Space charge characteristics and the electric field distortion after polarity reversal operation in two layers of oil-impregnated paper and oil

Abstract

The formation of space charge in the oil-impregnated paper and oil insulation system under HVDC condition can influence the electric field distribution. In the case of HVDC converter transformer, the distortion of electric field may affect its performance. It is, therefore, important to analyse factors that can affect space charge formation and dissipation characteristics such as moisture, temperature, electric stress level and ageing process. This paper mainly focuses on the effect of oil ageing on space charge characteristics in the oil-impregnated paper and oil system. The pulsed electroacoustic method was used to monitor space charge dynamics and these data were further incorporated into the model established using COMSOL to estimate its impact on electric field distribution. The results show that there is a significant electric field enhancement after polarity reversal operation due to the injected charges. It is also noticed that the status of the oil has a profound effect on the injected charge dynamics, therefore, the electric field enhancement.

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