Conference Agenda

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Session Overview
PD-M5: Static and Quasi-Static Fields
Friday, 19/Jul/2019:
10:50am - 12:40pm

Session Chair: Karl Hollaus
Session Chair: Ronan Perrussel
Location: Patio 44-55

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Computation of Eddy Losses in a 36 Pulse Rectifier Transformers

Sheppard Salon

RPI, United States of America

Rectifier transformers are growing in size and complexity due to the increased prevalence of large motor drives. In order to reduce the line harmonics, rectifiers with high pulse numbers are now being used. In this paper a 3 phase 36 pulse rectifier transformer is studied to find the extra winding losses produced by high radial flux concentrations between the phase breaks. Non-phase shifting transformers produce mostly axial flux in the window except near the ends of the winding. The size and orientation of the copper strands reduce the eddy current losses. In a rectifier transformer the field distribution is much more complex. A finite element analysis of a 3 phase transformer with a single core design using a delta primary and 18 extended delta secondaries was conducted to identify the losses and their distribution. We also identify the very large variations in eddy current losses which are necessary to determine the hot spot of the winding. A discussion of the effects of the harmonics in the waveform is also included.

Generalized finite element based study on the impact of permanent magnets' imperfections on performance measures of electric machines

Gerd Bramerdorfer

Johannes Kepler University Linz, Austria

This work is about analyzing the impact of permanent magnets’ tolerances on electric machine performance. A generalized model is presented allowing for the analysis of single mmf-harmonics of the permanent excitation or a combination of selected harmonics. The approach can be used both for the standard symmetric case as well as if tolerances are present. It is based on finite element simulations of the machine’s cross section utilizing a thin current layer in the air gap. Results reveal that these investigations can provide general insight in how the harmonics take effect on torque and linked fluxes of the stator coils. Thus, this study can be the basis for evaluating different machine configurations concerning their sensitivity to tolerance-affected permanent magnets.

An H2-LU preconditioner for MQS model based on Integral formulation

Salvatore Ventre1, Bruno Carpentieri3, Gaspare Giovinco1, Antonello Tamburrino1, Guglielmo Rubinacci2, Fabio Villone2

1University of Cassino and Southern Lazio, Italy; 2University of Naples “Federico II”,; 3University of Bolzano, Bolzano

In this paper, an effective numerical technique has been developed for solving MQS problems based on integral formulation. In the past, the authors proposed a compression technique in parallel enviroment, in order to tackle large-scale fully 3D problems. In this paper, the proposed technique is optimized by means of a preconditioner based on LU decomposition of a H2-matrix structure using ad hoc factorization. The results demonstrates that the proposed methodology performs much better than the existing one.

The Working Principle of Flux Switching Machines

Gerd Bramerdorfer1, Wolfgang Gruber1, Andrea Cavagnino2, Silvio Vaschetto2

1Johannes Kepler University Linz, Austria; 2Politecnico di Torino, Italy

This work is about clearly illustrating the working principle of flux switching machines. In the past, different topologies regarding stator-/rotor configurations were presented and evaluated. Moreover, optimization of the operational characteristics was considered. The focus was on optimizing the shape of utilized components. However, the principle of torque generation is not clear at first sight, as typically the number of poles of the magnetic field due to the permanent magnets and due to the winding arrangement are not of same number. The reason for generating a net torque considering an entire period is the flux modulation due to the rotor teeth. A thorough explanation is presented featuring both, theoretical aspects as well as numerical studies utilizing finite element simulations. Results can help to derive general understanding of the working principle and will facilitate the development of new configurations.

On the use of nonlinear complex polyharmonic finite element models of induction motors

Tomasz Garbiec, Mariusz Jagiela, Marcin Kulik

Opole University of Technology, Poland

The application of a nonlinear complex De Gersem - type polyharmonic finite element model in the steady-state analysis of three-phase solid-rotor induction motors is discussed. The effective magnetic permeability dependent on the fundamental time-harmonic of the magnetic field is used for representation of nonlinear effects. A new coupling scheme for the air-gap mesh nodes is proposed in order to make the model even more competitive to the time-stepping model. By means of comparative analysis of computed electromagnetic torque and harmonic losses it is shown that for relatively fine air-gap meshes omitting some nodes at the interface boundary results in reduction of the execution time by the factor of 100 with only slight loss of accuracy.

Prediction of Magnetic Loss inside Silicon Steel Laminations under AC-DC Hybrid Excitation

Xiaojun Zhao1, Jiawen Wang1, Lanrong Liu2, Junwei Lu3, Zhiguang Cheng2, Xiaona Liu1, Danhui Hou1, Yutong Du1

1North China Electric Power University, China, People's Republic of; 2Institute of Power Transmission and Transformation Technology, Baoding, China; 3Griffith University, Australia

Based on the engineering-oriented model TEAM P21C-M1, an experimental platform is established to obtain the magnetic properties and stray-field loss of the grain-oriented silicon steel under practical working conditions. In order to calculate the stray-field loss of magnetic materials under AC-DC hybrid excitation, an improved loss model is presented to investigate the stray-field loss of silicon steel laminations. This model is also used to calculate the magnetic loss of silicon steel laminations excited by 3-D multi-harmonic magnetic field. The stray-field loss of magnetic shielding is separated from the total load loss under AC-DC hybrid excitation and AC excitation, and the conclusion can be drawn that the DC magnetic field increases the magnetic shielding stray-field loss. The proposed modeling method is validated by comparing the calculated results of magnetic field and stray-field loss with the experimental results.

