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
Résumé
Abstract:
In this paper, the propagation mechanism of creeping discharges up to flashover for short air gaps is examined and described on various materials based on laboratory de-noised data (namely current, voltage and captured images). The main parameters considered for investigating the development of creeping discharges and their characteristics deal with the measurement, modelling and calculation of (i) their final/stopping length and morphology, (ii) their propagation velocity and (iii) the electric field distribution including the maximal magnitude (Emax) and the geometric coefficient (β) estimation. The obtained results evidenced that both length and velocity of discharges are emphasised for polyamide-based materials (namely PA6/50 and PA66/50) whereas their ignition remains inhibited for filled cycloaliphatic epoxy resin (FCEP) and ethylene propylene diene monomere (EPDM) surfaces. As the electric field is concerned, both analytical and numerical models are developed and their results are compared and discussed. It has been shown that the presence of a polymer acts as a barrier when being incorporated between an electrodes gap whose dielectric strength depends strongly on the used material. Moreover, the FCEP barrier, in comparison to other materials, exhibits a marked dielectric reinforcement and an enhanced stability of the system making it suitable to provide a better protection to high-voltage equipment against discharges effects.