GB703790A - Improvements in or relating to electric relay devices - Google Patents

Abstract

703,790. Load-shedding arrangements. VENNER. Ltd., [Formerly VENNER TIME SWITCHES, Ltd.]. Sept. 17, 1952 [Sept. 18, 1951], No. 21928/51. Class 38 (4) A consumption circuit is supplied through automatic switchgear adapted to allow unrestricted load on the circuit during conditions of normal supply system voltage but which disconnects the circuit from the supply system if the circuit loading exceeds a predetermined value during a period of reduced supply system voltage. In the arrangement shown in Fig. 13, the consumption circuit is connected between terminals 51, 96 supplied from mains terminals 33, 51 a resettable electromagnetic switch having contacts 34, 35 and operating coil 4 and the bimetal strip of an overload switch having contacts 86, 87, 89, 94. Switch coil 4 is connected across the mains in series 'both with the contacts 86, 87 and a further contact pair 62, 63 which are controlled by an eddy-current disc 8 having a shaded pole field system energized from the mains by a voltage coil 7 and a return spring 66 which opposes the torque produced by the field system and tends to tender the disc in a direction to close the contacts 62, 63. Under normal voltage conditions the torque due to the field system maintains contacts 62, 63 open so that, although the value of the load current. may be much more than sufficient to close the thermally operated contacts 86, 87, switch coil 4 is not energized and no limitation is imposed on the current in the load circuit. However, upon a predetermined reduction of mains voltage, spring 66 causes contacts 62, 63 to close, so that coil 4 is energized and effects disconnection of the load circuit of contacts 34, 35 if, or when, the load current is sufficient to close the thermal contacts 86, 87. These contacts, which latch but, may be reclosed, manually, and will remain closed if the circuit loading has been reduced to a value insufficient to close contacts 86, 87. Contacts 89, 94 provide a protective shunt path on the bimetal strip at high values of load current. The thermal switch may be provided with ambient temperature compensation. Its contact 86 is adjustable relatively to contact 87 to provide for load adjustment. Snap-action of the voltagecontrolled contacts 62; 63 may be provided by a stud 107 of magnetic material arranged on the disc 8 so as to move in the vicinity of the usual brake magnet 106. The yoke of the electromagnetic switch may provide the return path for the flux of the field system energized by coil 7. Specification 703,663 is referred to.