Space charge transport and redistribution driven by temperature fluctuation in polymer insulation under constant DC voltage

Abstract Under load switching or emergency load conditions, a surge in load current happens in the power system and generates temperature fluctuation in the insulation of the power equipment. The effect of temperature fluctuation on the space charge accumulation in the insulation is still unknown. This paper presents the space charge behavior in LDPE, cross-linked polyethylene (XLPE), and polypropylene (PP) under constant DC voltage with temperature fluctuation. It shows that the space charge redistributes when the temperature fluctuates, while the applied voltage is constant. Great heterocharge accumulates quickly near the low temperature electrode after the temperature fluctuation in LDPE and XLPE. The heterocharge dissipates quickly when the temperature recovers. And when the temperature increases, space charge packets form and transport in LDPE and PP. However, it accumulates a great amount of homocharge near the high temperature electrode in PP rather than heterocharge at the low temperature side. The homocharge does not dissipate and goes even deeper inside PP when the temperature drops. The higher the applied voltage or temperature fluctuation, the higher the amount of charge that accumulates inside the insulation. The different performance of insulation materials under temperature fluctuation is probably due to their different conduction properties. The influence of the temperature fluctuation is similar but different from that of the temperature gradient. Temperature fluctuation is a dynamic process and forces the space charge to redistribute due to its influence on the charge transport. The redistribution of space charge due to temperature fluctuation causes a greater electric field distortion rate. It may be the reason why DC equipment fails in the condition of load switching or load cycle.