Electrical methods for verifying internal pressure of vacuum interrupters after long-time service

Results of recent investigations dealing with the fundamentals of two new methods to check the vacuum inside the chamber, using only electrical parameters, are presented. With increasing pressure, the prebreakdown current changes in such a way that not only do the power frequency emission current patterns change, but also high-frequency current pulses, with a frequency range of ~30 to 300 kHz, appear superimposed on the emission current. It is reported under which conditions these pulse currents appear, how they can be detected, and how they correlate with the pressure. When the current is interrupted at a frequency range of ~10 to 90 kHz, the current switching capability and the reignition voltages change significantly with increasing pressure inside the vacuum chamber. The vacuum chamber loses its high-frequency current switching capability when the internal pressure is higher than ~10^-2 to 10^-1 Pa. The breakdown voltage and reignition voltages do not appreciably decrease even when the pressure rises to ~1 Pa