Study on overvoltage protection in HVDC LTT valve

The light-triggered thyristor (LTT), which can be directly fired by light, does not need gate electronics on the high-voltage side and is thus a near-ideal semiconductor device for a HVDC valve. In providing overvoltage protection for an LTT without losing its advantage of simple circuits associated with the thyristor, the overvoltage protection system adopted in the conventional electrically triggered thyristor is not necessarily appropriate. The authors have shown that high-speed protective gate pulses generated from the valve base electronics together with the valve arrester are sufficient for the LTT valve overvoltage protection. The adequacy of this protection strategy is demonstrated by factory type tests and also excellent service experiences.