GB790948A - Improvements in or relating to an apparatus for producing periodic m.m.f. impulses - Google Patents

Abstract

790,948. Rectifying. SIEMENS SCHUCKERTWERKE AKT.-GES. Nov. 15, 1955 [Nov. 15, 1954], No. 32707/55. Addition to 745,173. Class 38 (2). In a contact converter having in series with each contact 13 a switch choke 12 magnetized, before contact closure for phase angle control by a pulse producing circuit of the kind described in the parent Specification including a saturable choke 18, the premagnetization of choke 18 is made to vary with the supply volts in such a way that the output volts tend to remain constant. A resistor 8 in series with a rectifier 7 is connected across a rectifier 17 (and optionally across winding 16) in series with back-magnetizing winding 16 of the switch choke, this auxiliary circuit being energized from the main supply. During half-cycles when the pulse for premagnetizing the switch choke is not produced, back magnetization passes through choke 18 in such direction that it opposes that produced by D.C. in winding 20, and the value of volt seconds applied is restricted by resistor 8. The effect is to alter the back magnetization of the switch choke 16 and therefore the degree of voltage control so that output voltage fluctuations are reduced. The output voltage may be regulated by variation of D.C. in winding 20 or by variation of resistor 8. In an alternative construction, Fig. 2, the currents in different directions flow through different parts of the choke 18 which has a tapping connected to a, tapping on a resistor 19 connected between main supply phases. Rectifier 7 with winding 8 and rectifier 17 with winding 16 are connected respectively across different parts of resistor 19 and choke 18. In a modification the the premagnetization circuits may be connected in star and supplied through an auxiliary transformer from the main supply (Fig. 3, not shown). The resistor 8 may be replaced by a further saturable choke.