From the analysis of the degradation characteristics and causes of insulators, it can be seen that there are differences in electrical performance, partial discharge, temperature distribution, and other aspects between deteriorated insulators and good insulators. Based on these characteristics and differences, corresponding instruments or devices have been developed and different measurement methods have been studied. From the current detection methods, there are live detection and power outage detection; There are contact detection and non-contact detection. From the basis of measurement methods, there are generally several aspects as follows: 1. Direct observation method. Currently, for composite insulators, the most commonly used method for external physical defects is direct observation method, which is to use double tube observation eyes to observe under the tower, and pilot control power to discover common surface defects, such as cracks in the sheath, umbrella skirt, hardware, and other parts, as well as signs of electrical corrosion, pulverization, and leakage, If the above phenomenon occurs, the insulator should be replaced immediately. However, ground observation is not reliable enough, and it is necessary to climb the tower for inspection and it is difficult to detect faults inside the insulator, such as dendritic channels. 2. Insulator resistance measurement method: The insulation resistance of a good insulator is generally over tens of megaohms, while for inferior insulators, the insulation resistance is reduced or even zero. This method can be used for power outage or live measurement, and belongs to the contact type. When measuring, the relative humidity of the air should not be too high, otherwise it may be misjudged. In addition, extensive testing of transmission lines is not easy to carry out. 3. The characteristic of poor quality insulators using distributed voltage measurement method is reduced insulation, low sharing voltage, or even zero. By comparing this feature with the standard voltage distribution of a good insulator string, inferior insulators can be detected. This method requires live measurement, and commonly used tools on 35-550KV transmission lines include short-circuit forks, resistance voltage sharing rods, capacitance voltage sharing rods, and spark gap operating rods, all of which belong to contact measurement. This method, like measuring insulation resistance, needs to be carried out in good weather. Live contact operation, extremely dangerous! 4. The AC voltage withstand method also uses the decrease in insulation characteristics and voltage withstand of inferior insulators to determine inferior insulators. The pilot controlled power method is the most direct and authoritative way to determine the quality of insulators, and it is also the basis for testing the effectiveness of other methods and detecting the true damage of inferior insulators. However, this method requires the replacement of insulators and is difficult to measure on site