GB815366A - Improvements in and relating to electrical control systems - Google Patents

Abstract

815,366. Exciting dynamo-electric machines; automatic voltage control systems. BRITISH THOMSON-HOUSTON CO. Ltd. Dec. 12, 1956 [Sept. 14, 1955], No. 26339/55. Classes 35 and 38 (4). A retroactive control system employs an A.C. or D.C. generator having a permanent magnet pole and an opposing pole excited in proportion to the controlled quantity so as to produce a correcting voltage at the generator terminals dependent on the deviation of the controlled quantity. In its simplest form for use as a regulating exciter, the machine has two opposed poles, the permanent-magnet pole having long pole-horns which serve to shunt away the magnet-flux to the machine frame in response to the opposition of the excited pole. When the controlled quantity has the desired magnitude, no flux passes through the machine armature, and so no correcting voltage is generated. In a modification the winding may be on the pole-horns to create the leakage directly. Additional windings for stabilizing &c. may be used. In the more elaborate form shown in Fig. 8, the stator has two magnet poles 5, 5a, and two wound poles 4, 4a, arranged oppositely so as to produce crossed fluxes a, c passing through the two-pole armature 1. The resultant voltage output at brushes 8, 9 depends on the difference between these two fluxes. If the pole-horns 10 are not present, the two fluxes act independently to produce a steady reduction of output voltage as the controlled quantity increases. As shown, the cross fluxes are made inter-dependent by the use of the leakage-horns 10 and saturable yoke-parts A, B which limit the difference between the fluxes. This causes a very sudden reversal of the output voltage at the critical excitation. Fig. 9 shows a simple two-pole machine arranged as an inductor alternator with an output winding 21 on the pole-teeth connected through a rectifier 23 to the circuit, e.g. a generator field, at terminals 24, 25. A part of the output voltage is fed back to the control winding 6 to ensure reversal of generated voltage by means of a rheostat or non-linear resistor 27. Additional feed-back windings, e.g. 28, may be included.