Senior Staff Engineer, Underwriters Laboratories, Inc., Melville, NY
Professor of Electrical Technology, University of Bologna, Bologna,
Professor of Material Science, University of Bologna, Bologna,
Reliability Leader, General Electric Corporate Research and Development, Schenectady, NY
Pages: 13 Published: Jan 2000
During the service life of electrical equipment, organic electrical insulating materials used at elevated service temperatures can degrade as a result of progressive chemical reactivity. It is therefore essential that normal operating temperature limits be established for such materials. The traditional approach is to accelerate the degradation process with simultaneous testing at moderately elevated temperatures above the intended service temperatures of both the candidate material and a control reference material. With proper application of a chemical kinetic model, a service limit is established for the candidate material based on the comparative test performance, with the control having known long-term thermal service capabilities. There are practical limits on the maximum test temperatures and corresponding minimum test times to ensure an accurate representation of the service degradation mechanism during the test program. This results in an onerous, unavoidably protracted test time for these thermal aging studies. A number of relatively rapid analytical techniques have been proposed to reduce the test times without compromising the accuracy of the determined service limit. The most successful of these often involve hybrid testing, as a combination of a rapid analytical technique and part of the traditional program at the higher test temperatures and shorter test times, to result in a desirable and substantial reduction in test program times. This paper will review the principles of the traditional program, and the theory and initial results of a proposed hybrid technique based on oxidative stability testing using oxidation induction.
thermal aging, thermal endurance, Arrhenius, oxidation induction time, oxidation maximum time, oxidative stability, asymptotic kinetic model, isothermal DSC
Paper ID: STP13461S