Influence of moisture and temperature on the frequency domain spectroscopy characteristics of transformer oil

Transformer oil is an important liquid dielectric of oil-immersed transformers. Moisture and temperature bring a great harm on the transformer insulation. This research was carried out to find the influence of moisture and temperature on the frequency domain spectroscopy (FDS) characteristics of transformer oil. As a non-destructive diagnostic technique, FDS technique possesses characteristics of strong anti-interference ability and abundant information, which is very suitable for the measurement on spot. This paper focuses on the research of the relationship between moisture, temperature and dielectric properties of transformer oil with the help of IDAX300 measurement system. Oil samples of different moisture level, 8ppm, 20ppm, 27ppm and 42ppm, have been measured at different temperatures, 29°C, 40°C, 60°C and 80°C. Results shows that the relative permittivity, in low-frequency areas, increase rapidly with moisture content and temperature. The DC conductivity calculated from dissipation factor increases exponentially both with the increase of moisture content and temperature. This relationship can be described as a fitting formula. This finding can be used for the online diagnosis of transformer oil moisture content.