GB658823A - Improvements in and relating to earth leakage protection systems for electric motors, cables and other apparatus - Google Patents

Abstract

658,823. Protective cut-out arrangements. BROOKE, W., and BALDWIN, H. T. April 29, 1949, No. 11400. [Class 38(v)] In an earth leakage protective arrangement for a motor or other apparatus, the reclosure of a circuit breaker or contactor is prevented under fault conditions by a lockout relay energized by rectified A.C. which is, or which is derived from, current injected through the fault circuit. The motor B is supplied from lines L1...L3 through a contactor C which is closed by a coil C4 on the operation of a start button g and maintained closed by auxiliary contacts C5. When the contactor C is closed, auxiliary contacts C6 are changed over to connect the secondary winding M4 of a core balance transformer M to a bridgeconnected rectifier R supplying the coil S1 of the lockout and leakage relay S. The unbalance resulting from an earth fault such as that indicated at 12, causes the energization of the winding M4, which through the rectifier energizes coil S1. The relay contacts S2 are opened and the coil C4 is de-energized allowing the contactor C to open. The secondary winding f2 of an " injection " transformer f is now connected by the contacts C6 to the rectifier R as shown and current flows from the winding f2 through connection 20, contacts C6, rectifier R to the neutral point N1 of an inductance A, through winding A1 of the inductance, winding M3, fault path 12, earth and back through connection 15 to secondary winding f2. Thus the relay coil S1 is energized from the rectifier R by the current through this circuit and the relay contacts S2 are held open to prevent the reclosure of the contactor C until the relay S is de-energized by the removal of the fault 12. In modifications (Figs. 2 and 3, not shown) each transformer may be associated with its own individual rectifier and. a resistance may be used in place of the neutral point inductance A. Specifications 605,927 and 623,911 are referred to.