GB548296A - Improvements relating to unidirectional electrical inductive apparatus - Google Patents

Abstract

548,296. Converting; inductances. BRITISH THOMSON-HOUSTON CO., Ltd. April 3, 1941, No. 4473. Convention date, April 3, 1940. [Class 38 (ii)] [Also in Group XXXVII] In an electroresponsive device of the general character set out in Specification 266,359, [Class 38 (ii)], and applicable to the excess-current protection of A.C. systems by circuit-breakers of the flux-shifting type in which a unidirectional current impulse flows in the releasing winding or conductor, regardless of the instantaneous direction of the alternating-current the polarizing flux is obtained from permanent magnets which are preferably of the alloy described in Specifications 423,897 and 424,746, [both in Group 11], thereby avoiding the provision and maintenance of D.C. sources in remote circuit-breaker locating. The brakes-tipping device which is similar to that of Specification 500,472, [Group XXXVII], comprises a permanent magnet 17, preferably of the abovementioned alloy, maintaining the armature 20 in attracted position by means of laminated soft-iron poles 18, 19, the flux 17<SP>1</SP> through which is adapted to be reduced by flux set up in a core 23 of similar alloy which is spaced at its ends from the poles 18, 19 and traversed by a unidirectional flux due to current in coil 22. The latter is connected in series with windings 33, 34 on cores 24, 25 which are normally magnetized above the knee of the B-H curve by permanent magnets 28, 29 in the directions shown. Oppositelywound primaries 31, 32 connected to a line currenttransformer 30 are arranged so as to oppose and assist, respectively, the saturating fluxes due to the permanent magnets 28, 29, the arrangement being that normally the decrease in flux in one core is balanced by the increase in the other core and no material resultant appears in coil 22. On excess-current, however, the decrease of flux in one core carries the resultant below the knee of the B-H curve whereas increase in the other core is small due to saturation, and the resultant e.m.f. in winding 33 to 34 is sufficient to produce tripping, Figs. 2 and 3 (not shown). Since in each half-cycle of the A.C. there is always a resultant flux decrease, the induced e.m.f. is always unidirectional. Additional limbs are provided on the cores 24, 25 to provide a return path for the winding- fluxes, but since these limbs would normally be saturated by the permanent-magnet flux and hence of high reluctances, they have air gaps 26, 27 which are preferably adjustable for controlling the degree of saturation.