7/25/2019 Asset Maintenance TNBT Guideline rev 03 http://slidepdf.com/reader/full/asset-maintenance-tnbt-guideline-rev-03 1/88 Document Title Revision No: 3.0ASSET MAINTENANCE GUIDELINES Date of Approval: Sep 2015 (TTC) Page 1 of 88 Prepared by: ASSET MANAGEMENT DEPARTMENT TRANSMISSION DIVISION TENAGA NASIONAL BERHAD Revision Number Description of change recordBy Verifier Approver 1.0 New ASDU GM TTC 2.0 Changes are as per Appendi x 1 ASDU GM TTC 3.0 Review based on ITOMS Working Group recommendation OPU GM TTC @ Copyright TNB Transmission Division No part of this document may be reproduced or transmitted in any form whatsoever by any means, including, without limitation, electronic, photocopying, recording or otherwise, without the prior written consent of TNB Transmission Division. No information embodied in documents which is not in the public domain shall be communicated in any manner whatsoever to any party without the prior written consent of TNB Transmission Division.
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ASSET MAINTENANCE GUIDELINESDate of Approval:Sep 2015 (TTC)
Page 1 of 88
Prepared by:
ASSET MANAGEMENT DEPARTMENTTRANSMISSION DIVISION
TENAGA NASIONAL BERHAD
RevisionNumber
Description of change record By Verifier Approver
1.0 New ASDU GM TTC
2.0 Changes are as per Appendix 1 ASDU GM TTC
3.0Review based on ITOMS WorkingGroup recommendation
OPU GM TTC
@ Copyright TNB Transmission Division
No part of this document may be reproduced or transmitted in any form whatsoever by
any means, including, without l imitation, electronic, photocopying, recording or otherwise,without the prior written consent of TNB Transmission Division. No information embodiedin documents which is not in the public domain shall be communicated in any mannerwhatsoever to any party without the prior written consent of TNB Transmission Division.
3.4 High Voltage (HV) Outdoor Circuit Breaker .............................. .................... 183.5 Medium Voltage (MV) circuit breaker ..................... ...................................... 21
2 General Information .......... .................................................. ................................. 41
3 Critical and Non-Critical Lines ..................... ......................................... ............... 41
4 Line Inspection and Maintenance ........................................ ................................. 424.1 Line Inspection ........... .................................................. ................................. 42
4.2 Line Maintenance .............................. .................................................. .......... 425 Inspection Tasks and Maintenance Plan................................................. ............... 43
3.11 Cable PD detection for XLPE cable .............................. ................................. 493.12 Cable outdoor sealing end inspection ............................ ................................. 49
D. MAINTENANCE GUIDELINES FOR PROTECTION SYSTEM............................ 511 Scope ................................................................................................................... 51
2 General Information .......... .................................................. ................................. 51
3 Maintenance Plan ......................................... ......................................... ............... 52
E. MAINTENANCE GUIDELINES FOR STATIC VAR COMPENSATOR (SVC)EQUIPMENT ............................................................................................................... 741 Scope ................................................................................................................... 74
2 General Information .......... .................................................. ................................. 743 Inspection and Maintenance Plan ........................................ ................................. 74
3.1 Thyristor related equipment ................... ......................................... ............... 753.2 Control and Protection for SVC equipment ................... ................................. 76
1 Scope ................................................................................................................... 832 General Information .......... .................................................. ................................. 83
3 Objectives ............................................................................................................ 844 Maintenance Plan ......................................... ......................................... ............... 85
ASSET MAINTENANCE GUIDELINESDate of Approval:Sep 2015 (TTC)
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H. MAINTENANCE GUIDELINES FOR REMOTE TERMINAL UNIT (RTUS) ....... 86
1 Scope ................................................................................................................... 862 General Information .......... .................................................. ................................. 86
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To ensure the effective implementation of this guideline in Transmission Division
maintenance practice, subsequent departmental procedures and work instructions areto be prepared by Asset Maintenance Department. These documents shall provide:
· method, instructions and checklist to carry out inspection and maintenance task· recommendations on the corrective actions to be taken after observing findings/
results during inspection and maintenance task
3 Scope
The scope of this guideline covers all assets in substations, lines, cables, SVC, HVDCand secondary systems. Assets in Telecommunication System which are under TNB’s
ICT Division are covered in a separate document.
Equipment in operation consists of a large population with variety of manufacturers
which can be difficult to maintain as the maintenance procedures may be differentfrom one to another. Thus the Maintenance Guidelines is intended to serve majority of
the equipment installed in TNB transmission system. Nevertheless, specific
recommendations or instructions from the manufacturer need to be adhered to where
required.
4 Maintenance TypeFigure 1 shows the category of maintenance currently practiced in TNB Transmission
Division. Similar structure is also used in the computerized maintenance management
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Preventive maintenance is carried out at predetermined intervals or corresponding to
prescribed criteria as determined by OEM or TNB. Preventive maintenance isintended to reduce the probability of failure or the performance degradation of an
item. Routine/Scheduled maintenance is carried out at a fixed interval (time,
operations) e.g. OLTC oil replacement after 4 years or 100,000 operations whichevercomes first. Condition based maintenance is initiated as a result of knowledge of the
condition of an item from monitoring e.g. visual inspection, thermovision and
diagnostic tests
Corrective maintenance is carried out after a failure or unacceptable condition has
occurred and intended to restore an item to a state in which it can perform its required
function. Emergency/Breakdown maintenance is carried out immediately to prevent
danger to personnel, equipment, or system performance e.g. equipment requires repair
under tripping situation. Deferred maintenance is maintenance work that may be
programmed for later action e.g. defect found during inspection and the repair is plan
in the next available outage.
The maintenance tasks and interval stated in this document are primarily for preventive maintenance works.
5 MethodologyThe guidelines review and formulation was carried out based on manufacturers
recommendation, statutory requirement and TNB’s operation and maintenance
experience. Using the available information, RCM 2 processes were adopted in
formulating the maintenance guidelines. Probable root causes of failures were
identified and the respective mitigating actions were identified to prevent andminimise re-occurrence of failures. Several RCM 2 workshops were held and
members from the various units and departments in the division were represented.The departments involved were:
· Asset Management Department
· Asset Maintenance Department
· Asset Development Department
· Engineering Department
Following the workshops, an inspection and maintenance plan outlining maintenancetasks to be performed and their frequencies were then established.
In general, the inspection and maintenance plan for the assets are categorized based
on two broad categories:
· Non –
intrusive Inspection: Inspection tasks where no outage of substation
equipment is required.
· Intrusive Inspection/Maintenance/Overhaul:
Inspection/Maintenance/Overhaul where the equipment is required to be de-energized and therefore plant/equipment outage is compulsory.
