Ranran Lin

Calculation and Analysis of Stator End-Winding Leakage Inductance of an Induction Machine

This paper proposes an improved method for calculating the value of and for analyzing the frequency-dependence of the stator end-winding leakage inductance of an induction machine. The method was based on the stored magnetic energy, which was calculated by a 3-D time-harmonic finite element analysis. In this method, there were no rotary parts in the model of the simulated machine. The results of the analysis show that the stator end-winding is capable of influencing the end of the active region of the machine whereas the influence on the central part of the active region is small. In addition, the phenomenon that the stator end-winding leakage inductance, as well as the magnetic energy in the machine, relates to the frequency of the stator current is explored.

End-Winding Vibrations Caused by Steady-State Magnetic Forces in an Induction Machine

We conducted a 3-D electromagnetic analysis coupled with a 3-D mechanical analysis to analyze end-winding vibrations and deformation in an induction machine caused by steady-state magnetic forces on the end winding. Both the analyses were based on the finite-element method. The electromagnetic analysis was used to calculate magnetic forces. During the mechanical analysis, complex support structures in the end region were simplified. We first updated and validated the mechanical model according to a modal model obtained from a modal test, and afterward analyzed deformation, vibrations, and stresses. According to the analysis, the shape of the rotary dynamic deformation of the end winding caused by dynamic forces is similar to the most excitable mode shape though the natural frequency of that mode is much higher than the excitation frequency. The static deformation caused by static forces tends to expand the coil ends outward. Under both types of deformation, the nose portion of the coil ends experiences larger displacement, but von Mises stresses are larger mainly in the knuckle portion.

Analysis of Eddy-Current Loss in End Shield and Frame of a Large Induction Machine

This paper proposes an effective method of analyzing the eddy-current loss within the end shield and frame of an electric machine. The standard impedance boundary condition is applied to the conducting surfaces of complete 3-D models, and the models are solved by time-harmonic finite-element analyses. Measurement of the temperature rise is completed as a validation of the proposed method. The effect of the distances between the conducting surfaces and coil ends is studied by computing the eddy-current loss for a series of 3-D models having different distances. In addition, simplified 2-D models are used to study the influence of material nonlinearity. In brief, the proposed method is feasible in computing the eddy-current loss. The eddy-current loss within the regions close to the coil ends is larger than the other regions in the end shield and frame, but the total loss is quite small, compared, for instance, with the copper loss within the stator winding. Furthermore, the farther the end shield and frame are from the coil ends, the smaller the eddy-current loss is. Finally, it is found that the eddy-current loss is larger in the nonlinear case than in the linear case.

Axial Flux and Eddy-Current Loss in Active Region of a Large-Sized Squirrel-Cage Induction Motor

This paper analyzes the axial flux and the corresponding eddy currents inside the laminated cores of a large-sized squirrel-cage induction motor running under the steady-state operation in order for possible optimum design of large-sized induction motors used in industry. The analysis was based on a complete 3-D numerical model. In the model, the laminated cores were replaced by anisotropic solid bodies, and the eddy currents inside the end portion of the stator frame were modeled with the standard impedance boundary condition. A time-harmonic finite-element analysis based on the magnetic vector potential-electric scalar potential formulation was performed. According to the results, under steady-state no-load, the axial flux, caused mainly by the air-gap fringing flux and the end-winding leakage flux, appears in the end portion of the cores, and decays rapidly toward the middle of the cores. The corresponding planar eddy currents inside the laminations of the stator core are mainly concentrated near the edges of the stator teeth. The eddy-current loss is small, but the distribution of the loss over the laminations is definitely non-uniform.

3-D Finite Element Analysis of Magnetic Forces on Stator End-Windings of an Induction Machine

This paper aims to analyze the magnetic forces on the stator end-windings of an induction machine at full load by a 3-D time-harmonic finite element analysis. Under the steady-state condition, the radial, circumferential, and axial forces all consist of a constant component and a sinusoidal component with a double-frequency. The analysis shows that the forces on the knuckle part of the upper part of a coil end are larger than on the other parts and that the constant components and the amplitudes of the sinusoidal components of the forces on the same positions of different coil ends in a phase belt are nearly different. Finally, the analysis of stresses indicates that the stresses in a coil end, corresponding to the constant components of the forces, are small.

Validation of a Time-Harmonic Numerical Model for Solving Magnetic Field in End Region of a Radial-Flux Machine

We present an analysis of the magnetic field in the end region of a radial-flux rotating machine. In numerical simulations, we used three familiar boundary conditions to replace the modeling of the end shields and frame. We made measurements for comparison, and the simulation results were quite consistent with the measurements. Our analysis shows that the eddy current in the end shields and frame influences the magnetic field in the end region slightly and that the use of a homogeneous Neumann boundary condition or a standard impedance boundary condition (SIBC) to replace the end shields and frame can solve the magnetic field in the end region more accurately than a homogeneous Dirichlet boundary condition. Validation by the measurements demonstrates that 3-D current-driven time-harmonic model with suitable boundary conditions can be used to solve the magnetic field in the end region quite accurately.

A 3-D magnetostatic analysis and calculation of parameters in end region of an induction machine

This paper illustrates effective procedure and methods for both analyzing the magnetic field and calculating the relevant parameters in the end region of an induction machine used in the power system, by some numerical simulations on the basis of a 3-D magnetostatic model. The leakage self-inductance of the stator end coil is estimated by calculating the relevant flux and energy, respectively. The distribution of the magnetic energy and air-gap fringing flux in the end region is demonstrated as well. The magnetic forces exerted on the stator end coil, in addition, are studied and calculated. These results can be used in the estimation for transient conditions and in the improvements of the supports of end coils in large electric machines in the power system.