TRANSMISSION AND DISTRIBUTION MODULE 4 UNIT 1
Syllabus: Corona: Module 4 Unit 1: Phenomena, disruptive and visual critical voltages,
corona loss. Advantages and disadvantages of corona. Methods of reducing corona.
1. What is corona? Briefly explain the phenomenon of corona.
The ionization of air surrounding the high voltage transmission lines causing the conductors
to glow, producing a hissing noise, is called Corona Discharge or Corona Effect.
Visible Glow: A faint violet glow appears around the conductors.
Noise: A crackling or hissing sound is generated.
Power Loss: The ionization leads to energy dissipation as heat, resulting in power
loss.
Radio Interference: Corona discharge produces electromagnetic noise that can
interfere with communication systems.
Ozone Formation: Corona effect can lead to the formation of ozone (O₃), which can
corrode nearby materials.
This phenomenon occurs when the electrostatic field across the transmission line
conductors produces the condition of potential gradient.
The air gets ionized when the potential gradient at the conductor surface reaches the
value of 30kV/cm at normal pressure and temperature.
In transmission lines, conductors are surrounded by the air. Air acts as a dielectric
medium. When the electric field intensity is less than 30kV/cm, the induced current
between the conductors is not sufficient to ionize the air.
However, when the voltage of air surrounding the conductor exceeds the value of
30kV/cm, the charging current starts to flow through the air that is air has been
ionized.
The ionized air act as a virtual conductor, producing a hissing sound with a
luminous violet glow.
2. Mention advantages and disadvantages and also methods of reducing corona.
✅ 1. Use Larger Diameter Conductors
Increasing the conductor diameter reduces electric field intensity.
Lower field strength → less ionization → reduced corona.
Often achieved using hollow or stranded conductors.
✅ 2. Use Bundled Conductors
Two or more conductors are used per phase.
This increases the effective radius of the line.
Widely used in EHV and UHV transmission systems.
Benefit: Significantly reduces corona loss and radio interference.
✅ 3. Maintain Smooth Conductor Surface
Rough, dirty, or damaged surfaces increase corona.
DEPT. OF EEE/SIT/MYSURU 1
, TRANSMISSION AND DISTRIBUTION MODULE 4 UNIT 1
Polished and clean conductors reduce electric stress.
Avoid sharp edges and scratches.
✅ 4. Increase Spacing Between Conductors
Greater spacing reduces electric field concentration.
Helps in lowering corona formation.
Used in high-voltage line design.
✅ 5. Use Corona Rings (Grading Rings)
Metal rings fitted on insulators and terminals.
Distribute electric field uniformly.
Prevent field concentration at sharp points.
Commonly used in: Substations and transmission towers.
✅ 6. Improve Insulation Level
High-quality insulators reduce leakage and ionization.
Proper insulation limits electric field stress.
✅ 7. Operate at Optimal Voltage
Avoid operating near or above critical disruptive voltage.
Proper voltage regulation reduces corona activity.
✅ 8. Regular Maintenance
Remove dust, moisture, and pollution deposits.
Replace damaged conductors and insulators.
Ensures smooth surfaces and proper clearances.
Advantages of Corona Effect: Despite its adverse effects, the Corona Effect offers some
operational benefits in power systems:
Voltage Equalization: The discharge helps distribute voltage uniformly along the
conductor.
Surge Protection: Dampens voltage surges by releasing energy during ionization.
Reduction of Transient Oscillations: Reduces high-frequency oscillations in the system.
Disadvantages of Corona Effect: The Corona Effect in Transmission Line has several
downsides that engineers strive to minimize:
Power Loss: Dissipation of electrical energy as heat and light reduces system
efficiency.
Conductor Degradation: Prolonged corona exposure erodes conductor surfaces.
Noise and Interference: The discharge generates audible noise and electromagnetic
interference, affecting nearby communication systems.
Voltage Regulation Issues: Uneven voltage distribution can lead to system instability.
