Corona rings and Grading rings

Corona rings are toroidal shaped metallic rings which are fixed at the end of bushings and insulator strings. They are also called as anti-corona rings. Corona rings are used to prevent corona discharge that occurs in high-voltage power lines. way to reduce corona discharge is using corona rings.

How corona rings work?

Corona discharge occurs when the electric field (potential gradient) at the surface of conductors exceed a critical value, called as critical disruptive voltage. The value of critical disruptive voltage varies with atmospheric condition. Its value is roughly 30 kV/cm. The electric field greatest where the curvature is sharpest. Therefore, corona discharge occurs first at the points where the curvature is greatest - i.e. at suspension points, corners and edges. Corona rings are installed at these points to prevent corona formation.

Corona discharge on a corona ring
Image source: Wikimedia commons
A corona ring is electrically connected to the conductor, encircling the points where corona discharge may occur. Therefore, the corona ring distributes the electric field (or charge) across a wider area, because of its smooth round shape. Hence, it reduces the potential gradient below the critical disruptive value.

Manufacturers usually recommend aluminum corona rings to be installed at the conductor end of the string insulators for lines above 230 kV and on both ends of the insulator for 500 kV.

For more information, please visit what is corona ring.

What are grading rings?

Grading rings are very similar to corona rings. In fact, one can say, grading ring and corona ring are two different names for the same device. The difference is due to their main purpose of use and their placement. Grading rings encircle

are toroidal shaped metallic rings which are fixed at the end of bushings and insulator strings. They are also called as. Corona rings are used to preventthat occurs in high-voltage power lines. Corona discharge or corona loss is a significant issue with very high voltage power lines which causes power loss. Oneis using corona rings.Corona discharge occurs when the electric field (potential gradient) at the surface of conductors exceed a critical value, called as. The value of critical disruptive voltage varies with atmospheric condition. Its value is roughly 30 kV/cm. The electric field greatest where the curvature is sharpest. Therefore, corona discharge occurs first at the points where the curvature is greatest - i.e. at suspension points, corners and edges. Corona rings are installed at these points to prevent corona formation.A corona ring is electrically connected to the conductor, encircling the points where corona discharge may occur. Therefore, the corona ring distributes the electric field (or charge) across a wider area, because of its smooth round shape. Hence, it reduces the potential gradient below the critical disruptive value.are very similar to corona rings. In fact, one can say, grading ring and corona ring are two different names for the same device. The difference is due to their main purpose of use and their placement. Grading rings encircle insulators rather than conductors. Their main purpose is to reduce the potential gradient along the insulator. Grading rings help in equalizing the potential distribution over a string of suspension insulator . Hence, grading rings improve the string efficiency and prevent insulation breakdown. Grading rings also serve the purpose of corona rings to some extent.

Corona Ring

A corona ring also called an anti-corona ring, it is a toroid-shaped metal ring that is attached to a terminal of high voltage equipment. For system voltages 230kV and above, a corona ring is necessary. The primary role of the corona ring is to reduce corona discharge using corona rings which occur in high-voltage power lines.

Made from copper, steel, and aluminum the corona ring is packed in wooden case and cartons, Corona discharge occurs when there is an excessive localized electric field gradient as the diameter of the ring is inversely proportional to the voltage percentage of the lowermost insulators.

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Ashutosh Ambey's Post

Corona discharge occurs in high power discharge lines using corona rings which can help reduce the corona discharge because they can damage the insulators and may produce breakdown products. To suppress the corona discharge, the wire-to-ring current flow is being formed up instead of wire-to-air.

The hot end of the stack will have a far more voltage drop across the insulators because of the stack of insulators used for EHV insulation.

Accessories used with corona rings are:

• 400kv transmission line
• Bushing
• Corona discharge
• Surge arrester
• Composite insulators
• Grading rings

Features:

• Can be used on extremely high voltage apparatus
• Prolong the lifetime of insulator surfaces
• Can easily be installed on the insulators of antennas of high-power radio transmitters
• Increase the capacitance of the insulators

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