Operation and Maintenance of Sub - Stations Revised 030909

8/12/2019 Operation and Maintenance of Sub - Stations Revised 030909

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OPERATION AND

MAINTENANCE OFSUB - STATIONS.

BY

S.GANESH BABU.


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MAINTENANCE PHILOSOPOHY OFSUBSTATION EQUIPMENTS

In today's competitive market scenario power utilities areunder tremendous pressure to cut down their maintenancecosts as they form a significant portion of the operationcosts. This has led the utilities to adopt condition-basedmaintenance of the equipments rather than usual

preventive maintenance being carried out at a fixed interval

of time.

TYPES OF MAINTENANCE

Different types of maintenance being done on equipmentsare:

i) Breakdown maintenanceii) Preventive maintenance

iii) Condition based monitoringiv) Reliability centered maintenance


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Breakdown Maintenance

As the name implies the maintenance is carried outwhen the equipment fails. This type of maintenancemay be appropriate for low value items. However forcostly substation equipments, it is not desirable to waittill the breakdown of the equipment, as this costs more

to the utility as well as the availability and reliability ofpower gets affected. The revenue loss due to non-availability of the system shall be much more than thecost of the failed equipment. Therefore identifying thedefect before failure, is more appropriate to plan repair/ replacement.


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Preventive Maintenance

The preventive maintenance of equipment is beingmostly adopted by almost all the utilities. In this type ofmaintenance, the equipments are inspected at a pre-determined period. The frequency determined based onthe past experience and also guidance from themanufacturer of the equipment. This type ofmaintenance would require specific period of shut-

down. Maintenance procedure, periodicity ofmaintenance and formats for maintaining records forvarious types of sub-station equipments have beendiscussed separately in detail in a separate section.


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Condition Based Monitoring

This type of maintenance technique is adoptedto assess the condition of the equipment. Thecondition of the equipment is assessed based on

different condition monitoring tests. Some ofthe tests are done on on-line and some are doneon off-line. However, this type of maintenance

would need sophisticated testing equipmentsand skills for analyzing the test results.


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Reliability Centered Maintenance

This is the recent technique being adopted inmaintenance philosophy. The basic objectives ofreliability-centered maintenance are:

- Maintenance should keep the equipment at desiredlevel of performance

- Optimizing / minimizing the maintenance /shutdown period so as to enhance the availability of the

equipment.

- Deferring / avoiding the replacement of components

and major/minor over-hauls till it is absolutely

necessary.


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GENERAL REQUIREMENTS

Preventive maintenance shall be performed at a levelthat assures that the unscheduled outage performance ofCustomer owned equipment is at least as good as that ofthe TOs system to which it is connected.

Each facility owner shall have an established anddocumented program for the maintenance of allequipment critical to the reliable operation of the bulkpower system.

Maintenance programs can vary in range from strictadherence to manufacturers recommendations to RCM(reliability centered maintenance), as appropriate, butshould reflect Good Utility Practice.


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Maintenance of equipment shall be

performed such that the facility owner is ableto support any local interconnectionagreements. Loss of a piece of equipment dueto lack of sufficient maintenance can lead to

unnecessary higher operating costs andunnecessarily long outage time, consequentlycompromising transmission reliability.

Additionally, the maintenance of systemspare equipment must not be overlooked.


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Substation equipment shall be maintained byqualified personnel in accordance with applicable

industry standards and Good Utility Practice

Incorrect operation of equipment or equipment

failure should be thoroughly investigated anddocumented to determine the root cause of the

problem. Failures of equipment that adverselyimpact the transmission System should be

investigated in collaboration with the affectedtransmission owners.


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EQUIPMENT AND FACILITIES

Equipment diagnostic tools and tests can beutilized in the evaluation of the need forrequired maintenance. Examples include

dielectric testing and analysis, breaker timingthermo-graphy scans, and acoustic monitoring.The facility owners plan should be clear as tothe application, as appropriate, of these

diagnostic tools. Pass/fail ranges and testingintervals should be well documented.


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Thermo graphy scanning should be incorporated ininspections.

It is a non-contacting operation, which is applied to in-service equipment while energized and carrying load.Problems are detected either as a function of excessive

temperature rise (such as a poor connection) or asubnormal temperature (such as a cool transformerradiator fin signifying a blocked passage).

