Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
  • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
  • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
  • H01F1/12—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials
  • H01F1/14—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys
  • H01F1/147—Alloys characterised by their composition
  • H01F1/153—Amorphous metallic alloys, e.g. glassy metals
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
  • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
  • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
  • H01F1/12—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials
  • H01F1/14—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys
  • H01F1/147—Alloys characterised by their composition
  • H01F1/153—Amorphous metallic alloys, e.g. glassy metals
  • H01F1/15341—Preparation processes therefor
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/04—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering with simultaneous application of supersonic waves, magnetic or electric fields
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/008—Heat treatment of ferrous alloys containing Si
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
  • H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
  • H01F41/0206—Manufacturing of magnetic cores by mechanical means
  • H01F41/0213—Manufacturing of magnetic circuits made from strip(s) or ribbon(s)
  • H01F41/0226—Manufacturing of magnetic circuits made from strip(s) or ribbon(s) from amorphous ribbons

Definitions

• This invention relates to amorphous metallic transformer cores having increased operating induction; and more particularly, to a magnetic field annealing process that markedly increases the operating induction of large transformer cores.
• Soft magnetic properties of amorphous metallic transformer core alloys are developed as a result of annealing at suitable temperature and time in the presence of a magnetic field.
• One of the purposes for such annealing is to reduce the adverse effects of residual stresses which result from the rapid cooling rate associated with amorphous alloy manufacturing processes.
• Another purpose is to define the "magnetic easy axis" in the body being annealed; i.e. to define a preferred orientation of magnetization which would ensure low core loss and exciting power of the body being annealed.
• magnetic field annealing has been performed to minimize the core loss of the annealed body, as disclosed U.S. Patents 4,1 16,728 and 4,528,481 for example.
• annealing of amorphous alloys while under tensile stress has also been shown to result in 2
• This lost energy is referred to as core loss, and is represented quantitatively as the area circumscribed by the B- H loop generated during one complete magnetization cycle of the material.
• the core loss is ordinarily reported in units of W/kg, which actually represents the energy lost in one second by a kilogram of material under the reported conditions of frequency, core induction level and temperature.
• Core loss is affected by the annealing history of the amorphous metallic alloy. Put simply, core loss depends upon whether the alloy is under- annealed, optimally annealed or over-annealed. Under-annealed alloys have residual, quenched-in stresses, require additional energy during magnetization, and exhibit increased core loss and exciting power during magnetic cycling. Over-annealed alloys are believed to exhibit maximum atomic "packing" and/or can contain crystalline phases, the result of which is a loss of ductility and/or inferior magnetic properties such as increased core loss caused by increased resistance to movement of the magnetic domains. Optimally annealed alloys exhibit a fine balance between ductility and magnetic properties. ->
• a large transformer core that is a core weighing from about 40 to 400 kg.
• the large thermal mass of the core precludes uniform heating during the annealing process. Specifically, the outer layers of a large core tend to become over- annealed, whereas the interior sections of the core tend to become under- annealed. Given these conditions, transformer manufacturers currently anneal cores to minimize the core loss; but do not maximize the operating induction of the core. With such processes, core loss values of less than 0.37 W/kg (60 Hz and 1.4 T) and operating induction ranging from about 1.26 to 1.4 Tesla are typically achieved.
• Exciting power is the electrical energy required to produce a magnetic field of sufficient strength to achieve in the metallic glass a given level of induction (B). Exciting power is proportional to the required magnetic field (H), and hence, to the electric current in the primary coil.
• An as-cast iron-rich amo ⁇ hous metallic alloy exhibits a B-H loop which is somewhat sheared over. During annealing, as-cast anisotropies and cast-in stresses are relieved, the B-H loop becomes more square and narrower relative to the as-cast loop shape until it is optimally annealed. Upon over-annealing, the B-H loop tends to broaden as a result of reduced tolerance to strain and, depending upon the degree of over-annealing, existence of crystalline phases.
• the value of the exciting power for a given level of magnetization initially decreases, then reaches an optimum (lowest) value, and thereafter increases.
• the annealing conditions which produce an optimum (lowest) value of exciting power in an amo ⁇ hous metallic alloy do not coincide with the conditions which result in lowest core 4
• amo ⁇ hous metallic alloys, annealed to minimize core loss do not exhibit optimal exciting power.
• the present invention provides a method for obtaining maximum operating induction in a large transformer composed of magnetic amo ⁇ hous alloys.
• the magnetic amo ⁇ hous alloy is annealed to maximize operating induction, rather than to minimize core loss.
