GB610392A - Means for indirect forced commutation of static current converters in two-way connection - Google Patents

Abstract

610,392. Converting. ALLMANNA SVENSKA ELEKTRISKA AKTIEBOLAGET. April 4, 1946, No. 10393. Convention date, April 21, 1945. [Class 38 (ii)] For commutation in converting arrangements in which a pair of main valves are oppositely connected to each A.C. terminal and in series across the D.C. terminals, a pair of transition valves are connected to each pair of main valves without any intermediary transformer winding. The three A.C. phases 8 are connected to the junctions of pairs of oppositely connected valves 1, 4; 2, 5; 3, 6; which are also connected across D.C. circuit 7. Pairs of transition valves 11, 14; 12, 15; 13, 16 are also connected across the D.C. circuit, their junctions being connected to the A.C. terminals through commutating condensers 17, 18, 19. When commutating from valves 1 to 2, valve 11 is ignited so that condenser 17 discharges through valves 1 and 11 to transfer suddenly the load to valve 11, and then condenser 17 is charged in the opposite direction, the load being gradually transferred to the now ignited valve 2. Condenser 17 is left charged in the reverse direction ready for commutation from valve 4 to valve 5 by way of valve 15 in the reverse half-cycle of the same phase. Normally the time of commutation can be extended to recharge the condenser even during low load, but if necessary an additional valve and reactor may be associated with each valve, e.g. 22, 20 with valve 1 or 25, 24 with valve 3, for this purpose. A modification is described in which the junctions of each pair of transition valves are connected to the A.C. phase, and a condenser is connected between the other ends of these valves and the junction of another pair of valves connected in series across the D.C. circuit, so that only one commutation condenser is used. Since each commutation cannot be extended over more than 1/6th of a cycle to meet load fluctuations, auxiliary discharge circuits or a further condenser may be provided, Fig. 2 (not shown). The transition valve connected to the incoming main valve (especially in rectifiers) or even the third valve may be used to effect the commutation.