EHT SUB STATIONS
CODE CHARACTERISTIC FAULT
2. Maintenance Schedule for Circuit breakers of 33 KV and above
S.No. Item of maintenance Periodicity Remarks
1. A. SULPHER HEXA FLOURIDE (SF6) GAS CIRCUIT BREAKER 1 SF6 density monitoring Daily in each
shift If appreciable change is observed compared to earlier readings, leakage check to be carried out
2 Measurement of Humidity of SF6 gas Yearly Use Dew Point meter. If deviation from standard norms is observed, the evacuation, recycling and refilling of SF6 gas is to be carried out
3 Acid concentration measurement of SF6 Gas
Yearly 4 Air content measurement of SF6 gas Yearly
5 SF6 gas leakage test Yearly Check the complete breaker for SF6 gas leakage including the seal assembly of driving rod. If any leakage is detected the same should be arrested in consultation with manufacturer and after arresting the leakage the SF6 gas pressure is to be brought upto rated pressure by topping up SF6 gas
6 a. Checking of insulation of control circuit wirings
Yearly Minimum 2 Mega Ohms with a 500 V megger
b. Measurement of Insulation resistance across contacts (with breaker off) and pole to earth with breaker on
Yearly To be done by 2.5 KV megger or above
7 Evacuation, recycling and refilling of SF6 gas
5 yearly This may be done whenever the humidity in SF6 gas in excess of permissible value.
8 Checking the Br.level with spirit level Yearly
B AIR BLAST CIRCUIT BREAKER
1 Checking of air pressure Daily in each shift
If appreciable changes is observed, compared to earlier readings, leakage check to be carried out
2 Draining out condensed water from HP cylinders
Twice daily at 6 AM and
6 PM
Frequency of draining may be increased during rainy season and winter
3 Draining out condensed water from circuit breaker tanks
Monthly -do- 4 Visual checking of oil level in the dash
pot; checking of manometer readings
Monthly 5 Capatiance measurement for Grading
capacitors
Yearly
6 Measuring insulation resistance of control circuit wiring and measuring IR values
Yearly Minimum 2 Mega Ohms with a 500V Megger
7 Measurement of IR values across contacts (each break) with breaker off and pole to earth with breaker ON
Yearly Minimum 2.5 KV megger to be used
8 Checking the Br. Level with spirit level Yearly
C. VACCUM CIRCUIT BREAKERS 1 Measuring I.R values of the poles with
breaker open (i.e., across contacts) and breaker closed (pole to earth)
Monthly Record the value and compare with earlier values
2 High voltage test across contacts of each vacuum interrupter
Yearly To ensure dielectric strength of vacuum interrupters
3 Measuring insulation resistance of control circuit wiring
Yearly Minimum 2 Mega ohms with a 500 V megger
4 Anti condensation heathers Daily Ensure that heater is on and is working
D. MINIMUM OIL CIRCUIT BREAKER 1 Checking of oil leakage from guage
glass, drain valve and other joints
Daily 2 Testing of oil samples for dielectric
strength
Quarterly If the valve is low oil should be replaced with fresh tested oil.
Oil shall also be replaced after 12 trippings on fault or as per recommendations of manufac-turer. Oil filling instructions given by the manufacturer s hall be followed.
3 Measuring IR values across contacts with breaker off and pole to earth with breaker on
Quarterly
NOTE : Before closing MOCB on a fault, the operator should ensure that adequate oil level is available in the breaker by observing the guage glass and if adequate oil is not available, the breaker should not be test charged.
