激光诱导等离子体中聚焦程度对真空开关真空度检测的影响

Influence of Focusing Degree in Laser-induced Plasma on Vacuum Detection of Vacuum Switch

真空断路器作为一种绿色无污染的断路器,有望在高压、特高压等级的电力系统中取代SF_(6)断路器。真空开关真空度在线检测依然是一个国际性难题,基于激光诱导等离子体的真空开关真空度检测技术有望实现真空开关真空度的在线检测,但激光等离子体的形成过程复杂,激光聚焦程度直接影响激光等离子体的形成,需深入研究聚焦程度对激光等离子体的影响。首先,对不同聚焦光斑所产生的激光等离子体进行成像研究,结果显示减小聚焦距离和增大聚焦前束腰半径可以降低聚焦光斑尺寸,增强激光等离子体。同轴成像时,减小聚焦距离可使激光等离子体辐射强度最大增强77.5%,变异系数最大减小93.1%;增大聚焦前激光束腰半径可使强度最大增强32.9%,变异系数最大减小73.5%。其次,侧面成像的结果表明:减小聚焦距离的聚焦效果要优于增大聚焦前束腰半径,激光等离子体辐射更强。最后,激光等离子体的稳定性分析表明:聚焦光斑越小,激光等离子体越稳定,可以通过增大激光功率密度提高真空度检测精度。

Vacuum circuit breaker,as a kind of pollution-free circuit breaker,is expected to replace SF_(6) circuit breaker in high voltage and ultra high voltage power systems.On-line monitoring of vacuum switch vacuum degree is still an international problem.The vacuum detection method of vacuum switch based on laser-induced plasma is expected to realize the online detection of vacuum degree of vacuum switch.However,the formation process of laser-plasma is complicated,and the laser focusing degree directly affects the formation of laser-plasma.Therefore,the influence of laser focusing degree on laser-plasma needs further study.Firstly,the imaging of laser-plasma generated by different focal spots is studied.The results show that decreasing the focusing distance and increasing the beam waist radius can reduce the focal spot size and enhance the laser-plasma.In coaxial imaging,decreasing the focusing distance can increase the laser-plasma radiation intensity by 77.5%and decrease the coefficient of variation by 93.1%.Increasing the waist radius of the laser beam before focusing can increase the intensity by 32.9%and decrease the coefficient of variation by 73.5%.Secondly,the results of side imaging show that decreasing the focusing distance is better than increasing the waist radius before focusing,and the laser-plasma radiation is stronger.Finally,the stability analysis of laser-plasma shows that,the smaller the focal spot is,the more stable the laser plasma will be,and the accuracy of vacuum degree detection can be improved by increasing the laser power density.