Electrical Steels: Volume1: Fundamentals and basic concepts

Description

Electrical steels are critical components of magnetic cores used in applications ranging from large rotating machines, including energy generating equipment, and transformers to small instrument transformers and harmonic filters. Presented over two volumes, this comprehensive handbook provides full coverage of the state-of-the-art in electrical steels. Volume 1 covers the fundamentals and basic concepts of electrical steels. Topics covered include soft magnetic materials; basic magnetic concepts; magnetic domains, energy minimisation and magnetostriction; methods of observing magnetic domains in electrical steels; electromagnetic induction; fundamentals of a.c. signals; losses and eddy currents in soft magnetic materials; rotational magnetisation and losses; anisotropy of iron and its alloys; magnetic circuits; the effect of mechanical stress on loss, permeability and magnetostriction; magnetic measurements on electrical steels; background to modern electrical steels; production of electrical steels; amorphous and nano-crystalline soft magnetic materials; nickel-iron, cobalt-iron and aluminium-iron alloys; consolidated iron powder and ferrite cores; and temperature and irradiation dependence of magnetic and mechanical properties of soft magnetic materials. The companion Volume 2 describes performance and outlines applications. Cover Contents Acknowledgements Preface Common acronyms, symbols and abbreviations used in the text Introduction to Volume 1 About the authors 1 Soft magnetic material 1.1 Range and application of commercial bulk magnetic materials 1.2 Industrially important characteristics of soft magnetic materials 1.3 Families of commercial soft magnetic materials 1.4 Electrical steels 1.5 Global impact of energy wastage in electrical steels References 2 Basic magnetic concepts 2.1 Magnetic fields, flux density and magnetisation 2.1.1 Magnetic field (H) 2.1.2 Magnetic dipole moment (m) 2.1.3 Magnetic polarisation (J) 2.1.4 Magnetic flux density (B) 2.1.5 Permeability (µ) 2.1.6 Relationships between H, B and M 2.1.6.1 Hysteresis models 2.1.7 Demagnetising effects 2.2 Units in magnetism 2.3 Dimensional analysis of magnetic quantities 2.4 Crystal planes and directions References 3 Magnetic domains, energy minimisation and magnetostriction 3.1 Magnetic dipole moments and domains 3.2 Weiss theory and molecular field 3.3 Minimisation of free energy 3.4 Domain wall structure and motion 3.5 Domain changes occurring during magnetisation 3.6 Anisotropy energy 3.6.1 Anisotropy energy in materials with cubic crystal structure (Ek) 3.6.2 Uniaxial anisotropy energy (Eu) 3.7 Magnetostatic energy (Ems) 3.8 Fundamentals of magnetostriction 3.8.1 Stress–strain relationship in soft magnetic materials 3.8.2 Origin of magnetostriction in soft magnetic materials 3.9 Magnetoelastic energy (Eme) 3.10 Domain wall energy (Ew) 3.11 Work and energy in the magnetisation process 3.12 Static domain structure with minimum stored energy 3.13 Domain changes occurring during magnetisation 3.14 Energy (Eh) due to an externally applied field 3.15 Effect of an applied field on a domain wall 3.16 Magnetostriction in soft magnetic materials 3.16.1 Saturation magnetostriction along principal crystal axes 3.16.1.1 Saturation magnetostriction along the [100] direction 3.16.1.2 Saturation magnetostriction along the [111] direction 3.16.1.3 Saturation magnetostriction along the [110] direction 3.16.2 The special case of (110) [001] oriented silicon–iron 3.16.3 Saturation magnetostriction of a polycrystalline material 3.16.4 Variation of magnetostriction with flux density 3.17 The Barkhausen effect References 4 Methods of observing magnetic domains in electrical steels 4.1 Introduction 4.2 Powder techniques 4.3 Optical methods of surface domain observation 4.3.1 The magneto-optic effect 4.3.2 Domain observation using the longitudinal KMO effect 4.3.3 Observation of rapid domain wall motion using the KMO effect 4.4 Magnetic force microscope 4.5 Domain visualisation from surface field sensors 4.6 Observation of sub-surface domain features 