Electrophysical Conditions for Leader Initiation during Electrical Breakdown by High Pulsed Voltage in a Long Air Gap in a Two-Electrode “Point–Plane” Discharge System

Abstract The article presents the results of a computational and experimental determination of the electrophysical conditions for the emergence of a leader channel during an electrical breakdown of a long air gap in a point-to-plane, two-electrode discharge system (TEDS) using a standard high-voltage aperiodic switching pulse with a time shape of Tm/Тp ≈ 200/1990 μs and a positive polarity. A novel engineering approach to the substantiated selection of the key indicator of the streamer-leader transition in a long air gap in the TEDS is proposed, allowing to formulate the fundamental conditions for its onset and the emergence of a positive leader in the TEDS. Calculation relationships have been obtained for determining: the radius ri of the zone of an active impact ionization by air electrons near the potential electrode of the TEDS, the electron density nes in the channel of the developed streamer in the specified air ionization zone, and the maximum electron temperature Tms in the channel of this streamer transformed into a positive leader. The high-voltage experiments carried out confirmed the emergence in a long air gap of the TEDS (lmin = 1.5 m; Ud ≈ 611.6 kV) near its potential steel point electrode (r0 ≈ 15 mm; rc ≈ 3 mm) of a bright spherical zone with a radius of ri ≈ 30 mm of an intense ionization by electron impacts on the air, from which a plasma channel of a positive leader continuously develops towards the grounded steel plane of the TEDS at a speed of vL ≈ 105 m/s.