GB1018025A - Improvements in semiconductor rectifying installations - Google Patents

Abstract

1,018,025. Rectifying. MASCHINENFABRIK OERLIKON. June 22, 1964 [June 27, 1963], No. 25677/64. Heading H2F. In a polyphase semi-conductor rectifier installation for supplying an electric railway system, the rectifier elements are protected from power overloads by designing the rectifier supply transformer to have a high percentage reactance and by providing a series-connected inductance on the D.C. side, the combined effect of which is to drop the output voltage sharply on heavy current overloads (as illustrated graphically in Fig. 1, not shown). In the 9-phase embodiment shown in Fig. 2 the supply transformer secondary comprises phase windings 3a, 3<SP>1</SP>a, 3<SP>11</SP>a which are interwound, i.e. magnetically tightly coupled, and feed rectifier bridges 4a seriesconnected by inductances 5a. Fig. 3 (not shown) illustrates a 12-phase embodiment employing a series-parallel arrangement of bridge rectifiers. The 9- and 12-phase embodiments give respectively 18 and 24 ripple voltage pulses in the D.C. output per cycle of the supply. For railway systems of 2-5 MVA power range the normal percentage reactance of the supply transformer is stated to be 8-10%. It is stated that for an installation giving at least 12 pulses per cycle of the supply the transformer should have a percentage reactance at least half as much again as is normal. In a modification, not shown, rectifier elements may be used in parallel to absorb current peaks and satisfactory parallel operation of semi-conductor and mercury vapour rectifiers is said to be possible.