Surface discharge switch design: the critical factor

The authors report which dielectric properties are critical to designing a long-life surface discharge switch (SDS). Theory is correlated with experiment by evaluating the performance of a large group of polymeric and ceramic dielectrics. These dielectrics were tested in a single-channel, self-commutating SDS operating at approximately 35 kV and approximately 300 kA (oscillatory discharge) with a pulse length of approximately 20 mu s (1/4 period approximately 2 mu s). The performance of a dielectric is characterized by its shot-to-shot breakdown voltage and by its mass erosion. Theoretically, the voltage holdoff degradation resistance and the arc melting/erosion resistance of a dielectric can be qualitatively predicted from its 'formativity' and its 'impulsivity', respectively. The formativity and impulsivity are figures of merit calculated from the known thermophysical properties of the dielectric. The effects produced in dielectric performance by choice of electrode material (e.g., molybdenum, graphite, and copper-tungsten) and discharge repetition rate are also discussed.<
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