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The maintenance interval or frequencies are categorized into calendar time,
operational number and as required. Calendar time used is months and years. Thetime interval is normally determined by the statutory requirement, type of equipment
and probability of failure (P-F) interval of the equipment to be maintained. For
operational number, it is determined by the manufacturer ’s recommendation e.g.number of OLTC operation.
As for the as required maintenance interval, no specific interval has been defined. The
decision on the maintenance interval will be based on the operating environment of
the asset, operating duty of the asset, condition of the asset, performance of the asset,
age of the asset, criticality of the asset and event related e.g. condition assessment of
the asset. The Head of Department (HOD) may be required to carry out a RCM
analysis on the asset to be maintained.
6 Implementation and Data MonitoringAfter commissioning and prior to the equipment warranty expires, end-of-warranty
inspection and tests are carried out to determine the equipment condition. This is to
ensure equipment is acceptable for further operation in the network. Details of the
end-of-warranty test are covered in the Site Acceptance Test document. Once the end-
of-warranty test has been carried out successfully, the maintenance plan for the
equipment is finalised.
The maintenance interval outlined in this guideline is determined based on available
data at the point of the analysis. The guideline shall be reviewed in the future when
more data is collected and where reliability and efficiency indices could bedetermined.
Hence it is important that all observations during inspections, repair and replacement
work are properly recorded and documented by the Asset Maintenance Department inthe Plant Maintenance Module of the Enterprise Resource Management System
(ERMS).
7 Maintenance PerformanceIn ensuring that the objectives of maintenance are achieved, the maintenance
performance shall be monitored in terms of productivity, reliability and availability.
These performance indicators shall be specified in the respective Department’s KPI.The KPIs shall be set and recorded such that the KPIs are suitable for performance
trending and performance benchmarking with other utilities.
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8 Effective DateThis document is effective from 30th September 2008 and it supersedes any previous
document before this. However, this document will be reviewed and updated from
time to time when they are any changes to be made.
9 Acknowledgement
We wish to express our sincere gratitude and appreciation to the Asset MaintenanceDepartment, Engineering Department, Asset Development Department and Strategic
Development and Management Department and others who have contributed directlyor indirectly to make it possible for the Asset Management Department to formulate
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A. MAINTENANCE GUIDELINES FORSUBSTATIONS AND SUBSTATION PRIMARY
EQUIPMENT
1 ScopeThis section provides guidelines for maintenance of all transmission substations in
TNB Transmission system. There are two types of transmission substation designsused in TNBT:
· Conventional or Air-Insulated Substations (AIS) – This design consists ofair-insulated equipment installed in outdoor switchyards. There is a control
building within the same substation compound which houses protectiverelays, control panels, communication equipment and low voltage
switchgears.
· Gas-Insulated Substations (GIS) – This design utilizes SF6 gas-insulated
equipment. In TNBT, the GIS switchgears can be located inside a buildingor outdoor.
The maintenance guidelines determine the tasks to be done at the substation site (civil
and M & E works) as well as primary equipment within the substation and the
frequencies of these tasks. The primary equipment covered in this document includes
equipment in substations energized at 11kV, 22kV, 33kV, 66kV, 132kV, 275kV and
500kV as follows:
i. Circuit breakers
ii. Power transformers
iii. Earthing transformers
iv. Transformer cable tails
v. Instrument Transformers
vi. Disconnectors/earthing switches
vii. Surge arresters
viii. Reactor/capacitor banksix. Earth grid and earth mast
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i. Loose/corroded connection
ii. Tilting of busbar/broken clamp due to sinking foundationiii. Exposed LV busbar
iv. Encroachment of foreign objects
3 Inspection and Maintenance PlanAfter commissioning and prior to the equipment warranty expires, end-of-warranty
inspection and tests are carried out to determine the equipment condition as to ensureequipment is acceptable for further operation in the network. Details of the end-of-
warranty test are covered in the Site Acceptance Test document. Once the end-of-warranty test has been carried out successfully, the maintenance plan for the
equipment is finalized.
Inspection and maintenance of substation and substation primary equipment arecarried out on a planned routine basis or when situation warrants. The maintenance
shall be adequate to provide the acceptable degree of confidence when operating the
substation. The maintenance type and maintenance frequency required by plant or
equipment are determined based on the manufacturers’ recommendations in the
Operation and Maintenance Manual, utilities best practices and RCM analysis carried
out by TNB Transmission. This section describes the inspection and maintenance
tasks required and the maintenance plan for the substation equipment.
3.1 Entire Plant
3.1.1 VegetationThis includes grass cutting and weeding for existing landscaping if any
3.1.2 Fencing inspection
To ensure both fencing and access gate are in good condition
3.1.3 Drainage inspection
To ensure all drains are not clogged
3.1.4 Lighting inspection
Perimeter lighting, switchyard lighting and building lighting shall be inspected
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3.4 High Voltage (HV) Outdoor Circuit Breaker
HV Outdoor circuit breaker in TNB’s Grid network uses SF6 or minimum oilas the interrupting medium with the former constitutes majority of the circuit
breakers. Three types of circuit breaker operating mechanism are in usedmainly spring operation followed by hydraulic operation and pneumatic
operation. The maintenance activities for the HV circuit breakers are asfollows:-
3.4.1 Visual inspection
i. Inspect insulators for crack, burn mark and chipping
ii. Check motor, compressor (for pneumatic breakers), pump
(hydraulic breakers) for unusual noiseiii. Inspect for oil leak/air leak of the operating mechanismiv. Inspect control circuit and operating mechanism cubicles for the
following:-
- heaters operation
- clean vents
- seals and latch
3.4.2 Trip counter reading
3.4.3 Motor run hour reading
This applies to pneumatic and hydraulic operating mechanism
3.4.4 Water purging from the air reservoir/vessel
This applies to pneumatic operated mechanism without auto-water-purge
facility
3.4.5 Operating mechanism check
i. Check pump/motor/compressor operation
ii. Lubrication of linkages where necessary.iii. For spring type operating mechanism:
- Check dashpot for sign of oil leaks
- Check spring guides/limit indicator are in place
iv. For hydraulic type operating mechanism:- Inspect accumulator pre-charge pressure and replace worn out
seals if necessary
- Inspect accumulator for corrosion and repaint if required.
