to something below the partial pressure of water vapor at the temperature of the insulation. The more the vacuum is lowered below the partial pressure, the better the removal of the surface moisture. This process does not work well for moisture deep within solid insulation, as it would take an extremely long time for the moisture to work its way out to the surface from deep in the interior.

The vacuum to be drawn depends on the temperature of the insulation (removal of moisture by vacuum of moisture in freezing weather is unpractical without the application of heat). The drying process will be accelerated by providing a lower vacuum than listed.

Insulation Temperature ºC

Partial Pressure of water vapor Microns

Required vacuum Microns

25 105 100 or lower 20 85 80 or lower 15 50 45 or lower 10 36 32 or lower 5 26 23 or lower 2 22 20 or lower

Table 14 Required vacuum for flashing surface moisture

The hold time, or the duration that the vacuum must be held, depends on the relative humidity of the ambient air that entered the transformer during the exposure period, the time of the exposure, the

amount of air infiltration and the temperature at the time the vacuum is applied. Unfortunately, the relative humidity and the amount of infiltration is a very difficult thing to monitor. Extending the vacuum hold time for longer than the table below suggests is recommendable.

Hold time Hours Relative

humidity of ambient air

Expo-sure time (hours)

Insula-tion temp 21ºC or higher

Insula-tion temp 10ºC to 21ºC

Insula-tion temp under 10ºC

10 6 9 12 20 12 18 24 30 18 27 36 40 24 36 48

10 to 25%

50 30 45 60 10 15 23 30 20 25 38 50 30 40 60 80

25 to 50%

40 55 83 110 10 20 30 40 50 to

70% 20 40 60 80

Table 15 Vacuum hold times for flashing surface moisture

After the required hold time has been achived, break the vacuum with dry air or nitrogen that has a dew point lower than desired for the transformer. Repeat the dew point test after a period of at least 24 hours – this period is needed for the moisture content of the gas and insulation to stabilize. If the dew point is satisfactory, proceed with the final vacuum for filling. If the dew point is still not satisfactory, contact Pauwels for further instructions.

4.24.2 Removal of surface moisture by dry air recycling

A simple method for removal of surface moisture can be useful in some cases: i.e. when vacuum equipment is not directly at hand.

• Recycle transformer with dry air and maintain at all times a positive pressure on the tank (minimum 0.05 bar and maximum 0.2 bar)



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• Inflation point and bleeding point of dry air is preferably diagonally located.

• Total quantity of dry air required is about three times the tank volume of transformer.

• The total tank volume can be taken from oil content as shown on the nameplate.

• After passing–through a volume of dry air, equal to 3 times the tank volume, the bleeding point has to be closed and a positive pressure as mentioned above, has to be maintained for at least 3 days.

Re-measure dew point as described above.



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5 Commissioning



90



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5.1 Repeating pre-operational tests

The transformer should now be in operational condition with all related equipment (circuit breakers, remote control,…) installed and tested.

Pre-operational tests and checks on the transformer have been performed to section [3] Repeating these tests and checks is not necessary if energization follows within a few days or maximum within a few weeks.

However, depending on the works that are performed after assembling and testing the transformer and depending on the time to energization, it may be required to repeat some tests and checks just before energization.

5.1.1 Energization follows within 4 weeks after installation and testing

It is important to know if in this short period no other activities have been performed on the transformer that could possibly influence the fitness for use.

• In case no such activities took place, proceed with the commissioning procedure.

• In case some activities took place: repeat the necessary tests and checks according to section [3]

If applicable, check also if all connections of the ELASTIMOLD or PFISTERER type have been sealed voltage proof. Otherwise the transformer may not be energized.

5.1.2 Energization follows 4 weeks to 6 months after installation and testing

Repeat:

• Air venting procedure according to section [3] • All pre-operational tests and checks of

accessories according to section [3]

If applicable, check also if all connections of the ELASTIMOLD or PFISTERER type have been sealed voltage proof. Otherwise the transformer may not be energized.

5.1.3 Energization follows later than 6 months after installation and testing

In this case all tests and checks as well as the air venting procedure should be repeated before energization.

5.2 Operational system tests

Once the transformer has been (re-)checked and (re-)tested, some operational tests on the complete system – transformer, network and remote control facilities – are required.

Below instructions are meant as a general guideline. For more information, refer to the General Arrangement drawing, the Nameplate, Schematic drawings and documentation included in this IOM manual. Also use the information about the network configuration, remote control and protection system.

Write down the test results on a copy of the “Site commissioning report” section [9]

5.2.1 Alarm circuits and contacts

Alarms are mentioned as a warning for an abnormal situation on the transformer or its accessories that needs observation, action and follow up. There is no need to place the transformer out of service.

The most commonly used alarms are:

• Slow gas production (Buchholz or gas relay). • Temperature alarms (first stage oil and/or

winding temperature). • Oil level alarms (low and/or high level).



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• Internal pressure alarms. • Alarms on the cooling circuits (supply failures,

oil flow failures, etc.). • LTC alarms (supply failures, etc.).

Please consult also the Nameplate and Schematic drawings in the drawing section.

If an alarm is generated on the transformer, it should be checked if this alarm switches on the related alarms on the entire system (such as signal lamps, flag relays, buzzers, remote indicators, etc.).

5.2.2 Trip circuits and contacts

Trip contacts on the transformer or on accessories immediately place the transformer out of service in any abnormal situation that can damage the equipment or its environment.

The most commonly used trip contacts are:

• Quick gas production (Buchholz or gas relay). • Quick internal pressure rises. • Network protection relays (fed by current

and/or voltage transformers on the transformer).

• (O)LTC failure. etc.

If a trip is generated on the transformer, it should be checked if this trip immediately switches off the transformer from the network.

5.2.3 Remote control

Depending on the actual network control system, it should be checked that all functions work satisfactory both on the transformer (in the control cabinets) and in the remote control mode. The “Site commissioning report” is indicating both:

• M.K.: Marshalling Kiosk or Transformer Control Cabinet

• Client: All remote control equipment from the client

5.2.4 Temperature settings

Make sure all temperature settings are correct and equal to or lower than the values on Pauwels drawings (Nameplate and/or Schematic drawings). Never use higher settings than the ones indicated on these drawings, as this can cause too slow reaction (or no reaction at all) of the protective devices. Needless to say that serious damage may occur.

CAUTION Temperature settings ≤ values on Pauwels drawings

Carefully check the settings of:

• The thermostat(s) • Oil thermometer(s) • Winding Temperature Indicators (WTI’s) for the

different windings

5.2.5 Verification of overpressure relief devices

The same remarks apply as for the temperature settings.

5.2.6 Voltage relation check

Before switching on, a final check of the voltage relation between all incoming and outgoing voltages should be performed.

5.3 Energization

Once the transformer is fully assembled, checked and tested as described above, and after final checks and testing of the protection equipment, the



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transformer may be energized. If the ambient temperature is not lower than -20ºC.

