Substation maintenaince
Made By : Prabhat Hambire
Gavin Peterson
Viraj More
Operation and Maintenance 3
Operation and Maintenance 4
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Operation and Maintenance 8
✓Voltages at all levels shall be observed and to be maintained nearest to the rated
values.
✓ Trip circuit supervision of all breakers shall be checked every 2 hour.
✓Battery voltages, DC leakage, Charger condition, switch o f f AC supply to charger
(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
working condition.
✓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.
Note the oil and winding temperature and physically check-up by feeling the
temperature of transformers by hand.
✓ Note the tap position of various transformers.
✓ Check up for any oil leaks and red hot spots.
✓ Ensure that alarms and indications on annunciation panel are working
Operation and Maintenance 10
✓Check the diesel generator and trial run for 5 minutes daily once in the morning shift
and note down the voltage.
✓Check the entire yard for any unusual sounds, sparks and red hots during evening
shift.
✓ Check up gas pressures in SF6 breakers.
✓ Watering of earth pits to be done daily.
✓Ensure that lightning arrestor's leakage current (micro) ammeter reading is in safe
zone (Green).
✓ 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
relay indications if any at other end.
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Operation and Maintenance 12
i. Inspect insulators for crack, burn mark and chipping
ii.Check motor, compressor (for pneumatic breakers), pump (hydraulic breakers) for
unusual noise
iii. Inspect for oil leak/air leak of the operating mechanism
iv. Inspect control circuit and operating mechanism cubicles for the following:-
- heaters operation
- clean vents
- seals and latch
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Monitoring of operating timings is basically done with a aim of finding any problem in
operating mechanism, alignment of main/arcing contacts.
Precautions:
▪Ensure Proper shutdown is arranged.
▪Ensure that there are no joints in testing cable and the testing leads are not
touching any live point.
▪Do not connect the test set the energized equipment.
▪Ground cable must be connected first and removed at last.
▪Test equipment body should be earthed.
▪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
▪provided.
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Cooling System Fans Controls
▪Checking for correct rotation of fans and pumps to be ensured as reverse
rotation may not provide desired result.
▪Oil pumps need to be checked by observing their flow gauges.
▪Measurement of pump current reveals any abnormality.
▪Any significant imbalance of current between the terminals greater than 15-20% is
indicative of the problem with the pump motor.
▪Checking of Auto cooler ON function. (Temperature depended.)
BUCHOLZ Relays
For 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
spring loaded 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.
Operation and Maintenance 50
Failure of Paper Insulation
Oil leakage
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▪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.
▪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
with new one.
▪As CT primary carries heavy current, any loose joint may lead to arcing and welding
of terminal connectors.
▪In coastal and industrial areas where pollution levels are high, due to saline
atmosphere/ chemical contamination, porcelain insulators of electrical equipment shall
have higher creepages.
▪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 proper
sealing
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Operation and Maintenance 58
Measurement of Secondary Winding Resistance for Current Transformers
•Secondary winding resistance of CTs is measured with a digital or analogue Ohm
meter with leads.
•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.
•Earth provided if any in the secondary circuit of CT, should be removed prior to
measurement.
Evaluation :
Extreme low value of resistance indicates turn to turn shorting and a high value
indicates loose connection which is to be identified and tightened before repeating
the measurement.
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Operation and Maintenance 60
If you get higher TAN delta and high oil leakages then dienergise the CT ,take oil
sample and sent for DGA test.
Oil samples to be collected in 300ml bottles and to be sent to test lab for testing. Test
results should be comparable to factory values.
Deterioration 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.
Operation and Maintenance 61
Low Pressure indication in the pressure gauge.
When 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
requires 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.
Reading high pressure
Check 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 pressure
indication in the pressure gauge there is most probably a fault in the densitometer
itself which requires a replacement.
SF6 Gas leakage
If 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 where
gaskets are inserted.
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i. Inspect oil level
ii. Check for oil leakage
iii. Check for insulator chipping and its cleanliness
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 to
avoid phase angle errors.
