69kV and Above Oil Immersed Transformer Instruction Manual

5/20/2018 69kV and Above Oil Immersed Transformer Instruction Manual

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Power Transformer Instruction Manual

Version 1.0 Page 1 of 30

Oil Filled Power TransformerInstruction Manual

66 kV and above

JSHP Transformer Co., Ltd.


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Table of Contents

1.

General

2.Receiving

3.Moving and Handling

4.Storage

5.

Assembly and Installation

6.Processing and Vacuuming

7.Field Testing

8.Energization

9.

Maintenance

10. Attachments


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1. General

This manual applies to JiangSu HuaPengs (JSHP) modern liquid filled powertransformers with high voltage rating of 69 kV and above. It is developed to assist

in transformer receiving, installation, test and maintenance procedures.

1.1 Safety

The installation, operation and maintenance of power transformers present

many potentially dangerous situations such as falling, asphyxiation, highpressure and high voltage. Always observe safety precautions and follow all

applicable safety procedures such as OSHA requirements, local safety

requirements and safe working practices. Good judgment must be used wheninstalling, operating and maintaining power transformers.

1.2Contact information

In the event of shipping damage, or any information that is not covered in this

manual, contact JSHPs Service Department.

JSHP Transformer Co., Ltd.

68 Kunlun Development Zone

Liyang City, Jiangsu Province, P.R. ChinaPhone: +86-519-87319099

Fax: +86-519-87319215

Email: [email protected]


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2. Receiving

It is important that shipping damage be detected before the transformer is off-loaded. A though inspection of the unit and its accessories should be made as

soon as possible to identify any shipping damage. JSHPs transformers are

covered by warranty against defective materials and workmanship. This warrantydoes not cover shipping damage and therefore does not relieve the user of the

responsibility of accepting damaged transformer and/or it accessories from the

carrier.

2.1 Inspection on receipt

Representatives from both JSHP and the carrier should be present during theinspection. Any evidence of damage should be noted on the Bill of Landing.

Before removing the unit from rail car or truck, perform the following

inspections to identify any damage that may have occurred during shipment.

2.1.1 Impact recorder

Impact recorders are provided on all rails and some truck shipment. Theimpact recorder used by JSHP is a three way device capable of

measuring shocks in the longitudinal, vertical and transverse directions.

On shipments where impact recorders are provided, remove the tape in

the presence of JSHP and carriers representative. If the tape recorder

stopped or jammed before the transformer reached its destination,indicate this on the tape. Also write down the tape removal time and date

on the tape. Have a representative sign the tape.

To analyze the tape, it is best to do it indoor or in an area sheltered form

wind. Traces in longitudinal, vertical and transverse directions which are

less than3G, 2G and 2Gare considered acceptable. Impact higher than

those figures is considered rough handling and might cause shippingdamage. In this case, authorization is needed from JSHP to inspect the

unit further. If the traces indicate no probable shipping damage, the

receiving inspection may proceed.

Replace tape in the recorders, seal and ship back to JSHP at the

following address within one week:

JiangSu HuaPeng Transformer Co., Ltd.

No. 68 Kunlun Development Zone

LiYang City, JiangSu ProvincePR China 213300

Attn: Shipping Dept.


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2.1.2 External inspection

A damaged tank assembly may mean a faulty or damaged transformer. Itis important that the transformer be inspected before it is off-loaded. A

thorough inspection at this point saves time and cost of off-loading a

damaged transformer. In addition, proper claims can be filed if damageis found or hidden damage is suspected.

i. Transformer tank

Visually inspect transformer tank, cover, drain valve, radiator valves

and other external accessories mounted on the tank. Note any

external damage.

All welds or bolted-on flanges and covers should be in place and

secure, all valves and cabinet doors should be tightly sealed.

Check attached radiators for bent or dented fins.

Look for signs of oil leakage along weld seams on the exterior ofsmall power transformers which are normally shipped oil filled.

Check gas pressure in the tank for dry air or N2 filled units. Theseunits should have a positive or negative gas pressure in the tank if

there is no leak. Zero gauge pressure is a good indication of a leak.

Refer to section 2.4 for test for moisture entry if a leak is suspected.

ii.

Bracing, blocking and tie down

Inspect bracing, blocking, etc. Note all damage, shifting and

movement, etc. Take photos as well to substantiate possible claims.

Depressed steel platform cars usually have steels blocks welded tothe deck and placed tightly against the transformer base at each end.

Excessive impact could show up as dents in the base of the unit or

results in block movement. Side blocks are normally placed tightagainst the base and tank movement will result in as scratched paint.

Flat car or truck loads normally use wood braces and blockingtimbers. Some movement is expected, however, broken blocks or

crashed timbers indicate rough handling.

Anchoring or spring loaded tie down rods should be straight andtight. All nuts should be tight as well. Any bent or looseness

indicates movement of the unit.


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iii. Accessories inspection

Check the packing list against the materials received. Look formissing creates or containers.

Check radiators or coolers for dented or broken fins, loose ormissing fans, etc.

Check bushings and lightning arresters for cracked or broken

porcelains, oil leaks, porcelain shifts, etc.

Check conservator tanks for dents, cracks and leaks.

2.2 Internal inspection and tests

When required, follow the procedures listed below to conductor internal

inspection.

