Surface studies of dielectric materials used in spark gaps

Abstract

Dielectric materials commonly used as insulators in spark gaps (lexan, nylon, lucite,macor, boron nitride, delrin, and G-10) have been exposed to the byproducts of arcs in three different spark gap experiments. The first was a 60-kV, 0.05-C/shot spark gap using copper-tungsten or graphite electrodes at various pressures of N2 and SF6 gas. The second was a 5–30-kV, 4–25-kA, 0.1–0.6-C/shot, unipolar, pulsed spark gap using graphite, copper-graphite, copper-tungsten, brass, and stainless steel electrodes in N2 gas or air. The third was a 45-kV, 0.009-C/shot surface discharge switch. Surface analysis of these insulators indicates that most become coated with a thick layer of electrode material depending upon the type of gas, electrode, and insulator material used, and the conditions of the arc. However, lucite insulators inserted in the second spark gap using graphite electrodes and air showed no indications of deposited electrode material on the surface but did show small particles of graphite imbedded in the surface. The self-breakdown voltage (Vsb) statistics for spark gaps with insulator inserts show significant deviations from the Vsb statistics for spark gaps without insulator inserts, which may be due to deposits of insulator material onto the electrodes.