Distance protection performance during simultaneous faults

The paper considers the performance of both unswitched and switched distance protection schemes using polarised-mho relays on systems subjected to simultaneous faults. The disturbances considered are flashoverfaults to earth, cross-country earth faults and open-conductor plus earth faults on a double-circuit 132 kV transmission system. Consideration is also given to protection performance for double earth faults separatedby a star-delta transformer. Differences in protection philosophies of British and Continental relay manufacturers are highlighted and a comparison is given for switched schemes employing overcurrent starter units.