Dielectric spectroscopy measurements on oil impregnated paper / pressboard samples

Dielectric response analyses of oil-paper/pressboard insulation in power equipment have been introduced for condition monitoring. This paper presents results of a laboratory study where dielectric spectroscopy measurements in frequency domain were performed on oil impregnated pressboard samples containing different amount of moisture (0.6% - 4%). Such data are necessary for correct interpretation of the diagnostic measurements. The measurements were earned out in the frequency range of 0.1 mHz - 1 MHz at temperatures between 20 °C and 80 °C. The measured dielectric response data were used for obtaining information on the change of activation energy and dc conductivity of pressboard with moisture content. The responses obtained were used to derive master curves. Furthermore, the influences of the non-linear behaviour and oil layers on the total dielectric response were discussed.