Analysis of rotary transformer concepts for high-speed applications

In many applications electrical energy has to be transferred to rotating parts. Usually a cylindrical transformer with a rotating and a stationary part is used, which are separated by a small air gap. In order to achieve a high magnetic coupling, on both parts a highly permeable core material is employed. In high-speed applications the diameter of the rotary transformer should be small since the mechanical stresses can be high. Therefore, a high electrical frequency has to be selected. This high switching frequency would result in high core losses; ferrite would be the best suited material. However, ferrite is brittle and has a limited mechanical strength. Therefore, in this paper two concepts of rotary transformers are analyzed, where no core material is used on the rotating part. The major advantage of these concepts is a simple and mechanically robust design with a lightweight construction resulting in very small unbalanced mass.