ABSTRACT
A corona is a partial discharge and takes place at the surface of a transmission line conductor when the electrical stress, that is, the electric Šeld intensity (or surface potential gradient), of a conductor exceeds the breakdown strength of the surrounding air. In such a nonuniform Šeld, various visual manifestations of locally conŠned ionization and excitation processes can be viewed. These local breakdowns (i.e., corona or partial discharges) can be either of a transient (nonself-sustaining) or steady-state (self-sustaining) nature. These manifestations are called coronas due to the similarity between them and the glow or corona surrounding the sun (which can only be observed during a total eclipse of the sun). In nature, the corona phenomenon can also be observed between and within electrically charged clouds. According to a theory of cloud electriŠcation, such a corona is not only the effect but also the cause of the appearance of charged clouds and thus of lightning and thunder storms.
