Continuous Temperature Change Annealing Effect on Thermal-Electrical Properties of XLPE from High-Voltage Cables

The high voltage cables which reached the designed service years attracted much attention. Two retired 110 kV XLPE cables and a spare cable were selected, and the insulation XLPE was peeled. They were heat-treated at 90, 95, 100, 105, 110, and 115 °C by two inversely step heat-treatment processes. Then, the differential scanning calorimetry (DSC), and DC conduction current were measured. The results show that all the heat treatments did not result in further damage to the molecular structure. The step-heating process brought better results, the thermal and electrical properties were improved with a higher melting point, crystallinity, and a lower electrical conductivity when the heat treatment temperature was below 105 °C. However, the higher temperatures of 110 and 115 °C brought negative effects on the thermal-electrical performance. Finally, it is found that thermal-electrical properties for XLPE from the 30-year service cables could be enhanced if the heat treatments were given at proper temperatures.