GB564469A - Improvements in or relating to protective systems for electrical apparatus - Google Patents

Abstract

564,469. Protective cut-out arrangements. BUDD MANUFACTURING CO., E. G. July 1, 1943, No. 10702. Convention date, July 4, 1942. [Class 38 (v)] Failure of one of a pair of grid-controlled, reversely-connected valves 15, 16, shown as ignitrons in the circuit of a welding-transformer, causes opening of the circuits controlling the timed actuation of the grids 19, 20. The latter are connected to a timing-control means 23 for energizing them alternately, the control, circuits including gas-discharge tubes 24, 25 having their grids and cathodes connected to the means 23 and their anodes connected to the respective anodes of the valves 15, 16. The protective 'means comprises a saturable reactor 31 in series with a solenoid 33, which may be shunted by a capacity 32, and, as shown, a pair of reverselyconnected vacuum tubes 51, 52. When a valve fails, the normal alternating current in transformer 10 and reactor 31 is replaced by a series of unidirectional impulses which, owing to the retarded decay of flux in the non-conducting periods, causes a cumulative build-up of flux and hence core-saturation in reactor 31, so lowering its impedance. The resulting voltage increase in solenoid 33 opens at 41 the circuit of solenoid 35 which, at contacts 37, 38; disconnects the anodes of tubes 24, 25 from the main valves and so puts them out of operation. A manual switch 42 energizes solenoid 35 to restore the supply. The grids 54, 55 are preferably transformer-connected to a phasedisplacing circuit 62, 65, whereby the tubes 51, 52 only conduct for a small part of the halfwave in the neighbourhood of voltage-zero. In a simple form, these tubes and associated circuits are dispensed with, Fig. 1 (not shown). The invention is illustrated by a set of curves, Figs. 3-6 (not shown).