Frequency of operation should also be factored into thedetermination of maintenance periodicity. Trending ofequipment performance versus maintenance should beused to re-evaluate maintenance intervals.


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For equipment under warranty all required maintenance tomaintain warranty should be performed. It is suggestedthat equipment performance be reviewed prior to warrantyexpiration.

Maintenance of equipment should include diagnostics,overhauls and painting as required to maintain systemintegrity. Attention should be given to both the mechanicaland the electrical aspects of the equipment beingmaintained. Use of incorrect lubricants can adversely affectequipment performance.

Adequate spare parts should be kept on hand to supportmaintenance.

Manufacturers service bulletins must be acted upon in atimely manner.


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The failures in power transformers can be

broadly classified as:

specification, design / manufacturing

deficiency

Installation / operation / maintenancedeficiency

Adverse operating conditions

Aging.


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The country wide statistics:-

Design defect 35.7% Manufacturing Problems 28.6%

Material defect 13.1%

Transport and storage

problems 1.2% Incorrect Maintenance 4.8%

Abnormal over load.


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Adverse operating conditions

The life of a transformer is normally dependent on

the life of insulation. The rate of ageing is related

to temperature, moisture content and duration of

loading conditions.

Life expectancy of transformer will get diminished

through inadequate protection while operating inthe abnormal conditions such as:

Sustained overload conditions

Switching surges Lightning surges

Transferred surges


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Improper maintenance practices.

Poor / inadequate maintenance in the areas of oilleakage, oil quality, critical accessories such as tapchangers, bushings, protective instruments etc.

will cause trouble in transformer. In addition to

this, there are various trouble-shooting problemsencountered in the field, such as moisture,oxidation, solid contamination, gas bubbles, overcurrent, over voltage (transient or dynamic), over

temperatures, short circuit (mechanical forces)etc., for which sufficient care should be taken tosafeguard the transformer. Preventive maintenanceis strongly recommended to improve the reliability

of transformer.


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Suggestions to reduce failures.

Improved design and manufacturing practice

By adopting CAD and better shop floormanagement, more reliable units could bemanufactured to eliminate:

Poor short circuit withstand capability Manufacturing defects including cooling system

Problems associated with bushings

OLTC including selector/diverter switch Tertiary winding failure wherever provided


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Improved testing method

Transformer should be simulated to actual servicecondition first by sequential testing and then passingnecessary current which could result into temperature

rise. Thereafter conduction of all high voltageapplication tests could bring out insulation weakness.Simulated short circuit test if necessary on scaled modeland measurement of magnetic balance and

magnetization current could reveal abnormality.


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Problems external to transformer:

Load management

By adopting efficient load frequency management systemscould be better controlled avoiding damages andtransformer failure due to:

Overloading

Over fluxing and over voltage Hot joints and spark over Frequent feeder tripping due to reflected faults.

Failure of switchgear and battery:

This could be avoided by periodic testing and using properduty switch-gear and battery.


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Permissible limits for transformers for transformers.

A. Transformer

oila) BDV

- At the time of

first charging

600 kV (Gap2.5 mm)

Minimum

IS1866

- During O&M 50 kV (Gap2.5 mm)

Minimum

IS1866

b) Moisture

content

- At the time of

first charging

15 PPM (Max.) IS1866

- During O&M 25 PPM (Max.) -do-


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Permissible limits for transformers

c) Resistivity at 90

degree C

0.1-1012

Ohm-CM (Min.) IS - 1866

d) Acidity 0.2 mg KOH/gm (Max.) - do -

e) IFT at 27 degree C 0.018 N/M (Min.) IS1866

f) Tan delta at 90 degree

C

0.20 (Max.) -do-

g) flash point 126 Deg. C (Min.) -do-


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Permissible limits for transformers

B) Vibration level for

reactors

200 Microns (Peak to Peak)

60 Microns (Average)

C) Tan delta for bushing

at 20 Deg. C

0.007* IEC137

D) Capacitance forbushing + 5% variation

E) IR value for winding 1000 M-Ohm By 5.0/10.0 kV

Megger

F) Tan delta for windings

at 20 Deg. C

0.007* IEEE/C57.12.

