Presentation on theme: "Maintenance philosophy of POWERGRID INTRODUCTION: In todays scenario of power deficit, the availability of a transmission line is very critical as outage."— Presentation transcript:
Maintenance philosophy of POWERGRID INTRODUCTION: In todays 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.
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 findings of such analysis are circulated up to sub station level for increasing awareness 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 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. These documents are reviewed once in two years. The condition of spare equipments available in the stores is monitored at regular interval. The procedure of storing spare equipments is documented.
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: 1Healthiness of Event LoggerYES/NO 2Healthiness of Disturbance Recorders.YES/NO 3Healthiness of Line Fault Locators.YES/NO 4All metering instruments are working.YES/NO 5All protections are in service.YES/NO 6All annunciation facia are working.YES/NO 7Healthiness of PLCCYES/NO 8Healthiness of communicationYES/NO 9Proper maintenance of operation records.YES/NO Switchyard 1Proper identification of phases.YES/NO 2Equipment identification and numbering.YES/NO 3Condition of equipment/painting etc.YES/NO 4House keeping of switchyard.YES/NO 5Proper earthing of equipment.YES/NO
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
The main activities for various equipments are detailed below: TRANSFORMERS AND REACTORS Activity Condit ion Period Testing of oil for DGA and other oil parameters *W S/DHY Vibration measurements(for Shunt Reactors only)W S/D2Y % Measurement of BDV of OLTC oilS/DY Tan measurement for Bushings S/D2Y $ IR measurement of Windings (Polarization Index and D.A. Ratio)! S/D4 Y ** Tan measurement of Windings S/D4 Y** Measurement of Windings resistance at all tap positionsS/D4 Y** Frequency Response Maintenance of OLTC driving mechanismS/DY Checking of all remote indications (WTI and Tap position indicator) S/DY Electrical checking/testing of Pressure Relief Device,Buchholz relay, OLTC surge Relay and Checking /Replacement of the gaskets of terminal box S/DY Checking/testing of Buchholz relay by oil drainingS/DY Checking and Cleaning of Diverter Contacts (50,000 operations) S/DSOS Checking and calibration of OTI, WTIS/D2Y Filtration / Replacement of oil of OLTCS/DSOS Filtration/ Degassing of main tank oilS/DSOS *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 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 ActivityConditi on Period Dew Point measurement of SF6 gas S/D 3Y* HYERAULIC OPERATING MECHANISM Checking of oil pressure drop during duty cycle operation check S/D Y Checking of auto-starting/stopping of oil pump S/D Y II. PNEUMATIC OPERATING MECHANISM Functional checking of auto-startingof 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 S/D Y 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 *At time of commissioning then after 6 months and one & half years of commissioning and thereafter once in every three years.
D.BREAKER OPERATION CHECKS CB Operating Timings (Main, PIR, Aux.)S/DY * Static Contact ResistanceS/D2Y Dynamic Contact resistance(DCRM) Contact Travel,** Contact Speed,** Contact wipe, Arcing contact length S/D2Y Checking of Pole discrepancy relayS/DY Functional checks, duty cycle operation including rapid re-closing (O-0.3s-CO) S/DY Checking of all operation lock-outsS/DY Checking of all interlocksS/DY Checking of pressure settingsS/DY * - For all HV/EHV Circuit Breakers only ** - For 400kV BHEL, CGL & ABB make CBs only E. MEASUREMENT/ TESTING Checking of close/trip coil currentsS/DY Checking of healthiness of Operation Counter S/DY Capacitance and tan measurement ofgrading capacitors S/D4Y* * First time after one year from commissioning and then once in every four years
