GB683989A - Improvements in or relating to fault-responsive networks for electric circuits - Google Patents

Abstract

683,989. Protective cut-out arrangements. REYROLLE&CO.,Ltd., A. Sept. 27,1951 [Oct.10,1950], No.24729/50. Class 38 (v) A 3-phase circuit is protected against inter-phase or earth faults by a system comprising three saturable summation transformers c, d, e, each having three primary windings c<SP>1</SP>, c<SP>2</SP>, c<SP>3</SP> &c. respectively energised from the secondaries b<SP>1</SP>, b<SP>2</SP>, b<SP>3</SP>, of current transformers in the three phases, and three bridge rectifiers c<SP>5</SP>- e<SP>5</SP> respectively connected to the secondary windings c<SP>4-</SP> e<SP>4</SP> of the summation transformers, the rectifier outputs being additive so as to give a resultant output which is applied to a relay or other device. The transformation ratios for the three primary windings in each summation transformer are different, the same three ratios being present in each transformer but in different orders, the primaries being cyclically arranged with respect to the three phases. The ratios, e.g. 0.42: 1, 1: 1, 1.58: 1, are adjustable and are preferably chosen so that the resultant output does not vary more than 30 per cent for different types of fault and for the same fault magnitude. A non-linear resistance b is connected across the output circuit. In a modification, Fig. 2 (not shown), each secondary c4-e4 is connected at each end through rectifiers to one side of the output circuit, and at its mid-point to the other side.