| Pulse output switch is one of the key components in high-voltage electromagne t ic pulse simulation devices.It builds up a nanosecond pulse of higher amplitude and faster leading edge based on the initial pulse generated by the forestage Marx generator,The high electric and magnetic field energy of the nanosecond pulse is then radiated to the outside through the biconical antenna,testing the resistance to interference and damage of the electronic equipment.However,the output switch in a high-vol t ag e electromagnetic pulse simulation device has a breakdow n voltage drop phenomenon in sometimes during continuous breakdow n,which reduces the stability of the device operation.Therefore,research on the key factors affecting the breakdow n characteristics of pulse output switches has important engineering application value for optimizing the structural design and improving the stable operation of the devices.An experimental platform for gas dielectric breakdow n under nanosecond pulses is designed and built.It is runed with higher stability,as the average dispersion of the air-gap breakdown voltage under different conditions being around 0.05.The gap breakdow n value under nanosecond pulses is closely related to the applied energy(the integral of the applied voltage with time).The gap breakdow n voltage increases with the steepness of the pulse front,gas pressure and gap distance.Under dry conditi on s,charges will be generated inside the chamber(including surface)after the gap breakdow n.In the continuous breakdow n experiment,it is found that the criti c a l breakdow n voltage showed an upward trend with the increase of the applied pulse time interval,and the gap breakdown probability showed a downward trend under the same applied voltage.It can be speculated that the residual charges may have an impact on the gap breakdow n characteristics.A two-dimensional axisymmetric model of streamer discharge under nanosec o nd pulses is established based on the finite element method.The influences of some key factors including the applied voltage(steepness of the pulse front),the intern a l structure of the output switch(electrode radius and gap distance),and environ m e n t parameter(initial charge)on the development of streamer discharge are explor ed.Based on the changes of electric field strength,particle density,development rate and ionization radius during the development process of the streamer discharge,the influence mechanisms of the above mentioned three key factors on the discha rg e development are discussed in detail.To address the problem that charge generated may reduce the breakdow n stabi l i ty of the switch,the methods for dissipating charge are explored by combining simula t io n and experimental methods.The experimental results in a dry environment show that the charge dissipates exponentially,and it takes a long time to completely dissipa t e.The simulation results suggest that the charge mainly dissipate through surfac e dissipation and ion neutralization dissipation,and the latter commonly contribu t e s more.For the dissipation pathway along the surface,the dissipation speed of the charge increases significantly with the surface conductivity(after upgrading by 2-3 orders of magnitude).The influence of ambient humidity on surface conductivi ties is conside r ed,the experimental results indicate that when the relative humidity from 45%to 60%,the charge dissipation time constant decreased from 53min to 18.8min.For the ion neutralizat ion dissipation pathway,the simulation results show that the charge can be completely dissipated within a few minutes when the ion pair generation rate reach above 10~4.Then,ion wind is introduced in the experiment to increase the genera t io n rate of ion pairs,and the results show that most of the charges in chamber are dissipa t e d within five minutes. |
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