Thermal Endurance Data for Solid Insulating Materials

Abstract

The Arrhenius plotting procedure has been used as the base for extensive international standardization of the International Electrotechnical Commission (IEC) Publication #216. Thermal endurance data for approximately 50 insulating materials, tested and evaluated according to IEC #216 have been made available from Swiss and German laboratories. The data have been collected and used for the determination of the "Thermal Endurance Profiles" (TEP) which are in addition to the "Temperature Indices" (TI), a fairly new format in IEC-Publication 216, for describing the life time-temperature relation. These TEP's have been achieved by testing the thermal capability with different criteria and different endpoints. Additionally, the regression coefficient representing the slope of the Arrhenius curve respectively (the activation energy of the Arrhenius equation), has been recorded in the form of a doubling (or halving) endurance temperature interval. The reported data are discussed in respect to: the reproducibility of the test procedures; the feasibility of certain instructions; the lack of equivalence of TEP results when different criteria and/or different endpoints were selected; the importance of presenting the slope of the Arrhenius plot; and the problem of identifying accurately the insulating materials. The complexity of material reactions on thermal stresses and consequently the variety of verified thermal endurance predictions has to be recognized. Such considerations lead to the conclusion that single-point representation of thermal endurance should be avoided.