DEPT. OF EEE/SIT/MYSURU 2
Syllabus: Corona: Module 4 Unit 1: Phenomena, disruptive and visual critical voltages,
corona loss. Advantages and disadvantages of corona. Methods of reducing corona.
1. What is corona? Briefly explain the phenomenon of corona.
The ionization of air surrounding the high voltage transmission lines causing the conductors
to glow, producing a hissing noise, is called Corona Discharge or Corona Effect.
Visible Glow: A faint violet glow appears around the conductors.
Noise: A crackling or hissing sound is generated.
Power Loss: The ionization leads to energy dissipation as heat, resulting in power
loss.
Radio Interference: Corona discharge produces electromagnetic noise that can
interfere with communication systems.
Ozone Formation: Corona effect can lead to the formation of ozone (O₃), which can
corrode nearby materials.
This phenomenon occurs when the electrostatic field across the transmission line
conductors produces the condition of potential gradient.
The air gets ionized when the potential gradient at the conductor surface reaches the
value of 30kV/cm at normal pressure and temperature.
In transmission lines, conductors are surrounded by the air. Air acts as a dielectric
medium. When the electric field intensity is less than 30kV/cm, the induced current
between the conductors is not sufficient to ionize the air.
However, when the voltage of air surrounding the conductor exceeds the value of
30kV/cm, the charging current starts to flow through the air that is air has been
ionized.
The ionized air act as a virtual conductor, producing a hissing sound with a
luminous violet glow.
2. Mention advantages and disadvantages and also methods of reducing corona.
✅ 1. Use Larger Diameter Conductors
Increasing the conductor diameter reduces electric field intensity.
Lower field strength → less ionization → reduced corona.
Often achieved using hollow or stranded conductors.
✅ 2. Use Bundled Conductors
Two or more conductors are used per phase.
This increases the effective radius of the line.
Widely used in EHV and UHV transmission systems.
Benefit: Significantly reduces corona loss and radio interference.
✅ 3. Maintain Smooth Conductor Surface
Rough, dirty, or damaged surfaces increase corona.
DEPT. OF EEE/SIT/MYSURU 1
, TRANSMISSION AND DISTRIBUTION MODULE 4 UNIT 1
Polished and clean conductors reduce electric stress.
Avoid sharp edges and scratches.
✅ 4. Increase Spacing Between Conductors
Greater spacing reduces electric field concentration.
Helps in lowering corona formation.
Used in high-voltage line design.
✅ 5. Use Corona Rings (Grading Rings)
Metal rings fitted on insulators and terminals.
Distribute electric field uniformly.
Prevent field concentration at sharp points.
Commonly used in: Substations and transmission towers.
✅ 6. Improve Insulation Level
High-quality insulators reduce leakage and ionization.
Proper insulation limits electric field stress.
✅ 7. Operate at Optimal Voltage
Avoid operating near or above critical disruptive voltage.
Proper voltage regulation reduces corona activity.
✅ 8. Regular Maintenance
Remove dust, moisture, and pollution deposits.
Replace damaged conductors and insulators.
Ensures smooth surfaces and proper clearances.
Advantages of Corona Effect: Despite its adverse effects, the Corona Effect offers some
operational benefits in power systems:
Voltage Equalization: The discharge helps distribute voltage uniformly along the
conductor.
Surge Protection: Dampens voltage surges by releasing energy during ionization.
Reduction of Transient Oscillations: Reduces high-frequency oscillations in the system.
Disadvantages of Corona Effect: The Corona Effect in Transmission Line has several
downsides that engineers strive to minimize:
Power Loss: Dissipation of electrical energy as heat and light reduces system
efficiency.
Conductor Degradation: Prolonged corona exposure erodes conductor surfaces.
Noise and Interference: The discharge generates audible noise and electromagnetic
interference, affecting nearby communication systems.
Voltage Regulation Issues: Uneven voltage distribution can lead to system instability.
DEPT. OF EEE/SIT/MYSURU 2
