The irreversibility of dielectric strength of vacuum interrupters after short-circuit current interruption

The irreversibility of dielectric strength of commercial vacuum interrupters after a large number of consecutive short-circuit current interruptions is investigated in order to find out how dielectric performance of a vacuum interrupter degrades during its service life. Breakdown voltage data were measured in appropriate experiments in which the types of tested interrupters and arcing conditions were varied. It was found that for interrupters with poor contact material the dielectric strength can deteriorate severely, falling below limits required by standards. It is concluded that the most important for the irreversible decrease in the dielectric strength is the contact material, i.e. its erosion properties. It appears that contacts with axial magnetic field are less susceptible to irreversible changes in dielectric strength after short-circuit current interruption than contacts with transverse magnetic field.>