Effect of Form factor, Non-Uniform Contamination, and UV Radiation on Leakage Current in High-Voltage Insulators

Glass and silicone insulator strings on high-voltage lines often operate in areas with high levels of pollution and humidity, such as coastal areas near the sea, deserts, and industrial areas. This pollution, combined with humidity, can form conductive layers on the surface that allow leakage current (LC) to pass through, which sometimes increases to the point of causing a flashover. This study evaluates how geometry (form factor), non-uniform pollution, and aging due to UV radiation influence the magnitude of LC. This provides useful information for laboratory insulator testing, online LC monitoring systems in the field, as well as for the inspection and maintenance of electrical insulators. Two analyses are combined: (i) Cases in service of two strings of five RTV-coated glass insulators operating on a 66 kV line in a desert and coastal area of northern Chile. Here, visual inspections, hydrophobicity evaluations, contamination measurements (ESDD/NSDD), and LC tests under controlled relative humidity were performed in the laboratory. (ii) Laboratory tests with glass insulators with two different profiles (U120B and F120PF) under artificial contamination and humidity up to 100%, to deduce a mathematical expression that relates LC and the "Form Factor" of the insulators. The results show that non-uniform contamination on the surface increases the magnitude of LC compared to cases with uniform contamination, and that prolonged exposure to UV rays can cause permanent loss of hydrophobicity in silicone-coated insulators. For laboratory testing, a mathematical model is presented that estimates the magnitude of LC as a function of creepage distance, contamination (ESDD/NSDD), and relative humidity to which glass insulators are exposed. These analyses are used to report the condition of silicone insulators after several years of use and to estimate LC in online monitoring of glass insulators.