GB442150A - Protective arrangement for booster transformers - Google Patents

Abstract

442,150. Protective cut-out arrangements. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London, and MATHEWS, P., 7, Elsee Road, Rugby. Aug. 2, 1934, No. 22551. [Class 38 (v)] A booster transformer having its primary 2 in a shunt to the main circuit 1 and its secondary 3 connected to a transformer with a winding 5 in the main circuit 1, is protected by means of an overload relay 10 that is rendered immune from operation by throughshort circuit in the main 1 due to 4, 5 acting as a current transformer and producing current in the primary 2. The secondary 12 of a currenttransformer in the main 1 energizes a winding 11, which oppositely magnetizes two core portions 7, 8 of a current transformer 6 in the shunt circuit, both of which portions are linked by the winding 9 feeding the relay 10. The effect is that the iron of the cores is saturated on through-fault conditions in the main, but no resultant voltage is induced in 9. The resulting reduction in permeability due to saturation, however, demands more ampere-turns in the primary to produce a superposed flux required to give an operating voltage in 9, and by proper design the said ampere-turns may be made to increase with increasing fault current in 1 at a greater rate than the current injected into 2 by the transformer 4, 5. The Provisional Specification refers to Specification 303,221, [Class 38 (v)].