Space Charge Behavior in Cable Insulation under a DC-Superimposed Pulsed Electric Field

Under lightning and operating overvoltage, cable transmission lines are more prone to occur insulation degradation and breakdown resulting in power interruption. To study the mechanism of insulation breakdown under pulse voltage caused by overvoltage, an experiment about the dynamic characteristic of space charge at rising and falling edges in cross-linked polyethylene under DC-superimposed pulsed voltage was conducted. The experiment result shows that the change of space charge density at the rising and falling edges is opposite to the change of voltage amplitude: the space charge density decreases when the voltage amplitude increases, and increases when the voltage amplitude decreases. An analysis method from the perspective of forces acting on the space charge is proposed to explain this unusual phenomenon. The suddenly changed electric field at the rising and falling edges breaks the balance of force acting on the space charge, resulting injection and extraction of charge. The dynamic behavior of space charge is accompanied by the release of energy, which will destroy the microstructure of insulation material and result breakdown eventually. This study is of great significant to help reveal the essence of insulation failure and improve the performance of insulation materials.