Static Mho Distance and Pilot Relaying

Design principles and typical circuits are described for new directional-comparison static-relaying equipment for transmission-line protection. Mho distance units, with offset-impedance supervision, are used for phase faults. The equipment is designed for use with either carrier-current or microwave communications channels, uses semiconductor circuitry throughout, and features high speed: less than 1/2 cycle for 3-phase faults and less than 1 cycle for unbalanced faults.