Difference in Energization Mechanism caused by Change in Brush Ag Content in Sliding Energization of Steel Slip Ring and Ag Graphite Brush

Abstract

A brush-slip ring system enables the transfer of electrical current between stationary and moving parts. It is widely used mainly in the excitation mechanism of AC rotating machines. In recent years, various brush-slip ring systems have been developed. Their uses range from automotive alternators to grounding mechanisms for electric railways. Therefore, brush-slip ring systems require maintenance-saving features and improved reliability.

Until now, copper materials have been used for slip rings. In recent years, considering their mechanical strength and cost, the use of steel slip rings is increasing. However, the sliding contact energization characteristics of steel slip rings have not yet been elucidated.

In this study, we examined the V-I characteristics of a steel slip ring (S45C) and a Ag graphite brush (Ag content 50, 60, 70, 80, and 90wt%). As a result, the electrical characteristic of the steel slip ring was found to be unique. In addition, the effect of the Ag content of the brush on this characteristic cannot be ignored. Therefore, we estimated the contact point temperature for each brush Ag content using the φ-θ theory. Based on this, the current-carrying characteristics of the steel slip ring and Ag graphite brushes were clarified for each brush Ag content.