GB677247A - Improvements in or relating to direct current electric supply systems - Google Patents

Abstract

677,247. Control of D.C. motors. GENERAL ELECTRIC CO., Ltd., and SCOTT, P. June 1, 1950. [June 1, 1949] No. 14714/49. Class 38 (iii). [Also in Group XXXV] A D.C. supply system, which may be arranged to feed a D.C. motor so as to form a Ward-Leonard control system, comprises a main generator having a field winding fed from an exciter generator, wherein the excitation of the latter or of a pilot exciter generator is arranged to be depended upon a reference electrical quantity and upon the main generator P.D., the excitation current of the field of the exciter generator or pilot excitor generator being derived through a non-linear resistance tending to reduce the main generator excitation when the main generator P.D. or output current is relatively large. The Figure shows a Ward-Leonard motor control system in which a generator armature 10 is connected to the motor armature 13. The field 12 of the generator is fed from the armature 16 of the main exciter the field winding 17 of which is in turn fed from the armature 18 of an auxiliary exciter. The latter has three field windings 20, 21, 22. The winding 20, which is fed from the supply through a potentiometer 24, carries a steady reference current, the second winding 21 carries a current proportional to the output voltage of the main generator and is in opposition to the first winding 20, and the third winding 22 assists the second winding 21. The circuit of the winding 22 includes a metal rectifier 30 which, on account of its non-linear characteristic and of the position of its non-linear characteristic and of the position of the slider 27 on a resistance 26 acting as a control means, has a voltage across it so arranged in its voltage/current characteristic curve as to be at the critical value where the slope of curve changes rapidly when the current supplied by the main generator is at the required current limit. Thus the current in the field winding 22 is arranged to be responsive to the output current of the main generator by adjusting the position of the slider 27 or to the output voltage by supplying this winding 22 through a non-linear resistance from a potentiometer connected across the generator output. Instead of making the field winding 22 responsive to the main generator output current, it may be made responsive to the main generator voltage output by feeding it from a tachometer generator through a non-linear resistance from a potentiometer across the main generator. In order to limit the current on regeneration as well as on motoring a second rectifier 31 may be connected in parallel to and in reverse to the first rectifier 30. Instead of exciting a field winding of a pilot exciter generator to limit the main generator current, a similar effect is obtained by exciting a further field winding of the main excitation generator in the same manner. If desired, further field winding(s) may be provided to the pilot exciter to improve stability.