Analysis of a 36kV Vacuum Interrupter based on a triple junction shielding research

Triple-junctions on both fixed and movable side of the Vacuum Interrupter are substantially overstressed depending on voltage polarity due to the absence of voltage grading and/or shielding measures in a 36kV switchgear when its enclosure is earthed. As a result partial discharges, surface tracking or flashover along the Vacuum Interrupter ceramic could be initiated at these points resulting in a possible puncture at the center shield location during withstand test. If no puncture occurs the situation could eventually result in a complete breakdown at a higher voltage and/or longer voltage duration. The situation is worst at the location where the distance between the Vacuum Interrupter and the earthed system enclosure is the smallest. The addition of different shielding measures have been checked in order to fix the dielectric problem. An improved design implementing shielding measures applied at the critical points to avoid surface tracking, flashover and discharges at the required voltages is presented along with electrostatic simulations.