Effects of Isothermal Crystallization on Carrier Transport and Breakdown Characteristics of HDPE/LDPE Insulation

Abstract

In this paper, the influence of the crystalline morphology of high-density polyethylene (HDPE)/low density polyethylene (LDPE) blend on its electrical conductivity, breakdown performance and trap distribution were studied by using the method of isothermal crystallization. Five HDPE/LDPE blends were prepared by melt blending method, and they were cooled to 118°C for isothermal crystallization treatment for 0, 5, 10, 20 and 40 min. The experimental results show that HDPE/LDPE blend with 10min isothermal crystallization time has the lowest conductivity at 70℃, and its conductivity-temperature dependence is also low. As the isothermal crystallization time increases from 0 to 10min, both the DC and AC breakdown strengths of HDPE/LDPE blend increase, and further increase the isothermal crystallization time to 20 and 40min, the breakdown performance of HDPE/LDPE blend decreases significantly. The aggregate structure of HDPE/LDPE blend is closely related to its electrical properties. When the isothermal crystallization time is 10 min, the HDPE/LDPE blend shows a denser crystalline morphology and introduces many of deep traps measured by the isothermal discharge current (IDC) method. Therefore, space charge accumulation and local electric field distortion in the dielectrics are reduced. Also, the breakdown field strength of the HDPE/LDPE blend is improved.