Gas Sensitivity Studies On Single-wall Carbon Nanotube Detecting SF₆ Decomposed Components Under PD

SF₆ is widely used in Gas Insulated Switchgear (GIS) with the advantage of its high electric strength and excellent arc performance. During the continuous operation, the insulation defects in GIS will bring about partial discharge (PD), which leads to the decomposition of SF₆, generating different gas components. To detect and analyze decomposed characteristic components of SF₆ under PD is significant for fault diagnosis of GIS, however, how to detect the characteristic components from mixed gas components is the main puzzle.In this paper, nano gas sensor technology was applied to develop a new type of single-wall carbon nanotube gas sensor for detecting gas components of SF₆, based on the analysis of the lack of the exsiting detecting mothods to components. Micro-sensing mechanisms and macro-sensing characteristics of single-wall carbon nanotube gas sensors have been investigated through theoretical simulation and experiments.Adsorption models, between four types of gas components (SOF₂,SO₂F₂,SO₂,CF4) and SWNT, SWNT-OH, have been established by Materials Studio, and theoretical calculations were carried on, based on density functional theory (DFT).The micro-sensing mechanisms of SWNT-OH was focused on in this paper. First, the adsorption capacity of SWNT-OH on the four types of gas molecules was judged according to the the calculation results. Second, the difficulty levels of interaction between SWNT-OH and four types of molecules have been analyzed according to the molecular frontier orbital theory. Third, how gas molecules adsorbed on the SWNT-OH to influence electron transfer ability was investigated according to the results of energy gaps. Combined with the results of density of states, the hybridization of atomic orbitals was also investigated during the adsorption process between SWNT-OH and SO₂. Finally, the calculation results of SWNT-OH were compared with that of SWNT. Simulation results show that SO₂ was the most easily adsorbed on SWNT-OH, and the adsorption capacity of SWNT-OH on SO₂ was the largest among the molecules; the energy gap of SWNT-OH was reduced after adsorbing SO₂, which improved its ability of electron transfer; during the adsorption process, atom partial orbits tend to hybridization between SO₂ and SWNT-OH, which could help form electron transport channel, conducive to electron transfer between SWNT-OH and SO₂. Simulation results also indicated that the adsorption capacity of SWNT-OH on gas components was larger than that of SWNT.SWNT-OH and SWNT sensors were prepared,using interdigitated electrodes printed circuit board as the base. The standard gases SOF₂, SO₂F₂, SO₂ and CF4 were used to sensors experiments.The analysis and investigation were focused on the gas response of SWNT-OH sensor through the comparison of gas-sensing properties of two types of sensors. To explore the relationship between the rate of resistance change of SWNT-OH and the concentration of SO₂, their response curves were linearly fitted. Subsequently, the recovery characteristics and stability of SWNT-OH sensor were investigated as well. Experimental results indicated that SWNT-OH sensor had the fastest response speed and highest sensitivity to SO₂; it satisfied certain linear relations between the resistance change rate of SWNT-OH and SO₂ gas concentration; the SWNT-OH sensor could be self-recovery in the air, and the recovery time was short; to a certain extent, the SWNT-OH sensor met the stability requirements.