4 Checking the Br. Level with spirit level Yearly E. GENERAL MAINTENACE
(Common to all Breakers)
1 Operating time including Pre-insertion resistor (wherever applicable)
Yearly
2 Contract travel Yearly
3 Speed curves Yearly
Circuit breaker analyser may be used. Results are to be recorded and compared with the commissioning test result. If
4 Pole discrepancy
(for individual pole operted)
Yearly there is difference in the values, or if the values are beyond limits prescribed by the Manufacturer, the manufacturer has to be informed and all the operation checks are to be made in the presence of manufacturer
& remedial measures are to be taken
5 Functional checks duty cycle operation
including rapid reclosing Yearly
6 Checking of all operational lock outs Yearly 7 Checking of all interlocks Yearly
8 Contact resistance measurement Yearly Not to exceed 100 Micro ohms (by measuring DC voltage drop) 9 Checking of pressure setting sand
calibration of meters
Yearly 10 Through checking up of close and trip
coils
Yearly Resistance and pickup voltage are to be checked and compared with previous values (pre- commissioning results)
II OPERATING MECHANISM
A SPRING OPERATING MECHANISM
i) Checking conditions of spring tension Quarterly ii) Lubricating the motor bearings Quarterly iii) I.R values of motor winding Quarterly iv) Checking interlocking mechanism Quarterly
B PNEUMATIC OPERATING MECHANISM
i) Checking of air pressure Daily ii) Draining of moisture from air receiver,
visual inspection cleaning
Daily/
Weekly
Daily for central compressor unit and weekly for individual compressor unit
iii) Checking of tightness of compressed air pipes work and coupling
Yearly iv) Checking of cumulative running hour
of compressor v) Checking of air pressure drop during
duty cycle operation
Yearly Pressure drop in the air pressure to be checked for each sequence of operation and to be compared with data sheets
vi) Check for compressor running sound Monthly vii) Lubrication, greasing of moving parts
of the compressor
Yearly viii) Blowing out dust in the windings of
compressor motor
Monthly ix) Checking for proper functioning of
safety valves in compressed air system
yearly
x) Overhauling of compressor motors Yearly xi) Checking interlocks low and high air
pressure and correct operation
Yearly
C HYDRAULIC (ELECTRO) OPERATING MECHANISM
i) Checking of oil pressure and level Daily If appreciable change is observed as compared to previous readings, leakage check is to be carried out
ii) Visual check for oil leakage Daily iii) Checking for cumulative pump running
hours
Once in each shift iv) Replacement/topping up of oil As and when
required v) Visual checking of accumulator, main
valves and operating cylinders
Weekly vi) Checking of printing pressure of
nitrogen, nitrogen replenishment (if necessary)
Yearly
vii) Checking operating pressure of safety valve
Yearly viii) Checking oil pressure drop during duty
cycle operation
Yearly Drop in pressure of oil to be checked for each sequence of operation and to be compared with data sheets.
ix) Checking condition of oil Yearly If the oil is found to be contaminated, drain the oil and clean both oil tank and oil filter.
x) Overhauling of oil pump Yearly xi) Checking for tightness of oil pipe work
and couplings
Yearly xii) Checking of various pressure switches
for proper operation
Yearly
MAJOR MAINTENANCE AND OVERHAUL OF CIRCUIT BREAKER 1 Evacuation, recycling and refilling of
SF6 gas
5 yearly Assistance of manufacturer may be availed
2 Replacement of gaskets
3 Operating rod cleaning and inspection 4 Dismantling, cleaning and reassembly
of operating mechanism 5 Interrupting chamber overhaul
3 Maintenance schedule for Batteries/Battery chargers/ DC Distribution system
S.No Item of maintenance Periodicity Remarks
1 Cleaning of battery surface joints and all connections
Daily To be done on rotation so as to cover all the cells in10 days 2 Specific gravity measurement of pilot
cell
Daily -do- 3 Voltage reading of pilot cells Daily -do- 4 Visual checking of battery room
ventilation and lighting
Daily -
6 Application of petroleum jelly to joints and cell connections
Weekly - 7 Checking electrolyte level and topping
up with DM water
Weekly - 8 Shallow discharge (10 hour rate) and
recharging
Yearly The discharge to be done for a specified period
9 Readjustment of specific gravity Yearly - 10 Checking of healthiness of AC supply
to the charger
Daily - 11 Checking of float charging current
(DC)
16 Checking for DC earth fault Daily Earth fault to be attended immediately
17 Check of emergency lights Daily Fused lights to be replaced immediately
18 Auto-start and running up of DG set Daily - 19 Checking DC distribution
i. External Daily -
ii. Internal Quarterly -
20 Checking of all electrical connections of charger panel for tightness and cleaning
Quarterly -
21 Calibration of all meters and relays in the charger and the DCB Bs
Yearly -
4. Maintenance Schedule for Lightning Arrestors
S.No. Item of maintenance Periodicity Remarks
1 Visual Inspection Daily If chipping / crack in the insulators is observed
replacement action may be taken
2 Surge counter reading Daily -
3 Leakage current reading and analysis Once for shift
Should be in green zone
4 Earth resistance Quarterly -
5 Leakage current analysis Quarterly For gapless lighting arrestors only
6 IR value Yearly Compare results with those
obtained previously
7 Connections Yearly -
8 Calibration of leakage current ammeter Yearly -
9 Cleaning of Insulator Yearly -
5. Maintenance Schedule for Isolators
S.No. Item of maintenance Periodicity Remarks
1 Visual inspection Daily Visual inspection for cleanliness of insulation, proper alignment of contact arm blades, any abnormal noise and arcing will be carried out.
2 (a) Main contacts checking including Yearly Opportunity of shut down
earth switch high voltage terminal tightning contact resistance checking including cleaning and lubrication of main contacts
should be availed of whenever possible, the checks and measurements should be performed without disturbing the connections
2 (b) Main blades and main contacts checking of (i) alignment (ii) bolds, nuts, washers, cotterpins, terminal connectors, are in place and tight.
