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.
Inspec keywords: silicon alloys; magnetic cores; magnetisation; ferromagnetic materials; turbomachinery; electrical products industry; iron alloys; machinery production industries; transformer cores
Other keywords: transformers; magnetism; electrical machine manufacture; FeSi; material production; high quality electrical steel; rotating electrical machines; magnetic properties; electrical steels; metallurgical features; electrical machine cores; localised magnetisation conditions
Subjects: General electrical engineering topics; General topics in manufacturing and production engineering; Monographs, and collections; Electrical equipment manufacturing; Ferromagnetism of Fe and its alloys; Engineering materials; Magnetic cores; Machinery and equipment industry; Ferromagnetic materials; Magnetization curves, hysteresis, Barkhausen and related effects
This chapter analyses the properties and applications of soft magnetic materials and discusses the emergence of electrical steels and their various electrical engineering implementations. The authors discuss the fundamental properties of soft magnetic materials that are important to their functionality in engineering applications. These include saturation magnetisation, coercivity, permeability and energy losses. The development of new soft magnetic alloys requires a systematic search of countless possible alloying elements, now possible due to developments in rapid alloy processing, and a means of determining the magnetic potential of the most promising compositions. The largest single application of soft magnetic materials is found in power conversion equipment where energy is transmitted via magnetic flux. The authors finally discuss the global impact of the energy wastage in electrical steels which highlights the need for further development to further enhance the efficiency and ultimately continue to reduce these losses.
This chapter outlines the basic concepts of magnetism in order to further enhance the understanding of the magnetic properties of electrical steels. Starting from the simplest form of the magnetic dipole, the authors describe magnetisation, magnetic polarisation, magnetic flux density, permeability and the relationship between these concepts. The difficulty in modeling magnetic hysteresis in engineering disciplines is also analysed. Finally, the authors explain how the crystal structure affects the magnetism of silicon-iron electrical steels and the ideal grain orientation for optimised magnetic properties.
The magnetic domain structure of a magnetic material determines its magnetic properties. When the domain structure changes, perhaps due to factors such as temperature variation, mechanical stress or the presence of an external magnetic field, magnetic properties also change, in a beneficial or detrimental way. The physics controlling the formation and structure of domains, as well as the dynamics of so-called domain wall motion and domain rotation is quite well understood, but it is very complicated and difficult to apply to materials with complex metallurgical structure such as electrical steels. Magnetic domains of direct relevance to electrical steels are covered in Chapter 1 of Volume 2 of this book. In this chapter their origin and basic structures are explained.
For in-depth understanding and more accurate predictions of the performance of modern soft magnetic materials, particularly under a.c. magnetisation, the more complex structures present in real materials must be taken into account. This calls for methods of directly observing and quantifying static and dynamic domain structures. The following sections cover the most common domain observation techniques, roughly in chronological order of their first usage, which not surprisingly corresponds roughly according to their capability. These include powder techniques, optical methods such as the magneto-optical effect, magnetic force microscopy etc. They are all applicable for domain observation on any magnetic material but emphasis is placed on their relevance to electrical steels.
An electromotive force (e.m.f.) is induced in an electric circuit when magnetic flux linking with the circuit changes. This is often called electromagnetic induction which is very familiar to motor and transformer designers. It is very important in the characterisation and analysis of the performance and properties of soft magnetic materials under a.c. or any other form of changing magnetisation. Faraday's law was briefly introduced in Section 2.1.4. In this section its origins and measurement relevant to electrical steels are set out in more detail.
Waveform analysis is widely applied to measurement and computational analysis of B-H characteristics, magnetostriction and losses of electrical steels and other soft magnetic materials. The fundamentals of waveform analysis relevant to these applications are presented in this chapter for the benefit of readers who might be less familiar with the topic. The chapter gives a brief introduction to waveform analysis before focusing on the occurrence and common applications related to magnetic parameters particularly important in the application of soft magnetic materials in power devices.
An important property of a soft magnetic material is its loss when subjected to a time varying magnetic field. This is effectively the conversion of useful magnetic energy into some other form, such as thermal or acoustic energy. Energy conversion of this form is often loosely referred to as energy loss or power loss because, normally, in practical applications, it is a source of inefficiency. Such energy transfer in magnetic material is often referred to as iron loss and when the same steel forms part of a magnetic core, the same energy conversion is referred to as core loss. The physical approach to analyse and interpret these losses uses the Poynting theorem. In this chapter the individual loss components, such as eddy current losses and hysteresis losses, are introduced and their contribution to total loss in soft magnetic materials is discussed.
This chapter introduces fundamental aspects of the rotational magnetisation process and its general effect on losses and magnetostriction in both isotropic and highly anisotropic material, such as GO electrical steel. In a core assembled from electrical steel, the magnetic field and flux density probably will vary in magnitude from point to point within the material. Also, under a.c. magnetisation its time varying waveform might be non-sinusoidal. Furthermore, the direction of B and H at a given point within the core material might vary with time. These effects are loosely referred to as being rotational magnetisation phenomena.
