Hisashi Mogi

Eddy Current Analysis Considering Lamination for Stator Core Ends of Turbine Generators

In this paper, we introduce a calculation method for in-plane eddy currents produced by perpendicular flux at stator core-ends of turbine generators. In the method, the laminated core is subdivided into each electrical steel sheet by 3-D finite elements. The insulated layers of the sheets are modeled by the gap elements, which represent the magnetic resistance of the layers. The combination method of double nodes and anisotropic conductivity is proposed to consider the insulation between the steel sheets. It is especially required for the stator teeth with slits. The validity of the calculation method is verified by comparing the measured and calculated results in the case of a simple model that simulates the end part of the turbine generator. The method is also applied to the real machine to clarify the eddy current distribution.

Harmonic analysis of AC magnetostriction measurements under non-sinusoidal excitation

A new system for analyzing ac magnetostriction of electrical steel sheets, has been developed. This system has the following advantages: (a) AC magnetostriction waveforms can be precisely measured up to 4 kHz, and analyzed to harmonic components. (b) Non-sinusoidal flux density can be excited to simulate the distorted waveform in an actual transformer core.

AC magnetostriction hysteresis and magnetization direction in grain oriented silicon steel

A hysteresis curve of AC magnetostriction was measured, magnetizing a grain oriented silicon steel in the direction deviated from rolling direction of the sample. The AC magnetostriction curves were analyzed as harmonics in the interest of noise spectrum of such as a power transformer. The domain structure model in this magnetostriction process was proposed. The hysteresis was large in the magnetization direction inclined at 30 and 90/spl deg/ from the rolling direction.

In-plane eddy current analysis for end and interior stator core packets of turbine generators

This paper describes analyses of in-plane eddy currents, which are generated by the perpendicular flux at both of end and interior stator core packets of turbine generators. The 3-D finite element method considering lamination of the electrical steel sheets is applied to the calculation. The validity of the analysis is examined by a simple apparatus that simulates the stator core of the turbine generator. It is clarified that the in-plane eddy currents are generated not only at the end stator packets, but also at the interior packet due to the duct space. It is also clarified that the in-plane eddy current loss decreases as nearly half by the slits of the stator teeth.

In‐plane eddy current analysis for end and interior stator core packets of turbine generators

Purpose – The purpose of this paper is to investigate the distribution of in‐plane eddy currents in stator core packets of turbine generators, and to reveal the loss reduction effect by the slits in the stator teeth.Design/methodology/approach – The in‐plane eddy currents are calculated by a 3D finite element method that considers lamination of electrical steel sheets. First, this method is applied to a simple model that simulates the stator core of the turbine generators. The calculated losses are compared with the measured losses in order to confirm the validity. Next, the same method is applied to a 250 MVA class turbine generator.Findings – The validity of the calculation method is confirmed by the measurement of the simple model. By applying this method to the turbine generator, it is clarified that the considerable in‐plane eddy currents are generated not only at the end stator packets, but also at the top of the teeth of the interior packets due to the duct space. It is also clarified that the in‐p...

Estimation of iron loss distribution by image Helmholtz equation method

This paper proposes the image Helmholtz equation method to visualize iron loss distribution of magnetic materials. The Helmholtz-type equations carry out dynamic image analysis of a series of distinct magnetized domain images. The domain images derive the state transition matrices of which imaginary parts correspond to the phase lag components of magnetization. In the present paper, iron loss distribution of a grain-oriented electrical steel is studied by utilizing its scanning electron microscope (SEM) images. The result of analysis visualizes iron loss generating parts reflecting on the magnetic domains. Moreover, the solution of image Helmholtz equation demonstrates computing magnetization curves, which agree well with the experimental result.