GB709765A - Improvements in and relating to control systems for electric machines - Google Patents

Abstract

709.765. Control of D.C. motors. BRITISH THOMSON-HOUSTON CO., Ltd. Jan. 15, 1952 [Jan. 16, 1951], No. 1147/52. Class 38(3) [Also in Group XXXV] In an automatic control system for a D.C. hoist motor in which the output of a tachometer generator coupled to the motor is compared with a reference voltage to maintain the motor speed at a desired setting, an auxiliary winding is provided on the tachometer to boost its excitation when a descending load overhauls the motor. The motor 1 has its armature supplied from a Ward-Leonard generator 2, the field of which is energized by an amplidyne exciter 7 in accordance with the amplified difference between the output of the tachometer generator 10 and a reference voltage tapped off a potentiometer 9. The reference voltage is controlled according to the position of the cage in the shaft. In order to detect a power reversal when the load overhauls the motor, a voltage is taken across a shunt 19 in the armature circuit. A reversing switch 18 ganged with the main reversing gear (not shown) and a rectifier 21 ensure that winding 17 on a saturable reactor 14 is only energized by this voltage under overhauling conditions. The resulting increased output of the reactor 14 energizes the auxiliary winding 13 on the tachometer generator in a sense to boost the field of the main winding 11 and so prevent the speed rising above the pre-set value. In a modification, Fig. 2 (not shown) the motor speed is controlled by a regulated reversible booster generator in its field circuit, and the reversing arrangements are such that the current in the motor armature only reverses when the motor is overhauled by the load. Consequently the reversing switch and rectifier are omitted. It is stated that the motor may be supplied from a mercury vapour converter instead of a Ward-Leonard generator.