Abstract
<title>Abstract</title> <p> To address the low dielectric strength, non-uniform electric field and empirical selection of gas mixture in 500 kV eco-friendly gas-insulated current transformers, this paper combines insulation-structure optimisation for electric-field uniformity with multi-objective gas-mixture selection. Morris screening, Kriging surrogate and Sobol indices were used to reduce the seven-dimensional geometric design space to four main parameters, and then the dominant factors influencing the maximum electric-field strength Emax were determined; they are the high-voltage electrode fillet radius rhv and the normalised intermediate-electrode position hm. Based on the five goals of dielectric strength, thermal diffusion, detectability, environmental impact and cost, NSGA-II will be employed to optimise the N2/O2/He ratio and gas pressure. Run 1000 Monte Carlo simulations to find out how much manufacturing error, pressure fluctuation and temperature fluctuation affect the output. Combine AHP and entropy weights, and then calculate the Spearman correlation of the rankings. For the 500 kV case, the recommended configuration (r <sub>hv</sub> = 45 mm, hm = 0.52, α <sub>N2</sub> = 0.78, α <sub>O2</sub> = 0.21, α <sub>He</sub> = 0.01, p = 0.5 MPa) is 14% better than the dry-air and N2/CO2 schemes, 17% better than the SF6 scheme, and also exceeds the SF6 scheme. It has a robustness index η = 17.5 and M <sub>E</sub> ≥1.74 in 95% of the operating conditions. The above way is to provide a quantitative basis for the forward design and prototype verification of eco-friendly UHV current transformers. </p>