Sung-Chin Hahn

Experimental Verification and Finite Element Analysis of Short-Circuit Electromagnetic Force for Dry-Type Transformer

The short-circuit force induces critical mechanical stress on a transformer. This paper deals with experimental verification and finite element analysis (FEA) for short-circuit force prediction of a 50 kVA dry-type transformer. We modeled high voltage (HV) winding into 20 sections and low voltage (LV) winding into 22 sections as similar as those windings of a model transformer. With this modeling technique, we could calculate electromagnetic forces acting on each section of the windings of a dry-type transformer under short-circuit condition. The magnetic vector potentials, magnetic flux densities, and electromagnetic forces due to short-circuit current are solved by FEA. The electromagnetic forces consisting of radial and axial directions depend both on short-circuit current and leakage flux density. These results were used as input source of sequential finite element method (FEM) to predict the resultant mechanical forces considering the structural characteristics such as stress distributions or deformations of windings, accurately. The obtained resultant mechanical forces in HV winding are compared with those of the experimental ones.

Finite-Element Analysis of Short-Circuit Electromagnetic Force in Power Transformer

Transient electromagnetic forces in radial and axial directions induce critical mechanical stress on windings and transformers. In this paper, short-circuit electromagnetic forces that are exerted on transformer windings are investigated. A 3-D transformer model is considered to calculate the transient electromagnetic forces. The magnetic vector potential, magnetic flux density, and electromagnetic forces due to the short-circuit transient currents applied to the power transformer are analyzed by a coupled electromechanical finite-element method. The results obtained are compared with the analytical results and show good agreement. The numerical modeling technique dealt with in this paper is expected to be useful in the design of power transformers.

Coupled finite-element-analytic technique for prediction of temperature rise in power apparatus

In order to design the power apparatus such as bus bar or power cable, the current carrying capacity (or ampacity) should be determined exactly since it is limited by maximum operating temperature. The temperature rise in the power apparatus is due to Joules loss in the current carrying conductor and due to the induced eddy current in the tank. This paper presents a new technique that can be used to estimate the temperature rise in the extra high voltage bus bar. In this paper, the power losses are calculated from the magnetic field analysis for various materials when ac current flows into the single- and three-phase bus bar and are used as the input data to predict temperature rise for the thermal analysis. However, it is not easy to apply the heat transfer coefficient on the boundaries correctly, because the coefficient is not a constant, but depends on temperature as well as model geometry, etc. The heat transfer coefficient is calculated according to the model geometry and varying temperature and is coupled with the finite element method. The temperature distribution in the bus bar by proposed method shows good agreement with the experimental data, compared to that of the analytic method using fixed coefficient.

Static characteristics of linear BLDC motor using equivalent magnetic circuit and finite element method

This paper presents the static characteristics of the linear BLDC motor. An equivalent magnetic circuit model is derived for the prototype motor. The air-gap flux density is calculated using the equivalent magnetic circuit and compared with results from finite element analysis. The thrust force is measured for the prototype motor and is also compared with those from derived circuit model and FEA. These values agree well to show the validity of the equivalent circuit model. Using this equivalent circuit model, the thrust force density variation according to change of coil width to pole pitch can be expected at the design stage.

Optimal Design of Direct-Driven PM Wind Generator for Maximum Annual Energy Production

Optimal design of the direct-driven PM wind generator, coupled with finite element analysis and genetic algorithm, has been performed to maximize the annual energy production over the whole wind speed characterized by the statistical model of wind speed distribution. Particularly, the parallel computing via internet web service has been applied to loose excessive computing times for optimization.

Optimal Design of a Direct-Driven PM Wind Generator Aimed at Maximum AEP using Coupled FEA and Parallel Computing GA

Optimal design of the direct-driven Permanent Magnet (PM) wind generator, combined with FE. A (Finite Element Analysis) and Genetic Algorithm (GA), has been performed to maximize the Annual Energy Production (AEP) over the entire wind speed characterized by the statistical model of wind speed distribution. Particularly, the proposed parallel computing via internet web service has contributed to reducing excessive computing times for optimization.

An efficient investigation of coupled electromagnetic-thermal-fluid numerical model for temperature rise prediction of power transformer

This paper deals with coupled electromagnetic-thermal-fluid analysis for temperature prediction of a power transformer. Electric power losses are calculated from finite element method (FEM), and are used as input source of thermal-fluid analysis based on computational fluid dynamics (CFD). In order to accurately investigate the temperature distribution in a power transformer, the thermal problem should be coupled with the electromagnetic problem. The coupling method proposed in this paper is compared with the experimental values for verifying the validity of the analysis. The predicted temperatures show good agreements with the experimental values.

Finite element analysis of short circuit electromagnetic force in power transformer

The electromagnetic forces acting upon the transformer windings are calculated by numerical analysis in this paper. The electromagnetic forces consisting of radial and axial directions induce the injurious mechanical stress to windings as well as transformer itself. 3-Dimensional power transformer model by finite element analysis is considered to calculate the electromagnetic forces. The magnetic vector potential, magnetic flux density and electromagnetic forces of the power transformer are calculated numerically, and the results are compared with the analytical results.

Multi-physics Analysis for Temperature Rise Prediction of Power Transformer

In this paper, a method for multi-physics analysis of the temperature-dependent properties of an oil-immersed transformer is discussed. To couple thermal fields with electromagnetic and fluid fields, an algorithm employing a user defined function (UDF) is proposed. Using electromagnetic analysis, electric power loss dependent on temperature rise is calculated; these are used as input data for multi-physics analysis in order to predict the temperature rise. A heat transfer coefficient is applied only at the outermost boundary between transformer and the atmosphere in order to reduce the analysis region. To verify the validity of the proposed method, the predicted temperature rises in high-voltage (HV) and low-voltage (LV) windings and radiators were compared with the experimental values.

Characteristic analysis of high-speed Interior Permanent Magnet Synchronous Motor

This paper present characteristic analysis of high-speed Interior Permanent Magnet Synchronous Motor(IPMSM). Single-layer buried permanent magnet type and multi-layer type are modeled and investigated. Finite element analysis method is used to obtain the magnetic flux distributions of IPMSM. Parameters of IPMSM such as d-q axis inductances and torque curve are calculated and compared.