Modelling of Step-Lap Joints using the Harmonic Balance Method

Florian Toth, Dominik Mayrhofer, Klaus Roppert, Manfred Kaltenbacher

TU Wien, Austria

The harmonic balance method is applied to efficiently compute the steady state dynamics of non-linear magnetic systems. As an example problem we use a periodic section of a three phase transformer, where the step-lap joints are modelled in detail. A measurement-based material model is used to incorporate the non-linear, anisotropic behaviour of grain oriented electrical steel. Non-conforming grids are used to efficiently connect dissimilar meshes in air and steel domains.

Application of n-fold Rotational Symmetries to Eddy Currents Integral Model in the Time Domain

Guglielmo Rubinacci2, Antonello Tamburrino1, Salvatore Ventre1, Fabio villone2

1University of Cassino and Southern Lazio, Italy; 2University of Naples “Federico II”, Napoli

Group Theory is a powerful “tool” which has been extensively exploited to reduce the computational cost in numerical analysis of several physical problems, including computational electromagnetics.. This paper proposes the extension of the application of group theory to an integral formulation of the eddy current problems in the presence of n-fold rotational symmetries. The proposed approach is applied to the eddy currents computation in toroidal fusion devices, where rotational symmetries play a key role.

A New Application of Sensitivity Analysis Method to Interpret the Variation of the Mutual-Inductance Effect on FRA Response

Shuhong Wang, Song Wang, Shuang Wang, Hao Qiu

State Key Laboratory of Electrical Insulation and Power Equipment, Xi'an Jiaotong University, Xi'an, China, People's Republic of

Frequency response analysis (FRA) method has been globally accepted as a feasible and reliable technique to detect the inner faults of the transformer winding. As a graphic method, all the important information that reflects the deformation of the winding is hidden in the FRA signatures. Therefore, identifying and interpreting these valuable messages existing in the signatures as much as possible is always our target. This paper tries to provide a quantitative interpretation of the variation of mutual-inductances of a two-winding transformer winding equivalent circuit model effect on FRA response through the sensitivity analysis method. In this paper, firstly, the sensitivities of FRA response to mutual-inductances will be elaborately deducted by Tellegen theorem. Then, the variation laws of the sensitivities of FRA response to the mutual-inductances, including mutual inductances between high voltage (HV) discs, mutual inductances between low voltage (LV) discs and mutual inductances between HV and LV discs, will be investigated. Besides, it is believed that the contributions of this paper will help technicians have a new idea of the mutual-inductances effect on FRA results and enhance their abilities of FRA interpretations.

Combining Domain Decomposition and Model Order Reduction in 2D Simulations of Wireless Power Transfer

Antero Marjamäki, Paavo Rasilo

Unit of Electrical Engineering, Tampere University, Finland

In this paper domain decomposition and model order reduction techniques are combined to efficiently model wireless power transfer setups in which the sending and receiving coils move relative to each other. Domain decomposition is used to decouple the problem into two sub-domains which contain the coils and a master domain which contains the medium and the relative placement. The sub-domains are dictated by the coil design and only the master domain must be modified to vary the relative placement of the coils. Model reduction is used to reduce the amount of degrees of freedom of the sub-domain problems. This approach greatly reduces the overall complexity of the computations.

Fast and Accurate Solution of Integral Formulations of Large MQS Problems Based on Hybrid MPI/OpenMP Parallelization

Francesca Cau1, Andrea Chiariello2, Gaspare Giovinco3, Antonio Maffucci3, Guglielmo Rubinacci4, Pietro Testoni1, Salvatore Ventre3, Fabio Villone4

1Fusion For Energy (F4E), Barcelona; 2University of Campania “Luigi Vanvitelli”, Aversa; 3University of Cassino and Southern Lazio, Italy; 4University of Naples “Federico II”, Napoli

This paper presents an optimized strategy to parallelize the numerical solution of an integral model, based on the combined use of the MPI and OpenMP paradigms. The case-study analysed in this paper is a large 3D magneto-quasi-static problem associated to a real life device, such as the fusion reactor ITER, whose complexity implies a high computational burden, only affordable with parallel computing strategies. The hybrid approach MPI/OpenMP is applied to parallelized clusters of nodes: the job is shared at the node level by using the OpenMP paradigm, whereas the process level between nodes is implemented by using the MPI approach. This hybrid parallelization reduces both the allocated memory and the communication between nodes, thus lowering the demand of the system resources.

