Effect of Electrode Profile and Polarity on Performance of Pressurized Sparkgap Switch

Abstract

Sparkgap are most widely used closing switches in various high-voltage pulsed power systems and its reliable operation at desired voltage level is very essential. Conventionally by adjusting the filling gas pressure inside sparkgap switch, breakdown voltage level is altered but switching characteristics such as stability in hold-off voltage at various pressures, breakdown delay, plasma channel formation, and erosion rate are mainly dictated by adopted electrode profile and its dimensions, inter-electrode gap length and polarity. In this paper, experimental results obtained on breakdown characteristics of four different electrode geometries—Plane Parallel, Hemi-spherical, Bruce, and Rogowski and also a generalized criterion for fixing major dimensions of electrode and inter-gap length to ensure uniform electric field in the inter-electrode region are reported. All electrodes are of brass material and have common radius and thickness of 25 mm and 18 mm, respectively (surface finish <1 µm). Experiments performed on various electrode profiles in gap lengths of 2 mm to 5 mm range with pure nitrogen (N2) gas pressurization up to 50 psi reveal that among all profiles, Rogowski performs most reliably having stable hold-off voltage in wide operating range. Hold-off voltage magnitude and breakdown delay was commonly obtained higher for negative polarity in all trials. A comprehensive overview of experimental investigation reported herein compares suitability of various electrode profiles and polarity for reliable switching.

Flashover of Smooth and Knurled Dielectric Surfaces in Dry Air

“…This phenomenon has been previously discussed in [13], being a result of the ratio of the inter-electrode gap to the radius of the electrode edge. Asymmetric electric field distributions in (geometrically) symmetrical electrode arrangements have also been witnessed by researchers investigating sphere gaps in [15], toroidal electrodes in [16], and for a plane-parallel setup in [17]. In each case, one electrode is earthed, which ultimately leads to a polarity effect when testing with both positive and negative voltages.…”

“…6b), could be a result of (nominally) equally intensive, in terms of streamer current, similar to processes in [19], for positive and negative streamers propagating simultaneously in the interelectrode gap, with positive and negative charge injected by these streamers. Pressure has been shown to have an effect on breakdown voltage polarity in other research, such as in [17], as the pressure was increased from ~0.345 bar to ~1 bar (5 to 15 psi in [17]).…”