Eddy current magnetic loss

This restriction of eddy current paths results in a large decrease in eddy current power loss (i R loss). The ratio of the eddy current loss in a laminated core with n laminations to a solid core with the same cross sectional area is 1/n Commercial transformer cores are fabricated from thin sheets of metallic core material to take advantage of this effect. The eddy current loss P within laminations of a magnetic core is given by the classical eddy current power loss equation... 

Where B = induction magnetic flux (gauss), and r = surface resistivity (fl-cm per lamination). Therefore, interlaminar loss decreases with increasing surface resistivity. Figure 2 shows the surface resistivity required for t = 0.023 cm transformer core steel to maintain predicted interlaminar eddy current power loss, P, at B = 15 kG, and/= 60 Hz. 

Spinel ferrites, isostmctural with the mineral spinel [1302-67-6] MgAl204, combine interesting soft magnetic properties with a relatively high electrical resistivity. The latter permits low eddy current losses in a-c appHcations, and based on this feature spinel ferrites have largely replaced the iron-based core materials in the r-f range. The main representatives are MnZn-ferrites (frequencies up to about 1 MH2) and NiZn-ferrites (frequencies 1 MHz). 

Excessive healing of magnetic cores, as a result of harmonic frequencies due to hysteresis and eddy current losses (equations (1.I2) and (1.13)). 

An induction furnace, where the heating is due to eddy current losses itiduced by the magnetic field. 

The Enclosure is of non-magnetic material, therefore it will be devoid of hysteresis and eddy current losses. 

These balanced enclosure currents also induce electric fields into nearby structures, RCC beams and columns in the same way as the main conductors, and hence nullify most of the space magnetic fields. These space fields (fields outside the enclosure) are otherwise responsible for causing eddy current and hysteresis losses in the metallic (magnetic) structures, RCC beams and columns in the vicinity. The electrical bonding of enclosures thus... 

The enclosure is constructed of non-magnetic material, generally aluminium, in view of its low cost and weight as compared to copper The nonmagnetic material eliminates hysteresis and eddy current losses in the enclosure, as i result of mutual induction,... 

The influence of a induced field on a metallic (magnetic) structure is in the form of closed magnetic loops, which cause hysteresis and eddy current losses. These closed loops cannot be broken by insulating magnetic structures at bends or joints or any other locations. (Refer to Figure 28.32 for more clarity.) There is thus no treatment that can be applied to such structures or bodies in the vicinity of an IPB to protect them from the magnetic effects of the field if present in the space. 

Eddy currents are circular currents induced in wide areas within the core in the surrounding wires and structures by the presence of high magnetic fields. There is not much that a typical designer can do to reduce these losses. 

The magnetic bearing is made up of a series of electromagnets located circumferentially around the shaft to form the radial bearing. The electromagnets (Figure 5-42) are laminated to limit the eddy current losses. The shaft must be fitted with a laminated sleeve (see Figure 5-43) for the... 

Nearly no eddy current losses occur in electrically insulating magnetic materials. This is one of the reasons for the importance of oxidic materials, especially of spinels and garnets. Another reason is the large variability of the magnetic properties that can be achieved with spinels and garnets of different compositions. The tolerance of the spinel structure to substitution at the metal atom sites and the interplay between normal and inverse spinels allow the adaptation of the properties to given requirements. 

The real part is the magnetic permeability whereas the imaginary part is the magnetic loss. These losses are quite different from hysteresis or eddy current losses, because they are induced by domain wall and electron-spin resonance. These materials should be placed at position of magnetic field maxima for optimum absorption of microwave energy. For transition metal oxides such as iron, nickel, and cobalt magnetic losses are high. These powders can, therefore, be used as lossy impurities or additives to induce losses within solids for which dielectric loss is too small. 

Energy losses in soft magnetic materials arise due to both hysteresis and eddy currents, as described in the previous section. Eddy current losses can be reduced by increasing the electrical resistivity of the magnetic material. This is one reason why solid-solution iron-silicon alloys ( 4% Si) are used at power frequencies of around 60 Hz and why iron-nickel alloys are used at audio frequencies. Some magnetically soft ferrites (see Section 6.2.2.1) are very nearly electrical insulators and are thus immune to eddy current losses. Some common soft magnetic materials and their properties are listed in Table 6.19. Soft magnetic alloys are described further in Section 6.2.1.6. 

There are some notable differences apparent in Fig. 11.14 between the extinction curves for aluminum spheres and those for water droplets. For example, av is still constant for sufficiently small aluminum particles but the range of sizes is more restricted. The large peak is not an interference maximum aluminum is too absorbing for that. Rather it is the dominance of the magnetic dipole term bx in the series (4.62). Physically, this absorption arises from eddy current losses, which are strong when the particle size is near, but less than, the skin depth. At X = 0.1 jam the skin depth is less than the radius, so the interior of the particle is shielded from the field eddy current losses are confined to the vicinity of the surface and therefore the volume of absorbing material is reduced. 

Application of distorted voltage to a motor results in additional losses in the magnetic core of the motor. Hysteresis and eddy current losses in the core increase as higher frequency harmonic voltages are impressed on the motor windings. Hysteresis losses increase with frequency and eddy current losses increase as the square of the frequency. Also, harmonic currents produce additional PR losses in the motor windings which must be accounted for. 

---