Study On The Mechanism And Application Of 1-m Air Gap Discharge Under The Lightning Impulse Based On The Spatiotemporal Distribution Of Discharge Intensity And Spectrum

The trip struck by lightning seriously threatens the safety and stability of the power grid.The air gap and the insulator are the main external insulation forms of transmission lines.Meanwhile,the studies of the discharge mechanism and discharge characteristics of the air gap and the insulator under lightning impulses,as well as the suitable flashover criterion for air gap and insulator,are the basis for the further refinement of external insulation design in the power system.Therefore,aiming at the theory of long gap discharge and its application,the temporal and spatial distribution of light intensity and spectral lines of 1 m rod-plate gap discharge channel under the lightning impulses were observed to further reveal the physical discharge process in the air gap based on the em ICCD with ns-level exposure time and the grating spectrometer,and its application research was carried out combined with the external characteristics test of gap discharge under the lightning impulses.First,aiming at the spatial and temporal distribution of the light intensity and the emission spectral line in the discharge channel under the lightning impulses in rod-plate gap,based on em ICCD and spectrometer,through the design of synchronous trigger mode,the em ICCD delay scheme and the light intensity gain,and a large number of repetitive tests,the ns-level interval time series splicing method of light intensity and spectral line images with nanosecond-level exposure time was used to achieve the qualitative observation for the temporal and spatial distribution of the transient light intensity and emission spectral lines in the very weak discharge（streamer）channel and the very strong discharge（leader）channel.Based on the lightning flashover test platform constructed,the tests about the 50%discharge voltage(U_50%),volt-sec characteristic scatter,flashover form of 1 m rod-plate gap,single insulator,real tower insulator were designed and carried out.It laid a foundation for the application research combined with the gap discharge mechanism under lightning impulse.In addition,the calculation method of electron temperature and electron density in long gap discharge channel and its application range were analyzed based on the theory of atomic emission line diagnosis.Secondly,according to the observation and comparative analysis of the discharge light intensity images in the discharge channel of 1 m rod-plate gap under the standard lightning impulse,the differences of the ionization region morphology characteristics and ionization degree in the discharge channel under the different polarity lightning impulse as well as the difference between the breakdown and non-breakdown discharge process were discovered.It was proposed that there is no secondary streamer and leader restriking in the discharge channel of 1 m rod-plate gap under the lightning impulse.And the reasons for the differences were analyzed.The discharge process and law of 1m rod plate gap under positive and negative polarity lightning impulse were summarized on the basis of analysis results.Thirdly,combined with em ICCD and spectrometer,the distribution range of characteristic lines in the discharge channel under positive and negative polarity lightning impulse of 1 m rod-plate gap was measured and analyzed.Combined with the diagnostic theory of atomic emission spectrometry,the electron temperature and electron density in the lightning discharge channel of 1 m rod-plate gap at different positions and at different times were calculated by using the relative intensity and the Stark broadening of N and O atomic spectral lines.Based on the results of parameter calculation,the variation of electron temperature and electron density during the streamer-leader transition and the leader discharge stages near the rod and the plate electrode were analyzed systematically.The range of the average electron temperature and the average electron density in streamer-leader transition and leader discharge stages in different lightning impulse discharge processes were summarized.Finally,for the phenomenon that the direction and distribution of the electric field in the discharge gap and lightning impulse waveform affect secondary streamer,leader restriking and leader development speed found in 1 m rod-plate gap discharge tests,the flashover characteristics of the different insulation structures under the different lightning impulse voltage waveforms and the accurate flashover criteria were systematically studied.The test results,including U_50%,the voltage-second characteristics,and the discharge images,of 1 m rod-plate gap,the single composite insulator,the composite and the glass insulators in the true tower were compared and analyzed.And combined with the simulation of the electric field distribution,the reasons for the difference of U_50%and discharge form among the four insulation structures above were analyzed and explained.Based on the test data of the four insulation structures under the standard lightning and the short tail wave impulses,and the corresponding different flashover criteria,the influence of the flashover criterion on the calculation results of the lightning counterattack withstand level of the transmission line was analyzed by PSCAD simulation,and a refined flashover criterion suitable for lightning protection design was proposed:the leader development model established by the Voltage-second characteristic of the true tower insulator and the actual test waveform.And its application scope was discussed...