Effect of Crystal Morphology on Breakdown Properties of XLPE at Mesoscale

As a polymer material with a semi-crystalline structure, the macroscopic insulation breakdown properties of cross-linked polyethylene (XLPE) insulation materials under the action of electric fields are closely related to their crystal morphology at the mesoscopic scale. In order to study the effect of crystallization morphology of XLPE material on AC breakdown strength and analyze its mechanism of action, four different ways were used in this paper to control the cooling rate of the material during the crystallization process, and XLPE materials with different crystallization morphologies were prepared and obtained. The crystal morphology of the material was also characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), and its insulation properties were tested using a broadband dielectric spectrometer, DC conductivity, and AC breakdown platform. The experimental results show that the reduction of the cooling rate can prolong the crystallization time and effectively refine the crystal morphology inside the material, making the size of the spherical crystal larger and the crystallinity higher. The higher cooling rate leads to a lower dielectric constant and higher conductivity of the XLPE material, which also causes a decrease in the AC breakdown field strength of the material at different temperatures.