Impacts of copper products on characteristics of frequency domain dielectric spectroscopy of oil-paper insulation

The internal copper components in oil-immersed power transformer is susceptible to transformer oil impurities (acid, sulfur and other substances) by the transformer eventually leading to a transformer failure. The accelerated thermal aging tests are conducted on transformer oil-paper insulation to find an effective way to monitor the content of copper-based products and analysis the frequency domain dielectric spectroscopy of the transformer oil-paper insulation system with different contents of copper-based products by using two different sets of sample. The results show that the presence of copper-based products has a little effect on the real part of the complex dielectric constant of the oil-paper insulation, but a great effect on the imaginary part, especially in the middle frequency band (10⁰ Hz ~10⁴ Hz). The presence of copper-based products affects the formation of the relaxation mechanism of the oil-paper insulation. The enhanced interfacial polarization and ionic polarization led to the separation of the relaxation center in the middle band. The fitting for the frequency response curve before and after its change by two different relaxation model shows that the new relaxation model is effective.