In-Situ Monitoring of the Brush/Rotor Interface in a Homopolar Motor with Acoustic Emission

Homopolar motors have been proposed as an alternative propulsion means for ships. Such motors operate in a very harsh and demanding environment, making in-situ diagnostics and faultmonitoring systems a key issue for extended operation. In a typical homopolar motor, several thousand brushes are used, which are all in sliding contact with a copper rotor at a velocity of about 10 m/s. Wear and degradation of the brush and rotor are key issues that need to be understood in order to design a reliable motor. In this investigation, acoustic emission transducers were used to study the characteristics of the brush/rotor interface of a homopolar motor as a function of speed, load, materials, and other design parameters. The AE sensors were directly coupled to the brush in the homopolar motor test rig, and data were obtained over extended periods of time. The sensor signal demonstrated good sensitivity to brush/rotor contact conditions, brush contact load, and motor current polarity. The results show that AE is well suited for in-situ monitoring of the brush and rotor conditions.