GB355747A - Improvements in or relating to electric current transformers - Google Patents

Abstract

355,747. Current transformers. REYROLLE & CO., Ltd., A., Hebburn-on-Tyne, and BAYLES, J. W., 12, Neale Street, Fulwell, Sunderland. May 28, 1930, No. 16515. [Class 38 (ii).] In a current transformer arrangement comprising a main transformer and an auxiliary transformer energized from the same primary current, the secondaries are connected through a controlling impedance, preferably of low power factor, so that a circulating current is supplied from the auxiliary transformer to the main transformer to effect a compensation in the main transformer for ratio and phase-angle errors. The secondary windings A2, B2, Fig. 1, of the main and auxiliary transformers A, B are connected across loads D, E, respectively, which are. connected through a controlling impedance F. The impedance of F is high compared with the impedance of the loads D, E so that a circulating current which leads the primary current by a large angle is supplied from the secondary winding B<2> to the secondary circuit of the main .transformer. This divides into two components one of which passes through the secondary winding A2, the other flows through the load D. The controlling impedance F is provided with a closed iron magnetic circuit arranged to operate at a low flux density and has a small resistance and a comparatively large reactance so that the impedance varies approximately in accordance with the permeability of the core. In a modification shown in Fig. 5 the transformers have additional windings A3, B3 which are connected through the impedance F so that the circulating current only affects the magnetization. In another modification shown in Fig. 6 the connection through F is to a centre tap of the winding A<2>, an impedance G equal in value to D is included in the other branch of the secondary circuit of the rear transformer so that the circulating current divides equally and produces no magnetizing effect on the winding A<2> but still allows correction current to flow through the load D. One form of controlling impedance F, Fig. 7, comprises a winding F<1> embedded in a hollow iron core H and arranged so that the flux circulates in a radial plane. The load E for the auxiliary transformer is wound on the annular core H which is gapped at H<2>; the load D is the instrument &c. that is being supplied. In another form shown in Fig. 9 the core of the auxiliary transformer is formed with a hole B<4> and the impedance F<1> is wound so that it passes through B<4> and round the outside of the core. Specifications 169,093, 259,198, and 286,431, [all in Class 38 (ii), Electric currents, Converting &c.], are referred to.