Spectroscopic Study On Pulsed Discharge Plasma Of SF₆/Ar And SF₆/N₂ Mixed Gases

Sulfur hexafluoride?SF₆?has been widely used in gas-insulated equipment due to its excellent insulation property and arc extinguishing capability.However,the SF₆ has a lot of shortcomings,such as strong greenhouse effect and easy decomposition of non-uniform electric field,so it is crucial to research on the discharge of SF₆ gas and its alternative gases.The insulation metal defect which usually causes partial discharge?PD?to decompose the SF₆ is a common fault in the high voltage equipment.In order to improve the understanding of discharge mechanism of SF₆ mixed gases,the investigation on SF₆/Ar gas mixtures and SF₆/N₂ gas mixtures is carried out in this work.The PD which can be caused by metal protrusion defect was simulated by the needle-plate electrode using high-voltage pulsed discharge.Optical emission spectroscopy?OES?and cavity ring-down spectroscopy?CRDS?were used for analysis of the discharge.The results are summarized as follows:1.A PD device with OES plasma diagnostic system has been well established.The spatial and temporal characteristics of SF₆/Ar plasma are analyzed by measuring the OES spectra of F and Ar atoms.The spatial resolved results show that both F and Ar atom spectral intensities increase firstly from the plate anode to the needle and then decrease,under the conditions of the background pressure of 400 Pa,the peak voltage of-1000 V,the frequency of 2 kHz,the pulse width of 60?s,and the electrode gap of 5 mm–9 mm.However,the spatial characteristics of F and Ar are significantly different.The temporal distribution results show that the spectral intensity of Ar decreases firstly and then increases slightly,while the spectral intensity of F increases slightly during the duration of the pulsed discharge at the electrode gap of 5 mm and the pulse width of 40?s–80?s.2.The spatial evolution of SF₆/N₂ plasma is analyzed by measuring the OES spectra of F atoms.The plasma emission intensity,electron excitation temperature,vibration temperature,rotational temperature of the SF₆/N₂ plasma are measured in the different discharge pulse widths.The spatial evolution results show that the spectral intensities of the F atom increase firstly from the plate anode to the needle and then decrease,under the conditions of the background pressure of 400 Pa,the peak voltage of-1000 V,the frequency of 2 kHz,the pulse width of 60?s and the electrode gap of 5 mm–11 mm.The plasma parameter measurement results show that the plasma emission intensity trend is consistent with the vibration temperature and rotation temperature trend under the condition of pulse width of 20?s–250?s and electrode spacing of 5 mm.As the pulse width increases,the emission intensity increases firstly and then decreases.When the pulse width is about 100?s,the emission intensity appears to be the maximum value.As the pulse width increases,the electron excitation temperature gradually decreases.3.A CRDS plasma diagnostic system for discharge under low pressure has been established and a preliminary investigation of SF6/Ar/SO2 mixtures is performed.The results show that the detection sensitivity of the system is 1.55×10^-6 cm^-1,and the corresponding limit of detection for SO₂ is 2.75×10¹² cm^-3.Under the non-discharge condition,the number density of SO₂ is achieved to be 2.68×10¹³ cm^-3.