### Objective

Topology | Squirrel Cage Induction Machine (SCIM) |
---|---|

Model Types | Permeance / mmf electromagnetic model EM1.SCIM Analytical structural model [SM.ANL Analytical acoustic model AC1 |

Quantities | Sound power level during run-up (SWL) |

Geometry | Internal Rotor _Semi closed slots |

Winding | Shorted pitch distributed winding |

The aim of this validation case is to compare MANATEE results (obtained in a few seconds of computation with permeance/mmf model) with accurate experimental tests run in a semi-anechoic chamber using ISO 3744 standard to calculate the sound power level radiated by a traction induction motor.

### Machine

The studied machine is a traction squirrel cage induction machine with p=2 pole pairs, Zr=38 and Zs=48 stator slots.

### Results

The following graph favorably compares the calculation of natural frequencies with 2D FEA used in the article [R1]. For variable speed applications the accuracy on natural frequencies is less important, but if necessary MANATEE can be directly coupled to structural FEA for the computation of natural frequencies and Frequency Response Functions.

The next graph compares the calculation of the sound power level with MANATEE and during tests (run-up at no load). Measured noise including mechanical, aerodynamic and magnetic acoustic noise sources. At high speed, acoustic noise level is driven by aerodynamic noise due to fans. Aerodynamic noise is not calculated by MANATEE which explains the difference between MANATEE and tests. One can observe that two strong resonances occur close to 1250 rpm in tests, while only one resonance is observed in MANATEE simulation. This is probably due to the fact that the analytical model considers a cylindrical symmetrical stator, whereas the real machine is asymmetrical which leads to double structural modes. Another explanation could be the excitation of a secondary longitudinal mode which is not included in this MANATEE simulation based on 2D analytic models.
However, the strong resonance is correctly predicted by MANATEE and the noise level given by MANATEE is close from experiments. This means that **MANATEE can be efficiently use in the early electromagnetic design process to avoid this type of vibro-acoustic resonance**.
In that particular case the resonance is due to saturation effects which introduce a excitation force of wavenumber 2=Zs-Zr-4p, resonating with the stator stack elliptical mode m=2.

### References

[R1] Nguyen, M. K., (2014). Predicting Electromagnetic Noise in Induction Motors, Master’s Thesis, Royal Institute of Technology of Stokholm, Sweden.