Enhancing Flashover Performance of Gil Insulator by Functionally Graded Materials Under Temperature Gradient and Polarity Reversal Voltage

Insulators in direct current gas-insulated transmission lines (DC-GILs) are subjected to temperature variations and may encounter polarity reversal voltages. To minimize flashover faults of insulators, this study proposes an innovative multi-dimensional functionally graded material (MFGM) insulator. This design incorporates a surface coating composed of nonlinear conductivity material (SNCM) and a core constructed from permittivity-graded functional material (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\varepsilon$</tex>-FGM). Simulations and experiments were performed under polarity reversal scenarios and across various temperature gradients. The findings indicate that SNCM insulators can homogenize electric field (E-field) distributions before polarity reversal at different temperatures but exacerbate E-field distortion after polarity reversal at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{T}_{\mathbf{H V}}$</tex> temperatures of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{2 5}$</tex> and 50° C. In contrast, the MFGM insulator effectively manages Efield distributions across all temperature gradients, both before and after polarity reversal. This results in improvements in flashover voltage by <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$6.5 \%, 9.8 \%$</tex>, and 21.9 % at high temperatures of 25,50, and 70° C, respectively. These outcomes demonstrate the potential of MFGM insulators for practical implementation in DC-GIL systems.