Patent GB-584485-A (GB)
Title: Improvements in electric conversion systems
IPC: H02M7/15
Filed: 1942-03-02
Abstract: 584,485. Automatic control systems for electric supply systems ; converting. GENERAL ELECTRIC CO., Ltd., and THOMPSON, W. G. March 2, 1942, No. 2713. [Classes 38 (ii) and 38 (iv)] In a system in which at least one vapour electric arc converter and at least one dynamoelectric machine operate in parallel to supply power to a common load, the machine output is controlled, so that the ratio of machine output to total output is substantially constant, by the interaction of two differential windings associated with a common magnetic circuit, one winding being energized in dependence on the converter output and the other in dependence on the machine output. In Fig. 1 a grid-controlled threephase vapour arc rectifier 1 is supplied from A.C. mains 4 and operates in parallel with a D.C. generator 3, driven either by a prime mover or an A.C. motor connected to mains 4 (neither shown), to supply busbars 5. Generator 3 has, in addition to its shunt field 7 and differential series field 9, an auxiliary field winding 10 carrying the rectifier output current. Windings 9 and 10 act in opposition and control the generator to maintain the proportional division of load between rectifier and generator substantially constant under varying load conditions. Automatic control of the output voltage may be effected by grid control gear 2, of the rectifier. The following modifications Figs. 2-7 (not shown) are described :- (Fig. 2.) The arrangement of Fig. 1 extended to three rectifiers in parallel with three D.C. generators. The auxiliary field winding of each. generator is tapped for adjustment to suit the numbers of rectifiers and generators in service. An equalizer connection is provided between the generators. Simultaneous operation of tap changers on transformers supplying the rectifiers and shunt field regulators of the generators is referred to. (Fig. 3.) Indirect control of the D.C. generator by an A.C. motordriven D.C. booster, the field windings of which correspond to the windings 9 and 10 of Fig. 1 and the armature of which is -connected in series with the shunt field circuit of the generator which is then of the normal compound type. (Fig. 4.) The arrangement of Fig. 3 extended to two rectifiers in parallel with three D.C. generators. The booster field windings are tapped for adjustment to suit the numbers of rectifiers and generators in service. Either a single booster or an individual booster for each generator, driven from the A.C. mains, may be used. (Fig. 5.) A three-phase rectifier operating in parallel with a six-phase rotary converter connected, on its A.C. side, through a six-phase saturable reactor and phase-multiplying transformer to the mains supplying the rectifier. Two saturating windings for the reactor, carrying the output current of the rectifier and converter respectively, act differentially and thereby maintain the division of load. (Fig. 6.) An arrangement similar to that of Fig. 5 except that the rotary converter is three-phase and a D.C. booster having differential field windings carrying the load currents energizes a single saturating winding of the reactor. (Fig. 7.) A three-phase rectifier in parallel with a three-phase rotary converter, the output currents of each differentially energizing the field of an A.C. booster, driven by a synchronous motor from the A.C. mains, the output of which is in series with the A.C. supply to the converter. Parallel operation of a plurality of rectifiers and rotary converters is referred to.