Effect of temperature on dielectric loss factor of biodegradable transformer oil

This paper is aimed at the investigation of the effect of temperature on the dielectric dissipation factor of fresh and wetted natural ester oil. It is shown that tg$\delta$ increases with temperature; this increase is weak at the low temperature, in the range $20^{\circ}\mathrm{C}$ to $90^{\circ}\mathrm{C}$. An increase in temperature from the ambient to almost $80^{\circ}\mathrm{C}$ causes a threefold increase in loss factor. For temperatures higher than $110^{\circ}\mathrm{C}$, a noticeable increase in the value of tg $\delta$ is observed; this increase can reach two orders of magnitude. Also the presence of dissolved water in natural ester oil increases its loss factor.