The Difference Between Negative and Positive Coronas in Electrical Discharges

Understanding the differences between negative and positive coronas is crucial in the field of electrical engineering and material science. While in the context of coronavirus testing and infections, we use the terms negative and positive to denote the viral status, in the scientific context, a corona discharge refers to an electrical discharge brought on by the ionization of a fluid surrounding a conductor. This article will explore the concepts of negative and positive coronas and their applications in electrical systems.

What is a Corona Discharge?

A corona discharge is an electrical discharge that occurs due to the ionization of a surrounding fluid, usually air, by an electrically charged conductor. Coronas can be observed as a bluish or other colored glow in the air, and they emit light as a result of gas discharge. This phenomenon is most commonly seen near sharp metal conductors carrying high voltages.

The Basics of Negative Corona

A negative corona occurs when negative ions form by electrons attaching to oxygen atoms. These ions then accelerate towards other particles in the electric field. In air, negative coronas are generally preferred because they allow for a more intense corona discharge. Due to the uniform charge distribution, all particles become charged with the same polarity, which facilitates the formation of a stable corona.

The Basics of Positive Corona

In contrast, a positive corona occurs when all the electrons in the air are attracted inward towards the conductor. The polarity of the voltage on the highly curved electrode determines whether the corona is positive or negative. If the curved electrode is positive, it will produce a positive corona; if it's negative, a negative corona results. The physics behind these two phenomena are quite different due to the mass difference between electrons and positively charged ions, which significantly affects the ionization process.

Applications of Coronas in Electrical Systems

The behavior of coronas can vary significantly depending on the type of electrical system in use. In the case of alternating current (AC) transmission lines, both positive and negative coronas can occur on all phase conductors. However, for direct current (DC) transmission lines, positive corona is observed near the positive conductor, while negative corona is near the negative conductor.

The Role of Voltage and Pressure in Corona Formation

The formation of a corona requires that the electric field potential gradient at the surface of the conductor exceeds a critical value known as the dielectric strength or disruptive potential gradient of the fluid. In air at atmospheric pressure, this value is approximately 30 kilovolts per centimeter, but it decreases with pressure, making coronas more problematic at high altitudes.

Ozone Production in Coronas

An important consequence of the corona discharge process is the production of ozone. A negative corona generates significantly more ozone than a corresponding positive corona. This is due to the stronger ionization effects produced by the negatively charged ions, which have a higher ability to cause inelastic collision at common temperatures and pressures.

Conclusion

Understanding the differences between negative and positive coronas is essential for their effective application in various electrical systems, including power transmission and material science. The behavior and properties of these phenomena can significantly impact the performance and safety of electrical systems.

Key Takeaways:

A corona discharge is the ionization of a surrounding fluid by an electrically charged conductor. Negative coronas form when electrons attach to oxygen atoms, resulting in a more intense and uniform corona discharge in air. Positive coronas are formed when electrons are attracted inward towards the conductor, with their polarity determining the type of corona. The formation of a corona depends on the electric field potential gradient, which must exceed the dielectric strength of the fluid. Negative coronas produce more ozone due to enhanced ionization.

Related Keywords

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