GB393335A - Improvements relating to protective devices for use with potential transformers - Google Patents

Abstract

393,335. Protective cut-out arrangements. SOMERVILLE, T. B., 11, Entwistle Avenue, Davyhulme, Manchester, and ASSOCIATED ELECTRICAL INDUSTRIES, Ltd., Crown House, Aldwych, London. Dec. 12, 1931, No. 34518. [Class 38 (v).] In order that potential transformers supplying energy to apparatus such as voltage regulators &c. may be prevented from delivering other than a correct proportional voltage in case of fault in the transformer, an auxiliary potential transformer is provided and a protective relay which compares the output of the two transformers and ensures that if the ratio between such outputs does not remain constant the controlled apparatus is cut out of action or its operation is suitably modified. As shown in the Figure the main potential transformer 3 fed through fuses 4 from an alternator 2 supplies the controlled apparatus through leads 5 in its secondary circuit, which is also connected to one coil 8 of a differential relay 10 the other coil 9 of which is fed from the secondary of an auxiliary potential transformer 6 the primary 'of which is connected through fuses 7 to the bus-bars 1a, 1b, 1c. Resistances 11, 12 in the circuits of the opposing coils 8, 9 are adjusted so that when the main transformer is operating correctly the armature 13 remains unattracted but on a sufficient disturbance of the ratio of the forces exerted by the coils contacts 14, 15 are connected either to cut out the regulator or to insert a resistance in its operating circuit to modify its action. The resistances 11, 12 may be chosen so that the relay will operate when the current in the main transformer 3 fails but does not operate when the current supplied by the auxiliary transformer 6 fails.