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. Corona discharge or corona loss is a significant issue with very high voltage power lines which causes power loss. One way to reduce corona discharge is using corona rings. The role of a corona ring is to distribute the electric field gradient and lower its maximum values below the corona threshold, thus prevent corona discharge.
Application of corona rings creates a "wire-to-ring" current flow Instead of "wire-to-air" current flow that helps to suppress corona discharge. It works by modifying the electric field intensity to reduce the worst case rate of field change on the insulator, thereby reducing peak potential across air surrounded to lower breakdown voltage to about 10 kV per inch dry air, mains frequencies. A useful secondary role is to reshape the electric field distribution across a stack of insulators so that the potential drop per insulator is more even, thereby reducing the breakdown stresses on the insulator with highest voltage drop.
A stack of symmetrical insulators used for EHV insulation will have far more voltage drop across the insulators at the "hot" end of the stack. Brief but useful group discussion here. Here are some of their references re use of corona rings. Illustration of electric field distributions with and without corona ring on multi insulator string. See the "superb reference" paper above for discussion. It's about charge density - the ring increases the surface area and radius of curvature, reducing charge density below that which would cause significant corona from things like sharp edges at joints etc.
The corona ring at the line end of the insulators is connected to the power line. That corona ring is at the same high voltage as the power line. That corona ring is not earthed. Occasionally there is a second corona ring at the earth end of the stack. The corona ring at the earth end of the stack is the only corona ring that is earthed. You are right -- If, hypothetically, all the rings were earthed, then the wire-to-ring current flow would be just as bad and probably worse than the wire-to-air current flow corona without the rings.
The electric field will circulate on the ring instead of surface of the insulator so the corona discharge is reduced. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. How does corona ring help against corona discharge? Ask Question.
Asked 10 years, 3 months ago. Active 8 years, 2 months ago. However, they increase the capacitance of the insulators. Corona discharges only occur when the electric field potential gradient at the surface of conductors exceeds a critical value.
The electric field at a conductor is greatest where the curvature is sharpest, and therefore corona discharge occurs first at sharp points, corners and edges. However, some parts of high voltage circuits require hardware with exposed sharp edges or corners, such as the attachment points where wires or bus bars are connected to insulators. Corona rings are installed at these points to prevent corona formation.
The corona ring is electrically connected to the high voltage conductor, encircling the points where corona would form.
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