Investigation of pulse power thyristor thermal variations

This paper presents a study of temperature variations in a Pulse Power Thyristor (PPT) during and after discharge. The PPT studied was the SPT411BHT. The SPT411BHT is a 5000 V, 4600 A, 125 mm thyristor made by Silicon Power Corporation. In order to determine the temperature of the PPT silicon, a 125 mm diode with identical thermal properties is placed in series with the PPT. There is a strict relationship between the forward voltage and the silicon temperature of the diode. Measurement of the forward voltage of the diode before and after discharge will accurately predict the temperature increase of the silicon. Peak discharge currents will be varied from 30 kA to 90 kA. The forward voltage measurement circuit must be able to resolve millivolts in the presence of common mode voltages in excess of 2 kV. Also, the circuit must isolate the measurement equipment from the circuit. This paper will discuss the temperature measurement concept as well as the design details of the circuit used to measure the diode forward voltage.