2.2.1 Safety precautions

Do not allow anyone to enter the tank unless the oxygen content of gas

at the tank bottom is measured and considered acceptable. The oxygen

content should be at between 19.5% and 30%. For units shipped withnitrogen, purge air space with dry air first.

Always have a person stationed at the opening outside the tankwhenever anyone is in the tank.

Before removing any covers and fittings, Make sure that there is nogauge pressure in the tank and the oil level is under that particular

opening.

Fire extinguishers should be provided and smoking should not beallowed.

Ground transformer tank, all windings and all oil handling andprocessing equipment.

Do not perform electrical tests while the unit is under vacuum.

Do not walk on the cover while the unit is under vacuum.

2.2.2 Internal inspection preparation


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Extreme care must be taken to protect the transformer, especially its

insulation system from damage. Care should also be taken to prevent

foreign materials form entering the tank during inspection.

All personnel working on the top of the tank, while its open, should

empty all pockets and remove all watches and jewelry. Wear protectiveclothing and shoe covers.

All tools, hardware and any other foreign objects that will be used

during the inspection should be accounted for. If anything is droppedinto to the tank and cannot be retrieved, notify JSHPs representive

immediately.

Have provisions for closing the tank in case of rain or sudden weather

change.

For transformers shipped dry, follow the steps below to perform internalinspection.

Adjust the internal pressure to zero PSI before opening the tank.

Record the time tank is opened to determine total exposure time.

Do not open the tank if the transformer temperature is below 0C.

Circulate dry air. When transformer is opened and exposed to theenvironment, dry air (dew point of-40C) should be purged

through the tank to prevent moisture entrance. Clear plastic sheetsmay be placed over the manhole openings to reduce the air volume

required.

For transformers shipped oil filled, follow the steps below to performinternal inspection.

Adjust the internal pressure to zero PSI before opening the tank.

Lower the oil level to allow for a limited internal inspection.

Record the time tank is opened to determine total exposure time.

2.3 Perform internal inspections

For transformers shipped dry, the internal inspection should include, but not

limited to, the following:

Access the overall condition of the active parts and all components.

Check internal parts for tightness and damage.

Inspect coils and insulation. Look for misaligned spacers or loose blocks.

Look for loose insulation between the core and core clamps and any signs

of lamination shifting. Make sure core ground lead is not loose.


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Conduct core megger at500 volts. A minimum of 200 volts megohms isacceptable.

Check lead/cable for insulation abrasions, frayed strands at bushingconnecting stud. Look for broken lead supports.

Check contact alignment and tap leads of the off load tap changer. Make

sure operating mechanism is free of damage. Check the support of current transformers. Verify that all leads from the

CTs to the terminal blocks are secure and free of damage.

Look for debris at the bottom of the tank.

Look for signs of moisture such as rust or free water.

For transformers shipped oil filled, the internal inspection should include, but

not limited to, the following:

Access the overall condition of the active parts and all components.

Look for signs of moisture such as rust or free water.

Make sure core ground lead is not loose. A visual inspection, through the oil, should be made to look for evidence

of damage or loose parts.

The oil should be drained completely to allow a thorough inspection if there

are any indications of damage or if the impact recorders indicate excessiveimpact.

2.4Test for moisture

If moisture entrance is suspected, pressurize the tank to 6 PSI gauge pressure

with dry air and look for leaks with soap and bubbles. Check welded andgasketed joints. If the leaks are found, repair leaks and re-pressurize the tankto 6 PSI. Let the unit sit for at least 24 hoursand perform a dew point

measurement.

The dew point inside a transformer can be related to the partial pressure of

water vapour at the surface of the insulation material. This is called the vapour

pressure and it is measured in micrometers of mercury.

Once known, the vapour pressure and the temperature of the insulation

material determine the moisture content (percent by weight) at the surface of

the insulation material assuming that all the partial pressure of gases in the gasspace and in the insulation have come to equilibrium.

The attached chart, Figure 1, converts the measured dew point into the vapourpressure. The chart for determining moisture content from vapour pressure is

called the moisture equilibrium chart, Figure 2. using the two charts, the

moisture content can be determined.


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To make good judgment of moisture content, the actual temperature of the

insulation materials must be known as accurate as possible. The best way to

accomplish this is to make the dew point measurements in early morninghours when the insulation temperature, the tank pressure and the ambient

temperature are all still relatively equal. In addition, the vapour pressure must

be adjusted for any overpressure in the transformer tank.

Results which occur in the unacceptable range should be referred to JSHPs

service department.

2.5Damage claims

All shipping damage, both obvious and hidden, will be filed by JSHP. Whenobvious damage is observed, contact JSHP customer service immediately. A

damage report must be completed by the carrier. Under no circumstance is a

damaged shipment to be removed from the rail car or truck without written

authorization from JSHP.

All hidden damage claims should be filed if:

The impact recorders indicate transit impact has exceed 3G, 2G and 2G inthe longitudinal, vertical and lateral direction.

Prolonged period of 2-3 hours or more of vertical ribbon effect is recorded.

The impact recorders did not run full time.

Excessively rough handling is evident.

Contact JSHP customer service immediately if hidden damage is suspected.

The bill of landing should be signed with a statement Unit received withpossible hidden damage.


