Indirect detection of residual cf₄ in gas-insulated switchgear via conversion under dielectric barrier discharge

In this paper, a new diagnosis method for SF₆ gas-insulated switchgear (GIS) is proposed based on decomposition gas analysis. We focus on residual CF₄ gas in GIS, which is a decomposition gas generated in GIS via partial or arc discharge. Unlike other decomposition gases, which can be removed by the gas absorbent, CF₄ accumulates during in-service operation, enabling trend-based GIS condition monitoring. Because direct CF₄ detection using commercially available gas sensors is difficult, we propose a novel indirect detection method in which CF₄ is converted into CO and CO₂ by a dielectric barrier discharge (DBD). A DBD-treated artificial gas mixture composed of CF₄, O₂, and SF₆ was analyzed via Fourier transform infrared spectroscopy (FTIR). It was found that CO and CO₂ are simultaneously generated when the CF₄ gas concentration is higher than 100 ppm, which is close to the target CF₄ concentration for GIS diagnosis. To demonstrate rapid, simple, and on-site diagnostic capabilities, a commercial electrochemical CO gas sensor was employed to detect DBD-converted CO gas. The CO concentration quantified by the calibrated gas sensor was almost identical to that obtained via FTIR. As the CF₄-to-CO conversion rate is expected to improve with an optimum DBD reactor design, the proposed scheme could be applicable to GIS diagnosis.