GB1269502A - Improvements in thyristor firing circuits - Google Patents

Abstract

1,269,502. HVDC static converters. ENGLISH ELECTRIC CO. Ltd. 13 May, 1969 [16 May, 1968], No. 23305/68. Heading H2F. [Also in Division G1] In an HVDC converter groups of thyristors in a series chain, are fired simultaneously from a common pulse generator 14 the pulses from which are transmitted in the form of light waves (visible, infra-red or ultra-violet) through filamentary light guides 7, 9 to firing circuits local to the thyristors, the guides being coupled to a plane polarized light source through a polarized filter and the plane of polarization is controlled by the pulses from generator 14 such that light waves are transmitted through the filter only during a said pulse. Light waves in filaments 9 are converted to electrical signals by photo-transistors or photodiodes 10 to actuate pulse generators 11 which send firing pulses through distributing and gating circuits 13 to fire all the thyristors in groups 1 simultaneously. Alternatively there may be a respective pulse generator 11 and photo-sensor 10 for each thyristor. Light from a source 2 is directed through a polarizing filter 3, a solid crystal 4, and the polarizing filter 5. It is then focused by a lens 6 on to the end of a bundle of filamentary light guides 7. These guides enter a mixer or brancher 8 having output bundles of light guides 9. The crystal (e.g. of Yttrium iron garnet) when subjected to a magnetic field in response to a pulse from generator 14, rotates the plane of polarization of the plane polarized light through filter 3 to align with that at which the filter 5 imparts least attenuation so that the light wave impinges on the light guides 7 and the thyristors are fired. In the absence of an energizing field the plane polarized light through 3 passes through the crystal but is severely attenuated by filter 5 since this is polarized in a different plane and the thyristors will not be fired. Alternatively the crystal may be of ammonium dihydrogen phosphate disposed in an electrostatic field. The series strings of thyristors may be connected to form a bridge network.