Progress in the development of an 8-kV light-triggered thyristor with integrated protection functions

Light-triggered 8-kV thyristors with an integrated breakover diode were fab ricated. The adjustment of the breakdown voltage of the breakover diode (BO D) is realized by a well-defined curvature of the junction between the D-ba se and the n-base, A multiple amplifying gate structure, together with an i ntegrated turn-on curl ent limiting resistor, guarantees a safe turn-on beh avior in the case of overvoltage triggering as well as during light trigger ing. These thyristors have successfully been put into service at the Celilo Converter Station of the Pacific Northwest-Southwest HVDC Intertie by Bonn eville Power Administration in Portland/Oregon/USA. There, a mercury are va lve was replaced by a valve containing these light triggered thyristors wit h integrated overvoltage protection. In a further development, the amplifying gate structure was optimized in or der to simplify the fabrication process and to maintain the high light sens itivity while obtaining a higher dV/dt and a higher dI/dt capability, This was realized by shrinking the optical gate, by carefully adjusting the trig gering sensitivity of the amplifying gates and by widening of the turn-on c urrent limiting thyristor, With these measures, Initial investigations rega rding the integration of a forward recovery protection were also performed.