• the method of the present invention minimizes exciting power, significantly reducing the likelihood of "thermal runaway" at the higher operating induction. Utilization of such higher operating induction, in turn, markedly decreases transformer core size and, therefore, cost.
• the annealing process comprises the steps of (a) heating the core in the presence of an applied magnetic field to a peak temperature; (b) holding the core at the peak temperature in the presence of the magnetic field for a soak time at least 50% longer than that required to minimize power loss thereof; and (c) cooling the 5
• a large magnetic amo ⁇ hous metallic alloy core having an exciting power less than 1 VA/kg when measured at 60 Hz and an operating induction ranging from 1.40 to 1.45 Tesla. Further provided is a ferromagnetic amo ⁇ hous metallic alloy core having a power loss less then about 0.25 W/Kg.
• FIG. la is a graph depicting core loss as a function of temperature, the graph illustrating the core loss dependence of straight strip laboratory samples on 2 hour isochronal anneals conducted in a magnetic field at various temperatures
• FIG. lb is a graph depicting exciting power as a function of temperature, the graph illustrating the exciting power dependence of straight strip laboratory samples on 2 hour isochronal anneals conducted in a magnetic field at various temperatures
• FIG. 2a is a graph depicting core loss as a function of temperature, the graph illustrating the core loss dependence of actual transformer cores on 2 hour isochronal anneals conducted in a magnetic field at various temperatures;
• FIG. 2b is a graph depicting exciting power as a function of temperature, the graph illustrating the exciting power 6
• FIG. 3 is a graph depicting exciting power as a function of induction, the graph illustrating the induction level dependence of exciting power straight strip samples annealed at three different conditions
• FIG. 4 is a graph depicting exciting power as a function of test temperature, the graph illustrating exciting power dependence on test temperature for straight strip samples which have been annealed using three different conditions
• FIG. 5 is a graph depicting exciting power as a function of soak time, the graph illustrating the transformer core soak time dependence of exciting power
• FIG. 6 is a graph depicting exciting power as a function of induction, the graph illustrating the induction level dependence of exciting power for actual transformer cores which have been annealed in a magnetic field using different soak times.
• the term "amo ⁇ hous metallic alloys” means a metallic alloy that substantially lacks any long range order and is characterized by X- ray diffraction intensity maxima which are qualitatively similar to those observed for liquids or inorganic oxide glasses.
• the term “strip” means a slender body, the transverse dimensions of which are much smaller than its length. Strip thus includes wire, ribbon, and sheet, all of regular or irregular cross-section. 7
• annealing refers to the heating of a material, in the presence of a magnetic field for example, in order to impart thermal energy which, in turn, allows the development of useful properties .
• a variety of annealing techniques are available for developing these properties.
• the term "straight strip” refers to the configuration of a sample which is subjected to magnetic property measurements.
• the sample may be truly tested as a straight strip, in which case its length is much greater than that of the field/sensing coils.
• a more reasonable sample length can be used if the material under test is used as the fourth leg in a simple transformer core. In either case, the material under test is in the form of a straight strip.
• large magnetic core refers to a magnetic component which is used in any number of electrical applications and devices and which has a weight ranging from about 40 to 400 kg.
• a magnetic core is usually constructed from magnetic strip or powder.
• peak temperature refers to the maximum temperature reached by any portion of the transformer core during the annealing cycle.
• seal time refers to the duration over which a core is actually at the annealing temperature, and does not include core heating and cooling times.
• saturation induction and “operating induction” refer to two magnetic induction levels relevant to transformer core materials and the operation thereof. Saturation induction is the maximum amount of induction available in a material. Operating induction is the amount of magnetic induction used in the operation of a transformer core. For amo ⁇ hous metallic 8
• saturation induction is determined by alloy chemistry and by temperature. Saturation induction decreases as temperature is increased.
• the operating induction of a magnetic material is determined by the saturation induction.
• Transformers are designed to operate at magnetic induction levels less than the saturation induction.
• the primary reason for this design requirement involves the permeability ( ⁇ ) of the magnetic core material.
• magnetic field is applied by passing electric current through the primary coil. Thus, a large increase in the required magnetic field necessitates a large increase in the current through the primary coil.
• a large increase in the primary current of a transformer is undesirable for a number of reasons.
• Large current variations through a single transformer can degrade the quality of electric power through the neighboring electric power grid.
• An increase in the primary current will also result in increased Joule (I 2 R) heating within the primary coil. This electrical energy lost by conversion to heat detracts from the efficiency of the transformer.
• excessive current will cause excessive heating of the primary coil, which can lead to the physical deterioration and failure of the electrical insulation used within the coil. Failure of the electrical insulation will lead directly to failure of the transformer.