90.1980

G) Contact resistance of

bushing terminal

connectors

10 M. Ohm / Connector NGC.UK

Recomme

ndations

H) Turret Neutral CT

ratio erros

+ 39 IS2705

T


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Preventive Maintenance schedule for TransformersS.No.

Tasks assigned Shut Down (SD)Or

Without Shut

Down(WSD)

Periodicity

a. Checking of bushing oil level WSD Monthly

b. Checking of oil level in

Conservator

WSD Monthly

c. Checking of oil level in OLTCConservator

WSD Monthly

d. Checking of cooler oil pumpsand fans

i) Manual actuation WSD Monthly

ii) Auto Starting SD Yearly

e. Checking of oil leaks WSD Monthly


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Preventive Maintenance schedule for Transformerscontd

f. Checking condition of Silicagel in breather andregeneration if required

WSD Monthly

g. Measurement of BDV of oil WSD HalfYearly

h. Testing of oil for DGA andother oil parameters

WSD HalfYearly

i. Checking/Topping up of oillevel in oil seal ofbreather

WSD In caseof

requirement

j. Vibration measurements(for Shunt Reactors only)

WSD HalfYearly


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Preventive Maintenance schedule for Transformerscontdk. Measurement of BDV of

OLTC oilSD Yearly

l. Tan d measurement forBushings SD Yearly

m. i) IR!measurement ofWindings (PolarisationIndex and DA+ Ratio)

SD In 3Years

**

ii) Tan d measurement ofWindings SD In 3

Years**

iii) Measurement ofWindings resistance

SD In 3Years

**

iv) Measurement ofwindings ratio

SD If needed

v) Measurement of short

circuit Impedance

SD If needed.


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n. External cleaning ofRadiators

SD Yearly

o. Cleaning of all Bushings SD Yearly

p. Frequency ResponseAnalysis

SD If Reqd.

q. Maintenance of OLTCdriving mechanism

SD Yearly

r. Checking of all remoteindications (STI and Tapposition indicator)

SD Yearly

s. Electrical checking /testing of pressure reliefdevice, Buchholz relay,OLTC surge Relay andchecking/Replacement

of the gaskets of theterminal box

SD Yearly


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t. Checking/testing ofBuchholz relay byinjecting air or nitrogen

SD Yearly

u. Marshalling boxes ofICT/Reactor of:

SD Yearly

i) Cleaning of Marshallingboxes of ICT/Reactor

and OLTC

SD Yearly

ii) Tightening ofterminations

SD Yearly

iii) Checking of contactors,

space heaters,illumination etc.

SD Yearly

v. Checking and Cleaning ofDiverter Contacts

SD SOS (50,000

Opera

tions)


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w. Checking of oil level andcalibration of OTI, WTI

SD Yearly

x. Filteration /Replacement of Oilof OLTC SD In case ofrequireme

nt

y. Filteration / Degassing of maintank radiator oil

SD In case ofrequireme

nt

z. Testing of bushing CTs.

i) IR valve SD SOS

* Water content, BDV, SP, Resistance, Tan d, IFT.Total Acidity, 2-Furfuraldehyde etc.

** First time after one year from commissioningand then once in every three years.

+ Di-electric Absorption Ratio

! To be measured as per the followingcombinations:

N/E, N/LV and LV/E.


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FAILURE OF CIRCUIT BREAKERS

A circuit breaker is considered to have failed,when the breaker fails to operates after acommand is given or unable to interrupt the arcor withstand a system voltage.

interrupting chambers

pre-insertion resistor chambers

grading capacitors

support column including tie/operatingrods


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Dielectric failure inside interrupting chamber due to highmoisture in SF6 gas.

Insulation failure (live to earth) due to accumulation ofmoisture on tie rod during storage.

Failure of mechanical coupling between tie rod andoperating mechanism.

Failure of actuating valves in operating mechanism.

Failure due to foreign particles (eye pieces) insideinterrupter.

Failure due to high transient recovery voltage (TRV).


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Preventive Measures for Avoiding CB

Failures:

Introduction of state-of-the-art condition monitoring checks duringservice such as

Dynamic contact resistance measurement

Dew point measurement of SF6 gas. Contact travel measurement

Operating timings

Tan delta measurement of grading capacitors

Trip/close coil currents measurement

SF6 gas/hydraulic oil/air leakage monitoring.


