GB601673A - Improvements in or relating to means for the regulation of the speed of electric motors - Google Patents

Abstract

601,673. Automatic control systems for electric motors. APPLICATIONS MECANIQUES ET ELECTROTECHNIQUES APLEC SOC. ANON. Jan. 3, 1945, No. 251. Convention date, Dec. 11, 1943. [Class 38 (iv)] In a speed control system for electric motors, the supply circuit includes at least one electronic relay, the grid voltage of which is the difference between two D.C. voltages, one of constant value and the other a function of motor speed. In Fig. 2, D.C. motor 1 is supplied through electronic relay 4 and transformer 3 from source 2. The grid 7 of the relay is biassed by battery 9, associated with potentiometer 10, and tachometer dynamo 8. The potentials of battery 9 and generator 8 are in opposition and so connected that grid 7 becomes more negative with rising motor speed until, at a speed determined by the setting of potentiometer 10 the relay ceases to conduct with a consequent drop in motor speed until the generated e.m.f. of 8 is reduced to a value at which 4 again conducts. With large motors the supply may be passed through a number of electronic relays in parallel or part only of the load current may be passed through the relay. In Fig. 4 A.C. motor 31 is supplied by alternator 27, driven by motor 1. The speed of 31 is stabilized as motor 1 is subjected to the same control as in the first embodiment. In a further example an A.C. motor is connected to the supply in series with the primary winding of a transformer, the secondary of which is short-circuited by two electronic relays, grid controlled as in Fig. 2 to vary the conductance of the primary and consequently the voltage applied to the motor. In the Fig. 2 arrangement the motor 1 may be supplied directly from the mains without a transformer 3 while additional speed control is effected by the field excitation of tachometer 8.