When polymeric insulation systems are subjected to high electricalstresses, they are susceptible to localized degradation at stressenhancements caused by contaminants within the insulation or protrusionsat electrode/insulation interfaces. The degradation is referred to aselectrical treeing, tree-like structures of gas-filled channels growingfrom the stress concentration. There are three phases of electricaltreeing, tree initiation which is degradation leading to formation ofthe first channel, tree growth which is the extension of the channelsand the final breakdown when one or more of the channels bridge theelectrodes to produce failure. The growth phase is caused by partialdischarges (PD) within the channels. Although the PD characteristicshave received some attention in the past these studies have usedconventional narrow band PD detection equipment which gives informationon the apparent discharge magnitudes and repetition rates of the pulses.However, valuable information about the discharge processes, which isavailable from the pulse shape, is lost. This paper describes theinitial results of a study of the amplitudes, repetition rate and shapesof the discharge pulses observed during the growth of electrical treesin XLPE cable insulation using a wide band PD detector
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