Development of an opto-electrical probe for measuring impulse high-voltage across thyristors in HVDC valve of three-Gorges project

A high-voltage resistive probe is developed to measure impulse voltage (1.2/50/spl mu/s) distribution along thyristor units in HVDC converter valve with an optoelectronic system to transmit the measured signal. A pulse frequency modulation (PFM) mode is adopted for this transmitting system, owing to its immunity to high-intensity electromagnetic interference. Experimental results indicate that the undefined degree of the scale factor under lightning impulse for this measuring system is within /spl plusmn/1%, and therefore it can meet requirements specified by IEC60700-1.