I. Introduction
As the years of operation increase, the insulating and mechanical properties of composite insulators deteriorate to varying degrees due to the combined effects of UV, temperature, humidity, stress, dirt and other factors, leading to accidents such as broken strings and dropped wires, which seriously affect the safe and stable operation of the power grid [1]–[3]. In China, the performance of online composite insulators is mainly assessed by inspecting the insulators online and taking a small number of insulators for mechanical and electrical performance measurements. Although the commonly used testing methods can assess the condition of insulators to a certain extent, they are more often used as a means to detect the cause of faults [4]–[7].