1. Maintenance philosophy of POWERGRID
INTRODUCTION:
In today’s scenario of power deficit,
the availability of a transmission line
is very critical as outage of one line results
in loading restriction on other parallel lines
also
The equipments are vital elements of any
transmission system.
It is our experience that less attention is
being given to preventive maintenance of
Equipments and protection systems.
The equipments, if not properly maintained,
are more susceptible to failures as compared
to transmission lines and non operation of
protection systems.

2. The failure of sub station equipment can
cause consequential damage to other
equipments also. Recent example is failure
of one 400 KV circuit breaker at MSEB
Chandrapur with not operation of protection
System had caused collapse of Western
Maharashtra grid.
The down time of a system, due to failure of
equipment, is quite high.
IN VIEW OF ABOVE, PRIME IMPORTANCE
IS GIVEN TO
PREVENTIVE MAINTENANCE OF EQUIPMENTS,
PROTECTION SYSTEM AND TRANSMISSION
LINES IN
POWERGRID

3. Maintenance schedule has been prepared
for each and every equipment of sub station.
This consists of
Activities requiring shut down of equipments
Activities which do not require shut down.
Various activities are classified as per
frequency of testing i.e. monthly, half yearly,
yearly, two yearly, four yearly etc.
The test results of various maintenance
activities are recorded in a standard format
to avoid any ambiguity in recording the
results. This also improves the traceability
of the test records for one particular
equipment.

4. Acceptable / permissible limits for various
tests have been compiled in the form of a
document.
The permissible limits have been arrived at,
as per the recommendation of various
manufacturers and experience gathered by
POWERGRID.
The test results are analyzed, with reference
to deviation from acceptable limits / last test
results / commissioning results,
after converting them on a common base.
In case the result violates the prescribed
norms, the tests are repeated before deciding
about replacement.
Replacement is planned in co-ordination
with region.
The approving authority for various tests has
been identified in the document.

5. Based on consumption pattern of various
sub station equipments, norms have been
prepared for keeping the spare quantities
of various sub station equipment.
The availability of these spares is monitored
at Regional level.
In case of any item falling short of norms,
immediate action is taken for procurement
To increase the confidence of working
personnel, the P manuals have been
developed for various equipments giving
minute details of various parts.
Documents detailing various testing
procedures have been formulated.

6. The failure of sub station equipment is
analyzed to identify the reason of failure
and arriving at remedial measures to avoid
recurrence in future.
These reports are approved by Director (O),
POWERGRID. .
The findings of such analysis are circulated
up to sub station level for increasing
awareness
To monitor the maintenance checks for
various equipments, audit of each sub
station, once in two years, is carried out by
Regional team and discrepancies noticed
are complied with.
Similarly once in 4 years, audit by corporate
team is carried out.

7. The condition of spare equipments available
in the stores is monitored at regular interval.
The procedure of storing spare equipments
is documented.
These documents are reviewed once in
two years.
The feedback is sought from various sites about
periodicity of various tests / deletion of some
tests / inclusion of new test.
Various new tests, introduced recently, are
also added depending upon their utility.

8. A check list has been developed for higher
authorities visiting the sub stations. This list
includes various activities of sub station
Subsequent to visit to a sub station by
GM / ED, the check list is filled up and send
to Corporate center.

9. CHECK LIST FOR INSPECTION BY HODs.
Region:
Substation/Transmission Line:
Date of Visit:
Control Room: 1
Healthiness of Event Logger
YES/NO 2
Healthiness of Disturbance Recorders. 3
Healthiness of Line Fault Locators. 4
All metering instruments are working. 5
All protections are in service. 6
All annunciation facia are working. 7
Healthiness of PLCC 8
Healthiness of communication 9
Proper maintenance of operation records.
Switchyard
Proper identification of phases.
Equipment identification and numbering.
Condition of equipment/painting etc.
House keeping of switchyard.
Proper earthing of equipment.

