Thermal aging

Long term thermal aging testing is designed to monitor degradation of the insulation system. It involves aging the proposed EIS at three or more elevated temperatures with intermittent dielectric proof testing. After each heat cycle, samples are also subjected to a repeated series of environmental exposures, such as cold shock, mechanical stress and humidity.

Test results for the proposed EIS are then compared to a field-proven control EIS, running concurrently. At the conclusion of the aging program, the performance of the proposed EIS is compared to the control EIS. Ultimately, the rating issued to the proposed EIS is relative to the control EIS' previously established rating.

Details regarding thermal aging can be found in UL 1446, Paragraphs 12.1-12, 3.5 and IEEE 117. A typical thermal aging program lasts 12-18 months. Many international standards also require thermal testing of this duration.

One- or two-temperature thermal agings are reduced test programs used to evaluate modifications to an existing EIS. Recognition of these modified EIS is usually issued within three to six months of testing, depending on the test results.