Voltage Saturation Mechanism in V-I Characteristics for Natural Graphite Brush and Steel Slip-ring

Abstract

Sliding contact systems are widely applied to power transfer between stationary and moving devices. Natural graphite brush is indispensable for a sliding contact at a high peripheral speed exceeding 50m/s. In addition, steel is applied to slip-rings to ensure mechanical strength. However, the electric contact behavior at high-speed sliding has not yet been sufficiently clarified for steel. In this paper, as a result of our experiments for the electric contact behavior, heavily saturated V-I characteristics have been found. For the heavily saturated characteristics' the reasons for the specific saturation have been analyzed based on the estimation of the true contact point temperature and voltage drop. In conclusion, the saturation of the V-I characteristics is caused by the state transition at the contact point of the steel slip-ring from elastic to plastic, where the tensile strength of steel decreases at the contact point interface. This is also verified from the experimental values and the analysis of the contact point temperature.