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Does having two corona rings instead of just one on the line end of a tension insulator string help with corona formation?

Axel Witzel
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The number, shape and size of corona rings is a manufacturing/installation cost versus benefit calculation.

The ideal anti-corona electrode has a very large radius of curvature. Obviously that's quite expensive to manufacture and install.

You can reduce the cost with little degradation in corona performance by approximating the large surface with a number of small radius discs or bent rods.

As the electrode has to be self-supporting, resisting high winds and installation technicians, there comes a low voltage where it's cheaper to use a single electrode that's large enough, rather than make an array of smaller electrodes.

To answer your question, two rings of a given diameter will perform better than a single ring of the same diameter. There will be a single ring large diameter that performs as well as two smaller rings, but it may turn out to be more expensive than using two smaller rings.

You can see this 'approximating a large diameter' on the conductor bundles used for the overhead wires. I'm not too sure where the breakpoints are, but the bundles go up from 1 to 4 somewhere between 100 kV and 400 kV. There are a number of > 1 MV lines being built in the US and China, and they use a bundle of (IIRC) 16 conductors spaced round a circle of 1 metre or more.

Neil_UK
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  • If 1 large enough corona electrode has already been placed, then another 1 will add no benefit whatsoever? But why do we need two corona rings on a suspension insulator string? Why during testing, corona form only on the top corona ring on a tension insulator string but corona forms on both corona rings on a suspension insulator string? – Axel Witzel Mar 14 '23 at 07:06