GB646901A - Improvements relating to circuit arrangements for the control of a direct current relay - Google Patents

Abstract

646,901. Automatic control systems. WESTINGHOUSE BRAKE & SIGNAL CO., Ltd., STEVENS, S. A., and DUCKITT, H. Aug. 13, 1948, Nos. 21405/48 and 5821/49. [Class 38 (iv)] In a automatic voltage or current control system, the energy stored in the electromagnetic field of a relay is used to open the contacts of the measuring relay, the amount of opening varying inversely with the magnitude of the deviation measured. The voltage of the load L fed by a rectifier 26 from a 3- phase supply through a voltage regulator 24, is controlled by connecting the coil 2 of a polar relay across the load in series with an opposing reference voltage 40. Load voltage deviations cause contact 3 to close on to, e.g. contact 12, 2 (from rectifier 14 through resistors 21, 22) and short-circuiting control relay B. Control relays A and B are connected in series across the auxiliary D.C. supply from rectifier 14 and arranged so that neither is sufficiently energized to operate until one or the other is shortcircuited. Operation of relay A closes contact A2, operating an intermediate relay 32 controlling the field of a reversible motor 29 driving the voltage regulator 24. Simultaneously, the contact A1 is closed to energize a time-delay relay C which, after the delay (during which the voltage regulator is operating) opens the contact C1 to open the circuit supply to the control relay A. The transient induced current in the coil of this relay discharges through the polar relay 2, opposing the normal energization due to the load voltage. The contact 3 therefore opens, the distance moved depending upon the magnitude of the load voltage error, i.e. for small deviations the contacts open further than for large deviations when the relay is strongly energized. Opening the polar relay opens the control relay A, de-energizing the regulator controls and de-energizing the time-delay relay C so that the contacts C1 again close and the cycle is repeated, the polar relay reclosing the more rapidly the greater the load voltage error to be corrected. The intermediate relay 32 has slow release characteristics so that if the polar relay 2 recloses very rapidly, the relay 32 will still remain closed to effect continuous operation of the voltage regulator. In a modification, Fig. 2 (not shown), the relay 32 is omitted, the regulator being controlled directly by the control relays A, B, and the time delay relay C is normally energized, being de-energized by the control relay to effect the delayed opening of the control relay circuit. In a further modification, Fig. 1 (not shown), the polar relay has one pair of contacts only operating on the upper limit, and a single control relay operates the regulator,