Space Charge Characteristics of Electrothermally Aged Oil-Paper Insulation Under Slightly Nonuniform Electric Field

Abstract

To study the change characteristics of space charge in oil paper insulation under a slightly non-uniform electric field and a uniform electric field, the existing space charge measuring device was improved, and sphere–plate and column–plate electrode models were prepared. Oil paper insulation samples at different aging stages were obtained via electrothermal aging. The real-time waveforms of the space charge distribution in the samples at different aging stages were measured in the process of polarization with a direct-current (DC) voltage and depolarization with a DC voltage, and the effects of different electric-field types on the charge distribution and motion characteristics of oil paper insulation samples at different aging stages were examined. The results indicated that the existence of a slightly non-uniform electric field accelerated the change in the charge-density peak at the interface and increased the fluctuation range of the charge-density curve in the process of applying a DC voltage. With the aggravation of electrothermal aging, the amount of charge injected into the sample increased, and the slightly non-uniform electric field intensified this process, affecting the accumulation and dissipation of space charge in the sample. Electrothermal aging increased the trap distribution density and energy-level depth. However, for an oil paper insulation sample at the same aging stage, compared with the uniform electric field, the slightly non-uniform electric field had no obvious effect on the trap energy-level depth, but it increased the amount of trapped charge and changed the trap density distribution in the sample. The results of this study provide a theoretical basis for examining the influence of slightly non-uniform electric fields on the space charge distribution characteristics of oil paper insulation subjected to AC/DC combined electrothermal aging.