Research on transient electric field distribution of converter transformer valve side winding under polarity reversal

Converter transformer is the most important equipment in DC transmission system. Polarity reversal is a special working condition of converter transformer in service, and the polarity reversal test is also generally regarded as the most important experiment for converter transformer. In the calculation of the polarity reversal field, the permittivity and conductivity of the each dielectric material should be given. The insulation materials of converter transformer are oil and pressboard. The resistivity of pressboard is anisotropic, there is a great difference value between the directions of through and along the paper layer. Different polarity reversal durations have different experiment results during polarity reversal test process. In this paper, the electric field distribution of converter transformer valve side winding in a practical ±800 converter transformer under polarity reversal test voltage was calculated with field-circuit coupling method. The anisotropism of paperboard resistivity was taken into account during the calculation process. In order to analyse the influence of polarity reversal duration to the distribution of electric field, several different polarity reversal durations were set to contrast. The results of this paper could provide references for the research and design of converter transformer.