What is the impact of corona discharge on radio interference?

Short Answer:

Corona discharge has a direct impact on radio interference, especially in high-voltage transmission systems. When corona occurs, it produces high-frequency noise signals due to the sudden ionization and deionization of air around the conductor. These noise signals can interfere with nearby radio communication, particularly in the AM (Amplitude Modulation) frequency range.

This interference can cause crackling sounds, signal distortion, or loss of reception for radios near transmission lines. The problem becomes worse during bad weather or at night when corona activity increases. That’s why transmission systems are designed carefully to minimize corona effects and reduce radio noise.

Detailed Explanation:

Impact of Corona Discharge on Radio Interference

Corona discharge is a high-voltage phenomenon that occurs when the electric field around a conductor becomes strong enough to ionize the air. This creates a weak but continuous electrical discharge that releases energy in the form of light, sound, heat, and electromagnetic waves. One of the most noticeable and concerning side effects of this discharge is radio interference.

When corona occurs on a power line, especially on rough or dirty conductor surfaces, it generates electromagnetic disturbances, mainly in the radio frequency range of 30 kHz to 300 MHz. These disturbances can interfere with radio communication, TV signals, and even other sensitive electronic devices located near transmission lines.

How Corona Discharge Produces Radio Interference

  1. Generation of High-Frequency Pulses
    • The ionization and de-ionization of air molecules during corona discharge create sharp electrical pulses.
    • These pulses radiate electromagnetic waves that travel through space and interfere with radio signals.
  2. Non-Uniform Discharges
    • Unlike smooth current flow, corona is a non-uniform and impulsive discharge. This irregular behavior makes the interference more unpredictable and wide-ranging.
  3. Repeated Discharge Events
    • Each tiny ionization event contributes to a series of high-frequency spikes.
    • These spikes can overlap with radio signals, especially in AM and shortwave bands.
  4. Amplitude Modulated Interference
    • The electromagnetic waves generated by corona often fall in the same frequency band used by AM radios, leading to noise, buzzing, or crackling sounds.

Factors That Worsen Radio Interference

  1. High Voltage Levels
    • The higher the voltage, the stronger the electric field, and the more intense the corona discharge becomes.
  2. Conductor Surface Roughness
    • Sharp edges, corrosion, or dirt increase local electric field intensity, encouraging corona and producing more interference.
  3. Weather Conditions
    • Humid, rainy, or foggy weather lowers the breakdown strength of air, increasing corona activity and resulting interference.
  4. Proximity to Communication Devices
    • Radios located close to transmission lines are more affected due to their shorter distance from the noise source.
  5. Poor Conductor Design or Maintenance
    • If proper design standards are not followed, or if the line is not cleaned or maintained, corona becomes more common and severe.

Effects of Radio Interference from Corona

  • Distorted Audio Reception: People may hear buzzing or crackling sounds while listening to AM radio near power lines.
  • Reduced Signal Quality: Radio signals become weak or unclear, especially in rural areas with long EHV lines.
  • Loss of Communication: In severe cases, corona interference can block radio communication, affecting emergency systems.
  • Impact on Aviation and Marine Signals: Some navigational aids that rely on radio signals may also face disruptions near strong corona sources.

Solutions to Minimize Radio Interference

  1. Use of Bundled Conductors
    • Reduces electric field strength at the surface and lowers corona formation.
  2. Larger Diameter and Smooth Conductors
    • Helps reduce localized high field points that trigger corona discharges.
  3. Corona Rings and Grading
    • Evenly distributes electric field at terminals and connection points, especially in substations.
  4. Improved Conductor Materials and Coatings
    • Special anti-corrosive coatings can maintain surface smoothness and reduce field irregularities.
  5. Proper Line Design and Maintenance
    • Following design standards, keeping spacing adequate, and regular inspection can help reduce corona and its radio impact.
Conclusion

Corona discharge on high-voltage transmission lines produces high-frequency noise signals that can severely interfere with nearby radio communication. This interference mainly affects AM radio, causing unwanted noise, signal distortion, and reception loss. The problem becomes worse in bad weather and with poor conductor conditions. By using smooth, bundled conductors, applying proper coatings, and maintaining the lines, engineers can reduce corona discharge and its impact on radio interference, ensuring reliable communication and efficient power transmission.