Volatile Acid and Polymer Formation in Various Insulation Liquids Upon Accelerated Thermal Ageing

Insulation liquids perform a vital role in protecting power equipment, such as transformers, from thermal, electrical and environmental stress. Considering the poor fire-safety properties and low biodegradability of mineral oil as the leading kind of insulation liquid, alternative insulation liquids are of high interest for their implementation in power equipment. In this experiment we aimed to simulate the processes occurring in faulty power equipment by ageing four different kinds of insulation liquids (mineral oil, GTL-insulation liquid, synthetic ester and natural ester) under laboratory conditions. The use of optimized analytical routine methods has allowed us to monitor as well as quantify volatile acid and polymer formations upon ageing of insulation liquids. The ageing process under aerated conditions has led to the formation of formic, acetic and propionic acid, especially in natural ester, alongside notable polymerization effects. All other types of insulation liquids showed significantly lower amounts of volatile acids. Per contra, the experiments conducted under oxygen-free conditions resulted in minimal volatile acid and polymer build-ups in all four insulation liquids.