4.6.1 Electron microscope techniques 4.6.2 X-ray techniques 4.6.3 Freeze-in techniques for observing sub-surface structures 4.6.4 Visualisation of sub-surface domain structures using neutron irradiation 4.7 Use of magnetic bacteria for domain observation 4.8 Magneto-optical indicator films 4.9 Comparison of methods for observations on electrical steels References 5 Electromagnetic induction 5.1 Faraday's law 5.2 Lenz's law 5.3 Expressions for an induced e.m.f. Reference 6 Fundamentals of a.c. signals 6.1 Waveform terminology 6.2 Distortion factor 6.3 Distorted voltages on power systems 6.4 Distorted B or H waveforms due to non-linear magnetisation curves 6.5 Effect of the electric circuit on waveform distortion 6.6 General relationship between harmonics in B and H waveforms 6.7 Calculation of flux density under distorted magnetisation conditions References 7 Losses and eddy currents in soft magnetic materials 7.1 Physical and engineering approaches to magnetic losses 7.2 Energy dissipation derived from the area enclosed by a B–H loop 7.3 Derivation of the dependence of loss on B and H using the Poynting vector theorem 7.4 Hysteresis loss 7.5 Eddy current generation in a rod of conducting material 7.6 Eddy currents in a thin sheet 7.6.1 Skin depth and equivalent depth of uniform magnetisation 7.7 Classical eddy current loss 7.7.1 Reduction of eddy current loss by use of laminations 7.8 Separation of losses into eddy current and hysteresis components 7.8.1 Hysteresis loss components 7.8.2 Separation of total loss into two or three components 7.9 Total loss within a sheet 7.10 Total power loss of a strip expressed in terms of B and H References 8 Rotational magnetisation and losses 8.1 Vector representation of a pure rotating magnetic field 8.2 Rotational flux density 8.3 Torque curves and stored magnetocrystalline energy 8.4 Rotational hysteresis loss 8.5 Magnetic domain structures under rotational magnetisation 8.6 Combined alternating, rotational and d.c. offset magnetisation 8.6.1 Combined alternating and rotational magnetisation 8.6.2 Alternating magnetisation combined with d.c. offset fields 8.7 Rotational loss at power frequency 8.7.1 Distinction from rotational hysteresis loss 8.7.2 Total rotational loss in terms of B and H 8.7.3 Loss separation under rotational magnetisation 8.8 Magnetostriction under rotational magnetisation 8.8.1 Multidirectional magnetostriction 8.8.2 Simulation of rotational magnetostriction 8.9 Three-dimensional magnetisation References 9 Anisotropy of iron and its alloys 9.1 Magnetisation at an angle to a preferred crystal direction 9.2 Magnetisation at angles to an easy direction under a.c. magnetisation 9.3 Effect of strip width on magnetisation direction in anisotropic material 9.4 Effect of stacking method on apparent loss of anisotropic strips cut at angles to an easy axis References 10 Magnetic circuits 10.1 The basic magnetic circuit 10.2 Magnetic reluctance 10.3 Field and flux density distribution in a circular core 10.4 Iron cored solenoid 10.5 Flux density in a magnetic material measured by an enwrapping search coil 10.6 Field and flux density at the interface between two media 10.7 Forces between magnetised laminations References 11 Effect of mechanical stress on loss, permeability and magnetostriction 11.1 Effect of stress on simple magnetic domain structures 11.2 Stress sensitivity derived from domain structures 11.3 Effect of biaxial stress 11.4 Stress sensitivity of GO steel 11.5 Stress sensitivity of NO steel 11.6 Effect of bending stress 11.7 Effect of normal stress 11.8 Effect of stress on components of loss 11.9 Effects of building stresses in electrical machine cores 11.9.1 Clamping stress 11.9.2 Wound cores 11.9.3 Stacked cores 11.10 Slitting and punching stress in electrical steel 11.10.1 Background 11.10.2 Practical aspects of the cut edge region 11.10.3 Other cutting methods 11.10.4 Modelling the effect of the cut edge effect 11.10.5 Shrink fitted stator cores References 12 Magnetic measurements on electrical steels 12.1 Introduction 12.2 Effect of sample geometry (toroids, single strips, rings and single sheet) 12.2.1 