GB1209294A - Improvements in or relating to controlled valve-type converters - Google Patents

Abstract

1,209,294. H.V.D.C. converter systems. NAUCHNO - ISSLEDOVATELSKY INSTITUT POSTOYANNOGO TOKA. 17 Jan., 1969, No. 2739/69. Heading H2F. In an H.V.D.C. system, wherein a plurality of three-phase bridge convertor units are connected in series on the D.C. side, a faulty convertor is shunted by simultaneously firing all the mercury arc rectifiers in series in one phase of the convertor bridge, instead of using a separate by-pass rectifier as in known arrangements. In normal operation firing pulses from a pulse generator (not illustrated) and at the A.C. system frequency, are amplified in a six-channel amplifier 5 (Fig. 1) and fed via a transformer 6, transformers 7, and resistor/capacitor networks 8 to the grids of mercury arc valves 1 (detailed in Fig. 2, not shown). In the event of a fault (e.g. backfire, misfiring, arc back &c.) a protection unit 9 which receives inputs B from current transformers 13, 14, 15 in the convertor circuit and an A.C. mains input C renders the valves in the faulty phase arm non-conducting and produces an output voltage at the mains frequency. This output is transmitted via two conducting channels in a sixchannel thyristor switch 10, transformer 11 and pulse circuits 12 to the grid networks 8 of the valves in a selected phase, i.e. one which is not faulty as determined by the protection unit 9. Thereby the selected valves are fired and shortcircuit the convertor for a brief period during which the fault conditions may be cleared. Each pulse circuit 12 (Fig. 2, not shown) comprises a transformer (31) which receives the said protection circuit output and resulting outputs from its two secondaries are respectively fed, one via a capacitor and one directly, to two auxiliary rectifier bridges serially connected on their output side and which apply a fluctuating D.C. voltage to the grid networks 8 of the two selected valves which are to act as a shunt.