Overview

The listing of the thermal capabilities of electrical insulating materials, based on service experience, was found to be impractical, owing to the rapid development of polymer and insulation technologies and the long time necessary to acquire appropriate service experience. Accelerated ageing and test procedures were therefore required to obtain the necessary information. The IEC 60216 series has been developed to formalize these procedures and the interpretation of their results. Physico-chemical models postulated for the ageing processes led to the almost universal assumption of the Arrhenius equations to describe the rate of ageing. Out of this arose the concept of the temperature index as a single-point characteristic based upon accelerated ageing data. This is the numerical value of the temperature at which the time taken for deterioration of a selected property to reach an accepted end-point is that specified (usually 20 000 h). The term "Arrhenius" is widely used (and understood) to indicate a linear relationship between the logarithm of a time and the reciprocal of the thermodynamic (absolute or Kelvin) temperature. The correct usage is restricted to such a relationship between a reaction rate constant and the thermodynamic temperature. The common usage is employed throughout this standard. The large statistical scatter of test data which was found, together with the frequent occurrence of substantial deviations from the ideal behaviour, demonstrated the need for tests to assess the validity of the basic physico-chemical model. The application of conventional statistical tests, as set out in IEC 60493-1, fulfilled this requirement, resulting in the "confidence limit", (TC) of TI, but the simple, single-point TI was found inadequate to describe the capabilities of materials. This led to the concept of the "Thermal Endurance Profile" (TEP) in the second edition of this part of IEC 60216, incorporating the temperature index, its variation with specified ageing time, and a confidence limit. A complicating factor is that the properties of a material subjected to thermal ageing may not all deteriorate at the same rate, and different end-points may be relevant for different applications. Consequently, a material may be assigned more than one temperature index, derived, for example, from the measurement of different properties and the use of different end-point times. The responsible committee is DKE/K 183 "Bewertung und Qualifizierung von elektronischen Isolierstoffen und Isoliersystemen" ("Evaluation and qualification of electrical insulating materials and systems ") of the DKE (German Commission for Electrical, Electronic and Information Technologies) at DIN and VDE.

Document: references other documents

Document: referenced in other documents

Responsible national committee

DKE/K 183 - Bewertung und Qualifizierung von elektrischen Isolierstoffen und Isoliersystemen