Corona ring
Encyclopedia
A corona ring, also called anti-corona ring, is a toroid
Toroid (geometry)
In mathematics, a toroid is a doughnut-shaped object, such as an O-ring. Its annular shape is generated by revolving a plane geometrical figure about an axis external to that figure which is parallel to the plane of the figure and does not intersect the figure...

 of (typically) conductive material located in the vicinity of a terminal of a high voltage
High voltage
The term high voltage characterizes electrical circuits in which the voltage used is the cause of particular safety concerns and insulation requirements...

 device. It is electrically insulated. Stacks of more spaced rings are often used. The role of the corona ring is to distribute the electric field gradient
Electric field gradient
In atomic, molecular, and solid-state physics, the electric field gradient measures the rate of change of the electric field at an atomic nucleus generated by the electronic charge distribution and the other nuclei...

 and lower its maximum values below the corona threshold, preventing the corona discharge
Corona discharge
In electricity, a corona discharge is an electrical discharge brought on by the ionization of a fluid surrounding a conductor that is electrically energized...

.

Corona rings are often seen on van de Graaf generators, electrical insulators, Cockcroft–Walton generators, particle accelerator
Particle accelerator
A particle accelerator is a device that uses electromagnetic fields to propel charged particles to high speeds and to contain them in well-defined beams. An ordinary CRT television set is a simple form of accelerator. There are two basic types: electrostatic and oscillating field accelerators.In...

s, Lightning Arresters, high voltage bushing
Bushing (electrical)
A bushing is a hollow insulating liner through which a conductor may pass. Bushings appear on switchgear, transformers, circuit breakers and other high voltage equipment.- Description :...

 terminals, and other high voltage
High voltage
The term high voltage characterizes electrical circuits in which the voltage used is the cause of particular safety concerns and insulation requirements...

 equipment.

Corona rings are typically installed on very high voltage power line insulators. Manufacturers suggest a corona ring on the line end of the insulator for above 230 kV and on both ends for above 500 kV. Corona rings prolong lifetime of insulator surfaces by suppressing the effects of corona discharge.

Corona rings may also be installed on the insulators of antennas
Antenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...

 of high-power radio transmitters. They increase, however, the capacitance
Capacitance
In electromagnetism and electronics, capacitance is the ability of a capacitor to store energy in an electric field. Capacitance is also a measure of the amount of electric potential energy stored for a given electric potential. A common form of energy storage device is a parallel-plate capacitor...

of the insulators.

Corona discharge is a more serious problem in higher altitude locations, where the air is less dense.

Corona caps are caps with round edges; they are mounted on the ends of the insulators and play the same role as corona rings.
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