Study on Gas Diffusion Characteristics at the Insulation Interface of High Voltage Cable Accessories

In recent years, gas emission analysis has emerged as a promising approach for monitoring the insulation condition of high-voltage cable accessories. Among the influencing factors, gas diffusion behavior within the internal structure of cable accessories plays a critical role in determining the accuracy of insulation diagnosis. To investigate the diffusion and distribution characteristics of gases along insulation interfaces, this study first employed a gas permeability testing device to evaluate the longitudinal permeability of cross-linked polyethylene (XLPE) and silicone rubber (SiR). Subsequently, an interface permeability testing platform was constructed to experimentally assess the gas diffusion capability at the XLPE-SiR interface under varying pressure conditions. Based on the intrinsic gas permeability coefficient <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$P_{e}$</tex>, an interface gas permeability coefficient <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$P_{s}$</tex> was proposed to quantify the tangential diffusion along both bulk materials and interfaces. Experimental results reveal that while the intrinsic gas permeability of SiR is significantly higher than that of XLPE, it remains considerably lower than the diffusion capacity observed along the interface. Interface diffusion was dominated by tangential transmission, accounting for more than 64 % of total diffusion under all pressure conditions. Furthermore, the interface permeability decreased with increasing pressure, with the coefficient <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{P}_{\mathbf{s 1}}=\mathbf{2. 8 5} \times \mathbf{1 0}^{-\mathbf{5}} \mathbf{~ c m}^{\mathbf{3}} /(\mathbf{m i n} \cdot \mathbf{k P a})$</tex> at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{0. 1 ~ M P a}$</tex>, which dropped to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{P}_{\mathrm{s} 3}=1.83 \times 10^{-5} ~\text{cm}^{3} /(\min \cdot \text{kPa})$</tex> at 0.3 MPa, corresponding to a 36 % reduction. These findings provide theoretical insights and experimental data to support the engineering application of gas-based diagnostic methods for high-voltage cable accessories.