Development of Cu-Cr-Mo contact material for vacuum interrupters

Abstract

A new Cu-Cr-Mo contact material for vacuum interrupters was developed to improve the withstand voltage performance of the conventional Cu-Cr contact material. The new contact material has a harder and finer grain structure while having the same Cu ratio and electrical conductivity as the conventional material. This paper compares the new and conventional contact materials through withstand voltage, short-circuit current interruption and short-time withstand current tests. The results of the withstand voltage test show that the new material has a maximum 120% higher withstand voltage compared with the conventional Cu-Cr material. The short-circuit interruption test results show that the new material can interrupt short-circuit currents having a longer arcing time. However, the short-time withstand current test results show that the new material is welded three times more strongly than the conventional material. After conducting the above tests, the contact surface and cross sections were observed. After the withstand voltage test, the grain structure of the new material surface and cross section were finer than those before the test. We think that this finer grain structure improved the withstand voltage performance. After the short-circuit current interruption test, no significant difference was observed on the surfaces between the new and conventional contacts. The withstand voltage of the conventional contacts was probably not sufficient at high temperature, so we consider that the improved withstand voltage performance improved the interruption performance. After the short-time withstand current test, the interior of the base metal, not the welded contact surfaces, was torn apart in the welded portion and the contact surface of the new material was very irregular, severely deteriorating the withstand voltage performance and interruption performance. Since the new material is harder, the force required to tear the weld is higher: the weld strength of the new material is more than three times that of the conventional material. In the new Cu-Cr-Mo material, the withstand voltage performance and short-circuit current interruption performance are improved. However, the new material contacts were severely welded in the short-time withstand current test. Further study is required to solve this problem.