- Check hydraulic pump operation, measuring the time taken to
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3.5 Medium Voltage (MV) circuit breaker
MV circuit breakers in TNB’s Grid network are metal-clad and use vacuum or
minimum oil as the interrupting medium with the former constitute majority ofthe circuit breakers. The MV circuit breaker uses spring operation for the
operating mechanism. The maintenance activities for the MV circuit breakersare as follows:-
3.5.1 Visual inspection
i. Check all doors are properly closed
ii. Ensure switchgear door is locked with non-standard lock
3.5.2 Trip counter reading
3.5.3 Trip circuit healthy check
3.5.4 Airborne ultrasound test
3.5.5 Routine inspection
i. Inspect the spout and shutterii. Check discoloration of tulip contacts/busbar due to heat or
improper contactiii. Clean vacuum bottle (applicable to vacuum circuit breaker)
iv. Inspect railing alignment for blockagev. Check operating mechanism for signs of overheating
3.5.6 Lubrication
i. Grease contact fingers
ii. Lubricate linkages and operating mechanism as recommended bymanufacturer
iii. Check trip hook for LV switchgear.
3.5.7 Interlock system check
i. Inspect for both electrical and mechanical interlock
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3.7 Earthing Transformer
3.7.1 Visual inspection
i. External connection checks
ii. Check of terminal blocks, oil level gauges, HV termination and other
accessories for being fully sealed/moisture proof
iii. Oil level indicator and oil leak checks
iv. Checks for oil leak at cable boxes and cablesv. Paint/protective coating and corrosion checks
vi. Transformer/cable guards inspection (for open bushing terminations)vii. Checks for leaking valves and valve positions
viii. Checks for name plate visibility/readable
ix. Silica gel & container glass inspectionx. Inspection of protective housing for Buchholz relayxi. Check conservator filling cap for tightness (for MTM transformers)
3.7.2 Oil sampling
i. Analysis of dissolved gasses in oil (DGA)
ii. Moisture/water content in oiliii. Neutralization index (acidity) of oil
iv. Dielectric breakdown of oil
3.7.3 Routine inspection and operational checks
i. Check cable termination condition at cable boxes.
ii. Rectify moisture condensation in cable boxes.
iii. Simulation test on micro-switch for PRD (if installed) and Buchholz
relay
iv. Buchholz relay check (for flag/alarm operation and fascia indication)
v. Test of MCB and alarm circuitry
vi. Valve position check
3.7.4 Diagnostic tests
i. Power factor test on winding and bushingsii. Insulation resistance test with polarization index
The above tests are carried out periodically or when required, in order to
determine the overall condition of the earthing transformer.
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3.8 Transformer Cable Tails
This covers power cable connections between transformers, earthing
transformers, switchgears and neutral earthing resistor inside the substation.
3.8.1 Visual inspection
i. Check for leaks at transformer cable box
ii. Check termination oil leak/ discoloured
iii. Cable sheath earth connection
iv. If applicable inspect the SVL – cracks / tightnessv. If applicable check the cable sealing ends.
3.8.2 Cable accessories inspection
i. Inspect earthing connections at terminations
ii. Inspect cable support structure at transformer terminationsiii. Inspect general condition of cable trenchesiv. Inspect general condition of cable markers (if installed along cable
route in the substation)
3.8.3 Insulation resistance measurement with polarization index
3.8.4 Cable sheath insulation test
3.8.5 On-line partial discharge measurement
This is a diagnostic test and may only be performed upon directives by HOD
when situation warrants or on selected cables.
Table 3.8 Maintenance plan for transformer cable tails
No. Details Intrusive/ Non-
intrusive
Interval
3.8.1 Visual inspection N 2 Months
3.8.2 Cable accessories inspection N Yearly
3.8.3 Insulation resistance measurement I As required
3.8.4 Cable sheath insulation test I 4 Years
3.8.5 On-line partial discharge measurement N As required
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3.17 SF6 Gas-Insulated Switchgears (GIS)
Most of SF6 GIS installations in TNB’s Grid network are in-door and located
at power stations and urban areas. GIS installation requires minimalmaintenance. Based on the manufacturers’ recommendations in the Operation
and Maintenance Manual, utilities best practices and RCM analysis carried out by TNB Transmission, the maintenance type and frequency required by GIS
are determined. The maintenance activities for the GIS are as follows:-
3.17.1 Visual inspection
i. Record the SF6 pressure from the density gaugeii. Check for oil leaks (applicable to hydraulic or hydraulic-spring
operated breakers)
iii. Check that all earth switches and disconnectors are locked withnon-standard padlocksiv. Check heater operation of control cubicle to prevent condensation
v. Check ‘ON/OFF’ indicator for correct indication
vi. Check earth connections
vii. Check for oil leaks at cable termination compartment
3.17.2 Motor run hour reading
Record motor run hour for circuit breakers with pneumatic and hydraulic
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B. MAINTENANCE GUIDELINES FOROVERHEAD TRANSMISSION LINES
1 ScopeThis section outlines the maintenance guidelines for 66kV, 132kV, 275kV and 500kV
transmission line network in Transmission Division. The guidelines describe the
maintenance works to be carried out and their frequencies.
2 General Information
Overhead transmission lines are meant to transmit electricity at high voltages fromgenerating plants/high voltage substations to customers. The transmission line
network in the Transmission Division’s system ranges from 66kV to 500kV.The total
length of transmission line network that is maintained by Transmission Divisionconstitutes more than 17,000 circuit-km.
Based on the analysis of failure modes on lines tripping history, it is concluded thatthe common causes of tripping are due to the followings:-
i. Lightning
ii. Encroachment activities
iii. Danger trees/bamboo shoots
iv. Broken cross arms
v. Line hardware failures (e.g. broken insulator strings, conductor snaps)vi. Others (e.g. relay faulty/malfunction, faulty surge arrestor and circuit
breaker, etc.)
3 Critical and Non-Critical LinesThe inspection frequency is determined by the area category of the lines which are:
a) Critical/Special (C)
This category includes transmission lines or sections of lines that fall into at
least one of the following conditions:
i. Highly loaded or strategic lines (to be determined by SPOD)
ii. Road/railway/river/line crossing
iii. Highly polluted areasa. Agricultural area with high usage of fertilizer or pesticide
b. Industrial area e.g. cement plant or steel plantc. Marine area or sea shores.
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b) Non-Critical (NC)This category includes transmission lines in areas other than described in (a)
above (e.g. rural, residential etc.)
The respective region(s) shall identify the criticality of lines/sections of lines based on
the above criteria. Any lines or sections of lines that do not fall within any of the
conditions as described above, but need special maintenance requirements, shall
nevertheless be attended to as required (e.g. soil erosion places).
4 Line Inspection and Maintenance
Failure modes have shown that other than lightning, most line tripping could be
avoided by ensuring healthy operation practice and carrying out thorough monitoringactivities. The controllable failures are addressed by categorizing the transmission
lines maintenance program into 2 major categories which are line inspection and line
maintenance.
