Substation Maintenance

KARIKALAN. MKARIKALAN. M
www.elecsolution.comwww.elecsolution.com

Voltages at all levels shall be observed and to be maintained nearest to the ratedVoltages at all levels shall be observed and to be maintained nearest to the rated
values.values.values.
Trip circuit supervision of all breakers shall be checked every 2 hour.Trip circuit supervision of all breakers shall be checked every 2 hour.Trip circuit supervision of all breakers shall be checked every 2 hour.
Battery voltages, DC leakage, Charger condition, switch off AC supply to chargerBattery voltages, DC leakage, Charger condition, switch off AC supply to charger
(once in a shift) and observe any fall in DC battery voltage.(once in a shift) and observe any fall in DC battery voltage.(once in a shift) and observe any fall in DC battery voltage.
Communication equipment such as PLCC, P&T and wireless shall always be inCommunication equipment such as PLCC, P&T and wireless shall always be inCommunication equipment such as PLCC, P&T and wireless shall always be in
working condition.working condition.
Check the loading on the transformers and capacitor banks. Load current in all theCheck the loading on the transformers and capacitor banks. Load current in all theCheck the loading on the transformers and capacitor banks. Load current in all the
three phases and in neutral circuit (wherever available) to be checked.three phases and in neutral circuit (wherever available) to be checked.
Note the oil and winding temperature and physically check-up by feeling theNote the oil and winding temperature and physically check-up by feeling the
temperature of transformers by hand.temperature of transformers by hand.
Note the tap position of various transformers.Note the tap position of various transformers.
Check up for any oil leaks and red hot spots.Check up for any oil leaks and red hot spots.
Ensure that alarms and indications on annunciation panel are workingEnsure that alarms and indications on annunciation panel are workingEnsure that alarms and indications on annunciation panel are working
10Operation and Maintenance

Check the diesel generator and trial run for 5 minutes daily once in the morning shiftCheck the diesel generator and trial run for 5 minutes daily once in the morning shift
and note down the voltage.and note down the voltage.
Check the entire yard for any unusual sounds, sparks and red hots during eveningCheck the entire yard for any unusual sounds, sparks and red hots during evening
shift.shift.
Check up gas pressures in SF6 breakers.Check up gas pressures in SF6 breakers.
Watering of earth pits to be done daily.Watering of earth pits to be done daily.
Ensure that lightning arrestor's leakage current (micro) ammeter reading is in safeEnsure that lightning arrestor's leakage current (micro) ammeter reading is in safe
zone (Green).zone (Green).
Check up the batteries, exhaust fans in the battery room.Check up the batteries, exhaust fans in the battery room.
Whenever feeders trip, find out the position of breakers at other end and note downWhenever feeders trip, find out the position of breakers at other end and note down
relay indications if any at other end.relay indications if any at other end.

i. Inspect insulators for crack, burn mark and chippingi. Inspect insulators for crack, burn mark and chippingi. Inspect insulators for crack, burn mark and chipping
ii. Check motor, compressor (for pneumatic breakers), pump (hydraulic breakers) forii. Check motor, compressor (for pneumatic breakers), pump (hydraulic breakers) for
unusual noiseunusual noiseunusual noise
iii. Inspect for oil leak/air leak of the operating mechanismiii. Inspect for oil leak/air leak of the operating mechanismiii. Inspect for oil leak/air leak of the operating mechanism
iv. Inspect control circuit and operating mechanism cubicles for the following:-iv. Inspect control circuit and operating mechanism cubicles for the following:-
- heaters operation- heaters operation
- clean vents- clean vents
- seals and latch- seals and latch

Monitoring of operating timings is basically done with a aim of finding any problem inMonitoring of operating timings is basically done with a aim of finding any problem in
operating mechanism, alignment of main/arcing contacts.operating mechanism, alignment of main/arcing contacts.
Precautions:Precautions:
Ensure Proper shutdown is arranged.Ensure Proper shutdown is arranged.
Ensure that there are no joints in testing cable and the testing leads are not touchingEnsure that there are no joints in testing cable and the testing leads are not touching
any live point.any live point.
Do not connect the test set the energized equipment.Do not connect the test set the energized equipment.
Ground cable must be connected first and removed at last.Ground cable must be connected first and removed at last.
Test equipment body should be earthed.Test equipment body should be earthed.
Clean the surface / terminal where the connection for testing is to be made.Clean the surface / terminal where the connection for testing is to be made.
Clean earth point with sand paper / wire brush where earth terminal is to beClean earth point with sand paper / wire brush where earth terminal is to be
provided.provided.provided.

Note the down the timings of various operations of CB viz. CO, OC, OCO byNote the down the timings of various operations of CB viz. CO, OC, OCO by
giving appropriate command.giving appropriate command.giving appropriate command.

The permissible pole discrepancy as per IEC 56The permissible pole discrepancy as per IEC 56The permissible pole discrepancy as per IEC 56
between 2 poles ---- should not be beyond 1/6 of cycle (3.33 ms)between 2 poles ---- should not be beyond 1/6 of cycle (3.33 ms)
Between 2 breaks ---- should not exceed 1/8th of a cycle (2.5ms).Between 2 breaks ---- should not exceed 1/8th of a cycle (2.5ms).
if these are not within the limits the same is to be corrected by:if these are not within the limits the same is to be corrected by:
i. Equalizing the SF6 pressure in different polesi. Equalizing the SF6 pressure in different poles
ii. Make necessary adjustment plunger of trip of close coilii. Make necessary adjustment plunger of trip of close coil
iii. Adjustment in operating mechanismiii. Adjustment in operating mechanism
iv. Changing trip / close coil if requirediv. Changing trip / close coil if required
It is also necessary to measure the timings of auxiliary contacts from the point of viewIt is also necessary to measure the timings of auxiliary contacts from the point of view
of variations with respect to main contactof variations with respect to main contact

Purpose of measuring contact resistance measurement is to assess the condition ofPurpose of measuring contact resistance measurement is to assess the condition of
the main contacts against erosion or misalignment of the main contacts.
.the main contacts against erosion or misalignment of the main contacts.
.the main contacts against erosion or misalignment of the main contacts.
Test arrangementTest arrangementTest arrangement
Kelvin's 4 terminal methodKelvin's 4 terminal method
Evaluation of Test ResultEvaluation of Test Result
The value of the contact resistance for a new circuit breaker should be aroundThe value of the contact resistance for a new circuit breaker should be around
50 micro-ohms per break.50 micro-ohms per break.
If the value of the contact resistance exceeds the permissible limits, this could lead toIf the value of the contact resistance exceeds the permissible limits, this could lead to
over heating of contacts. Monitoring contact resistance values is very goodover heating of contacts. Monitoring contact resistance values is very good
techniques for assessing the condition of main contactstechniques for assessing the condition of main contacts

