Introduction and Formation of Corona Discharge
– Corona discharge is a process where a current flows from a high potential electrode into a neutral fluid, creating a plasma region.
– The potential gradient determines if corona discharge occurs, with higher gradients leading to ionization and conductivity.
– Corona discharge is often seen as a bluish glow around pointed metal conductors carrying high voltages.
– It can also occur in weather conditions, such as thunderstorms, where charged objects interact with the air.
– Improved insulation, corona rings, and rounded shapes for high voltage electrodes can suppress corona discharges.
– Corona discharge forms when the electric field at the conductor’s surface exceeds the dielectric strength of the surrounding fluid.
– Highly curved regions on electrodes, such as sharp corners or small diameter wires, are prone to corona formation.
– The curvature creates a high potential gradient, causing the air to break down and form plasma.
– Smooth, large-diameter rounded shapes on high voltage equipment help prevent corona formation.
– Coronas can be positive or negative, depending on the polarity of the voltage on the curved electrode.
Effects and Consequences of Corona Discharge
– Corona discharge leads to power loss for electric utilities, making it an unwanted side effect in high voltage applications.
– Current leakage caused by coronas can overload circuits in equipment like televisions, X-ray machines, and particle accelerators.
– Corona discharges generate gases like ozone and nitric oxide, which are corrosive and toxic to humans and the environment.
– The gases produced by corona discharges can degrade and embrittle nearby materials.
– Improved insulation and corona suppression techniques help mitigate the negative effects of corona discharge.
Applications of Corona Discharge
– Corona discharge is used in various applications, such as air filtration, photocopying, and ozone generation.
– It is employed to remove unwanted electric charges from aircraft surfaces during flight.
– Corona discharge is utilized in the manufacture of ozone and for sanitizing pool water.
– In electrostatic precipitators, it helps remove solid pollutants from waste gas streams or particles from air-conditioning systems.
– Corona discharge is also used in ionization processes for mass spectrometry and ion mobility spectrometry.
Comparison of Positive and Negative Coronas
– Positive and negative coronas have different physics due to the mass difference between electrons and positively charged ions.
– Negative coronas generate more ozone compared to positive coronas.
– The production of ozone is an important consideration when studying coronas.
– The polarity of the curved electrode determines whether a positive or negative corona occurs.
– Positive and negative coronas have distinct characteristics and behaviors.
Problems and Mechanism
– Corona discharges can generate audible and radio-frequency noise near electric power transmission lines.
– Power transmission equipment is designed to minimize corona discharge formation.
– Corona discharge causes power loss, audible noise, electromagnetic interference, purple glow, ozone production, and insulation damage.
– Sensitive animals can experience distress due to corona discharge.
– Electrical components such as transformers, capacitors, motors, and generators can be damaged by corona.
– Corona rings can be used to suppress coronas by spreading the electric field over a larger area.
– These toroidal devices decrease the field gradient below the corona threshold.
– Corona suppression is important in electric power transmission to reduce power loss and interference.
– Elastomer items like O-rings can be protected from ozone cracking through corona suppression.
– Plastic film capacitors operating at mains voltage can maintain their capacitance by avoiding local vaporization caused by corona discharges. Source: https://en.wikipedia.org/wiki/Corona_discharge
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A corona discharge is an electrical discharge caused by the ionization of a fluid such as air surrounding a conductor carrying a high voltage. It represents a local region where the air (or other fluid) has undergone electrical breakdown and become conductive, allowing charge to continuously leak off the conductor into the air. A corona discharge occurs at locations where the strength of the electric field (potential gradient) around a conductor exceeds the dielectric strength of the air. It is often seen as a bluish glow in the air adjacent to pointed metal conductors carrying high voltages, and emits light by the same mechanism as a gas discharge lamp. Corona discharges can also happen in weather, such as thunderstorms, where objects like ship masts or airplane wings have a charge significantly different from the air around them (St. Elmo's fire).
In many high voltage applications, corona is an unwanted side effect. Corona discharge from high voltage electric power transmission lines constitutes an economically significant waste of energy for utilities. In high voltage equipment like cathode ray tube televisions, radio transmitters, X-ray machines, and particle accelerators, the current leakage caused by coronas can constitute an unwanted load on the circuit. In the air, coronas generate gases such as ozone (O3) and nitric oxide (NO), and in turn, nitrogen dioxide (NO2), and thus nitric acid (HNO3) if water vapor is present. These gases are corrosive and can degrade and embrittle nearby materials, and are also toxic to humans and the environment.
Corona discharges can often be suppressed by improved insulation, corona rings, and making high voltage electrodes in smooth rounded shapes. However, controlled corona discharges are used in a variety of processes such as air filtration, photocopiers, and ozone generators.
