Field Monitoring of Leakage Currents in Overhead Transmission Lines for Condition-Based Insulator Maintenance

The reliability of high-voltage electrical transmission systems is strongly influenced by the performance of insulators exposed to contaminated environments. Soluble and insoluble contamination on the surface of insulators, combined with natural moisture, can cause significant increases in leakage current, surface discharges, and eventually flashover events that lead to power outages. In this context, condition-based maintenance emerges as a fundamental strategy for maintaining insulators, reducing the risk of failure and optimizing the resources allocated to washing, inspecting, and replacing insulators. This article presents the results of field monitoring campaigns of leakage current carried out on 500 kV overhead transmission lines located in areas characterized by industrial pollution, marine aerosols, and desert dust. A non-intrusive, low-energy consumption new monitoring system was implemented, capable of continuously acquiring environmental variables and leakage current directly from insulator strings in service. Data analysis allowed the characterization of leakage current behavior as a function of relative humidity and the identification of critical contamination activation thresholds, including harmonic-domain indicators such as current total harmonic distortion