Electromagnetic Fields in Electrical Engineering

This book is the collection of the contributions offered at the International Symposium on Electromagnetic Fields in Electrical Engineering, ISEF '87, held in Pavia, Italy, in September 1987. The Symposium was attended by specialists engaged in both theoretical and applied research in low-frequency electromagnetism. The charming atmosphere of Pavia and its ancient university provided a very effective environment to discuss the latest results in the field and, at the same time, to enjoy the company or colleagues and friends coming from over 15 countries. The contributions have been grouped into 7 chapters devoted to fundamental problems, computer programs, transformers, rotating electrical machines, mechanical and thermal effects, various applications and synthesis, respectively. Such a classification is merely to help the reader because a few papers could be put in several chapters. Over the past two decades electromagnetic field computations have received a big impulse by the large availability of digital computers with better and better performances in speed and capacity. Many various methods have been developed but not all of them appear convenient enough for practical engineering use. In fact, the technical and industrial challenges set some principal attributes and criteria for good computation methods. They should be relatively easy to use, fit into moderately sized computers, yield useful design data, maintain flexibility with m1n1mum cost in time and effort.

1. Fundamental Problems.- Introductory Remarks.- Power Losses in Electrotechnical Sheet Steel under Rotational Magnetization.- AC High Magnetic Field Generation Due to Eddy-Current Concentration Effect.- Scalar Potential Models for Magnetic Fields of Volume Current Distributions.- The Electrodynamics of Ampere and Neumann.- A Contribution to the Theory of Skin-Effect.- 2. Computer Programmes.- Theoretical aspects.- Introductory Remarks.- Impedance and Losses in Magnetic Cylindrical Conductors.- Errors of Solution of Classical and Variational Finite Difference Method Applied to Transient Electromagnetic Field Analysis.- Analysis of Electromagnetic Shielding Problems Using the BEM.- The Use of the Boundary Element Method in Transient Open Boundary Problems.- Calculation of Electric and Magnetic Field by Means of the Method of Tubes and Slices.- Practical Use.- Introductory Remarks.- Perturbation Finite Element Method of Electromagnetic Field Calculation for Eddy-Current Coupling.- Macro-Element in Cartesian Coordinates.- Analysis of Transients in Electrical Circuits Containing Initially Magnetized Ferromagnetics for Impulse Excitation.- 3-D Reactance Calculation of Air-Core Coils with Magnetic Screening.- 3. Transformers.- Introductory Remarks.- A Method for Losses Evaluation in Large Power Transformer Tanks.- The FEM Analysis of Magnetic Field in Converter Transformers During Faults.- Additional Losses in Frequency Tripler Windings.- Stray-Load Losses in Yoke-Beams of Transformers.- Influence of Structure Geometry, Screens and Eddy Currents on the Critical Distance of Tank Wall in Power Transformers.- Numerical Analysis of Inrush Currents in Transformers.- Improvement of Transformer Core Loss by Use of Low-Loss Electrical Steel.- Currents and Forces in Conductors of Rectangular Cross Section.- 4. Electrical Machines.- Synchronous Machines, DC and Linear Motors.- Introductory Remarks.- Magnetic Shielding of Turbo-Generator Overspeed Test Tunnels.- An Equivalent Circuit Model for Inverter-Fed Synchronous Machines.- Magnetic Field and Force of Linear Induction Motor Fed from Non-sinusoidal Source.- Electromagnetic Parameters of a Turbogenerator Determined by the Finite Element Calculation.- Analysis of the Implications of Main Field Entities on Commutation in Field-Regulated.- Induction Machines.- Introductory Remarks.- Coupling of the Finite Element and Boundary Element Methods by Iterative Technique.- Effect of Magnetic Saturation on the Air-Gap Flux Density Wave in Polyphase Induction Machines.- Hybrid Simulation of Electromagnetic Field in Squirrel-Cage Winding.- Induction Machine with Anisotropic Multilayer Rotor Modelling the Electromagnetic and the Electrodynamic States of a Symmetrical Machine with Deep Bar Cage in Solid Iron Rotor Core.- Peculiarities of Electromagnetic Field in Slots.- 5. Mechanical And Thermal Effects.- Introductory Remarks.- Numerical Analysis of Effect of Material and Structural Parameters on Magnetic Bearing Performance.- The Finite Element Method Solution for the Stationary Two-Dimensional Thermal Problem.- Force Calculation in Electromagnetic Devices.- Electromagnetic Fields and Forces in a Linear Induction Motor During Direct Current Braking.- Numerical Analysis of Electromagnetic and Temperature Fields in Induction Heated Ferromagnetic Slabs.- 6. Various Applications.- Introductory Remarks.- Computer-Aided Modelling and Simulation of Fast Transient Phenomena in Large Coils.- Remote Electromagnetic Propulsion in the Presence of a Metallic Shield.- Application of the Harmonic Analysis Technique to Determining Eddy Currents in Conducting Plates.- Numerical Field Calculation of Earthing Systems.- Computer-Aided Design Technique for Proportional Electromagnets.- Reluctance Network Analysis of Coupled Fields in a Reversible Electromagnetic Motor.- 7. Synthesis.- Introductory Remarks.- The State of Art in the Synthesis of Electromagnetic Fields.- Comparative Analysis of Numerical Methods for Shape Designing.- Synthesis of a Turbo-Generator Nonlinear Parametric Model for the Analysis Problems of Power Industry Systems Regimes.