GB530198A - Improvements in or relating to the protection of electric rectifier systems - Google Patents

Abstract

530,198. Protective cut-out systems. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. June 30, 1939, No. 19044. Convention date, June 30, 1938. (Class 38 (v)] [Also in Group XXXV] An A.C. supply 10... 12 energizes a D.C. load circuit 13, 14 over rectifiers 18 &c. in parallel between the 6-phase secondaries of transformer 15. Shunts 33, 33<1> arranged in the cathode circuits are interconnected by the moving coil 35 of a centre-zero relay, the fixed contacts 41, 42 of which are respectively connected to the trip coils of breakers 47, 54 in the anode-leads 28, 31. Backfire in a rectifier causes the appropriate relay to deflect in the direction to trip only the faulty one, and preferably with a time-delay so as to allow other relays to extinguish the backfire by momentarily opening the ignition circuit. The latter includes the rectifier-electrode 26 and a gas-discharge device 55 having its anode connected to the anode-lead 28 or 31 and its grid connected to the appropriate secondary 59 of a transformer, the circuit being completed through the star-point, the + lead 13, rectifier 18, and contacts of a continuously-energized relay 65. The latter and the corresponding relay 77 of rectifier 19 have their coils short-circuited, on backfire, by contacts of relays 73, 74 energized in series from current transformer 70 in the supply line. When the backfire is thus extinguished, relays 65, 77 remake the ignition circuits and operation of the rectifiers is resumed. In a modification, Fig. 3 (not shown), the relay 65, when de-energized opens the grid circuit of device 55 and closes at back contacts the circuit to a negative-bias source, so blocking the device. The invention is also applicable, Fig. 4 (not shown), to a pair of six-anode rectifiers in parallel with a relay connected across the cathode circuits as in Fig. 1.