Breakdown Characteristics and Electrical Life Evaluation of 500 kV EHVAC Cable Insulation at Different Temperatures

This study investigates the effect of operating temperature on the breakdown strength and aging life parameter of cross-linked polyethylene (XLPE) insulation for 500 kV extra-high voltage alternating current (EHVAC) cables. The test samples were cut from a properly degassed real 500 kV XLPE cable. The continuous-rising voltage breakdown tests and step-up voltage breakdown tests were conducted at 30 °C, 50 °C, 70 °C, and 90 °C, respectively. The results show that, the AC breakdown strength decreases with increasing operating temperature regardless of the thickness of XLPE samples. When the temperature is 70 °C or below, increasing the thickness of samples effectively slows down the decreasing trend of the breakdown strength. However, at 90 °C, increasing the sample thickness cannot resist the decrease in AC breakdown strength. By analyzing the aging life curves of the XLPE samples at different temperatures, it is found that the aging life parameters of the XLPE samples at 30 °C and 90 °C are 18 and 14, respectively. It is perceived from testing results that even after continuous operation for 40 years, the tested XLPE material can possess AC breakdown strengths of 44.6 MV/m and 28.3 MV/m at 30 °C and 90°C, respectively. This study provides a reference basis for the design of insulation thickness and the electrical life assessment of 500 kV EHVAC cables during the long-term operation.