What is the difference between a grading ring and a corona ring?

A grading ring is used to ensure a uniform voltage distribution along the length of an electrical device. This is important for surge arresters so each MOV disc in the arrester is energized at the appropriate voltage.

A corona ring is traditionally used to electrically shield external hardware to prevent corona from developing. This corona could lead to degradation of insulating materials or create interference to electronic communication.

Surge arresters below 500 kV system voltage do not typically need corona rings.

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