Analysis of PD-generated SF/sub 6/ decomposition gases adsorbed on carbon nanotubes

Chemical byproducts analysis has been recognized as a powerful diagnosis method for SF
₆
gas-insulated switchgear (GIS). The authors have previously demonstrated that a carbon nanotube (CNT) gas sensor could detect partial discharge (PD) generated in SF
₆
gas. However, PD-generated decomposition gas species, which were responsible for the CNT gas sensor response, have not been identified yet. In this paper, two kinds of experiments were conducted in order to identify the responsible decomposition gas species. At first, the decomposition gas molecules adsorbed on CNTs were analyzed by Fourier transformation infrared (FTIR) spectroscopy. FTIR absorbance was observed around 735 cm
^-1
after CNTs were exposed to PD generated in SF
₆
. In the second experiment, the CNT gas sensor responses to typical SF
₆
decomposition products (HF and SF
₄
) were examined. The CNT gas sensor responded to these gases in the same way as to PD generated in SF
₆
. SF
₄
response was larger than HF response. Based on these results, SF
₄
and SOF
₂
emerged as candidates for the responsible decomposition gases. Electrochemical interactions between adsorbed gas molecules and CNT were discussed based on theoretical predictions of molecular orbital calculations. The calculation results suggested that both of SOF
₂
and SF
₄
could increase the CNT gas sensor conductance