Experimental investigation and numerical simulation of electrical tree growth in polyethylene under AC voltage

This paper reported the growth of electrical tree in low density polyethylene under AC voltage. Specimens of double needle geometry were achieved by compression molding. The evolutions of electrical tree length and discharge magnitude versus aging time were studied. The tests were carried out until dielectric breakdown of the polymer happens. Firstly, ionization of the cavities occurs inducing a rapid propagation of electrical tree. Secondly, the growth slows down resulting to the rise of gas pressure in the tree channels. The decrease in growth rate is also attributed to the increase of the electric conductivity of channel walls. This process is highlighted by the inception and the extinction of partial discharges. The presence of space charge affects the growth of tree. For the modelling of electrical tree, we have considered a model with two concentric spheres. The simulation results were validated by the experimental tests