Effect of Testing Temperature Gradients on Dielectric Polarization Parameters of Transformer Oil-Paper Insulation

Frequency domain spectroscopy (FDS) plays an important role in analyzing the aging state of power transformer oil-paper insulation and ensuring the stability of power systems. However, in the existing research, the oil-paper insulation’s FDS is collected under a uniform testing temperature field, overlooking the impact of testing temperature gradients existing in actual transformers. To address this issue, the FDS of oil-paper insulation samples is measured under various temperature gradients. Subsequently, logarithmic-derivative spectroscopy (LDS) is obtained from the measured FDS, and an improved equation is proposed to fit the LDS and extract four polarization parameters related to the oil-paper insulation’s aging state. Furthermore, the changing patterns of the above parameters are analyzed at a microscopic scale based on the dielectric relaxation theory, and the quantitative equations between each polarization parameter and testing temperature gradients are established. To validate the accuracy of established equations, new samples are prepared and the calculated relative error (RE) in each parameter is less than 15%. Finally, this research provides a potential method for eliminating the impact of testing temperature gradients on oil-paper insulation’s FDS.