Neutral Atom Density at Current Zero in Interruption of Intense-Mode Vacuum Arc

Neutral atom density in intense-mode vacuum arc just before current zero as a determinant factor for the current interruption success or failure was measured by Shack-Hartmann laser wavefront sensors. The electrode selected in this study was Cu50Cr50 wt.% and the contact diameter of 6 mm. 50-Hz sinusoidal current of 2 kArms or 4 kArms was applied to the electrode gap and current of 1 kAp was superimposed just before current-zero point, and transient recovery voltage with height of 25 kV was applied to the electrode gap at current zero. The neutral atom density in the 4.5-mm gap was about 2.5–4.0 × 10¹⁹ m^-2 for the current of 2 kArsm, and 5.0–8.0 × 10¹⁹ m^-2 for the current of 4 kArms, respectively. In the intense-mode vacuum arcs, the anode surface was heated during high-current arc period, and the critical neutral atom density for TRV of 25 kV was suggested to be around 5.0–8.0 × 10¹⁹ m^-2.

I. Introduction

VACUUM circuit breakers (VCBs) are widely installed in low- and medium-voltage-class AC networks because they are compact, maintenance-free, and environmentally friendly [1], [2]. Improvement of interruption capacities of the VCBs is required for the realization of SF6-free current breaking devices. The current interruption capabilities of the VCBs are highly dependent on plasma parameters such as a neutral atom density. Measuring such plasma parameters and elucidating the vacuum arc phenomena is indispensable for the development of high-voltage-class VCBs.