Abstract
High-speed electric machines are gaining importance in the field of traction drives and aviation due to their high power density. The evaluation of the mechanical stress in the rotor is one crucial part in the design process for this type of machines. The mechanical stress cannot be measured directly. Accordingly, a validation of the calculated mechanical stress is difficult and normally not performed. Instead of the mechanical stress, the deformation at the rotor surface can be measured using a spin test machine with distance sensors. The deformation can then be used to validate the calculation results.In this paper, the mechanical load exerted on an IM rotor for a 60,text{kW}/20000,frac{1}{text{min}} high-speed electric machine and an PMSM rotor for a 75~text{kW}/25000,frac{1}{text{min}} high-speed electric machine is analysed in detail. The mechanical stress and the deformation are calculated and analysed using a FEM simulation model. Then, a spin test is performed on the two rotors. First, the burst speed is determined by operating two rotor samples above their defined test speed. Then, the deformation is measured at the rotor surface for different operating speeds and the defined test speed. The measurement and the simulation results are compared and discussed.It can be shown that the two designs do not exceed the maximum mechanical stress for the defined operating range. In the deformation measurement of the IM rotor, a plastic deformation up to varepsilon _{text{IM, pl}} = 8 μm and elastic deformation up to varepsilon _{text{IM, el}}=22 μm can be seen. In regards to plastics, PMSM rotor expands up to varepsilon _{text{PMSM, pl}}= 5 μm. The maximum elastic deformation of the PMSM rotor is varepsilon _{text{PMSM, el}}=40 μm. The comparison of the calculated and the measured elastic deformation shows good accordance for the two rotor types. Both models are capable of describing the deformation and the state of stress in the rotors. In burst tests, both rotors withstand rotational speeds far above the defined test speed.
Highlights
High speed electric machines are gaining importance for applications such as machine spindles, turbochargers and pumps, and for traction drive applications for vehicles and aviation [1,2,3,4]
The mechanical stress cannot be measured directly. This measurement method is applied to two different rotor types of a high speed electric machine and the results are compared to the results of the mechanical FEM simulation models
The burst tests of the IM and the Permanent Magnet Synchronous Machine (PMSM) rotor are made to validate the mechanical strength of the rotors
Summary
High speed electric machines are gaining importance for applications such as machine spindles, turbochargers and pumps, and for traction drive applications for vehicles and aviation [1,2,3,4]. The mechanical stress cannot be measured directly In this work, this measurement method is applied to two different rotor types of a high speed electric machine and the results are compared to the results of the mechanical FEM simulation models. The materials are just modelled for the elastic case since the rotors should be high-fatigue-resistant and no plastic deformation should occur. To avoid material failure and according to ensure a high fatigue resistance of the rotors, the maximum mechanical stress occurring during the operation of an electric machine should always be in the elastic area. Simulation model the FEM simulation models of the PMSM and the IM rotor are introduced They are used in order to calculate the deformation and the mechanical stress due to centrifugal forces and thermal expansion. A cylindrical bearing is assigned to enable the rotation
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