Continuous load switching for step-transformers - involves thyristor rectifier bridge with firing controlled via four pulse circuits

摘要

For the continuous load switching for step-transformers the two ac-points of a rectifier bridge are connected to the two arms of the tap selector. The rectifiers of the bridge are thyristors. The two dc-points of the bridge are interconnected via two diodes in series, to the centre of which a load line is connected. The blocking voltage across the diodes is used to feed control circuits which fire the thyristors. Each of the four switching circuits generates in its monostable relaxation oscillator pulses for firing one thyristor. The relaxation time can be continuously altered within suitable time intervals by varying the value of the setting resistors. By inserting an inverter into one of the two signal voltage lines from the diodes a common reference potential is obtained for all four pulse circuits which also have a common power supply. By paralleling a diode to each setting resistor a very small recovery time is achieved. The advantages claimed are small number of components, increased operating reliability and economical working.