Broadband Frequency Domain Dielectric Spectroscopy of Cellulose Insulation Material in Transformer

Frequency domain dielectric spectroscopy is widely used in the moisture assessment of transformer oil-paper insulation. However, the dielectric mechanism of oil-paper insulation still needs further exploration. Based on the broadband frequency domain dielectric spectroscopy, this article studied the dielectric properties of transformer cellulose insulation without oil immersion, and analyzed the effects of moisture and temperature. The results show that there are four relaxations in cellulose insulation: low-frequency dispersion, interfacial polarization, hydroxyl orientation polarization and absorbed water orientation polarization. With the increase of moisture content, the three relaxations except for hydroxyl orientation polarization all move to high frequency, which is similar to the effect of temperature on dielectric process. In addition, the relaxation strength of absorbed water orientation polarization increases with the increase of moisture and temperature. This research reveals the composition of broadband dielectric spectroscopy of cellulosic based insulation material and may provide a theoretical reference for the dielectric mechanism of oil-immersed paper.