Electrical Insulation Performance under HVDC and Polarity Reversal Conditions in Oil-Immersed DC Converter Transformers

In HVDC power systems, an oil-immersed AC/DC converter transformer is the main apparatus used in their composition. As for the development of these converter transformers, it is necessary to enhance their electrical insulation performance while taking specific DC behaviors such as DC electric field distribution, DC charge accumulation and DC polarity reversal characteristics into consideration. In this paper, the electric field distributions in an oil-impregnated pressboard composite structure, which models the structure in actual DC converter transformers, were calculated under AC, DC-steady state and DC-polarity reversal conditions, by analysis with the Finite Element Method (FEM), and their electrical insulation performances were investigated and discussed. The results showed that it is…