Some aspects of generator backup protection in relation to synchronous-machine performance during h.v.-system faults

The fault performance of large generator units is considered in relation to the selection of generator-backup-protection settings, and a method of determining protection performance is presented, based on a simplified analysis of generator fault currents and neglecting rotor-angle swings. The validity of this approach is demonstrated and the method is used to determine the fault performance of negative-phase-sequence current and overcurrent protection. Alternative methods of overcurrent protection are examined which appear to provide improved backup protection for internal and external faults.