Improvements in and relating to methods of protecting electric transformers

Abstract

Abstract 176,134. British Thomson - Houston Co., Ltd., and Holbrook, H. S. Dec. 1, 1920. Transformers.-In a circulating-current system for protecting a transformer, in which current transformers 5, 6 are provided in the primary and secondary circuits of the main transformer to be protected, a trip coil 7 being connected in shunt across the secondaries of the transformers 5, 6, a reactance 10 is placed in parallel with the primary 2 of the main transformer and is connected across the terminals of the secondary of the transformer 5 in order to compensate for differences in the ratio of the input and output currents of the main transformer. These differences may be caused by variations in the supply voltage and the load, or by the rush of magnetizing-current which takes place when the main transformer is connected to the supply circuit. The core of the reactance is made of the same material and is worked at the same flux density as that of the main transformer in order that the current taken by the reactance may bear a constant ratio to that taken by the main tranformer. In order that a small reactance may be used, the reactance is preferably connected in series with the secondary 9 of a potential transformer whose primary 8 is in parallel with the primary 2 of the main transformer.

Inventors

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