Pilot wire relays
Pilot wire relays
(OP)
Sir,
What is the purpose of giving pilot wire relays in all terminals? Is it not enough providing (summation)CTs in all terminals and providing pilot wire relay at one only and also providing intertrips to other terminals from the relay?
What is the purpose of providing resistance to pilot wire loops?
Please give answer.
with regards,
appunni
What is the purpose of giving pilot wire relays in all terminals? Is it not enough providing (summation)CTs in all terminals and providing pilot wire relay at one only and also providing intertrips to other terminals from the relay?
What is the purpose of providing resistance to pilot wire loops?
Please give answer.
with regards,
appunni






RE: Pilot wire relays
Also, since the relay has to trip a circuit breaker at a remote end you find that the resistance ot the cables connecting the trip coil (or aux relay) at the remote end to the differential relay become more and more significant and you reach a point where the voltage drop in the cable would be such that there would be insufficient voltage available to energise the trip solenoid or aux relay at the remote end.
A pilot scheme overcomes all of these difficulties and the ends of the circuit being protected can be very distant.
A pilot scheme can tolerate only so much pilot resistance. Some are designed for a maximum pilot resistance. For shorter distances between ends (where the resistance of the pilots will be less), you add resistance to the pilots via adjustible padding resistors to bring the pilot resistance up to the design level.
RE: Pilot wire relays
If the relay instruction manual is unclear, you might refer to Pilot Protective Relaying book by Walt Elmore (retired) from ABB. Else, review applicable information of single-function electromechanical pilot-wire protection:
http://www.abbus.com/abbrelays/pdf/ILsIBs/Cs41/419714l.pdf
http://www.abbus.com/abbrelays/pdf/ILsIBs/Cs41/41-971.3M.pdf
http://www.abbus.com/abbrelays/pdf/ILsIBs/Cs41/419712h.pdf
http://www.abbus.com/abbrelays/pdf/400/41_471e.pdf
RE: Pilot wire relays
Sir, In an ordinary differential relay, the relay is placed in a location where the potential across the relay is neglibly small as the lead plus CT resistance to either side will be almost equal. But in pilot wire relays are on terminal ends. In a current circulation scheme, how can this be achieved? If it is not, will there not be spill current in the pilot wire relays which may make operation during external faults? I request for your expert and detailed comments.
With regards,
appunni
RE: Pilot wire relays