Norms of Protection

For Transmission & Distribution Lines

Notes

i.        On some of the old 220KV lines one distance scheme with backup directional IDMT 3 O/L & E/L relays were provided.

ii.      On some of the 132KV grid lines, only distance scheme is available

iii.    Very few 66KV lines are in service (which are also being phased out)

Busbars : All 220 KV busbars will have busbar protection scheme with main and check  

    zone.

For POWER STATIONS

Breaker failure protection:      The LBB protection scheme will be provided for all 220KV stations (along with busbar protection scheme)

Transformers

i.           No Buchholz relay for transformers below 500 KVA capacity

ii.         Transformers upto 1500 KVA shall have only Horn gap protection

iii.       Transformers above 1500 KVA and upto 8000 KVA of 33/11KV ratio shall have one group control breaker on HV side and individual LV breakers if there is more than one transformer.

iv.       Transformers above 8000 KVA shall have individual HV and LV circuit breakers.

v.         The relays indicate above shall be provided on HV and LV

vi.       LAs to be provided on HV & LV for transformers of all capacities and voltage class.

vii.     OLTC out of step protection is to be provided where Master follower scheme is in operation

viii.   Fans failure and pumps failure alarms to be connected.

ix.       Alarms for O.T., W.T., Buchholz (Main tank & OLTC) should be connected.