FYH Anti-corona Ring

Corona Ring

Corona rings are annular metal rings that are fixed to the ends of bushings and insulator strings. They are also referred to as anti-corona rings. Corona rings are used to prevent corona discharges that occur in high voltage transmission lines. Corona discharge or corona loss is a major problem in EHV transmission lines that cause power loss. One way to reduce corona discharge is to use corona rings.

How do corona rings work?

Corona discharge occurs when the electric field (potential gradient) on the surface of a conductor exceeds a critical value, called the critical destruction voltage. The value of the critical destruction voltage varies with atmospheric conditions. The value is about 30 kV/cm. The electric field is greatest where the curvature is sharpest. Therefore, corona discharges occur first at the points of greatest curvature - i.e., suspension points, corners and edges. Corona rings are installed at these points to prevent corona formation.

Corona rings are electrically connected to conductors around points where corona discharges may occur. Thus, due to its smooth circular shape, the corona ring distributes the electric field (or charge) over a wider area. As a result, it reduces the potential gradient below the critical damage value.
Manufacturers typically recommend installing aluminum corona rings at the conductor end of string insulators for lines above 230 kV and at both ends of insulators for 500 kV.

What is a grading ring?

A grading ring is very similar to a corona ring. In fact, it can be said that grading rings and corona rings are two different names for the same device. The difference lies in their primary purpose of use and location. Grading rings surround an insulator rather than a conductor. Their main purpose is to reduce the potential gradient along the insulator. Grading rings help to balance the potential distribution on the string of suspension insulators. As a result, graded rings increase string efficiency and prevent insulation breakdown. The graded rings also act as corona rings to some extent.

Effect of corona tube diameter.

The more the diameter of the corona tube is increased, the smaller the percentage of voltage on the bottommost insulator will be. On the other hand, increasing the corona tube diameter will increase the voltage shared by the topmost insulator.

Influence of corona ring diameter.

The larger the diameter of the ring, the lower the percentage of voltage on the lowest insulator. However, the rate of decrease is very slow. On the other hand, a larger ring diameter will lead to an increase in the voltage of the uppermost unit.

Accessories used in conjunction with corona rings are

400kv transmission lines
Bushing
Corona discharge
Surge arresters
Composite insulators
Grading rings

Features

Can be used for ultra-high voltage equipment
Extends the life of insulator surfaces
Easy installation on the antenna insulator of high-power radio transmitters
Increases the capacitance of the insulator

 Applications

GIS (gas insulated switchgear), substations, lightning arresters, high voltage bushings, shunt reactors, power transformers, power cables (accessories), high voltage laboratories (high voltage test equipment), high voltage capacitor banks, high voltage transmission lines (overhead lines), current transformers, voltage transformers, etc.

Uses

 For decreasing the corona and making the cable operate safely, our company design one special corona coils. It use aluminum alloy material, improve the electric filed in the preformed fitting end, increase the corona voltage one time.

Anti- corona model parameter specification table:

How are corona rings used?

Corona rings and corona ring combinations are necessary above 230kv, while high altitudes, high contamination and tight phase spacing may require the use of corona rings at lower system voltages.
What is the purpose of corona rings?
Smooth, large diameter spherical corona rings control the electric field by suppressing the generation of corona. The diameter of the corona sphere must be increased to obtain corona suppression.
What are the types of products used with corona rings?
There are specific types of products that are used with corona rings, i.e. there are specific types of products that are used with corona rings, i.e.

Corona discharge

Power
Insulators
Power transmission lines
Ring guards
Voltage measurement
Grading rings

Anti-corona Installation diagram

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