Abstract
Within large turboalternators, the excessive local temperatures and spatially distributed temperature differences can accelerate the deterioration of electrical insulation as well as lead to deformation of components, which may cause major machine malfunctions. In order to homogenise the stator axial temperature distribution whilst reducing the maximum stator temperature, this paper presents a novel non-uniform radial ventilation ducts design methodology. To reduce the huge computational costs resulting from the large-scale model, the stator is decomposed into several single ventilation duct subsystems (SVDSs) along the axial direction, with each SVDS connected in series with the medium of the air gap flow rate. The calculation of electromagnetic and thermal performances within SVDS are completed by finite element method (FEM) and computational fluid dynamics (CFD), respectively. To improve the optimization efficiency, the radial basis function neural network (RBFNN) model is employed to approximate the finite element analysis, while the novel isometric sampling method (ISM) is designed to trade off the cost and accuracy of the process. It is found that the proposed methodology can provide optimal design schemes of SVDS with uniform axial temperature distribution, and the needed computation cost is markedly reduced. Finally, results based on a 15 MW turboalternator show that the peak temperature can be reduced by 7.3 °C (6.4%). The proposed methodology can be applied for the design and optimisation of electromagnetic-thermal coupling of other electrical machines with long axial dimensions.
Highlights
In recent years, the research on electrical machines has gradually become increasingly integrated, comprehensive, and synergistic, expanding from a single physical field to multiple physical fields, including electromagnetics, thermal, noise, and structure
Under pre-set constraints, the width of the iron core segment and the width of the radial ventilation duct of single ventilation duct subsystems (SVDSs) were optimized within the design space to reduce the maximum temperature of the stator
The grey dots in the figure represent the uniform duct dimensions within the original alternator of Figure 8. It was evident from the optimization results that the trend of the iron core segment widths along the axial direction was opposite to the trend of the radial ventilation duct widths
Summary
The research on electrical machines has gradually become increasingly integrated, comprehensive, and synergistic, expanding from a single physical field to multiple physical fields, including electromagnetics, thermal, noise, and structure. For many lower speed applications, the main design limits are usually considered to be a combination of electromagnetic and thermal [1]. Both these physical fields are deeply coupled with the characteristics interacting with each other. The losses generated by the electromechanical conversion process will raise the temperature. The increase in temperature increases the resistance losses due to the positive temperature coefficient of resistivity. The steady-state temperature of the motor is the result of a balance between the generation and dissipation of heat, the cooling system being the decisive factor
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