GB1147146A - Improvements in or relating to electrical converting apparatus - Google Patents

Abstract

1,147,146. Semi-conductor circuits. WESTINGHOUSE ELECTRIC CORP. 17 Oct., 1966, No. 46226/66. Heading H3T. [Also in Division H2] A converter, particularly for use in highvoltage D.C. transmission systems, comprises a plurality of series-connected thyristors provided with arrangements for distributing transient and steady state voltages uniformly across the thyristors and with means for limiting the rate of change of current; said thyristors being triggered, by one or more circuits responsive to electro-magnetic radiation. Fig. 1 (not shown) relates to a high-voltage rectifying system utilizing a 3-phase bridge, each arm of which consists of three parallel paths each containing a series arrangement of four groups of ten to thirty series-connected thyristors. Inductors (44, 46) or transformers ensure uniform current distribution between parallel paths. Each thyristor is shunted by a resistance capacitance network 68, 76, 70 (Fig. 2A) so as to provide uniform voltage distribution. A saturable or non-saturable inductor 80, damped by a resistor 82 is included in series with each thyristor so as to reduce the rate of build-up of current. If a further saturable or non-saturable inductor 84 is included as shown, only a single inductor 80 is necessary in each series circuit. A damping diode may be included in series with resistor 82 (Fig. 2B, not shown). As shown in Fig. 3, each thyristor 66 . . . 66<SP>111</SP> is triggered by a control thyristor 140 via a transformer 100 having a Zener diode 142 as a voltage limiter. Capacitor 132 is charged via a bridge rectifier 160 from a circuit 110, 112 connected across part of the A.C. supply and is discharged via winding 102 when thyristor 140 is triggered by a light pulse from 152 being received by a photo-resistor 150 or photo-transistor. The master firing control circuit 152 may utilize a laser diode or xenon arc arranged to radiate appropriately timed pulses to a plurality of detectors 150 each associated with one or more groups of seriesconnected thyristors. Alternatively, circuit 152 may emit U.H.F. radio waves of different frequencies for respective groups of thyristors. In Figs. 6, 7 (not shown) the bridge 160 is omitted and a further thyristor or emitter follower interposed between device 150 and thyristor 140. In Fig. 5 (not shown), a single radiation responsive device 150 is directly connected to the control electrode of each main thyristor. Modifications.-The inductor 80 may be replaced by a split ferrite core around each thyristor carrying a winding connected to a damping resistor. A mono-stable multi-vibrator may be included between the radiation detector 150 and the control thyristor 140. In Fig. 4 (not shown) the control thyristor 140 is replaced by a gate-controlled switch. Reference has been directed by the Comptroller to Specifications 1,072,740, 1,077,556 and 1,082,783.