GB388454A - Improvements in or relating to protective gear for alternating current systems - Google Patents

Abstract

388,454. Protective cut-out systems. ROSS, T. W., 10, Broadoaks Road, Sale, Cheshire, and ASSOCIATED ELECTRICAL INDUSTRIES, Ltd., Crown House, Aldwych, London. Sept. 11, 1931, No. 25585. [Class 38 (v).] Protection of bus-bars S to which incoming or outgoing lines A, B, C or generators or transformers are connected is afforded by means of an induction relay, as 2a, associated with, and controlling the connection of, each line. Each relay has a field winding 3a energized by current transformers 6a in its particular line so as to be responsive to residual current in that line, and an operating winding 4a connected across the secondary of an auxiliary transformer, the primary of which is in series with the field winding 3a. The secondaries of the auxiliary transformers 8a, 8b, 8c are connected in a closed pilot circuit P, in which normally no current flows, but on the occurrence of a fault on the bus-bars producing a residual current in one or more lines, the auxiliary transformer appropriate to that line or lines will energize all the operating windings 4a over the pilot circuit P, and the relays of which the field windings 3a receive residual current will cut out the appropriate lines. With an external fault the currents induced in the circuit P cancel one another out so that the relays do not operate. Preferably relays of the " Translay " type are used so as to provide restraint by means of their biasing windings on the field magnets, and prevent creeping. Turn ratios for the transformers 6a, 8a, &c. are given in the Specification, which refers also to the use of instrument transformers existing in the lines and to tappings for the auxiliary transformers. The invention is also described in its application to a duplicate bus-bar system, Fig. 2 (not shown), in which two sources and four lines are selectively connectable to the bus-bars and each has a protective arrangement similar to that of each line of Fig. 1. In order, however, to meet the case where different lines &c. may be connected to different busbars, the pilot circuit is duplicated, each pilot circuit being associated with its own bus-bar, and tha connection of the auxiliary transformers thereto is dependent on the position of the selector switch of the line pertaining to that transformer. In addition, the bus-bar-coupler circuit-breaker is provided on either side with a similar protective arrangement so as to be included in the protected area.