On the electrical endurance characterization of insulating materials by constant and progressive stress test

Expressions for the generalized probability distributions of failure times obtained from constant-stress and progressive-stress tests are presented. Three types of life models are considered for this purpose, i.e. linear inverse-power and exponential models, and a threshold life model based on the inverse-power law. Moreover, two types of progressive-stress tests are examined, i.e. tests at linearly increasing voltage starting either from zero or from a selected electrical field or voltage value. It is shown that both constant and progressive-stress tests can provide a complete electrical endurance characterization of the tested insulation, once the generalized probability distribution has been defined appropriately. However, while the constant-stress tests have a significant advantage in providing shorter test times compared to the progressive-stress tests, the latter tests give rise to less dispersed data. Examples of insulation characterization by constant and progressive-stress tests on XLPE and EPR specimens are given.<
>