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Failure of CVTs

Preliminary failure analysis of failed CVTs have revealedthat main reasons of CVT failures are:

High value of tan delta Secondary voltage abnormal

High value of capacitance

Oil leakage Humming sound.


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Besides the above following problems werealso observed in one make of CVT:

Snapping of bellow connection

Burning of damping resistor

Burning/failure of lightning arrestor Failures of capacitor stacks

Blackening of insulating oil in EMU tank

The only remedial measures suggested to avoidfailures is to do the proper condition monitoringchecks of CVTs at site.


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FAILURES OF SURGE ARRESTORS

Analysis of failure of surge arrestors haverevealed failures mostly due to prematuredegradation of ZnO discs. To minimize the

failure of surge arrestors it is suggested thatsurge arrestors are monitored online forpresence of third harmonic resistive current in

the leakage current flowing through surgearrestors. Leakage current up to 500 micro Ampis generally considered within acceptable limits.


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MAINTENANCE TECHNIQUES

The maintenance techniques to be adoptedshould meet the following criteria:

Field staff should be able to carry out such tests

and interpret the test results Testing procedure to be evolved after detailed

discussions with the supplier of the equipmentand testing equipment

written procedure to be made available to theoperating staff

Preventive maintenance schedule for surge arrestors


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Preventive maintenance schedule for surge arrestors

Sl.

No

Tasks assigned Shut down /

without shut

down

periodicity

1. Checking of leakage

current, 3rdharmonic

resistive current

WSD Yearly.

2. Testing of counters SD Yearly

3. Cleaning of LA insulator SD Yearly.

4. Measurement of

capacitance and tan

delta.

SD Yearly.


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GENERAL CHECKS / MAINTENANCE INSPECTION

The equipment should be inspected at the regular intervalas per the guidelines. In addition the manufacturerguidelines should also be followed. The general checksnormally required to be done are:

General cleaningCleansing of all insulators ofCB/CT/CVT/Isolators for salt/dirt deposition, if any.

Dust protectioneven though the operating mechanismare made of steel and surface treated, still some rusting maytake place. If any rust stains are observed the same may becleaned with emery paper and paint the same against therust protection. For protection against rust, grease G ortectyl 506 is suggested.


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Tightness checkAt the time of first

inspection, all bolted joints on thebreaker and operating mechanism shallbe tightened up. All the wiring joints inthe terminal box of the operating

mechanism shall be re-tightened at theregular intervals. Re-tightening has to berepeated only after bigger overhauls. Any

SF6 gas leakage has to be detected withsuitable gas leak detector.


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LubricationBearings of the breaker andoperation mechanism of isolators and breaker

are to be lubricated with grease G after majoroverhauls.

Treatment of gasketsAny gasket opened onceshould be replaced by new one. All sealingsurfaces and O-rings shall be sparsely greased ofappropriate type for better sealing against this

surface and at the same time providingprotection against rusting/corrosion.


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Treatment of contact surfaces

Copper surfaces should be cleaned and madeoxide / sulphate free. If required, to be cleanedwith cloth and solvent (Trichloroethane) or steel

brushing. After steel brushing, the surface needto be cleaned for loose particles and dust withthe dry cloth / solvent (Trichloroethane)


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Silver contact surfaces if required to becleaned, the same to be done with soft

cloth and solvent (Trichloroethane).Steel brushing or grinding is notpermitted.

Aluminum contact surfaces should becleaned with steel brush and emerycloth. Afterwards, clean it with dry

cloth and apply a thin layer ofpetroleum jelly.


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Moving contact surfaces:Silvered: Cleaned if necessary, with soft clothand solvent (tri-chloro ethane). No steelbrushing.

Non silvered: Cleaned as silvered surfaces, canbe steel brushed. After steel brushing they shall

be thoroughly cleaned from loose particles anddust.

Lubrication: Lubricant - Grease K is applied in a

very thin layer on the surfaces of the movingcontact and the puffer cylinder. The superfluousgrease is carefully removed.


