Performance analysis and design of loss-of-excitation relays. I

A study of two extreme LOF (loss-of-excitation) cases has revealed the necessity for adaptive relaying to speed up tripping of the faulted generator. The natural phase coordinate machine parameters are adopted for phase coordinate simulation. The method allows the seen impedance by the relay to be computed without any simplifications other than those already used by manufacturers to produce the machine parameters. While the seen impedance by the relay is now obtained from time-variant parameters, in this study the relay setting makes use of the conventional dqO parameters for verification of present-day relay performance