The behavior of vacuum arcs between spiral contacts with small gaps

The application of small gaps in high-current vacuum interrupters highlights the interdependence of the contact design, the contact gap, and the arc behavior. In this investigation, a framing camera was used to record the appearance and motion of drawn vacuum arcs between spiral-petal contacts with final gaps of 2 to 3 mm. After the rupture of the molten metal bridge, a high-pressure arc column formed and expanded across the width of the spiral arm. With a single arc column for the duration of the half-cycle, an intense anode spot formed if the peak current exceeded /spl sim/15 kA. Compared to results previously obtained at larger gaps, the arc motion was greatly reduced, and severe contact damage was observed at lower currents.