In this work, AC treeing behaviour of filler-free EPR is studied at room and liquid nitrogen (77 K) temperatures to determine tree-inception voltages as well as to understand possible tree-initiation processes. Since trees in cable insulation often initiate at semi-conducting interfaces, experiments are also performed with semi-conducting needles. Additionally, it is observed that while trees at room temperature are dense, those at cryogenic temperature are rather sparse. In order to quantify these structures, fractals are employed to measure their relative dimension.
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