GB220737A - Improvements in and relating to protective apparatus for alternating electric current systems - Google Patents

Abstract

220,737. British Thomson-Houston Co., Ltd., and Fitzgerald, A. S. May 31, 1923. Addition to 193,434 and 216,254. Protective arrangements.- Split conductor feeders and interconnectors and other similar pairs of parallel oonductors adapted normally to carry alternating current in a predetermined ratio, both conductors to be isolated in the event of fault, are protected by a winding energized responsively to the difference between t h e normal ratio and the exist. ing ratio due to fault and connected to the primary of a biassing transformer as described in the parent Specification as modified in the Patent of addition 216,254. As shown in Fig. 1, the feeder 12 divided into two splits 13, 14 is protected by an ordinary split-conductor transformer 19 the, secondary of which supplies difference current to the two halves of the divided primary winding 26, 26<1> of a biassing transformer having intermediate flux paths as described in Specification 216,254. The divided secondary winding 27, 27<1> is connected to the tripping circuit and the restraining winding which, by the disposition of the windings is not in inductive relation with the other two, is connected across a current transformer 29 in the unsplit portion of the feeder. With heavy through currents the inherent want of balance of the transformer 19 is compensated for by the saturation of the biassing transformer 24 and the resulting reduction in the inductive action between the primary 26, 26<1> and secondary 27, 27<1>. The modified biassing transformer in which the transformer core is divided into two parts as described in Specification 216,254 may be used instead of the biassing transformer shown in Fig. 1. The split inductor transformer and the biassing transformer may be combined into a single structure as shown in Fig. 3. The splits directly energize the windings 26, 26<1> which by difference current energize the secondary winding 27, 27<1> and by through current saturate the magnetic circuit, thereby affecting the inductive relations between the primary and secondary, and compensating for inherent out of balance of the biassing transformer. If the splits are designed to be normally unequally loaded in a predetermined ratio, the exciting windings of the transformer 19, and its equivalent in the combined arrangement shown in Fig. 3, are chosen so as to give no flux normally.