Patent GB-682743-A (GB)
Title: Arrangement of static current converters
IPC: H02M7/06
Filed: 1951-01-23
Abstract: 682,743. Converting. ALLMANNA SVENSKA ELEKTRISKA AKTIEBOLAGET. Jan. 23, 1951 [Jan. 24, 1950; Aug. 5, 1950], No. 1694/51. Class 38 (ii). In a converting circuit comprising a number of constituent static converters operating with mutual phase displacement, the influence which one converter during its commutation exerts on another converter, through inductive connection with adverse effect on the deionization of that other converter is completely or partially compensated. Fig. 4 shows how, in the inverting system of Fig. 1, the voltage rises sharply to d (somewhat less than d<SP>1</SP>, the theoretical maximum) after a short deionization period of reverse voltage following the combined firing and commutation period A. The compensation reduces the height of d. In a rectifying system the inductively transmitted effect of commutation in other valves may retard commutation but does not affect deionization. The compensation may be effected by connecting a capacitor in series or parallel with the line, by centrallytapped inductor 3 wound on common cores with air-gaps, and connecting the outer terminals of the line (or valve, see Fig. 9, not shown) winding of the main transformer, or by arrangements of windings of transformers 1, 2, whereby the S.C. reactance measured between the valve windings of two transformers 1, 2 is made larger than the sum of the S.C. reactances measured between the valve windings and the A.C. line. Common or series connected line windings 11, 12 may lie between coaxial valve windings 13, 14 of different converters, so that the leakage inductance between 13 and 14 is much larger than between 13 and 11 and 12 and 14, Fig. 10. Longitudinally-disposed valve windings 23, 24 may be closely coupled with line windings 21, 22 but have loose mutual coupling through equalizing windings 25, 26 which may have an inductor 27 in circuit, Fig. 11. For very high line voltages a further transformer may couple the line and equalizer winding circuits, Fig. 15 (not shown). The equalizing winding may be connected in series aiding or opposing relationship with the line windings, either directly or through a transformer which may have an adjustable ratio for voltage regulation. Three arrangements with different core constructions are described, in which the paralleled equalizing windings are connected in series with the line windings and are tapped for voltage regulation, Figs. 12, 13, 14 (not shown). A synchronous compensator 50 and the A.C. line may be connected respectively to what in preceding circuits are the line and compensating windings, Fig. 16. Fig. 17 shows two transformer pairs having windings 51, 52, and 61, 62 connected to the synchronous compensator, there being valve windings 53, 54 on one pair and combined equalization and line windings 65, 66 on the other. The cores of each transformer pair may form one structure. Switches 67, 68 enable one or other of the constituent converters to be disconnected, if necessary, without disturbance to the rest of the circuit. The transformer pair carrying the line windings may be combined into one transformer, Fig. 18 (not shown). Fig. 19 shows a modification in which the synchronous compensator 50 and the line 87 are connected to paralleled windings 85, 86 in series with the windings 81, 82 on another limb, to give a phase displacement of, say, 7.5. This circuit may be modified to enable any constituent converter to be cut out, Fig. 20 (not shown). To assist deionization where the compensation of transference of interference is incomplete, and when the commutation time is affected by regulation it may be necessary to reduce the rate of regulation.