Impact of Films on the Long-Term Behavior of Stationary Electrical Connections and Contacts in Electric Power Systems

Stationary electrical connections and contacts, such as power connections, are commonly applied in electric power systems used for generation, transmission and distribution of electric energy. Several different degradation mechanisms can increase the contact resistance and might therefore reduce the power connection's lifetime. The degradation by film development is often considered as a reason for contact failure. In this research work, the impact of film development produced by chemical reactions, such as oxidation, on the long-term behavior of stationary electrical connections and contacts was studied with crossed rods. Typical material systems for electric power systems were considered in this study: Cu-ETP bare, silver-, nickel- or tin-coated, Al99.5 and AlMgSi0.5. The initial contact resistance and the plastic deformed area of the considered material systems was measured in experimental tests. The film's impact was further determined through comparative experimental studies in air and inert gas. During the experimental tests on perpendicularly crossed rods, other degradation mechanisms were suppressed. The film's impact within the formation phase was studied in more detail. Moreover, the dependency on different environments was tested. Supplementary studies were performed at low forces as well as analytical assessment of the impact of radial and axial film growth on circular contact points. As result, a general description of the interactions between film development, time, material and temperature at circular contact points is presented in this book. An additional chapter considers the long-term behavior of power connections operated in areas with harsh environmental conditions. For over two and a half years, long-term field tests investigating bolted busbar joints were conducted in desert and tropical rainforest environments.