Relationship between Brush Current Change and Contact Voltage Drop in Sliding Contact with Steel Slip Ring and Various Silver Graphite Brushes

A brush-slip ring system is a mechanism used to transfer electrical current between stationary and moving parts. This mechanism is widely used, mainly in the excitation mechanisms of AC rotating machines. In recent years, the diversification in brush-slip ring systems has been remarkable. The usage range of these systems has extended to automotive alternators and grounding mechanisms for electric railways. Therefore, brush-slip ring systems require maintenance cost savings and greater reliability. To date, copper-based materials have generally been used for slip rings. Recently, because of advantages in terms of mechanical strength and cost, slip rings based on steel are being used increasingly. However, the sliding contact energization characteristics of steel slip rings have not yet been determined. In this work, contact voltage drop-brush current (V-I) characteristic tests were conducted using a steel slip ring and silver (Ag)-graphite brushes to determine the electrical characteristics of this system. As a result, an increased contact voltage drop was shown to be suppressed at a brush current of approximately 4-6 A. Then, based on the contact voltage drop at this time, the maximum temperature in the area between the slip ring and the brush was calculated using the φ-θ theory. As a result, we have shown that the nonlinearity of the V-I characteristics in the steel slip rings is associated with the steel transformation point. In addition, the maximum temperature point transition during the change in the brush Ag content is determined.