GB497064A - Improvements in and relating to electric transformers - Google Patents

Abstract

497,064. Transformers. BRITISH THOMSON-HOUSTON CO., Ltd. June 9, 1937, No. 16017. Convention date, June 12, 1936. [Class 38 (ii)] Fifth harmonic disturbances in a three-phase transformer are prevented by dividing the core limbs longitudinally and providing means whereby the fundamental waves of the fluxes in the halves of each limb are phase displaced by 36‹ in respect of one another. In one arrangement, Fig. 1, the magnetic circuit cornprises three frame cores 12, 13, 23, arranged as shown, magnetic connections 5 being provided between these frame cores and having such magnetic reluctance that the fundamental fluxes in each pair of frame core limbs 1a, 1b, 2a, 2b, 3a, 3b have 36‹ phase difference. The connections 5 may have their reluctance adjusted to the desired value by damper windings 6 and the frames may be linked by a delta winding 4 for suppression of third harmonics. The magnetic connections may be made between the yokes of the outer core 13 and the middle points of the yokes of the inner cores 12, 23 and the delta winding 4 may be arranged on the yokes. In an alternative arrangement, the yokes and/or the limbs are divided wholly or partly by rows of shortcircuited bolts instead of by air gaps, additional bolts forming part of the delta winding which is thereby enabled to link the limb or yoke halves. In another arrangement, Fig. 6, the core yokes are solid and the limbs are subdivided a winding 4 having equal numbers of oppositely wound turns on the respective halves of each limb being supplied with an auxiliary threephase voltage in quadrature with the primary voltage and of such a value as to produce the required 36‹ phase displacement between the component fluxes in each main limb. The winding 4 may be supplied from a tertiary winding 5 arranged in star connection as shown. If the limb slots are extended into the yokes, the winding 4 may be arranged on the yokes.