FDS-Based Study of Space-Charge Polarization in Transformer Oil with Experiment-Driven Simulation

Journal article, 2026

The performance of space-charge polarization has a significant impact on the dielectric properties of transformer oil, particularly its nonlinear behavior observed in frequency domain spectroscopy (FDS) measurements. However, directly isolating the contribution of space-charge polarization from the measured permittivity remains challenging, and the relationship between charge dynamics and FDS results is difficult to elucidate. In this study, we investigate space-charge polarization in transformer oil through a combined approach of FDS experiments and simulation. The permittivity associated with space-charge polarization is separated using measurements under combined AC and DC voltages. Simulations are then employed to analyze the experimental results and to uncover the mechanisms behind permittivity variations, focusing on the evolution of ion transport. Additionally, the approximate ion concentration and mobility are estimated. The results indicate that ions accumulate at the electrode boundaries once they arrive, giving rise to a distinct loss peak when the polarization density reaches maximum. As the frequency decreases further, diffusion effects become dominant, leading to a reduction in the imaginary part of permittivity. Higher applied voltages and temperatures are shown to enhance the motion speed of charges, causing the loss peak to shift toward higher frequencies. This study provides an experiment-driven simulation method to study the space-charge polarization based on FDS measurements.