Effects of Thermal Aging on the Electrical, Dielectric and Thermophysical Properties of Cooling and Insulation Liquids in Electric Aircraft

Reducing fuel consumption and operating costs, limiting greenhouse gas emissions, and promoting the sustainability of the aviation industry are driving the consideration of more efficient aircraft as well as alternative fuels and propulsion systems. The influence of thermally accelerated aging on the electrical, dielectric and thermophysical properties of four coolants is investigated to gain insight into the thermal stability and lifetime of these coolants. The results show that the electrical and dielectric properties of the different liquids change differently after thermal aging. The breakdown voltage of the lubricant decreases significantly with aging. In contrast, the breakdown voltage of one synthetic ester and the mineral oil-based transformer oil decreases slightly and remains almost constant for the other synthetic ester. The dielectric properties of all liquids especially those of the lubricant decrease and its acid number increases significantly. However, thermal aging has no significant effect on the thermophysical properties of any of the liquids.