Propagation of creeping discharges in air depending on the electric field direction and insulator materials under lightning impulse voltage

Abstract

International audienceAbstract:This paper is devoted to the influence of the direction of the applied electric field (namely perpendicular and parallel to the insulator surface) and the type of insulator materials on the propagation of creeping discharges (pattern and stopping length) in presence of air under standard lightning impulse voltage. The investigated materials belong to two distinguished families among the mostly used in electrical industry: (i) thermoplastics (namely polyamide 6 and polyarylamide), and (ii) one cycloaliphatic filled epoxy resin. It is shown that the stopping discharges length on a solid/air interface covers generally 55% of the creeping distance for both polarities under perpendicular E-field right before the flashover. While with parallel E-field, the stopping length is included between 20 to 30% for positive polarity and less than 25% for negative polarity. Also, the application of a perpendicular E-field is more straitened than the tangential one due mainly to the dielectric constant of polymers. Numerical simulations show that the electric field is more reduced for perpendicular E-field inferring that discharges (streamers) lengthen and develop easily at lower voltage levels

Ignition and advancement of surface discharges at atmospheric air under positive lightning impulse voltage depending on perpendicular electric stress and solid dielectrics: modelling of the propagating phenomenology

“…However, the voltage values needed for discharges ignition is more elevated than those recorded for polyamides. Moreover, flashover occurs for polyamides when the discharges length reaches 60% of the leakage distance while that it ranges from 45% through 50% of the leakage distance for FCEP and EPDM [32]. The increase of discharges radius due to voltage is likely explained by the raise of particles density (electrons, positive and negative ions), constituting the plasma channel and are likely to participate to the discharges channel elongation because of photoionization as reported by Serdyuk et al [33].…”

Investigation of oil level and type of solid insulator on creeping discharges propagating under an ac electric field

“…Solid/liquid or solid/gas interfaces can be seen in oil or gas-filled high voltage equipment such as power transformers, capacitors, bushings, and circuit breakers. These composite insulation systems are subjected to different stresses and when the tangential electric field at the interface exceeds a threshold value, discharges can be initiated and propagated over the interface (Douar et al, 2015). These discharges are commonly called creeping discharges.…”

“…These discharges are commonly called creeping discharges. Due to the frequent occurrence of creeping discharges, the insulation system can undergo irrecoverable damage, and finally, this may lead to flashover (Douar et al, 2015).…”

Creeping discharges features propagating in air at atmospheric pressure on various materials under positive lightning impulse voltage – part 2: modelling and computation of discharges’ parameters

“…Moreover, the flashover occurs through (i) a positive discharge from the anode induced by a negative streamer (when 0.3 cm ≤ d < 1 cm) or (ii) a negative leader that generates a negative streamer from the top of its channel (when 1 cm ≤ d ≤ 5 cm). Douar et al [44] investigated the influence of the electric field (E-field) direction on various solid dielectrics in air (namely polyamide 6, polyarylamide and one cycloaliphatic epoxy resin) under lightning impulse voltage (1.2/50 µs). They demonstrated that the application of a perpendicular E-field of a positive polarity over polyamide 6 is more straitened than a tangential E-field under similar conditions while epoxy interface behaves oppositely.…”