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 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 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.
Long exposure photograph of corona discharge on an insulator string of a 500 kV overhead power line. Corona discharges represent a significant power loss for electric utilities.
The corona discharge around a high-voltage coil
Corona discharge from a spoon attached to the high voltage terminal of a Tesla coil.
A variety of forms of corona discharge, from various metal objects. Notice, especially in the last two pictures, how the discharge is concentrated at the points on the objects.
In electronics, electrical breakdown or dielectric breakdown is a process that occurs when an electrically insulating material, subjected to a high enough voltage, suddenly becomes a conductor and current flows through it. All insulating materials undergo breakdown when the electric field caused by an applied voltage exceeds the material's dielectric strength. The voltage at which a given insulating object becomes conductive is called its breakdown voltage and, in addition to its dielectric strength, depends on its size and shape, and the location on the object at which the voltage is applied. Under sufficient voltage, electrical breakdown can occur within solids, liquids, or gases. However, the specific breakdown mechanisms are different for each kind of dielectric medium.
Electrical breakdown in an electric discharge showing the ribbon-like plasma filaments from a Tesla coil.
A Tesla coil, showing several forms of electrical breakdown. On the right side of the aluminum high voltage terminal (top right) is a purple corona discharge. At the end of the wire projecting from the terminal (top left) is a brush discharge. The fluorescent tube lying on the stand is lit by a glow discharge induced by the radio frequency electric field. At bottom the Tesla coil apparatus is lit by an intense white light from an electric arc in a
Dielectric breakdown within a solid insulator can permanently change its appearance and properties. As shown in this Lichtenberg figure