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3. Moving and Handling

When no shipping damage is detected, the customer should remove thetransformer from the rail car or truck and move it to the installation or storage site.

Extreme caution must be used in moving a transformer. Unsafe practices mayresult in serious injury or even death. Unsafe practices may also result in major

damage to the transformer, substation equipment or moving equipment.

3.1Before the move

The outline drawing of each transformer included with this manual has

information on the weight of the unit, clearances required, and the locations oflifting eyes, jacking pads and mounting pads.

The new location should have been prepared and certified as ready, and the

pathway along which the transformer will be moved should have been clearedof all obstacles.

Before positioning the transformer on a permanent or temporary pad, thefoundation and surroundings should be checked carefully. Because of the

weight of a power transformer is normally heavy and the weight is

concentrated in a relatively small area, there is considerable stress on both thetransformer and its foundation.

In addition to the strength required to support the unit, the mounting mustprovide for maintenance and service access to the transformer.

3.2Move preparation

3.2.1 Newly received transformer should be inspected in accordance with the

procedures described in the Receiving section of this manual.

3.2.2 For transformers that are to be moved from storage, pre-move inspection

and processing should be performed.

Follow the steps below to prepare the move.

List all accessories and equipment that must be disconnected beforemoving.

Relieve pressure in the tank.

Match mark, disconnect and remove all accessories that must beremoved.

Clean and seal all tank openings created by the removal ordisconnection immediately.


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Wrap, identify and store all removed items in a dry location pendingreinstallation.

Inspect the tank exterior for damage or deterioration.

Release and remove and bolts or nuts fastening the transformer to itsfoundation.

Order, if necessary, damaged components during disassembly.

3.3 Actual move

The outline drawing of each transformer included with this manual has

information on the various weights of the transformer and the precise location

of the various lifting, pulling eyes, skid noses and jack bosses, etc.

When making a decision on the moving technique, take into consideration the

size and weight of the transformer, the job site condition and the type andcapacity of the lifting and moving equipment.

3.3.1 Lifting and moving transformer by crane

Whenever possible, the transformer should be lifted and positioned by

crane. Moving by swing crane should not be attempted if working space

is inadequate or overhead obstacles do not permit the crane boom to beraised or moved effectively.

When a crane is used to lift the unit, lift hooks or hitches should beattached only to the lifting eyes built into the tank and the cables must be

held apart by a spreader to prevent bending the lifting lugs or putting too

much strain on other parts of the tank. Safety ropes or guide lines shouldbe attached only to the towing eyes at the tank base and the load shouldbe carefully controlled during the lift operation. The load should never

be permitted to swing freely.

Before the transformer can be lifted, the internal pressure should be less

3 PSI.

3.3.2 Moving transformer by rolling or skidding

When lifting a transformer by crane becomes impractical, the

transformer can be moved along the ground by rolling or skidding.

Although the actual moving procedures will vary with the size and

weight of the transformer, the condition of the ground over which itmust be moved, and the travel distance. To ensure a successful move,

the following precautions should be observed.


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i. The work surfaces including truck bed, railcar deck, skid way or

rollway and foundations must be as level as possible and absolutely

firm.

ii. Use jack bosses to raise the unit when necessary. Do not attempt to

raise the unit by placing jacks under the base, drain valves, pipeconnections or other attachments. Use the outline drawing for any

special instructions. Generally there are four jack bosses, one at each

corner. When lifting a transformer completely, use all the jacking

pads provided. To avoid springing the base, all jacks should beloaded evenly. Interlocked hydraulic jacks are recommended for this

purpose.

iii. When the transformer is to be moved on rollers, all rollers used must

be of the same diameter and evenly and closely spaced. The use of

sound hardwood rollers greater than 6 in diameter or steel rollers

greater than 4 in diameter spaced on centers with less than 12separation must be used. Rollers must extend at least 2 beyond the

tank base.

iv. Movement of the transformer should be controlled at all times. A

tow and drag winching system is recommended with one winch

pulling in the direction of movement and a second acting as a brake.

v. Towing cables must be attached only to the jack pads or

towing/pulling eyes provided. The tow cables should never belooped around the tank or attached to the radiators/coolers, pipes, etc.

spreading yokes should be used if the hitch configuration will placeundue strain on the towing/pulling eyes on the tank.

vi. When turning a transformer, it is a good practice to place the

plywood or lubricated steel sheets under the base to minimize

turning resistance. Use pulling eyes only to attach the cable. As forlateral movement, it should be accomplished by the use of the

towing/pulling eyes provided for the purpose.

vii.Keep the transformer level at all times. The transformer must never

be tilted more than 15 from the vertical in any direction.


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4. Storage

Generally a transformer should be set up in a permanent location, assembled andprocessed for operation as quickly as possible after receiving inspection is

complete. However, if the transformer needs to be stored before installation, the

following rules should be followed.

4.1 Storage location

The foundation should be firm and relatively level. If a transformer is to bestored on a timber platform, support timbers should be closely and evenly

spaced. Transformers should never be stored on rollers, blocks or jacks. When

transformers are to be partially or fully activated during storage, theconditions of access and ventilation appropriate to permanent location should

apply.

