What is the difference between 67N and 67NI protection functions in Vamp relays?
Directional earth fault protection (67N) in Vamp relays is capable of protecting against intermittent (recurrent) earth faults.
However, transient intermittent earth fault which typically appears in underground cable networks when cable insulation level is reduced, transient intermittent earth fault protection (67NI) should be used.
Additionally, 67N can be based on either calculated zero sequence signals (Uo & IoCalc) or directly measured zero sequence signals (Uo & Io1 or Io2) but 67NI needs to have directly measured signals (Uo & Io1 or Io2).
However, transient intermittent earth fault which typically appears in underground cable networks when cable insulation level is reduced, transient intermittent earth fault protection (67NI) should be used.
Additionally, 67N can be based on either calculated zero sequence signals (Uo & IoCalc) or directly measured zero sequence signals (Uo & Io1 or Io2) but 67NI needs to have directly measured signals (Uo & Io1 or Io2).