4.1 Line Inspection
Line inspection shall be carried out while the line is energized and shall include the
following activities:
i. Ground patrol & rentice inspection
ii. Aircraft warning light system inspection
iii. Tower Top Inspection (TTI)
iv. Aerial inspection
v. Thermography scanvi. Rentice clearing
vii. Clearing of ground access pointviii. Measurement of tower footing resistance
4.2 Line Maintenance
Generally, maintenance actions are carried out based upon the condition of the linecomponent that is observed during inspection. Line maintenance works shall include
repair, replacement and refurbishment/overhaul works. Maintenance works on the line
component may be carried out by the following two methods:-
i. Live-line maintenance – maintenance work that is carried out using live line
tools and techniques on high voltage overhead transmission lines 132kV,275kV and 500kV. Maintenance of high voltage overhead transmission
lines shall be carried out using live-line maintenance technique in the
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event that the outage is not permitted due to system constraint or possible
high risk that could jeopardize system’s reliability.
ii. Dead-line maintenance – maintenance work that is carried out by the
respective regions of Asset Maintenance Department of TransmissionDivision on non-critical lines, where line outage is permitted by the
System Operation Department of Transmission Division.
5 Inspection Tasks and Maintenance Plan
Inspections of Right-of-way (ROW), conductors and towers shall be carried out on a planned routine basis or when situation warrants. This section describes the inspection
tasks and the maintenance plan required.
5.1 Ground Patrol
· Tower/Line components
i. Check for broken glass insulators or chipped porcelain insulatorsii. Check for missing, bending or corrosion bracing
iii. Check for operation of aircraft warning light (This task is best done inthe evening e.g. during thermovision inspection)
iv. Check stubs for signs of corrosion or soil erosion near tower legsv. Check for visibility and corrosion danger and phase plates
vi. Check for missing step boltsvii. Check for general condition of pole, tower, cross-arm, conductors,
fittings(including spacers and dampers) and earthwire
viii. Check for any dropped or moved spacer or vibration damperix. Check for corrosion or soil erosion at stays and stay anchors
x. Check for corrosion or damaged anti-climbing devicesxi. Check for corrosion or broken earth tape connection
xii. Check air craft warning spheres
· R.O.W./access route activities:Visual checks on:
i. vegetation conditionii. access roads
iii. centre pathsiv. construction activities under/near transmission lines
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ix. trees above 6 feet height within R.O.W.
(Note: Transmission lines that traverse urban areas where there are active
construction activities should be patrolled at shorter intervals to prevent any
encroachment to the transmission lines. In the case of vegetation in R.O.W., certainlocal authorities require more frequent cutting of vegetation to ensure good aesthetics
of the local surrounding. In such cases, compliance to conditions imposed by local
authorities is necessary).
5.2 Aircraft Warning Light Maintenance -
This task is performed on aircraft warning light equipment where the
installation of such equipment is required by DCA. Maintenance is carried out
to examine the integrity of the aircraft warning light system which includes,
ensuring:-
i. Battery electrolyte is at adequate level
ii. Connectivity of cables is intact
iii. High intensity light bulbs are in good operating condition (including
reserve bulb)
iv. Cleaning of control box and solar panels etc.
5.3 Tower Top Inspection
This task entails climbing the tower while the line remains energized to visually
inspect the condition of the top part of line/tower components. It is imperative
that the safety clearances as outlined in the Line Maintenance Engineering
Guidelines are followed to carry out this task.
i. Check insulator pin for corrosion and/or pollution deposits conditionii. Check for detrimental cracks (for timber cross-arms) or bent/corroded
steel cross-arms
iii. Check insulator for cracks
iv. Check for connectivity and/or corrosion of earth bond atearthwire/OPGW cross-arms. Retighten if necessary.
v. Check for any displaced or dropped dampersvi. Check visibility and corrosion of air borne number plate
vii. Check stability and signs of corrosion of maintenance platformviii. Check condition of fittings
ix. Check condition Transmission Line Arrester (if applicable)
5.4 Aerial Inspection
This task may only be performed as and when required upon directives by
Heads of Departments in Transmission Division. Examples of situationsrequiring aerial inspection are listed below:-
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i. Emergency patrols to quickly locate faults after line trippingii. Inspection of overall conditions of towers and R.O.W. after floods or
monsoon season
iii. Patrols for lines traversing lands which are inaccessible using groundtransportation
5.5 Thermographic Scanning
i. Thermography scan of transmission lines that includes joints, mid-
span joints and clamps and to check for hotspots which indicatedeteriorating/loose connections.
5.6 Rentice Clearing
i. Cutting of vegetation within rentice area
5.7 Ground Access Point Maintenance
i. Maintaining ground access points for lines/towers so that access totowers is available at all times, especially when emergency work at
the tower location is required.
This task may only be performed as and when required upon directives byHeads of Departments in Transmission Division.
5.8 Tower Footing Resistance Measurement
i. Tower footing resistance (TFR) (to measure earth resistance at tower base)
This task may only be performed as and when required upon directives by
HOD. Due consideration to be given to towers where the soil resistance mayvary due to seasonal changes or changes of soil condition and section of lines
that have experienced tripping due to lightning.
5.9 Lowest Conductor Height Measurement
i. Check for excessive sags of lowest conductor in accordance with
Section 3.13.8 of TNB Transmission Electrical Safety Rules (for
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C. MAINTENANCE GUIDELINES FOR
TRANSMISSION UNDERGROUND ANDSUBMARINE CABLES
1 Scope
This section outlines the maintenance guidelines for 132kV, 230kV and 275kVunderground and submarine transmission cable network in the TNB Transmission
Division. The guidelines describe the maintenance works to be carried out and theirfrequencies.
2 General InformationUnderground transmission cables are commonly used in urban areas where there island constraint to build overhead transmission lines. The total circuit length of
underground cables that is maintained by TNB constitutes more than 700 km. Thereare 2 types of transmission cables used in the TNB transmission system. They are:
· Oil-filled cables
· XLPE insulated cables
Oil-filled cables are normally used as submarine cables in providing power
connection crossing the sea or the straits.
Based on the analysis of failure modes on transmission cables tripping history, it is
concluded that the common causes of tripping are due to the followings:· Human intervention
· Poor cable and accessories quality
· Poor workmanship on joints
3 Inspection and Maintenance PlanMaintenance of transmission cables and cable accessories shall be carried out on
a planned, routine basis. The maintenance works are aimed to provide acceptable
degree of confidence when operating the cables. This section describes the
inspection and maintenance tasks required and the maintenance plan for thetransmission cable.
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3.1 Cable route patrol
Inspection is carried out while the cable is in service and it includes the
following activities:
i. Check for missing or damaged cable markers/sign boardsii. Check for excavation/piling activities near/along the cable route and
condition of cable accessories e.g. underground oil pressure tankiii. Check physical condition of cable joint box/cable bridge/link box and
pressure gauge.iv. Check for condition of manhole cover (if applicable)
3.2 Offshore patrol for submarine cable
Regional Asset Maintenance office is required to seek cooperation from Jabatan
Laut Malaysia or relevant authority in monitoring maritime activities in the non-anchoring zone of the submarine cable and maintenance of the beacon house.
