Statistical Stress-Duration Characteristics of High Voltage Insulation

New statistical models are developed for analysis and prediction of stress-duration characteristics of high voltage insulating systems. These models take into account available knowledge on insulation breakdown probability as a function of the test voltage applied for a limited duration as well as the characteristics of the delay time to breakdown. Special reference is made to the behaviour of the models at low probability which is particularly important for the evaluation of the risk of failure. The analytical tools developed are justified on the basis of experimental results obtained with transformer oil and compressed SF6