DC Electric Field Calculation Model of Oil-Paper Insulation Considering Charge Transport Behavior

The precise calculation of the direct current (DC) electric field within oil-paper insulation is indispensable for the accurate insulation design of converter transformers. Nevertheless, the DC electric field derived from the traditional resistivity-dielectric constant model (RC model) often falls short of accuracy, primarily due to its inadequate consideration of space charge behavior. The bipolar charge transport model, which incorporates the dynamics of charge behavior, has garnered significant attention from researchers. However, prevalent models rely heavily on empirical or idealized parameters, leading to notable discrepancies between calculated results and experimental measurements. To address this challenge, this paper presents a model that takes charge transport behavior into account, with all key parameters meticulously determined. Upon comparing the model’s predictions with measured results, the Pearson correlation coefficient for the electric field curve in 0.2 mm oil-impregnated paper reached an impressive 0.997, while the mean absolute error was 0.549. The findings highlight several key points: 1) The Richardson constant should not be arbitrarily assigned a theoretical value. 2) The injection barrier can be calculated using the conductivity and relative dielectric constant of the material. 3) The trapping coefficient can be deduced from the trap energy level density, carrier mobility, and relative dielectric constant. 4) The carrier mobility, trap energy levels, and trap energy level density should be derived from the measurement results of the isothermal surface potential decay method. These results provide a technical approach for accurately calculating the DC electric field, paving the way for more precise insulation designs in converter transformers.