The study of the characteristics of dielectric breakdown in com-mercial polyethylene, under applied high-voltage impulses, divides naturally into two parts:one concerned with single-impulse breakdown during "the period of rise of overvoltage impulses and the other con¬cerned with multiple-impulse breakdown at gradients below the threshold level for single-impulse breakdown.nSingle-impulse breakdown is shown to be a function of rise rate, and to be characterized by breakdown gradients that exceed the dc breakdown level for very high rise rates but that may fall well below the dc level for lesser rise rates. It appears to be independent of thick¬ness in the range from 1.5 to 26.5 mils. The fact that single-impulse breakdown data fit an extremal distribution suggests the applicability of the weakest-link theory.
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