All transformers stored in temporary locations should be grounded as thoughthe installation was permanent. Ground connections to both the tank and

installed accessories should be checked carefully. Heaters should be

connected and energized to prevent condensation in closed compartments.

4.2 Storage duration

It is important to know the duration of the storage so proper procedures can be

followed. Generally speaking, the storage duration can be classified as less

than 3 months, between 3 and 18 months and over 18 months.

The storage period should be considered as beginning on the date of shipmentfrom the factory. All in-transit time and all time consumed in the receivingprocess should be included in determining which storage classification is

applicable. An internal inspection is recommended if a transformer is shipped

without oil and will be stored for more than 3 months.

4.2.1 For units to be stored for less than 3 months, the storage procedures

are intended to preserve the as-delivered condition of the transformer.

Where practical, transformers not immediately energized should bepositioned in a permanent location and placed in a semi-active storage

condition. Where storage in a temporary location is necessary, inactive

storage is acceptable, however, the control cabinet and LTC controlcabinet heaters should be energized to prevent condensation.

i. When the transformer is stored in a semi-active mode on a

permanent pad, the transformer should be assembled, fitted with allthe accessories, processed for installation, filled with oil and have

all control cabinets and heaters energized.


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ii. When the transformer is stored in an inactive mode on a temporary

pad, the transformer should be kept either in dry air (or nitrogen)

or oil filled.

When transformers are received filled with factory oil, they can be

stored for up to 3 months in the as received condition withoutfurther attention.

To store the transformers in dry air, a positive pressure of 2-3 PSI

should be maintained at all times. A reserve air supply controlledby a pressure regulator should be connected to the tank. The air

supply should be coupled to the tank via the pressure vacuum

regulator. Both the reserve air supply and tank pressure should bemonitored daily during the first 7 days of the storage period. Gauge

readings should be taken approximately the same time each day

and recorded carefully. If supply and tank pressure remain stable

during this period, the interval between readings may be extended.

To store the transformers in nitrogen, a positive pressure of 0.5-5

PSI should be maintained at all times. For normal pressurization, 2PSI is recommended. If the tank is pressurized during warm

weather (above 25C), a 3 PSI reading is recommended.

Connections to the tank, installation of gauges or regulators andmonitoring procedures should be the same as described above for

dry air.

4.2.2 For units to be stored between 3 and 18 months, the transformers

should be filled with oil to the proper level. Transformers withconservators should be filled to about 20 below the cover. The spaceabove the oil should be pressurized by dry air or nitrogen to 3 PSI.

Control cabinet and LTC control cabinet heaters must be energized to

prevent condensation.

4.2.3 For units to be stored more than 18 months, the transformer should be

completely assembled and fully functional. All accessories should be

installed and connected. All heaters, fans and pumps, etc. should beconnected and operational. Stored equipment should be tested and

maintained as though operational.

4.2.4

Accessories storage. Accessories not mounted on the transformer tank

at the factory or not installed immediately after receiving must be

protected from damage or deterioration during storage. Carefully

reseal shipping boxes opened for inspection and store inside to preventdamage. All items stored outdoors should be covered and protected

from the weather.


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Accessories stored outdoors and are not protected properly from the

weather are susceptible to rust and other moisture related damage.

4.2.5 Removal from storage. During long storage, moisture may accumulate

in transformer insulation if the transformer is not properly stored.

Excessive moisture in the insulation lowers its dielectric strength andmay cause failure

For transformer stored dry, a dew point measurement should be made

before relieving the storage pressure in the tank. When making a dewpoint measurement, follow the instructions provided with the dew

point tester. The dew point of the gas sampled should be below the

acceptable limits shown on the moisture equilibrium chart, Figure 1.1% moisture in the insulation system is considered acceptable.

For transformers stored oil filled, an oil sample should be measured for

moisture content. An acceptable limit is 15 ppm.

5. Assembly and Installation

Assembly and installation methods vary with the size and type of the transformer,

and facilities for handling transformers and their components. JSHPs Parts Listand Shipping Instructions should be used for items that are detached for shipment.

These items should be reassembled on the transformer as instructed below.

5.1Ground the tank

Before assembling the transformer, the tank should be permanently groundedby means of the grounding connection provided at the bottom of the tank. The

ground cable must be of correct size and must be 4/O or larger.

5.2Contamination prevention

Carefully plan for control of all tools, hardware and other objects that are

going to be used in the assembly process.

5.3Bushing installation

Remove bushings from their crates with care using rope or nylon slings. Make

sure not to damage or chip any of the porcelain skirts on the bushings. If the

porcelain is chipped or cracked, or if there is any other damage to the bushing,

contact JSHP for further instructions. Always make sure that the top end ofthe bushing is higher than the lower end when handling bushings.


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Place the bushing on a suitable surface for cleaning. The cover removed from

the crate can be used as a base with rugs to cushion the bottom threads. Never

rest the porcelain section on the bushing on anything. Use bushing flange forsupport as necessary.

Clean the bushing well using a rag dampened with a fast drying solution suchas denatured alcohol. Check MADS prior to using any solvent. All bushing

surfaces which will be inside the tank should be wiped clean and tried to

prevent contamination of the oil in the tank.