Dynamic Contact Resistance Measurement is a signature of change in contactDynamic Contact Resistance Measurement is a signature of change in contact
resistance of CB during operation.resistance of CB during operation.resistance of CB during operation.
A DC current is injected through the CBA DC current is injected through the CB
and the current and voltage drop areand the current and voltage drop are
measured and the resistance is calculated.measured and the resistance is calculated.measured and the resistance is calculated.
The graphs of resistance vs. timeThe graphs of resistance vs. time
data provide useful informationdata provide useful information
on the condition of the main and alsoon the condition of the main and also
Arcing contact of CB.Arcing contact of CB.
It plots the variation in contact resistance while first, the arcing,It plots the variation in contact resistance while first, the arcing,
and then the main contacts engage and disengage during C-O operation.and then the main contacts engage and disengage during C-O operation.

Transducers and fixtures are attached to operating rod or interrupting chamber forTransducers and fixtures are attached to operating rod or interrupting chamber for
measuring contact travel. When CB closes contact travel is recorded. Contact bouncingmeasuring contact travel. When CB closes contact travel is recorded. Contact bouncing
and any other abnormality is also pointed out by contact travel measurement. If contactand any other abnormality is also pointed out by contact travel measurement. If contact
travel is recorded with DCRM the length of the arcing contact shall also be monitoredtravel is recorded with DCRM the length of the arcing contact shall also be monitored
Why DCRM…Why DCRM…
i. Reflects useful information on Contact conditioni. Reflects useful information on Contact condition
ii. Gives prior indication of deterioration Operating mechanism linkagesii. Gives prior indication of deterioration Operating mechanism linkages
iii. Certain mechanical weaknesses, undetected by travel measurement, are reflectediii. Certain mechanical weaknesses, undetected by travel measurement, are reflected
in DCRM measurement.in DCRM measurement.
Main contacts: 40 to 80 micro-ohmsMain contacts: 40 to 80 micro-ohms
Arcing contacts: 125 to 600 micro-ohmsArcing contacts: 125 to 600 micro-ohms

Purpose: is to be detected any incipient weakness in the HV insulation.Purpose: is to be detected any incipient weakness in the HV insulation.Purpose: is to be detected any incipient weakness in the HV insulation.
Test Setup:Test Setup:Test Setup:
Connect LV cable to the middle of the double interrupterConnect LV cable to the middle of the double interrupter
ii. Connect HV cable to the other end of grading capacitor to be testedii. Connect HV cable to the other end of grading capacitor to be tested
iii. Ground the opposite end of the grading capacitor using earth switchiii. Ground the opposite end of the grading capacitor using earth switch
iv. Measurement to be done in UST modeiv. Measurement to be done in UST mode
v. Follow the procedure provided by the equipment supplier.v. Follow the procedure provided by the equipment supplier.v. Follow the procedure provided by the equipment supplier.
vi. Measurement to be made at 2 kV first and then at 10 kV.vi. Measurement to be made at 2 kV first and then at 10 kV.
Operation and Maintenance 26

In a perfect capacitor, the voltage and current are phase shifted 90 degrees and theIn a perfect capacitor, the voltage and current are phase shifted 90 degrees and the
current through the insulation is capacitive. If there are impurities in the insulation,current through the insulation is capacitive. If there are impurities in the insulation,current through the insulation is capacitive. If there are impurities in the insulation,
the resistance of the insulation decreases, resulting in an increase in resistive currentthe resistance of the insulation decreases, resulting in an increase in resistive current
through the insulation. It is no longer a perfect capacitor. The current and voltage willthrough the insulation. It is no longer a perfect capacitor. The current and voltage will
no longer be shifted 90 degrees. It will be something less than 90 degrees. The extentno longer be shifted 90 degrees. It will be something less than 90 degrees. The extent
to which the phase shift is less than 90 degrees is indicative of the level of insulationto which the phase shift is less than 90 degrees is indicative of the level of insulation
contamination, hence quality/reliability. This “Loss Angle” is measured and analyzed.contamination, hence quality/reliability. This “Loss Angle” is measured and analyzed.

An increase in the value of tan delta indicates the deterioration of cellulose insulationAn increase in the value of tan delta indicates the deterioration of cellulose insulation
whereas increase in both tan delta and capacitance reveals entry of moisture in thewhereas increase in both tan delta and capacitance reveals entry of moisture in the
insulation.insulation.
Tan delta <= 0.7% (0.007)Tan delta <= 0.7% (0.007)
Tan delta measurement indicates the condition of insulator..Tan delta measurement indicates the condition of insulator..
1.Chemical deterioration due to time and temperature, including certain cases of1.Chemical deterioration due to time and temperature, including certain cases of
acute deterioration caused by localized overheating;acute deterioration caused by localized overheating;
2. Contamination by water, carbon deposits, bad oil, dirt and other chemicals;2. Contamination by water, carbon deposits, bad oil, dirt and other chemicals;
3. Severe leakage through cracks and over surfaces;3. Severe leakage through cracks and over surfaces;3. Severe leakage through cracks and over surfaces;
4. Ionization.4. Ionization.4. Ionization.

Dew Point is the temperature at which moisture content in SF6 gas/airDew Point is the temperature at which moisture content in SF6 gas/air
starts condensing. Measurement of dew point of SF gas in a circuit breaker revealsstarts condensing. Measurement of dew point of SF6 gas in a circuit breaker revealsstarts condensing. Measurement of dew point of SF6 gas in a circuit breaker reveals
the change in the value of dielectric properties of SF6 gas.the change in the value of dielectric properties of SF6 gas.
When Moisture density is highWhen Moisture density is high
SF + 3H O ................H SO + 4 HFSF4 + 3H2O ................H2SO3 + 4 HFSF + 3H O ................H SO + 4 HF
Hydrogen fluorides and H SO formed during these reactions attack the materialsHydrogen fluorides and H2SO3 formed during these reactions attack the materialsHydrogen fluorides and H2SO3 formed during these reactions attack the materials
containing silicon-dioxide (SIO2) viz. glass / porcelain.containing silicon-dioxide (SIO2) viz. glass / porcelain.
Test Setup:Test Setup:Test Setup:

