Effect of temperature on the impulse life expectancy of crosslinked polythene

The Weibull statistical method is widely used to predict the failure of electrical insulation in terms of stress and time (or, in this case, the number of applied impulses) for a given temperature. In the present work the probability of breakdown has been determined for flat-disc samples of crosslinked polythene, subject to repeated application of impulse voltages for various stresses and temperatures. The results obtained indicate that an extension of the Weibull equation to include temperature is valid. Hence the probability of failure P for a given number of impulses n with the sample at stress E and temperature T is given by P(E, n, T) = 1 ¿¿ exp[¿¿(E/E0)b ¿¿ (n/n0)a ¿¿ (T/T0)c], where E0, n0 and T0 refer to a probability value of 63.2%