Distribution System Overhead Switch Bare Copper Contact Degradation: Copper Oxide Impedance, Thickness, and Composition

Overhead (OH) medium-voltage air-break electric distribution switches with bare copper contacts located within a six-mile proximity of the Pacific Ocean coast in San Diego Gas & Electric's (SDG&E) service territory have been observed with corrosion and have a higher replacement rate than similarly aged OH inland switches which do not exhibit the same corrosion growth. These OH failures are associated with extended outages, increased System Average Interruption Duration Index (SAIDI), and increased System Average Interruption Frequency Index (SAIFI). This research has been investigating copper corrosion properties leading to the formation of high-impedance oxides that may be associated with OH bare copper contact switch failure along the coast. Using scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and electrochemical impedance spectroscopy (EIS) the copper oxide thickness, impedance, and composition were quantified. Cuprite and atacamite were identified as the two primary copper oxides formed at the surface of the switches. Atacamite was the thickest oxide layer identified. Cuprite and atacamite were found to have significantly higher impedance than bare copper. The oxides' impedance could restrict current flow, leading to increased contact heating. As a conclusion, bare copper contact switches should not be installed in areas near the coast.