Transformer cores

Selenium is added up to 0.1% to silicon steels (2—4% Si) used in transformer cores to enhance the development of the secondary recrystallization texture which, in turn, improves the magnetic characteristics. Selenium alloying additions to the melt may be made as elemental Se, nickel—selenium, or ferroselenium. The recovery depends on the melting practice and method of addition. Normally, it is in the range of 66%, but may be as high as 90%. 

Loss component of current supplying the hysteresis and eddy current losses to the voltage transformer core (it is the active component)... 

Overvoltage may saturate transformer cores and generate harmonics... 

The nonahydrate and other hydrated aluminum nitrates have many apph-cations. These salts are used to produce alumina for preparation of insulating papers, in cathode tube heating elements, and on transformer core laminates. The hydrated salts are also used for extraction of actinide elements. 

Magnetite is the ancient lodestone used as an early compass. More recently, ferrites have found use as memory devices in computers, as magnetic particles on recording tapes and as transformer cores. 

Metallic glasses (a) High Fe or Co containing glasses (e.g. Feo.7Po.2Co.i) Low-loss ferromagnetic ribbons for use in transformer cores... 

Soft ferriles have a slender S-shaped hysteresis loop with low rcntanencc and low ciicreivc force permitting easy magnetization and demagnetization with little magnetic loss. These ferrites are uniquely suited to low-ioss inductor and transformer cores for radio, television, and carrier telephony. 

There are two principal uses for glassy metals. Because metal glasses have no barriers for domain wall movement they are excellent soft magnetic materials. Thin ribbons have been used for transformer cores since the 1960s. Metallic glasses have very good corrosion resistance and very low damping. 

Aluminum nitrate is used in antiperspirants, for tanning leather, as a corrosion inhibitor, in the preparation of insulating papers, on transformer core laminates, in incandescent filaments, and in cathode ray tube heating elements (HSDB 1995). 

Several other archery bow manufacturers have installed catalyst-heat systems for making wood-plastics but little is known about their production. A number of pilot plant operations have been installed in the United States but little of this proprietory information is available. Pilot plant quantities of cutlery handles have been produced for market studies, a laminated type of flooring was produced using a styrene-polyester composite cured in a hot press, parquet flooring using the catalyst-heat system is presently being produced for market studies. Many other small volume items, such as, jewelry, bird calls, transformer cores, etc. are finding their way into the market place. 

Fig. 9.17 Range of soft ferrite components (i) TV scanning yoke (components kindly supplied by Philips Components Ltd.) (ii) UR core and TV line output transformer (iii) E core for switched mode power supply (iv) wide band transformer core (v) core giving good magnetic shielding (vi) high Q (adjustable) filter core (cf. Fig. 9.48) (vii) precision ferrite antenna for transponder (viii) multilayer EMI suppressors (ix) toroids for laser and radar pulse applications (x) typical EMI shields for cables, ((ii)—(x) Courtesy of Ferroxcube UK .)...

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. 

Ferrites are compounds of the type MeO. Fc203 exhibiting the technically important ferromagnetic properties. The main advantage of ferrites, as compared with ferromagnetic metals, is an electrical conductivity lower by orders of magnitude, so that the power losses due to the effect of eddy currents in coil and transformer cores are... 

Natural and synthetic iron oxides not possessing pigment properties are used as raw materials in the production of hard and soft ferrites (see Section 5.5.5.2, Electro- and Magneto-Ceramics) for radio, television and telephone technology, for adhesive magnets, for rotors in dynamos, for low-loss magnetic layers, for DC-motors, for transformer cores, for electronic calculators and high frequency furnaces. This amounts to an annual worldwide production of more than 300 10 t/a. 

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