Short Answer:

Corona in power transmission is affected by various factors such as line voltage, conductor size, surface condition, atmospheric conditions, and spacing between conductors. When voltage exceeds a certain level, the air around the conductor gets ionized, leading to corona discharge. The intensity of corona depends on how strong the electric field becomes near the conductor surface.

If the conductor is thin, dirty, or has sharp edges, corona forms more easily. Similarly, humid or polluted air reduces the breakdown strength of air and increases corona. By controlling these factors, engineers can minimize corona effects and reduce power loss and noise.

Detailed Explanation:

Factors Affecting Corona in Power Transmission

Corona discharge is an unwanted electrical phenomenon that occurs in high-voltage transmission lines when the electric field around a conductor becomes strong enough to ionize the surrounding air. This leads to the formation of a bluish glow, hissing sound, and power loss in the form of light, heat, and noise. The occurrence and intensity of corona are influenced by several physical, electrical, and environmental factors.

Understanding these factors is important in the design and operation of high-voltage systems to prevent energy loss, interference, and equipment damage. Let’s explore the major factors affecting corona in detail:

1. Line Voltage

• The most important factor affecting corona is the operating voltage of the transmission line.
• When the voltage exceeds a certain critical value (known as disruptive critical voltage), the surrounding air begins to ionize, resulting in corona discharge.
• Higher voltages create stronger electric fields, increasing the chance and intensity of corona.

Key Point: Corona is more likely in systems operating above 220 kV, especially in long-distance transmission lines.

2. Conductor Size and Radius

• The radius of the conductor greatly affects the surface electric field.
• Larger diameter conductors have a lower surface electric field, reducing the chance of ionization.
• Smaller or thin wires concentrate electric fields at their surface and encourage corona formation.

Key Point: Using conductors with larger diameters helps in minimizing corona effects.

3. Conductor Surface Condition

• Conductors with rough surfaces, sharp edges, dust, or corrosion lead to uneven electric fields.
• These irregularities act like sharp points and increase the local electric field, making corona more likely to occur.

Key Point: Smooth, clean, and well-maintained conductor surfaces help reduce corona risk.

4. Spacing Between Conductors

• The distance between adjacent phase conductors affects the strength of the electric field in between.
• Closely spaced conductors result in stronger mutual electric fields, increasing the chance of corona discharge.

Key Point: Proper spacing reduces electric field interaction and corona discharge.

5. Atmospheric Conditions

• Humidity, rain, fog, and dust in the air reduce its dielectric strength, allowing easier breakdown of air molecules.
• In humid or rainy weather, water droplets collect on conductors and increase field intensity at those points.

Key Point: Corona is stronger in bad weather and becomes more visible and noisy.

6. Air Pressure and Altitude

• At higher altitudes, air pressure is lower, reducing the insulating strength of the air.
• This makes it easier for air to get ionized, increasing the risk of corona.

Key Point: Transmission lines at higher elevations are more likely to experience corona discharge.

7. Frequency of Supply

• Higher frequency causes more rapid voltage change, which can enhance corona discharge.
• However, for most transmission lines operating at 50 or 60 Hz, the effect is relatively small compared to other factors.

Key Point: While frequency plays a role, voltage and conductor condition are more critical in practical systems.

8. Pollution and Contaminants

• Dust, smoke, and chemical particles in polluted environments coat conductors and reduce the surface smoothness and air insulation strength.
• These particles attract moisture and form conductive layers that trigger corona discharge.

Key Point: Areas near industries or coastal zones often have more corona-related problems.

Conclusion

Corona in power transmission is influenced by many factors including voltage level, conductor size and shape, spacing, surface condition, weather, and pollution. When these factors increase the electric field strength near the conductor surface beyond a certain limit, corona discharge begins. By carefully selecting conductor materials, maintaining surface cleanliness, optimizing line design, and monitoring environmental conditions, engineers can reduce corona effects and ensure safer, more efficient power transmission.