Physical interpretations concerning nonlinear conductivity phenomena across no-load switching contacts

An experimental survey concerning physical interpretations of the dominant phenomena which may develop during the operation of no-load switching contacts in laboratory environments is presented. Measurements are performed on industrial switches with the following nominal values: isolation switches 400 V/100 A, isolation switches 20 kV/200 A, and fuse isolators 20 kV/ 100 A. It is shown that beyond a threshold field intensity (corresponding to smaller currents than the nominal values) a nonlinear current-voltage relationship may develop, leading to bistability and negative differential conductance phenomena. This has been attributed to the dominating tunnelling current component between oxidized (or nonideally contacted) metallic surfaces at high electric fields, resulting in an increased effective area of contact