Environmental aging of insulating materials

Abstract

Predicting the useful life of organic materials has been made possible by the use of Arrhenius plots. Recently, data have become available to show the combined effects of the humidity and temperature on the aging performance of moisture-sensitive materials. A method is developed to use such information to calculate the predicted life of a material operating in enclosed (warm) electrical equipment in a room of known temperature and humidity. Although several assumptions must be made in this development of predicted life, guidelines for selecting reasonable assumptions are indicated. First, an explicit assumption is made that the period selected for measurement of room temperature and humidity is typical of the room conditions over the life of the equipment under consideration. Second, the assumed temperatures for the iso-aging curve calculations should span the room temperature and the equipment operating temperature. Finally, the assumed relative humidity for translation of the iso-aging curve should be somewhat above the humidity at the calculated equivalent temperature in order to allow a conservative prediction. >