Model vacuum circuit breaker with a contact system in a vacuum chamber with optical access (four glass windows), with a pneumatic drive to move the lower electrode (grounded cathode) with an averaged velocity of 1.25 m/s, with a pumping system (roughing pump and turbomolecular pump) to evacuate the chamber down to 10^-7 mbar pressure, and with an AC pulse current source based on a capacitor bank. The fixed anode and the movable cathode are disc-shaped electrodes of CuCr (60/40) with a diameter of 30 mm.
\n", "procedure": "The vacuum arc is ignited by contact separation. 50 Hz sinosoidal currents with peak values from 1 to 7.5 kA have been studied.
\n" }, "medium": { "name": "Cu-Cr metal vapour", "properties": "Cu-Cr metal vapour from electrode erosion with time dependent and inhonogeneous distribution strongly dependent on the cathode and anode evaporation by cathode and anode spots.
\n" }, "target": { "name": "Cu-Cr", "properties": "No target (electrodes can be considered as the target)" }, "diagnostics": { "name": "electrical measurements, high-speed imaging, optical emission spectroscopy, OES, temperature measurement", "properties": "Electric measurements:
\nArc current measured with Rogowski coil (PEM CWT 1500), arc voltage measured with voltage probe (Tektronix P6015A, bandwidth 75 MHz), recording with an oscilloscope.
High-speed imaging of the arc:
\nHigh-speed camera Photron Nova S12 (HSC 1) with frame rate 20000 fps and exposure time of 0.7 \u2013 1.7 \u00b5s.
Optical emission spectroscopy (OES) of the arc:
\nintensified video OES with spectrograph Andor Shamrock SR-750i and camera Photron Nova S16 (HSC 2) combined with image intensifier Hamamatsu C10880 with frame rate 200 000 fps and exposure time of 0.7 \u2013 1.7 \u00b5s.
Measurement of anode surface temperature:
\na) high-speed camera Photron Nova S6 (HSC 3) with narro band filter (MIF) with central wavelength 891 nm and FWHM 10 nm with frame rate 22 500 fps and exposure time 5 \u00b5s.
\nb) NIR fiber spectrometer Hamamatsu C114GA with temporal resolution of 1,25 ms and exposure teime of 50 - 200 \u00b5s adapted by an optics to the measurement of an area of 3 mm^2 at the anode centre (starting of the measurements 1 ms before current zero).
Optical emission spectroscopy (OES) of the arc:
\nRecording of the spectra over the arc cross section at the position of 1 mm below the anode surface.
Measurement of anode surface temperature:
\nAnode surface temperature distribution was deduced from records of Nova S6 by correction of the arc radiation and comparison with NIR measurements.