Investigations on stationary electrical joints with a bare and a silver or nickel coated contact partner regarding the permissible temperature limit according to ANSI IEEE and IEC

In electric power transmission, copper and aluminum are mainly used as conductor materials. To improve the contact behavior, the contact surfaces of e.g. high-voltage switching devices are often coated with silver or nickel. Due to economic reasons, connecting conductors are usually uncoated. In that case, an electrical joint with only one coated contact partner is formed. With respect to the permissible temperature limit for this kind of electrical joints, a contradiction between IEC 62271 1:2007/A1: 2011 and the ANSI IEEE C37.100.1:2007 exists. The limiting temperature given in the IEC is the one of the surface material with the higher valid temperature limit. On the contrary, the limiting temperature according to the standard of the ANSI IEEE is the one of the surface with the lower valid temperature limit. One major intention was to investigate the physical temperature limits of connections with only one coated contact partner. Therefore, joints with bus bars made of copper and aluminum and different coatings have been set up and aged at different temperatures. The joint resistance is measured time-dependent and evaluated. Additional investigations of the microstructure and mechanical properties were done to understand the physical aging processes.