Research On Acoustic Emission Signal Generated By Spherical Metal Particles Colliding With Electrodes In DC GIL

Gas insulation line(GIL)has some features such as large transmission capacity and less cover of an area.But the pollution of metal particles will reduce the insulation strength of DC GIL,which is inevitable.Acoustic emission is a phenomenon that the material is deformed or fractured by internal forces or external forces,and the stress and strain energy can be released in elastic wave form.Metal particles collide with the electrode will produce acoustic emission signal,and the acoustic emission signal contains abundant information,can reflect the diameter and other information about particles.However,there are few researches on the de-noising and characteristics of acoustic emission signals caused by the collision between spherical metal particles and electrode in DC GIL.In this paper,the acoustic emission signals generated by metal particles and electrodes in DC GIL are studied from the aspects of measurement,de-noising,feature extraction,characteristics'theoretical value and experimental value.This paper set up a experimental platform,which can detect the acoustic emission signal by acoustic emission sensor.The influence of partial discharge on acoustic emission signal detection is analyzed by experiments.The experiments and analysis show that the acoustic emission sensor embedded in the low voltage electrode reduces the sensitivity of acoustic emission sensor to partial discharge by 25 times,and the ultrasonic wave generated by partial discharge has no obviously influence on the detection of acoustic emission signal.What's more this paper discussed the insufficient of existing de-noising evaluation index and wavelet de-noising methods,proposed a composite evaluation index suitable for acoustic emission signal and a optimal wavelet de-noising algorithm based on this composite evaluation index.The de-noising effect of the experimental signal and the simulation signal explained that,the new composite evaluation index proposed in this paper can evaluate the wavelet de-noising effect of acoustic emission signal well,the optimal wavelet de-noising algorithm proposed in this paper can make a optimal wavelet de-noising for acoustic emission signals contained white noise or colored noise.This paper analysis commonly used characteristics of acoustic emission signal,and choose amplitude,frequency and RMS as characteristics of acoustic emission signals in this paper,according to the feature of acoustic emission signal in DC GIL,and then select feature extraction methods for the three features above.The analytical formulas of the velocity before collision is deduced based on the kinematics formula(called as collision speed latter).Because this formulas ignore the coefficient k about surface charge.Therefore,the calculation value of collision velocity is verified by simulation.By contrasting calculation value and simulation value,we can find that,the coefficient k has a small effect on the calculation value,which is less than 0.7 percent.Therefore,it is possible to replace the simulation value with the velocity calculation value,which lays the foundation for the derivation of characteristic theory value.This paper put forward segmentation plastic collision model.And the analytic expression of the characteristic theoretical value of acoustic emission signal is obtained base on collision model and collision velocity,then the influence of parameters on theoretical value is obtained.When particle material change by aluminum,brass,to stainless steel,the acoustic emission signal amplitude theoretical value increases gradually.When particle material change by aluminum,stainless steel to brass,the frequency decreases gradually.When the diameter of particles gradually increase,the theoretical value of the amplitude increases,and the theoretical value of the main frequency decreases gradually.When the intensity of the electric field increases gradually,the theoretical value of the amplitude increases,and the theoretical value of the main frequency increases gradually.The influence of experimental parameters on the experimental value of acoustic emission signals' characteristics was studied through experiments.The data show that,within the the scope of experiments,The amplitude and frequency of the acoustic emission signal obtained by experiments are consistent with the results through theoretical derivation,so the correctness of the theory is verified.Within the the scope of experiments,when particle material change from brass to aluminum,to stainless steel,The root-mean-square of acoustic emission signal decreases.The root-mean-square characteristic increases with the increase of particle diameter and intensity of electric field.Through the comparison of experiments and theoretical derivation,we can know that,the root-mean-square of acoustic emission signals is determined by the particle kinetic energy and other factors,or only by other factors.In the end,this paper discusses the application of acoustic emission signal in engineering and qualitatively describes the application of different acoustic emission signal characteristics.