Study of the Combined Effects of the Air-Gap Transfer for Maxwell Tensor and the Tooth Mechanical Modulation in Electrical Machines

The Maxwell Tensor (MT) method is widely used to compute global forces or local surface forces for vibroacoustic design of electrical machines under electromagnetic excitation. In particular, the air-gap MT method is based on a cylindrical shell in the middle of the air gap. This article proposes to quantify the differences between the air-gap MT and the magnetic force wave experienced by the stator. In particular, the air gap to stator transfer and the tooth mechanical modulation effects are studied. A new formula is proposed to extend the tooth modulation effect to tangential forces. A numerical application is performed with a turbo-alternator to illustrate the respective and combined effects of both phenomena. This article highlights that the tooth mechanical modulation is relevant even for electrical machines with a high number of teeth. In addition, the combination of the two phenomena has a clear impact on the calculated surface force. Therefore, it is recommended to take into account the air-gap transfer for any study of the tooth mechanical modulation effect.