Corona ring
![Corona discharge on insulator string of a 500 kV transmission line.](/Images/godic/202501/16/Corona_discharge_11119.JPG")
![Corona rings on insulator strings on a 400 kilovolt transmission line in France.](/Images/godic/202501/16/Corona_rings_on_insulators1120.png")
![(left) Grading rings on 1.4 million volt x-ray generator at US Bureau of Standards in 1947. (right) Corona caps and rings on Cockcroft-Walton particle accelerator from 1937, now in Science Museum, London.](/Images/godic/202501/16/Million_volt_x-ray_machine_Bureau_of_Standards_19471120.jpg")
![](/Images/godic/202501/16/Cockcroft–Walton_generator1120.jpg")
A corona ring, also called an anti-corona ring, is a toroid of conductive material, usually metal, which is attached to a terminal of high voltage equipment. The role of the corona ring is to distribute the electric field gradient and lower its maximum values below the corona threshold, preventing corona discharge. Corona rings are used on very high voltage power transmission insulators and switchgear, and on scientific research apparatus that generates high voltages. A very similar related device, the grading ring is used around insulators.