High-Impedance Bus Differential with Overcurrent Protection
High-Impedance Bus Differential with Overcurrent Protection
(OP)
I am trying to learn about relaying and on one high-impedance bus differential scheme I noticed it utilizes current elements in the CT circuit. What is the purpose of this? I think one purpose is to detect breaker failure in the event one breaker fails to trip but what are the other uses?






RE: High-Impedance Bus Differential with Overcurrent Protection
RE: High-Impedance Bus Differential with Overcurrent Protection
Overcurrent protection is also provided to respect the limits of the bus itself.
A failed breaker should have its own breaker failure protection. The O/C on the bus may or may not trip for a failed breaker but it is not intended to. Either way, in the case of a failed breaker you do want to clear the entire bus, so as long as that happens in an acceptable time frame all is good. O/C on a bus is typically set high, and could very likely be much higher than fault current from say a single phase to ground fault.
RE: High-Impedance Bus Differential with Overcurrent Protection
The overcurrent function built in to the new digital relays has fairly limited usefulness, mostly used for breaker failure. The relay documentation should cover this.
David Castor
www.cvoes.com