Browsing by Author "Belahcen, Anouar, D.Sc., Aalto University, Finland"

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Finite-Element Modeling and Calorimetric Measurement of Core Losses in Frequency-Converter-Supplied Synchronous Machines
(2012) Rasilo, Paavo
School of Electrical Engineering | Doctoral dissertation (article-based)
This thesis deals with the modeling and measurement of core losses in salient-pole wound-field synchronous machines. A numerical iron-loss model for ferromagnetic core laminations has been implemented to be used within the 2-D finite-element (FE) analysis of electrical machines. The developed model combines existing models for eddy currents, magnetic hysteresis, and excess eddy-current losses in the laminations. These losses are globally coupled to the FE solution of the magnetic field in the 2-D cross-section of an electrical machine. Numerical results obtained with the iron-loss model show that the hysteresis losses can be neglected from the FE field solution without a significant loss of accuracy in order to improve the convergence properties of the model and to speed up the computation. Coupling of the eddy-current losses and the related skin-effect phenomenon to the FE solution is more essential to predict the losses correctly, especially on the rotor side. The numerical model is applied to minimize the total electromagnetic losses by modifying the shape of the rotor pole shoe. A calorimetric measurement system has been designed and built for experimental determination of the core losses. A 150-kVA synchronous generator is used as the test machine in the measurements, and its core losses are determined both with grid and inverter supply as a function of the load. Three prototype rotors identical in geometry but stacked of 0.5-mm insulated silicon-iron (Fe-Si) sheets and 1-mm and 2-mm uninsulated steel plates are used in the tests. According to the measurement results, the losses in the rotors stacked of the thicker sheets increase much more severely as a result of loading and inverter supply than those in the Fe-Si rotor. When compared to the measurement results, the numerical model proves to estimate the core losses sufficiently, especially in the case of the 0.5-mm Fe-Si rotor. The modeling of the uninsulated laminations is found to be more challenging, since these may conduct currents also in the axial direction. The losses in the steel frame around the stator core are found to be extremely significant with voltages above the rated value. It is concluded that the 2-D model is also a suitable method to estimate the frame losses.