DANGER If the ambient termperature is very low or can be expected (below -20ºC), special precautions should be taken before energanization. Contact Pauwels for further instructions.

It is usefull to start here with a log-book, recording all important readings and observations for each transformer, will be helpfull for the maintenance and for identifying problems during the life time of the transformer. It is highly recommended to take an oil sample for DGA prior to energisation. This analysis forms a benchmark for all future DGA’s.

5.3.1 Minimum oil stabilising period after final oil filling

The transformer oil should be stabilised after final oil filling. This condition will be normally fulfilled if the transformer has been filled some days or weeks before energisation.

5.3.1.1 Transformer with forced oil circulation using pumps

Have the pumps run for at least 2 hours and wait for :

• minimum 8 hours if high voltage ≤ 245 kV • minimum 24 hours if high voltage > 245 kV

CAUTION The pumps may not be switched on if oil temperature is below –10 ºC. In this case follow the required waiting times for transformers without pumps, energise at no load conditions and wait until oil temperature raised above -10ºC. Proceed with pumps running.

5.3.1.2 Transformers without forced oil circulation using pumps.

Wait for :

• minimum 16 hours if high voltage ≤ 245 kV • minimum 48 hours if high voltage > 245 kV

5.3.2 First energizing at no load conditions.

Set the (O)LTC/DTC for the right voltage ratio. Lock the DTC drive against mal-operation while the transformer is under voltage.

To reduce the inrush-current during the first energizing, it is advisable to set the (O)LTC two or three steps out of the voltage ratio, so that more turns are in service (refer to the Nameplate). This can only be done if the transformer is of a variable flux design.

1. Switch on the voltage: 2. Check the secondary voltage (and eventually

the tertiary voltage). 3. Check the no load current.

NOTE During the first energizing, a noise-peak can be detected. This peak will be dissapear after a few minutes upto an hour.

A general observation of and around the equipment is suggested and should include a general awareness of what is happening to all the equipment located in the electrical substation. Unusual noises and disturbances should be investigated. such as :

• Fans, pumps, etc.. operating when they should not

• Circuit breakers or other equipment operating at odd moments.

• LTC taps changes too frequent or no changes at all.

• Oil leaks. Small quantities of oil can spread over large areas and can collect a lot of dust very quickly.



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5.3.3 Loading the transformer

DANGER Do not energize the transformer at operation load within 24 hours after putting at no load condition.

Set the (O)LTC in the right position and check the outgoing voltage. (If parallel-operation with other transformers is provided, the voltage ratio should be the same for all transformers). If an AVR (automatic voltage regulator) is provided, the tap changer will automaticly run to the right position.

1. Switch on the load 2. Check and record the following:

° Voltages and load currents ° Ambient temperature, oil and winding

termperatures and oil level(s).

Condition of accessories (as dehydrating breathers, fans, pumps etc...)



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6 Maintenance



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6.1 Transformer maintenance

6.1.1 Safety during maintenance

Remember that hazardous voltage is present on an energized transformer, so proper safety precautions must always be observed when working on this equipment. Consult the safety instruction in section [0] before starting any maintenance activities.

DANGER Never perform maintenance or attempt to climb on any part of a transformer unless all proper safety precautions have been taken, including de-energizing and proper terminal grounding.

6.1.2 General maintenance guidelines

Transformers are very reliable electrical equipment if well maintained and working under normal operation conditions. Nevertheless, failures due to improper maintenance or abnormal operation conditions may cause the transformer to be out of service for a long time. This will especially be the case when custom made parts have to be ordered and installed. As power supply may often be critical, it is absolutely worth spending the necessary time on a good maintenance program.

Remarks:

1. Transformer logbook: It is recommended to record readings and observations for every transformer in a logbook. This should not only be done during the warranty period but during the complete lifetime of the transformer.

2. Special service conditions: Special attention must be paid when the transformer operates under abnormal conditions. a) Bushings exposed to dust or chemically

laden air must be kept clean to prevent flashovers from occurring due to the formation of conducting deposits on the porcelain.

b) Transformers installed near a seacoast must be kept well painted to avoid corrosion by salt air.

c) Unusual service conditions: It happens sometimes that units have to be relocated to another location. Due to this new environment, it may happen that the originally agreed upon performances of the unit are not 100 % as designed for. Therefore, the intention of having a transformer operated under unusual operating duty, frequency of operation, difficulty of maintenance, parallel operation, reverse power operation, unbalanced voltage conditions, or special insulation requirements must be brought to the attention of your nearest Pauwels Transformers Representative.

6.1.3 External cleaning

Use an oil solvent to thoroughly remove all oil that appears on the outside of the tank or on the gaskets. This oil, later showing up on the painted surface, often gives the false impression of a leak.

The bushing porcelains must be kept free from dust and dirt and have to be inspected at least once a year. Abnormal conditions such as sandstorms, salt deposits, dust, or chemical fumes require regular cleaning to avoid accumulations to the external surface. Accepted methods of hot line washing or cleaning with solvents may be used.

Keep the heat radiating surfaces of the transformer clean. External surfaces of forced oil heat exchangers should be periodically cleaned as a particular dusty location may dictate. Transformers near the seacoast or in corrosive atmosphere areas should be painted regularly to prevent corroding or rusting of metal parts.

If it becomes necessary to remove a radiator or air-cooled oil cooler, first close the valves, top and bottom, and bolt them in the closed position. Next, drain the oil from the radiator by removing the drain plug from the bottom header and the vent plug from the top. After draining the oil, remove the radiator. If the radiator/cooler is removed for any length of time, the transformer valves should be sealed with gaskets and covered with suitable plates. This also applies to the radiator-cooler openings.

All breathers and small openings in pressure relief valves (and pressure vacuum bleeders on sealed



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tank system and inert gas system units) must be kept clean and in operating condition.

All ground buses and wiring leads to ground must be kept in good condition. Proper relay operation depends on low ground resistance. Ground resistance must be measured annually

6.2 Periodic Inspection of transformers in service

6.2.1 Oil levels and silica gel

The oil levels in the tank and load tap changer mechanism compartment should be checked at two-week intervals during the first month of operation and annually after that.

Check the condition of the silica gel in the air breathers weekly. Replace if necessary.

6.2.2 Oil quality

Regular testing of the oil quality is required. Dielectrical strength and water content are standard oil tests to be performed on an annual basis. DGA is highly recommended as well.

6.2.3 Venting

At moments when the transformer is not energized, it is advised to use this opportunity to vent the air or gas bubbles from the different places where air vents are installed. Like on top of radiators, manholes, pipes, conservators with atmoseal bag, etc., wherever applicable.

The basic conditions that must be fulfilled before venting is allowed are the following:

• the transformer is de-energized and suitable grounding has been done

• the internal pressure is higher than the ambient pressure

• venting is only allowed on places filled with oil. This is not always the case when related to nitrogen cushioned sealed tank systems.

