GB682425A - Improvements in and relating to electric protective systems for motors and other equipment - Google Patents

Abstract

682,425. Protective cut-out arrangements. BROOKE, W., and BALDWIN, H. T. Sept. 26, 1950, No. 23519/50. Class 38 (v) In an earth leakage lockout arrangement for a motor M or other apparatus, a rectified current injected through an earth fault circuit by means of an artificial neutral point impedance U is applied to the D.C. winding of a transductor A to effect the energising of a relay K which opens and remains open to prevent the closing of a contactor C until the fault has been cleared. Thus so long as the fault indicated at 24 persists, a circuit is established from a transformer secondary winding RS<SP>2</SP> and a rectifier E to earth, through earth connection W, the fault, line X, impedance U, auxiliary contacts C4 of the contactor C and the D.C, control winding A4 of the transductor. The A.C. windings A<SP>1</SP> A<SP>2</SP> of the transductor now have minimum impedance and the coil of the relay K is energised from the rectifier F in series with the A.C. windings. The relay contacts K<SP>1</SP> open the remote control protective circuit of Specification 669,133, [Group XI], de-energise a relay H which opens the circuit of the closing coil C<SP>5</SP> of the contactor, the contactor being maintained open so long as the fault remains. Should the fault occur when the motor is in use the contactor is opened by an earth leakage protective circuit which is combined with the lockout arrangement. In Fig. 1 on the occurrence of the fault 24, current flows from the line X through the fault 24, the earth, connection W, resistances T, S, contacts C4 and impedance U to lines Y, Z. The fault current in this circuit establishes a potential across the resistance S, which potential, after rectification by a rectifier G<SP>1</SP>, is applied across a further D.C. control winding A<SP>3</SP> on the transductor. The relay K is energised and opens its contacts K<SP>1</SP> to open the contactor C. the changeover of the contacts C4 to the position shown then render ing the lockout circuit effective. In an alternative arrangement for use where the supply neutral is earthed, the winding A<SP>3</SP> is energised on the occurrence of a fault by a core balance transformer, Fig. 2 (not shown). Specifications 605,927, 623,911, 636,720, 658,823 and 665,576 also are referred to.