Remote Control of Network Protectors

Two low-voltage a-c networks have been installed in Tennessee, using a radically different protective scheme. The customary master relays, phasing relays, and associated current transformers have been omitted from the network protectors using in their place a remote-control system of pilot wires operated from relays at the supply substation which protect the high-voltage cable feeders. In contrast with previous pilot-wire-protected network systems utilizing looped primary circuits with secondary transformer fuses^1,2, these networks retain the radial supply and electrically operated secondary air circuit breakers of the more conventional systems. Previous experience has pointed to operating advantages of a remote control system provided a thoroughly reliable installation could be secured at a reasonable cost. The system described does not exceed the cost of conventional relay installations and it is felt that inherent hazards to reliability have been overcome.