Patent GB-703742-A (GB)
Title: Improvements in and relating to stabilizing circuits
IPC: H02P9/32
Filed: 1952-01-28
Abstract: 703,742. Magnetic amplifiers. BRITISH THOMSON-HOUSTON CO., Ltd. Jan. 28, 1952 [Feb. 1, 1951], No. 2278/52. Class 40 (4) [Also in Group XXXV] In a voltage regulating system, the excitation of an amplidyne 3 is controlled by differential field windings 64, 65 which are energized by the push-pull output of a pair of magnetic amplifiers 40, 41. As shown in Fig. 1, the amplidyne constitutes a pilot exciter which controls the output of a main exciter 2 to the field winding 67 of a,three-phase alternator 1. The system comprises a comparison circuit 4 and push-pull magnetic amplifier stages 5, 6 operating in cascade. In the comparison circuit, a current proportional to the average terminal voltage of the alternator is derived over a transformer 8 and a polyphase rectifier 7 and acts in opposition to a reference current fed from a current standard 14 over a bridge rectifier 11. Deviation of the alternator voltage from a value determined by the setting of an adjustable resistor 10 causes a resultant unidirectional current to act in control windings 24, 25 of the first amplifier stage 5 over a sensitivity-adjusting resistor 68. This stage comprises a pair of magnetic amplifiers 18, 19 each with two load windings 20, 22 and 21, 23 which are connected in series with rectifiers 30-33 to tappings 37, 38 on a centre-tapped transformer 36 so that successive half cycles of current alternate between the two load windings of each amplifier. The outputs of the first amplifier stage act in push-pull on the control windings 46, 47 of the second amplifier stage 6, shunt rectifiers 34, 35 and 58, 59 being provided to by-pass the inductive current from the load during the intervals when the load windings are not conducting. Both amplifier stages are similar and include negative feedback windings 28, 29, 52, 53 and stabilising windings 26, 27, 50, 51 which are energised over transformers 79 and 80 by transient current changes in the outputs of the pilot and main exciters. In addition, the second stage includes bias windings 48, 49 which are excited over an adjustable potentiometer 83 by a rectified supply from a transformer 15. The system is arranged so that a resultant, current from the comparison circuit causes an adjustment of the amplidyne output voltage. When the resultant current is zero, the magnetic amplifiers are adjusted to provide a balanced push-pull output so that the magnetic fields produced by windings 64, 65 neutralize each other. Balance adjustment is effected by the distribution, over an adjustable potentiometer 76, of rectified current from transformer 15 to the control windings 24, 25. Hunting of the amplifier system is damped by an auxiliary amplidyne winding 63 which is short-circuited by an adjustable resistor 72. Alternatively, winding 63 may be omitted and damping effected by shunt resistors 91, 92, Fig. 3, or shunt capacitors, Fig. 4 (not shown). An under-excitation limit circuit 73 may be fitted to prevent the alternator pulling out of synchronism. Specifications 539,835 and 670,838, [both in Group XXXV], are referred to.