• the heat generated in the primary coil can also heat the magnetic core of the transformer.
• thermo runaway As the temperature of the magnetic core is increased, the saturation induction of the magnetic material decreases. For a transformer performing at a fixed operating induction, the thermally induced decrease in saturation induction creates the same effect as an additional increase in the operating induction. Additional electric current is drawn through the primary coil, creating additional Joule heating. The temperature of the magnetic core of the transformer is further increased, exacerbating the situation. This uncontrolled increase in transformer temperature associated with "thermal runaway" is another common reason for failure of transformer cores in the field.
• transformers are typically designed such that the operating induction of the core under standard conditions is no more than about 80 to 90% of the saturation induction of the core material.
• the present invention provides a method for annealing large magnetic cores composed of amo ⁇ hous metallic alloys that permits increased operating induction and decreased exciting power without inducing thermal runaway. It is desirable to operate a large magnetic core at as high an induction level as possible so that the cross-section of the core can be minimized. That is, a transformer core works on the basis of the number of lines of magnetic flux, not on the flux density (induction). The ability to increase operating flux density permits use of smaller magnetic core cross-sections, while utilizing a given flux. Substantial benefits are thereby derived from manufacture of magnetic core sizes that are smaller for transformers of given ratings.
• the optimum annealing temperature and time for amo ⁇ hous metallic alloys presently used in transformer manufacture is a 10
• FIG. la The dependence of magnetic core loss on annealing temperature for straight strip samples of METLAS ® alloy 2605 S A- 1, after having been annealed for 2 hours, is shown in Figure la.
• core loss is high because of insufficient annealing, which results in the magnetic easy axis not being well-defined.
• core loss is high at higher temperatures because of the onset of crystallization in the amo ⁇ hous metallic alloy. The lowest core loss is seen to result at about 360°C for the straight strip samples.
• Figure lb shows the dependence of exciting power on annealing temperature for straight strip samples of METLAS ® alloy 2605 SA- 1 , after having been annealed for 2 hours.
• Annealing is a time/temperature process.
• Figure 5 shows the dependence of exciting power on "soak time" during annealing of a magnetic core. It is significant that, again, exciting power decreases with increased soak time. This illustrates the option of using either annealing cycle soak time or temperature to develop the method of the present invention on a commercial scale.
• Figure 6 shows the dependence of magnetic core exciting power on induction for cores which have been annealed using different soak times.
• EXAMPLE 2 Three single phase wound magnetic cores for use in commercial distribution transformers were made using 6.7" wide METGLAS ® alloy SA-1, having a nominal chemistry FegoBuSig. Each core weighed about 1 18 kg, and care was taken to minimize thermal gradient effects in the cores during heat- up and cool-down. These three cores were annealed using a soak time of 20 minutes and a peak temperature of about 370°C rather than the normally used peak temperature of about 355°C. The results of exciting power and core loss measurements on these cores, which were annealed at higher temperature, are shown in comparison to those of cores which have been annealed conventionally in Figure 2a and 2b, respectively.
• Example 2 produced by annealing at increased peak temperature, are comparable to those produced in Example 1 by annealing for extended soak times.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Physics & Mathematics (AREA)
• Power Engineering (AREA)
• Crystallography & Structural Chemistry (AREA)
• Dispersion Chemistry (AREA)
• Thermal Sciences (AREA)
• Electromagnetism (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Manufacturing & Machinery (AREA)
• Manufacturing Cores, Coils, And Magnets (AREA)
• Soft Magnetic Materials (AREA)
• Heat Treatment Of Articles (AREA)

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• 1999
  • 1999-02-04 CN CNB998045977A patent/CN1153228C/zh not_active Expired - Fee Related
  • 1999-02-04 AU AU25855/99A patent/AU2585599A/en not_active Abandoned
  • 1999-02-04 CA CA002320084A patent/CA2320084A1/en not_active Abandoned
  • 1999-02-04 JP JP2000530920A patent/JP2002503028A/ja active Pending
  • 1999-02-04 EP EP99905767A patent/EP1064660A1/en not_active Withdrawn
  • 1999-02-04 BR BR9907677-2A patent/BR9907677A/pt not_active Application Discontinuation
  • 1999-02-04 KR KR1020007008580A patent/KR20010040702A/ko not_active Application Discontinuation
  • 1999-02-04 WO PCT/US1999/002494 patent/WO1999040594A1/en not_active Application Discontinuation
• 2001
  • 2001-12-20 HK HK01108939A patent/HK1038094A1/xx not_active IP Right Cessation

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