Reliability evaluation with Weibull distribution on AC withstand voltage test of substation equipment

For the development of a 'short-duration ac withstand voltage test', an insulation specification of substation equipment, there is a precise method of reliability evaluation using a Weibull distribution function. Regarding this method, there remains a subject of handling coexistence of multiple voltage levels. This paper first defines the two reliability evaluation methods, 'independence method' and 'accumulation method', applying to Weibull evaluation for coexistence of multiple voltage levels in relation to their physical meanings. Next, the influence of the Weibull parameter values are examined on the cumulative fault probabilities and test voltages calculated using these methods. When the time shape parameter a>1, the accumulation method gives higher values than the independence method; When a=1, the two methods give the same values; When a Index Terms--Short-duration ac (power-frequency) withstand voltage test, temporary overvoltage, Weibull distribution, reliability evaluation, cumulative fault probability, substation equipment.