This chapter discusses the unique anisotropy of the magnetic properties of electrical steels. The most significant point in the case of electrical steel is that the stored magnetocrystalline energy becomes extremely high if the magnetisation in a single grain moves away from a preferred {100} direction of magnetisation. Magnetisation within grains in a sheet of electrical steel tends to remain oriented along preferred directions unless an extremely high external field or mechanical stress is applied to change the energy balance. The deviation between B and H in a sheet varies according to the type of material anisotropy, the magnetising frequency, peak flux density and the influence of microstructure and magnetic domain structure. In this chapter some practical effects of the phenomenon particularly relevant to the measurement or characterisation of anisotropic materials are introduced.
This chapter introduces magnetic circuit terminology and forms of analysis commonly used in electrical steels applications. An appreciation of magnetic circuits, based mainly on Ampére's circuital law and Faraday's law of electromagnetic induction, is needed to understand design and operation of magnetic measurement systems and the function of magnetic materials in magnetic cores.
Mechanical stress can causes magnetoelastic energy to be stored in a magnetic material. When this happens the magnetic domain structure changes to minimise the total energy. This, in turn, affects all the structure sensitive magnetic properties such as losses, permeability and magnetostriction. This chapter opens with an explanation of the effect of stress on simple domain structures in iron or SiFe single crystals. This knowledge can be used to understand the practical stress sensitivity characteristics of real materials discussed in Chapters 5, 6, and 8 of Volume 2 of this book.
This chapter will give an overview of the most currently used measurement methods applicable to electrical steels with a particular focus on methods which have been standardised or are in the process of standardisation. Although termed magnetic measurements almost all of the methods discussed are electrical measurements from which the magnetic properties can be calculated. The most fundamental of these is commonly referred to as the B-H curve which characterises the response of the magnetic material to an applied field. The authors discuss the effects of simple geometry on measurement characteristics and the various sensing methods. These include flux density sensing, A.C. measurements of losses and permeability, magnetostriction measurements, on-line measurements, surface insulation testing and Barkhausen noise measurement.
This chapter outlines the background and history of electrical steels and the motivation behind their development and implementation in modern engineering. Early transformer, generator and motor developers soon realised that cores constructed from solid iron resulted in prohibitive eddy current losses, and their subsequent designs mitigated this effect with cores consisting of bundles of insulated iron wires and, later, laminated sheets of steel. Therefore, the demand for the first `electrical steel' became apparent. The authors discuss the chemical and physical properties found to be essential in achieving the best magnetic properties in electrical steels. These requirements include thickness, chemical composition, grain size, crystal orientation and coatings.
Current production methods of electrical steels follow the process routes used in typical steel sheet product process, starting with the production of the liquid steel from either the basic oxygen steelmaking process (BOS) using liquid iron produced in blast furnaces as the main constituent, or electric arc steel making where the main constituent is steel scrap produced by recycling. There is no particular advantage for electrical steels in using either route. This chapter considers the production methods of electrical steels and the effects of each method on the final composition and crystal structure and microstructure.
This chapter discusses the advent of nano-crystalline and amorphous soft magnetic materials and their properties and production methods. The magnetic material is produced commercially in the form of ribbon much thinner than any electrical steel, so eddy currents are naturally low under a.c. excitation. This, combined with inherent large resistivity, leads to low losses. No grain boundaries are present to impede domain wall motion, so hysteresis losses are low and very high permeability can be achieved. It was soon recognised that amorphous ribbon was indeed an exciting new class of engineering material which not only could replace conventional soft magnetic materials in many applications but could also satisfy magnetic requirements in entirely new applications.
This chapter focuses on the magnetic properties of nickel-iron, cobalt-iron and aluminium-iron alloys, which are established soft magnetic materials. The authors consider how each alloy presents varying magnetic properties allowing them to be used for different scenarios. Properties such as magnetic permeability, saturation magnetisation, magnetostriction constant and magnetocrystal anisotropy constant are discussed and compared across the different alloy compositions.
This chapter discusses the production and applications of iron powder and ferrite magnetic cores. More recently, iron and SiFe bulk components have been developed and commercialised for applications requiring mass produced, cheap, mechanically strong and dimensionally accurate net shape cores for magnetic components. These iron and silicon iron compressed components are commonly referred to as soft magnetic composite (SMC) cores or consolidated powder cores. General advances in powder metallurgy have resulted in their applications in many sectors, particularly as functional materials, replacing laminated cores for small motors and actuators in the automotive and aerospace industries. The authors focus on the magnetic properties of these cores such as magnetisation, magnetic permeability and loss components.
All magnetic properties of engineering materials are temperature dependent to varying degrees. This is to be expected since their intrinsic saturation magnetisation, magnetostriction and magnetocrystalline anisotropy are all temperature sensitive. These determine the domain structure within a magnetic material, hence the magnetic properties at any temperature. This chapter summarises the temperature dependence of structure insensitive magnetic properties of important soft magnetic materials. This is followed by a presentation of temperature characteristics of structure sensitive properties of some families of commercial soft magnetic materials. The chapter concludes with sections covering low temperature characteristics, approaches to modelling temperature effects, possible effects of temperature gradients in magnetic cores and the general effects of irradiation on magnetic properties.
