AC creeping discharges propagating over solid–gas interfaces

Abstract

This study is aimed at the characterisation of surface discharges propagating over different solid materials namely glass, bakelite and epoxy resin immersed in three gases and their mixtures (namely SF 6 , N 2 and CO 2 , SF 6 /N 2 and SF 6 /CO 2 ) under AC voltage (50 Hz) in a point-plane electrode system. It is shown that the stopping length of discharges (L f ) increases linearly with the applied voltage and decreases when the gas pressure is increased. L f is longer in CO 2 and N 2 than in SF 6 [L f (N 2 ) > L f (CO 2 ) > L f (SF 6 )]; and the increase of SF 6 content in the investigated mixtures leads to a significant decrease of L f . Also, for a given gas, L f is slightly longer with glass and bakelite than that with epoxy resin indicating that the higher the dielectric constant, the longer the discharge is. Thus, the density of the discharge branches and L f reduce when the thickness of insulators increases and/or their dielectric constant decreases. Such observations evidence the implication of capacitive charge effect and electric field in the development of creeping discharges.

Electrical Detection of Creeping Discharges over Insulator Surfaces in Atmospheric Gases under AC Voltage Application

“…It is obvious that, as the dielectric permittivity increases, the electric field on the center of the disc insulator sample also increases, while, the flashover voltage levels decrease for all the cases considered. Such an observation can be correlated with results reported in research works [5] where the stopping length of creeping discharges is examined, showing that insulator discs made of higher dielectric permittivity materials are responsible for the propagation of longer streamer channels on their surface for both N 2 and CO 2 , but also for SF 6 . AC breakdown test results of point-plane arrangements for different gap distances, presented in [7], also showed that the insulating performance of CO 2 is better when compared to N 2 , without a dielectric material between the electrodes.…”

“…In [3], the effect of the dielectric permittivity on streamer propagation along insulating surfaces using electrical and optical techniques is reported. The morphology and propagation length of creeping discharges and their dependence on voltage waveform, voltage levels, dielectric material and gaseous medium have been extensively studied in more recent works [4][5][6][7]. Reported works using dust figure [8] and Pockels effect methods [9] always constitute very interesting optical approaches.…”

Triple Point Surface Discharge Photography in Atmospheric Gases Using Intensified High-Speed Camera System

“…This work investigates the development of surface discharges over disc-shaped solid insulator samples under strongly nonuniform electric field conditions at power frequency energisation. The insulator materials examined were pure polytetrafluoroethylene (PTFE) and epoxy resin as they are frequently met in the assemblies of medium-and high-voltage equipment and are characterised by considerably different relative permittivities (εr), typically 2.1 for PTFE and 3.5 for epoxy resin [1]. As gaseous insulating media, atmospheric gases were examined namely, technical air (21% O2/79% N2), nitrogen (N2) of 99.998% and carbon dioxide (CO2) of 99.8% purity.…”

Surface Discharge Mechanism on Epoxy Resin in Electronegative Gases and Its Application

“…To design a composite insulation for SF 6 -free power equipment, it is necessary to investigate the fundamental surface discharge characteristics of the composite insulation and identify its weaknesses. Extensive research has been conducted on the surface discharge mechanism in different materials under different electric fields formed by AC, DC, and impulse voltage [10,[14][15][16]. Béroual et al [10,14,15] presented the experimental characterization of discharge propagation over insulators such as Bakelite, epoxy, and glass immersed in a single gas or mixture gas, under lightning impulse, DC, and AC voltages.…”