Light-Triggered Thyristors For VAR Generator Applications

EPRI has sponsored work to develop high power thyristors which can be directly triggered by light signals. One application for these devices is in VAR generator systems for electric utility use. Because the triggering signal is carried by electrically insulating fiber optics cable, excellent insulation of high voltage components from control circuitry is achieved, and false firing due to electromagnetic noise is virtually eliminated. This paper describes the thyristor design concepts which relate to light triggering; the trade-offs in device characteristics which must be considered; and the performance which has been achieved. Appropriate light sources, fiber optics light distribution systems, thyristor packages, and a test module for light-triggered thyristors are described.