Examine the contacts, heck to determine that they are aligned and contact surfaces bear with a firm uniform pressure, check contact surfaces, replace any pitted or burnt contacts or smoothen down the surface of the contacts with fine sand paper depending upon the condition of the contacts.
Yearly
See the bolts, nuts, washers, cotter pins and terminal connectors are in place and tight. If the switch in group operated inter phase linkage, line operating parts, rods, levers, bearings etc. should be cleaned and lubricated, as required to the manufacturers recommendations
3 Operating mechanism Checking of
- Linkages including transmission gears
- Stopper bolts - Limit switch setting - Greasing of drive
- Greasing of auxiliary switch contacts
- Position and tightening of cable glands (before start of the rainy season)
Quarterly Check the isolator operation. If the operating efforts appear to be excessive check the rotor bearings, all the linkages for the proper operation
4 Insulators MOM box cleaning and lubrication of operating mechanism hinges locks, joints on levers, etc, check all mounting booth for tightness
Yearly Opportunity of shut down should be availed of whenever possible
5 Visual check of Auxiliary contact Quarterly The check should be done for any arcing marks on contacts, burning of switch housing etc.
6 Checking for proper functioning of space heaters, illumination etc.
Quarterly 7 Checking of electrical/ mechanical inter
locks
Yearly 8 Earth-switch – checking of
- Correct operation of earthin switch - Alluminium/Copper flexible (if
provided)
9 Checking of earth connections Yearly - Structure
- MOM Box
Standard Acceptance Norms for Isolator during preventive maintenance S.No Type of Isolator and name of
Manufacturer
Voltage (KV)
Current rating/
Value of contact resistance Between terminal pads 1 220 KV HEB
NOTE : The values of contact resistance given above are the measured during type tests, the measured values during site tests should be within 120% of the values indicated.
6. Maintenance Schedule for Current Transformers S.No Item of Maintenance Periodicity Remarks
1 Visual check
(Porcelain, Unusual noise, discolouration of terminals etc.)
Daily
2 Oil leakage Daily Visual check only
3 Oil level Monthly To be recorded
4 Space heater and lighting of marshalling box
Monthly Operation check 5 Cleaning of marshalling box and
junction boxes
Half- yearly
6 All connections Yearly Check for looseness
7 IR value Yearly Compare with
pre-commissioning test results
8 Earth resistance Yearly
9 Tan Delta test Yearly Compare with factory test
results 10 Cleaning of Insulator Yearly
11 DGA oil sample including BDV and moisture content
4 to 5 days after first charging
Oil sample to be taken after obtaining permission from manufacturer
Maintenance for CVTs
S.No Item of Maintenance Periodicity Remarks
1 Oil leakage Daily Visual checks
2 Cattering sounds Daily If present, measure capacitance and compare with the designed value
3 Oil level Monthly To be recorded
4 Earthing of PLCC link (in case it is not being used)
Monthly -
5 H.F. Bushing Monthly Check for any breakage
6 Spartik gap cleaning Yearly If accessible 7 Cleaning of insulator Yearly
8 Capacitance measurement Yearly Compare with the factory test results/designed value
9 Earthpit resistance Yearly
8. Maintenance schedule for earth pits in sub-stations S.No Item of Maintenance Periodicity Remarks
1 Watering of earth pits Daily 2 Measurement of earth resistance of
individual pits
Half-yearly 3 Measurement of combined earth
resistance of all the pits
Half-yearly 4 Checking of interconnections
between earth pits and tightness of bolts and nuts
Quarterly
Special Note :
Complete and comprehensive record of pre-commissioning test result for each equipment is to be maintained and periodical test values must be compared with the pre-commissioning Test results for taking appropriate action.
The following are guidelines for maintaining voltage and specific gravity of the cells at a uniform value :
a. When the battery is to be stored for long period, before putting into service, necessary care is to be taken for proper storage, other-wise there may be possibility of oxidation which may have adverse impact on the porosity of the plates. The Cells will develop uniform poraoity only after repeated charge/discharge cycles and adjustment of specific gravity has to be made thereafter in all the Cells.
b. Variation in the quantity of Distilled water while topping up or failure to tope up some cells may also contribute to the variations in cell voltage and specific gravity
c. After installation of the battery, if voltages and specific gravities are not uniform and varying then equalizing charge shall be made by adjustment of electrolyte, ie., in addition or removal of electrolyte and/or addition of Distilled water is made until the specific gravities are uniform. This adjustment may be repeated after some cycles of operation ie., after 30 or 45 days.
d. Batteries should not be kept under continuous Boost Charge. Batteries shall be on float charge only. After sufficient discharge of the Battery (as indicated by the Voltage and specific gravity of the Cell, Battery shall be kept under Boost charge for the required number of hours only to get the normal voltage and specific gravity.