Influence of Temperature Aging on Oxidation Stability and Activation Energy of Insulating Liquids

Insulation liquids are mainly used in oil filled transformers for their cooling and insulating properties. Besides a testing of electrical properties, there is also important to monitor oxidation stability and activation energy as the factors which can decide on an application possibility of the insulating liquid. The main aim of this paper is to describe the influence of temperature aging on the oxidation stability and activation energy of tested insulating liquids (common petroleum based product and Dioctyladipate - di(2-ethylbexyl) ester of adipic acid - synthetic based liquid). Both liquids were exposed to a long-term thermal aging at the temperature of 90 degrees C for 3000 hours. A thermogravimetry was applied to determine the activation energy, oxidation stability tests were performed by differential scanning calorimetry.