Mechanism of Space Charge Packets Transport in LDPE driven by the Temperature Fluctuation under constant DC voltage

In case of an emergency power supply or short-term overload, a rapid load change can generate temperature fluctuations across the insulation of the power equipment. Failures are possible in conditions where temperature fluctuations are affecting HVDC equipment. In this study, the space charge characteristics and dynamics in LDPE under DC voltage that is subjected to temperature fluctuation are tested and analyzed. The results show that space charge packets form inside LDPE under high electric fields when a temperature fluctuation is applied. The speed of the charge packet decreases with time and the higher the temperature fluctuation, the more pronounced the resulting charge packet is, and the faster it can move through the insulation. The experimental results verify that the temperature fluctuation under constant DC voltage can form and drive the movement of space charge packets. The Bipolar Charge Transport Model was used to simulate space charge packets due to temperature fluctuation with consideration of the transient temperature distribution. Simulation results indicate that the temperature fluctuation forms a new temperature gradient and forces the space charge re-distribute: the charge mobility decreases with the decreased temperature across the sample; the re-distributed space charge distorts the electric field, generating a step-like electric field distribution. The mobility and the step-like electric field generate peaks of the charge velocity, which is the direct cause for the formation and migration of space charge packets. The temperature fluctuation can force the existing charge to redistribute and can drives space charge packet movement.