Venting is also required when components are replaced which are situated in places where oil is involved.

6.2.4 External circuits and control equipment

The following must be inspected 30 days after installation and once a year after that.

• Control circuit voltage. • Excess heating of parts - evidence by

discoloration of metal parts, charred insulation, or odor.

• Freedom of moving parts (binding or sticking is not allowed).

• Excessive noise in relay coils. • Excessive arcing in opening circuits. • Proper functioning of timing devices,

sequencing of devices, relief device alarm contacts, thermometer contacts, etc.

• Check the heaters in the control cabinets. • Also check temperature settings. These

settings can be lower than the ones indicated on the schematic diagrams but never higher.

• Evidence of water or liquids in control cabinets and in air-filled cable boxes.

6.2.5 (On) Load tap changer – (O)LTC

We refer to the specific documentation of the (O)LTC for maintenance instructions. Also check the oil quality and oil level on a regular basis.

6.2.6 De-energized tap changer – DTC

Beside the specific maintenance instructions in the documentation, the DTC has to be switched over its total range for at least ten times and this has to be done minimum twice a year.



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6.2.7 Cooling system

Regarding naturally cooled transformers and transformers equipped with air-cooled oil coolers, there is, in general, no need for taking special steps to keep the inner side (oil circuit) of the cooling surfaces clean, as long as the oil is in good condition. If, however, formation of sludge in the oil has set in, the sludge may deposit in horizontal surfaces in radiators and coolers. In such a case, the radiators and the coolers should be rinsed in connection with the changing of oil and overhauling of the transformer. If the sludge does not loosen by flushing with oil, use benzine, trichlorethylene, etc., and afterwards flush with oil.

The other side that is exposed to the elements by dust, sand, etc., has to be cleaned as mentioned before.

6.2.8 Fans

6.2.8.1 Bearings

Fan motors are executed with sealed ball bearings lubricated with heavy-duty grease that do not require any maintenance as experienced by our fan suppliers and also by Pauwels’ after service engineers during many decades. The bearings are from the so-called “maintenance free” type; it is advisable to know the general maintenance instructions on bearings as mentioned by bearing, motor and fan manufacturers.

6.2.8.2 Periodical fan operation

During extended periods of reduced transformer capacity not requiring fan operation, it is required that the fans be activated on a periodical base (bi weekly for 1 hour), to assure satisfactory operation when required. This is valid for all electrical motors of fans, pumps etc.

6.2.8.3 Other

Make sure that the drain holes (closed with a plastic plug upon delivery) are open (to allow draining of condensation) and check also that the fan blades can rotate without any obstruction of foreign objects (like bird’s nests etc.).

6.2.9 Temperature

The life of a transformer is highly dependent on the temperature prevailing in the windings and the core of the transformer under operation. It is therefore important that the temperature is continually kept under observation (e.g. via a remote sensing system towards a dispatch center).

Even with a low temperature of the cooling medium (ambient air), the transformer can be overloaded. Hence the permissible overload must not be judged only from the temperature rise of the oil above the cooling medium, because the temperature drop winding-oil increases with the 1.6th power of the increase of load. The ANSI/IEC Loading Guide may be used on condition that the ”assumed characteristics at rated load” as mentioned in the applicable standard, will be replaced by ”actual characteristics after testing”. This means that the actual ratio for no load and load losses including the actual top oil and average winding rise has to be used for good judgment on allowable overload situations.

In case of doubt, Pauwels has to be consulted.

Normally, it is not possible to place a temperature measuring device directly on the windings of a transformer, except in a few special cases where fiber optics are mounted in the windings to measure direct temperatures. Pauwels uses a method by means of which an artificially obtained temperature is measured, which follows the temperature in one or more of the windings of the transformers.

This device is installed if the design specifications called for a Winding Temperature Indicator or ”WTI”. In case a ”WTI” is not installed, the top oil temperature indicator related to the ambient temperature will give a reasonable indication about the load conditions.



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If, without an increase in load or change in environmental conditions, there is a tendency for the temperature of a transformer to rise, the reason may be that in some way the cooling is reduced (e.g.: fans out of service).

Another reason for abnormal temperature may be that the oil has started to form sludge deposits in the radiators, on the windings and/or on the core of the transformer. The cooling of the active part is then reduced, and its temperature will increase. However, the latter situation is considered to be a very abnormal one.

If abnormal temperature rises have been found, the thermometer should first be checked for proper functioning.

The overload capacity is sometimes limited by the accessories of the transformer (e.g. bushings, tap changers, etc.) After every continuous overload of 20 % or more, an investigation is recommended.

6.2.10 Inspection of tank, cover, gaskets and valves

Tank, cover, gaskets and valves require annual inspection for leakage, etc. All required replacements or adjustments should be accomplished as soon as possible.

Groundings: Check the transformer grounding connections and all groundings of accessories.

Painting: Check the transformer painting and repaint (parts) if necessary.

Gaskets: We refer to the installation chapter, section [3] for advice on whether to re-use gaskets or not.

Valves: In case leakage is detected on the driving shaft, re-tighten the compression gland. Use only graphite-free sealing material when changing packings.

6.2.11 Periodic electrical testing

6.2.11.1 Power factor test

It is recommended to perform a power factor test whenever the unit has been de-energized for longer periods (> 1 month) or when the unit is opened for any reason. In addition, it is recommended to perform the test on an annual basis.

We refer to section [3] for more information about this test and the required values.

6.2.11.2 Accessories

Test all accessories once a year. Examine all instruments, electrical cables and conductors, signaling and operating devices to the control room or control board. Megger testing is also recommended once a year.

6.3 Periodic inspection of transformers in storage

1. Keep the bushings and the external surfaces clean.

2. Check the gas pressure if a gas pressure installation is still connected.

3. Keep the unconnected valves closed. 4. Check the silica gel air dryer at least once a

month; replace the silica gel if necessary. Check also the level of the oil lock. The color change must start at the oil lock side of the air breather, otherwise air is coming in through a leak.

5. Check the oil level of the transformer once a month (in case of a dropping oil level, inspect the tank for possible leaks).

6. Check whether the panel heater in the control cabinet is functioning, especially before and during wintertime.

7. Check the external painted surfaces and the cable box for paint damage or corrosion once a year.



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In case of any irregularity, repair it as soon as possible or contact the manufacturer Pauwels.

CAUTION Store the transformer in a dry, cool and properly ventilated area.

6.4 Maintenance inspection chart

The maintenance inspection chart (see table below) lists suggested rules for performing inspections, recordings and maintenance.

Remarks:

Not all items necessarily apply to the specific transformer, because some accessories or features may not be available.

6.4.1 Frequency indications

D = daily (especially during the first weeks of

energization) W = weekly M = monthly S = semi-annually (6 months) A = annually WR = when required F = according to the (O)LTC documentation section [7].

