Improvements in or relating to devices for the detection of insulation faults with respect to earth in polyphase alternating current electrical networks with an insulated neutral

摘要

1,020,103. Fault testing. CHARBONNAGES DE FRANCE. May 8, 1964 [May 10, 1963], No. 19331/64. Heading G1U. [Also in Division H2] A circuit for indicating insulation faults with respect to earth of a network 2 supplied with polyphase A.C., e.g. from a transformer 1, with insulated neutral, comprises semi-conductor rectifiers 7A-7C connecting each phase to a common point 5 which is connected to earth through a resistance 8 and a current measuring instrument 10. The meter 10 may be calibrated in ohms and checks the overall insulation of the three phases as it will give the same indication for a resistance fault R on one phase as for 2R on two phases or 3R on three phases. A relay 9 may be included in the circuit to open the circuit-breaker 3 if there is a fault. The rectifiers 7A-7C may be protected by fuses 14A-14C and indicator lamps 15A-15C may be connected across the fuses.