Ageing phenomena of cellulose/oil insulation in natural ester and mineral oil

Degradation of electrical insulation due to ageing by combination of thermal, oxidative and hydrolytic processes is one of the main factors that affect power transformer service life. A better understanding of ageing phenomena is of great importance for transformer condition assessment. This enables reliable operation and affords application of adequate mitigation action to slow down the degradation process of insulating materials and extend transformer service life. This issue is all the more important when new insulating liquids as natural esters are being applied in growing number in transformer industry. For these reasons, this paper is focused on the ageing phenomena of cellulosic materials (paper and pressboard) impregnated with different insulating liquids as natural ester,…