Dielectric‐Breakdown Properties of Ester Oil Prepared from Thermally Degraded Rice Oil

Abstract

The vegetable‐insulating oils are used in electrical systems recently. Most of vegetable‐insulating oils are manufactured from new oils. In this paper, we propose to develop the insulating oils from the used cooking oil. The used cooking oils that means thermal degraded—vegetable oil has high kinematic viscosity that does not meet the JIS values. In this study, the kinematic viscosity of thermal degraded oil was decreased using ester exchange reaction. We simulated the thermally‐degraded rice ester oil as used cooking oil, and investigated the potential of used cooking oil as insulating oil. We manufactured rice ester oil after thermal degradation before and after the ester‐exchange reaction and measure kinematic viscosity, AC breakdown voltage, moisture amount and volume resistivity for oil samples. We evaluated the degree of thermal degradation of the sample oil using total polar molecule (TPM). The results are described as follows. (1) The kinematic viscosity and volume resistivity of the rice oil increased with the thermal degradation progress (increase in TPM). The kinematic viscosity of the rice ester oil at each TPM value decreased after the ester‐exchange reaction. (2) After vacuum deaeration (2 h at 80°C and 22 h at room temperature), the moisture content of the rice oil before and after the ester‐exchange reaction was almost the same. (3) The AC breakdown strength after ester‐exchange reaction was higher than that of the untreated oil. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.