GB505778A - Improvements in or relating to three-phase transformers and three-phase choking coils - Google Patents

Abstract

505,778. Transformers; chokes. SIEMENS - SCHUCKERTWERKE AKT.- GES. Nov. 16, 1937, No. 31513. Convention date, Jan. 28, 1937. [A Specification was laid open to inspection under Sect. 91 of the Acts, May 17, 1938.] [Class 38 (ii)] A three-phase transformer or choke coil is provided with a separately-excited single phase auxiliary winding for producing an auxiliary flux system for balancing out harmonics in the main flux system. In an arrangement in which a three-limbed core 8, Fig. 2, is provided with a divided yoke at one or both ends, the auxiliary winding 7 is located on one of the yoke parts. In an arrangement comprising a five-limbed core, Fig. 3, the auxiliary winding 10, 11 is arranged on one or both of the normally unwound outer limbs. In both these arrangements, a short-circuited or squirrel-cage winding 9 or 12 is provided to ensure subdivision of the auxiliary flux. The auxiliary winding may be excited from separate exciter windings on the core limbs or it may be connected across appropriate points on the main winding which may be star, delta, or zigzag connected. These points may be selected to give a 30‹ phase displacement between the auxiliary flux system and one phase of the main flux system to-effect suppression of 5th and 7th harmonics. Alternatively, a first auxiliary winding 19 on a subdivided yoke at one end of the core may be connected to the main windings 28 as shown in Fig. 6, to produce an auxiliary flux 20‹ phase displaced from one phase of the main flux-system, in which case a second auxiliary winding 24 is provided as shown on a limb of the subdivided yoke at the other end, whereby the 11th and 13th harmonies also are balanced out.