Electricity has to travel long distances to reach the different consumers. Technology is advancing daily to overcome the various factors affecting the smooth travel and arrival of this energy. Transformers, transmission lines, insulators, towers etc. play a vital role in this energy transfer.
High voltage power transmission is widely used because of its major good characteristics. Due to this high voltage of transmission, partial discharges of electrical energy is likely to occur through the conductors which are termed as the corona. This article is all about corona discharge and its effect on power systems.
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| Fig 1. Power line transmission system |
What is corona effect?
Long distance transmission lines are used in extra high voltage (EHV) power systems to transfer the electrical energy from the generating stations to the various consumption centers. These extra-high voltage lines tend to have losses. Spontaneous discharges occur on these EHV lines while they are active in nature. These unwanted discharges are referred to as corona.
When the high voltage power lines (conductors) are active, the ionization of air surrounding the conductors produces an electric field. When the strength of this electric field is strong enough another unwanted conductive path occurs around these power lines. This conductive path, therefore, causes a partial discharge of electricity which is termed as corona effect.
Due to the ionization of air molecules surrounding the power lines, a bluish colored light occurs around the conductors This corona discharge emits ozone and nitrogen dioxide gases. Due to the liberation of the ozone gases, a hissing sound is also produced from the power lines. And these corrosive gases are harmful to the human beings.
Factors enhancing the corona discharge
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| Fig 2. Corona discharge |
Due to the ionization of air molecules surrounding the power lines, a bluish colored light occurs around the conductors This corona discharge emits ozone and nitrogen dioxide gases. Due to the liberation of the ozone gases, a hissing sound is also produced from the power lines. And these corrosive gases are harmful to the human beings.
Factors enhancing the corona discharge
- Atmospheric conditions- The physical state of the atmosphere also contributes to the corona discharge. Rainy, snowy, foggy, stormy atmosphere increase the moisture content of the air. So these atmospheric conditions can increase the corona discharge than a clear atmospheric condition.
- The condition of the conductors- The size and shape of the conductors also affect corona discharge. The irregularities on the surface of the conductor also contribute to the partial discharge of electricity.
- The spacing between the live power lines- If the spacing between the adjacent power lines is small, electric field strength between the conductors will be more. So the power lines should maintain their tolerable spacing between adjacent lines.
Effects of corona
As mentioned before corona discharge produces gases and ultraviolet rays that are harmful to the human beings and animals. Corona discharge causes losses to the power utility systems if they fail to use good corona suppressing agents.
Corona discharge may damage the insulation inside the transformers, generators and other power system devices. This damage of the insulation may result in device failures. So thus the cost for maintaining a smooth power system increases. Electromagnetic interference in the power lines also increase the losses in power flow. So due to these effects, the power system devices are designed in such a way to minimize the corona discharge.
How to reduce the corona effect in power lines?
- Corona controlling rings are widely used to suppress the corona discharge.Corona rings can reduce the potential gradient caused by corona by acting as a guard ring around the live conductors.
- Bundled or hollow conductors also help in reducing corona discharge to an extent.
- The increase of the diameter of the power line conductor also reduces the corona discharge.
- The spacing between the adjacent conductors also should be taken into account while considering the corona reduction. If this distance is small, corona effect will be more.
Even though the corona is an unwanted side effect in power systems, it has several applications in various industries. Corona effect is used in the production and use of ozone gases for welding industries and various other applications. It also has applications in the creation of electro-chemical processes, photocopying machines, polymer industries and photographic applications.
