Wear of the Arcing Contacts and Gas Under Free Burning Arc in SF$_{6}$ Alternatives

Abstract

In gas insulated substations, the main trend is to move from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathrm{SF}_{6}$</tex-math></inline-formula> to more environmentally friendly alternatives. The main <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathrm{SF}_{6}$</tex-math></inline-formula> alternatives are mixtures based on <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathrm{CO}_{2}$</tex-math></inline-formula> , with additives of O2 and the fluorinated gases <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathrm{C}_{4}\mathrm{F}_{7}\mathrm{N}$</tex-math></inline-formula> or <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathrm{C}_{5}\mathrm{F}_{10}\mathrm{O}$</tex-math></inline-formula> . Mixtures with fluorinated additives of up to 10% were investigated in a test setup with a free burning arc. Gas composition was measured for each gas after mixing, and in-between some arcing sequences. Gas mixtures were investigated by three mobile gas analyzers and by three laboratories. The results showed that for clean gas mixtures, all methods showed comparable results. Determination of the heavily arced gas mixture decomposition is challenging and requires detailed laboratory analysis. A range of decomposition rates were shown for both <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathrm{C}_{4}\mathrm{F}_{7}\mathrm{N}$</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathrm{C}_{5}\mathrm{F}_{10}\mathrm{O}$</tex-math></inline-formula> . In addition, the influence of the gas used for arcing on the arcing contacts made of Cu/W ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$20/80$</tex-math></inline-formula> wt%) was investigated. A higher mass loss on the anode than on the cathode was found for all contacts. There is an indication of a higher erosion rate for arcing contacts used in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathrm{SF}_{6}$</tex-math></inline-formula> alternatives than for those used with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathrm{SF}_{6}$</tex-math></inline-formula> , but further investigation is required. No major differences were found during visual inspection of the pins.