Transition from Sleeve Bearings to AMBs in 1 MW High-Speed Motor for Turbomachinery – Lessons Learned –

We present a 1 MW high–speed motor featuring a levitating rotor supported by active magnetic bearings (AMBs), addressing an expected growing market demand for oil–free and gearless drives for high–speed turbomachinery. Our internally developed bearing concept leverages our extensive experiences in the field of electrical high–voltage machines, revealing both synergies as well as novel challenges. This article focuses on the lessons learned during the design, manufacturing, and commissioning of these AMBs. We discuss the critical physical boundaries influencing material selection and the trade–offs necessary for manufacturability and the consistency of elements like interference fits. A test run at 15 000 rpm serves as a proof-of-concept, demonstrating the reliability, stability, and vibration levels of the magnetic levitation with overall satisfactory results. However, in the frequency range below 300 Hz we still see room for improvement. Low–frequency housing modes coincide with the broadband excitation of the magnetic bearings causing higher–than–expected vibration amplitudes, although still acceptable. We conclude by proposing enhancements to the bearing controller and emphasize the critical need for structural stiffening of the motor's housing and bearing shield to effectively decouple controllable rotor modes from unavoidable housing vibrations, which is essential for future performance optimization.