Monitoring and maintenance may include the following activities:i. Check condition of beacon light.
ii. Monitor maritime activities in the ‘non-anchoring zone’.
iii. Check overall condition of the beacon house.
3.3 Oil containment and alarm system inspection for oil-filled cable
i. Check for any operation of oil pressure alarm systemii. Check for oil leaks at cable sealing ends
iii. Check the condition of earthing connections
iv. Record oil pressure from gauge.v. Carry out lamp test at control panel
3.4 Operation test for oil containment alarm system for oil-filled
cable
3.5 Thermographic scanning
i. Check for hot spots on clamps, connections and overall thermal
condition of outdoor cable sealing ends
3.6 Cable accessories and supporting structures inspectioni. Inspection of cable bridge support structure
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D. MAINTENANCE GUIDELINES FORPROTECTION SYSTEM
1 Scope
This section outlines the maintenance guideline for all protection and control schemes
installed in TNB transmission network. Where applicable, this section shall be appliedto Generation and Distribution protection maintenance scope of work and the
frequencies shall be decided by the respective owners. The purpose of performingmaintenance as stipulated in this Guideline is to ensure that all protective systems
component installed in the transmission network are in good working order. It is notintended to resolve design and commissioning related issues and failures
The boundary of the protection scope of maintenance is from the terminal blocks
(inclusive of terminal blocks) of the marshalling kiosks or/and local control panel (e.g.transformers/GIS) to the secondary equipment panels (e.g. Relay/control panels, RTUinterface panels). Marshaling Kiosk is under the ownership of Primary team.
This guideline determines the tasks to be done on the protection relay systems and
frequencies of these tasks. Protection relays are devices that detect and response to
any abnormalities in the system and initiate appropriate control action(s) such that the
power system is affected the least. At present, transmission grid system is also
equipped with system protection scheme such as Force Generator Tripping Scheme
(FGTS), ATTEND, DIHS, UVLS etc. These special protection schemes shall be
tested by AMNT from time to time upon request and coordination from National Load
Dispatch Center (NLDC).
2 General Information
There are four types of relays:
a) electromechanical
b) static (analogue)
c) digital
d) numerical
Protection relays in operation consist of large population with variety of
manufacturers that can be difficult to establish common maintenance procedures, as
one model is different from another. The maintenance frequency of the protection
system (which requires plant outage) will be based on the type of relay used for Main
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protection. For plants where the Main protection consists of electromechanical and/or
static relay, the frequency of maintenance (which requires plant outage) will be done inevery two years. For plants where the Main protection consists of digital and/or numerical
only, the frequency of maintenance (which requires plant outage) will be done in every
four years. The frequency of maintenance is determined based on the availability ofinternal supervision function on the protection relay.
From Reliability Centered Maintenance (RCM) analysis, three major failure modesfor the relays were identified:
§ Internal relay faulty – in static, digital, numerical relays, this will result in
changing the faulty cards or modules whereas in electromechanical relays, the
moving parts may get worn out after being in operation for a number of years.
§ Wrong settings – this failure mode can be attributed to staff configuring or
keying the wrong settings especially after maintenance work was done. There
were also cases were the relay themselves are giving such problems. For
instance, the potentiometer for the reach settings for static distance relay maywear out after so many years in operation.
§ Other (e.g. Faulty connections) – inputs include CT and VT signals to therelays and outputs include trip and alarm signals. There are many possibilities
that contribute to this failure mode where there is no signal coming in or goingout of the relays.
3 Maintenance Plan
Currently, protection systems in TNB consist of static, numerical, digital and
electromechanical relays. For maintenance purposes, the relays/schemes are groupedinto the following functional units:
a) Line/Cable/Hybrid Feeder Bay b) Power Transformer/ Generator Transformer/ Reactor Bay
c) Capacitor Bank Protectiond) Bus Coupler, Bus Section and Busbar Protection
e) Generator Protection
The types of relays/schemes used for each of the above functional units are shown in
section 4: Types of relay used in TNB Transmission Protection scheme.
The following are the inspection and maintenance task for all protection relays in the
network and the detailed plan including the inspection and maintenance cycle for thevarious types of relays:
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3.1 Distance Relays
(i) Check and confirm power supply unit is healthy
(ii) Check CB and Isolator auxiliary contacts to relay(iii) Check Local Alarms & annunciation (Facia & Substation Control System)(iv) Check Tele-protection signals
(v) Measurement of CT and VT input to relay(vi) Confirm settings and configuration
(vii) Functional Test
· Distance Reach check
· Timing test
· Power Swing Blocking operation
· Switch On To Fault functions
· Voltage Transformer Supervision functions
·
Directional Earth Fault if in used (includes external DEF )· Stub function if in used (include external Stub relay)
(viii) Confirm the operation of the tripping circuits(ix) Check for lock out operation
Table 3.1 Maintenance plan for Distance Relays
No Details (I/N) Interval
Digital/Numerical Non
Digital/Numerical
1 Check and confirm power supply unit is
healthy
N 2 Years 2 Years
2 Check CB and Isolator auxiliary contacts to
relay
N 2 Years 2 Years
3 Check local alarms and annunciation I 4 Years 2 Years
4 Check Tele-protection signals I 4 Years 2 Years
5 Measurement of CT and VT inputs to relay N 2 Years 2 Years
6 Confirm settings and configuration I 4 Years 2 Years
7 Functional Test I 4 Years 2 Years
8 Confirm operation of tripping circuit I 4 Years 2 Years
9 Check for lock out operation I 4 Years 2 Years
3.2 Current Differential and Current Comparison Relays
(i) Check and confirm power supply unit is healthy
(ii) Check CB and Isolator auxiliary contacts to relay
(iii) Check Local Alarms & annunciation (Facia & Substation Control System)
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3.3 Pilot Wire Protection Relays
(i) Check and confirm power supply unit is healthy(ii) Check Local Alarms & annunciation (Facia & Substation Control System)(iii) Check condition and integrity of pilot wire
(iv) Measurement of CT inputs to relay(v) Confirm settings and configuration
(vi) Functional Test
· Pilot wire supervision
· End to end injection tests