• Make the connections to the kit from CB pole ensuring that regulating valve is fully• Make the connections to the kit from CB pole ensuring that regulating valve is fully
closed at the time of connections of the Dew point kit.closed at the time of connections of the Dew point kit.closed at the time of connections of the Dew point kit.
• By regulating the flow rate of SF6 gas (0.2 liter/min to 0.5 liter/min -ref. IEC 480),• By regulating the flow rate of SF6 gas (0.2 liter/min to 0.5 liter/min -ref. IEC 480),• By regulating the flow rate of SF6 gas (0.2 liter/min to 0.5 liter/min -ref. IEC 480),
the value of dew point is observed till it becomes stable.the value of dew point is observed till it becomes stable.
If the regulating valve is provided at outlet of the dew point kit, then dew point for• If the regulating valve is provided at outlet of the dew point kit, then dew point for• If the regulating valve is provided at outlet of the dew point kit, then dew point for
rated pressure is to be monitored.rated pressure is to be monitored.
Evolution of test resultsEvolution of test results
There are two sources of moisture ingress in SF6 gas after it is filled in CB. ExudationThere are two sources of moisture ingress in SF6 gas after it is filled in CB. ExudationThere are two sources of moisture ingress in SF6 gas after it is filled in CB. Exudation
of moisture contained during manufacturing from insulation materials used in Circuitof moisture contained during manufacturing from insulation materials used in Circuit
Breakers and permeation of moisture through sealed sections, i.e., gaskets, O-Rings,Breakers and permeation of moisture through sealed sections, i.e., gaskets, O-Rings,
etc.etc.

The measurement of insulation resistance is carried out to check theThe measurement of insulation resistance is carried out to check theThe measurement of insulation resistance is carried out to check the
healthiness of the transformer insulation.healthiness of the transformer insulation.
The measurement of insulation resistance is done by means of megger of 2.5 kV forThe measurement of insulation resistance is done by means of megger of 2.5 kV for
transformer windings with voltage rating of 11 kV and above and 5 kV for EHVtransformer windings with voltage rating of 11 kV and above and 5 kV for EHV
transformers.transformers.
Safety Precautions :Safety Precautions :
 It has also to ensured that high voltage and low voltage windings are isolated along It has also to ensured that high voltage and low voltage windings are isolated along
with the concerned isolators.with the concerned isolators.
 In case transformer is having a tertiary windings, ensure the isolation are the same In case transformer is having a tertiary windings, ensure the isolation are the same
prior to commencement of the test.prior to commencement of the test.
 Also the jumpers and lighting arrestors connected to the transformer have to be Also the jumpers and lighting arrestors connected to the transformer have to be
disconnected prior to start of testing after issue of PTW.disconnected prior to start of testing after issue of PTW.
Bushing porcelain may be cleaned by wiping with a piece of the dry cloth.Bushing porcelain may be cleaned by wiping with a piece of the dry cloth.
As the windings possess a substantial capacitance, the current carrying cords shouldAs the windings possess a substantial capacitance, the current carrying cords should
only be touched after the electric charge have been removed from them.only be touched after the electric charge have been removed from them.

Test Procedure:Test Procedure:
IR measurements shall be taken between the windings collectively (i.e. with all theIR measurements shall be taken between the windings collectively (i.e. with all the
windings being connected together) and the earthed tank (earth) and between eachwindings being connected together) and the earthed tank (earth) and between each
winding and the tank, the rest of the windings being earthed. Following measurementswinding and the tank, the rest of the windings being earthed. Following measurements
are relevant for Auto-transformer, three winding transformer and reactor.are relevant for Auto-transformer, three winding transformer and reactor.

HV lead of the test kit to be connected to the shorted bushing top and LV lead to beHV lead of the test kit to be connected to the shorted bushing top and LV lead to be
connected to the test tap of the bushing under test: Test is to be carried out inconnected to the test tap of the bushing under test: Test is to be carried out inconnected to the test tap of the bushing under test: Test is to be carried out in
ungrounded specimen test mode (UST) at the rated test voltage of the kit.ungrounded specimen test mode (UST) at the rated test voltage of the kit.
Winding Tan delta:Winding Tan delta:
Dissipation factor/ Loss factor and capacitance measurement of winding is carried outDissipation factor/ Loss factor and capacitance measurement of winding is carried outDissipation factor/ Loss factor and capacitance measurement of winding is carried out
to ascertain the general healthiness of the ground and inter winding insulation ofto ascertain the general healthiness of the ground and inter winding insulation of
transformer and reactors.transformer and reactors.
Test Combinations:Test Combinations:

The purpose of this test is to check for any abnormalities due to loseThe purpose of this test is to check for any abnormalities due to lose
connection, broken strands and high contact resistance in tap changers.connection, broken strands and high contact resistance in tap changers.
Test Setup:Test Setup:

Resistance shall be measured between the line and the neutral terminal and average ofResistance shall be measured between the line and the neutral terminal and average of
3 sets of reading shall be taken as tested value for star connected winding with3 sets of reading shall be taken as tested value for star connected winding with
neutral brought out.neutral brought out.
For transformers provided with delta connected windings such as tertiary windings ofFor transformers provided with delta connected windings such as tertiary windings of
auto transformers, measurement shall be made between pairs of line terminals andauto transformers, measurement shall be made between pairs of line terminals andauto transformers, measurement shall be made between pairs of line terminals and
resistance per windings shall be calculated per formula given below:resistance per windings shall be calculated per formula given below:
Resistance per winding = 1.5 x Measured valueResistance per winding = 1.5 x Measured valueResistance per winding = 1.5 x Measured value
Resistance at 75 degree C may be calculated as per the following formula.Resistance at 75 degree C may be calculated as per the following formula.Resistance at 75 degree C may be calculated as per the following formula.
R75 = Rt (235+75) / (235+t).R75 = Rt (235+75) / (235+t).
Note : Ensure that direct current circulating has settled down before the measurementNote : Ensure that direct current circulating has settled down before the measurement
is done.is done.is done.

