Investigate On The Sputter Erosion Model Of Electrical Arcing Contact And Its Experimental

Electrical contacts are widely used in power system. Arc discharge occurs when contacts make or break current. Contact erosion caused by arc discharge has important effect on the life and reliability of contacts. Since insufficient theoretic study on arc erosion, selecting contact material is mainly depend on experiments, which is quite expensive and time-consuming. For improving the new contact material development, it is necessary to establish arc erosion model to reveal the relationship between arc energy and material properties. Arc erosion involves evaporation and molten droplet sputter, and this thesis pays the efforts on sputter erosion. In order to find out the characteristics of sputter erosion, a model of fluid flow in molten pool based on hydrokinetic theory is presented which considers the coupling effect between heat transfer and fluid flow. With a commercial software, the distribution of fluid field and the flowing velocity of the molten pool are calculated. The result shows that sputter has the characteristics of randomness and discreteness for the micro liquid, which is caused by the characteristics of turbulence. On the other hand, for the whole molten pool, the volume of sputter is statistic and can be predicted. Based on the characteristic of sputter, two models for evaluating the sputter erosion of electrode are established. The first is called energy fluctuating erosion model which based on the energy fluctuating of molten pool. It points out that sputter is the result of competition between kinetic energy of droplets and surface bandage energy of molten pool. When the kinetic energy of droplets exceeds the surface bandage energy of molten pool, the droplet will escape from the molten pool and the sputter occurs. The simulation results show, 1) the volume of sputter is not linearly changed with the increase of current, it becomes higher abruptly when current increase. 2) dynamic-viscosity coefficient has significant influence on sputter erosion when it is at the range of 0.1～1.0 and it has little influence when it is below 0.1. The second model is called statistic erosion model. From the study, we know that sputter probability is mainly affected by the turbulence, blowing up of air bubble inside the molten pool zone and boiling over of the molten pool. Further study shows that size, geometric shape and temperature of the molten pool are three essential parameters in representing the characteristics of the molten pool. The sputter probability is determined by the above three parameters. From the simulation results, it can be found that for alloy, the larger content of refractory metal is, the less erosion of the contact material. The results also indicate that increase the material properties such as density, heat capacity, latent heat of fusion and melting point and etc. can decrease sputter erosion. A series of experiments are performed with resistive, inductive and lamp loads for AgSnO2, AgNi10 and AgNi0.15 contact materials to verify the feasibility of the theoretical models. The erosion of contact materials and hence the microstructure and composition change of contact surface are assessed, measured and analyzed through SEM and EDS. The results show that under all loads, the increasing sequence erosion of contact is AgSnO2