Abstract:

The nonlinear characteristics of oil-paper insulation are not considered in the traditional transformer insulation design. The finite element method is used to couple electromagnetic field, temperature field and other multi-physical fields for the simulation calculation, focusing on the study of the conductivity of oil-paper composite insulation with the temperature nonlinear changes in the transient electric field distribution of the converter transformer valve-side winding end of the law and features.The effect of oil and insulating pressboard conductivity ratio on the valve-side electric field is studied. The results show that when considering the temperature-conductivity nonlinear characteristics, the electric field distribution at the valve-side terminal of the converter transformer is more concentrated, the distortion phenomenon is significant. And with the increase of the conductivity ratio, the electric field distribution on the valve side terminal is becoming increasingly concentrated. The high field strength values are distributed in the oil gap of the insulating pressboard at the terminal of the valve-side winding. The proposed research provides the reference for transformer insulation design.

Key words: converter transformer, polarity reversal, nonlinear characteristics, transient electric field, oil-paper insulation, temperature effect