Insulator Degradation by High Current Discharges
Engel, Thomas G.
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The degenerative action produced by 300 kA, repetitive arc discharges on the surface of various insulator materials is investigated as a function of insulator and electrode material and the ambient atmosphere used. The insulator damage produced by the 20 is wide oscillating pulse is characterized by a shot-to-shot decrease in surface breakdown voltage of the insulator and a loss of insulator mass. The insulators under investigation include a broad group of ceramic, polymeric, and elastomeric materials which have been tested with graphite, molybdenum, copper, and copper-tungsten electrodes. Typically, the ambient gas used in the tests was atmospheric air although some tests were conducted in pure nitrogen, pure oxygen, and admixtures thereof. Models have also been developed which predict hold off voltage degradation, mass erosion, and hold off voltage conditioning for the insulator. The conditioning of an insulator is characterized by an increase in its surface hold off voltage in the initial stages of the test. In these models, insulator performance is predicted by its HDR (i.e., hold off voltage degradation resistance), MVC (mass vaporization coefficient), and HVC (hold off voltage conditioning) figures of merit which are calculated using the pertinent thermo physical properties of the material. The relationship between the figures of merit is also discussed.