GB470145A - Improvements in and relating to electric transformers - Google Patents

Abstract

470,145. Transformers. BRITISH THOMSON-HOUSTON CO., Ltd. Oct. 26, 1936, Nos. 29059, 29060, 29061, and 29062. Convention dates, Oct. 25, 1935, Nov. 2, 1935, Nov. 2, 1935, and Nov. 23, 1935. [Class 38 (ii)] In polyphase transformers the core structure is arranged so that two sets of polyphase fluxes phase displaced by 30‹ may circulate, and the relative reluctance of the different core parts is so determined either by dimensioning, selection of material, or by loading by auxiliary windings that for each closed flux path substantially equal and opposite magnetomotive forces are required for the development of 5th and 7th harmonic fluxes. Thus the magnetizing current may be made substantially free from these harmonics. Figs. 1 and 8 show alternative forms of core in which each winding limb 1, 2, 3 is joined to each of the others through separate yokes 12, 23, 31, whereby one set of fluxes circulate in the yokes 30‹ phase displaced from the fluxes in the winding limbs. Fig. 13 shows another arrangement in which the same effect is obtained by forming slots 90 in the yokes, the slots extending over unequal parts of the limbs so as to equalize the effective length of all the yoke portions. In other arrangements conductive inserts, or auxiliary windings formed by linking together a row of clamping bolts are used to split up the yokes into parts effectively connecting each limb to each of the others. The Specification further demonstrates that a core having three wound limbs and two unwound limbs united by common yokes may be made to form an equivalent of the other core structures referred to. Auxiliary windings connected in a closed circuit or individually connected to adjustable saturated chokes may be provided on the yokes to enable the magnetomotive forces required for the harmonics in question to be adjusted. In order to compensate for 5th and 7th harmonics present in the line to which the transformer is connected, the core structure may be designed so that the 5th' and 7th harmonic components of the magnetomotive forces do not completely cancel out but leave a resultant which absorbs the harmonics in the magnetizing current.