5 Operation & maintenance of LT Switchboards (LTPCC, PDB, ACDB, DCDB, WDB)
LT switchboards are installed in all LBDS under PPDS for distribution of 3 phase & single phase power for lighting up the substation, AC & DC control supply for all the switchboards & transformers and street lighting. Therefore proper operation & routine maintenance of all the LT Switchboards are necessary to avoid failure of lighting circuit and protection system of the power system.
1.1. Operation of LT Switchboards (LTPCC, PDB, ACDB, DCDB, WDB)
1. Switching ON and Switching OFF of LT switchboards (Incoming, Outgoing) as per SOP locally when required according to load requirements, instructions from NMDC authorities and requirements of downstream consumers.
2. Switching operation will be done from switchboards in LOCAL mode.
3. In case of tripping of feeder, Shift in-charge should inform to CCC and site incharge (contractor) about the incident.
4. Incident report explaining root cause, remedy & other relevant details will be prepared and submitted to NMDC authority.
5. Shift in-charge/Engineer should doubly ensure about the healthiness of circuit before charging of feeder if it has tripped on any type of fault.
6. Maintaining records of all the operations, charge-uncharged feeder details and records of loads such as voltage, current, power factor, frequency, connected load, energy consumption on hourly/daily/weekly/fortnightly/monthly/quarterly/half yearly and yearly basis.
7. Maintaining records of power failures, breakdown, shutdown etc with proper reasons.
8. Operation will be done in three shifts & general.
9. To protect the system from any fault, ensure protection system & control power system is working properly.
10. Observing the Switchgear continuously and reporting problem to NMDC authority
11.Maintaining cleanliness around the panels/Switchboard.
1.2. Maintenance of LT Switchboards (LTPCC, PDB, ACDB, DCDB, WDB,MLDB)
Maintenance of electrical equipment is necessary to enhance the life expectancy of the electrical system. To avoid or mitigate the rate of failure of electrical system, routine or scheduled maintenance to be performed on the system. The maintenance of the system to be done as per Standard Maintenance Procedures.
The maintenance scope (include both preventive & breakdown maintenance) is indicative only and shall include other maintenance activities required for satisfactory & smooth operation. Preventive Maintenance shall be routinely carried out as per the details provided.
Breakdown maintenance shall be provided as and when the situation warrants with a failure/fault in the system.
Though the following list contains several individual jobs they could be executed in a combined scope as in the servicing or overhauling of the component.
1.1.1. Inspection & Maintainence Checklist Of Lt-Switchboards
A.DAILY INSPECTION CHECKLIST
1. The switchboard shall be completely equipped with circuit breaker(ACB & MCCB), miniature circuit breakers, relays, contactors, MPCB, measuring instruments, operating switches, push buttons, fuses, indicating lamps, annunciators, diodes, cables, Surge arrestor etc. Regularly observe the status of all the installed equipment in all the switchboards and maintain record if found any equipment faulty.
2. Visually inspect front & rear side of SWBDs. If any abnormalities found inform to NMDC authorities and take preventive measures to avoid any mishap.
3. To avoid rodent entry ensure no extra gap or opening in the switchboards and also ensure all the doors of panel are in closed condition. If any extra gap or opening in the panel, fill those gap or openings.
4. Observe that whether the status of all the installed equipment in charged & uncharged feeders is as per Scheme or not.
5. Feeders under breakdown/shutdown should be tagged with LOTO.
6. Inspect for evidence of overheating or any damages in equipment.
In addition to above, following should also be attended
B.MONTHLY MAINTENANCE CHECKLIST
1. Attend checklist of daily schedule.
2. Issue PTW for maintenance
3. Maintain cleanliness of all the installed equipment using cotton linen cloth or cleaning agent.
4. Investigate for evidence of moisture condensation in breaker chamber. If found, put the space heater ON.
5. Check the healthiness of all the installed equipment (mentioned above).
6. Check breaker ON/OFF operation & Spring charge/discharge indication. Record & check whether the breaker counter reading is increasing or decreasing. If decreasing, it needs to be rectified. If breaker counter’s reading crosses 1000, breaker needs detailed maintenance as mentioned in annual maintenance scheme.(for Air Circuit Breaker(ACB))
7. Inspect for evidence of overheating.
8. Check overcurrent & earth fault setting in ACB & MCCB.
9. Check all wiring for tightness of connections and possible damage to insulation.
10. Check earthing system & panel lighting.
11. Operate the breaker Electrically & Manually and observe the movement of tripping & closing coil plunger.(For ACB) and check operation of MCCB.
12. Visual inspection of the breaker and remove dust and contaminants from the ACB housing, Do not use compressed air.
13. Check the tightness & dressing of all the control cables, earthing wires & CT, PT links.
14. Ensure all spare control cables are insulated and tape the unused cables.
15. Inspect Fuses rating as shown on scheme & check continuity for all the fuses.
16. Check the CT & PT cables, TB link and test link block tightness.
17. Record & verify the Relay measurement, parameters, and protection settings as per approved data.
In addition of the above, following should also be attended
C.QUARTERLY MAINTENANCE CHECKLIST
1. Attend checklist of daily & Monthly schedule.
2. Spare feeder ON/OFF operational check (Test position )
3. Perform change over for Section 1&2 in those LT SWBD where the scheme has provided.
4. Inspect for evidence of overheating
5. Check all negative/Positive interlock
6. Check the all Compartment Door earth tightness
7. Check doors and gasket for damage.
8. Check door handles, locking bars, keys and interlocks for positive operation.
In addition to above, following should also be attended
D.HALF YEARLY MAINTENANCE CHECKLIST
1. Attend checklist of daily, Monthly & quarterly schedule.
2. Inspect the interrupter operating mechanism carefully for loose nuts, bolts and damaged parts. All cam latch and roller surfaces should be inspected for damage or excessive wear.
3. Perform a visual inspection of the MCCB, CT, PT, CTF, Bus-bar and remove dust, contaminants from the breaker housing, insulators, Do not use compressed air.
4. Lubrication On all sleeve, and roller bearings apply sufficient amount of lubricant.
5. Check for proper mounting of TB’s MCB’s on rail channel
6. Ensure that there is no binding or friction between shutter & ACB contact shrouds during rack in/out and ensure that free movements of ACB during rack IN/OUT
E.ANNUAL MAINTENANCE CHECKLIST
1. Attend checklist of daily, Monthly, quarterly & half yearly schedule.
2. Breaker-Insulation resistance between Poles (500V)(In ACB)
3. CT & PT wire tightness & TB link tightness
4. Cleaning and applying petroleum jelly
5. Rack IN/OUT Mechanism operational check
6. Bus bar IR (PCC,PDB)
7. CT/PT IR, Ratio, Winding Resistance Test
8. Coil Resistance Measurement (Closing and Tripping)(For ACB)
9. Functional Check of Tripping Unit Of ACB
10. Contact Resistance Measurement Of ACB
11. Pick & drop test of electromechanical relay(Wherever applicable)
12. Breaker section-Lubrication All sliding and rotational parts of linkage
13. Rack IN/OUT mechanism and roller operational check.
14. Spring charge motor cut-off limit switch operational check
15. Test to be conducted on current & potential transformer: Ratio test, Winding resistance, Insulation resistance. Compare the test result with last test result. .(Wherever applicable)
16. Control busbar-Cleaning, bus tightness, space heater functional check, IR test (Wherever applicable)
If any abnormality found, inform site in-charge