Analysis of an accelerated trip scheme for faults in the secondzone of protection of a transmission line

An analysis of a scheme of accelerated trips for faults in the second zone of a transmission line distance protection system is given. By the use of the two-port network theory, variations of the sequence currents and voltages are analyzed when the fault occurs on the protected line followed by a trip of the circuit breaker on the other side. The analysis is supported by tests performed on a laboratory model of a power system. The new scheme can improve sensitivity and avoid improper operation. Thus, it may be possible to use this scheme instead of pilot protection and alleviate any problems caused by the nonavailability of a sufficient number of communication channels for remote control and relaying