This post’s subject is corona effect or corona discharge. This phenomenon is common in medium and high voltage transmission lines.
How it occurs?
Air isn’t a perfect insulator, it has electrons and ions in normal conditions. In the presence of a sufficient strong electric field, these free electrons and ions are accelerated. In addition to that, dust particles, air or humidity, become ionized when potential difference between transmission lines reaches some dozens of kilovolts/meter. When closer to energized conductor, higher the electric field intensity.
Light emission is caused when ions and molecules collide and capture a free electron. Electric potential polarity determines if corona is negative or positive. This phenomenon is aggravated when there are damaged conductors or with irregular surface, defective insulators and dust accumulation on transmission lines.
Corona effect problems
- Power loss, due to electric energy dissipation on air, instead of being transmitted on conductor. The losses increase when air becomes humid.
- Discharges cause short duration voltage and current pulses, that produce high frequency electromagnetic waves, which cause interference in devices that use radiofrequency such as radios and TVs.
- Ozone gas is produced and causes corrosion on conductors.
Mitigation measures
To mitigate this effect, it’s necessary to reduce the electric field and increase the necessary limit voltage to generate corona discharge. These measures are:
- Increase distance between conductor cables.
- Increase conductor’s diameter. Because a bigger curvature radius reduces electric field concentration.
- Put more than one conductor in parallel (bundle conductor), for the same phase (voltage signal). It will increase the effective diameter and surface area, reducing corona discharge.
- Use corona rings, are metallic parts in toroidal shape, they’re electrically linked to transmission line and put on insulators’ terminals. Where there’s higher probability to occur corona effect, due to pointy parts and extremities. With ring shape, charge is distributed to a bigger area, reducing discharge.
Corona effect applications
The corona effect serves for something? The answer is yes and some applications are:
- Ozone production for some applications.
- Electrets manufacturing for microphones.
- Production of charged surfaces on photocopies.
- Remove toxic particles from air using ions and free radicals generated by corona effect.
