Short Answer:

Corona loss occurs in high-voltage transmission lines when the surrounding air gets ionized, causing energy to be lost as light, heat, sound, and chemical reaction. To reduce corona loss, engineers use specific methods such as increasing conductor size, using bundled conductors, and smoothing the conductor surface to reduce the electric field strength at the conductor surface.

Other effective methods include increasing the spacing between conductors, using corona rings, and maintaining clean and dry conditions. These steps help in lowering the intensity of corona discharge and improve the overall efficiency and safety of power transmission systems.

Detailed Explanation:

Methods to Reduce Corona Loss

Corona loss is an unwanted power loss in high-voltage transmission lines due to the ionization of air around the conductors. It is more severe in extra high voltage (EHV) lines, especially above 220 kV, and can cause energy loss, noise, radio interference, and damage to equipment. Since corona cannot be completely eliminated at very high voltages, engineers focus on minimizing its occurrence and effects through thoughtful design and preventive measures.

Here are the most effective methods used to reduce corona loss:

1. Using Larger Diameter Conductors

A thicker conductor has a larger surface area, which reduces the surface electric field intensity. When the electric field is weaker, it becomes harder for air molecules to ionize, thus reducing corona discharge.

• Effectiveness: Very effective for reducing both visual corona and associated losses.
• Additional Benefit: Also helps in reducing resistance and improving current-carrying capacity.

2. Using Bundled Conductors

Instead of using one conductor per phase, engineers often use two or more conductors (called a bundle) tied together in a specific arrangement. This technique spreads the electric field over a larger surface area.

• Effectiveness: Significantly reduces corona loss in high-voltage systems.
• Additional Benefit: Also reduces noise and improves line stability.

3. Increasing Conductor Spacing

When conductors are placed too close together, the electric field between them becomes intense, increasing the risk of corona. By increasing the spacing, the mutual electric field strength is reduced.

• Effectiveness: Very effective in reducing corona formation between phases.
• Design Consideration: Commonly used in tower design for EHV transmission lines.

4. Using Smooth Surface Conductors

Rough or damaged conductor surfaces create sharp points that intensify the local electric field, encouraging corona formation. Smooth surfaces reduce these points and help control the field strength.

• Effectiveness: Helps reduce localized corona discharges.
• Additional Benefit: Prolongs conductor life and reduces maintenance.

5. Using Corona Rings

Corona rings are metallic rings placed around high-voltage terminals or conductors to evenly distribute the electric field. This reduces the maximum field at any single point and prevents corona initiation.

• Effectiveness: Commonly used in switchgear, transformers, and insulator ends.
• Visual Benefit: Often seen in substations and power plants.

6. Operating Below Critical Disruptive Voltage

Every transmission line has a specific critical disruptive voltage above which corona starts. By designing systems to operate just below this threshold, corona discharge can be avoided.

• Effectiveness: Works well in medium-voltage systems.
• Limitation: Not always possible in long-distance high-voltage transmission.

7. Maintaining Clean and Dry Insulators

Dirt, moisture, and pollutants on conductors or insulators reduce the air’s insulating strength and encourage corona. Regular cleaning helps in keeping corona levels low.

• Effectiveness: Especially useful in industrial or coastal areas.
• Maintenance Role: Should be a part of regular inspection programs.

8. Using Better Conductor Materials

High-conductivity materials such as aluminum alloy or copper reduce resistance and allow for better current distribution, minimizing localized heating and field intensity.

• Effectiveness: Indirectly helps in reducing corona by improving current handling.
• Cost Factor: Slightly higher cost but better performance in the long run.

Conclusion

Reducing corona loss is important for improving the efficiency, safety, and lifespan of high-voltage transmission systems. Methods like using larger or bundled conductors, smooth surfaces, increasing spacing, using corona rings, and keeping insulators clean are all proven strategies. By applying these techniques, engineers can effectively minimize corona-related energy losses and interference, ensuring stable and reliable power transmission even under challenging environmental conditions.