Numerical modelling of negative corona discharge in SF₆at atmospheric pressure

Abstract

This paper presents a numerical simulation of the first negative corona in SF6 at atmospheric pressure, in a point-to-plane electrode system. A few experiments are first carried out in order to acquire a basic knowledge of the physical processes involved in the first negative corona. Since it does not seem convincing that photoemission would be the predominant secondary process at the cathode surface, field effect emission will be introduced into the numerical modelling of the ignition and development of the first negative corona. The axial and radial development of the discharge is also optically measured. Continuity equations of electron, positive- and negative-ion densities are numerically solved on a non-uniform mesh with a monotonic upwind scheme for conservation law (MUSCL) method. These equations are coupled with Poisson's equation by using the classical method of disks introduced by Davies. The novelty of this model bears upon the choice of the boundary conditions which take field effect emission into account. According to the numerical simulation, this secondary effect could indeed explain the fast rise time of the typical negative corona current pulse, and enables numerical simulation results to be in agreement with the experimental ones.

Numerical modelling of negative discharges in air with experimental validation

“…The axial space charge density plot, figure 5(d), clearly demonstrates an abrupt rise in concentration and fast movement of the charge particles during this phase. The positive space charge region is now reduced to 0.05 mm away from the needle followed by an increase of the negative charge concentration 10 up to a distance of 0.3 mm. The dense plasma formation can also be observed in the 2D charge density distribution, figure 6(b).…”

“…Different values of γ have been used in the literature and they often fall in the range from 10 -3 to 10 -2 [9][10][11][15][16].…”

“…The negative corona discharge has been well studied experimentally and the most distinctive feature is often regarded to as Trichel pulses [8]. Numerical modelling work on this subject has mostly been limited to 1D-1.5D models [9][10][11]. Regarding dielectric barrier discharge, 2 most simulation work have concentrated on the positive discharge in a needle--plane geometry while attention on the negative polarity is not as extensive.…”

“…Important Trichel pulse parameters include the individual pulse shape, their magnitude and frequency of occurrence. Regarding the modelling side of the phenomenon, most of the work have been undertaken in 1D-1.5D (continuity equations are solved in 1D along the symmetry axis while Poisson's equation is solved using the effectively 2D disc method) [9][10][11]15]. Reports on full 2D simulations are rather limited [27].…”

Numerical Modelling Point-to-Plane of Negative Corona Discharge in N2Under Non-Uniform Electric Field

“…A number of numerical studies of corona discharge were also carried out in atmospheric pressure nitrogen [9,19,20] . The mechanism of corona discharges has been investigated in the past using mathematical models ranging from analytical models [21,22] , mixed simulation models [23,24] , to Monte Carlo models [25,26] .…”