GB1161834A - Improvements relating to Alternating Current Regulator Circuits. - Google Patents

Abstract

1,161,834. Control systems for inductive loads. WESTINGHOUSE BRAKE & SIGNAL CO. Ltd. 21 Dec., 1967 [20 Jan., 1967], No. 3209/67. Heading H2H. [Also in Division G3] In order to prevent asymmetrical magnetization or saturation of an inductive load-such as a transformer-fed from an A.C. source by way of controlled switching devices the switching devices are so controlled that, upon switching on, the voltage applied to the load increases at a relatively slow rate but upon switching off or on a failure of the supply, the voltage across the load decreases rapidly. A load 7 is supplied from an A.C. source 1, 2 by way of a transformer 5, 6 and a pair of reversely connected thyristors 3, 4, the gating signals for the thyristors being produced by a driver circuit 8 under the control of a circuit which includes a timing network 20, 21 and transistors 18, 22. Upon switching on a capacitor 15 rapidly charges from the source 1, 2 by way of a transformer 10 and a full wave rectifier 14. The rectifier 14 also establishes a potential across resistors 19, 20, thereby causing the capacitor 21 to take up a charge. The potential at the base of transistor 22 then gradually increases, whereupon the control signal from a potentiometer 11 to the driver circuit 8 thus causing the driver circuit 8 to advance the firing angles of the thyristors 3, 4 from an initial maximally retarded angle to the normal operating angles selected by the potentiometer 11. Thus, the voltage applied to the primary winding 5 of the transformer is increased from a low to the normal value during a period dependent upon the long time constant circuit 20, 21. Should the supply disappear for any reason, the transistor 18 becomes conductive to discharge rapidly the capacitor 21, thus ensuring that whatever the length of the period during which the supply is absent, the timing network 20, 21 is in its normal state when the supply is resumed. In other embodiments, the two transistors 18, 22 may be replaced by a thyristor or a single transistor in which latter case the bridge 14 and capacitor 15 is duplicated. In yet a further embodiment, a signal representing the voltage across the load 7 is also fed into the driver circuit 8 when the voltage across the load is regulated to constancy. If desired, the contacts of a contactor may be incorporated between the source and the load with further contacts between the source and the transformer 10.