Purpose : This has been considered as one of the important tools by all the powerPurpose : This has been considered as one of the important tools by all the power
utilities for detecting any incipient fault in the transformers and the reactors.utilities for detecting any incipient fault in the transformers and the reactors.
These gases come out and get collected in the Buchholz relay when the quantity isThese gases come out and get collected in the Buchholz relay when the quantity is
more. However, these gases dissolved in the oil if the quantity is less.more. However, these gases dissolved in the oil if the quantity is less.
The gases which are of interest are hydrogen, methane, ethane, ethylene, acetylene,The gases which are of interest are hydrogen, methane, ethane, ethylene, acetylene,
carbon mono-oxide, carbon di-oxide, nitrogen and oxygen.carbon mono-oxide, carbon di-oxide, nitrogen and oxygen.
Evaluation of Gases: Relationship with temperature of different fault gasses is givenEvaluation of Gases: Relationship with temperature of different fault gasses is given
belowbelow
Methane CH4 > 120° C Ethane (C2H6) > 120 ° CMethane CH4 > 120° C Ethane (C2H6) > 120 ° C
Ethylene (C2H4) > 150°C Acetylene (C2H2) > 700 ° CEthylene (C2H4) > 150°C Acetylene (C2H2) > 700 ° C

Regular oil sampling at intervals of 1 year is recommended.Regular oil sampling at intervals of 1 year is recommended.
"Top" or "middle“ oil sampling valve: Sampling for gas analysis"Top" or "middle“ oil sampling valve: Sampling for gas analysis
"Bottom" oil sampling valve: Sampling for other analyses"Bottom" oil sampling valve: Sampling for other analyses
Oil analyses must be performed for samples taken from the followingOil analyses must be performed for samples taken from the following
reservoirs:reservoirs:
Transformer tankTransformer tank
ConservatorConservator
Tap selector compartment -OLTCTap selector compartment -OLTCTap selector compartment -OLTC

To measure the vibrations of core /coil assembly in the tank of the reactor. MovementTo measure the vibrations of core /coil assembly in the tank of the reactor. Movement
of the core-coil assembly and shielding structure caused by the time–varying magneticof the core-coil assembly and shielding structure caused by the time–varying magnetic
forces results in vibration of the tank and ancillary equipment.forces results in vibration of the tank and ancillary equipment.
Evaluation:Evaluation:
The average amplitude of local maximum points shall not exceed 60µm (2.36 miles)The average amplitude of local maximum points shall not exceed 60µm (2.36 miles)
Peak-peak. Within any individual reading shall not exceed 200µm (7.87 miles).Peak-peak. Within any individual reading shall not exceed 200µm (7.87 miles).

 Check the up and down and operation of tab changer for the full range before Check the up and down and operation of tab changer for the full range before Check the up and down and operation of tab changer for the full range before
attempting electrical operation.attempting electrical operation.
Ensure the handle that handles interlock shall not allow electrical operation when Ensure the handle that handles interlock shall not allow electrical operation when Ensure the handle that handles interlock shall not allow electrical operation when
the handle is inserted.the handle is inserted.
 Check for any discontinuity during tab changing operation by connecting an Check for any discontinuity during tab changing operation by connecting an
analogue multimeter at cross HV and LV bushing and change the tab position fromanalogue multimeter at cross HV and LV bushing and change the tab position from
maximum to minimum.maximum to minimum.
 In the event of single phase tab changer check their tab position agree and are In the event of single phase tab changer check their tab position agree and are
reach simultaneously at motor drive unit headreach simultaneously at motor drive unit head
 Check for accurate indication of mechanical position indicator in all positions. Check for accurate indication of mechanical position indicator in all positions.
Generally the temperature of OLTC compartments is a few degrees Celsius less thanGenerally the temperature of OLTC compartments is a few degrees Celsius less than
the main tank. In case the temperature is found to be higher than this indicates a signthe main tank. In case the temperature is found to be higher than this indicates a sign
of internal problem and the OLTC compartment need to be opened.of internal problem and the OLTC compartment need to be opened.

Min BDV should be 50 kV and moisture content should be less than 20 PPM.Min BDV should be 50 kV and moisture content should be less than 20 PPM.

Cooling System-Fans-ControlsCooling System-Fans-Controls
Checking for correct rotation of fans and pumps to be ensured as reverse rotationChecking for correct rotation of fans and pumps to be ensured as reverse rotation
may not provide desired result.may not provide desired result.
 Oil pumps need to be checked by observing their flow gauges. Oil pumps need to be checked by observing their flow gauges.
 Measurement of pump current reveals any abnormality. Measurement of pump current reveals any abnormality.
 Any significant imbalance of current between the terminals greater than 15-20% is Any significant imbalance of current between the terminals greater than 15-20% is
indicative of the problem with the pump motor.indicative of the problem with the pump motor.
Checking of Auto cooler ON function. (Temperature depended.)Checking of Auto cooler ON function. (Temperature depended.)
BUCHOLZ Relays:BUCHOLZ Relays:
For testing of the contact functions, buchholz relays are provided with a test knob onFor testing of the contact functions, buchholz relays are provided with a test knob on
the cover. Unscrew the protective cap and press down the knob by hand. The springthe cover. Unscrew the protective cap and press down the knob by hand. The spring
loaded knob with a pin inside the relay actuates first the alarm device and then theloaded knob with a pin inside the relay actuates first the alarm device and then the
tripping device. After testing, screw on the protective cap again.tripping device. After testing, screw on the protective cap again.

Failure of Paper InsulationFailure of Paper Insulation
Oil leakageOil leakage

 All terminals of unused CT secondary terminals are to be properly shorted to avoid All terminals of unused CT secondary terminals are to be properly shorted to avoid All terminals of unused CT secondary terminals are to be properly shorted to avoid
development of abnormal voltage and subsequent failure of CTs incase they left open.development of abnormal voltage and subsequent failure of CTs incase they left open.
The Tan delta tap is to properly earthed to avoid damage of insulation. The Tan delta tap is to properly earthed to avoid damage of insulation. The Tan delta tap is to properly earthed to avoid damage of insulation.
 All corona shields are to be provided and any damaged corona shield to be replaced All corona shields are to be provided and any damaged corona shield to be replaced All corona shields are to be provided and any damaged corona shield to be replaced
with new one.with new one.
As CT primary carries heavy current, any loose joint may lead to arcing and welding As CT primary carries heavy current, any loose joint may lead to arcing and welding As CT primary carries heavy current, any loose joint may lead to arcing and welding
of terminal connectors.of terminal connectors.
 In coastal and industrial areas where pollution levels are high, due to saline In coastal and industrial areas where pollution levels are high, due to saline
atmosphere/ chemical contamination, porcelain insulators of electrical equipment shallatmosphere/ chemical contamination, porcelain insulators of electrical equipment shall
have higher creepages.have higher creepages.
 Marshalling boxes, CT terminal boxes are to be properly sealed to prevent any dust, Marshalling boxes, CT terminal boxes are to be properly sealed to prevent any dust,
rain water and insects. Door gaskets are to be changed periodically to give properrain water and insects. Door gaskets are to be changed periodically to give proper
sealingsealing

