## 1 Introduction  
High-voltage insulators on overhead power lines have long been exposed to the outdoors and are susceptible to pollution and salt contamination. Salt contamination and industrial pollution may cause flashovers and line outages, thereby affecting the power supply and reducing the reliability of the power system. To prevent insulator flashovers, maintenance staff need to periodically wash the insulators [1, 2]. Currently, various maintenance procedures are available to minimize flashovers caused by contamination and industrial pollution. Among the available maintenance procedures, periodic washing is the most common method to remove pollutants from the surface of insulators [3]. Furthermore, the equivalent salt deposit density (ESDD) and non-soluble deposit density (NSDD) are regularly used to assess the severity of site pollution [4]. In terms of maintenance, utilities often adopt periodic maintenance procedures when abnormal conditions are observed on the insulators. Although this method can effectively prevent flashovers due to contamination and industrial pollution, it requires a significant amount of manpower and cannot accurately ensure the insulation of the insulators [5, 6]. Therefore, one of the challenges for maintenance is how to assess the condition of insulatorsand determine the washing schedule. Considering the variability of weather and pollution conditions, periodic washing may not be an efficient strategy. Generally speaking, the progress of insulator discharge increases with the leakage current, which is observable when the surface of the insulator is contaminated and wet. Therefore, by observing the surface discharge and leakage current of the insulator, one can roughly understand its insulation and whether it has reached all the stages of the pollution flashover mechanism. In addition, it indicates how close the insulator string is to flashover. However, the leakage current is influenced by weather conditions such as temperature, relative humidity, pressure, wind speed, ultraviolet exposure, and the type and layers of pollution on the surface of the insulator [7; 8]. The relationship between discharge and leakage current can be determined through experiments. Table 1 illustrates the correlation between leakage current and surface discharge phenomena in the ceramic insulator. The experiment reveals that the leakage current is extremely low when the surface is clean and dry; 1 mA is the normal leakage current in the clean and dry state. When the relative humidity reaches a certain level, for example, 80% or more, the leakage current exceeds 1 mA, indicating that more obvious corona or sparks can be observed [9; 10; 11; 12]. Therefore, both relative humidity and pollution conditions must combine to form a larger corona or spark. This leakage current typically initiates at 2 to 3 mA. When the leakage current exceeds 10 mA, due to the heat generated at the discharge roots, the pollution dries out in their vicinity, and the dry band is formed. Subsequently, a spark occurs, causing discharges along small portions of the insulation. If the leakage current exceeds 100 mA, an extended partial arc occurs. This arc discharge is highly unstable. Therefore, if an extended partial arc discharge, due to an extremely large leakage current, is observed, the insulator should be cleaned immediately. As mentioned above, the leakage current is a more meaningful parameter as it provides information on all stages of the pollution flashover mechanism and indicates how close the insulator string is to flashover. From a literature survey, it is evident that insulator contamination is related to weather parameters such as temperature, relative humidity, pressure, wind speed, and ultraviolet [13; 14; 15; 16].