Bushings with draw lead leave the factory with the conductor ends loosely

sealed. Dirt and moisture may accumulate in the conductor tube. To clean this,

draw a cloth saturated with cleaning solvent through the hollow conductor.Make several passes until the cloth comes out clean. If the bushing comes

with a corona shield, make sure not to make any dent on the shield.

To install bushings, first relieve tank pressure to 0 PSI by loosening a manholecover, a shipping cover or a plug, whichever is most convenient to vent the

transformer.

If the transformer is shipped without oil, start flowing dry air through the

transformer. Record the time to determine how long to hold vacuum on the

unit before filling.

For draw lead bushing installation, follow the steps listed below.

i. Remove the bushing shipping plate. Inspect the gasket and make sure

there is no damage. Clean the bushing mounting boss and install thegasket.

ii. Pass a pull wire down through the center tube of the bushing and

attach it to the small hole in the top of the cable terminal stud. Lower

the bushing into the transformer opening. Do not allow slack in thepull wire as it may allow the lead to become kinked below the end of

the bushing.

iii. Install the locking pin at the top of the bushing and remove the pull

wire. Thread the terminal cap in to position. Make sure the gasket is in

place. Tighten the terminal cap to seal against the gasket. Torque thestud nut and cap as directed by the bushing manufacturers installation

instructions.

iv. Install and tighten the bushing flange hardware to apply even pressureto the flange. Hardware should be tightened alternating across the

flange.


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v. Check all leads to maximize clearance to ground or to other electrical

parts.

For bottom connected bushings, follow the steps listed below.

i.

Lower the oil level when the transformer is shipped oil filled. Do notdrain oil below the top clamping ring.

ii. If the transformer is shipped dry, start flowing dry air through the

transformer and record the time.

iii. Remove the bushing cover plate. Inspect the gasket to make sure there

is no damage. Clean the bushing mounting boss with a solvent.

iv. Place the bushing into the right position on top of the transformer.

Install the internal transformer connectors to the bottom of the bushing

studs and tighten the bolts alternately and evenly with a wrench.Secure the bushing on the transformer cover by tightening all the bolts

evenly in several steps. Do not attempt to pull the bolts down to the

final setting on the first tightening. Allow time between eachtightening to allow the gasket to seat properly.

v. Connect the internal bushing cables to the internal bushing spades.

vi. Check all leads to maximize clearances to ground or to other electrical

parts.

5.4

Radiator installation

Do not remove the shipping cover until ready to install radiators. Verify that

all radiator valves on the tank are closed before removing the shipping covers

on the radiator flanges. Use care to prevent gasket and paint damage. It is

recommended that the radiators be lifted from the crate with manila rope withsling spreaders and be placed across suitable supports while preparing for

mounting to the tank.

Inspect for moisture or contamination inside the radiators headers. Contact

JSHP is contamination is found. Make sure the flange face is free of paint or

other material. Clean gasket groove and flange face and install gaskets.

Lift the radiator by lifting eye in the top header and swing it into position over

the valves. Bolt the radiator header to the valves with the bolts provided and

pull down evenly all the way around. Attach radiators with mounted fans firstand then attach the remaining radiators. Leave the radiator valves closed.

Touch up the paint when necessary.


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For transformer shipped or stored with oil, do not allow oil level to fall below

the top of the top coil clamping ring. If there is insufficient oil in the tank, stop

the radiator filling process and add oil before completing radiator filling. If theunit was shipped or stored over-filled with oil, the radiator valves should be

opened at this time to lower the oil level. Loosen the top radiator header plug

and slowly open the bottom radiator valves one at a time. This will allow theradiators to be filled from the bottom, avoiding trapping of gases or air

pockets in the radiator. As the oil becomes visible around the header plug or

when all of the gas is purged from the radiators, tighten the header plug and

open the top valve. After all radiators have been filled with oil and the oiladjusted to the 25C level, remove the top header plug, then reinstall using

Teflon pipe thread tape on the plug to prevent future leaks.

For transformer shipped or stored dry, leave the radiator valves closed until

the unit is ready for oil filling.

5.5

Cooler installation

Coolers should be placed plat on suitable support with fans on the top side.

Remove the shipping covers and make sure there is no internal contamination.The gasket groove and flange faces should be clean.

5.6Conservator installation

Install the conservator per outline drawing. Make sure flow pipe is correctly

aligned before tightening the tank down.

Following the mounting of all accessories, a final internal inspection should beperformed if any work has taken place inside the tank. Electrical connectionsshould be checked for tightness. Bushing gasket sealing and the draw lead

connections should be checked as well. Also check all leads for maximum

clearances. In addition, check the liquid float and operation of the indicator for

free movement.

Finally, verify all tools and foreign materials that have been used inside the tank

have been removed.

Reinstall all manhole and hand hole covers and other covers where a device has

not been installed.

Ground bushings to protect personnel and the transformer.

Record the time that the transformer is closed to determine total exposure time.


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6. Processing and Vacuuming

Tests to be performed after final processing (24 hours):

Leak test. Apply 6 PSI of dry air on the unit. Log readings until pressurelevels off indicating no leak.

Core ground test. Hold a steady voltage for 3minutes with a megger. Theminimum reading should be 200 voltsmegohms.

Ratio test. Complete readings on all taps and compare with test reportfrom factory.

Check all current transformers including hot spot heating coil circuit for

open circuit using an ohmmeter.

