Effect of Temperature and Electric Field on Partial Discharge Characteristics in XLPE and Nano-MgO/XLPE During Electrical Tree Growth

Investigations about the effects of temperature and electric field on electrical tree growth and partial discharge (PD) characteristics of crosslinked polyethylene (XLPE) and nano-MgO doping XLPE (MgO/XLPE) with mass concentration of 0.5% under power frequency voltage were carried out in this paper. Meanwhile, a method of PD signal extraction based on color-coded diagram was presented, which can effectively reflect the time distribution characteristics of PD phase and amplitude during the whole electrical tree growth. The results of the experiments show that the shape of the electrical tree in XLPE develops from small branch tree to bush tree, and then develops to a large sparse bush tree as temperature rises. Meanwhile, the change of the aggregation state of the material at high temperature may cause electric field distortion, which makes the PD intensity increase. As the voltage increases, the shape of the electrical tree develops from bush tree to large branch-pine tree, and the PD intensity increases, which may be related to the increase of the electric field at the tip of the needle and the end of the electrical tree. In addition, nano-MgO doping impairs PD at high temperature. However, since the electrical insulation strength of MgO/XLPE is lower than that of XLPE at high temperature, this promotes the growth of electrical tree in MgO/XLPE. Therefore, although nano-MgO doping impairs PD at high temperature, it does not show good resistance to AC tree growth. © 2020 Chin. Soc. for Elec. Eng.