· Inter-tripping circuit
· Timing test
(vii) Confirm the operation of the tripping circuits
(viii) Check for lock out operation
Table 3.3 Maintenance plan for Pilot Wire Protection Relays
No Details (I/N) Interval
Digital/Numerical Non
Digital/Numerical
1 Check and confirm power supply unit ishealthy
N 2 Years 2 Years
2 Check local alarms and annunciation I 4 Years 2 Years
3 Check condition and integrity of pilot wire I 4 Years 2 Years
4 Measurement of CT inputs to relay N 2 Years 2 Years
5 Confirm settings and configuration I 4 Years 2 Years
6 Functional Test I 4 Years 2 Years
7 Confirm operation of tripping circuit I 4 Years 2 Years
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3.4 Auto Re-close Relays
(i) Check and confirm power supply unit is healthy(ii) Check CB auxiliary and “Sync-check input” contacts to relay(iii) Check Local Alarms & annunciation (Facia & Substation Control System)
(iv) Confirm settings and configuration(v) Operational Test with actual breaker
(vi) Check for lock out operation
Table 3.4 Maintenance plan for Auto re-close Relays
No Details (I/N) Interval
Digital/Numerical Non
Digital/Numerical
1 Check and confirm power supply unit ishealthy
N 2 Years 2 Years
2 Check CB auxiliary and “Sync-checkinput” contacts to relay
N 2 Years 2 Years
3 Check local alarms and annunciation I 4 Years 2 Years
4 Confirm settings and configuration I 4 Years 2 Years
5 Operational test with actual breaker I 4 Years 2 Years
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3.8 Transformer Differential Relays
(i) Check and confirm power supply unit is healthy
(ii) Check Local Alarms & annunciation (Facia & Substation Control System)(iii) Measurement of CT input to relay(iv) Confirm settings and configuration
(v) Functional Test
· Operational test
· Biased characteristic test
· Inrush Blocking
· Over-excitation / Over-fluxing if in used
· Timing test
(vi) Confirm the operation of the tripping circuits
(vii) Check for lock out operation
Table 3.8 Maintenance plan for Transformer Differential Relays
No Details (I/N) Interval
Digital/Numerical Non
Digital/Numerical
1 Check and confirm power supply unit ishealthy
N 2 Years 2 Years
2 Check local alarms and annunciation I 4 Years 2 Years
3 Measurement of CT input to relay N 2 Years 2 Years
4 Confirm settings and configuration I 4 Years 2 Years
5 Functional test I 4 Years 2 Years
6 Confirm the operation of tripping circuits I 4 Years 2 Years7 Check for lock out operation I 4 Years 2 Years
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3.9 Restricted Earth Fault Relays
(i) Check and confirm power supply unit is healthy(ii) Check Local Alarms & annunciation (Facia & Substation Control System)(iii) Confirm settings and configuration
(iv) Operational and Timing Test(v) Confirm the operation of the tripping circuits
(vi) Check for lock out operation
Table 3.9 Maintenance plan for Restricted Earth Fault Relays
No Details (I/N) Interval
Digital/Numerical
Non
Digital/Numerical
1 Check and confirm power supply unit ishealthy
N 2 Years 2 Years
2 Check local alarms and annunciation I 4 Years 2 Years
3 Confirm settings and configuration I 4 Years 2 Years
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3.10 Standby Earth Fault Relays
(i) Check and confirm power supply unit is healthy(ii) Check Local Alarms & annunciation (Facia & Substation Control System)(iii) Confirm settings and configuration
(iv) Operational and timing test(v) Confirm the operation of the tripping circuits
(vi) Check for lock out operation
Table 3.10 Maintenance plan for Standby Earth Fault Relays
No Details (I/N) Interval
Digital/Numerical Non
Digital/Numerical
1 Check and confirm power supply unit ishealthy
N 2 Years 2 Years
2 Check local alarms and annunciation I 4 Years 2 Years
3 Confirm settings and configuration I 4 Years 2 Years
4 Operational test with actual breaker I 4 Years 2 Years
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3.11 Stub Protection
(i) Check and confirm power supply unit is healthy(ii) Check line Isolator auxiliary contacts to relay(iii) Check Local Alarms & annunciation (Facia & Substation Control System)
(iv) Confirm settings and configuration(v) Functional Test
· Transfer or Inter-trip tripping if available
· Timing test
(vi) Confirm the operation of the tripping circuits(vii) Check for lock out operation
Table 3.11 Maintenance plan for Stub Protection Relays
No Details (I/N) Interval
Digital/Numerical Non
Digital/Numerical
1 Check and confirm power supply unit ishealthy
N 2 Years 2 Years
2 Check line Isolator auxiliary contacts to
relay
N 2 Years 2 Years
3 Check local alarms and annunciation I 4 Years 2 Years
4 Confirm settings and configuration I 4 Years 2 Years
5 Functional test I 4 Years 2 Years
6 Confirm the operation of tripping circuits I 4 Years 2 Years
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3.12 High Impedance Busbar Differential Relays
(i) Check and confirm power supply unit is healthy(ii) Check Local Alarms & annunciation (Facia & Substation Control System)(iii) Confirm settings and configuration
(iv) Operational and Timing Test for all zones(v) Test on CT Supervision Circuit
(vi) Check the condition of the tripping circuits
· Isolator auxiliary contact in tripping circuit for all bays
· Transfer trip to remote end if applicable(vii) Check for lock out operation
Table 3.12 Maintenance plan for High Impedance Busbar Differential Relays
No Details (I/N) Interval
Digital/Numerical Non
Digital/Numerical
1 Check and confirm power supply unit is
healthy
N 2 Years 2 Years
2 Check local alarms and annunciation I 4 Years 2 Years
3 Confirm settings and configuration I 4 Years 2 Years
4 Operational and timing test for all zones I 4 Years 2 Years
5 Test on CT supervision circuit I 4 Years 2 Years
6 Check condition of tripping circuits N 2 Years 2 Years
7 Check for lock out operation I 4 Years 2 Years
3.13 Low Impedance Busbar Protection Scheme (Centralized and De-centralized)
(i) Check and confirm power supply unit is healthy(ii) Check Local Alarms & annunciation (Facia & Substation Control System)
(iii) Check CB and Isolator auxiliary contacts to relay
(iv) Measurement of CT inputs from all bays
(v) Confirm settings and configuration
(vi) Check the condition of the tripping circuits (negative check)
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3.22 Switch-sync (Point of Wave) relays
Table 3.16 Maintenance plan for Switch-sync (Point of Wave) Relays
No Details (I/N) Interval Digital/Numerical
Non
Digital/Numerical
1 Operational check and inspection I 2 Years 2 Years
3.23 Reverse Power, Negative Phase Sequence, Over Excitation, Loss Excitation
and Under Impedance Relays
Maintenance of these relays will be carried out upon request and completemaintenance task/checklist is to be provided by Power Plant Operator/ Generation
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E. MAINTENANCE GUIDELINES FOR STATIC VARCOMPENSATOR (SVC) EQUIPMENT
1 ScopeThis section outlines the maintenance guidelines for SVC equipment in TNB
Transmission Division. The guidelines describe the maintenance works to be carried out
on SVC equipment and their frequencies.
