Significant measurements for determining the stability of high-temperature magnet-wire insulation

Test methods for evaluating the stability of high-temperature magnet-wire insulation are described. Reduction in dielectric strength during uninterrupted exposure to high temperature is used to define the insulation life which would be obtained with comparatively ideal operating conditions. Moisture resistance, as measured by power factor after humidification, is proposed as a criterion for determining the ability of a material to withstand such adverse operating hazards as moisture absorption or mechanical shock. Results have been obtained which indicate that deterioration rates, calculated from measured reduction in dielectric properties at high temperatures, may be experimentally verified at lower temperatures. When this is true, justification is provided for the extrapolation of data to lower, operating temperatures. Conversely, the absence of similar aging trends at different, accelerated temperatures should serve notice that care must be taken in the extrapolation of data to low temperatures.