GB119906A - Improvements in or relating to Protective-devices for Electrical Cables or Cable-networks. - Google Patents

Abstract

119,906. Bisacre, F. F. P., and Merz & McLellan. Oct. 16, 1917. Protective arrangements.-In a protective system, not involving the use of split conductors or pilot wires, alternating electromotive forces are imposed on each feeder section in opposition, and having a frequency different from that supplied to the feeders. The trip coil circuits are tuned to the frequency of the imposed electromotive forces, or any suitable device adapted to respond to the required frequency may be used, such as a relay whose moving element moves only under impulses of the desired frequency. The feeder currents may be alternating or direct. As shown applied to an underground three-phase system, each end of a feeder section A is in series with the secondary C<2> of a transformer through the primary C<1> of which current of the required frequency is sent by a generator D. The generators D may be synchronized in any manner. Each feeder section also includes the primaries E<1> of transformers, the secondaries E<2> of which are in tuned circuits, including the trip coils H for operating the circuit breakers J. The coils H are adjusted so as not to respond to current of less than a predetermined value. Leakage current may pass through potential transformers K where such are used, the neutral points being earthed, or through impedances k. The application to an overhead system is described, the impedances k or transformers K being replaced by condensers, which it is said may perform a double function, being used with or as voltmeters or lightning arresters. The frequencies imposed may be different in different sections of the feeder system or network to enhance the discriminating action of the tripping devices.