Temperature effect on frequency domain spectroscopy characteristics of oil impregnated pressboard

To investigate the effect of temperature on the frequency domain spectroscopy (FDS) test results of transformer oil-paper insulation and for accurately assessing the aging condition and moisture content in pressboard, FDS experiments are performed on the oil-impregnated pressboard sample at different temperatures. The temperature effect on the dissipation factor tanδ, real capacitance C\´ and imaginary capacitance C" of the oil impregnated pressboard in frequency domain ranging from 1 mHz to 1 kHz are analyzed. The results show that, tanδ, C\´ and C" obviously increase in lower frequencies range while having no obvious increment in higher frequencies when measurement temperature rises. Moreover, with the increasing of temperature, both tanδ and C" curves shift to the higher frequency, while the minimum values of tanδ and C" increase slightly. The frequency range where C\´ changes rapidly, shifts to higher frequencies. It is revealed that temperature has a significant impact on the FDS test results. At higher temperatures, based on the FDS results, the conductivity of oil-paper insulation and the evaluated moisture content of pressboard will be higher, and lead to a more serious aging judgment for on-site transformer solid insulation.