The use of corona ring (ring shield) depends of the type of insulator, equipment, configuration, system voltage, weather conditions, contamination, and altitude among other factors. As Saltan posted above, for 550 kV BIL (115 kV nominal) normally corona ring is not required unless severe environment condition happens.
The purpose of corona ring is to reshape the electric field, thus, reducing electrical discharge (corona effect) on the component shielding the hardware and insulators, preventing discharge by lowering potential gradients, thereby reducing power loss and radio and TV interference.
Non-ceramic Insulators (NCI) normally start at 138kV (650 kV BIL). Pin and cap Insulators can vary starting normally at 230kV (900 kV BIL) or 345kV depending upon your engineering tolerances and insulators in the strings.
Surge arresters use corona ring for nominal voltage above 138 kV (~650 kV BIL). Bus and hardware may use grading rings for 345 kV (1050 kV BIL) and above.
Calin100- ELECTRO is a electric field simulation software used for design and analysis of HV electric equipment such as Insulators, bushings, arrester, transformers, shielding, connectors and hardware, etc.
If you would like additional details contact directly to info@integratedsoft.com
