GB893420A - Electric remote control system - Google Patents

Abstract

893,420. Control of A.C. motors. SOC. TECHNIQUE POUR L'INDUSTRIE NOUVELLE S.A. June 21, 1960 [July 31, 1959], No. 21664/60. Addition to 866,175. Class 38 (3). [Also in Group XXX] The two-phase motor control system for railway switch points described in the parent Specification is modified so that the centre point, instead of one end, of each phase is earthed, thereby increasing the safety of the equipment in relation to the phase voltage. The supply is connected to terminals P1a P1b and P2a, P2b, across which are auto transformers I and II, whose centre points are connected to the earthed neutral N. Consequently, it is now the centres of the windings M1, M2 of the motor M which are interconnected by switches N and R during changeover. Reversal of the motor is now achieved by reversing the connections to winding M1 by contacts G3, G4 while keeping those to M2 unchanged. As shown, supervisory current from S reaches rectifier V, via L4 and half of M2, where alternate half-waves are blocked and so return to earth through a circuit which includes the other half of M2, the whole of M1, leads LI ... L3 relay coil H and indicating relay NR, operation of which indicates continuity. Change-over of the points is effected by the energization of relays E, F and G, when the windings M1, M2 are connected to respective phases of the supply and supervisory current is cut off, so isolating the indicating relays NR, RR by the consequent opening of contacts H1. A polarized relay B3, energized in the appropriate direction when the driven element T operates switch R at the end of its travel, de-energizes relays E, F, G to restore the circuits to the inactive state shown and receives its supply from a transformer B5. One side UV of this transformer has opposed half-windings to cancel voltages induced from the other side XY which is across phase II, but a voltage from P1 and neutral, applied to UV, induces a voltage at O relative to X and Y so that current for relay B3 flows from O back to X and Y through a circuit which includes the two halves of transformer I and the rectifier V. An alternative path through transformer II is blocked by choke B4; this is double wound so that it does not impede the motor current which flows in opposite directions in each half.