Evaluation of unfilled and nanofilled oil/paper insulation system under thermal aging

The service life time of oil filled transformers is mainly dependent on its insulating system; either the mineral oil or oil/paper insulation. Thermal aging of these transformer insulating systems is carried out in this work. Accelerating aging is achieved by inserting the samples in an electric oven at 120 degrees C for 8 weeks. The effect of aging is evaluated considering different tests. Firstly, the creeping flashover voltage of oil/pressboard is studied considering epoxy coated and non-coated pressboards. Also, the effect of thermal aging on the breakdown voltage of oil/kraft paper insulation as well as transformer oil is carried out. All the aforementioned tests are performed considering unfilled transformer oil (base oil) as well as the same base oil modified by adding 0.08 g/l of MgO nanofiller. The effect of thermal aging considering all the studied cases is discussed and interpreted. Finally, it is found that the epoxy coating and nanofillers significantly affect the performance of oil/paper insulation system.