Corona Ring Design Impact on the Electric Field Distribution Surrounding an Insulator String

Insulator strings are used on high-voltage transmission lines to insulate the line conductors from the grounded transmission towers. The electric field distribution along an insulator string is not uniform when an AC voltage is applied on it. To prevent unwanted phenomena such as corona discharge or flashover from happening, the electric field near the energized end of the insulator string must be minimized. This can be done by installing a corona ring. It is important to obtain a suitable design of corona ring so that the electric field magnitudes can be reduced significantly. Therefore, the effect of the design of corona ring on the electric field distribution along a 10-unit porcelain insulator string was evaluated by using Finite Element Analysis (FEA) in this work. From the simulation results, it was found that the parameters of the corona ring such as the vertical height of the corona ring along the insulator string, the outer diameter of the corona ring, and the inner diameter of the corona ring tube have an impact on the electric field distribution surrounding the insulator string. At the end, a suitable design of corona ring is proposed, which gives the lowest electric field magnitude along the insulator string based on the results obtained. A suitable design of corona ring for the modelled 10-unit porcelain insulator string was found to be 350 mm outer diameter of the corona ring, 65 mm inner diameter of the corona ring tube and 300 mm vertical height of the corona ring along the insulator string.