Field experience and long-term stability of high current contacts

A large number of static electrical contacts were investigated with respect to their long-term stability of contact resistance. The contacts studied were of two types: (1) an aluminum to aluminum busbar contact, and (2) an aluminium to nickel-plated-copper clamped contact. Both contact types were subjected to the same electrical load: 500-1000 A, RMS. The contacts were operated in an indoor environment. Investigations of the contacts were made annually 8-11 years after commissioning. The contact resistances were recorded and treated statistically. It was found that the type (1) contacts were stable, whereas the type (2) contacts showed a significantly increasing contact resistance. In addition, metallographic investigations were performed on selected contacts. Correlations were found between the contact resistance value and the extent of material deterioration at the contact surface.<>