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
