Tensile strength of electrical insulating paper in natural ester and mineral oil

Aging of transformer insulating material in natural ester insulating oil was compared to that in conventional transformer oil. Aging of insulating paper has been studied by performing accelerated thermal aging test. Sealed aging test vessels containing copper, laminated core, Kraft/Diamond paper, and insulating oil (natural oil or mineral oil) were aged at 140°C during 500, 1000 and 1500 hours. The extent of paper degradation after aging was determined using paper tensile strength in the aged fluid. The Kraft/Diamond Paper aged in conventional transformer oil degraded at a significantly faster rate than in natural ester insulating oil.