Effect of temperature on dielectric response characteristics of oil impregnated pressboard

To investigate temperature effect on dielectric response measurement results of transformer oil-paper insulation, and for more accurate assessment of insulation condition and moisture content in pressboard, the time-domain return voltage (RV) and frequency domain spectroscopy (FDS) experiments are designed and performed on oil-impregnated pressboard at different temperatures. The variations of characteristic parameters of RV spectra and FDS curves of the dissipation factor tanδ, real capacitance C′ and imaginary capacitance C″ at different temperatures are compared. The changing trends and reason are analyzed. Temperature influences on evaluating moisture content and aging status with dielectric response measurements results are investigated. The results show that, with temperature increasing, the peak of RV spectrum curve shifts to shorter charging time, and peak values of both charging time and voltage decrease. Tanδ, C″ curves shift to higher frequency, while the minimum values of tand and C″ increase slightly. C′ increases, especially in lower frequency range. It is revealed that, temperature effect on test results should be considered for evaluating moisture content and aging condition of pressboard. Otherwise, it will lead to a wrong aging judgment for on-site transformer solid insulation.