Measurement of Secondary Winding Resistance for Current TransformersMeasurement of Secondary Winding Resistance for Current TransformersMeasurement of Secondary Winding Resistance for Current Transformers
•Secondary winding resistance of CTs is measured with a digital or analogue Ohm•Secondary winding resistance of CTs is measured with a digital or analogue OhmSecondary winding resistance of CTs is measured with a digital or analogue Ohm
meter with leads.meter with leads.
•It is to be ensured that associated CTs are not in charged condition. For example, main•It is to be ensured that associated CTs are not in charged condition. For example, main•It is to be ensured that associated CTs are not in charged condition. For example, main
and tie CTs for differential relays should not be in charged condition.and tie CTs for differential relays should not be in charged condition.
•Earth provided if any in the secondary circuit of CT, should be removed prior to•Earth provided if any in the secondary circuit of CT, should be removed prior to
measurement.measurement.
Evaluation :Evaluation :
Extreme low value of resistance indicates turn to turn shorting and a high valueExtreme low value of resistance indicates turn to turn shorting and a high value
indicates loose connection which is to be identified and tightened before repeatingindicates loose connection which is to be identified and tightened before repeating
the measurement.the measurement.

If you get higher TAN delta and high oil leakages then dienergise the CT ,take oilIf you get higher TAN delta and high oil leakages then dienergise the CT ,take oil
sample and sent for DGA test.sample and sent for DGA test.
Oil samples to be collected in 300ml bottles and to be sent to test lab for testing. TestOil samples to be collected in 300ml bottles and to be sent to test lab for testing. Test
results should be comparable to factory values.results should be comparable to factory values.results should be comparable to factory values.
Deterioration of oil quality and oil DGA indicates violation it shall be taken out fromDeterioration of oil quality and oil DGA indicates violation it shall be taken out from
service and overhauled/ minor damages if any are attended, before the CT fails.service and overhauled/ minor damages if any are attended, before the CT fails.service and overhauled/ minor damages if any are attended, before the CT fails.

Low Pressure indication in the pressure gauge.Low Pressure indication in the pressure gauge.
When there is low pressure indication in the pressure gauge (pointer is in the range ofWhen there is low pressure indication in the pressure gauge (pointer is in the range of
alarm pressure) then there is either a fault in the pressure gauge itself, which requiresalarm pressure) then there is either a fault in the pressure gauge itself, which requires
replacement or there is a leakage in the CT. Refill the gas in the CT.replacement or there is a leakage in the CT. Refill the gas in the CT.
Incase the pressure drops again, put the CT out of service.Incase the pressure drops again, put the CT out of service.
Reading high pressureReading high pressure
Check the gas pressure in the CT. The exact dependency between filling pressure andCheck the gas pressure in the CT. The exact dependency between filling pressure and
temperature of the CT depend on SF6 gas curves. When there is high pressuretemperature of the CT depend on SF6 gas curves. When there is high pressure
indication in the pressure gauge there is most probably a fault in the densitometerindication in the pressure gauge there is most probably a fault in the densitometer
itself which requires a replacement.itself which requires a replacement.
SF6 Gas leakageSF6 Gas leakage
If there is any indication of leakage (e.g. pressure gauge shows low pressure) the leakIf there is any indication of leakage (e.g. pressure gauge shows low pressure) the leak
can be found by means of a Halogen detector. Critical areas are all those wherecan be found by means of a Halogen detector. Critical areas are all those where
gaskets are inserted.gaskets are inserted.gaskets are inserted.

The following points can be possible sources of SF6 -gas leakage:The following points can be possible sources of SF6 -gas leakage:The following points can be possible sources of SF6 -gas leakage:
1. rupture disc1. rupture disc1. rupture disc
2. flange-connection between the housings2. flange-connection between the housings
3. primary conductor outlet3. primary conductor outlet
4. top flange of the insulator4. top flange of the insulator
5. bottom flange of the insulator5. bottom flange of the insulator
6. secondary bushing6. secondary bushing
7. pocket of the densitimeter sensor7. pocket of the densitimeter sensor
8. SF6 gas - valves8. SF6 gas - valves

These surface properties of silicone rubber eliminate the need of cleaning on the longThese surface properties of silicone rubber eliminate the need of cleaning on the long
run. A simple visual control can be of the surface after raining. If any water pearls canrun. A simple visual control can be of the surface after raining. If any water pearls canrun. A simple visual control can be of the surface after raining. If any water pearls can
be seen, the hydrophobicity is working; and cleaning is not necessary.be seen, the hydrophobicity is working; and cleaning is not necessary.
Depending on the degree of pollution, silicone insulators can be cleaned by means ofDepending on the degree of pollution, silicone insulators can be cleaned by means ofDepending on the degree of pollution, silicone insulators can be cleaned by means of
thethe
following material:following material:
a) Soapy watera) Soapy watera) Soapy water
b) Steam jet with car shampoo (1%)b) Steam jet with car shampoo (1%)b) Steam jet with car shampoo (1%)
A change of colour of the silicone,A change of colour of the silicone,
has no influence on the hydrophobic properties.has no influence on the hydrophobic properties.

i. Inspect oil leveli. Inspect oil level
ii. Check for oil leakageii. Check for oil leakage
iii. Check for insulator chipping and its cleanlinessiii. Check for insulator chipping and its cleanliness
If oil leak is observed in anyone stack, the entire CVT is to be replaced.If oil leak is observed in anyone stack, the entire CVT is to be replaced.
CVTs are tuned units and replacement of anyone stack is not recommended toCVTs are tuned units and replacement of anyone stack is not recommended to
avoid phase angle errors.avoid phase angle errors.

