GB690436A - Improvements relating to magnetic amplifiers and to automatic voltage regulating arrangements employing such amplifiers - Google Patents

Abstract

690,436. Automatic voltage control systems. SIEMENS BROS. & CO., Ltd., and DOUBLE, H. S. June 29, 1951 [June 30, 1950], No. 16431/50. Class 38 (iv). [Also in Group XXXIX] In a rectifying system in which automatic regulation of the D.C. load voltage is effected by saturable reactors in the A.C. circuit, the control current of the reactors is derived from two magnetic amplifiers connected in cascade, each amplifier being arranged to give an increased D.C. output in response to a decrease in its D.C. input or an increase in the A.C. energizing voltage. The D.C. input to the first amplifying stage is obtained from a bridge circuit which gives an increased output as the D.C. load voltage falls, while the two amplifying stages are selected such that their combined characteristics cause the change in the control current of the reactors for a given change in the A.C. supply voltage to have a greater degree of variation when the A.C. voltage is at A low limit than when it is at an upper limit. As shown, the rectifying system comprises a threephase star-delta transformer TR and a full-wave dry rectifier MR, the load windings I of saturable reactors CHA, CHB and CHC being connected between the transformer primary windings and the star point. The D.C. load voltage is obtained between terminals TL after smoothing by chokes CHS, CHSS and condenser Q. The saturable reactors are controlled by cumulatively acting D.C. current and voltage windings II, III and opposed bias windings IV. Variation of the D.C. load voltage is detected over terminals BB by a bridge circuit VSN comprising barretters or other non-linear resistors BRX, BRY and fixed and adjustable resistors YXA, YYA and YXB, YXB respectively, the output of the bridge being applied to the control windings V of a magnetic amplifier comprising reactors CHK, CHL and constituting the first amplifying stage. This amplifier has A.C. windings VI and a D.C. current feed-back winding VII which is energized over a full wave rectifier ARB and acts in opposition to the control winding. The amplifier is energized from the A.C. supply over a transformer TRB and its output is applied over a potentiometer PR to the control winding of a similar amplifier CHE, CHF which constitutes the final amplifying stage and supplies the voltage windings III of reactors CHA, CHB, CHC. In operation, a fall in the D.C. load voltage causes a rise in the output of the bridge VSN and consequently a fall in the output of the first amplifying stage and a rise in the final stage output. The ampere-turns of the voltage windings of the reactors are thus increased and effect an increase in the D.C. load voltage. If the A.C. supply voltage rises, the cumulative effects of the two amplifiers cause a reduction in the voltage winding current of the saturable reactors with a consequent rise in the impedance of the load windings and stabilization of the D.C. load voltage.