GB262767A - Improvements in and relating to electrical distribution systems - Google Patents

Abstract

262,767. British Thomson-Houston Co., Ltd., (Assignees of Blake, D. K.). Dec. 8, 1925, [Convention date]. Switching systems; systems depending on the use of transformers.-High voltage mains 1 are connected to a low-voltage network 4 by feeders 7 including circuit-breakers 5, transformer 3 and automatic circuit-breakers 6. Each feeder is associated with a relay 9 for tripping the circuitbreaker 5 on occurrence of reverse energy flow in the feeder from the network due to either a fault or to the magnetizing current of the transformer being drawn from the network due to circuit-breaker 5 being opened. The relay 9 has a voltage coil 10 and a current coil 11 connected across the secondary of an easily saturated current transformer 8 so that the coil is sensitive to small magnetizing currents and yet is not damaged by heavy fault currents. When the circuit-breaker 5 is reclosed, the current coil 11 serves to ascertain when there is equality of voltage and phase on opposite sides of the circuitbreaker 6 and thereupon to energize the closing coil 19. As applied to a polyphase system, there is a relay 9 provided for each phase, the " opening " contacts of the relays being connected in parallel so that a fault on any phase trips the circuit-breaker 6, and the " closing " contacts being in series so that all phases have to be correct as regards voltage and phase before the circuit-breaker is closed.