Coefficient of Variation of the Positive-Impulse Breakdown of Long Air-Gaps

Extensive impulse breakdown tests on long air-gaps show that the coefficient of variation C = σ/U50% × 100% depends on the form of the impulse. Tests were performed on three different gaps of 3, 5.90 and 8.75 meters long. The value of C for each form of the impulse was estimated by applying approximately 700 shots at appropriate voltage levels. The procedure used allowed C to be estimated with a confidence interval, at the 95% level, in the order of ±0.1 C.