• The colour of oil indicated through the gauge glass gives some indication of the• The colour of oil indicated through the gauge glass gives some indication of the
healthiness of the internal components.healthiness of the internal components.healthiness of the internal components.
• Any abnormal heating may also be observed through Thermo vision scanning.• Any abnormal heating may also be observed through Thermo vision scanning.• Any abnormal heating may also be observed through Thermo vision scanning.
• Maintenance of Marshalling box gaskets, tightening of secondary terminal• Maintenance of Marshalling box gaskets, tightening of secondary terminal
connections and tightening of primary terminal connections, etc., are also to beconnections and tightening of primary terminal connections, etc., are also to beconnections and tightening of primary terminal connections, etc., are also to be
ensured for healthy operation.ensured for healthy operation.
CAPACITANCE & TAN DELTA MEASUREMENTCAPACITANCE & TAN DELTA MEASUREMENT

Item - Oil Level Indicator on EMUItem - Oil Level Indicator on EMU
Earlier - Oil Presence IndicatorEarlier - Oil Presence Indicator
Now - Oil Level IndicatorNow - Oil Level Indicator
Benefits - Visual Monitoring of LevelBenefits - Visual Monitoring of Level

. Inspect insulators for cracks, or burns or pollutants deposits. Inspect insulators for cracks, or burns or pollutants deposits
ii. Check motor drive cabinet for the following:ii. Check motor drive cabinet for the following:
- Heater operation- Heater operation
- Miniature circuit breaker (MCB)- Miniature circuit breaker (MCB)
iii. Clean ventilation openingsiii. Clean ventilation openings
iv. Check motor drive cabinet is properly latched and seals are in goodiv. Check motor drive cabinet is properly latched and seals are in goodiv. Check motor drive cabinet is properly latched and seals are in good
conditionconditioncondition
v. Check for visible misalignment/over travel/discoloration of primaryv. Check for visible misalignment/over travel/discoloration of primary
contactscontacts
vi. Check for leakage of grease at insulator base and motor gearvi. Check for leakage of grease at insulator base and motor gear
vii. Check earth tape connections from the disconnectors to the substationvii. Check earth tape connections from the disconnectors to the substation
earthing systemearthing system

Primary contact routine inspectionPrimary contact routine inspection
Where possibleWhere possible
i. Check tightness of bolts and nutsi. Check tightness of bolts and nuts
ii. Check springs of female contact for rust and its elasticityii. Check springs of female contact for rust and its elasticity
iii. Check contact fingers for pitting marks, erosion, corrosioniii. Check contact fingers for pitting marks, erosion, corrosion
iv. Check for alignment of primary contacts and arcing tipsiv. Check for alignment of primary contacts and arcing tips
v. Check arcing tips for excessive arc damagev. Check arcing tips for excessive arc damagev. Check arcing tips for excessive arc damage
vi. Check for simultaneous closing of all blades for 3 phasesvi. Check for simultaneous closing of all blades for 3 phasesvi. Check for simultaneous closing of all blades for 3 phases
The alignment of Disconnectors is very important for smooth operation. The limitThe alignment of Disconnectors is very important for smooth operation. The limit
switches, the healthiness of auxiliary contacts needs to be checked periodically.switches, the healthiness of auxiliary contacts needs to be checked periodically.switches, the healthiness of auxiliary contacts needs to be checked periodically.
Mis -alignment leads to Hot Spots and breakage.Mis -alignment leads to Hot Spots and breakage.Mis -alignment leads to Hot Spots and breakage.

Operating mechanism functional checkOperating mechanism functional check
i. Check linkages, rods and levers for smooth operation, ensure all jointsi. Check linkages, rods and levers for smooth operation, ensure all joints
are secured tightlyare secured tightlyare secured tightly
ii. Lubrication of bearings with appropriate approved grease for nonii. Lubrication of bearings with appropriate approved grease for nonii. Lubrication of bearings with appropriate approved grease for non
sealed bearingssealed bearings
iii. Grease rotating and hinges pointsiii. Grease rotating and hinges points
iv. Check alignment of auxiliary contactsiv. Check alignment of auxiliary contacts
v. Grease operating mechanism of the auxiliary contactsv. Grease operating mechanism of the auxiliary contacts
vi. Check operation of interlocksvi. Check operation of interlocks
vii. Check operation of motorvii. Check operation of motor
viii. Check operation of all safety interlocksviii. Check operation of all safety interlocks
ix. Operate ON/OFF switch to ensure proper functioningix. Operate ON/OFF switch to ensure proper functioning

PurposePurpose
Purpose of measuring contact resistance measurement is to assess the condition ofPurpose of measuring contact resistance measurement is to assess the condition of
the male and female contacts against erosion or misalignment of the main contacts.the male and female contacts against erosion or misalignment of the main contacts.
Contact resistance of disconnector switch contacts should be measured to check theContact resistance of disconnector switch contacts should be measured to check the
healthiness of the current carrying parts.healthiness of the current carrying parts.healthiness of the current carrying parts.
Instrument RequiredInstrument RequiredInstrument Required
Micro ohm meter of 100 A or more current injection capacity with accessories isMicro ohm meter of 100 A or more current injection capacity with accessories is
required for this test.required for this test.required for this test.
EvaluationEvaluationEvaluation
If the value of the contact resistance exceeds the permissible limits, this could lead toIf the value of the contact resistance exceeds the permissible limits, this could lead to
over heating of contacts. Monitoring contact resistance values is very goodover heating of contacts. Monitoring contact resistance values is very goodover heating of contacts. Monitoring contact resistance values is very good
techniques for assessing the condition of main contacts.techniques for assessing the condition of main contacts.
Maximum permissible contact resistance value for isolators is 300 micro ohms.Maximum permissible contact resistance value for isolators is 300 micro ohms.

CLEANING OF CONTACT SURFACESCLEANING OF CONTACT SURFACES
Silver-faced contact surfaces (bolted)Silver-faced contact surfaces (bolted)
1. Clean with cold cleaning agent Trichloroethylene (Without destroying silver plating1. Clean with cold cleaning agent Trichloroethylene (Without destroying silver plating
of surface)of surface)
2. Apply tin layer of Grease.2. Apply tin layer of Grease.
Galvanized contact surfaces (bolted)Galvanized contact surfaces (bolted)
1. Clean using steel wire brush1. Clean using steel wire brush
2. Apply tin layer of grease immediately.2. Apply tin layer of grease immediately.
LUBRICANT DETAILSLUBRICANT DETAILS
1) For all pins and bushes, Shafts and bushes------ AP3—Multipurpose grease or equal1) For all pins and bushes, Shafts and bushes------ AP3—Multipurpose grease or equal1) For all pins and bushes, Shafts and bushes------ AP3—Multipurpose grease or equal
2) For all sliding contact parts— Petroleum jelly or equalent.2) For all sliding contact parts— Petroleum jelly or equalent.2) For all sliding contact parts— Petroleum jelly or equalent.
3) For fixed contact parts--------- Anti corrosive compound for electrical joints-ACC503) For fixed contact parts--------- Anti corrosive compound for electrical joints-ACC50
or equalent.or equalent.

