REVERSE VOLTAGE SURGE PROTECTION FOR HIGH-VOLTAGE THYRISTORS

摘要

ABSTRACT OF THE DISCLOSUREA thyristor is shunted by a metal oxide varistorin series with switching means which switches abruptlyfrom a normal high-resistance state to a low-resistance,current conducting state when the thyrsitor is subjectedto a transient surge of reverse bias voltage the magnitudeof which is higher than a predetermined repetitive peakmagnitude and is nearly equal to the level at which thethyrsitor turns on in an avalanche breakdown mode. Thevoltage-current characteristic of the varistor is coordin-ated with the reverse breakdown characteristic of thethyristor so that surge current will divide therebetween insuch proportions that the maximum reverse current flowingthrough the thyrsitor is lower than a predetermined criticalmagnitude which can damage the same, whereby the thyristoris able safely to particpate in the surge-energy dissipatingprocess.