Lifetime prediction of HV silicone rubber insulators based on mechanical tests after thermal ageing

In this paper, polydimethylesiloxane (PDMS) as a candidate for high voltage insulation applications is investigated as to the aging behavior at different temperatures in air. Three models according to ISO 11346, to Gillen et al, and to Hoang and Lowe were applied to determine endurance limits in terms of a time-to-failure after aging in hot air. Aging was performed in air from 150 to 170°C. Tensile tests were performed on unaged and aged PDMS specimens at ambient temperature using strain-to-break values as a performance indicator for the degree of aging. For PDMS, the effects of aging were found to depend strongly on the aging conditions. The activation energies and corresponding lifetime predictions for the chosen temperature range derived from these models are compared and interpreted as to their practical relevance. As a measure of the endurance limits, the decrease in strain-to-break to 50%, of the value of the unaged reference state was applied. Data used for the various models indicate that although all three methods are based on Arrhenius behavior, different lifetimes can be deduced. Despite all the differences, Gillen and ISO approach seems to give more reliable trends in lifetime than the H and L method.