It is observed that corona discharge occurs mostly at sharp corners, edges near the conductor fixing points. Corona rings also called grading rings are hallow metallic rings having large diameter and will have a smooth surface. These corona rings are placed suitably to metal clamps, joints to encircle the conductors surface. This have the advantage of shifting of high stress point shifted from conductor surface to corona ring surface. As the diameter and surface area of the ring is higher than that of the conductor.
This helps in:
- Field distribution is made uniform
- Surface stress is reduced to much lower value
- Corona discharge is eliminated
- Dust deposition is also minimized