Research On Electrical Properties Of High-power Density DC Relay

With the development of aerospace,new energy vehicles and other industries and the reform of the power system,DC relays are developing in the direction of high power,miniaturization,high reliability and long life.The high voltage and high current put forward higher requirements on the arc extinguishing and erosion resistance of the contact,and there are many factors affecting the electrical performance of the contact.At present,there are few studies in this field at home and abroad.Therefore,under the condition of DC high voltage and high power,the effects of environmental atmosphere,transverse magnetic field and breaking speed on the electrical performance of the contact are studied,which is of great significance for improving the electrical performance and reliability of the relay.In this paper,the problems existing in the original contact simulation device of the research group are improved.Based on the improved device,a set of relay contact electrical performance experimental system is built which can simulate contact operation under different magnetic induction and seperating speeds in different ambient atmospheres under high voltage and high current conditions,and can collect and store voltage and current signals in real time.Experiments of CuW70 and CuMo85 contacts are conducted under DC resistive 200-500V and 40-150A in different ambient atmospheres,specifically Air,N₂,CO₂,O₂,Ar,mixture of 80%CO₂ and 20%Ar,and mixture of 50%CO₂ and 50%Ar,at atmospheric pressure.The arc extinguishing performance of CO₂ was the best,while that of Ar was the worst.The break arc duration of the mixed gas of CO₂ and Ar show“intermediate effect”.The erosion rate of N₂ is the smallest,while O₂ shows the highest erosion rate.The total erosion rate of the anode and cathode of CO₂ and Ar mixed gas show“optimal effect”.The surface deformation area of the contact surface is the smallest in CO₂,and the contact surface in N₂ and Ar are relatively flat.The contact resistance values in O₂ and Air are higher,and the variation range are larger,while those in N₂ and CO₂ are lower and stable;Percentages of welding in making operations are in general higher than those in breaking operations.Air shows good welding resistances,while mixture of 80%CO₂ and 20%Ar shows the worst.Higher current levels generally cause more welding occurrences than higher voltage levels.Experiments of CuW70 contact pairs are conducted with a DC supply voltage 200-500V and various resistive load currents under contact opening speeds varied from 70mm/s-100mm/s and transverse magnetic field varied from 50mT-80mT.The results show that when the opening speed increases,the total break arc durations become shorter,and the metallic phase and the gaseous phase durations become shorter.When the magnetic field increases,the total break arc durations become shorter and the gaseous phase durations become shorter.When the opening speed is 85 or 100 mm/s,the metallic arc durations become shorter as the magnetic field increases.As the magnetic field increases,the mass loss of the contact anode becomes smaller.The mass loss of contact anode decreases as the opening speeds increase.Experiments are conducted for the contact materials CuMo85,CuW70,CuCr50 and their different pairing under the conditions of DC voltage and current 270VDC/100A and surrounding atmosphere of Air and nitrogen.The welding resistance,breaking arc duration and mass erosion were measured and analyzed.Experimental results showed that the CuW70material has good anti welding ability,but its arcing duration and anti erosion ability does not necessarily have the advantage.The values order sequence of breaking arc duration,mass erosion and welding resistance in Air is different from that in nitrogen.Experiments are conducted for the contact materials AgW60,CuW60,Cu and their different pairing under the conditions of DC voltage and current 270VDC/200A and surrounding atmosphere of carbon dioxide and nitrogen.The mass erosion,contact resistance and breaking arc duration were measured and analyzed.Experimental results showed that the breaking arc duration of Cu material is much lower than that of AgW60 and CuW60.The corrosion resistance of Cu in carbon dioxide is significantly better than that of AgW60 and CuW60.The corrosion resistance of AgW60 and CuW60 in nitrogen is better than that in Cu.The anti-welding ability of the three materials in their symmetric pairings in carbon dioxide and nitrogen can be ranked as AgW60>Cu>CuW60.The“intermediate effect”occurs in the anti-welding properties of the asymmetric pairings.The relationships between the number of operations required for welding and the average welding force is approximately in an inverse proportional function.