6.4.2 Maintenance activity to perform

1. Visual inspection and reading 2. Cleaning and examination 3. Taking oil sample, testing for dielectrical

strength, water content and DGA. 4. Filtering 5. Lubrication 6. Operating test 7. Testing electrical circuits 8. Megger test electrical circuits 9. Inspection / cleaning of contacts 10 Changing contacts



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Maintenance activity to perform COMPONENT 1 2 3 4 5 6 7 8 9 10 Painting of tank, cover and metal parts: repaint if necessary A

Condition of gaskets, absence of oil leaks: retighten or replace gaskets if necessary

A

Conservator A Radiators: similar temperature on bottom side of all radiators (indication for formation of sludge)

A

Fans attached on radiators A S A A A Fans: plugs on drain holes removed? A Coolers with fans incorporated A S A A A Coolers water-cooled, (oil side) WR

Coolers water-cooled, (water side) S-WR

Valves WR Oil pumps with motor WR A A A Oil of transformer main tank A 4 WR Bushings A Magnetic oil level indicators D WR A A A Buchholz relay W WR A A A Temperature indicator(s) D WR A A A Thermostats WR A A A Flow indicators for oil and water D WR A A A Pressure gauges for oil and water D WR A A A Pressure relief device M A A A A Dehydrating breather for main tank W WR Nitrogen cushion on sealed tank system

5D

Nitrogen equipment for units with inert gas pressure system (positive pressure nitrogen system)

D WR A A A

Manual driving mechanism for de-energized tap changer (DTC) A A A A A

Load tap changer: F - Main contacts of LTC F 6S - Oil of LTC compartment 7A WR - Oil level indicator of LTC D WR A A A

Remarks indicated in the table 4 If the transformer is operating in extremely high ambient temperatures and/or high loads or overloads, sampling and analysis should be performed on a more frequent basis. 5 During cold ambient temperatures the nitrogen pressures will drop. The first weeks after putting the nitrogen blanket on the top of the oil are critical as well, since the nitrogen will dissolve in oil and the nitrogen pressure tends to drop below the minus 5 PSI setting of the pressure/vacuum bleeder on the main tank. It is required to adjust the nitrogen pressure up to + 5 PSI. 6 The (O)LTC and DTC have to be switched over the total range for at least 10 (ten) times. 7 First oil check has to be performed after about 20.000 tap changes, regardless of which (O)LTC-type is used in the transformer. More detailed information on (O)LTC maintenance can be found in the available documentation.



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Maintenance activity to perform COMPONENT 1 2 3 4 5 6 7 8 9 10 - Thermostat WR A A A - Pressure relief device M A A A A - Motor drive unit A S A A A - Automatic system for operation A A A - Dehydrating breather for LTC W Lightning arresters A A Protective relays A A A A All groundings (including CT groundings) A A

Re-tightening of all bolts + nuts at electrical connections S

De-energized tap changer (DTC) (3)S

Table 16 Maintenance inspection chart



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6.5 Troubleshooting

6.5.1 Electrical malfunction

Electrical malfunction. Observations made The power supply tripped while switching on the transformer. ↓ Abnormal high noise after several hours of service. ↓ Overheating at no load ↓ Overheating at normal load ↓ Unequal or unstable voltages on phases at equal load on all phases. ↓ Trip by internal transformer fault (Buchholz, Pressure relay, Load tap changer,…) ↓ Trip by external protection relays during normal service (Time current, ground fault, etc.) ↓ Possible cause of malfunction Rectification measures X Supply voltage is too high, leading to

excessive inrush current / core loss. Do not exceed 105% of the ref. voltage; reset the tap changer in the right position.

X X Wrong protection relay setting. (inrush current, etc.)

Check and reset protection relays.

X X Circulation current between parallel transformers.

Check all parallel operation conditions; set tap changers for the same voltage ratio.

X Loose parts on the core/windings; possibly caused by transport damage.

Switch off; consult the manufacturer.

X Cooling system is insufficient. Check that valves of all coolers are in the right working position. Check air, oil and water supply. Check fan / oil pump operation. Note: At OFAF cooling, oil pumps always have to be in operation (even at no load)

X X Overloading. Fault on the thermometer. Ambient temperature is too high.

Reduce load. Check the thermometer. Check for faults in the secondary network.

X X Heavy peek loads, start currents etc. Bad contacts on internal or external connections. Internal transformer or tap changer fault.

Check for change of the load. Consult the manufacturer for further actions.

X Malfunction of the measuring instrument. Internal transformer fault.

Check the measuring instrument. Switch off; consult the manufacturer.

X Fault or short-circuit in the secondary network. Internal transformer fault.

Check the secondary network. Repeat all checks and tests as if it were the first energization. Consult the manufacturer.

Table 17 Electrical malfunction troubleshooting chart



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6.5.2 Mechanical malfunction or malfunction of accessories

Observations made Oil level is not correct. ↓ Alarm on Buchholz, gas relay. ↓ Alarm on temperature devices. ↓ Fans or oil pumps do not work. ↓ Insulation resistance is too low. ↓ Power factor is too low. ↓ Visual oil leaks. ↓ Possible cause of malfunction Rectification measures X Level indicator is defective.

Low oil level due to oil leak(s). Repair or replace level indicator. Locate oil leak(s); repair leak(s). Replace leaking device or gasket(s).

X Insufficient air venting during erection. Fault gas production.

Gas analysis is recommended. Consult manufacturer for further actions.

X The ambient temperature is too high. Overloading. Malfunction of the temperature devices. Malfunction of the cooling system.

Reduce load. Check / replace temperature device.

X Defect on temperature detecting system. Devices are defective.

Check detecting system. Replace defective devices.

X Contamination on bushings, etc. Penetration of humidity in the insulation system.

Clean-up external bushings, terminals,… Consult the manufacturer.

X Degradation of the insulation system.

Clean-up external bushings, terminals,… Consult the manufacturer.

X Defective gaskets. Tighten bolts. Replace gaskets.

Table 18 Mechanical malfunction troubleshooting chart



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6.6 Oil quality

One of the most important parameters in transformer maintenance is the oil quality. Testing the oil quality on a regular basis gives good indications on the oil quality itself and on the working conditions of the transformer. Before taking any steps towards oil replacement, be sure that the cause of the problem has been found and eliminated.

Remarks:

Changing the oil in a transformer has to be in line with the filling procedures described earlier in this IOM Manual. The change should be as complete as possible, because usually a mixture of old and new oil will soon acquire the properties of the poorer quality.

Important oil characteristics to test:

• Color and appearance • Dielectrical strength (∗) • Water content (*) • Neutralization value • Sediment and/or precipitable sludge • Dielectric dissipation factor • Resistivity • DGA (*) • Presence of inhibitor • Presence of particles (*)

Testing and evaluating the above parameters has to be in accordance with IEC 60422 or corresponding ASTM standards.

