Tadashi Tokumasu

3-dimensional electromagnetic analysis and design of an eddy-current rail brake system

This paper describes a method of estimating the braking force of an eddy-current rail brake system using the three-dimensional finite element method. The analyzed braking force characteristics agreed with the measurements and hence the validity of this method was confirmed. This method is used to design the optimum practical rail brake system.

Magnetic field analysis of stator core end region of large turbogenerators

In order to estimate the losses and temperature rise at the end of electrical machines, it is important to clarify electromagnetic behavior in the core end region. In this paper, the method of evaluating the leakage flux of the stator end region of large turbogenerators, combining three-dimensional magnetic field analysis and phasor diagram analysis of the end leakage flux is described. Moreover, the result of applying this method to a 60 Hz-1000 MW turbogenerator is also described.

Simulation for Design Purposes of Magnetic Fields in Turbine-Driven Generator End Region

Flux analysis by the three-dimensional finite element method is applied to the end region design of large-capacity turbine-generators. Analysis has been done considering three-dimensional electric currents of end region windings and anisotropies of iron cores provided at the end regions. It becomes possible to quantitatively evaluate the effects of flux shunts which has been impossible to do with two-dimensional analysis, and to control leakage flux of end regions. Significant informations on the influence of the relative lengths of stator and rotor cores on end region flux and the optimum stator core end design of large-capacity turbine-generators with lower short-circuit are described.

Convergence Acceleration of Time-Periodic Electromagnetic Field Analysis by the Singularity Decomposition-Explicit Error Correction Method

This paper proposes a novel method for the improvement of the convergence to a steady state in time-periodic transient nonlinear eddy-current analyses. The proposed method, which is based on the time-periodic finite element method and the singularity decomposition-explicit error correction method, can extract poorly converged error components corresponding to the large time constants of an analyzed system. The correction of the extracted error components efficiently accelerates the convergence to a steady state. Numerical results verify the effectiveness of the proposed method.

Circulating Currents in Stator Coils of Large Turbine Generators and Loss Reduction

Stator coils transposed by 540deg are widely used as one of the solutions to reduce the circulating current loss in the coil strands of turbine generators. However, the difference of the leakage fluxes in the two coil end parts, which is possibly caused by the coil end length deviation, the winding pitch, and the presence of the connection rings, may induce unbalanced voltage in the stator coil strands, which increase circulating current loss even in the transposition coils. This paper describes the mechanism and the analysis results of the circulating current increase in the coil strands due to the coil end flux difference. Then, some new schemes to reduce the circulating current loss are proposed and discussed.

Air-cooled large turbine generator with multiple-pitched ventilation ducts

On the air-cooled turbine generators, windage loss is the substantial factor of generator losses. One solution for the windage loss reduction is to minimize the amount of coolant air with the multiple-pitched ventilation ducts in the stator core. However, non-uniform duct distribution leads to the circulating currents in the stator bar strands which increase coil losses and cause significant distribution of strand loss. This paper presents circulating currents due to multiple-pitched ventilation ducts and some schemes to reduce the circulating current loss, such as new transposition systems of coil strand

Convergence Acceleration in Steady State Analysis of Synchronous Machines Using Time-Periodic Explicit Error Correction Method

This paper develops the time-periodic explicit error correction (TP-EEC) method for the convergence acceleration to a steady state in transient analysis of synchronous machines. The methods to deal with the movement of the rotor and different time-periodicity in the fixed and moving parts of the mesh are investigated. Furthermore, we propose the novel TP-EEC method based on the polyphase time periodic condition. Numerical results verify the effectiveness of the developed methods.

Eddy current analysis in the stator end structures of large capacity turbine generators

In the stator core end region of the large capacity turbine generators, the leakage magnetic flux induces eddy current loss in the metal structures. In this paper, the results of three-dimensional electromagnetic field analyses of the stator end structures are described. It is demonstrated that the eddy current loss dependency on the power factor can be explained with the phasor diagrams on the magnetic flux. Then the relationship between the end structure and the current source is discussed.

Parallel Time-Periodic Finite-Element Method for Steady-State Analysis of Rotating Machines

This paper investigates the parallelization of the time-periodic finite-element method in nonlinear magnetic field analyses of rotating machines. The developed method, which can obtain the steady state solutions directly, provides large granularity even in the small-scale problems compared with the ordinary parallel FEM based on the domain decomposition approach. Furthermore, we apply the parallel TPFEM to analyses of induction motors which have different time periodicities in stator and rotor regions due to the slip. Numerical results verify the effectiveness of the developed method.

Time-Domain Parallel Finite-Element Method for Fast Magnetic Field Analysis of Induction Motors

This paper investigates the effectiveness of the time domain parallelization in magnetic field analyses of practical electric machines. We propose an efficient procedure to parallelize transient as well as steady-state analyses by generalizing the formulation of the parallel time-periodic finite element method. The proposed method is called the time domain parallel finite element method (TDPFEM) because it can be applied to both transient and steady-state analyses. Additionally, we derive a special condition of the slip to reduce computational costs for steady-state analyses of induction motors by using a half-cycle polyphase time-periodic condition.