GB694756A - Improvements in and relating to voltage regulators - Google Patents

Abstract

694,756. Automatic voltage control systems; inductances. BRITISH THOMSON-HOUSTON CO., Ltd. April 19, 1951 [May 2, 1950], No. 9180/51. Classes 38 (ii) and 38 (iv). [Also in Group XXXIX] The output voltage of an alternator is controlled by supplying its field from the A.C. output via a rectifier and saturable reactor, the reactor being controlled by a mag. netic amplifier having a permanent magnet as a reference m.m.f. The voltage of the alternator 1 is detected by connecting a resistor 24 and condenser 25 in series across the output to provide a frequency compensated voltage divider, the voltage across the condenser being rectified at 26 and applied to control windings 22, 23 of the amplifier 6 (and also to a biasing winding 38 on reactor 31). The output of amplifier 6 controls the excitation of winding 37 to vary the saturation of reactor 31, thereby controlling the magnitude of the current that flows (in alternate half-cycles) through load coils 32, 33 and rectifiers 34, to the field winding 4. Amplifier 6 consists of a permanent magnet 12 (surrounded by a shorted turn 41 to reduce the effects of a pulsating flux due to the current in the load windings) the magnet being shunted by laminated core members 9, 10, 11, 13, including air gaps 16, 17, and also shunted by two cores 14, 15 of relatively small cross-section, and made of a magnetic material having a very sharp knee in its magnetization characteristic. The flux of the permanent magnet would saturate the cores 14, 15, were it not for an opposing flux due to control windings 22, 23 wound on the cores 14, 15. Load windings 19, 20 are wound on cores 14, 15 respectively (under the windings 22, 23) and, on alternate half-cycles, pass current from a transformer 5 through winding 37 via rectifiers 21. The pulsating flux in core 14 or 15 due to the unidirectional current pulse through winding 19 or 20 aids the flux due to the permanent magnet. Hence at some point on the pulse waveform the total flux causes the core to saturate, the reactance of the winding falls sharply and current is passed to the winding 37. The point at which the core saturates is determined by the control current in windings 22, 23 which controls the degree of magnetization of the cores. In a modification, Fig. 2, the axis of the permanent magnet 12 is parallel to the cores 14, 15, and the main portion of the core comprises upper and lower members 42, 43. A magnetic shunt 44 is inserted between members 42 and 43 and airgaps are included in this path. In a further modification, Fig. 3 (not shown), the core is made symmetrical by placing the cores 14, 15 on opposite sides of the core which contains the permanent magnet. Specification 670,838 is referred to.