Catalytic Effects of Iron and Copper on Degradation of Natural Esters at Different Temperatures

Natural esters are renewable, highly available, and have a high ignition point. It is considered a suitable alternative to mineral oil in the future development of low-carbon networks and smart grids. The bare silicon steel and copper used in transformers can promote aging of natural esters and shorten their service life. In this article, natural esters containing copper and iron are used for accelerated thermal aging at 100 °C, 120 °C, and 140 °C, and the physicochemical and electrical properties of the natural esters are tested. It is shown that the physicochemical and electrical properties of natural esters are substantially destroyed with increasing temperature. Copper is more catalytic and conductive, resulting in natural esters containing copper having inferior physicochemical and electrical property indices than those containing iron. However, the measured content of iron ions in the oil is much higher than that of copper ions in the oil. It can be seen that the catalytic ability of metals mainly depends on the elemental species rather than the elemental content. The above studies can provide theoretical guidance to reveal the mechanism of deterioration of natural esters by temperature and transition metals in transformers with bare copper and steel.