Short Answer:
The corona effect in high-voltage transmission is a phenomenon where the air around a conductor becomes ionized due to very high electric fields. This causes a faint glow, hissing noise, and sometimes power loss. It usually occurs when the voltage on the conductor exceeds a certain critical level, especially in bad weather like fog or rain.
Corona effect leads to energy loss, interference with communication signals, and damage to equipment over time. To reduce this effect, conductors with larger diameters or bundled conductors are used, and proper spacing between lines is maintained.
Detailed Explanation:
Corona effect in high-voltage transmission
Introduction to Corona Effect
When electricity is transmitted at very high voltages, the electric field around the conductors becomes very strong. If this electric field exceeds a certain limit, it causes the surrounding air to break down and become partially conductive. This breakdown leads to the formation of a corona, which is a bluish glow around the conductor, along with a crackling sound. This is known as the corona effect.
The corona effect is mostly visible during the night and is more prominent in conditions like fog, dust, or rain, which lower the breakdown strength of air.
How the Corona Effect Occurs
- Electricity flowing through a high-voltage conductor creates an electric field around it.
- When the field becomes strong enough (typically above 30 kV/cm), it ionizes the surrounding air.
- Ionized air allows a small discharge of electricity, producing a visible glow, sound, and energy loss.
- This discharge does not lead to a full short circuit but continuously leaks small amounts of power.
The point at which corona begins is called the critical disruptive voltage.
Main Effects of Corona
- Power Loss
A continuous leakage of current due to ionization causes energy loss in the form of heat and light. This reduces the efficiency of power transmission. - Noise and Light
Corona produces a hissing or crackling sound, especially in rainy or foggy weather. A faint bluish light is also visible at night around the conductors. - Interference with Communication Lines
The high-frequency noise generated by corona can disturb nearby telephone or radio signals. - Material Damage
The chemical reactions due to corona can lead to corrosion of conductors and insulators over time. - Voltage Drop
Since corona results in the flow of unwanted current, it causes a small voltage drop along the transmission line.
Factors Affecting Corona Effect
- Voltage Level: Higher voltages increase the corona effect.
- Conductor Size: Thicker conductors reduce electric field strength and lower corona loss.
- Conductor Surface: Smooth conductors reduce corona; rough or damaged surfaces increase it.
- Weather Conditions: Rain, fog, and dust lower air insulation and increase corona.
- Spacing Between Conductors: Wider spacing reduces electric field intensity and suppresses corona.
Methods to Reduce Corona Effect
- Using Larger Diameter Conductors
A bigger conductor reduces the electric field around its surface, delaying corona onset. - Bundled Conductors
Instead of one thick wire, multiple smaller wires are grouped together. This method reduces corona effect significantly. - Smooth Surface Conductors
Conductors with polished and smooth surfaces are used to avoid sharp edges that intensify electric fields. - Proper Spacing Between Lines
Adequate distance between the conductors and from the ground helps in reducing field intensity. - Good Maintenance
Keeping conductors clean and undamaged helps control corona formation.
Conclusion
The corona effect in high-voltage transmission is an unwanted phenomenon caused by ionization of air around conductors. It results in energy loss, noise, and communication interference. Although it is natural at very high voltages, it can be reduced through design techniques like using larger or bundled conductors and maintaining proper spacing. Understanding and controlling the corona effect is important to ensure efficient and reliable power transmission.