∗ Pauwels gives more severe values than IEC 60422 or corresponding ASTM standards and/or additional information. Further information about this can be found later in this IOM manual.

6.7 Oil sampling

Accurate sampling methods are extremely important for the reliability of the test results. Oil sampling has to be in line with the applicable standards. The instructions below are a general guideline in oil sampling but do not replace the applicable standards (see explanation given for the individual tests).

CAUTION Sampling when the transformer tank is under negative pressure may cause an air bubble to be drawn into the tank. This may result in catastrophic dielectric failure (and explosion).

Since the test results of a sample may be very odd, we recommend taking a second sample at the same time. In case of doubt the second sample can be used for confirmation.

6.7.1 Taking samples for general oil testing purposes

The instructions below must be followed for dielectric strength, water content, power factor and interfacial tension. Testing has to be in line with ASTM D 923 or IEC 60475.

• Use a clean dry screw cap bottle with a capacity of one liter for collecting samples. Clear glass bottles are considered best, as the visual characteristics and the condition of the oil can be ascertained quickly. Store and ship the oil sample in a dark box, as exposure to bright light for prolonged periods may affect certain properties.

• Samples are to be taken from the sampling valve of the transformer tank (or from the outlet of the treatment equipment) or from the bottom of the drum. If the transformer has just been filled, then it should be allowed to settle for up to three days for a large transformer. Up to 8 hours waiting time is required for a drum. Samples taken too soon may produce incorrect test results (e.g. dielectric strength



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will test low). If the transformer is or has been operating, samples can be taken at any time.

• Drain off sufficient liquid to be sure that a true specimen of the main tank oil is obtained, and not one that has been stagnant in the pipework or in the valve. Therefore, drain off three or four liters of oil into a clean bucket before taking the oil sample. Rinse the clean container several times with oil prior to taking the actual sample.

• The oil can contain a large amount of dissolved water, invisible to the eyes but easily detected by test. If the sample bottle contains liquid water, contact Pauwels immediately. It is preferred that the temperature of the oil be equal or warmer than the ambient air to prevent contamination by condensation.

• A period of 12 hours should be observed between taking the sample and performing tests, to allow the oil to stabilize and become homogeneous.

6.7.2 Taking samples for DGA tests

For DGA tests it is always recommended to take a spare sample. This spare sample can be used if something happens to the first sample, or if the analysis is very odd. Testing has to be in line with ASTM D 3613 or IEC 60567.

• Use dry clean syringes, equipped with a 3-way syringe valve. Record the transformer serial number, the ambient temperature, the oil temperature and the date of sampling.

• The sample is to be taken from the oil sampling valve. The location of this valve is indicated on the General Arrangement drawing.

• If oil circulating pumps are installed on the transformer, they should be operated for a minimum period of one hour before taking any oil samples.

• Allow 3 to 4 liters of oil to run into a clean bucket to ensure a true sampling of the tank oil.

• Attach the 3-way syringe valve and the sampling syringe to the sampling valve (using an adaptor).

• Open the sampling valve very slowly and allow the oil to flow through the 3-way valve into the

clean bucket without injecting air bubbles into the stream. Avoid bubbles in the sample by using the 3-way syringe.

• Flush the syringe by using the 3-way valve. Let the oil in the syringe and push the oil to the bucket, using the syringe plunger. Repeat this procedure several times until the syringe is clean and filled with oil, completely free of gas bubbles. Close the 3-way valve to the syringe.

• Close the sampling valve and remove the syringe. Place the syringe in the syringe box.

Take the spare sample following the same procedure.

6.8 Dielectrical strength

Oil sampling has to be in line with ASTM D 923 or IEC 60475. The test should be performed in a well-equipped laboratory according to the applicable standards.

Required values for transformers in service:

• > 60 kV/2.5 mm (as tested per IEC 60156) • > 30 kV/2.54 mm (as tested per ASTM D 877)

If values are lower, the oil should be filtered or streamlined. Test the oil annually or even more frequently if the operation condition of the transformer questions the continuity of the oil quality in general.

Low insulating oil strength may also be an indication that the transformer insulation contains excess moisture. Further evaluation should be made such as power factor tests and taking oil samples to determine moisture content in oil.

Remarks:

If some work has been carried out on a transformer and the oil has, during that time, been exposed to the humidity of the air, the breakdown value of the oil should be checked.



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6.9 Moisture content

Transformer oil is hygroscopic and therefore it absorbs moisture from the air. The absorption of moisture is minimized by the oil preservation system. The oil conservator system with a silica gel breather also minimizes the entry of moisture as long as the silica gel is properly renewed or regenerated as soon as its ability to absorb moisture begins to diminish. Check also whether the oil lock in the silica gel breather is properly filled with oil (check maximum and minimum oil level indications in lock).

Moisture content in ppm is related to the operation conditions of the transformer. Moisture in oil can lead to reduction of the dielectric strength in oil and windings. The table below gives the maximum allowable ppm of water in oil.

Temperature (° C)∗ Maximum water content (ppm)

- 20 5 - 10 9 0 16 10 20

Table 19 Water in oil

Example:

In case 50 ppm moisture is detected in oil that is sampled at 10° C oil temperature, free water has been created already and this water might have been absorbed inside the windings and other critical parts of the transformer. This is a dangerous situation for the transformer.

6.10 Particles in oil

The breakdown strength of oil decreases when the moisture content increases at the same sample temperature. A further reduction in the breakdown

∗ The indicated temperature is the lowest temperature the oil can reach, non-service conditions considered as well.

strength of oil occurs when iron, copper, aluminum or cellulose particles are situated in the oil and tests in this field show that the dielectrical strength of the oil is very poor in this case.

Larger and conducting particles decrease the breakdown voltage most, whereas fine particles can be agglomerated or be dispersed, so that particle chains can be developed. It is also known that particles may cause partial discharges.

If severe formation of particles has set in, the oil changes its color and gets darker. The appearance of the oil is usually muddy. By filtering, it is possible to remove the sludge but, having once started, the formation of sludge will increase with time. Such oil should be completely changed as soon as the service conditions permit it.

For the reasons mentioned above, Pauwels has produced its own criteria for particles in new transformer oil. We take these criteria into account before testing a transformer. The same values can be used for transformers in service.

Particle size Maximum amount of particles in 10 ml sample (0.338 fl.oz)

all Particles ≥ 1.5 µmof which : 2500

Particles ≥ 5 µm 1500 Particles ≥ 20 µm 30 Particles ≥ 30 µm 10

Table 20 Particles in oil

Since each measurement will produce different results, it is a practical matter to provide 5 or 6 measurements. The average of measurements is then the base for the determination whether the particles are within the required limits.

Remarks:

Another process of ageing, associated with the formation of sludge, is the increase of the content of free acids in the oil. If this content does not exceed 0.5 mg KOH per g (500 ppm) and apart from this the oil shows good properties, then it is fit for use. If this is not the case, the oil should be changed. New transformer oil as supplied by Pauwels Trafo contains an acidity (free acids in the oil) lower than 0.1 mg KOH/gr.



