Behavior of HVDC Thyristor Valve on the Critical Turn-Off Condition and Optimized Gate Firing System

When a thyristor valve is operated in a current discontinuity mode, one or more thyristor devices of the valve can be overstressed due to the critical, turn-off phenomena. An adequate gate firing s stem is indispensable to y prevent such a thyristor contingency. In thi. s paper, a thyristor critical turn-off is discussed in detail and the optimized gate system is presented with the demonstration of site test carried out in Hokkaido -Honshu HVDC link in Japan.