3.CURRENT TRANSFORMERS Measurement of Tan and Capacitance S/D2Y* DGA and testing of other parameters of oilS/DSOS Thermovision Scanning of CT and Top domeW S/DY Checking of Bellow ExpansionW S/DM N2 Pressure CheckingS/D2Y *- 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/DY Checking for any breakage or cracksin cementing joint S/DY Capacitance and Tan measurement S/D3Y * Measurement of voltage in S/Y MBW S/D6 M** Thermo vision Scanning of Capacitor stacksW S/DY *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 Checking of leakage current *(Third Harmonic Resistive Current) W S/DY Testing of countersW S/DY Measurement of Capacitance and Tan and IR of each stack S/DSOS 5.SURGE ARRESTERS * Leakage current measurement to be carried out after annual maintenance
6. ISOLATORS AND EARTH SWITCHES MAINTENANCE OF OPERATING MECHANISM Linkages including transmission gearsS/DY Stopper boltsS/DY Cleaning of auxiliary switch contacts and greasing with silicon grease S/DY Lubrication of operating mechanism. Hinges, lock joints on levers, Bearings S/DY Checking of all mounting bolts for tightnessW S/DY MAIN CONTACTS Cleaning and lubrication of main contactsS/DY AlignmentS/DY Main contact resistance measurementS/D4Y Tightness of Bolts, nuts and pins etc.S/DY Cleaning of support insulators and checking of insulator cracks, if any S/DY Checking of InterlockS/DY EARTH SWTICH Checking & Alignment of earthing bladesS/DY Cleaning of contactsS/DY Contact resistanceS/D4Y Operation of earthing switchS/DY Checking of Aluminum / Copper flexible conductor S/DY Checking of earth connections of structure and MOM box S/DY
7. WAVE TRAPS Tightness & cleanlinessS/DY General inspection / cleaning of tuning unitS/DY 8. AIR CONDITIONING PLANT Checking of oil pressure switch. LP/HP, cutout switches, solenoid valve, thermostat, Humidistat etc. S/DY Checking Operation of Level switchS/DHY Checking Water qualityW S/DHY Cleaning of nozzles for cloggingS/DQY Lubrication of moving partsS/DHY Terminal connection checkingS/DHY Cleaning of Bus Bars, Insulators etc.S/DY Tightness of the connectionsS/DY Checking of all interlocksS/DY 9. BATTERIES AND DC DISTRIBUTION SYSTEM Checking control cards of charger & Measurement of test point voltage values S/DY Battery Impedance testingW S/DY Discharge test of Battery SetW S/D3Y Checking of any earth fault (If E/F relay not provided) W S/DM Testing of DC E/F and Under Voltage relaysS/DY
10. FIRE PROTECTION SYSTEM Cleaning/Replacement of Air FilterWS/DM Checking of compressor oil and replace if necessary S/DQY Maintenance & cleaning of compressor valves, gaskets, valve plates and replace, if necessary S/DQY Operation check of low oil level switchS/DQY Cleaning and checking for seating of the breather valve S/DQY Cleaning of NRV/HP tankS/DY General overhaulS/DSOS DetectorsW S/DM i)Sequence test for annunciation in Control Room panel ii)Smoke test iii)Cleaning I.DIESEL ENGINE Checking/replacement of fuel oil filter Lube oil filter, Air filter S/DY Pump OverhaulingS/DSOS Checking of belt tightnessS/DQY Cleaning of oil strainerS/DQY Checking of alignment of pump setS/DY OverhaulingS/DSOS Checking of pressure of the hydrant system at the remotest end, auto-starting of pumps, diesel engine etc. S/DY Operation of Deluge system, check outlet pressure check alarm, check starting of Diesel/electrical pump. S/DY
15.PREVENTIVE MAINTENANCE SCHEDULE FOR DG SET Replacement of oil filter after recommended running hours W S/DY/SO S Check for fan hub, drive pulley andwater pumpW S/DY Replacement of Air cleaning elementW S/DY Check for Governor linkages, fuel transfer pump, fuel line connections W S/D Y Drain Sediments from fuel tank, change fuel filter and clean fuel tank breather W S/D Y Stator winding IR measurementS/DY Checking/Cleaning of Slip ring and itsbrushesS/DY Testing of protection/control relays and a. alarms S/DY Check for air leaks and exhaust RestrictionsS/DY