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CONDITION BASED MONITORINGTECHNIQUESCIRCUIT BREAKERS

Operating timings measurement Contact resistance measurement Contact travel measurement Dew point measurement of SF6 gas/air

Tan delta measurement of grading capacitors Vibration measurement Operational lock-out checks Trip/close coil current measurement SF6 gas/hydraulic oil Air leakage monitoring SF6 gas leakage test

P i ibl li i f CB


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Permissible limits for CBsA ).Dew point of SF6

gas

Dew point values as per Annexure

II

B) Dew point ofoperating air

-45 Deg. C at ATM. Pressure

C) CB Operating

timings

400 kV 220 kV

a) Closing time(Max.) 150 MS 200 MS

b) Trip time (Max.) 25 MS 35 MS

c) Close/trip time,

Pole discrepancy

Phase to Phase

(Max.)

3.33 MS 3.33 MS

- Break to break

(Max.) of same

2.5 MS 2.5 MS

Dew point values


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Dew point values.BHEL -15 -36 At the time of

commissioning

-7 -29 During O&M

-5 -27 Critical

M&G -- -39 At the time of

commissioning

-32 During O&M

CGL -15 -35 At the time ofcommissioning

-10 -31 During O&M

ABB -15 -35 At the time of

commissioning-5 -26 During O&M

NGEF -15 -36 At the time of

commissioning

-7 -29 During O&M

-5 -27 Critical


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Note:Dew point of SF6 gas varies with

pressure at which measurement is carried out.So it is to be ensured that if measurement isdone at pressure other than atmospheric

pressure, it needs to be converted to theatmospheric pressure as given.

Ci it B k ti d


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Circuit Breakers continued

D) PIR time

BHEL make 12-16 MS ManufacturersRecommen

dations

CGL make 8-12 MS

ABB make 8-12 MS -do-

NGEF make 8-12 MS

M&G make 8-12 MS

TELK make 8-12 MS

ABB make (HVDC) 8-12 MS

B k td


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Breakers contdE) PIR opening time

prior to opening

of main contacts

(ABB, CGL,

NGEF make CBs)

5 MS (Min.) at rated

pressure

F) Pir and main

contacts overlap

time [BHEL,

M&G, ABB(imported) make

CBs]

5 MS (Min.) at rated

pressure

G) Tan delta of

grading

capacitors

0.007 at 20 Deg. C

H) Capacitance of

gradingcapacitors

Within + 10% / - 5%

of the rated value

IEC 358

I) Contact

resistance of CB

150 M. Ohm

J) Contact

resistance of CB

terminal

connector

10 M. Ohm per

connector

NGC, UK

recommendations


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Breakers Contd

K) IR value:

1. Phaseearth 1000 M Ohm (Min.) by

5.0 / 10.0 kV Megger

2. Across open

contacts

1000 M Ohm (Min.) by

5.0/10.0 kV Megger

3. Control cables 50 M Ohm (Min.) by 0.5

kV Megger

B k i d


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Breakers continued

L) Pressure switch

settings

- SF6 gaspressure

switches

Within + 0.1 Bar of setvalue

- Operating air

pr. Switches

Within + 0.1 Bar of set

value

- Operating oil

pr. Switches

Within + 1.0 Bar of set

value

M) BDV of oil used

for MoCB

- At the time offilling

40 kV at 2.5 mm Gap(Min.)

Mfgs.Recommendation

- During O&M 20 kV at 2.5 mm Gap.

(Min.)

Mfgs.

Recommendation

Preventive Maintenance schedule for Circuit


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Breakers

S.No. Tasks assigned Shut Down

(SD) OrWithout

Shut Down

(WSD)

Periodi

city

A. SF6 CIRCUIT BREAKERS

a. Checking of SF6 gas pressures

(wherever pr. Gauges provided)

WSD Monthly

b. Checking of oil leaks from Grading

Capacitors

SD Monthly

c. SF6 gas leakage test SD Yearly

d. Dew Point measurement of SF6 gas SD 2 Yearly@


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Preventive Maintenance schedule for Circuit Breakers

B. AIR BLAST CIRCUIT

BREAKERS

a. Checking breaker air pressure WSD Monthly

b. Air (Pressure) Leakage check WSD Monthly

c. Dew Point Measurement of

operating air at the outlet of Air

Drier

WSD Yearly


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C. MOCBs

a. Checking for oil leakage/oil

level

WSD monthl

y

b. Testing of oil for BDV WSD Yearly


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e. Functional checks, duty cycle

operation including rapid re-

closing (0-0 3s-CO)