Entropy Snapshot Filtering for QR-based Model Reduction of Transient Nonlinear Electro-Quasistatic Simulations

Fotios Kasolis, Markus Clemens

University of Wuppertal, Germany

Approximations of the entropy of a transient nonlinear electro-quasistatic field system induce an ordering of high-fidelity snapshots, in terms of their information content. The resulting ordering enables a direct reduction of the snapshot matrix and hence, a QR-based / SVD-free model reduction framework. Numerical experiments for a three-dimensional surge arrester verify the benefits of the proposed method, both in terms of accuracy and computational effort.

Comparison of Two Electro-Quasistatic Field Formulations for the Computation of Electric Field and Space Charges in HVDC Cable Systems

Christoph Jörgens, Markus Clemens

University of Wuppertal, Germany

Electro-quasistatic (EQS) field simulations are used to calculate electric field and space charge distributions in high voltage direct

current (HVDC) cable systems. The constant voltage results in the accumulation of space charges and a time varying electric field. To

simulate the electric field different EQS formulations are introduced in literature. In a first formulation, the electric field and the space

charge density are updated consecutively via the continuity equation and the electrostatic Poisson equation. In the second EQS

formulation, the continuity formulation is reformulated using the electric scalar potential and only the electric field is updated per time

step. To compare both EQS formulations, the electric fields are simulated in different HVDC cable systems. Simulation results of the

electric field in a cable insulation result in relative errors of less than 2 % between the numerical computation the analytic solution.

Simulation results of a cable joint show instabilities for the field-space charge update EQS formulation, whereas the scalar potential EQS

formulation yield the results.

Effectiveness Evaluation of Dynamic Mode Decomposition for Model Order Reduction of Quasi-Magnetostatic Problems

Sarbajit Paul, Jung-Hwan Chang

Dong-A University, Korea, Republic of (South Korea)

Model order reduction (MOR) is considered as a good alternative to reduce the computational scale for quasi-magnetostatic problems. The aim of this work is to introduce the use of dynamic mode decomposition (DMD) as an promising tool for MOR to

analyze its effectiveness in solving quasi-magnetostatic problems. Using a singualr value decomposition (SVD) based DMD, TEAM problem 21a-0 is analyzed and compared with the full model to ensure the effectiveness of DMD.

Equivalent-Circuit Model for Axisymmetric High-Temperature Superconducting Film: Application to Contactless jC Measurement System and Pellet Injection System

Takazumi Yamaguchi1,2, Teruou Takayama1, Hiroaki Ohtani2,3, Atsushi Kamitani2

1The Graduate University for Advance Studies SOKENDAI; 2Yamagata University, Japan; 3National Institute for Fusion Science

An equivalent-circuit model (ECM) is proposed for analyzing the shielding current density in an axisymmetric high-temperature superconducting (HTS) film. It is applied to not only the simulation of two contactless measurement systems of the critical current density but also that of a pellet injection system. As a result, it is found that the ECM is an effective tool for analysis of the shielding current density in axisymmetric HTS devices.

Modelling Nonlinear Steady State Induction Heating Processes

Klaus Roppert, Florian Toth, Manfred Kaltenbacher

Institute of Mechanics and Mechatronics, TU Wien, Vienna, Austria

In this work, an efficient simulation strategy for a fully coupled nonlinear magnetic thermal problem is presented. The solution dependent magnetic subproblem is solved with a harmonic balancing scheme, with the main focus on the correct choice of the material model (magnetization curve). Exploiting scale separation between magnetic and thermal time scales, the nonlinear thermal problem can be considered in transient as well as steady state case. To further increase computational efficiency, a non-conforming interface approach is used, based on jump operators and penalty terms. Furthermore, different types of excitations are investigated, including eddy currents in inductors, based on a power balance approach.

Cauer Ladder Network Representation of Multi-Turn Coil Considering Skin and Proximity Effect

Kengo Sugahara1, Hassan Ebrahimi2, Akihisa Kameari2, Tetsuji Matsuo3, Tadashi Tokumasu4, Yuji Shindo5

1Kindai University, Japan; 2Science Solutions International Laboratory; 3Kyoto University; 4Toshiba Infrastructure Systems & Solutions Corporation; 5Kawasaki Heavy Industries, Ltd.

This paper proposes Cauer Ladder Network (CLN) representation of multi-turn coil considering skin and proximity effect. When native finite-element method is applied on the analysis of multi-turn coils, each wire has to be subdivided into sufficiently fine elements and requires long computation time. Therefore, semi-analytical approach for multi-turn coil combined with homogenization method has been proposed to reduce the computational resources. Aside from the semi-analytical approach, a novel and effective model order reduction method, called CLN method, has also been proposed in which linear quasi-static electromagnetic fields are expressed by a linear combination of a sequence of static electric and magnetic field modes. In this paper, we combine the semi-analytical approach and the CLN method to analyze multi-turn coils with high-order coupling between each wire.

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