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

The oil-impregnated paper plays a critical role in the reliability and safety of converter transformer, which is suffered by the accumulation of charges on oil-impregnated paper, leading to distorting the electric field and overvoltage. In addition, the problem of temperature rise is more prominent in contrast with the power transformer, which is attributed to the DC magnetic bias and harmonic current. As a consequence, the performance deterioration of oil-impregnated paper is a comprehensive result from multiple factors including thermal stress and electric field. Surface fluorination has obvious effect on the characteristics of the insulating material based on our previous work. This paper is dedicated to research effects of temperature on the charge characteristic of fluorinated oil-paper insulation under the coupling of DC and pulse voltage. The conclusions can be drawn that The strong electronegativity of fluorine and the tiny voids generated by fluorination contributes to capturing carriers for inhibiting the increase level of carrier mobility. The temperature rise has more influence in modifying the trap depth of the fluorinated paper in contrast with the trap density.