Experimental Research On Dynamic Welding Mechanism Of Electrical Contacts

Dynamic welding is an important phenomenon in electrical contact applications. Dynamic welding may occur in both making and breaking operations of contacts, which will instantly lead to the failure of switching devices. Therefore, the research of the phenomenon of contact dynamic welding and its mechanism is of great significance to improve the contact ability of anti-welding and electrical life of switching devices.Firstly, in order to meet the test requirements, the original test system of contact welding in the laboratory has been improved both in mechanical part and electrical part. Then, using the improved system, a test on contact we lding has been carried out under five kinds of breaking force. During the test, the waveforms of contact voltage, displacements of the stable and movable contacts and the force suffered by the stable contact have been captured and stored.Secondly, the waveforms recorded during the test have been analyzed by LabVIEW program. It confirms the existence of welding in separation, of which the probability of occurrence is 6.7% in this test. In addition, the study finds that the occurrence of welding in separation is always accompanied with a significant preceding voltage pulse, during which the contact gap length remains constant and the force on stable contact remains zero. Thus, we infer that the occurrence of welding in separation is caused by strong material transfer between contacts rather than contact bounce. Similarly, the analysis on the waveforms of welding in closing finds that it occurs suddenly and randomly. In addition, the arc before welding may have two different mechanisms,(1) the mechanical bounce of contacts leads to the separating and closing movement, which results in the emergent and extinguishment of the arc, respectively;(2) there is arc discharge in the short contact gap and it will lead to strong material transfer and thus forming several metal bridges, which eventually makes arc extinguished.Finally, based on the analysis of the operation numbers when welding occurs, we know that with the increase of breaking force, the operation numbers increases when welding occurs for the first time and thus the anti-welding ability of contacts will significantly enhance. This relationship is fitted by different formulas and thus we find the optimal formula among them. What's more, the arcing duration in breaking and making for different operation cycles can be obtained by calculating the contact voltage waveform through LabVIEW programs. It can be inducted by analyzing the arcing duration that with the increase of the operation numbers, the arcing duration in making and breaking does not increase or decrease monotonically under a certain separation force; but with the increase of the separation force, the average arcing duration in breaking and making decreases in a fluctuation way.