Transient Space Charge Measurement In XLPE Under DC Superimposed with Impulse Voltages

This work explores the space charge dynamics in HVDC cable insulation at the edges of DC-superimposed operating impulse voltage. Based on a composite voltage coupling circuit, a pulsed electro-acoustic (PEA) test platform suitable for impulse voltage was established. An automatic phase-shifting matching technique was introduced to achieve space charge measurements at different phases of the impulse voltage under various polarization durations. The findings reveal that the polarity of charge distribution within the sample alternates between homopolarity and heteropolarity over time, irrespective of the impulse voltage polarity. When a homopolar impulse is superimposed, the heteropolar charges mainly originate from ionic charges, and the higher the impulse amplitude, the more significant the heteropolar charge distribution. Nevertheless, once the impulse voltage ceases, the charge distribution eventually stabilizes in homopolarity. Under heteropolar impulse superposition, heteropolar charges result from the charge hysteresis phenomenon. Compared with homopolar superposition, the internal charge distribution changes less over time. This is mainly attributed to the effects of periodic reversal of the electric field polarity, which leads to cyclical processes such as charge injection, extraction, recombination, and impurity dissociation.