What is corona effect? Advantage and Disadvantage of Corona
The Corona Effect is the phenomenon of electric discharge in high voltage transmission lines and substations. Hissing noise and violet glow were observed under the corona effect. Power loss, damage to high voltage electrical components, and noise are observed due to corona discharge in the Transmission line.
Why does corona effect in transmission line?
Due to high voltage in the transmission line or substation component, the localized electric field is created around the conductor or the high voltage component. It will discharge a small amount of electric charge to the localized atmosphere and the corona effect is created. Corona is available in all types of transmission lines however noticeable corona effect is observed only in high voltage transmission lines over 400KV and above.
The intensity of Corona also depends on the atmosphere and weather conditions. During rainy seasons high corona is observed due to the presence of moisture on the conductor surface and localized atmosphere.
Factors affecting corona loss
Corona depends on the following factors of the transmission line.
- Size of the conductor:
Corona depends on the cross-sectional area of the conductor. A larger cross-sectional area can provide a large surface area on the conductor. In that case, it will cover the larger atmosphere area to discharge the same amount of charge and it will reduce the corona. Reducing of the diameter of the conductor, corona discharge increases in that case.
As corona discharge, a localized atmosphere, the weather condition in the atmosphere also depends on corona discharge. During rainy seasons, the atmosphere is very ionized as compared to the dry weather, and the breakdown voltage is also reduced. In that case, the high corona is found in rainy seasons as compared to dry weather.
- Line Voltage
Corona discharge mainly depends on the line voltage. At the low voltage level transmission line, there is no noticeable corona observed. At high voltage, the localized atmosphere air is highly ionized and it will easily reach the breakdown voltage of Air.
- Spacing between conductor
At low space between the conductors is creating high electro static stress on the surface of the conductor and it will increase corona phenomena. After calculation of the corona discharge value, the spacing between the conductors is finalized during the design of the transmission line.
Advantages and Disadvantages of Corona
Mainly transmission line has been designed in a way to minimize corona discharge. However, some advantages of corona discharge were also observed along with various disadvantages.
The advantages of corona discharge are:
- Due to corona phenomena, surrounding air becomes conductive and it will increase the virtual diameter of the conductor. After increasing the virtual diameter of the conductor, the maximum potential gradient also reduced
- In corona phenomena, the charge dissipated to the surrounding air. During a voltage surge, partial energy will dissipate in the form of corona discharge and it will reduce the transient effect of the voltage surge.
The Disadvantages of corona discharge are:
- As the corona phenomena discharge the electric charge, it will create power loss in the transmission line, and the overall efficiency of the transmission line is also reduced.
- Corona effects generate Ozone and it will deteriorate the conductor due to chemical reaction.
- Under corona phenomena, non-sinusoidal voltage and current produced and will affect the power quality of the transmission line. It may also cause inductive interference in the neighboring communication medium.
- In the transmission line, only power frequency (50/60 Hz) travel and it will not create any disturbance in the radio, TV, and other communication frequency. Under the corona effect, discharge current or voltage does not follow any particular frequency. Due to this the radio, TV, or another communication medium can be affected by the corona discharge.
How to reduce the corona effect in the Transmission line?
Reducing the corona effect is the most important part for the design of a high voltage transmission line or substation. Corona effect cannot eliminate fully, however it can be significantly reduced by using the following steps.
- Size of the conductor: Corona effect depends on the surface area of the conductor. By increasing the size or cross-sectional area of the conductor, the corona effect can be minimized. Further use of a bundle conductor instead of a single conductor also increases the effective diameter of the conductor and it will help to reduce the corona effect.
- Increasing Conductor spacing: by increasing the distance between the conductors, the corona effect can be minimized. However, spacing cannot increase after a certain distance due to the huge construction costs and requirements of a larger area.
- Reducing of sharp points: At a sharp point, the surface area is very low and due to this high corona produce. By reducing sharp points, the corona effect can reduce.
- Using corona ring: Generally, the corona effect is high at the start or end points and any sharp points of the transmission line. After the installation of corona rings, the effective surface area will increase at those points. By using of corona ring we can reduce the corona effects at those points.