Properties of intermediate-frequency vacuum arc under axial magnetic field

This paper presents an experimental study of the intermediate-frequency (400-800 Hz) vacuum arc under axial magnetic field (AMF). Arc-voltage noise at the first current semiwave is inconspicuous even if the current is not interrupted successfully. This fact is attributed to the application of a sufficiently strong AMF provided by the current flowing through a short vacuum gap. The influence of the current frequency on peak arc voltage and the rate of rise of the arc voltage are investigated. Interrupting ability of a vacuum interrupter (VI) with cup-type AMF contacts made from CuCr50 is examined. It is found that the upper limit of current interruption is inversely proportional for frequencies in the range from 400 to 800 Hz. Phase shift of AMF is studied by the finite-element method based on a simplified symmetric model. The results show that the phase-shift angle increases with the current frequency and influences intermediate-frequency current interruption of VI with AMF contacts.