GB584199A - Improvements in and relating to electric control systems - Google Patents

Abstract

584,199. Control of D.C. motors. BRITISH THOMSON-HOUSTON CO., Ltd Dec. 13, 1944, No. 25033. Convention date, Dec. 14, 1943. [Class 38 (iii)] [Also in Group XXXVIII] In a system in which a rheostat 16 for controlling the speed of a motor 10 is varied in accordance with the setting of a master potentiometer 11 (see Group XXXVIII), the motor 10 is supplied from an adjustable voltage generator 12 driven at a constant speed. The field winding 12a of the generator is excited from a crossarmature - flux-excited, direct - armature - fluxcompensated dynamo-electric machine 15, which is provided with a main field winding 15a connected across the supply and a voltage control field winding 15b wound in opposition to the first winding. When the motor is at rest, the voltage of generator 12 is zero so that the main field winding is unopposed and the excitation of machine 15 a maximum, causing the generator voltage to rise rapidly. The excitation of winding 15b thus increases so that the net excitation of machine 15 decreases. The voltage of generator 12 then increase at a decreasing rate until a balance point is reached at which further decrease of excitation of machine 15 will cause a decrease of voltage of generator 12. The voltage of generator 12 and thus the speed of motor 10 can then be varied by adjusting rheostat 16.