Electrical treeing in XLPE insulation in frequency range between 20 and 500 Hz

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Description/Abstract

Electrical tree is one of the main reasons for long term degradation of polymeric materials used in high voltage ac applications. In this paper we report an investigation of electrical tree growth characteristics in XLPE samples from a commercial XLPE power cable. Electrical treeing has been grown over a frequency range from 20 Hz to 500 Hz and images were taken using CCD camera without interrupting the application of voltage. The fractal dimension of electric tree is obtained using a simple box-counting technique. Contrary to our expectation it has been found that the fractal dimension prior to the breakdown shows no significant change when frequency of the applied voltage increases. Instead, the frequency accelerates tree growth rate and reduces the time to breakdown. A new approach for investigating the frequency effect on trees has been devised. Besides looking into the fractal analysis of tree as a whole, regions of growth are being sectioned to reveal differences in terms of growth rate, accumulated damage and fractal dimension.