GB409713A - Improvements in and relating to electric converting apparatus - Google Patents

Abstract

409,713. Converting. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Willis, C. H. ; 184, Prospect Avenue, Princeton, New Jersey, U.S.A.) Oct. 1, 1932, No. 27310. Convention date, Oct. 1, 1931. (Class 38 (ii).] Apparatus for transmitting energy in either direction between a D.C. circuit 10 and a polyphase A.C. circuit 11 comprises a polyphase inductive network 12 and a plurality of electric valves 20 .... 31 interconnecting the circuits, and means for producing in, or introducing into, the network an alternating potential having a frequency which is a harmonic of that of the A.C. circuit, for effecting commutation of the current between the valves under any desired power factor conditions on the A.C. side. In the arrangement shown in Fig. 1, the network 12 comprises the six phase mesh connected windings 15, and two star-connected windings 16, 17 having independent neutrals. The grids of the valves are excited from the secondary windings 19 of a grid transformer, the primary winding 18 of which may be energized from any source of the desired frequency. If the A.C. circuit 11 is connected to an independent source for determining its frequency and wave form, the winding 18 may be energized from the circuit 11 through a phase-shifting transformer 18<a>. The voltages applied to the grids should preferably be of peaked wave form, as described in Specification 390,184. The harmonic frequency is supplied to the network by means of a frequency changer comprising a synchronous motor 33 driving a single-phase synchronous generator 34 connected between the neutrals of the windings 16, 17. The effect of the harmonic voltage in distorting the wave forms in the network 12, and rendering it possible to commutate the currents between the valves under conditions where commutation would otherwise be impossible, is explained with the aid of diagrams. In a modification, Fig. 2 (not shown), the harmonic voltage is introduced into an open delta tertiary winding inductively associated with the network. In another modification, Fig. 3 (not shown), the network is inductively associated with two starconnected tertiary windings, between the neutrals of which the harmonic voltage is introduced. In a further form, Fig. 4, the harmonic voltage is obtained by connecting a condenser 38 between the two neutral points of the star-connected windings 16, 17 of the network 12. Specification 409,682 also is referred to.