Experimental Study On The Influence Of Atmosphere And Contact Material On The Electrical Performance Of High-power-density DC Relay

In recent years,with the continuous expansion of the application field of high-power-density DC relay,high voltage,large current,small volume and long service life have become its development trend.At the same time,it also puts forward more stringent requirements for its arc extinguishing,anti-erosion,anti-welding and other electrical properties.From the perspective of providing theoretical guidance for the development and manufacturing of related products and breaking the technological monopoly of foreign countries,it is of great significance to study the key factors affecting the electrical performance of high-power-density DC relay.In this thesis,a set of experimental platform which is able to simulate the contact operation of high-power-density DC relay contacts under the conditions of different environmental atmospheres,different voltages and currents,different transverse arc blowing magnetic fields,and collect and store relevant data and waveforms at the same time is set up.Meanwhile,the defects and deficiencies of hardware and software of the platform are improved and supplemented,that is,the contact slider and permanent magnet bracket are improved,and an accurate and efficient contact welding force calculation program is compiled based on Lab VIEW platform.In this thesis,the electrical contact experiments of Cu,Cu W50,Cu W60 and Ag W60contacts under the resistive load of 200-500VDC/40-150A were carried out in six atmospheres,i.e.N₂,CO₂ and other four atmospheres at atmospheric pressure.The effects of environmental atmosphere and contact materials on the breaking arc duration,erosion,contact resistance and welding of contacts were studied.The results show that mostly the arc duration is the longest in O₂ and the shortest in Air.There are"optimal effect","intermediate effect"and"worst effect"in the arc duration between pure gas and mixed gas.Among the contacts,Ag W60 has the longest arcing time,Cu has the shortest,Cu W60 is slightly shorter than Cu W50.In terms of erosion,generally O₂ is the most serious,N₂ is the lightest and its material transfer direction is different from other atmospheres.The erosion amount of Ag W60 is the largest and that of Cu is the smallest.The erosion resistance of Cu W60 is slightly better than that of Cu W50.In terms of contact resistance,the contact resistance of O₂ is the largest,air is the second,and0.5CO₂+0.5Ar is mostly the smallest,while the contact material shows no obvious common influence on contact resistance.In terms of welding,O₂ has the strongest resistance to welding in all atmospheres,followed by Air.Ag W60 has the strongest resistance to welding in all materials,followed by Cu.In this thesis,a symmetrical and asymmetrical pairing experiment of Cu,Cu W60 and Ag W60 contacts in N₂ and CO₂ at atmospheric pressure was conducted under 270VDC/200A resistive load.The results show that Cu（-）-Agw60（+）has the best resistance to welding and Cu（+）-Cuw60（-）has the worst.The anti-welding performance is better when Ag is used as anode than as cathode,and when Cu is used as cathode than as anode.In this thesis,the experiment of Cu in N₂,CO₂ and transverse magnetic fields of 30,50,70,90 and 110 m T under the resistive load of 200-500VDC/40-150A show that normally the stronger the magnetic field is,the shorter the arc duration is,and the gradient of the arc duration with the magnetic field does not decrease monotonously but fluctuates with the change of the magnetic field.And when the magnetic field is constant,the increasing or decreasing trend of the arc duration in different atmospheres are different.The increase of magnetic field will lead to the increase of anode and total erosion of the contacts,and the increase of material transfer in CO₂.Based on the experimental data of the arc duration of Cu contacts under various voltage and current conditions,various magnetic fields and various atmospheres,a mathematical model which can characterize the influence of voltage and current,transverse magnetic field and gas physical parameters on the arc duration to some extent was established by PCA-BP Neural Network fitting.The results show that the model has a high goodness of fit.The arc duration is slightly positively related to the current,specific heat capacity,thermal conductivity and free potential of the gas,and slightly negatively related to the voltage,magnetic field,relative molecular weight,viscosity and electrical affinity of the gas.When the model is used to predict the experimental results under other conditions,it is more suitable for high voltage and high current conditions than for low voltage and low current conditions.