SD Yearly

f. Checking of all operation lock-

outs

SD Yearly

g. Checking of all interlocks SD Yearly

h. Checking of pressure settings SD Yearly

i. Cleaning of Breaker Interrupter,Support insulators, PIRs and

Grading Capacitors

SD Yearly


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F. CONTROL CABINET

a. Checking of tightness of all cable

terminations in MB

SD Yearly

b. Checking of door sealing gasket

and replacement thereof, if

necessary

WSD Yearly

c. Repainting of metallic surfaces (ifrequired)

WSD Yearly

d. Checking of space heater WSD Yearly

@ At time of commissioning then after 6 months and one & halfyears of commissioning and thereafter once in every twoyears.

* For All HV/EHV Circuit Breakers only** For 400 kV BHEL, CGL make CBs only

+ First time after one year from commissioning and then once inevery three years.

M i t T h i f I t t


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Maintenance Techniques for Instrument

Transformer

Instrument transformers are generally the most reliableEHV network equipment. However, violentfailure/blasting due to primary insulation of instrument

transformers may lead to considerable damage tonearby equipments and O&M personals. In order toavoid violent failures following maintenance techniqueshave been adopted like measurement of tan delta and

capacitance, insulation measurements, DGAmonitoring, recovery voltage measurement etc.


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Tan Delta and Capacitance Measurement

(CT/CVT)

Testing mode for CTs: CTs provided with test stepshave to be tested in UST mode whereas CT with test

step are to be tested in GST mode. Before carryingout the test it may be ensured that jumpers aredisconnected and CT/CVT porcelene housing /insulators are thoroughly cleaned.


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Testing mode for CVTs:

HF panel and neutral terminal of EMU transformerare to be disconnected and isolated from groundbefore carrying out the test. The testing kit which is

similar as used for grading capacitors for CB is to beconnected between HV/HF points andmeasurements are done in UST mode. In the eventof test values deviating from the base values,

individual capacitor stacks are to be tested in USTmode.

Secondary Winding Resistance (CTs)


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Secondary Winding Resistance (CTs)Testing procedure

After ensuring, necessary precautions have been taken,connect leads of O meter between different terminals ofCT secondary course. Select the range of O meter as per

pre-commissioning / factory test results. Followingprecautions are considered essential:

Test links should be open in the CT MB prior tomeasurement of secondary resistance

It should be ensured that associated CTs are not incharged condition. For example main and tie CTs for

differential relays should not be in charged condition. Any earth provided in the secondary circuit of CT should

be removed prior to measurement.

Secondary voltage measurement for CVTs


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Secondary voltage measurement for CVTs

Failure of capacitor elements in C1 or C2 sideresults in change in output voltage. Regular andclose monitoring of secondary voltages using 0.2

or 0.5 accuracy class multi meters, secondaryvoltage change can be monitored. If voltage of aparticular phase CVT drifts by more than + 1volts, it requires thorough investigation.

P i ibl li it f CT


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Permissible limits for CTsA) IR value

1. Primary

earth 1000 M

Ohm (Min.) by5.0/10.0 kV Megger

2. Secondaryearth 50 MOhm (Min.) by 0.5 kV

Megger

3. Control cables 50 M-Ohm (Min.) by 0.5 kVMegger

B) Tan delta value 0.007*at 20 Deg. C

C) Terminal Connector 10 M-Ohm per connector NGC, UK

Recomme

ndations

D) CT ratio errors + 3% - Protection cores IS2705

+ 1% - Metering cores -do-


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Preventive maintenance schedule of CTs


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Preventive maintenance schedule of CT s

e. CT ratio test SD If needed

f. DGA and testing of other parameters

of oil

SD If needed

g. Thermo - vision Scanning of CT and

Top dome

WSD Yearly

h. Checking of Bellow Expansion WSD Monthly

i. Visual inspection CT for oil leakage

and crack in Insulator etc.

WSD Monthly

Preventive maintenance schedule of CTs


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MARSHALLING BOX

a. Checking of oil leakage WSD Monthly

b. Checking of healthiness of gaskets WSD Monthly

c. Checking of space heater &

Illumination

WSD Yearly

d. Checking the tightness of all

connections including earthing

SD Yearly

e. Cleaning of marshalling box and

junction box

* First time after one year from

commissioning and then once in every

three years.

