Online monitoring the discharging products of SF6 with photoelectron ionization mass spectrometry

Sulfur hexafluoride (SF6) is a gas used in electrical substations at electric power plants as an insulator in circuit breakers and switchgear. SF6 gas can generate a variety of decomposed products due to discharge or overheat inside the high-voltage devices. The discharging fault inside of the electric device insulated by SF6 is closely related to the composition and content of SF6 gas discharge products. Some of the byproducts are active and unstable, which create difficulties on testing them and have to be analyzed through a variety of testing methods. Gas chromatography, gas chromatography-mass spectrometry and infrared spectrometry have been developed to rapidly analyze the discharge products, but these methods are time-consuming and very hard to realize the in situ analysis and on-line diagnostics. An online monitoring system for discharging products of SF6 with photoelectron ionization (PEI) time-of-flight mass spectrometry was developed in this paper. It can be used for diagnosis of discharging fault inside of the electric device by real-time monitoring for discharging products of SF6. The mass spectrum of SF6 gas discharge products and the kinetics were investigated using a gas discharging study with home-made low direct current voltage system. The main byproducts of SO2F2, SOF2, SO2 and SF4 can be clearly detected. This method is expected to provide the power production field with online mass spectrometry monitoring and track the fault inside of the SF6 electrical equipment on its running condition. ©, 2015, Chinese Society for Mass Spectrometry. All right reserved.