GB643978A - Improvements in or relating to electrical power supply equipment - Google Patents

Abstract

643,978. Automatic control systems for supply circuits. STANDARD TELEPHONES & CABLES, Ltd. July 19, 1946, No. 21670. [Class 38 (iv)] A D.C. load is fed from a 3-phase source through separate phase autotransformers which are automatically adjusted to balance. either the phase voltages or currents and to maintain the load voltage between limits. As shown, Fig. 2, the load is supplied through a star-delta transformer SDT from a 3-phase supply #A, #B, #C; each phase of the transformer input is taken from one of the autotransformers WA, WB, WC, the tappings CA, CB, CC of which are each automatically adjusted by a separate reversible motor (not shown). The tapping motors are controlled through relays operated by (a) high and low limit relays HV, LV, at the D.C. output, and (b) the D.C. limit voltmeters AM, BM, CM, which have each two differential windings energized from two of the rectifier bridges RA, RB, RC connected between each phase and neutral, N. The load is maintained within 1 per cent of standard and the voltages of at least two different pairs of phases are maintained within 1 per cent of each other. When both load and phase voltages are beyond the limits, the load is corrected first and the phase voltage balance effected next.. Phase current balance may be effected by replacing the voltmeters AM, BM, CM, by ammeters having each two windings in separate phases.