| Lightning accidents are one of the reasons that endanger the stable operation of the power grid.Most of the accidents are caused by lightning strikes on transmission lines that cause insulators to flashover and form power frequency freewheeling short circuits.Therefore,the development of a lightning protection device that can effectively interrupt the power frequency freewheeling is of great significance to the stable operation of the power grid.The recoil structure arc extinguishing device is a self-energy lightning protection device,and its design idea is: First,use the energy of thunder and lightning to form a recoil air blowing arc,cut the long flashover arc into multiple short arcs,and then completely release the arc energy through continuous airflow.Finally,the insulation of the arc extinguishing channel is restored and the reignition of the arc is suppressed.According to the above concepts,this paper studies the mechanism of interrupting power frequency freewheeling and suppressing reignition of the recoil structure arc extinguishing device by analyzing arc theory,establishing numerical models,modeling simulation,and experimental application analysis The research results are of great significance to the upgrade and improvement of the device.The main tasks are as follows:(1)Analyzing the development characteristics of power frequency arc,it is concluded that the introduction of recoil airflow and the near-cathode effect of enhancing power frequency arc can effectively interrupt power frequency freewheeling and suppress reignition.Combined with MHD magnetic fluid theory,the force and flow process of the arc in the recoil tube are analyzed.The power frequency arc is mainly subjected to the self-magnetic compression force in the recoil tube,and the flow mode is turbulent flow.According to the theory of power frequency arc extinguishment and reignition,the arc extinguishment criterion is determined.(2)The geometric structure and working principle of the arc extinguishing device with recoil structure are introduced.The trigger model of recoil airflow is established,the principle of recoil airflow triggering is analyzed,and the coupling process of recoil airflow and other physical state variables is clarified.(3)The Mayr arc model in the 35 k V low-current grounding system was established by MATLAB/Simulink simulation software.It is concluded that the recoil structure will show two arc extinguishing modes,zero-crossing arc extinguishing and impact arc extinguishing under different power dissipation conditions.(4)Based on the MHD magnetic fluid theory,a multi-physics geometric model of the recoil structure arc extinguishing device is built.The recoil airflow has already cut off the arc Joule heat source channel in about 1 ms,and then under the strong convection heat dissipation effect,the arc channel is completely insulated at 5 ms.During the arc extinguishing process of the recoil structure,there are recoil airflow and cavity backflow,which has the effect of accelerating the cooling of the recoil structure and prolonging the action time of the airflow.For each return strike of multiple lightning strikes,the recoil structure can generate corresponding recoil airflow to suppress the reignition of the power frequency arc.(5)Scientific experiments have been used to verify the ability of the device to withstand the large current of lightning impulse,and the 50% discharge voltage of lightning impulse is measured.A power frequency freewheeling interruption test platform with a recoil structure arc extinguishing device is built,and the device can interrupt a power frequency freewheeling arc of 0.912 k A in about 0.9 ms.(6)The field operation data of the recoil structure arc extinguishing device was compared and analyzed.The operating data showed that the recoil structure arc extinguishing device greatly reduces the lightning trip rate in Xishuangbanna,Yunnan. |
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