کرونا CORONA

CORONA کرونا

Air is not a perfect insulator, and even under normal conditions, the air contains many free electrons and ions. When an electric field intensity establishes between the conductors, these ions and free electrons experience forced upon them. Due to this effect, the ions and free electrons get accelerated and moved in the opposite direction. The charged particles during their motion collide with one another and also with the very slow moving uncharged molecules. Thus, the number of charged particles goes on increasing rapidly. This increase the conduction of air between the conductors and a breakdown occurs. Thus, the arc establishes between the conductors.

The undesirable effects of the corona are:

1. The glow appear across the conductor which shows the power loss occur on it.
2. The audio noise occurs because of the corona effect which causes the power loss on the conductor.
3. The vibration of conductor occurs because of corona effect.
4. The corona effect generates the ozone because of which the conductor becomes corrosive.
5. The corona effect produces the non-sinusoidal signal thus the non-sinusoidal voltage drops occur in the line.
6. The corona power loss reduces the efficiency of the line.
7. The radio and TV interference occurs on the line because of corona effect.

Corona decreases the efficiency of transmission lines. Therefore, it is necessary to minimize corona.The following factors may be considered to control corona:

1. Conductor diameter – For reducing corona loss, this method of increasing conductor diameters is very effective.Diameters of conductors can be increased by using hollow conductors and by using steel-cored aluminum conductors(ACSR) conductors.
2. The voltage of the line – Voltage of transmission lines is fixed by economic considerations. To increase the disruptive voltage the spacing of the conductors is to be increased, but this method has some limitations.
3. Spacing between conductors – If the space between conductors increases, then the voltage drops between them also increases due to increase in inductive reactance.