GB783057A - Improvements in or relating to electric contact converters - Google Patents

Abstract

783,057. Converting. SIEMENS-SCHUCKERTWERKE AKT.-GES. March 5, 1956 [March 4, 1955], No. 6900/56. Class 38 (2). In a contact converter which has switching chokes 3 for creating circuit opening and closing current steps, for back-magnetizing the chokes 3 to a suitable extent of circuit closing, each choke 3 carries an auxiliary winding 9 connected in series with the winding 10 of an auxiliary saturable choke 11, an asymmetrical alternating voltage being applied across the series connection. The asymmetrical voltage may be derived from the series connection of sources of A.C. 13, and of variable D.C. 14; from an A.C. source connected in series with a rectifier having a resistor connected across it, Fig. 9 (not shown), or from an A.C. source connected in series with a rectifier through which D.C. is passed, Fig. 10 (not shown). The D.C. source may be a three-phase rectifier, Fig. 8 (not shown). The direct components of the asymmetrical voltages may be variable to control the degree of back magnetization of switch chokes 3. Fig. 6 shows the voltage across winding 10 having a direct component Ug, the voltages E2 and A resulting from the circuit closing and opening stages of the switch choke 3. With zero direct component the whole alternating voltage would be absorbed by the choke 10, its core being taken round its hysteresis loop between saturation in opposite directions, areas E2 and A being equal. As shown in Fig. 6, the result of the direct component is that core 11 is saturated in one direction but not in the other, the asymmetry freeing volt seconds R2 for back magnetization of choke 3, area E2 being reduced. Hatched are V2 represents ohmic loss.