Operation and Maintenance 68
•The colour of oil indicated through the gauge glass gives some indication of the
healthiness of the internal components.
• Any abnormal heating may also be observed through Thermo vision scanning.
•Maintenance of Marshalling box gaskets, tightening of secondary terminal
connections and tightening of primary terminal connections, etc., are also to be
ensured for healthy operation.
CAPACITANCE & TAN DELTA MEASUREMENT
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i. Inspect for cracks, pollutant deposits on insulator housing
ii. Check for operation of pressure relief vent
iii. Check earthing connection from surge arresters to the ground
iv. Check condition of surge counter and leakage current gauge
v. Record reading of surge counter and leakage current gauge
Whenever one stack fails, it is better to change the entire arrester as otherwise the
stressed stacks will start failing along with the new stack.
Routine Test:
Insulation resistance measurement.
Thermo vision image.
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Operation with unbalance phases may cause over stressing of some of the capacitors
causing further damage.
Best 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
from this.
Increased C 🡪 shorting of elements.
Decrease in C 🡪 Opening of elements
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1. Verify ventilation of battery room or enclosure.
2. Inspect physical and mechanical condition.
3. Inspect anchorage, alignment and grounding.
4. Cleanness of the unit.
5. Clean corroded/oxidized terminals and apply an oxide inhibitor.
6.Inspect bolted electrical connections for high resistivity using one of the following
methods :
a. Use of low resistance ohmmeter.
b. Verify tightness of accessible bolted electrical connections by calibrated torque-
wrench method.
Operation and Maintenance 90
Bulging of Battery:
If 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 from
service.
A certain amount of bulge is normal.
Battery Capacity test:
Battery Capacity Test can be performed if required to confirm the AH capacity and to
identify the failed capacitors.
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This Procedure outlines the steps in identifying "Hot Spots" on equipment at a
substation utilizing the Thermovision camera.
Thermovision camera is capable of identifying the heat generated by individual
substation components operating at temperatures above their equipment design
ratings using Infra red (IR) technology.
Basically, the I2R losses produce the heat that IS observed by the camera as a "hot
spot“.
Points to be noted:
❖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 wrong
connector type.
❖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 two
operators working together for each scanner is recommended.
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❖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 light
blue to red to white being the hottest.
❖Readings were not taken from different angles as a check on the accuracy of
temperature.
Evaluation of Results:
Hot spot category Recommended Corrective Action
Critical (C): [i.e. T≥50ºC] Immediate Corrective Action (ICA)
Less Critical (LC): [i.e. 15ºC≤ΔT<50ºC] Action with in a Month (AWM)
Non Critical (NC): [i.e. ΔT<15ºC] Quarterly Monitoring
Operation and Maintenance 99
Spot Temp.
0 120.0
1
Area Temp.
0 123.0
Line Max Temp.
0
B-Phase Line side isolator clamp CT-side clamp is very hot. Attention should be
required.
Operation and Maintenance 10
0
Spot Temp.
0
Area Temp.
0 161.3
Line Max Temp.
0 160.3
-Phase Breaker side Cable isolator Clamp is at elevated temperature.
Attention should be taken.
Operation and Maintenance 10
1
❖ Capacitors should be maintained periodically once a month.
❖Capacitors including bushings should be cleaned of dust etc. All connections should
be checked for tightness.
❖ 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.
Repair immediately by applying fast curing M-Seal or Araldite.
❖ There is a short or a trip on any phase :
Identify and replace the damaged unit. If no spare is available, remove equal units from
other phases and balance.
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These 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, thus
decreasing the over voltages across capacitors to protect them.
❖The enclosure, support insulators, bushing insulators, electrodes, and other parts are
visually inspected.
❖If there are burning marks on the surface of the graphite electrodes, they are
smoothed by using a file and a grinding cloth.
❖The copper electrodes, support and bushing insulators are cleaned by wiping with a
cloth.
❖Tightness of the lower, upper and auxiliary electrodes and that all graphite
electrodes to be checked.
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