04_ageing marker - 2004 on Solid Dielectrics...

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2004 Infernational Conference on Solid Dielectrics, Toulouse, France, July 5-9. 2004 Possibilities for Using Space Charge Quantities as Aging Markers and as Tool for Material Ranking B. Alijagic- Jonuz, P.H.F. Morshuis, J.J. Smit Delft University of Technology, High Voltage Technology and Management Mekelweg 4,2628 CD Delft, The Netherlands Abstract: Space charge is often brought in connection with electrical aging: in some cases as a cause and in some a consequence of aging, sometimes even both. This makes space charge related quantities possibly useful for different purposes; aging markers or for research on the influence of fillers on the electrical performance of insulating materials or for material rankiig. We studied epoxy and polycarbonate (PC) (with and without filler), both new and long-term stressed, and examined all three mentioned aspects of possible applications of space charge related quantities. Breakdown tests on new and previously stressed test specimens were used to check if long-term stress triggered any changes (electrical aging) in the materials. We will show that space charge quantities can be used aging markers in the case of PC and PC with Ti02 - filler (PCTi02) which were stressed at 100 kV/mm for 850 hours. There was no aging of the polycarbonates at 60 kV/mm according to breakdown tests which was confirmed by space charge measurements. According to breakdown test there was also no aging of the epoxy test specimens which had been stressed with 60 kV/mm for 860 hours. The space charge measurements however gave some indication of a very early stage of aging. Material ranking was only partly successful: it was concluded that proper material ranking is only possible if the applied poling fields for space charge measurements are higher than electrical threshold for space charge accumulation. INTRODUCTION When a material is stressed with a sufficiently high DC electrical field, space charge will start to accumulate in the material [l], [2]. The contribution of the space charge to the total electrical field in the material CM be considerable and may cause accelerated aging of the material. On the other hand, the space charge accumulation is sensitive to changes in the material structure due to aging (distribution and depth of trapping sites are aging-sensitive). We studied three materials (new and previously electrically stressed): polycarbonate with and without filler (PC and PCTi02) and epoxy. Breakdown tests were used to check if there was a decrease of the electrical breakdown strength due to long-term exposure to electrical stress. Space charge measurements were used to check if space charge related quantities could be of use aging markers for PC, PCTi02 and epoxy. The measurements were also used to examine the influence of the Ti02 filler on the 0-7803-83486/0%20.00 02'2004 IEEE.
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04_ageing marker - 2004 on Solid Dielectrics...

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