Research of simultaneous measurement of space charge and conduction current in cross-linked polyethylene

To overcome the weak correlation between space charge and conduction current caused by individual measurement, a specialized system based on pulsed electro-acoustic method (PEA) was designed to perform simultaneous measurement of space charge and conduction current for plate sample. Firstly, electric pulse response during space charge measurement was simulated to analyze the interference during conduction current measurement caused by electric pulse. To solve this problem, fast time division technique was employed. And then, this paper presents the measurement results of space charge distribution and conduction current in cross-linked polyethylene (XLPE) sample under various electric fields at ambient temperature. Finally, displacement current density distribution was calculated according to spatial and temporal distribution of space charge. Conduction current density distribution was obtained by subtracting displacement current density from external current density. The results show that the charge packet continuously appears from anode and migrates to cathode under high electric fields above 70 kV/mm. It significantly distorts the electric field near charge packet insider XLPE. The maximum conduction density also appears at the position of charge packet. Furthermore, the calculated velocities are similar at the rear and front side of charge packet. The calculated negative differential mobility probably is the main mechanism of the charge packet formation.