109

Should the flash point, when tested according to ISO 2719 or ASTM D92, be less than 130 degrees and should the oil also smell burnt, then a decomposition (cracking) of the oil may have occurred. In that case a DGA should be performed and/or the transformer should be inspected (lifted or the manholes opened) to make sure that there is no local overheating of core or windings.

6.11 Dissolved Gas Analysis on transformer oils from the main tank of a transformer

Sampling has to be done in accordance with IEC 60567 or ASTM 3613

Analysis has to be performed in accordance with IEC 60567

6.12 Frequency of analysis

DGA should be performed as frequently as possible, but at least once a year as long as the values remain below the limits of Table 21. See also 6.13.1 for actions in case of values exceeding the limits of table 1.

6.13 Evaluation

Compare the results with the values in table 1.

Name gas Symbol Gas

Concentrations [ppm]

Rates of production* †

[ml/day]

Rates of production †‡

[ppml/day] Hydrogen H2 150 5 Methane CH4 130 0.33

Carbondioxide CO2 5000/10000$ 30 Carbonmonoxide CO 1000 3

Ethane C2H6 90 0.25 Ethylene C2H4 50 2 Acetylene C2H2 5 ** 0.1††

Table 21 Limits for normal values for Pauwels Transformers

* Rates of production [ml/day] = (Δc x V) / (Δt x 1000) Δc = difference in concentration over the observed period [ppm]

V = volume of the transformer [I] Δt = expired period between measurements [days]

† To have a reliable rate, intervals should be longer than 2 weeks ‡ rates of production [ppm/day] = Δc/Δt

Δc = difference in concentration over the observed period [ppm] Δt = expired period between measurements [ period]

$ 5000 ppm for transformers with sealed conservations system (atmoseal…), 10000 ppm for transformers with open breather conservation system ** If a communicating OLTC-conservator is in use, this value will be 270ppm †† if a communicating OLTC-conservator is in use, this value will be 1 ml/day

Remarks:

• IMPORTANT: In many cases, acetylene (C2H2) is a sign of severe electrical problems. Therefore, the presence of acetylene always should be considered as serious and treated as such.

• If C2H2/H2-ratio is higher than 2, a

contamination from the OLTC-compartment is probable. If this is the case, DGA of the main tank can be unreliable.

• If CO2/CO-ratio is lower than 3, paper

deterioration is possible. This has to be checked with a FAL-analysis (specific analysis for paper deterioration). For evaluation: contact Pauwels.

• Values for rates of production tend to be higher

in relatively new transformers and can exceed the values in table 1 for new transformers (<1 year).

• When calculating rates of production, intervals

should be longer than 2 weeks to provide an acceptable accuracy of results.

• Rates of new samples should be calculated

relative to the latest historical sample, not to the sample that needed to be confirmed when the period between the two successive samples is too short for reliable evaluation of rates,



110

• ppm = µl/l



111

6.13.1 Actions

6.13.1.1 First DGA-sample of a transformer

Level gas > table 1?

Level C2H2 > table 1? Alert condition Resample ASAP

Concentration gas > table 1?

NORMAL-status Resample ≤ 1 year

Concentration C2H2 > table 1?

ALERT-status Check rate immediately

ALARM-status Contact Pauwels

Check rate immediately

First DGA-sample of a transformer

Evaluate with respect to historical data

NO

NO

NO

YES

YES

YES



112

6.13.1.2 Historical DGA-data are available

6.14 Replacement of defective parts

Always follow the applicable safety instructions when working on a transformer. Follow the installation instructions (section [3]), use the available drawings (section [6]) and/or specific documentation (section [7]) for the part or accessory to replace or repair.

In case of any difficulty contact your Pauwels contact person or PTS for advice or assistance.

6.14.1 Ordering replacement or spare parts

Replacement or spare parts should be ordered through the responsible Pauwels division:

• Warranty related aspects: contact your Pauwels contact person.

• Non warranty related aspects: contact the Pauwels Transformer Service Division. Their coordinates are avialable in section [0].

Use the “Parts ordering form” in section [9], provide all the relevant information (transformer serial number, part description and numbers on General Arrangement Drawing, …) and send it to either your contact person or Pauwels Transformer Service.

ALARM-status Consider to shut down

Contact Pauwels Immediately

Resample within 2-4 weeks

Historical DGA data available ?

Concentration gas > table 1? NORMAL-status Resample ≤ 1 year

ALERT-status Contact Pauwels

ASAP R l ≤ 3 th

Concentration C2H2 >

Rate C2H2 > table 1?

ALARM-status Contact Pauwels immediately

Resample immediately

Rate new sample > table 1?

Shut down ! Inform Pauwels

immediately

Rate gas > table 1? ALERT-status

Resample ≤ 6 months

ALERT-status Contact Pauwels

ASAP for evaluation and further actions

Take new sample ASAP

Concentration gas > table 1?

Rate gas > table 1?

NORMAL condition Resample ≤ 1 year

ALERTstatus Resample ≤ 6 months

Evaluate as first DGA-sample of a transformer

NO

NO

NO

NO

NO

NO

NO

NO

YES

YES

YES

YES

YES

YES

YES

YES

NO



113

7 Forms, checklists



114

Receiving inspection report Date of report: Transformer Serial No: 1

Customer and Equipment information

A Customer information Customer Name: Contractor Name: User name: Purchase Order No: Additional information:

B Equipment information

Rating: MVA KV Arrival location: Date of arrival: Transport by: VESSEL TRAIN TRUCK PLANE Additional Information:

2

Arrival conditions of the equipment

Equipment inspected by (name and function):

Has the transformer been subjected to all recommended arrival inspections and tests? YES NO

Visual external inspection of the transformer: OK NOK Inspection of all means for blocking and securing: OK NOK Absence of oil leaks: OK NOK Inspection of the impact recorder: OK NOK Recorder type and serial number: Highest readings or recordings: Inspection of the inert gas pressure system OK NOK Tank pressure (> 0.05 bar): Pressure of gas bottle in use (> 3 bar):

Is the equipment (transformer and parts) undamaged and complete? (if No, specify below) YES NO

Remarks on arrival of the equipment:

3 Appendices

4 Date, name(s), function and signature(s)

Remarks: Complete this report and send it to your Pauwels contact person. If there is any damage or missing material, follow the procedures mentioned in the IOM manual.



116

117

Energization Report

Date of report: Transformer Serial No: 1 Customer and Equipment information

A Customer information Customer Name: Contractor Name: User name: Purchase Order No: Additional information:

B Equipment information

Rating: MVA KV Site location: Delivery date: Additional Information

2 Energization information Energization date: Energization hour: Atmospheric condition: Ambient temperature:

Additional information concerning energization conditions:

Have all the tests and inspections listed in the “Site commissioning report” been performed? YES NO

Has a copy of the “Site commissioning report” been sent to Pauwels (in case erection and commissioning has not been done or supervised by Pauwels)?