Oil quality check

Oil samples from the transformer should be taken from the oil sampling valveat the bottom of the tank. Oil samples from tankers or drums should be taken

from the bottom as well.

Before the oil can be pumped into the transformer, it should have thefollowing characteristics:

Moisture content < 15 ppm

Gas content < 0.5%

Dielectric strength: > 35 kV (ASTM 877), > 60 kV (ASTM 1816, 0.08

gap) Oil power factor. The maximum allowed is 0.5% at 90C

Processing for transformers shipped or stored oil filled

If any oil must be removed or added for any reason, the oil may be replaced

by one of the following methods.

i. If oil must be removed below the top of the core or below the top of a

350 kV BIL or above terminal board, the oil must be complete removedand vacuum processed per section 6.4 below.

iii. If limited amount of oil, such as make up oil, is removed, it may be

allowed to add the oil through the manhole by laying the hose on top ofthe core and directing the oil along the top of the core. Adding additional

amount of oil entails a greater risk of aeration of the oil and the

possibility of entrapping air bubbles in the windings. This method istherefore not preferred and should only b used when there is no other

alternative.


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If this method is used, a minimum of 24 hour sit time must be observed.

Vacuum filling procedure

Equipment needed for vacuum filling:

Vacuum pump, approximately 150 CFM capable of 200 microns in theblank-off condition.

Filter press, approximately 30 gallons per minute.

Extra set of filters.

Vacuum gauge.

Vacuum pipes or flexible hoses (2 diameter minimum).

Oil supply lines and connections.

Vacuum valve.

Dry air supply.

The principal function of vacuum treatment is to remove trapped air andmoisture from the insulation. Small gas bubbles have much lower dielectric

strength than the solid and liquid insulation and may cause dielectric failure if

located in high stressed areas.

The transformer should be oil filled on relatively clear days when the

humidity is less the 70%. The oil temperature must be 0C or higher.

Before setting up the vacuum filling procedure the conservator and the air bag

should be checked carefully for any defects and contamination.

Follow the procedures below for vacuum filling:

i. Pressurize the air bag with 0.5 PSIG so that the air bag will be flat andstraight prior to oil filling. This work can be done on the ground before

the conservator is installed on the mounting bracket.

ii. Connect the vacuum line and vacuum gauges in preparation for pulling

a vacuum. An oil sight gauge (or tube) should be installed as well.

iii. Check all radiators or coolers to make sure that all the valves are open

and bolted to the open position.

iv. All transformers should be filled through bottom filling valve.v. Make sure equalization is achieved between main tank and LTC and

between conservator tank and its bladder.

vi. Pull a vacuum to1 torr.


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vii. Hold a vacuum of at least 1 mm for a minimum of 4 hours, plus an

additional hour for each hour the transformer was open for inspection

and assembly. The vacuum must be held for a minimum of 8hours at1 torr. or lower for transformers rated up to 350 kV BIL, 12 hoursfor

450-550 kV BIL, 24 hoursfor 650-750 kV BIL and 48 hours ??for

825-1050 kV BIL. During this period, the vacuum level should berecorded at least once every hour.

viii. At the end of vacuum hold cycle, the oil filling process can then be

started. An oil temperature of 50-75C is recommended as highertemperature oil will speed up the impregnation of solid insulation.

ix. During oil filling, the vacuum level should be maintained at 5 torr.orless. The operator should observe the oil sight gauge. When oil level

reaches approximately 10-12 inchesform the top of the cover, the oil

filling process should be stopped by closing the top filling valve.

x. Break the vacuum with dry air or nitrogen. The main transformer

should then be pressurized to approximately 0.5 to 1 PSIG. The

vacuum fittings should also be removed at this time and the ventsealed.

xi. Open the top filling valve. Fill the conservator tank until the oil levelgauge on the conservator register 25C or higher depending on oil

temperature. As the oil is being pumped into the conservator the

pressure in the bag should be observed and air bled off as the oil levelrises. The pressure in the bag should not exceed 2 PSIG during filling.

The vent valves on the conservator tank should be open to relieve theair pressure in the conservator that will build as the oil is pumped intothe conservator.

xii. Inject 1 PSIG into the bladder. Oil should discharge from the

conservator tank filling valve. Install the male plug on the valve rightafter. Adjust oil level so the gauge corresponds to the oil temperature.

Level correction with temperature should be considered.

xiii. Close top filling valve and remove fill line.

xiv.

Air that is entrapped in various locations should be bled off as follows:

Normally the air entrapped in the top of the main transformer canbe bled off through the gas monitor.

Some transformers are designed with bushing wells or turrets.There will be vent valves through which the air must be bled off.


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There are some designs in which the top cover will be crowned.These will have piping with vent valves through which this air

must be bled off.

In other cases there are vent valves on the conservator from which

the air must be bled off.

xv. Check thoroughly that all vent valves are closed so that oil will not be

forced out of them.

xvi. Check the gas monitor to make sure that all air has been purged from

the piping leading to the gas monitor. If this is not done, the gasmonitor will trip and show gas in the transformer.

xvii. It is recommended that the gas monitor be checked one week after thetransformer has been oil filled to confirm that it is reading in the

normal range. If it is not, more than likely there is air entrapped wither

in the gas monitor or the line that must be bled off.

