Effect of Temperature Gradient on Electrical Tree in XLPE From 0 to-196 °C

Cross-linked polyethylene (XLPE) is widely used in a warm dielectric (WD) superconducting cable. As other insulating materials, electrical tree is a threat to XLPE. When XLPE is used in cable termination connected to a high-temperature superconducting cable and a WD superconducting cable, there will he a steep temperature gradient. With the growth of the tree, the temperature gradient will be influenced by the change of temperature. In the experiment, nine temperature gradients were prepared and applied on the samples. An ac voltage was employed to initiate electrical tree in XLPE samples. Three tree structures have been observed, and they change with the gradient. In the same tree, the branch will also change in respect to its growth. Both the tree length and width are suppressed by the decrease of temperature. With the change of temperature gradient, the decrease of temperature influences the fractal dimension and accumulated damage obviously. In the gradient 1-5, the speed of tree growth in the first 20 min is much higher, while trees in the other gradients grow slowly.