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

In gas insulated substations, the main trend is to move from SF
$_{6}$
to more environmentally friendly alternatives. The main SF
$_{6}$
alternatives are mixtures based on CO
$_{2}$
, with additives of O2 and the fluorinated gases C
$_{4}$
F
$_{7}$
N or C
$_{5}$
F
$_{10}$
O. 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 C
$_{4}$
F
$_{7}$
N and C
$_{5}$
F
$_{10}$
O. In addition, the influence of the gas used for arcing on the arcing contacts made of Cu/W (
$20/80$
$\text{wt}\%$
) 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 SF
$_{6}$
alternatives than for those used with SF
$_{6}$
, but further investigation is required. No major differences were found during visual inspection of the pins.