Numerical Calculation Model for Obtaining Parameters of Insulation Materials in HVDC-GIL Subjected to Transition Field

In this paper, we compare the differences in the charge accumulation for two different models about conductivity: one in which the conductivity value of the spacer is invariant with time (steady-state conductivity, Model I) and one in which the conductivity value can vary dynamically with time (dynamic conductivity, Model II). The time for the potential distribution to reach a stable state is 8078 s in Model I and 7932 s in Model II. After the charge accumulation reaches saturation, the charges migrate to the middle of the spacer under the applied electric field. Maximum tangential field strength is <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${2.56} \times {10}^{6}\ \mathrm{V}/\mathrm{m}$</tex> in Model I and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${2.84} \times {5}\ \mathrm{C}/\mathrm{m}^{3}$</tex>, which is much smaller than the charge density in the spacer. The mechanism underlying the charge accumulation phenomenon is the differences in the conductivity value distribution caused by a time-varying temperature gradient field. This paper can provide a more precise theoretical basis for the selection and modification of HVDC-GIL spacer.