Contact voltage analysis for degraded contact surfaces by power arcing phenomenon

Contact resistance is usually determined by the ratio of the voltage to the current and the increase of this value means that the contact interface is degraded. However for high currents, this ratio is not constant so Ohm´s law does not apply. In this paper, we study the electrical behaviour through degraded surface materials (Ag and Ag with various metal oxides) aged by break arcing up to 90A at 42V_DC with a contact force of 14N. In order to make a current voltage characteristic, the samples are tested with increasing current (I) from 50mA to 75A and then decreasing from 75A to 50mA. The main result is that the proportionality between the current and the voltage is ensured up to 70mV. Beyond this value this proportionality is lost and voltage break down takes place at different level of fritting voltage. However this phenomenon is frequently observed during the first applied current ramp (increasing), and disappears at the decreasing current ramp and during further tests. Discussions here are given concerning the constant fritting voltage over a wide current range being related to the breakdown of thin oxide films on the degraded surface and/or the creation of additional contact spots.