For Rust protection, grease G 0r Tectyl- 506 is recommended.For Rust protection, grease G 0r Tectyl- 506 is recommended.
Earth Switches:Earth Switches:
 The earth switch is a safety device and smooth operation is to be ensured by proper The earth switch is a safety device and smooth operation is to be ensured by proper
alignment.alignment.
 The earth blade contacts are to be cleaned properly for proper contact and contact The earth blade contacts are to be cleaned properly for proper contact and contact
resistance to be measured to ensure healthiness.resistance to be measured to ensure healthiness.
 The earth connection from blade to earth is to be carefully checked. All the joints The earth connection from blade to earth is to be carefully checked. All the joints
should be tightened.should be tightened.
 Flexible copper braid connections are provided and healthiness ensured. Flexible copper braid connections are provided and healthiness ensured.
 All moving parts should be lubricated for smooth operation. All moving parts should be lubricated for smooth operation.

i. Inspect for cracks, pollutant deposits on insulator housingi. Inspect for cracks, pollutant deposits on insulator housingi. Inspect for cracks, pollutant deposits on insulator housing
ii. Check for operation of pressure relief ventii. Check for operation of pressure relief vent
iii. Check earthing connection from surge arresters to the groundiii. Check earthing connection from surge arresters to the ground
iv. Check condition of surge counter and leakage current gaugeiv. Check condition of surge counter and leakage current gauge
v. Record reading of surge counter and leakage current gaugev. Record reading of surge counter and leakage current gauge
Whenever one stack fails, it is better to change the entire arrester as otherwise theWhenever one stack fails, it is better to change the entire arrester as otherwise the
stressed stacks will start failing along with the new stack.stressed stacks will start failing along with the new stack.
Routine Test:Routine Test:
Insulation resistance measurement.Insulation resistance measurement.
Thermo vision image.Thermo vision image.

Operation with unbalance phases may cause over stressing of some of the capacitorsOperation with unbalance phases may cause over stressing of some of the capacitors
causing further damage.causing further damage.
Best way to check the healthiness of a capacitor is to check the capacitance with aBest way to check the healthiness of a capacitor is to check the capacitance with a
capacitance meter, partial or complete failure of a capacitor can be established fromcapacitance meter, partial or complete failure of a capacitor can be established from
this.this.
Increased C  shorting of elements.Increased C  shorting of elements.
Decrease in C  Opening of elementsDecrease in C  Opening of elements

Leakage:Leakage:
The leakage in welded seam or in terminal cap -After cleaning and abrading by emeryThe leakage in welded seam or in terminal cap -After cleaning and abrading by emery
cloth apply Araldite or solder the spot carefully.cloth apply Araldite or solder the spot carefully.
Over Heating:Over Heating:
Over heating due to over voltage.Over heating due to over voltage.
Low Current:Low Current:
Lower current than rated current due to low voltage and loose connection.Lower current than rated current due to low voltage and loose connection.
- Tighten Carefully.- Tighten Carefully.
Abnormal Bulging:Abnormal Bulging:
Gas formation due to internal arcing causing unit to bulge or burst – Change the unitGas formation due to internal arcing causing unit to bulge or burst – Change the unitGas formation due to internal arcing causing unit to bulge or burst – Change the unit

Improper Balancing33KV Capacitor Bank Improper Balancing33KV Capacitor Bank Improper Balancing
In the event of failure of one capacitor unit (say in R-phase) it is observedIn the event of failure of one capacitor unit (say in R-phase) it is observed
that balancing is done by removing one capacitor each from Y and B-that balancing is done by removing one capacitor each from Y and B-that balancing is done by removing one capacitor each from Y and B-
phases as shown in figure below. This arrangement is not correct, since itphases as shown in figure below. This arrangement is not correct, since it
results in unequal voltage distribution between the capacitors in seriesresults in unequal voltage distribution between the capacitors in series
groups.groups.groups.

Correct method of balancing is, to connect equal number of capacitors of identicalCorrect method of balancing is, to connect equal number of capacitors of identical
rating in each series group in all the three phases on one star bank, to maintain equalrating in each series group in all the three phases on one star bank, to maintain equal
voltage distribution across series groups.voltage distribution across series groups.

1. Verify ventilation of battery room or enclosure.1. Verify ventilation of battery room or enclosure.
2. Inspect physical and mechanical condition.2. Inspect physical and mechanical condition.
3. Inspect anchorage, alignment and grounding.3. Inspect anchorage, alignment and grounding.
4. Cleanness of the unit.4. Cleanness of the unit.
5. Clean corroded/oxidized terminals and apply an oxide inhibitor.5. Clean corroded/oxidized terminals and apply an oxide inhibitor.
6. Inspect bolted electrical connections for high resistivity using one of the following6. Inspect bolted electrical connections for high resistivity using one of the following
methods :methods :
a. Use of low resistance ohmmeter.a. Use of low resistance ohmmeter.
b. Verify tightness of accessible bolted electrical connections by calibrated torque-wrench method.b. Verify tightness of accessible bolted electrical connections by calibrated torque-wrench method.

Bulging of Battery:Bulging of Battery:
If a battery bulges severely on charge, this is not normal. It is an indication of aIf a battery bulges severely on charge, this is not normal. It is an indication of a
blocked valve or an overcharge situation. Such a battery should be removed fromblocked valve or an overcharge situation. Such a battery should be removed from
service.service.
A certain amount of bulge is normal.A certain amount of bulge is normal.
Battery Capacity test:Battery Capacity test:
Battery Capacity Test can be performed if required to confirm the AH capacity and toBattery Capacity Test can be performed if required to confirm the AH capacity and to
identify the failed capacitors.identify the failed capacitors.

This Procedure outlines the steps in identifying "Hot Spots" on equipment at aThis Procedure outlines the steps in identifying "Hot Spots" on equipment at a
substation utilizing the Thermovision camera.substation utilizing the Thermovision camera.
Thermovision camera is capable of identifying the heat generated by individualThermovision camera is capable of identifying the heat generated by individual
substation components operating at temperatures above their equipment designsubstation components operating at temperatures above their equipment design
ratings using Infra red (IR) technology.ratings using Infra red (IR) technology.
Basically, the I2R losses produce the heat that IS observed by the camera as a "hotBasically, the I2R losses produce the heat that IS observed by the camera as a "hot
spot“.spot“.
Points to be noted:Points to be noted:
 A Thermal vision scan of the electrical system at peak load will give an indication of A Thermal vision scan of the electrical system at peak load will give an indication of
the hot spots In the circuit Identify which of the hot spots is the result of wrongthe hot spots In the circuit Identify which of the hot spots is the result of wrong
connector type.connector type.connector type.
 Since the Scanning Operator will be working In high voltage substations, all safety Since the Scanning Operator will be working In high voltage substations, all safety
work practices, clearances, etc must be known and observed A minimum of twowork practices, clearances, etc must be known and observed A minimum of two
operators working together for each scanner is recommended.operators working together for each scanner is recommended.

