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 SF6 to more environmentally friendly alternatives. The main SF6 alternatives are mixtures based on CO2, with additives of O2 and the fluorinated gases C4F7N or C5F10O. 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 C4F7N and C5F10O. In addition, the influence of the gas used for arcing on the arcing contacts made of Cu/W (20/80wt%) 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 SF6 alternatives than for those used with SF6, but further investigation is required. No major differences were found during visual inspection of the pins.

Trace Analysis of C4F7N Insulating Gas Mixtures by Spontaneous Raman Spectroscopy and Gas Chromatography

“…For instance, C 2 F 6 possesses a GWP of 11,000, while CF 4 boasts an atmospheric lifetime of 50,000 years . The formation of these byproducts is affected by multiple factors, such as buffer gas composition, arc current, temperature, circuit breaker geometry, and others . Chen et al found that C 2 F 3 N began to form when heated to 500 °C for 72 h .…”

“… 7 The formation of these byproducts is affected by multiple factors, such as buffer gas composition, arc current, temperature, circuit breaker geometry, and others. 36 Chen et al found that C 2 F 3 N began to form when heated to 500 °C for 72 h. 37 Li et al discovered that C 4 F 7 N/N 2 mixtures that use O 2 as an additional buffer gas have an increased CF 4 concentration and a decreased C 2 F 6 concentration when discharged. 38 These parameters also affect the insulating ability of C 4 F 7 N. For example, as the distance between the arc contacts in a circuit breaker increases, the insulating efficiency of the gas is improved.…”