10. For monitoring the healthiness of various
sub station equipments, following state of
art tests have been introduced.
Third harmonic leakage current
measurement for lightening arresters
Thermo vision scanning of sub station
equipments
Capacitance and Tan delta measurement
for transformer / reactor bushing, winding,
grading capacitor, current transformer
and capacitive voltage transformer (CVT)
Dynamic contact resistance measurement
for circuit breakers
Battery impedance testing
Frequency response analysis for transformer
Dissolved gas analysis for transformer oil

11. Activity Condition Period
The main activities for various equipments are detailed below:
TRANSFORMERS AND REACTORS
Activity
Condition
Period
Testing of oil for DGA and other oil parameters *
W S/D HY
Vibration measurements (for Shunt Reactors only)
2Y %
Measurement of BDV of OLTC oil
S/D Y
Tan measurement for Bushings
2Y $
IR measurement of Windings
(Polarization Index and D.A. Ratio)!
4 Y **
Tan measurement of Windings
4 Y**
Measurement of Windings resistance at all tap positions
Frequency Response Analysis
Maintenance of OLTC driving mechanism
Checking of all remote indications
(WTI and Tap position indicator)
Electrical checking/testing of Pressure Relief
Device,Buchholz relay, OLTC surge Relay and
Checking /Replacement of the gaskets of terminal box
Checking/testing of Buchholz relay by oil draining
Checking and Cleaning of Diverter Contacts
(50,000 operations)
SOS
Checking and calibration of OTI, WTI 2Y
Filtration / Replacement of oil of OLTC
Filtration/ Degassing of main tank oil
* Water Content, BDV, Sp. Resistance, Tan, IFT, Total Acidity, 2-Furfuraldehyde etc.
** First time after one year from commissioning and then once in every four years.
% Vibration measurement, 3M and 6M after commissioning
@ Base Signature before commissioning for all ICTs/Reactors
$ Tan Delta measurement of Bushing within guarantee period after commissioning.
! Di-electric Absorption Ratio
 To be measured as per the following combinations:
N/E, N/LV and LV/E.

12. A. SF6 CIRCUIT BREAKERS
Activity
Condition
Period
Dew Point measurement of SF6 gas
S/D
3Y*
*At time of commissioning then after 6 months and one & half years of
commissioning and thereafter once in every three years.
HYERAULIC OPERATING MECHANISM
Checking of oil pressure drop during duty cycle operation check
S/D Y
Checking of auto-starting/stopping of oil pump
II. PNEUMATIC OPERATING MECHANISM
Functional checking of auto-starting of air compressors and dryers
S/D Y
Maintenance of Air Dryer, if provided
W/S/D HY
Checking of air pressure drop during duty
cycle operation
B. AIR BLAST CIRCUIT BREAKERS
Dew Point Measurement of operating air at the
outlet of Air Drier
W S/D Y
C. MOCBs
Testing of oil for BDV
W S/D Y

13. D.BREAKER OPERATION CHECKS
CB Operating Timings (Main, PIR, Aux.)
S/D
Y *
Static Contact Resistance 2Y
Dynamic Contact resistance(DCRM)
Contact Travel,** Contact Speed,**
Contact wipe, Arcing contact length
Checking of Pole discrepancy relay Y
Functional checks, duty cycle
operation including rapid re-closing
(O-0.3s-CO)
Checking of all operation lock-outs
Checking of all interlocks
Checking of pressure settings
* For all HV/EHV Circuit Breakers only
** - For 400kV BHEL, CGL & ABB make CBs only
E. MEASUREMENT/ TESTING
Checking of close/trip coil currents
S/D Y
Checking of healthiness of Operation
Counter
Capacitance and tan measurement of grading capacitors
4Y*
* First time after one year from commissioning and then once in
every four years

