GB1184416A - Improvements in and relating to Polyphase Power Control - Google Patents

Abstract

1,184,416. Control of A.C. motors; supply systems for consumption devices. GENERAL ELECTRIC CO. 29 Jan., 1968 [2 March, 1967], No. 4453/68. Headings H2H and H2J. A three-phase induction motor has stator windings 12, 14, 16 whose neutral terminals are connected to a delta network comprising a pair of back-to-back silicon controlled rectifiers in each leg. Time-delay pulse generators 84, 86, 88, serve as triggering devices for the units 54, 56, 58, respectively, each generator being connected in series with a transformer primary winding 90, 92, 94. In the case of the generator 84, for example, the winding 90 is coupled to secondary windings 96, 98, and the other triggering circuits are similarly coupled. Each pulse generator may comprise a currentlimiting resistor in series with a variable resistor as well as a capacitor and the transformer primary winding. A triac is in parallel with the variable resistor and capacitor, and has its gate connected to the junction of the latter two compoents through a diac. Alternating pulses are provided in the primary winding after the capacitor charges to the breakdown voltage of the diac. The charging time of the capacitor depends upon the setting of the variable resistor, which may be replaced by a transistor receiving an external control signal. The system may be used for supplying polyphase machines other than induction motors. The pairs of silicon controlled rectifiers in the delta network may be each replaced by a triac.