Question

SUBSTATION RELAY PROTECTION QUESTION:

If there are multiple HV feeder lines from different locations connected to a busbar in a substation, is directional overcurrent protection better than distance protection? Or can both of these schemes be used to isolate the fault.

Answer 1

both of these schemes be used to isolate the fault.:

The directional over current relay operates whenever there will be a power reversal takes place by the fault. under normal condition no power reversal hence the relay will not operate. but when the fault occurs there will be a power reversal and the relay operates and it will isolate the faulty line.

Due to HV feeder lines it is better to use distance protection also because if any over current flows through or any other fault in the middle of the line or at some place of the line , the distance relay will operate by comparing the faulty impedance or admittance with the normal impedance or admittance(by v/i ratio.) ,

Finally the directional relays are suitable at source side and the distance protection or relays are suitable for long line protection. hence it is better to use both combinations.