While they are often used together and share a similar appearance, a corona ring and a grading ring have distinct primary functions.

• A corona ring's main purpose is to prevent corona discharge by lowering the electric field gradient around a high-voltage point. It is typically used for system voltages above 230 kV.

• A grading ring, on the other hand, is primarily used to equalize the electric field and voltage distribution along a string of insulators. This is important because without the ring, the electric field is strongest at the conductor end of the insulator string. The grading ring helps to distribute the stress more uniformly across all the insulators, preventing premature electrical breakdown and improving the overall efficiency and lifespan of the insulator string.

In many modern applications, a single ring can be designed and placed to perform both functions, but their fundamental roles are different.