Corona Rings

Corona Rings are metallic rings which are fixed at the end of bushings and insulators.  Corona rings work by distributing the electric field uniformly along the surface and preventing areas of high electric stress concentration which can cause corona.  Usually, sharp edges can cause the formation or corona as the electrical gradient exceeds the critical voltage for the formation of corona. 

The corona ring is connected to the conductor.  Hence, it is at the same potential as the conductor.