Magnetron Discharge Characteristics for Fixed Shield and Floating Shield Vacuum Interrupters

The pressure inside vacuum interrupters (VI) is determined using the magnetron pressure measurement method. Typically, multiple pressure measurements are made during VI production to extrapolate and estimate the pressure at the end of its service life. The accuracy of these measurements depends on the voltage and magnetic field applied across the VI electrodes. At low fields, the magnetron discharge may not occur or have too low a magnitude to accurately identify the peak discharge current. At high fields, the magnetron discharge may occur before one of the fields has reached their final values - referred to as a pre-strike, and results in underestimation of the pressure in the VI. This paper demonstrates the selection of optimal voltage and magnetic field using experiments in the magnetron calibration setup. The behavior of the magnetron discharges at various voltages and magnetic fields are shown for fixed shield and floating shield VIs. Measurements at optimal voltage and magnetic field are free of noise and pre-strikes, making them more accurate.