Analysis on characteristics of electric field under direct current polarity reversal voltage in combination insulation

This paper is based on the mathematical model of the transient electric field, which involves both epsilon (permittivity) and gamma point difference method with the parameter theta is used for the time discretization, and finite element method for the space discretization. The numerical results are compared with the analytical solution of a typical oil-paper insulation model. The effects that different gamma and voltage reversal time intervals have on the electric field distribution, in the ends of valve-side windings and the bushing barrier system of converter transformer, are examined under polarity reversal voltage (PR), changing from one steady state to another.