Research on Steady and Polarity Reversal Electric Field of Converter Transformer Considering Nonlinear Temperature Coefficient of Oil-paper Insulation

Abstract

Converter transformer suffers from AC/DC composite voltage, and the internal insulation system has high temperature during operation. the electrical conductivity of the oil-paper insulation will be affected by the temperature gradient, which ultimately affects the electric field distribution. The study in consideration of nonlinear temperature coefficient is still not sufficient. This paper established a converter transformer coupling calculation model and analyzed the steady and polarity reversal electric fields under the influence of temperature. The electric field considering the nonlinear temperature coefficient was compared with that obtained by the traditional method. The results show that, the maximum electric field in oil increased by 84.9% in the steady state. The maximum tangential electric field along the oil-paper interface nearly doubled. During polarity reversal, the maximum electric field decreased, and the electric field change rate became faster.