corona

Ther are 4 distinct type of electrical breakdown of air, namely: Glow discharges , Corona , Sparks and Arcs.

Glow discharges are relatively cold breakdown, where coronas are relatively hot breakdowns.

Coronas have been a problem on power lines because coronas can destroy wire insulation and crack porcelain insulators.

What is corona ?

A corona is a partial discharges and takes place on the surface of a transmition line conductor, when the electric stress, of a conductor exceeds the breakdown strength of the surrounding air.

or we can say :

Corona is a luminous partial discharge due to to ionization of the air surrounding a conductor caused by electrical over stress.

Manifestation of corona.

• It manifests it self by a visual corona, which appear as bluish tuffs, streamers, and/or glows arround the conductor, being more or less concentrated at irrugularities on the conductor surface.
• The second manifestation of corona is known as audible corona, which appears as a hissing or frying sound when ever the conductor is energized above the threshold voltage.

From where did the name corona come from ?

Called corona due to the similarity between the corona manifestation on the conductors and the glow or corona due to the sun.

Two important voltage parameters.

• The disrupitive critical voltage : The minimum voltage at which the ionization occurs in fair weather.
• The visual critical voltage : which is higher than the disruptive critical voltage.

Disadvantages of corona.

Some of the disadvantages of corona :

• It is accompanied by power loss.
• The charging current under corona condition increases.
• Radio interference (RI) and Television interference (TVI).
• Owing to the formation of the corona, ozone gas is produced which chemically reacts with the conductor and causes corrosion.

Factors affecting corona.

• Line configuration : Delta configuration and Horizatal configuration.
• Line voltage.
• Frequency of the voltage.
• Conductor : Conductor hight and Condition of condutor surface.
• Size of conductors and their spacing.
• Atmosphere.

                         THIS IS A SIMPLE DEFINATION ABOUT CORONA