GB858095A - Improvements in or relating to tap-changing switches - Google Patents

Abstract

858,095. Transformers. JANSEN, B. Sept. 19, 1957 [Sept. 28, 1956], No. 29509/57. Class 38 (2). A transformer on-load tap-changing arrangement includes a non-linear resistor for restricting the short-circuit current between taps. As contact K moves between contacts Ha, Hb connected to taps A, B of a transformer winding, it first engages contact ha, and then leaves contact Ha, at which it draws an arc. The load current then flows through resistor Ra having such a characteristic that the voltage across it varies inversely as the cube of the current, through it, and the voltage across Ra falls to a small value to reduce similarly the restriking voltage at contact Ha. When contact K connects contacts ha, hb the non-linear resistor Rb, which carries only the difference between half the load current and the circulating current has a high value to restrict the latter current, but as contacts K and ha open its value falls to reduce the restriking voltage. A resistance having a required characteristic may be selected by connecting a number of variable and linear resistors to form a network (Figs. 2, 3, 4, not shown). There may be further switching steps, each comprising a contact connected to a combination of linear and non-linear resistors (Fig. 5, not shown). To protect the switch against overloads due to short-circuits and lightning sparkgaps fa, fab, fb are arranged so that in series with the non-linear resistors Ra, Ra2 they shortcircuit the switch and linear resistors Ra2, Rb2, Fig. 6.