Effects of Moisture on Surface Charge Behavior of Fluorinated Oil-impregnated Paper under DC and Pulse Voltages

The oil-paper insulation is widely implemented in converter transformer. Moisture has detrimental influence on the lifespan of oil-paper insulation. Meanwhile, the degradation velocity can be accelerated when the operating overvoltage occurs. Direct fluorination is an effective approach to modify the surface property of insulating material. Hence, for investigating the effects of moisture on charge behavior of fluorinated oilimpregnated paper under DC and pulse voltage, the specimens of being fluorinated for 5, 30 and 60 min respectively are treated in the sealed container with relative humidity of 20%, 40% and 60% for 30 min. From the research, conclusions can be drawn that the specimen of being fluorinated for 30 min has the best performance in water absorption. The moisture has less influence in modifying the deep trap depth of fluorinated paper and introduces more shallow traps. Meanwhile, the dissipating velocity becomes lager when the pulse frequency increases from 300 to 500 Hz. On the contrary, the velocity gets smaller when the frequency sequentially increases to 700 Hz.