Check list for safe charging of Pooling Sub Station of Wind Farm

Check list for safe charging of 220∕33 KV Pooling Sub Station of a Wind Farm

1.     Phase sequence to be checked at CVT or line PT end (relay panel), bus PT end (bus coupler panel & 33 KV bus end (33 KV Bus PT or incomer feeder panel end).

2.     As DG supply is used for backup power in ACDB so phase sequence with grid power should be checked to avoid mal operation of isolators & OLTC.

3.     Till the operation of DG, we must keep aux. trafo (say 100 or 250 KVA) out of service by keeping 33 KV bus isolator open to avoid back feeding in 33 KV bus & flashing with grid power during charging of 33 KV bus through power transformer (say rating 100 to 150 MVA). Do not forget to paste “Do not operate” Tag for such isolators.

4.     All non relevant isolators must be kept open & AC DC supply should be made off. Put in local mode. Don’t forget to paste “Do not operate” Tag on such isolators.

5.     HF terminal of R & B phase CVT should be connected to PLCC system & not earthed. Knife type Earth switch of LMU should be kept open.

6.     Earth switch of all isolators should be open & any temporary earthing in the switch yard if done during execution must be removed.

7.     Emergency light should be kept ready in case of DG or grid power failure. Emergency lights (110 or 220 or 48 volt DC) are provided in control room.

8.     Part I & Part II or phase I & phase II of 33 KV bus (IPS tube or conductor or bus bar) should be kept separated initially keeping bus coupler in open condition.

9.     Line (220 KV & above in case of PGCIL & 66∕132∕220 KV in case of state grid) will be charged up to the line isolator once grid end breaker will be closed. Line breaker should be kept open at PSS.

10. The main bus 1 (2 bus system) will be charged through closing of line breaker & power transformer (50 or 100 or 125 MVA or XYZ MVA) will be charged through main bus 1. Accordingly bus PT 1 will be in ckt.

11.  All pre commissioning checks of power transformer which includes air releasing from main tank, OLTC tank, HV LV bushing, Buchholz relay etc should be done in correct sequence in presence of OEM engineer. Air cell to be checked & charged again in case, oil level is observed down in prismatic display at conservator which may be due to oil taken in NIFPES.

12. 33 KV bus isolator of power trafo should be kept open initially & should be closed after observing stable operation of trafo. For aux. power we can charge 33 KV bus after some time (say 15 minutes) but all 33 KV incomer feeder breakers should be kept open say min for 12 hours. DG should be made off before this transition to avoid any chances of back feeding.

13. All bird nests in IPS tubes & trafo body should be removed safely without harm to birds if any.

14. NIFPES or FPS (Fire protection system) of power trafo should be taken in line by opening relevant valve in presence of OEM engineer.

15. Power Trafo should be kept charged on no load for min. 12 hrs then only power to be extended to WTG for grid commissioning. During this 12 hrs, abnormal sound & any oil leakages to be observed & OTI∕WTI temp. to be recorded on hourly basis.

16. Necessary testing kit especially stability testing kit should be available at site as grid engineers may check again stability of bus bar & trafo. before charging the system.

17. Electrical operation of all isolators & interlocking to be checked properly in advance.

18. Unused CT core should be shorted & properly earthed. Unused PT core should be kept open. CT secondary terminal S1 or S2 should be earthed as per scheme.

19. Open gland holes in the terminal blocks, CRP, ACDB & all MBs should be sealed by puff seal or white putty or plastic cap.

20. All gantry isolators (breaker by pass scheme) should be kept open & locked as same will be used in emergency in case of failure of breaker.

21. Tan delta point of CT, CVT & PT should be properly earthed.

22. Suitable rating hand gloves (min. 2 pair) & earth rods (1 set-3 nos.) & torch should be kept in control room in advance.

23. In case breaker & isolator operation is done through SCADA then one site engineer should be in switchyard at a safe distance from equipments during first charging. He should be in close coordination with SCADA operator.

24. Whenever power is feed through gantry isolator (breaker by pass scheme) then power to trafo. should be feed through bus coupler only.

25. Ensure 100% completeness & alignment of bus isolators on 33 KV bus both for phase I & phase II to avoid bus shutdown in later stages. It ensures manpower safety also.

26. Safety clearances to be ensured both at 220 KV & 33 KV side considering site peak wind speed.

27. Tightness of all clamp, connectors & terminations at MB & CRP should be re ensured before charging the system.