2 General Information
SVC is used mainly to provide voltage control during daily load cycles, dynamicreactive power reserves in the event of network disturbances such as loss of generation
and/or loss of transmission and also for damping of active power oscillations. At
present, there are two SVC installations located at KL North substation (KULN) andYong Peng North substation (YGPN).
The major equipment in SVC installation are Circuit breaker, Transformer, Thyristor-switched capacitor (TSC), Thyristor-controlled reactor (TCR), Filter banks and
secondary equipment. The maintenance strategy for SVC equipment is based on
manufacturer ’s recommendation and TNB maintenance experience.
In deriving the maintenance guidelines, SVC equipment are divided into four major
groups as follows:-
a) Thyristor related equipment b) Control and Protection for SVC Equipment
c) SVC Primary Equipmentd) Auxiliary equipment
3 Inspection and Maintenance PlanMaintenance of SVC and related equipment shall be carried out on a planned, routine
basis. The maintenance works are aimed to provide acceptable degree of confidence
when operating the SVC. This section describes the inspection and maintenance tasks
required and the maintenance plan for the SVC equipment.
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3.2 Control and Protection for SVC equipment
The control system must provide stable operation under normal as well as
contingency conditions whilst the protection system is designed such that allequipment is fully protected and any equipment which is operating in abnormal
way is properly removed from service. All SVC protections are properlycoordinated between each of the SVC equipment and with the AC system
protection (where required).
3.2.1 VarMaster Control Local and Remote panel
No Details Intrusive/
Non-Intrusive
Interval
i Visual inspection on cleanliness,
cubicle lights and heaters.
NI Monthly
ii Confirm correct readings areindicated on the meters and
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3.2.3 Protection Relays for the SVC Primary Equipment
The maintenance task for the protection relays for the SVC Primary equipment
follows the maintenance task for the protection relays as mentioned in
Maintenance Guideline for Protection Systems.
3.3 SVC Primary Equipment
The SVC Primary equipment consists of transformer, circuit breaker, isolator,
current transformer, voltage transformer, capacitor, reactors and switchyard. The
maintenance task for the SVC primary equipment follows the maintenance task forequipment as mentioned in Substation Maintenance Guidelines.
3.4 Auxiliary EquipmentAuxiliary equipment includes ventilation, air conditioning, fire detection and
fighting system, building condition and etc. as appropriate. The maintenance taskfor these items follows the maintenance task for Building and Entire plant as
mentioned in Substation Maintenance Guidelines. Additional maintenance taskwhich is considered important is also to be carried out.
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F. MAINTENANCE GUIDELINES FOR HIGHVOLTAGE DIRECT CURRENT (HVDC)
EQUIPMENT
1 ScopeThis section outlines the maintenance guidelines for HVDC equipment in TNB
Transmission Division. The guidelines describe the maintenance works to be carriedout and their frequencies.
2 General Information
HVDC is used mainly for long distance transmission, interconnection of powersystems, long submarine cables and to increase efficiency in power control. At present, there is only one HVDC converter station in Gurun and the station provides
interconnection of the power networks between Malaysia and Thailand.
The maintenance guidelines cover equipment in HVDC convertor station. Themaintenance strategy for HVDC equipment is based from manufacturers’
recommendation and TNB maintenance experience.
In deriving the maintenance guidelines, HVDC convertor station is divided to five
major areas as follows:-
a) Convertor equipment
b) DC Primary Equipmentc) AC Primary Equipment
d) Control, Instrumentation and Protection
e) General services and auxiliary equipment
3 Inspection and Maintenance PlanMaintenance of HVDC equipment and related equipment shall be carried out on a
planned, routine basis. The maintenance works are aimed to provide acceptable
degree of confidence when operating the HVDC equipment. This section describes
the inspection and maintenance tasks required and the maintenance plan for the
HVDC equipment.
3.1 Converter Equipment
This includes equipment required for conversion from AC to DC and vice versa.
The convertor equipment is located in the Valve hall. It consist of indoor air
insulated suspension type thyristor and direct water cooling system for the
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3.2.1 DC Filter Active Part
DC Filter active parts are used to eliminate higher harmonic and minimize
telecommunication interference. The maintenance activities are as follows:-
No Details Intrusive/
Non-Intrusive
Interval
i Visual Inspection N 2 Monthly
ii Replace backup batteries, clean
pcbs, lubrication and greasing
I Yearly
iii Replace fan bearings I After 30000 hrs ofoperation
iv Check tightness of connections I 5 Years
3.2.2 DC Voltage Divider
The maintenance task for DC Voltage divider follows the maintenance task forCapacitive Voltage Transformer as mentioned in Substation Maintenance
Guideline.
3.2.3 High Speed Ground Switch
High speed ground switch is used for continuous operation during neutral line
fault where the switch is closed and the DC current will return to the ground.The maintenance task for High Speed Ground Switch follows the maintenance
task for HV Circuit breaker as mentioned in Substation MaintenanceGuideline.
3.2.4 DC Filter Circuit Breaker
The maintenance task for DC Filter Circuit Breaker follows the maintenance
task for HV Circuit breaker as mentioned in Substation Maintenance
Guideline.
3.2.5 DC Disconnector, Grounding Switches and Valve Hall Earthing switches
The maintenance task for DC Disconnector, grounding switches and valve hall
earthing switches follows the maintenance task for Disconnectors as
mentioned in Substation Maintenance Guideline.
3.2.6 DC Filter Capacitors, DC Filter Reactors and Smoothing Reactors
The DC filters consist of capacitor and reactors and they are used to eliminate
the lower harmonic content. The smoothing reactors are used to reduce rate ofrise of DC current for DC side fault and it also forms part of high frequency
noise filtering. The maintenance task for DC Filter Capacitors, DC Filter
Reactors and Smoothing Reactors follows the maintenance task for
Compensation Equipment as mentioned in Substation Maintenance Guideline.
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3.2.7 DC Switchyard
The DC switchyard is similar to AC substation switchyard. The maintenance
task for DC switchyard follows the maintenance task for AC Switchyard asmentioned in Substation Maintenance Guideline.
3.3 AC Primary Equipment
AC Primary equipment provides the interfacing between the convertor
equipment and the AC network or the Transmission grid. The equipment andthe maintenance task are described in the following clause.
3.3.1 AC Filter Capacitors, AC Filter Reactors and Capacitor Subbank
The AC filters consist of capacitor and reactors and they are used to eliminate
the harmonic content. The Capacitor subbank is used for compensation ofreactive power absorbed by the converter. The maintenance task for AC Filter
Capacitors, AC Filter Reactors and Capacitor subbank follows themaintenance task for Compensation Equipment as mentioned in Substation
Maintenance Guideline.
