A Possible Method for Magnetostrictive Reduction of Vibration in Large Electrical Machines

This paper introduces a magnetic bimorph concept as a means of manipulating magnetostriction in the stator teeth so that components of magnetostrictive force act to cancel out selected components of Maxwell force. This leads to zero net electromagnetic excitation of targeted vibration modes and reduces the vibration and resultant noise emission from the machine. The proposed noise reduction technique is suitable for large electrical machines with vibration modes that experience tooth rocking at natural frequencies within the range of acoustic interest. Experimental and finite-element investigations illustrate that this concept is a practical and low-cost method to implement without degrading the performance of the machine. A finite-element investigation has shown that the contributions to vibration of a large electrical machine from Maxwell forces in the air gap and the magnetostriction effect in the stator iron are comparable. Magnetostriction can act either to reduce or increase the overall modal excitation compared to the excitation of Maxwell forces.