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We discuss the assessment of breakdown probabilities by means of the up-and-down method. The exact maximum likelihood estimates for a number of response patterns are calculated for three different distribution functions and are compared with the estimates corresponding to the normal distribution. Estimates of the 50% probability breakdown voltage and of the scale parameter of the breakdown probability functions are inves tigated.

The accuracy of discharge onset prediction via the figureof-merit concept for a strongly electronegative gas is examined. A coaxial system is employed, for which the inner electrode possesses a surface roughness of Ra=35 pm. With SF6 as the insulating medium a reference discharge-onset characteristic is obtained for gas pressures up to 0.8 MPa. From a knowledge of this onset characteristic, the direct calculation of discharge onset voltages in other strongly electronegative gases is undertaken by utilizing the figureof-merit concept.For gas pressures in the range O.02

This paper discusses the assessment of breakdown probability by means of the up-and-down method. The Dixon and Mood approximation to the maximum-likelihood estimate is compared with the exact maximum-likelihood estimate for a number of response patterns.Estimates of the 50D probability breakdown voltage and the scale parameter of the breakdown probability function are considered, and the estimation bias is investigated.