Space Charge Research on LDPE in Thermal Waves at Ultra-low temperatures

The effect of thermal waves caused by overcurrent on the space charge accumulation characteristics of the insulation at ultra-low temperatures is still unknown. This article investigates the space charge accumulations of LDPE under different thermal waves and 40 kV/ mm at ultra-low temperatures. The test temperatures are controlled synergistically by the heating rod and liquid nitrogen. LDPE barely accumulates charge at ultra-low temperatures, but charge buildup is obvious under thermal waves. The LDPE accumulates homocharge on the high-temperature side. On the low-temperature side, it accumulates heterocharge first, and then becomes homocharge after temperature stabilization. The electric field inside the sample increases slightly. The lower the initial temperature, the less charge accumulates inside the sample. After the recovery of temperature, the positive charge accumulated in the anode increases slightly. Moreover, the charge accumulated in the LDPE is frozen inside the sample and cannot be dissipated.