SD Yearly


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Preventive Maintenance Schedule for CVTs


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Preventive Maintenance Schedule for CVT s

VISUAL CHECKING OF

EARTHING HF POINTa. Visual checking of earthing HF point

(in case it is not being used for

PLCC)

SD Yearly

b. Checking for any breakage or cracks SD Yearly

c. Checking of oil leaks WSD Monthly

d. Cleaning of CVT capacitor stacks

and tightness of terminalconnections

SD Yearly

e. Capacitance and Tandmeasurement

CVT

SD Once in 3

years



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f. Measurement of voltage atmetering points in control

Room

WSD Monthly

g. Testing of EMU tank oil for

BDV

SD Once in

6

years

h. Thermo - vision Scanning of

Capacitor stacks

WSD Yearly



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Preventive Maintenance Schedule for CVT s

MARSHALLING BOX

a. Checking of spacer heater &

Illumination

WSD Yearly

b. Checking and tightness of all

connections including earth

connections

SD Yearly

c. Cleaning of marshalling box

and junction box

SD Yearly

d. Checking of healthiness ofgaskets SD Yearly


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Table 14Comparison of Gas Limits


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Table 14. Comparison of Gas Limits

Gas

Dobble 95% Norm

PPM

IEEE Limits

PPM

Hydrogen 511 200

Methane 134 100

Ethane 26 30

Ethylene 17 30

Acetylene 0.6 1

CO 1,749 3,000CO2 15,485 30,000

Total

Combustibles2,024 3,360


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OLTC MAINTENANCESCHEDULE

I nsp. I nspection check Remarks.


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freq Item

Dail

y

Digital

counter onthe driving

mechanism

No. of tap

changingOpns.

Conducted.

Records the cumulative no. of Opns

carried out .

Tap changerconservator

Oil level. If low, top up new tested oil. If level

goes up without adding oil, report to

the manufacturer.

ExplosionVent.

Diaphragm

Plate.

Replace if cracked or broken.

Space heater

in the driving

mechanism

---- Heater to be switched on, if ambient

temp. goes below 20 deg C, and

switched off when exceeds 30 deg C


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yrly

or

every

5000

Opns.

Oil inthe

divertor

switch

BDVof

Oil.

Replace or filter if BDV is lessthan 24 KV,at gap 2.5mm between

spheres of 12.7mm(IS:335).

Increase inspection frequency, if

oil deteriorates faster.

yearly Gasket Joints. Oil Leak Tighten the bolts evenly or replace


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the gaskets.

yearly O rings in thebevel gear box

Oil leak Replace O rings if leak isobserved. Dip the O rings in

transformer oil before use.

Yearly Universal joints

and otherdriving Shaft

parts.

--- Apply Grease to prevent rusting.

Use servo Gem EP2, or anyequivalent.

Yearly Gas vent on theconservator

--- Clean if clogged with carbon orDust particles.

Yearly Gas and oiloperated relay

Correct

working

Rectify defects if any.


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Yearly Aux. Relay andcontactors.

Rusting of core, dirt on

contacts, chattering etc.,Clean or

replace.

Yearly Timer relays Time settings Adjust if the

values are

disturbed.

Yearly Control CableConnections.

For loose connections at

relay, rotary and push

button switches, Hand

operation and interlockswitch, Motor, Aux.

Transformer, TB terminals

Tighten the

connections.

yearly Lubricating

i

Low oil level. Add or Replace oil.

I N 68 (Bh H d l 68


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in

the gear box

of driving

mechanism.

Iso No.68,(Bharat Hydrol 68

BP, Enklo 68HP, Servo

System 68, I.O.C Perfecto 68

Castrol)

Yearly Electrical

DrivingMechanism

More than 2 Meg

ohms,measured

at 20 deg C with

500 volt meggar.

Low meggar value calls for

investigation and rectify.

Yearly Feed back

data

---- To be given to the

manufactureras per his proforma.


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50,000

operations or 5

years since

commissioning,

which ever is

earlier.

Divertor

Switch

Contact

compartment

Thickness

of Arcing

contacts.

