Dynamic Characteristics Simulation Analysis And Test For 3D Arc Of Electrical Apparatus

Electric arc is a kind of plasma with extra high temperature,strong light and good conductivity,which widely occurs between the contacts during on-off process of the electrical apparatus.The existence of arc has an important influence on the reliability and life of electrical apparatus,especially for DC relay with small volume,the electric arc will do greater harm as it has no natural current zero-crossing point and no extra arc-extinguishing device.Nowadays simulation and test are the main methods of electric arc research.Numerical simulation helps to deeply understand arc mechanism and influence factors,providing theoretical direction for finding arc extinguishing methods.Test helps to intuitively acquaint the morphological feature of arc,providing verification means for the numerical simulation.Taking the DC relay as the research object,the 3D magnetohydrodynamic model of arc is established and electric arc is simulated and analyzed in this paper.And the arc is tested by a high speed camera combined with optical imaging system and 3D reconstruction is also carried out.Based on the theory of 3D magnetohydrodynamics(MHD),this paper establishes the numerical simulation model of the DC relay arc,provides physical performance parameters of the air plasma and determines the boundary conditions of the simulation model of DC relay arc.On the basis of the coupling of fluid field,thermal field and electromagnetic field of arc plasma,the commercial computational fluid dynamics software FLUENT is secondarily developed,and the steady state characteristics of DC relay arc under the condition of natural air are simulated and analyzed.Then the temperature field,electric field,fluid field and morphological characteristics of the arc are studied.By the method of variable control,this paper analyzes the influence of thermal conductivity and electrical conductivity of arc plasma on its temperature and voltage.And the variation of arc temperature and voltage is also analyzed with variation of gas pressure,metal vapor concentration and contacts material parameters.By means of the high speed camera,the dynamic process of DC relay contacts is recorded and by the image processing technique,the dynamic characteristics curve of contacts is acquired.Combined with dynamic mesh model,the dynamic changes of the arc during the breaking process of the contacts are simulated and analyzed.Compared with the test results of arc voltage curve,the effectiveness of simulation model is validated.Based on the binocular vision theory,a virtual binocular vision measurement system is built in this paper,which is made up of two plane mirrors with certain angle and a high speed camera,and it is calibrated by Zhang's camera calibration method.The 3D measurement system of electric arc composed of the image acquisition card,lighting system,fixing device of electrical apparatus and collecting equipment of voltage and current is designed,so as to carry on the dynamic collection of are images during the breaking process of DC relay contacts.By MATLAB software,the arc images are processed and the three-dimensional morphology of the arc is reconstructed.The reconstruction method is applied on the cone model with the known size and the results prove its feasibility and accuracy.