14. 4. CAPACITVE VOLTAGE TRANSFORMERS
3.CURRENT TRANSFORMERS
Measurement of Tan and Capacitance
S/D
2Y*
DGA and testing of other parameters of oil
SOS
Thermovision Scanning of CT and Top dome
W S/D Y
Checking of Bellow Expansion M
N2 Pressure Checking 2Y
*- First time after one year from commissioning and then once
in every two years.
4. CAPACITVE VOLTAGE TRANSFORMERS
Visual checking of earthing HF point (in case it is not being used for PLCC)
S/D Y
Checking for any breakage or cracks in cementing joint
Capacitance and Tan measurement
3Y *
Measurement of voltage in S/Y MB
W S/D
6 M**
Thermo vision Scanning of Capacitor stacks
*First time after one year from commissioning and then once in
every three years. For CVTs in which isolation of neutral of intermediate
PT is not possible at site, this test is not required to be carried out.
** If secondary voltage violate norms, voltage measurement interval to be
as per CVT replacement norms
5.SURGE ARRESTERS
Checking of leakage current *(Third Harmonic Resistive Current)
W S/D Y
Testing of counters
Measurement of Capacitance and Tan and IR of each stack
S/D
SOS
* Leakage current measurement to be carried out after annual maintenance

15. 6. ISOLATORS AND EARTH SWITCHES
MAINTENANCE OF OPERATING MECHANISM
Linkages including transmission gears
S/D Y
Stopper bolts
Cleaning of auxiliary switch contacts
and greasing with silicon grease
Lubrication of operating mechanism.
Hinges, lock joints on levers, Bearings
Checking of all mounting bolts for tightness
W S/D
MAIN CONTACTS
Cleaning and lubrication of main contacts
S/D Y
Alignment
Main contact resistance measurement 4Y
Tightness of Bolts, nuts and pins etc.
Cleaning of support insulators and checking of
insulator cracks, if any
Checking of Interlock
EARTH SWTICH
Checking & Alignment of earthing blades
S/D Y
Cleaning of contacts
Contact resistance 4Y
Operation of earthing switch
Checking of Aluminum / Copper flexible
conductor
Checking of earth connections
of structure and MOM box

16. 8. AIR CONDITIONING PLANT
7. WAVE TRAPS
Tightness & cleanliness
S/D Y
General inspection / cleaning of tuning unit
8. AIR CONDITIONING PLANT
Checking of oil pressure switch. LP/HP, cutout switches, solenoid valve, thermostat, Humidistat etc.
S/D Y
Checking Operation of Level switch HY
Checking Water quality
W S/D
Cleaning of nozzles for clogging QY
Lubrication of moving parts
Terminal connection checking
Cleaning of Bus Bars, Insulators etc.
Tightness of the connections
Checking of all interlocks
9. BATTERIES AND DC DISTRIBUTION SYSTEM
Checking control cards of charger
& Measurement of test point voltage values
S/D Y
Battery Impedance testing
W S/D
Discharge test of Battery Set 3Y
Checking of any earth fault
(If E/F relay not provided) M
Testing of DC E/F and Under Voltage relays

17. 10. FIRE PROTECTION SYSTEM
Cleaning/Replacement of Air Filter
WS/D M
Checking of compressor oil and replace
if necessary
S/D QY
Maintenance & cleaning of compressor valves, gaskets, valve plates and replace, if necessary
Operation check of low oil level switch
Cleaning and checking for seating of the breather valve
Cleaning of NRV/HP tank Y
General overhaul
SOS
Detectors
W S/D
i) Sequence test for annunciation in
Control Room panel
ii) Smoke test
iii) Cleaning
DIESEL ENGINE
Checking/replacement of fuel oil filter
Lube oil filter, Air filter
Pump Overhauling
Checking of belt tightness
Cleaning of oil strainer
Checking of alignment of pump set
Overhauling
Checking of pressure of the hydrant system
at the remotest end, auto-starting of pumps,
diesel engine etc.
Operation of Deluge system, check outlet
pressure check alarm, check starting of
Diesel/electrical pump.

18. 15.PREVENTIVE MAINTENANCE SCHEDULE FOR DG SET
Replacement of oil filter after
recommended running hours
W S/D
Y/SOS
Check for fan hub, drive pulley and water pump Y
Replacement of Air cleaning element
Check for Governor linkages, fuel
transfer pump, fuel line connections
Drain Sediments from fuel tank, change
fuel filter and clean fuel tank breather
Stator winding IR measurement
S/D
Checking/Cleaning of Slip ring and its brushes
Testing of protection/control relays and
alarms
Check for air leaks and exhaust Restrictions

19. THANK YOU