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Unformatted text preview: IEEE Transactions on Electrical Insulation Vol. EI-14 No.6, December 1979 THE STATISTICAL ANALYSIS OFA HIGHVOLTAGE ENDURANCE TEST ON AN EPoxY G. C. Stone and M. Kurtz Ontario Hydro Research Division Toronto, Canada and R. G. van Heeswijk Dept. of Elec. Engineering University of Waterloo Waterloo, Canada ABSTRACT This paper is concerned with the accelerated aging of solid insulating materials, as a means of estimating their service lives and identifying superior dielectrics. The assumed failure mechanism is electric treeing. A constant-stress accelerated aging experiment on a transparent epoxy at three voltage levels is described. All factors thought to be important in the electric treeing mechanism were rigidly con- trolled, and the inception and growth intervals were measured separately. The results indicate that the times to inception and failure are three-parameter Weibull distributed, whereas the growth period may be either Lognormal or three-parameter Weibull distributed. The Inverse Power Law could not be con- firmed. There was little correlation between the inception and growth intervals. Statistical analysis showed that there is much uncertainty in these results, and this is true for most published accelerated aging tests done to date. The general applicability of accelerated aging tests is questioned. INTRODUCTION Of the many polymers used for high-voltage insula- tion, the epoxies, usually combined with suitable fillers, have gained particular prominence because of their high mechanical and electrical strengths. For electric utilities perhaps the most important insulation application for epoxies, in the near future, will be as spacers in SF6-insulated systems for voltages up to 750 kV. In these and other applications, design stresses tend to increase as the technology for apparatus develops and new design approaches are adopted. With this trend, power utilities are increasingly concerned with the prediction of the service life of components insulated with epoxies. In addition, utilities are interested in evaluating the claims of manufacturers in order to choose the best component with the minimum cost. The primary objective of the work reported in this paper was to develop a careful test technique which can aid in determining which material (from the two or more tested) is likely to last longer in service. Secondly, attempts were made to estimate service lives. The assumed failure mechanism was electric treeing, since the application of interest is in a dry environ- ment in equipment which is operated at the highest voltages in a power system. Electric treeing has been identified as the failure mechanism operative in some HV epoxy-insulated equipment within Ontario Hydro....
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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.
- Spring '11