GB623911A - Improvements in and relating to earth leakage protection systems for electric motors, cables and other apparatus - Google Patents

Abstract

623,911. Protective cut-out arrangements. BROOKE, W., and BALDWIN, H. T. May 28, 1947, No. 14151. Addition to 605,927. [Class 38(v)] In a modification of the earth leakage protection system of the parent Specification alternative means are provided to prevent the reclosure of the circuit breaker or contactor while a fault persists, and comprises a lockout or leakage relay energized directly or indirectly through the fault path. Fig. 1 shows a motor B controlled by a contactor C which' closes under the action of its coil C<SP>4</SP> when a gas-filled triode J fires on the closing of a switch D as described in Specification 568,336. In the event of an earth fault, say 12c on line X, a circuit is established from connection C<SP>1</SP> through neutral point inductance A, changeover switch C<SP>5</SP> operated by contactor C, line 13, relay coil S<SP>2</SP>, line 14, earth and fault path 12c to line X, the potential established across the inductance A operating the relay S to open contacts S<SP>1</SP>. This interrupts the current through coil C<SP>4</SP> and the contactor C opens to protect the motor B. At the same time the switch C' connects the inductance A to the coil R<SP>2</SP> of a relay R which is now energized by the secondary winding F<SP>5</SP> of a transformer F through the fault path. Contacts R<SP>1</SP> open to prevent the re-energization of coil C<SP>4</SP> and contacts R<SP>3</SP> close to light a fault indicating lamp E which is supplied from a secondary winding F<SP>6</SP>. When the fault is removed the relay coil R<SP>2</SP> is de-energized and contacts R<SP>1</SP> reclose to permit the reclosure of the contactor. In a modification (Fig. 4, not shown), the relay R may be energized by the anode current of a further triode having its bias system controlled through the fault path. This overcomes the need for the operating current of relay R to pass through the fault path. In Fig. 2 a second triode K and inductance AA are used instead of relay S. When a fault occurs the bias resistance La of the triode K is parallelled by an inductive circuit comprising line 22, switch C<SP>5</SP>, inductance AA, line 24, line X, fault 12c, earth and line 25. The triode K fires, energizes relay R to open contacts R<SP>1</SP> so interrupting the anode current of triode J and opening the contactor C. While the fault remains, the reclosure of the contactor is prevented as the operation of switch C<SP>5</SP> has re-established the inductive biasing circuit through inductance A. Fig. 3 (not shown), illustrates the application of the latter arrangement to a circuit having a manually closed circuit breaker with a " no-volt no-close " coil, a further relay carrying out the functions of switch C<SP>5</SP>. Specification 605,932 also is referred to.