Although the corona ring can improve the overall distributed voltage of the composite insulator, its effect is not as uniform as that of the disk-shaped insulator string, but it can obviously reduce the field intensity at the connection between the mandrel and metal fitting.The improvement of field strength is related to the selection of appropriate outer diameter and pipe diameter of corona ring.(The experimental results show that the larger the diameter R of the high voltage end corona ring is, the lower the end field strength and average field strength at the ring side. When R > 10mm, the end field intensity can be reduced to below the air breakdown field intensity (3.0kV/cm). If the radius R of the corona ring is too small, the field strength will increase at 10% of the insulation distance from the high voltage side. The larger the radius R of the corona ring is, the lower the average field strength and the more uniform the electric field distribution will be. Therefore, 250mm ~ 300mm is recommended for the radius R of the corona ring at the high voltage end of 500kV.)

It also has a great relationship with the distance of the corona ring deep into (raised) the umbrella skirt.When the depth distance of the corona ring Δh≈0,the joint of mandrel and metal at the open plane of the corona ring will bear the maximum field strength,if it exceeds the air breakdown field strength (3.0kV/cm), a serious corona discharge will occur.This kind of concentrated electric field will make the micro pores, material defects or different interfaces in the silicone rubber material produce leakage marks,that is to say,25% ~ 30% of the operating voltage should be sustained on the insulator string of about 6% length,which accelerates the aging of the mandrel and the sealing performance of the silicone rubber sheath is damaged due to electrical erosion and perforation, leading to the string breaking accident of the composite insulator mandrel.

In addition, during line construction and project completion acceptance, the vast majority of units do not conduct acceptance according to the depth size of composite insulator corona rings.It is generally adopted to visually observe whether the openings of the upper and lower corona rings of composite insulators are aligned to check the entire installation quality. Because some employees are not clear about the principle of corona ring, the reversed installation has been found in the project. When the corona ring on the high voltage side of the composite insulator is correctly installed, the field strength at the end of the metal fitting is 14.12kV/cm, and when inverted, it is 30.79kV /cm.