Contact Resistance and Overtemperature Behavior of New and pre-Arced Power Engineering Contacts as a Function of Ambient Temperature and Contact Force

Inhalt:
Switching devices for power engineering are progressively decreasing in size. As a result, focus on overtemperature behavior and electrical resistance within their various contact components becomes exceedingly important, especially for the contact tips. Their behavior is important for new devices as well as for devices during their service life. Thus contacts as manufactured, as well as contacts after arcing are investigated in this paper by varying parameters such as contact force and environmental temperature using a programmable model switch. The dimensions of the model switch as well as the freely adjustable testing conditions are set according to a 160A rated molded case circuit breaker (MCCB). Silver/graphite (Ag/C), silver/nickel (Ag/Ni), silver/tungsten (Ag/W) and silver/metal oxide (Ag/SnO2) and their combinations were investigated. It can be shown that Ag/Ni40 and Ag/SnO2 12WPD show a stable or even decreasing contact resistance with elevated temperature while Ag/C4 and Ag/W60 end up with increased values. Results obtained are discussed on the basis of electrical conductivity, hardness as a function of temperature, the influence of arcing as well as the roughness of the contact surfaces.