Improvements in and relating to earth leakage protection systems for electrical circu

摘要

860,430. Protective cut-out arrangements. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. May 8, 1957 [Feb. 16, 1956], No. 4879/56. Class 38 (5). An earth-leakage protective system for preventing the closure or reclosure of a circuitbreaker during the existence of an earth fault includes a relay controlling the circuit-breaker, the relay having an operating winding, a permanent magnet to retain the relay in an operated condition and a winding for overcoming the permanent magnet under the control of a local circuit including a source of current connected between earth and a conductor on the outgoing side of the circuit-breaker. The system may be generally in accordance with any of the arrangements of Specification 675,514. In the arrangement shown, the operation of a pushbutton switch 7 causes the energization of the operating winding RA of the relay from a transformer 8 and rectifier 9. The relay closes its contacts R1 in a contactor coil circuit and is held closed by the permanent magnet (not shown). The operation of a " start " switch 5 causes the energization of the contactor closing coil C to close main contacts C1 . . . C3 and holding contacts C4, and the opening of contacts 11 in the local circuit. In the event of an earth fault, a winding RB of the relay is energized from a core-balance transformer 14 and overcomes the permanent magnet to open the contacts R1 so that the contactor is opened. The local circuit is now completed by the closure of the contacts 11 and by the fault path so that current may flow from the source 8 and the rectifier 9 through star-connected rectifiers 10, the phase conductors 1, motor 2, the fault path, earth and the winding RB to prevent the operation of the relay and the reclosure of the contactor. If an earth fault should occur when the contactor is open, current flowing in the local circuit will prevent the closing of the contactor as described above. The switch 7 may be provided with normally-closed contacts in series with the coil C so that the contactor cannot be closed when the winding RA is energized.