Diagnosis Of Post-arc Microscopic Characteristics Of Vacuum Arc Based On Langmuir Probe

Vacuum interrupters are widely used in distribution equipment for their environmental and maintenance-free advantages.The post-arc microscopic characteristics of vacuum arcs are important parameters to characterize the opening performance of vacuum interrupters.When the post-arc residual plasma does not diffuse outside the gap in time,there is a risk of re-breakdown,resulting in the failure of the vacuum interrupter to open the short circuit current.Existing work on the microscopic properties of vacuum arcs is mainly through optical diagnostic methods such as emission spectroscopy,absorption spectroscopy,and laser-induced fluorescence,which are cumbersome and costly to operate.Compared with optical diagnosis,Langmuir probe has the features of small size,low cost,simple structure,easy operation,and relatively simple theoretical model.However,the post-arc residual plasma is a non-thermal equilibrium plasma,and the traditional Langmuir probe diagnosis method is not applicable.This article aims to study the use of the Langmuir probe working in the electron saturation region to diagnose the post-arc microscopic characteristics of the vacuum arc.Design a The post-arc microscopic characteristics diagnosis system is used to measure the residual plasma parameters after the arc through experiments,which provides a theoretical basis for the optimal design of the interruption performance of the vacuum interrupter.In this paper,through analyzing the development process of vacuum arc,the principle of post-arc sheath expansion and the method of electrostatic probe for post-arc plasma diagnosis,a post-arc microscopic characteristic diagnosis system based on Langmuir probe is designed from several aspects such as probe structure,control system and data processing procedures.On this basis,a vacuum arc post-arc microscopic characteristic diagnosis experimental platform is built based on the switch test synthesis circuit.By changing the experimental conditions such as short-circuit current size,contact opening distance size and contact structure,the post-arc microscopic characteristics are qualitatively analyzed under different conditions,and the reliability of the experimental results is verified by comparing with the existing studies conducted by probe diagnosis,emission spectroscopy diagnosis and simulation modeling methods.The results show that at short-circuit currents of 2-5.5 k A and contact openings of6-14 mm,the post-arc electron density is 10¹¹ cm^-3 orders of magnitude with a decay time of 25μs,and the post-arc electron density increases with short-circuit current and decreases with contact openings,which is consistent with arc theory.At a current of 5k A and a contact opening distance of 10 mm,the vacuum interrupter with longitudinal magnetic contacts has a lower electron density and faster residual plasma dispersion at the current crossing point than with transverse magnetic contacts;the double-break vacuum switch with the longitudinal-transverse magnetic combination has a better effect on post-arc plasma dispersion than other combinations.When the short-circuit current is 5 k A,the contact spacing is 18 mm,and the contact diameter is 70 mm,the residual plasma at the current crossing point is mainly concentrated in the center of the upper and lower electrodes,and the electron density decreases by 4×10⁹ cm^-3 for every1 mm increase in the radial distance at this position,i.e.,the electron density is linearly related to the radial distance;with the recovery of the medium,the residual plasma gradually diffuses outward from the gap.The residual plasma is mainly concentrated near the cathode at 9μs after the current zero,and the electron density at the cathode is much higher than that at the anode at this time.