GB506280A - Improvements in or relating to three-phase transformer or choking coil arrangements - Google Patents

Abstract

506,280. Transformers and inductances. SIEMENS-SCHUCKERTWERKE AKT.-GES. Nov. 24, 1937, Nos. 32416 and 32417. Convention dates, Nov. 24, 1936 and Feb. 27, 1937. [Class 38 (ii)] To suppress harmonics such as the 5th and 7th in a 3-phase transformer or choking coil, the arrangement is such that three or more 3-phase flux systems of fundamental frequency are produced which are displaced by angles alpha1, alpha2, &c. with respect to each other and in which the vectors polygon formed by the fluxes multiplied by the associated magnetising force and iron path length and displaced through Kalpha1, Kalpha2, &c., where K is a number divisible by 6 and lying between two adjacent odd harmonics other than the third and multiples thereof, is closed. As shown in Fig. 3 each limb of a three-phase core is split into three sections by slots and the main fluxes in those sections produced by the main winding 1 are displaced with respect to each other by means of auxiliary windings 2, 3, 4, 5 connected in star and delta. These auxiliary windings arc dimensioned to force a phase displacement of e.g. 20‹ The arrangement is designed so that the voltages produced in the main winding when phase displaced by the phase angle multiplied by the number divisible by six nearest to the harmonic form a closed polygon. In a modification, instead of a slotted core, three cores arranged side-by-side are used. In a further modification shown in Fig. 9 each core limb has a single slot, the three-phase displaced fluxes for each phase being comprised by Ua, Ub and Uc. In a modification of this the slots are arranged at the comers of the core. A further modification is shown in Fig. 15 in which the flux division is obtained by slotting the yoke, the three groups of three phase fluxes being U, V, W; Ua, Va, Wa and Uc, Vc, Wc, of which Wa and Wc each have two components. In a further modification the three sets of three-phase fluxes are obtained by means of three single-phase three-limbed cores. Fig. 24 shows an arrangement in which four sets of three-phase fluxes are obtained. The core is formed by two sections, each limb being slotted so as to form for each phase 4 elements a-d. A further modification is shown in Fig. 25 in wh:ch the four fluxes a-d per phase is obtained by double slotting each limb. In a further modification a four-flux system s obtained by means of a five-limb core with the three main limbs slotted, the fourth set of fluxes being formed by the fluxes in the outer limbs and yokes. A further modification is shown n Fig. 32 in which three groups of fluxes are obtained by slotting the yokes, orie yoke having two slots. Various connections of auxiliary windings for flux distribution are described. Short-circuited conductor bars 25, 26 which may be folded over as shown at 42, Fig. 37 may be provided to reduce leakage across the slots.