YES NO

Has energization been successful and without any problems? YES NO

Remarks on energization:

3 Appendices

4 Date, name(s), function and signature(s)

Remark: Pauwels will confirm receipt of this report.



118

119

Parts ordering form (1)

Parts price request

1 Customer information A Customer information Customer: Customer P/O No (1): Contact Person: Tel: Fax: Additional information:

B Transformer information Transformer serial No: Rating: MVA KV Date of energization:

2 Information on parts delivery Type of parts: Replacement of defective parts Spare parts Delivery terms: Delivery address:

Tel: Fax:

3 Parts Item No (2) Description Type/Specifications # Unit Price Total Price

Currency: Total price:

4 Date, name, function and signature Date Name and function Signature

(1) When ordering parts: an official Purchase Order with reference to our quotation is required. (2) Item No’s are provided on the General Arrangement drawing and materials list (in IOM manual).



120

121

Site commissioning report

Cover sheet

Project Customer customer reference Order number SIte Country PTS reference Serial number MVA HV MV LV Vector group Attached test result sheets Date

122

Mechanical inspection Tx.Nr. Before start of erection. Visual inspection of main tank for transport damages Visual inspection of crates containing transformer parts. If there is a visible damage, write a report. If possible, take photgraphs of this damage and notify the client/insurance company. Remarks : Inspection of shock indicator or shock recorder. Type : Enregistreur Indicateur Electron. Longitudinal dir. : ≤ 0.5 g Y/N Y/N Y/N Transversal dir. : ≤ 0.8 g Y/N Y/N Y/N Vertical dir: ≤ 0.3 g Y/N Y/N Y/N If applicable, measurement of core-to-tank insulation (PTS IR or IR3)) After erection

General check OK NOK NA ground connections of all accessories mm mm distance between lightning rods & ground check position of all valves Position of flap valves (radiators) oil level transformer oil level tap changer desaeration of relevant parts absence of oil leaks absence of tools on transformer markings, terminal plate, rating plate air breather(s) : oil lock, silica gel condition painting Pauwels’s representative Client’s representative Name Name Signature Signature : PTS MI

damage no damage damage no damage

123

Mechanical & electrical checks Tx.Nr. ON LOAD TAP CHANGER. OK NOK NA Are all the necessary supply voltages present ? Synchronisation of motor drive / tap changer Manual test of end posistions Electrical test of end positions Local electrical control of tap changer Remote electrical control of tap changer Heating : functioning and control OFF LOAD TAP CHANGER OK NOK NA Synchronisation of drive / tap changer Functional test Funtioning of mechanical interlocks LINKS INSTALLED UNDER TX COVER OK NOK NA Voltage Check position of links --> operating voltage CONTROL CABINET OK NOK NA External wiring completed Current transformers connected or short circuited All wiring insulation tested with 500V (except remote) position ind / AKM Trafoguard / DIGEM Tightmess of connections Phase rotation of incoming supply Rotation of each fan Rotation of each pump Operational tests & checks of measuring andcontrolling devices OK NOK NA Manual control of fan operation Thermal device control of fan operation Manual coantrol of pump operation Thermal device control of pump operation Breaker contact operation of pump control Oil flow indicator(s) Automatic change over of supply voltage Heating : functioning and control Indication of “Fans working” and contact (if applicable) Indication of “Pumps wordking” + contact (if applicable) Indication of “Tap changer running” + contact (if applicable) Pauwels’s representative Client’s representative Nom: Name: Signature: Signature:PTS ME

124

ALARM CONTACTS Tx.Nr. C.C. CLIENT NA Buchholz transformer Buchholz cable boxes Oil level transformer minimum Oil level tap changer maximum Oil level tap changer minimum Oil temperature alarms Winding temperature alarms (primary) Winding temperature alarms (secondary) Winding temperature alarms (tertiary) MCB cooling supply C.C. supply-control relay(s) MCB tap changer supply Tap changer suppy-control relay Aux.contacts of fan MCB’s Aux. contacts of pump MCB’s TRIP CONTACTS C.C. CLIENT NA Buchholz transformer Tap changer protective relay Buchholz cable boxes Overpressure relief device 1 Overpressure relief device 2 Overpressure relief device on cable boxes Oil temperature trip Winding temperature trip (primary) Winding temperature trip (secondary) Winding temperature trip (tertiary) Non return flap valve (Sergi) INDICATION CONTACTS C.C.. CLIENT NA Check all applicable signalisation contacts Pauwels’s representative Client’s representative Name Name Signature Signature PTS ATC

125

Verification of overpressure relief device mbar NA overpressure relief device 1 on transformer overpressure relief device 2 on transformer overpressure relief device on cable boxes Pauwels’s representative Client’s representative Name Name Signature Signature PTS TS

Tx.Nr. Temperature settings ≤ values on Pauwels drawings

Thermostat degrees C NA start fans (pumps) alarm trip

Oil thermometer degrees C NA stop fans (pumps) or alarm 1st stage start fans (pumps) or alarm 2nd stage alarm trip

WTI (primary) degrees C NA stop fans / pumps (1) start fans / pumps (2) stop fans / pumps (2) start fans / pumps (2) alarm (1) alarm (2) or trip

WTI (secondary) degrees C NA stop fans / pumps (1) sart fans / pumps (1) stop fans / pumps (2) start fans / pumps (2) alarm (1) alarm (2) or trip

WTI (tertiary) degrees C NA stop fans / pumps (1) start fans / pumps (1) stop fans / pumps (2) start fans / pumps (2) alarm (1) alarm (2) or trip

126

Insulation resistance measurement Tx.Nr. Date : Atmospheric condition Ambient temperature Oil Temperature Tap changer position Megger Make Type : HV – LV + Tank LV – HV + Tank Applied voltage kV Applied voltage kV 1 min 1 min 2 min 2 min 3 min 3 min 4 min 4 min 5 min 5 min 6 min 6 min 7 min 7 min 8 min 8 min 9 min 9 min 10 min 10 min Polarization Index (value 10 min / value 1 min) Core – Tank insulation resistance measurement Applied voltage max.. 5000 V. Measured value MΩ Make sure the link is re-established and tightened after measurement Pauwels’s representative Client’s representative Name Name Signature Signature PTS IR2

127

Insulation resistance measurement Tx.Nr. Date : Atmospheric condition Ambient temperature Oil Temperature Tap changer position Megger Make Type : HV – MV + LV +Tank MV – HV + LV + Tank LV – HV + MV + Tank applied voltage Applied voltage Applied voltage kV kV kV 1 min 1 min 1 min 2 min 2 min 2 min 3 min 3 min 3 min 4 min 4 min 4 min 5 min 5 min 5 min 6 min 6 min 6 min 7 min 7 min 7 min 8 min 8 min 8 min 9 min 9 min 9 min 10 min 10 min 10 min Polarization Index (valeu 10 min / valeur 1 min) Core – Tank insulation resistance measurement Applied voltage max.. 5000 V. Measured valur MΩ Make sure link is established and tightened after measure Pauwels’s representative Client’s representative Name Name Signature Signature PTS IR3

