Prefire Properties of High Pressure Gas Spark Switches for Fast Linear Transformer Drivers

Prefire is the unexpected breakdown of gas switch at triggered mode and have to be limited at extremely low level in fast linear transformer driver (FLTD). In this paper, the dispersion of breakdown voltage as well as prefire characteristics of high pressure gas spark switches under typical working conditions of FLTD was investigated and reported. Tested switches included a three-electrode field-distortion gas switch (TFGS) and a six-stage multichannel gas switch (SMGS), which had compact structure and low inductance. The results showed that the self-breakdown voltage of both TFGS and SMGS obeyed three parameter well-bull distribution and the dispersion of Ub at ±90 kV could reach 4% of TFGS and 14% of SMGS, respectively. The dispersion of Ub was remarkably influenced by the floating potential of middle electrode. By grounding the triggering electrode via a kilohm resistor, the dispersion of Ub decreased to 2% in TFGS and 6.5% in SMGS, respectively. When a voltage equalization method by cascade resistors was introduced, the dispersion of Ub in SMGS dramatically decreased to 4.4%. In repetitive operation at triggered mode, the prefire rate of TFGS reached 0.9% at γ = 80% working coefficient and decreases with the decrease of γ, being 0.3% at γ = 72% and 0.2% at γ = 65%, respectively. The prefire rate of SMGS was much higher, reaching 1.7% at γ = 72% and 0.7% at γ = 65%, and decreased to 0.6% and 0.3%, respectively, after applying the equalizing resistors. Generally, the prefire rate of SMGS was somewhat higher than that of TFGS with the same working coefficient and the floating potential limiting was imperative for prefire inhibition.