Effect of current intensity and polarity on the electrical performances of slip ring contacts

In this investigation, the effect of current has been studied on sliding electrical contacts between bulk gold-alloy wires and gold-alloy plated rings. Two parameters have been examined: current intensity, and direction of current. For this purpose, a model slip ring has been used which includes 4 electrically independent groups of 4 rings. For each group, the electrical diagram requires the current to flow alternately from the wires to the ring (cathode ring) and from the ring to the wires (anode ring). The contact voltage has been measured with an equivalent 4-probes method, and the morphology of the worn surfaces has been observed thanks to an optical microscope and a Scanning Electron Microscope (SEM); its composition has been characterized by Energy Dispersive X-ray spectroscopy (EDX). First, the results show that the current allows to reduce the contact voltage and the wear of surfaces. Secondly, the results show an influence of the polarity of the current: the anode rings present much higher contact voltage, and a greater loss of the gold-plating compared to the cathode rings. In this paper, the results obtained are presented and a hypothesis is proposed to explain the polarity effect on the contacts.