Influencing mechanism of temperature on the electric field distribution and interface charge accumulation in oil-pressboard insulation under DC voltage

Abstract The operational temperature regime of a transformer critically influences the electric field topography and the interface charge dynamics within the oil-pressboard insulation. Employing the Kerr electro-optical phenomenon, this manuscript delineates the development of a thermal-modulated electric field mapping apparatus for oil-pressboard insulation. Empirical analyses on the electric field and interface charges under variable thermal conditions revealed the following: 1) within the single-oil-spacing model, an escalation in temperature engenders an amplified electric field intensity in oil, a diminished interface charge density, an augmented disparity between the polarization charge density and the ascertained charge magnitude, and at 80 °C, the discerned interface charge polarity is antithetical to the polarization charge. Hereupon, an oil-pressboard equivalent charge paradigm predicated on the Schottky emission schema was posited. At 20 °C, Schottky emission accounted for 0.95% of the interface charge, primarily as polarization charge; at 80 °C, it rose to 60.11%, with Schottky-derived charge density increasing by a factor of 1713.4, indicating its dominance. (2) Pertaining to the double-oil-spacing model, an elevation in temperature to 80 °C transposes the electric field distribution in oil, and the equivalent charge polarity discerned at 60 °C and 80 °C is counter to that observed at 20 °C. This effect indicates that after thermal enhancement, the interface charge polarity in the oil-pressboard composite aligns with the Schottky injection charge polarity, inverting the electric field distribution in the oil. (3) The employment of oil-polytetrafluoroethylene model presents the far less influence exerted by Schottky charge injection, and furtherly ensure the influencing mechanism of temperature on electric field in oil-pressboard.