GB833364A - Improvements in and relating to high voltage current transformers - Google Patents

Abstract

833,364. Protective cut-out arrangements. GENERAL ELECTRIC CO. July 18, 1956 [July 18, 1955], No. 22257/56. Class 38 (5). [Also in Group XXXV] A current transformer (see Group XXXV) comprises a primary winding 11 surrounded by a grounding shield 31, secondary windings 12, 13 interlinked with the primary winding, and a grounding cable 35 connected to the shield 31 and interlinked with at least one secondary winding to enable protection to be provided against internal faults in the transformer. The cable 35 in Fig. 1 interlinks both secondary windings and is connected to earth through a spark gap 59 or switch 58. The transformer forms part of a differential protective arrangement for the isolation of sections 43, 46 of a -supply bus 40 by circuit-breakers 42, 44, 47 on the occurrence of a ground fault. The secondary winding 12 is connected in series with the secondary winding of a current transformer 50 and on a ground fault occurring in section 43 the differential current actuates relays 51, 52 to trip the circuit-breakers 42, 44 and isolate section 43. The section 46 may be isolated in a similar manner by circuit-breakers 44, 47. A shield 23 is connected through a housing 21 to the current transformer terminal 19 so that a fault on conductor 45 appears as a fault in the section 46. If an internal fault occurs in the transformer, fault current flows to earth through the cable 35, which is linked with the secondary windings 12, 13 so that the currents induced in these windings are altered and the balanced circuits are upset, causing the three circuit-breakers to open. The loop of the cable 35 around the winding 12 may be omitted so that an internal fault in the current transformer results in the opening of the circuit-breakers 44, 47 only. Modifications described involve the use of cable type or bushing type current transformers.