Abstract
This paper reports the AC dielectric‐breakdown characteristics of a rice‐oil‐based electrical insulating oil as a function of oil temperature as well as the influence of thermal degradation on its performance (kinematic viscosity, AC dielectric breakdown, moisture amount, total acid number, and pour point). We manufactured rice ester oil using the ester‐exchange reaction. The results demonstrated the following. (i) The kinematic viscosity of the rice ester oil was lower than that of the rice and mineral oils. (ii) The AC breakdown strength of the rice ester oil was higher than that of the mineral oil. The AC breakdown strength of both insulating oils increased with the increase in the oil temperature. (iii) The moisture content of the rice ester oil was larger than that of the mineral oil. (iv) The total acid numbers of the rice ester and mineral oils were almost the same. (v) The pour point of the rice ester oil was higher than that of the mineral oil. In addition, the rice ester oil exhibited high resistance to heat stress compared with the mineral oil, but the former was unsuitable for use in cold climates. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.
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