Date of Award

1993

Publication Type

Doctoral Thesis

Degree Name

Ph.D.

Department

Electrical and Computer Engineering

Supervisor

G.R. Govinda Raju

Rights

info:eu-repo/semantics/openAccess

Abstract

The electron swarm parameters in gases, such as drift velocity, mean energy, diffusion coefficient, ionization and attachment coefficients, are obtained in uniform fields by both the Monte Carlo method and the Boltzmann equation analysis. These studies provide basic data to visualize the fundamental processes operative in the discharge. The influence of a magnetic field, applied perpendicularly to the electric field, with a focus on the influence on ionization coefficient and transverse and perpendicular drift velocities has been studied by the Monte Carlo method.

In SF6 the nonequilibrium behaviour of electrons in nonuniforrn fields was fount.I that to be significant in nonunifonn fields and high pressure breakdowns such as streamer and corona discharges.

The streamer formation and propagation in SF6 is simulated by the Monte Carlo method in which photoionization is included as a secondary source of electrons and the space charge field is calculated according to the Poisson equation. The simulated streamer shape explains. for the first time. the expelimental observation in SF6.

Negative and positive corona discharges are also studied in SF6 • Because of the nonunifonnity of the applied field and its distortion due to space charge, the Poisson equation is solved on a sub-uniform cell to improve the accuracy. The development of electron avalanches is due to the ionization and photoionization in the high field region. while the quenching of the avalanches is due to the space charge field suppression. Also the accumulations of positive and negative ions are studied in detail and compared for different voltage polarities. The theoretical analysis of streamer and corona discharges has the advantage that it avoids the equilibrium assumptions used by other authors.

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