GB356181A - Improvements in or relating to protective arrangements for electrical apparatus - Google Patents

Abstract

356,181. Protective cut-out arrangements. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, and WILSON, W., of General Electric Co., Witton, Birmingham. June 2, 1930, No. 17055. [Class 38 (v).] A protective arrangement comprises two separate circuits adapted respectively to carry currents at different parts of the apparatus to be protected, and a relay including a plurality of coils connected in the two circuits in such a way that those coils in one circuit are in series with one another, and so arranged that the currents in different coils, acting oppositely normally fail to effect operation of the relay. The relay is arranged to operate on reversal of current at one part relatively to that of another, or on a disturbance of ratio of currents in those parts and in a direction depending on which circuit carries a current of too large a relative ratio. A double-fulcrum beam relay has coils 9, 11 in series with a current transformer 12, and a coil 10 in series with a current transformer 13, the transformers 12, 13 being similar as regards cores and secondaries but having their primaries proportioned to produce equal secondary currents. The turns in the coil 9 equal the combined turns of coils 10, 11, which are normally additive, so that the relay is inoperative, and the ratio of turns of coils 10, 11 is preferably 4: 1. When the degree of unbalance between the currents on either side of the transformer or other apparatus 1 (or in the adjacent ends of a pair of parallel feeders) reaches a predetermined amount, or when reversal of current direction occurs, the beam of the relay tilts one way or the other to cut out the apparatus. An induction relay as described in Specification 319,292, [Class 38 (v), Electric switches &c.], may replace that shown, and the relay coils may be connected across shunts in a D.C. circuit. The compensating impedance may be omitted by opposing the effects of coils 10, 11 and giving them a turn ratio 2: 1, or alternatively each plunger may be acted on by two coils, one in each current transformer circuit.