Patent GB-521125-A (GB)
Title: Improvements in or relating to alternating current switching arrangements
IPC: H01F38/02
Filed: 1938-11-08
Abstract: 521,125. Inductances; converting. PATENTVERWERTUNGS-GES. HERMES. Nov. 8, 1938, Nos. 32436, 32437, 32438, 32439 and 32440. Convention dates, Nov. 8, 1937, Nov. 12, 1937, Nov. 18, 1937, Nov. 26, 1937, and Dec. 15, 1937.. [Class 38 (ii)] Relates to A.C. switching arrangements (particularly commutator switch converters as described in Specification 492,369) wherein the current wave is flattened in the neighbourhood of the zero value by a saturable choke in series with the switch contacts, and consists primarily in making the core of the choke of a spirally wound strip of magnetic material. A wide variety of forms in which one or more strips are wound to form cores of circular or .rectangular shape, Figs. 1 and 2, cores with multi-start spirals, Figs. 3 and 4 (not shown), cores with circumferential cooling slots between concentric spirals, Fig. 5 (not shown), cores of substantial and preferably circular crosssection, Fig. 13, obtained by using narrow strip and side by side spirals of different diameters are described. The strip is of material having a sharp bend in its magnetization curve, e.g., a nickel-iron or silicon-iron alloy, and is preferably loosely wound to avoid impairing its magnetic properties which are further developed by heat-treatment in a magnetic field. Skin effect in the windings may be reduced by using a number of thin conductors in parallel. These may be arranged as separate windings with their adjacent ends connected together. Fig. 8 shows an example of such an arrangement, the wind point of each winding being connected to the core. Advantage may be taken of the potential distribution thus obtained to cut away the core insulation at these points so as to admit a liquid or gaseous cooling medium to the core. Capacity effects in the windings may be reduced by using a number of disc coils. These may be of tapered section, Fig. 11, or of differing diameters, Fig. 12, to permit of better utilization of the space within the core ring. Where magnetic biassing is to be. introduced by means of a D.C. exciting winding. the latter is preferably in the form of one or more straight conductors passing axially through the core. A single conductor 61, Fig. 16, may form the D.C. exciting winding and the clamping means for a number of superposed chokes 41, 42, 43 for a polyphase switching arrangement. Where a group of chokes are used for each phase of a polyphase converter, Fig. 17, their D.C. exciting windings 61, 62, 63 may be connected in series and fed by an auxiliary rectifier which may be of the commutator switch type having its contacts 32 actuated synchronously with the contacts of the main converter. The latter may be regulated (1) by angular displacement of the rotor of a synchronous motor actuating its switch contacts or (2) by variation of the D.C. exciting current for magnetically biassing the choke cores. When the contacts of the main converter and auxiliary rectifier are drive by the same motor regulation by the first method automatically causes regulation by the second method. Regulation by the second method may, however, be effected independently by a variable resistance 14. Specification 490,509, [Group XXXVII], also is referred to.