Electrical Tree Growth in Polyethylene during the DC Voltage Rise and the Influence of the Tree Defect Size

In order to investigate the electrical tree properties during the voltage rise and the influence of the tree defect on the tree propagation, the cross-linked polyethylene (XLPE) samples with different electrical tree defects which were generated by an AC stress were prepared and the voltage-regulating experiment is carried out. The typical needle plate was used where the tip radius of needle was 5µm and the distance between the needle tip and the sample bottom was about 1.5mm. The regulating voltage rose at a constant speed of 500V/ s for 10 seconds and maintained for 5 minutes. The progress was repeated until the electrical tree grew. After that the voltage was maintained at 30kV for 2 hours and then declined as the same regulation way. It was shown that the electrical tree grew remarkably at a typical branch shape during the voltage rise, while the tree had little change at DC voltage or declining voltage. As the tree defect length increases, the tree increment during the voltage rise decreases but the total tree increment over the experiment would increase. Space charge behavior around the tree tip would be applied to describe the tree characteristics at the rising DC voltage and DC voltage.