Theoretical Studies of the Cumulative Effects Related to the Application of Strong Electric Fields on the Lifetime of Solid Insulation Structures

The cumulative breakdown process of solid dielectrics results in partial discharge and degradation. As the pulse number or the time increases, the total insulation performance of a solid insulation structure decreases and the breakdown probability increases until the final breakdown occurs. A formula to describe the breakdown probability ( P) in the cumulative breakdown process is presented and a lifetime formula is defined as 1/ P. By assuming that the breakdown voltage ( V
_BD
) conforms to the Weibull statistical distribution, a lifetime formula is derived with V
_BD
and its relative variance ( δ) as the key parameters. It is found that the longest lifetime and the operation voltage conform to a power relation with 1/ δ as the power exponent. In practice, δ should be as small as possible if a long lifetime is expected.