Epstein frame 12.2.2 Single sheet tester 12.2.3 Rings and toroids 12.3 Sensing methods 12.3.1 Flux density sensing 12.3.2 Magnetic field measurement 12.4 A.C. magnetic measurements of losses and permeability 12.4.1 The wattmeter method 12.4.2 Digital interpretation of the wattmeter method 12.4.3 Localised measurements 12.4.4 Measurements under simulated operational conditions 12.4.5 D.C. biased a.c. measurements 12.5 2D and rotational magnetic measurements 12.5.1 Measurement principles 12.5.2 Magnetisation systems 12.5.3 Loss measurement 12.6 Magnetostriction measurements 12.6.1 Magnetostriction parameters 12.6.2 Magnetostriction measurement transducers 12.6.3 Rotational magnetostriction 12.7 On-line measurements 12.7.1 Practical challenges 12.7.2 Non-enwrapping systems 12.8 The d.c. magnetic measurements 12.8.1 Quasi-static measurements 12.8.2 Point-by-point measurement 12.8.3 Vibrating sample magnetometer 12.8.4 Coercimeters 12.8.5 Demagnetisation 12.9 Surface insulation testing 12.10 Barkhausen noise measurement References 13 Background to modern electrical steels 13.1 History and development of electrical steels 13.1.1 Laminations 13.1.2 Increased resistivity 13.1.3 Purification 13.1.4 Grain size 13.1.5 Crystal orientation 13.1.6 Coatings 13.2 Metallurgical requirements and control 13.2.1 Thickness 13.2.2 Chemical composition 13.2.3 Grain size 13.2.4 Crystal orientation 13.2.5 Coatings References 14 Production of electrical steels 14.1 Chemical composition 14.2 Hot rolled coil production 14.3 Cold mill processing 14.3.1 Grain oriented electrical steel 14.3.2 Non-oriented electrical steel 14.4 Final property assessment 14.5 Future development 14.5.1 Grain oriented electrical steel 14.5.2 Non-oriented electrical steels References 15 Amorphous and nano-crystalline soft magnetic materials 15.1 Amorphous materials 15.1.1 Production of amorphous magnetic materials 15.1.2 Composition 15.1.3 Magnetic structure 15.1.4 Coatings and surface treatment 15.1.5 Stress sensitivity 15.1.6 Magnetostriction 15.1.7 Consolidated Fe-based amorphous material (POWERCORE) 15.1.8 Bulk amorphous material 15.2 Nano-crystalline magnetic materials 15.2.1 Production of nano-magnetic material 15.2.2 Magnetic properties 15.2.3 Coating and surface treatment 15.2.4 Stress sensitivity 15.3 General properties of amorphous and nano-materials 15.3.1 Families of amorphous materials 15.3.2 Commercial materials 15.4 High silicon micro-crystalline ribbon 15.5 Applications of amorphous and nano-crystalline ribbons References 16 Nickel–iron, cobalt–iron and aluminium–iron alloys 16.1 Introduction 16.2 Iron, cobalt and nickel 16.2.1 Iron 16.2.2 Nickel 16.2.3 Cobalt 16.3 Nickel–iron alloys 16.4 Perminvar 16.5 Cobalt–iron alloys 16.5.1 Stress dependence of magnetic properties of Co–Fe alloys 16.6 Aluminium–iron alloys 16.7 Applications 16.7.1 Ni–Fe alloys 16.7.2 Co–Fe alloys References 17 Consolidated iron powder and ferrite cores 17.1 Background 17.2 Consolidated iron and SiFe powder cores 17.2.1 Production 17.2.2 SMC compositions for power applications 17.2.3 Magnetic properties 17.2.4 Loss components in SMCs 17.2.5 Applications of iron-based SMCs 17.2.6 Opportunities for future developments 17.3 Soft ferrites 17.3.1 Basic structure 17.3.2 Production 17.3.3 Magnetic properties 17.3.4 Loss components in ferrite cores 17.3.5 Applications References 18 Temperature and irradiation dependence of magnetic and mechanical properties of soft magnetic materials 18.1 Effects of temperature on structure insensitive magnetic properties 18.1.1 Saturation magnetisation Ms 18.1.2 Resistivity 18.1.3 Magnetocrystalline anisotropy constants 18.1.4 Magnetostriction constants 18.2 Effect of temperature on permeability, coercivity and losses 18.3 The d.c. and a.c. properties of silicon steels at elevated temperatures 18.4 Temperature dependencies of magnetic properties of various material 18.5 Modelling high temperature performance 18.6 Magnetic properties at cryogenic temperatures 18.7 Effect of non-uniform temperature gradients in magnetic core laminations 18.8 Effect of irradiation on soft magnetic materials References Index Back Cover