 Hot Spots show up as light blue, yellow, orange, red or white on a dark blue Hot Spots show up as light blue, yellow, orange, red or white on a dark blue
background The temperature of the hot spot Increases as the color goes from lightbackground The temperature of the hot spot Increases as the color goes from lightbackground The temperature of the hot spot Increases as the color goes from light
blue to red to white being the hottest.blue to red to white being the hottest.
 Readings were not taken from different angles as a check on the accuracy of Readings were not taken from different angles as a check on the accuracy of
temperature.temperature.
Evaluation of Results:Evaluation of Results:
Hot spot category Recommended Corrective ActionHot spot category Recommended Corrective Action
Critical (C): [i.e. T≥50ºC] Immediate Corrective Action (ICA)Critical (C): [i.e. T≥50ºC] Immediate Corrective Action (ICA)
Less Critical (LC): [i.e. 15ºC≤ΔT<50ºC] Action with in a Month (AWM)Less Critical (LC): [i.e. 15ºC≤ΔT<50ºC] Action with in a Month (AWM)
Non Critical (NC): [i.e. ΔT<15ºC] Quarterly MonitoringNon Critical (NC): [i.e. ΔT<15ºC] Quarterly Monitoring

Spot Temp.Spot Temp.
0 120.00 120.0
11
Area Temp.
0 123.0
Line Max Temp.Line Max Temp.
00
B-Phase Line side isolator clamp CT-side clamp is very hot. Attention should beB-Phase Line side isolator clamp CT-side clamp is very hot. Attention should be
required.required.

Spot Temp.Spot Temp.
0
Area Temp.
0 161.3
Line Max Temp.Line Max Temp.
0 160.30 160.3
R-Phase Breaker side Cable isolator Clamp is at elevated temperature.R-Phase Breaker side Cable isolator Clamp is at elevated temperature.
Attention should be taken.Attention should be taken.

To ensure safety of operating staff by limiting voltage gradient at ground level in theTo ensure safety of operating staff by limiting voltage gradient at ground level in the
substation.substation.
To provide a sufficiently low resistance path to earth to minimize the rise in earthTo provide a sufficiently low resistance path to earth to minimize the rise in earth
potential with respect to a remote earth fault.potential with respect to a remote earth fault.
All metallic objects which do not carry current and installed in the substation such asAll metallic objects which do not carry current and installed in the substation such as
structures, parts of electrical equipments, fences, armoring and sheaths of the lowstructures, parts of electrical equipments, fences, armoring and sheaths of the low
voltages power and control cables should be connected to the earthing electrodevoltages power and control cables should be connected to the earthing electrodevoltages power and control cables should be connected to the earthing electrode
system.system.
ElectrocutionShockElectrocutionShock
Electrical accident depends on……Electrical accident depends on……Electrical accident depends on……
1. Current amplitude.1. Current amplitude.1. Current amplitude.
2. Duration of current flow.2. Duration of current flow.
3. Voltage level.3. Voltage level.
Resistance of human body --- 300 Ohms to 1000 OhmsResistance of human body --- 300 Ohms to 1000 Ohms
Dry condition > 10000 OhmsDry condition > 10000 Ohms

The potential difference between two steps of a person standing on the substationThe potential difference between two steps of a person standing on the substation
floor during the flow of earth fault current is known as step potential.floor during the flow of earth fault current is known as step potential.

Current ElectrodeCurrent Electrode
Earth Electrode on testEarth Electrode on test
Potential ElectrodePotential Electrode

By adding series capacitance in transmission line the inductive reactance gets partiallyBy adding series capacitance in transmission line the inductive reactance gets partially
neutralized, thus decreasing the adverse effects of inductive reactance and enhancingneutralized, thus decreasing the adverse effects of inductive reactance and enhancingneutralized, thus decreasing the adverse effects of inductive reactance and enhancing
the Power Transmission Capability of the Transmission Line.the Power Transmission Capability of the Transmission Line.

Capacitors should be maintained periodically once a month.Capacitors should be maintained periodically once a month.
Capacitors including bushings should be cleaned of dust etc. All connections shouldCapacitors including bushings should be cleaned of dust etc. All connections should
be checked for tightness.be checked for tightness.
Any rusty portion should be cleaned and then given a coat of paint.Any rusty portion should be cleaned and then given a coat of paint.
Check for leakage/seepage of oil on any equipment. These cannot be tolerated.Check for leakage/seepage of oil on any equipment. These cannot be tolerated.
Repair immediately by applying fast curing M-Seal or Araldite.Repair immediately by applying fast curing M-Seal or Araldite.
There is a short or a trip on any phase :There is a short or a trip on any phase :
Identify and replace the damaged unit. If no spare is available, remove equal units fromIdentify and replace the damaged unit. If no spare is available, remove equal units from
other phases and balance.other phases and balance.

These spark gaps are inserted in parallel with capacitor banks such that in case of overThese spark gaps are inserted in parallel with capacitor banks such that in case of over
voltage across capacitors, the spark gaps breakdown and become conducting, thusvoltage across capacitors, the spark gaps breakdown and become conducting, thusvoltage across capacitors, the spark gaps breakdown and become conducting, thus
decreasing the over voltages across capacitors to protect them.decreasing the over voltages across capacitors to protect them.
The enclosure, support insulators, bushing insulators, electrodes, and other parts areThe enclosure, support insulators, bushing insulators, electrodes, and other parts are
visually inspected.visually inspected.
If there are burning marks on the surface of the graphite electrodes, they areIf there are burning marks on the surface of the graphite electrodes, they are
smoothed by using a file and a grinding cloth.smoothed by using a file and a grinding cloth.
The copper electrodes, support and bushing insulators are cleaned by wiping with aThe copper electrodes, support and bushing insulators are cleaned by wiping with a
cloth.cloth.
Tightness of the lower, upper and auxiliary electrodes and that all graphiteTightness of the lower, upper and auxiliary electrodes and that all graphite
electrodes to be checked.electrodes to be checked.

KARIKALAN.M

Substation Maintenance

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