Failure analysis of CuCr contacts of Vacuum interrupter

The Copper-Chromium (CuCr) contact material is the most widely used material for the contacts of the vacuum interrupters (VI). Performance of the VI is greatly influenced by the properties of contact materials. During switching operations, such as short-circuit current interruption, a vacuum arc is generated which in turn produces melted and resolidified layers at the contact surface. Melting followed by welding of CuCr contact results the failure of Vacuum interrupter. This paper correlated the switching performance and the metallurgy of the contacts, specifically in cases where the contacts have welded. The paper reports important factors like microstructure, Cr distribution, conductivity, hardness etc. which significantly affect the welding performance of the contacts. The conductivity and hardness of the contacts were measured by using an eddy current based conductivity meter and Vickers hardness tester respectively. The failure of contacts because of welding has been discussed with respect to conductivity and distribution of Cr as seen in its microstructure. The contacts were also characterized by X-ray diffraction and scanning electron microscopy to correlate the data.