| Long air gap discharge is the key problem of the extern insulation design of high voltage power transmission system and important foundation for the lightning physics.The air insulation strength decreases significantly with the increase of altitude and decrease of gas density.One of the main factors in the gas phase state parameters affects the electrical insulation properties are air pressure.In this dissertation,stream discharge is taken as the research object,experimental observations and simulations are used to study the effect of air pressure on stream discharge in air gap and the simulation model of stream discharge initiation is established which considers the influence of air pressure.This study not only provides a basis for the configuration optimization of extern insulation of high voltage power transmission and transformation system in high altitude areas,but also lays a theory foundation for the high-altitude lightning physics.First,a low-pressure long gap discharge chamber was developed,and an integrated design of current measurement,electrode and chamber body was proposed which achieve accurate measurement of discharge current in a closed space.Method was proposed to uncouple two influencing factors of air pressure and humidity,which achieved control of air pressure in the chamber.A synchronous observation platform for low pressure long gap streamer discharge characteristics was established to realize synchronous observation of discharge voltage waveform,discharge current waveform,streamer discharge optical images and shock wave images.Secondly,the influence and mechanism of gas pressure on the initial characteristics of streamer discharge were studied.Under constant electric field reduction and different gas pressure,important parameters such as average initial voltage,initial time delay distribution,development length and 2D branch angle of streamer discharge were obtained through experiments.The influence of gas pressure on the initial characteristics of streamer was studied.A simulation model of the inception of stream discharge was established which considered the influence of gas pressure,and the influence of gas pressure on the average initial field strength of the streamer and the dispersion of the initial time delay was analyzed.The rationality of the model was verified by experimental results.Finally,the effect of gas pressure on the characteristics of shock waves in streamer discharge was studied.Shock waves observation under three pressure conditions of 0.2 bar,0.4 bar and 0.6 bar were carried out,and development parameters of spherical shock wave generated by streamer discharge under different pressure conditions were obtained.The influence of pressure on the development speed of shock wave and the relative intensity of shock wave evolution in time domain is analyzed.The 1D radial thermal hydrodynamic model of streamer discharge at low pressure was established.The relative gas density,radial pressure distribution and time domain evolution parameters of discharge channel under different pressure conditions were obtained.The rationality of using the gray scale variation to characterize the change of shock wave intensity was verified.Furthermore,the time-domain evolution of shock wave intensity under different injection currents of streamer discharge was analyzed. |
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