Material Selection of Metal Conductors for Environmentally Friendly Switchgear Based on Gas Breakdown Characteristics

The choice of metal conductor materials in ecofriendly gas-insulated equipment impacts the insulation properties of $\mathrm{C}_{4} \mathrm{~F}_{7} \mathrm{~N} / \mathrm{CO}_{2}$ gas mixtures. This study investigates the breakdown characteristics of $\mathrm{C}_{4} \mathrm{~F}_{7} \mathrm{~N} / \mathrm{CO}_{2}$ gas mixtures with electrode metal materials including stainless steel, copper, tungsten copper, and aluminum alloy by establishing a simulation test platform for power frequency and lightning breakdown discharges. The results showed that when the electrode metal material was copper, the $\mathrm{C}_{4} \mathrm{~F}_{7} \mathrm{~N} / \mathrm{CO}_{2}$ gas mixture had the best power frequency insulation performance. The power frequency insulation performance of the $\mathrm{C}_{4} \mathrm{~F}_{7} \mathrm{~N} / \mathrm{CO}_{2}$ gas mixture was similar for stainless steel and tungsten copper electrode materials, ranking just below copper. By contrast, aluminum alloy electrodes resulted in the poorest power frequency insulation performance for the gas mixture. In the low-pressure range of $0.1-0.2 \mathrm{MPa}$, the differences in power frequency insulation performance among the four materials were particularly pronounced. For lightning impulse insulation, the $\mathrm{C}_{4} \mathrm{~F}_{7} \mathrm{~N} / \mathrm{CO}_{2}$ mixture exhibited relatively superior performance with stainless steel and copper electrodes. Under positive and negative lightning impulse voltages and pressures of $\mathbf{0. 1 5 - 0. 2 5 M P a}$, the $\mathbf{U}_{\mathbf{5 0} \%}$ values for the gas mixture with the four metal electrodes followed this order: stainless steel had the highest $\mathrm{U}_{50 \%}$, followed by copper, while aluminum alloy showed the lowest $\mathrm{U}_{50 \%}$, with tungsten copper falling between copper and aluminum alloy. From the perspective of mixed gas power frequency and lightning breakdown voltage, environmentally friendly gas insulated equipment can choose copper and stainless steel as metal conductive materials.