Oil Filling When Core and Coil Assembly Are Below 0C

i. Pull a vacuum of 5 torr. for 4 hours.

ii. Following this, spray hot oil through the cover of the transformer. The

oil should be sprayed so that the stream is broken up into droplets formore efficient heating of the core and coils. Maintain a vacuum of

10mm or better on the transformer during the oil spraying operation in

order to prevent oxidation of the oil and to aid in the removal of gas

from the insulation.

It will probably be necessary to maintain some oil in the bottom of the

unit to feed the output pump. Usually 12 to 24 inches of oil level in thebottom will be sufficient. Do not allow the oil level in the bottom to

exceed 36 inches. A clear plastic hose can be used as an oil level

indicator. Pump the oil from the bottom of the transformer throughfilters, through degasification and dehumidification equipment,

through the heat exchanger, and finally back to the cover of the

transformer.

The oil temperature entering the tip of the transformer should be ashigh as possible but should not exceed 90C. Continue spraying the

hot oil under vacuum until the temperature of the core and coils is wellabove 0C. The temperature of the core and the coils will be at

equilibrium conditions when the output oil temperature becomes

constant, and will be within 5C of the temperature of the input oil.


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The heating rate can be increased by closing the bottom valves to the

coolers or radiators and by blanketing the outside of the tank to restrict

heat loss.

iii. After the temperature of the core and coils has been elevated above

0C, drain all oil from the tank and coolers or radiators. It will benecessary to break the vacuum in order to drain the oil. The vacuum

must be broken with dry air (-60C dew point) to prevent condensation

in the tank.

iv. As soon as the oil is drained from the tank, immediately start the

vacuum treatment.

Open all valves to all radiators, pumps, coolers, or other cooling equipment.

Pull vacuum to 1 torr. and hold for 8 hours prior to filling. Then admit oil

(60C) into the top filter press valve while holding the vacuum level at 5 torr.

until oil reaches the normal level as shown by the liquid-level gauge. Thenproceed as explained on Section 6.4.

Safety precautions

Never leave a transformer that is under vacuum unattended.

Never walk or stand on a transformer cover when the unit is under vacuum.

Never apply any voltage to a transformer that is under vacuum.

7. Field Testing

The following tests must be performed before the transformer can be energized.

Oil dielectric strength. The minimum value should be over 40 kV (ASTMD-877) or 35 kV (ASTM D-1816, 0.04 gap)

Oil power factor. The maximum allowed is 0.05% at 25C or 0.3% at

100C

Oil water content. The maximum 15 ppm

Ratio test. The maximum allowed is within 0.5% of calculated value. Thetested value should also be very close to the factory test results.

Insulation power factor and capacitance including bushings. The

maximum allowed power factor is 0.5% corrected to 20C. Capacitance

should not vary for more than 5%compared with factory test results.


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Core ground test. The core ground should have been tested during the

internal inspection. If the internal inspection is not done, the core ground

should be tested at this time.

Winding resistance. The resistance of transformer windings can be

measured using either the resistance bridge method or the Drop inPotential method. The values reported on the factory test report are

corrected to either 75 or 85C. Correct the measured value to the same

temperature base for comparison.

Current transformers. All current transformers must either have their

secondary windings short circuited or connected to a load before a voltage

is applied. Never open the secondary circuit of a current transformer whilethe primary is carrying current. A high voltage might develop which can

be harmful to personnel or equipment.

Accessories test. For transformers furnished with thermometers formeasuring oil and winding temperatures, the settings for the signaling

should be made per customer standard. In addition, all indicators such as

fault pressure relays, pressure relief devices, etc. should be tested. Followinstructions provided and check that all signals, trappings, etc., are going

through.

Fan motors. The direction of fan motors rotation should be checked to

ensure correct fan cooling.

8. Energization

8.1Check the following before energization.

Transformer tank and neutral bushing(s) are properly grounded.

The connections to lines, bus bars and ground are secure.

No bushings and arresters are strained.

All bolts and gaskets are sufficiently tightened.

All relays are adjusted to specifications.

No tools or equipment are left on the transformer.

The off load tap changer is in the desired position and is locked in place

with a padlock. All insulating oil is at its proper position.

Valves from the conservator to the main tank should be in open position.

All radiator/cooler valves should be open and bolted.

All paint damage is repaired.

Silica gel in conservator tank breather should be blue.

Terminal connections in control cabinet are tight.


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Place shorting straps across the full CT winding for all CT are notconnected to load. All CT secondary circuit must be grounded, whether

the CT is in use or not, either in the transformer control cabinet or at the

load.

Shorting straps on winding temperature indicator CT terminal block and

line drop compensator CT terminal block should be removed. Similarly,shorting straps on all other CTs that connected to loads should be

removed.

Make sure heaters in control cabinet are in working condition.

Bleed gas detect relay.

Remove all temporary shipping plugs.

Reset all drag hands on alarm gauges and the LTC position indicator.

8.2Sitting time

To guarantee complete oil penetration and dissolving of any gas bubbles in the

insulation, the transformer should not be energized until sufficient time haspassed to allow oil to dissolve any gas bubbles which were formed in the

vacuum filling process. The following table sows the recommended sit time

based on units BIL rating.