3.3.2 AC Filter Resistors
No Details Intrusive/
Non-Intrusive
Interval
i Visual Inspection NI 2 Monthly
ii Cleaning , check tightness of
connections
I Yearly
3.3.3 Converter Transformer
The converter transformer consists of three single-phase, three-winding
transformer. The converter transformer is used to stepdown/up the AC voltageto commutation voltage for the converter equipment. The maintenance task for
Converter transformer follows the maintenance task for Power Transformer asmentioned in Substation Maintenance Guideline.
3.3.4 AC Current and Voltage Transformers
The AC Current and Voltage transformers are used for AC,DC Filters and
shunt reactors. The maintenance task for these instrument transformers followsthe maintenance task for current transformer and voltage transformer asmentioned in Substation Maintenance Guideline.
3.3.5 AC Switchyard
The maintenance task for HVDC station’s AC switchyard follows the
maintenance task for AC Switchyard as mentioned in Substation MaintenanceGuideline.
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3.4 HVDC Control and Protection
HVDC control system is designed such that to provide the desired power
transmission level. The control system must provide stable operation undernormal as well as contingency conditions.
The protection system is designed such that all equipment is fully protected andany equipment which is operating in abnormal way is properly removed from
service. All HVDC protections are properly coordinated between each of theHVDC equipment and with the AC system protection (where required).
The monitoring system provides operation information related to HVDCsystem, HVDC station, auxiliary equipment and station alarms. The
maintenance activities for HVDC control and protection are as follows:-
No Details Intrusive/
Non-Intrusive
Interval
i DC Protection and Pole ControlFunction test
Intrusive Yearly
ii Teleprotection Intertrip test Intrusive Yearly
iii Converter TransformerProtection test
Intrusive Yearly
iv AC Protection relays Intrusive Yearly
v Circuit breaker trip test Intrusive Yearly
The maintenance task for secondary DC supply system follows the maintenance
task as mentioned in Protection equipment maintenance guidelines.
3.5 General services and auxiliary equipment
Auxiliary equipment includes ventilation, air conditioning, fire detection and
fighting system, building condition and etc. as appropriate. The maintenance
task for these items follows the maintenance task for Building and entire plant
as mentioned in Substation maintenance guidelines.
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G. MAINTENANCE GUIDELINES FOR
SUBSTATION CONTROL SYSTEM (SCS)
1 Scope
The section outlines the maintenance guidelines for substation control system (SCS)installed in TNB Transmission network. The guidelines describe the tasks to be done on
the equipment and the frequencies of these tasks.
2 General Information
The Substation Control System (SCS) are installed in substations for the collection, processing, storage, retrieving, and distribution of data obtained from substation
equipment and other sources. SCS also supports the operation of power system by providing local monitoring and control facilities as well as providing interface to SCADA
master station for remote operation.
The SCS is designed to be an expandable, technology adaptable, modular hierarchy ofsegments, elements and subsystems. It is not expected that SCS equipment will require
extensive scheduled preventive maintenance. Advancements in technology, with self-
supervision features, have eliminated most preventive maintenance requirements.
· Operational Availability (OA)Operational Availability is measured from the issuance of fault reports to the
rectification of the problem.
· Mean Down Time (MDT)Maximum MDT is the maximum time for Maintenance Team toclear/repair/normalized the fault from the issuance of fault report to the rectification
of the problem.
·
Preventive MaintenancePreventive maintenance includes all scheduled maintenance action performed toretain SCS in specified condition. Scheduled maintenance includes the periodic
inspections, condition monitoring, critical item servicing, software back up andcalibration.
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· Corrective MaintenanceCorrective Maintenance includes unscheduled maintenance actions performed as a
result of SCS failure to restore the SCS to a specified condition. The tasks include
failure identification, isolation of faulty equipment, replacement and retesting.
· Failure ModesSCS failure could cause a total or partial failure to the Network, Station, and Bay
Level control and monitoring function. The SCS is designed such that a single failureshall not affect the operation and functions of both network level and station level.
The SCS is designed such that a single failure shall not affect the operation andfunctions of more than one bay or diameters.
Possible Failure includes:
Subsystem and Functions Failure ModeHuman Machine Interface Total Partial
Gateway Total
Station Level Controller Total Partial
Bay Controller Unit Total Partial
Internal Communication Network:
Single Bay Total Partial
Multiple Bay Impossible Impossible
3 Objectives
The primary objective of SCS maintenance is to achieve and sustain the operationalavailability (OA) and mean down time (MDT) objectives of the SCS at the least life cycle
cost.
It also describes the general concept and plan for maintaining Substation Control System(SCS) Hardware (HW) and Software (SW) in support of SCS operational objectives. This
guideline is applicable for maintenance support of SCS HW and SW until the end of thesystem life cycle.
This guideline also serves to:
i. Document SCS maintenance strategiesii. Optimize maintenance costs
iii. Standardize maintenance activitiesiv. Help achieve TNBT’s business plans and targets
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H. MAINTENANCE GUIDELINES FOR REMOTE
TERMINAL UNIT (RTUS)
1 Scope
The section outlines the maintenance guidelines for all Remote Terminal Units (RTUs)installed in TNB Transmission network.
These guidelines determine the tasks to be done on the equipment and the frequencies of
these tasks.
2 General Information
The maintenance guidelines cover the Remote Terminal Unit and include the SupervisoryInterface Panel and the I/O wiring between the RTU and the Supervisory Interface Panel,
as shown in Figure 1 below. These guidelines does not cover plant auxiliary contacts,heavy-duty interposing relays and transducers mounted in control panels, DC system and
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2.1 Failure Modes
· Hidden Failure
A functional failure that does not manifest itself until function is required.
· Partial FailureA failure that results in reduced performance or functionality of any of the RTU’s primary functions. For example, an RTU is said to have suffered a partial failure
when 16 out of its total 128 analog measurements cannot register any readings.
· Complete FailureFailure which results complete loss of all of the RTU’s primary functions.
3 Objectives
The primary objective of RTUs maintenance is to achieve and sustain the operationalavailability (OA) and mean down time (MDT) of the RTUs at the least life cycle cost.
The guidelines also serve to:
i. Document RTU maintenance strategiesii. Optimize maintenance costs
iii. Standardize maintenance activities
iv. Improve RTUs operational reliability and availabilityv. Help achieve TNBT’s business plans and targets
4 Maintenance Plan
4.1 Failure Mode, Effect and Criticality Analysis (FMECA)
FMECA study performed on the RTU established that the most appropriate maintenancestrategy involves operating the RTU to failure and restoring it back to service as soon as
possible.
The FMECA also identified the need to perform regular periodic inspections to ensurethat the RTU’s operating environment is within specified limits, and to conduct periodic
functional checks to resolve any hidden failures before they manifest themselves.
4.2 Preventive Maintenance
Periodic inspections shall be carried out on all RTU sites to: