Chemical Structure and Breakdown Behaviors of a New AC 500kV XLPE Submarine Cable Insulation with Different Thermal Aging Conditions

With the rapid rise of new energy industry and the recent development of offshore wind power market, there is a great market for submarine cable products. In recent years, China has vigorously developed marine power transmission technology. The 500kV power interconnection project in Zhoushan is currently the world's highest voltage and longest routing XLPE cable project. This paper studied the chemical and electrical characteristics of a new AC 500kV XLPE submarine cable insulation with different thermal aging condition. Results show that the aging rate is greatly accelerated after the occurrence of white opaque patches. In the thermal aging process, the carbonyl peak at 1710 cm-1 gradually increased. A new peak appeared at 1170 cm-1, which was the stretching vibration peak of -C=O-. The carbonyl index increases continuously. XRD results show that the height of the diffraction peak significantly decreases and only one diffraction peak remains after 160 days aging. As the aging time increases, the $a$ relaxation peaks of the XLPE samples have a tendency to shift to lower temperature. The crystallinity of the sample firstly increases and then decreases obviously after aging 110 days. Compared with the fresh sample, the breakdown voltage of the 160-day aged samples declined more than 40%.