Moisture and temperature effects on conduction and losses in modified rape-seed insulating oil

In this paper, we have investigated the dielectric properties (losses, conductivity) of a modified rape-seed oil (RS50). Dielectric spectroscopy has been done over a wide frequency range (10^-2-10⁶Hz) and conductivity measurements according to CEI 61620 standard. The parameters investigated are temperature (-20degC to 120degC) and water content. Frequency spectra of the dissipation factor tgzeta at different temperatures are typical of losses by conduction (in the low frequency range) and of losses by dipole relaxation (in the high frequency range). The influence of temperature is well explained by conduction and relaxation theories taking into account viscosity change. The increase of conductivity with temperature is rather large: a factor of 10³ from -20degC to 120degC. Up to about 200% of relative humidity, no significant influence of moisture on the dielectric properties (permittivity, losses, conductivity) has been observed. These results are then discussed in correlation with potential applications of this oil in electrical systems.