Experimental Research On Gas Switch Triggered By Plasma Jet

For our country,the distribution of energy and power load centers presents an unbalanced characteristic,and it is difficult to meet the power demand of the power load centers.To solve this problem,China vigorously develops large-capacity long-distance UHV(Ultra High Voltage)power transmission technology.Baihetan-Jiangsu ±800 k V UHV Hybrid DC transmission project is its application demonstration project.However,when the receiving end fails,a large power surplus will be generated on the DC bus,so the excess energy must be quickly discharged.But,the closing time of the traditional power switch is greater than 1ms,which can not meet the application requirements of fast discharge protection.Secondly,the power electronic switch with high voltage and large capacity needs multiple components in series and parallel,which has complex structure and high cost.The gas switch triggered by the plasma jet is not only low in cost,but also able to achieve a fast conduction of about hundreds of microseconds under a very low operating coefficient,and can be used as a fast closing element to undertake fast energy discharge tasks.This paper first analyzes the working principle of the gas switch triggered by plasma jet and the ablation mechanism of the trigger cavity and electrode,which lays a theoretical foundation for the design of the gas switch,the improvement of the trigger life and the test of the switch’s ability to withstand large currents.Subsequently,the main electrode and trigger cavity of the gas switch are designed.The main electrode adopts transverse magnetic electrode,which can make the arc rotate.The arc rotates at the edge of the electrode at high speed to avoid local excessive ablation of the electrode,thereby improving the ability of the gas switch to withstand large currents.The trigger cavity consists of two trigger cavities,which conduct in turn.Trigger cavity can achieve high-performance,long-life plasma jet.The main electrode and trigger chamber are assembled in a sealed tank to form a prototype of gas switch,which has passed the insulation test.Immediately,a gas switch trigger test platform was built to study the influence of the structure size of the trigger cavity and the cavity material on the trigger life,and the trigger life of the gas switch triggered by the plasma jet was increased to 583 times,which met the engineering requirements.In order to determine the degradation process of the trigger cavity in the trigger life cycle,the variation rules of the surface flashover voltage of the first trigger cavity,the residual voltage of the energy storage capacitor when the second trigger cavity is on,the conduction delay of the second trigger cavity and the conduction delay of the main gap are obtained through experiments.Finally,in order to test whether the gas switch can withstand the large current specified in the project,a large current test platform is built to test the large current withstand ability of the gas switch.The test results show that multiple high-temperature and high-energy arc combustion will cause severe ablation of the main electrode of the gas switch and its surrounding connecting parts.Therefore,the main electrode structure and connection parts of the gas switch have been improved and optimized,thereby improving the ablation resistance of the electrode,so that the switch can meet the requirements of the project to withstand large currents.