FAEEE2B5d01 - IEEE Transactions on Electrical Insulation...

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IEEE Transactions on Electrical Insulation Vol. 28 No. 5, October 1993 777 Complex Electrical Thermal and Radiation Aging of Dielectric Films Javaid R. Laghari Department of Electrical and Computer Engineering, State University of New York at Buffalo, Buffalo, NY ABSTRACT A review of the effects of electrical, thermal and radiation stresses, singularly or simultaneously, on dielectric films is car- ried out. The types of accelerated aging under these stresses and the statistical methods used to evaluate the experimental data for life, including the two-parameter Weibull and the log- normal distributions, are described briefly. The experimental life models currently used for aging are discussed. Recent data on the complex electrical/thermal/radiation aging of dielectric films is described. 1. INTRODUCTION AILURE in electrical components used in electric pow- F er generation, distribution and conditioning such as rotating machinery, capacitors and transformers is often attributed to the breakdown of electrical insulation due to presence of degrading stresses, such as electrical and thermal, and other stresses associated with the environ- ment in which they serve, including radiation. Some of the degrading stresses are prevalent in specific applications. These stresses, depending on the nature of the equipment and its environment, may combine into a multistress situation and cause the aging process to ac- celerate further. The ability of the insulating material to withstand multifactor stress aging is of utmost impor- tance in the evaluation of the material itself. Specifically, the time to breakdown (or lifetime) of insulation under the applied stress is of major interest in aging studies. A large variety of tests have been performed for this purpose Aging under multifactor stress recently has generated considerable interest. A comprehensive bibliographic sur- vey is available which includes major publications on the multistress aging of polymeric insulators [l]. The inter- est in simultaneous stress tests is obvious since the results obtained are quite different when stresses are applied sin- gularly or sequentially [2,3]. Singular electrical and thermal, and simultaneous elec- trical and thermal stresses have been investigated most commonly since the presence of these two stresses is al- most unavoidable in most applications. Various experi- ments have been performed and models proposed to pre- dict life under singular or combined electrical and thermal stress. A majority of these experiments are performed with the aging process accelerated by stresses, significant- ly exceeding the normal operating stress. Extrapolating life and behavior of these materials when aged under ac- celerated conditions to that under a real environment is one of the key goals of aging studies, and is achieved by using any of the several aging models available which fits the experimental data [4,5]. Of these, the most fre- quently used models are the inverse power model [6,7, 81 and the exponential model [8,9] under electrical stress only. Correspondingly, for thermal stress alone, mainly
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This note was uploaded on 06/08/2011 for the course ELECTRICAL 124 taught by Professor Ghjk during the Spring '11 term at Institute of Technology.

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FAEEE2B5d01 - IEEE Transactions on Electrical Insulation...

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