Composite insulator is widely used in transmission lines because of its excellent performance, but its electric field distribution is extremely uneven. So it is necessary to install grading ring. Reasonable grading ring installation strategy can uniform the electric field of composite insulator to reduce the probability of flashover. However, the installation of the grading ring reduces the electrical gap, resulting in an increase in the probability of bird dung flashover. Insulation grading ring can increase the insulation strength of the grading ring, reduce the flashover probability of bird dung flashover and reduce its damage. Therefore, the study of grading ring is helpful to reduce the occurrence of bird damage accidents.

According to the actual insulator size and the model of the wine cup tower, the model is modeled by using AutoCAD, and then the simulation model is built by using COMSOL Multiphysics. This paper mainly studies the electric field distribution of composite insulator after installing grading ring or insulation grading ring.

The insulating grading ring can increase the insulation strength of grading ring on the basis of slightly reducing the surface electric field of composite insulator.

(1) The bird droppings trip accident in Ningxia accounts for 70% of the total number of bird damage accidents. The installation of grading rings on both sides reduces the electrical distance of composite insulators, increases the probability of bird damage trip accidents, and the probability of single string accident is higher.

(2) The maximum field intensity of the space electric field is larger when the bird dung is coplanar with the conductor than when the bird dung is opposite. When the length of bird dung is greater than 800mm, the growth rate of spatial maximum field strength increases significantly. The bird dropping flashover probability of insulated coating grading ring is lower, which can effectively reduce the bird dropping flashover probability of composite insulator.

(3) Insulation coating material has a great influence on the spatial electric field of composite insulators. Considering the insulation strength and spatial electric field distribution, it is more appropriate to select silicone rubber as insulation coating material.