128

Oil test results Tx.Nr. Sampling date Atmosperic condition Ambient temperature Oil temperature Testing date Ambient temperature Oil temperature Dielectrical strength Instrument used Make Type : Sample 1 Sample 2 Sample 3 Sampling Location Sampling Location Sampling Location

1 kV 1 kV 1 kV 2 kV 2 kV 2 kV 3 kV 3 kV 3 kV 4 kV 4 kV 4 kV 5 kV 5 kV 5 kV 6 kV 6 kV 6 kV

Average kV/2.5mm Average kV/2.5mm Average kV/2.5mm PPM water content Sample 1 Sample 2 Sample 3 ppm ppm ppm Pauwels’s representative Client’ s representative Name Name Signature Signature PTS OT

129

Voltage ratio test Tx. Nr. Test performed by bridge Test performed by voltmeter Instrument make : Instrument type : if V-metre A-B V B-C V C-A V

if by V-meter, note measured phases and volts if by bridge, note injected phases, measured phases and values

tap.pos.

1 2 3 4 5 6 7 8 9

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Pauwels’s representative Client’s representative Name Name Signature Signature PTS VR

130

Vector group test Tx.Nr. Applied voltage A – B V B – C V C – A V Measured voltage V V V V V V Equations

Vector group = Pauwels’s representative Client’s representative Name Name Signature Signature PTS VG

c

b

a A

C B

c

b

a A

C B

c

A

C B

A

C B

131

Winding resistance measurement Tx.Nr. note selected terminals tap pos

1 _Ω _Ω _Ω 2 _Ω _Ω _Ω 3 _Ω _Ω _Ω 4 _Ω _Ω _Ω 5 _Ω _Ω _Ω 6 _Ω _Ω _Ω 7 _Ω _Ω _Ω 8 _Ω _Ω _Ω 9 _Ω _Ω _Ω

10 _Ω _Ω _Ω 11 _Ω _Ω _Ω 12 _Ω _Ω _Ω 13 _Ω _Ω _Ω 14 _Ω _Ω _Ω 15 _Ω _Ω _Ω 16 _Ω _Ω _Ω 17 _Ω _Ω _Ω 18 _Ω _Ω _Ω 19 _Ω _Ω _Ω 20 _Ω _Ω _Ω 21 _Ω _Ω _Ω 22 _Ω _Ω _Ω 23 _Ω _Ω _Ω 24 _Ω _Ω _Ω 25 _Ω _Ω _Ω 26 _Ω _Ω _Ω 27 _Ω _Ω _Ω 28 _Ω _Ω _Ω 29 _Ω _Ω _Ω 30 _Ω _Ω _Ω

Secondary winding ;

_Ω _Ω Oil Temperature

_Ω Winding temperature

Tertiary winding : _Ω

_Ω _Ω

Pauwels’s representative Client’s representative Name Name Signature Signature PTS WR

132

Tg delta measurement Tx.Nr. Date Atmospheric condition Ambient temperature Oil temperature Tap changer position Test device Make Type HV – LV + Tank % L-GND(CH- L&CG-G red)

HV – Tank % L-Guard(CH-G red)

HV – LV % (CH-L red)

LV – Tank % H-Guard(CL-G red)

LV – HV + Tank % H-GND(CH-L&CL-G red)

HV – MV + LV + Tank % MAKE THE NECESSARY CONNECTIONS ON THE TERMINALS

MV – HV + LV + Tank % LV – HV + MV + Tank % HV + MV - LV + Tank % HV + LV - MV + Tank % MT + LV - HV + Tank % Pauwels’s representative Client’s representative Name Name Signature Signature PTS TD

133

Current transformer checks Tx.Nr. Location : Name Specs. Ratio Insulation resistance with 2500V P1= Kneepoint voltage determination NA P2= Voltage S1= Current

S2= Connections tightened or shorted

Location Name Specs. Ratio Insulation resistance with 2500V P1 = Kneepoint voltage determination NA P2 = Voltage S1 = Current

S2 =

Connections tightened or shorted Location Name Specs. Ratio Insulation resistance with 2500 V P1 = Kneepoint voltage determination NA P2 = Voltage S1 = Current

S2 = Connections tightened or shorted

Location Name Specs. Ratio Insulation resistance with 2500V P1 = Kneepoint voltage determination NA P2 = Voltage S1 = Current S2 =

Connections tightened or shorted

Location Nom Specs. Rapport Insulation resistance with 2500 V P1 = Kneepoint voltage determination NA P2 = Voltage S1 = Current S2 =

Connections tightened or shorted Pauwels’s representative Client’s representative Name Name Signature Signature PTS CT

134

Zero phase sequence impedance determination Tx.Nr. 1) Short circuit on HV winding 3) LV winding open, no load 3) Apply single phase voltage between Hv winding and HV neutral (220 – 240 V) 4) Measure currents going to each phase measured line current average current ZPS Impedance tap pos applied V A B C (A+B+C)/3 applied V / av.Curr. lowest nominal highest Pauwels’s representative Client’s representative Name Name Signature Signature PTS ZPSI

135

Automatic voltage regulation check Tx.Nr. Device(Type) Make Serial Number Simulate the P.T. voltage and balance the relay on this voltage (no presignal). While the bandwidth is set at 1%, increase the voltage by approximately 1.2 %. After the set time delay the tap should move to a lower position (more winding turns in primary). Lower the simulated P.T. voltage to approximately 1.2 % below the desired P.T. voltage. The tap should move to a higher position (less winding turns in primary). Y N Did the relay pass this function test ? OK NOK NA Check undervoltage blocking

Check overvoltage rapid return

Check various time delays features

Pauwels’s representative Client’s representative Name Name Signature Signature PTS AVR

136

CONCLUSION Tx.Nr. Corrections to be made.

Other remarks.

The transformer is / is not ready to be energized

Remark regarding minimum rest period before energizing. Transformer equipped with oil pumps :

let the pumps operate for 2 hours if HV is lower than 245 kV : minimum rest period of 8 hours if HV is higher than 245 kV : minimum rest period of 24 hours

Transformer without oil pumps :

If HV is loweer than 245 kV : minimum rest period of 16 hours after filling If HV is higher than 245 kV : minimum rest period of 48 hours after filling

Representative Pauwels Trafo Service Representative Client Name : Name : Signature Signature Date : Date :



137

8 Special instructions



138



139

8.1 Special instructions

No special instructions applicable.

52951390 Pawels Trans A

Documents

general arrangement

leakage path

phase neutral

parts ordering

forced oil

vector group

pauwels project

protecting