GB849164A - Improvements in or relating to electromagnetic relays - Google Patents

Abstract

849,164. Electrically-released switches; electromagnetic relays; protective cut-out systems. TELEMECANIQUE ELECTRIQUE. Jan. 24, 1957 Feb. 6, 1956], No. 2615/57. Class 38 (5). A relay intended to control a load circuit via a main contactor and to open the circuit should the current in the latter reverse or decrease below a certain minimum, comprises, Fig. 1, a magnetic yoke having cores 1, 2 connected by a bar 3 and coils 26, 27 adapted, respectively, for connection in the controlling-circuit and the load circuit. A ring 4 of " Siconal " (Registered Trade Mark) having magnetic remanence properties is interposed between the core 1 and bar 3 whilst a non-magnetic ring 20 is interposed between the core 2 and the bar. An armature 13, 28 pivoted at 21 is biased by a spring 12 so that a bridging contact 16 thereon normally disengages a pair of fixed contacts 17. In a modified relay, Fig. 3, a U-shaped yoke 31 is formed of laminations having magnetic remanence properties and carries a controlling coil 33 and load-circuit coil 34, the contact-carrying armature being pivoted at 37 and biased to the open position by a spring 39. In use as a reverse current relay Rr, Fig. 4, the controlling winding is denoted by Rr53 and the load circuit winding by Rr54, the load circuit by 59 and the main contactor operating coil by Di58. To close the main contactor contacts Di61 the start button is pressed to energize an auxiliary relay Rd57 whereby contact Rd62 closes and coil Rr53 is energized across a normally-closed auxiliary contact Di60 of the contactor. The relay Rr closes its contact Rr55 and the contactor coil Di58 is energized. Closing of the contactor energizes the coil Rr54 which, in conjunction with the remanent magnetism, holds the relay Rr closed against the action of its opening spring, reversal of the load circuit current permitting the spring to open the relay. The auxiliary relay Ra having a winding Ra56 controls contacts Ra to prevent repeated operation of the contactor Di should the start button be held depressed under fault conditions in the load circuit. In use as an " under current " relay Ri, Fig. 5, having a controlling coil Ri64 and load circuit coil Ri65, the load circuit is denoted by 67 and the main contactor by L. Closure of the start button energizes coil Ri64 across the normally-closed auxiliary contacts L70, L71 of the contactor whereby contact Ri66 closes to energize the contactor which thereupon closes the load circuit contacts L75. Thus, initially, the relay Ri is held closed by the coil Ri65 in conjunction with the remanent magnetism. The contact L71 is opened through a time-delay mechanism upon closing of the contactor, the time delay being sufficient to allow the load circuit current to attain its normal value. When the contact L71 opens a current passes through the coil Ri64 in the reverse direction, the circuit including resistances 76, 77 and a rheostat 72. Thus the coil Ri64 acts in opposition to the coil Ri65 and the magnetic remanence and upon a subsequent fall in the load circuit current, the relay Ri is opened by its spring.