This paper describes application of carbon nanotube (CNT) gas sensor to detection of SF6 decomposition products generated by positive or negative DC corona discharge. The present authors have demonstrated CNT gas sensor-based partial discharge (PD) detection, aiming to develop a new diagnosis method of gas-insulated switchgear (GIS) filled with high pressure SF6 gas. In our previous studies, PD was generated by ac high voltage because most of GIS are designed and operated for conventional high voltage ac (HVAC) power transmission lines. In recent years, however, the electrical power industry has shown a trend shifting from HVAC to high voltage dc (HVDC) power transmission, which has many advantages such as higher power capacity and lower power loss. This technological trend motivated us to explore and expand the application of CNT gas sensor to detection of SF6 decomposition products generated by dc corona discharges. It was found that the CNT gas sensor exhibited significant response to dc corona discharge depending on the voltage polarity. In order to elucidate the mechanism of the polarity effect, SF6 decomposition products were analyzed by Fourier transformation infrared (FTIR) spectroscopy as well as using a gas detection tube. Based on comparison between the polarity effects on the CNT sensor response and the decomposition products, a possible contribution of HF to the CNT gas sensor response was suggested.
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