Brush/slip ring current collector performance and anomalies during compulsator commissioning

During recent tests associated with a model scale compulsator development program at The University of Texas at Austin Center for Electromechanics (UT-CEM), the performance of severe duty trailing arm brush current collectors was evaluated. The original material of choice for the brush slip ring design was 70075-T6 aluminum to minimize machine mass and simplify slip ring assembly on the rotor shaft. The slip rings have a nominal diameter of 5.5 in. The combination of CM1S copper, trailing arm brushes, and aluminum slip rings performed well up to about 80% full speed, although the design did not appear to be very damage tolerant. As testing continued at higher speeds, one of the slip rings began to exhibit small shallow arc pits in the brush track on the slip ring outer diameter. This was observed on only one slip ring and had no apparent affect on machine performance. Left unchecked, this shallow arc damage can cause a high speed brush to "bounce" excessively during a run and cause more severe damage, as well as increase the circuit impedance from the arcing. This paper presents a general description of the observed brush performance during normal and fault conditions. It also includes a description of mechanical analysis and field strength measurements done around the brushes in an effort to explain the "one brush" bouncing. Brush and slip ring design upgrades (including a reinforced brush actuator for increased brush down-force and a newly implemented two-layer aluminum and steel slip ring design) are discussed.