The Investigation of Copper-Chromium Contacts in Vacuum Interrpters Subjected to an Axial Magnetic Field

The characteristics of a vacuum arc between CuCr contacts under an axial magnetic field have been investigated. Test samples were made of CuCr contacts, and the arcing voltage was measured. The arcing voltage of the CuCr contacts under an axial magnetic field is lower than that of pure copper contacts by 10-20 V. From the measurement of the post-arc current and interruption test results, it was found that the arc concentrates and a part of the electrode melts at a rather low current, but that the electrode melting does not affect the interrupting capability. Also, the insulation characteristics were measured. With respect to voltage conditioning, high-current conditioning improved the breakdown voltage by 50 percent for a 20-mm gap and by 100 percent for a 3-mm gap. These test results show that CuCr contacts, used with axial magnetic fields, are promising for use in high-voltage and high-power vacuum interrupters.