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.

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

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.

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.

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.

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.

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.

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.

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.

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

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 SOS @ 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.

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

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

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

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

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

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.

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

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