GB301558A - Improvements in and relating to electric transformers - Google Patents

Abstract

301,558. British Thomson-Houston Co., Ltd., Wellings, J. G., and Mayo, C. G. Sept. 6, 1927. Transformers, par. ticularly current transformers f o r supplying a thermal or overload relay are arranged so that the ratic diminishes with increasing primary current, an auxiliary primary winding being provided to oppose the excitation of the main primary and being arranged so that its excitation increases only slightly as the excitation of the main primary increases, so that the transformer output increases at a greater rate than that at which the main primary current increases. The main core 23 has the same radial dimensions as, but several times the axial length of, the auxiliary core 24, which is arranged to be saturated so that the current in its secondary 25 (and therefore in the auxiliary primary 26 of the main core) does not increase in proportion to the current in the main primary 15. The main secondary 27 is wound over the core 23, the cores are then brought together, and the windings 25, 26 are wound over both cores, a preferably inductive impedance Z being arranged in the circuit and being obtained by winding an extension of this winding circumferentially round the main core, which thus serves as the core of an open-cored reactor. Examples of ratios and turns for the windings are given in the Specification.