GB373766A - Improvements in and relating to the conversion of polyphase currents into single phase currents - Google Patents

Abstract

373,766. Frequency changing; phase changing. LÍBL, O., 2, Neue Bismarckstrasse, Hermsdorf, Berlin. May 9, 1931, No. 13819. [Class 38 (ii).] In means for converting polyphase current into single phase current of lower frequency by transformers and rectifiers so arranged that succeeding phases of the polyphase current a1, b1, c1, &c. have different amplitudes and the anodes of the rectifiers are rendered conductive in such order that a single phase current wave is built up in the load circuit as indicated in Fig. 1, provision is made for introducing counter voltages into the short-circuit path produced under conditions of low power factor in the load circuit. Fig. 2 shows an arrangement in which a three-phase network R, S, T supplies current to a pair of phase multiplying transformers P1, P2 wound so as to produce secondary phases of graded amplitudes. The secondary phases are associated with the anodes of a pair of rectifiers G1, G2, the circuits of which are completed at appropriate intervals by switches S1 .. S6 operated synchronously with the supply current. The single phase load M is connected between the cathodes F1, F2 and the star points of the transformers so that one half cycle of the load current is derived from successively conducting anodes of the rectifier G1, and the other half cycle from successively conducting anodes of rectifier G2. A short-circuit path through the two rectifiers is formed when, due to a lagging or leading current, switches associated with different rectifiers need to be closed simultaneously. Circulating current is prevented, however, by causing the switches to close in such sequence that two equal voltages obtained from corresponding phases on the two transformers are in opposition in the short-circuit path.