GB1035328A - Earth leakage protective device - Google Patents

Abstract

1,035,328. Transistor relay circuits. WALLACETOWN ENGINEERING CO. Ltd. Feb. 18, 1965 [Nov. 21, 1963], No. 46105/63. Heading H3T. [Also in Division H2] An earth-leakage lock-out protective arrangement includes a silicon controlled switch SCS1, a constant bias generating means CBGM applying a bias to the switch of a value too low to render it conducting, pulse generating means PGM to apply to the switch an intermittent bias which with the constant bias renders the switch intermittently conducting and means RO for producing pulses antiphased with respect to those of the pulse generating means to render the switch non-conducting after each conducting period. An earth leakage relay RLA is connected in series with the switch SCS1 and is associated with delay means C4, C5, D4 so that the relay remains continuously operated by pulses of current through the switch SCS1 and maintains open its contacts RLA/1 in series with a lock-out relay RLB. In the event of earth leakage, current induced in the secondary winding of a core-balance transformer CBT applies a bias sufficient to render the switch continuously non-conducting so that the earth leakage relay RLA releases and closes its contacts RLA/1. The lock-out relay RLB is now energized and operated to open and lock-out a main contactor MC. When the main contactor is open and an earth fault exists, current flows through an auxiliary primary winding SAW of the core-balance transformer, auxiliary contacts CAC of the contactor, supply conductors SL and the fault path. Current is then induced in the secondary winding FAW of the transformer and biases the switch SCS1 so that it. is non-conducting, the relay RLA is not energized and the contactor MC cannot be closed.