Calibration methods of carbon nanotube gas sensor for partial discharge detection in SF6

The authors proposed a new type of gas sensor for high sensitive detection of decomposition products generated by partial discharge (PD) in SF6 gas. The sensor employed carbon nanotubes (CNTs) as gas sensing transducer and was fabricated by electrokinetic manipulation of CNTs using dielectrophoresis. Due to complicated gas decomposition process of SF6 gas, calibration of the CNT gas sensor is an essential and challenging subject in order to realize reliable and stable detection of PD under practical conditions. In this paper, two methods for the CNT gas sensor calibration were proposed and tested. The first method was based on initial conductance dependence of the CNT gas sensor response. The CNT gas sensor response to PD increased almost linearly with the amount of CNT trapped onto the sensor electrode, which could be quantified by the initial conductance of the sensor. However, the calibration accuracy of this method was about 50 % and was not high enough for practical use. The second method employed NO2 (nitrogen dioxide) as calibration gas because of the similarity in the CNT sensor response to PD decomposition products and NO2. It was found that the accuracy of the NO2 calibration was about 10 % and far better than the first method. Finally, effectiveness of the NO2 calibration was demonstrated by a PD monitoring test in which two CNT sensors were simultaneously exposed to SF6 decomposition products with identical concentration.