Temperature and thermal aging effects on the Frequency Domain Spectroscopy measurement of oil-paper insulation

Transformer oil-paper insulation system is continuously subjected to thermal stress which is a key factor inducing its deterioration. Dielectric response of oil-paper insulation in frequency domain is being gradually used by power utilities for assessing the condition of transformer oil-paper insulation system, and the Frequency Domain Spectroscopy (FDS) measurement is a promising method. It is important to understand the effects of temperature and thermal aging on FDS results for accurately assessing the condition of oil-paper insulation system. In this paper, the accelerated thermal aging experiments are performed on an oil impregnated pressboard sample at high temperature. Dielectric responses of sample in frequency domain are investigated during the aging process, and at the same aging condition, FDS measurements are repeated at different temperatures. Experiment results show that measurement temperature and thermal aging process significantly impact the FDS results of the oil impregnated pressboard sample in lower frequencies. The dissipation factors (tandelta), real capacitance and imaginary capacitance all increase with the increment of measurement temperature and thermal aging time, especially in lower frequencies.