GB1164841A - Improvements in Thyristor Circuits - Google Patents

Abstract

1,164,841. Rectifying. ENGLISH ELECTRIC CO. Ltd. 4 May, 1967 [6 May, 1966], No. 20280/66. Heading H2F. [Also in Division H3] In a thyristor circuit including a string of series-connected thyristors 3, a number of pulse transformers 8, 9 and 10 are connected in cascade, each transformer being inductively coupled to a group of thyristors of the string, such that a control means connected to the primary 10A of one of the transformers 10 causes substantially simultaneous firing of the thyristors. The string of thyristors may form a H.V.D.C. converter and can be controlled from a pulse generator 14 which is at earth potential and drives a light source 15. A photo-cell 17 and pulse amplifier 18 at a higher potential transfer the triggering pulses to the pulse transformers which may have ferrite cores. An additional transformer may be connected between the triggering winding of each transformer and gate-cathode circuit of a respective thyristor. The power supply for the pulse amplifier 18 may be obtained from an R.C. grading network 6, 7 connected to equalize the voltage across each of the thyristors. A string of series-connected thyristors may be divided in half (Fig. 2, not shown), each half (20, 21) having cascade connected firing transformers as in Fig. 1 and the primaries of the first firing transformers being connected via a transformer (19) to the pulse amplifier 18. In this circuit the power supply of the pulse amplifier is obtained from across the string via a transformer (25) and bridge rectifier (26). The photo-cell firing arrangement in Fig. 1 may be replaced by a light-sensitive thyristor, a single pulse transformer with full primary-secondary insulation or a chain of transformers having progressively smaller degrees of insulation to ground. Each thyristor may be replaced by a number of thyristors in parallel supplied from the same secondary winding or from an auxiliary winding on an isolating transformer, the primary of which is fed from an auxiliary secondary winding on the main pulse transformer 8, 9, 10.