Multi-zone current differential protection for transmission networks

The main idea of this paper is to combine the multi-zone operating features of a pilot aided distance scheme with the unit protection features of a current differential relay. The combination, a pilot aided multi-zone differential protection scheme can cope with main or primary relay failure, incorrect measured or communicated data and the problems caused by a "stuck" circuit breaker. Simulation studies are used to illustrate the benefits of the scheme when applied to the main and back-up protection of a double circuit EHV transmission network.