GB317494A - Improvements in and relating to electric transformers - Google Patents

Abstract

317,494. Gee, F. W., and Ferranti, Ltd. Feb. 17, 1928. Systems depending on the use of static transformers.-In a regulating transformer, two pairs of tapping switches are associated with the secondary windings, the switches of each pair being adapted to be moved in turn while the load current is diverted so that the load circuit is not interrupted, the pairs of switches being also adapted to be moved to such relative positions that either positive or negative boost may be obtained at will. In one arrangement, Fig. 1, two secondary windings c are associated with a primary winding a, one pair of tapping switches d being connected to one end of the primary n of a boosting transformer. The other pair of tapping switches e are connected through an autotransformer winding k to the other end of the winding n, circuit breakers f being provided so that the load current may be diverted while tap changing is in progress. Boost of one sign is reduced to zero by moving the switches e by steps in turn to the positions occupied by switches d, boost of opposite sign being obtained by moving the switches d to a position above switches e. In an alternative arrangement, Fig. 2, a single secondary winding c is employed. In this case the tapping switches are associated with two primaries n on the boosting transformer, the reactance between these windings being relied on instead of the winding k, Fig. 1, for reducing circulating current when the tapping switches of a pair occupy different positions tap changing is being effected. Fig. 5 shows a polyphase arrangement in which three pairs of secondaries c are associated with a deltaconnected primary a. These secondaries are arranged to apply variable and reversible boost obtained as described above to the secondary side of a power transformer comprising a deltaconnected primary n associated with secondary windings m connected through auto-transformers k to one set of tapping switches e, the other set of tapping switches d being connected together to form the star point of the secondary winding system. In an alternative polyphase arrangement, the auto-transformers k are dispensed with, the secondary windings m being split to provide the, necessary impedance to circulating currents occurring during tap changing.