BIL (kV) Sit time (hours)

350 or less 12

450 to 550 16

650 to 750 24

825 to 1050 48

8.3

Energizing the transformer

Applying full voltage and allow the transformer to operate for at least 2 hourswithout load. Listen for abnormal noises. Check for excessive vibrations.

After applying full voltage, the transformer can be loaded. The transformershould be closely observed during the first few hours of operation under load.

Check gauges to see if specified limits are exceeded.

After several days of operation, check the oil moisture content and dissolved

gas level.


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9. Maintenance

Proper maintenance is essential in ensuring trouble free transformer operation.

Power transformers in service are often subjected to various electrical, mechanical

and thermal stresses. In order to avoid faults, it is important to carefully inspectand maintain the transformers.

Certain items on a transformer must be inspected regularly to ensure proper

operation and long service life. The frequency of these inspections is determinedby the size and type of the transformer, the operating environment and the

importance of the unit.

Internal inspections should be only conducted when there is a suspicion of trouble,

when oil is removed from the tank. In the event a transformer is opened for

inspection, follow the same procedures and precautions as for an initial

installation.

Spare transformer should be inspected and maintained in the same manner as

transformers in operation.

9.1External maintenance

i. Regular annual inspection is required on transformer tank, tank cover,

gaskets and valves.

ii. Cleaning is another part of external maintenance. Use solvent to

thoroughly remove any oil that is on the tank or the gasket.

The bushing porcelain must be kept clean and inspected yearly. Abnormal

conditions such as sand and dust, salt deposits, chemical fumes, etc.

require more frequent cleaning to avoid accumulations on the surface.

Acceptable methods are hot line washing and washing with solvent.

Keep the heat radiating surface of the transformer clean. External surfaces

of coolers should be periodically cleaned. Transformers near the sea coastor in highly corrosive environment should be painted regularly to prevent

corroding or rusting of metal parts.

All breathers and small openings in pressure relief valves and pressure-

vacuum bleeders must be kept clean and in good operating condition.

All ground buses and wiring leads to ground must be kept in goodcondition.

9.2Cooling systems


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Cooling fan motors use pre-lubricated sealed ball bearings that do not require

lubrication maintenance. During extended periods of reduced capacity notrequiring fan operation, it is suggested that fans be run periodically to ensure

proper operation.

External cooling surfaces should be cleaned annually to remove any

accumulation of dirt or debris that may block external air passages of radiators

or coolers so that free air flow can be maintained.

9.3Temperature

Transformer temperature, oil and/or winding, is one of the major factors thatdetermine the life of a transformer. Therefore it is important to monitor the

transformer temperature on a regular basis.

If the temperature of a transformer rises without load increase, it is possiblethat some of the cooling is impaired. This situation should be carefully

investigated.

9.4Oil

Transformer oil is hygroscopic thus easily absorbs moisture from the air. Theabsorption of moisture is minimized by the conservator system with a silica

gel breather. The gel should be properly renewed or regenerated as soon as its

ability to absorb moisture begins to diminish. A change of gel colour fromblue to pink indicates saturation with moisture.

If the transformer oil has been exposed to air while work has been carriedout on the transformer, the oil should be checked for moisture content anddielectric strength. A similar check of the oil should be made on all

transformers at regular intervals. IEC standards provide guidance for the

acceptance, maintenance, continued use and reclamation of insulating oil.

In addition to oil quality checks, oil levels in the tank and LTC mechanism

compartment should be checkedweekly during the first month of operation

and annually afterwards.

In addition, dissolved gas analysis should be performed to provide earlywarning of evolving problems within the transformer and to allow preventiveactions to be taken before serious damage occurs.

9.5External circuit and control equipment

The following should be inspected 30 days after installation and once per year

afterwards.


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Control circuit voltage.

Excessive heating of parts as evidenced by discoloration of metal parts,charred insulation or odor.

Freedom of moving parts.

Excessive noise in relay coils. Excessive arcing in opening circuit.

Evidence of water or oil in the control cabinet.

Proper functioning of timing devices, sequencing of devices, relief devicealarm contacts and thermometer contacts.

9.6Accessories

All accessories should be tested once a year. Inspect all apparatus, electricalcables and conductors, signaling and operating devices to the control room or

control board.

9.7Paint

The paint of the transformer should be free of damage when the unit is putinto service or storage. In order to ensure maximum corrosion protection, all

damage, such as chipped paint or scratches through to the bare metal, should

be fixed and the paint thickness should be restored to its minimum value as

soon as possible.

If bare metal is exposed, the area must be sanded down to blend the damaged

area into the undamaged paint surface. Wipe the sanded area clean with

denatured alcohol or a solvent to remove dust or oil. The area must then bebrush or spray painted with primer, intermediate coat and finish coat. If the

primer is not damaged, lightly sand the damaged paint surface to smoothrough edges. Brush or spray on the intermediate coat and then the finish coat

to restore or exceed the original finish thickness.


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10. Attachments

Figure 1. Dew Point to vapour Pressure Conversion Chart


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Figure 2. Moisture Equilibrium Chart

69kV and Above Oil Immersed Transformer Instruction Manual

Documents

abovejshp transformer

assistin transformer

damaged transformer

event of shipping damage

evidence of damage

generalthis manual

presence of jshp

tape removal time