The Vacuum Interrupter Contact

A survey of developments in electric contact design for vacuum interrupters is presented. The major emphasis is placed upon those characteristics of contact design that have led to practical vacuum interrupters. A brief description is given of the different modes of vacuum arc that have been observed and how these modes occur during one-half cycle of high current arcing. In the main body of the paper the design philosophy behind vacuum interrupter contact design is presented. It is shown that only two classes of contact have achieved practical utilization. The first of these design classes causes a magnetic field to be impressed at right angles to the arc current and hence, causes the arc to move rapidly over the contact face. The second design class impresses a magnetic field parallel to the arc current. This forces the arc into a diffuse mode with many widely separated cathode spots and a diffuse current collection at the anode even at very high currents. Each of these contact designs is discussed and their advantages and disadvantages are deline- ated.