Replace all the contacts if

thickness of any one of the

arcing tips is reduced to 2mm.

To be done in the presence of

authorized company rep.


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Every 10years Tap Selector Electric discharges on thesurface of insulators,condition of fasteners,

moving and stationery

contacts, smooth operation of

a gears and other moving

parts.

Report tomanufacturer if any

thing abnormal is

observed.

Battery and Battery Charger


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Following test may be carried out for determining thehealth of battery/battery charger.

Capacity test/discharge test of battery bank

Measurement of impendence of battery cell

Checking of electrolyte level and topping up with DMwater

Checking of emergency DC lighting to control room

Checking of electrical connection of charger panel fortightness and cleaning

Checking of electrical connection of battery for tightness

Checking of tightness of all electrical connection of DCdistribution board

Preventive Maintenance Schedule for Isolatorsand Earth Switches


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and Earth SwitchesS. No. Tasks assigned Shut Down (SD) Or

Without Shut

Down (WSD)

Periodicity

A. Operating Mechanism

a. Linkages including transmission gears SD Yearly

b. Stopper bolts SD Yearly

c. Cleaning of auxiliary switch contact &

greasing with silicon grease

SD Yearly

d. Lubrication of operating mechanism,hinges, lock joints on levers,

bearings

SD Yearly

e. Checking of all mounting bolts for

tightness

WSD Yearly

Preventive Maintenance Schedule for Isolators and Earth Switches


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B. MAIN CONTACTS

a. Cleaning and lubrication ofmain controls

SD Yearly

b. Alignment SD Yearly

c. Main contact resistancemeasurement

SD Once in2 yrs.

d. Tightness of bolds, Nuts and

pins etc.

SD Yearly

e. Cleaning of support insulators

and checking of insulator

cracks, if any

SD Yearly

Preventive Maintenance Schedule for Isolators and Earth Switches


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C. EARTH SWITCH

a. Checking and Alignment ofearthing blades

SD Yearly

b. Cleaning of contacts SD Yearly

c. Contact resistance SD Yearly

d. Operation of earthing switch SD Yearly

e. Checking of alumunium Copper

flexible conductor

SD Yearly

f. Checking of earth connections of

structure and MOM box

SD Yearly


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PREVENTIVE MAINTENANCESCHEDULE


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FOR WAVE TRAPS

S.No.

Tasks assigned Shut Down(SD) Or

Without Shut

Down (WSD)

Periodicity

a. Tightness & Cleanliness SD Yearly

b. General inspection / cleaning of

tuning unit

SD Yearly

A PROCEDURE FOR FILLING OF


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EQUIPMENT FAILURE REPORT (EFR)

Whenever there is a failure of any equipment or part of anyequipment during operation and maintenance which may

result in the outage of the said equipment the EFR is

required to be filled up.

Each failure report has to be given a specific report numberfollowed by the name of the sub-station / serial number of

the failed equipment and date of failure.

Time of occurrence of equipment failure or noticing of

failed equipment also to be written. Mention to be made as to when the fault was discovered i.e.

during testing, commissioning, operation and

maintenance.

Name of the main equipment which has failed may be


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given along with the name of the manufacturer / supplier /

sub-vendor.

Specify the type of faulty unit/equipment as given by themanufacturer for example in breakers it could be SF6

3AT3/3AT2; SF6 HPL, ABCB DLF 245 NC2 etc.

Specify the item designation i.e. bay name in which faulty

equipment was erected / located, including the Sr. No. /Badge Number as given on the name plate.

Specify the faulty component in the unit and the part

number as per the O&M manual of the manufacturer

Specify the type of failure i.e. burnt / flashover / mal-operation / mechanical fault / open circuit / short circuit /

operating error / setting etc.

Specify short / brief description of occurrence off l d h f


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fault and cause thereof

Specify the remedial action taken.

Specify the reference of the document from which

part number / fault diagnosis has been done, so

that it may help in analysis of fault.

Equipment failure may occur during tripping /due to suspected fault / mal-functioning of some

other equipment. Report number therefore to be

specified.

The above documents should be signed by themaintenance engineer and counter signed by the

substation in -charge.

Th k


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Thank you,

Wish you all a successfulprofessional career

Documents

Operation and Maintenance of Sub - Stations Revised 030909