The Influence of the Thickness of the Insulation Paper to the Oil-paper Electrical Strength in the High Altitude Area

the Oil-paper insulation is composed of insulating paper and insulating oil, which has been widely used in the transformer inner insulation, the bushing and the switchgear insulation. The electrical properties of the Oil-paper insulation is heavily influenced by the thickness of the insulation paper. To explore the effect of the insulating paper with different thickness in high altitude. The electrical strength of the insulation paper with five kinds of thickness (0.15, 0.2, 0.3, 0.4, and 0.5) were tested with two different kinds of electrode. The insulation paper absorption rate were tested after the vacuum oil soaking treatment. The test results shows that with the increasing of the paper thickness, the oil absorption rate decreased from 38.29% with 0.15mm to 9.53% with 0.5mm.The average electrical strength of the Oil-paper with cylinder electrode decreased with the increasing of the thickness, from the 55.87kV/mm with the thickness of 0.15mm to 34.32kV/mm with the thickness of 0.5mm. The average electrical strength of the sphere electrode were lower than the test data with the cylinder electrode with the similar trend. The surrounding of the puncture holes also were observed with the optical microscope to analyze the breakdown mechanism.