MXPA00007648A - Amorphous alloy with increased operating induction - Google Patents

Abstract

A large magnetic amorphous metallic alloy core is annealed to minimize exciting power rather than core loss. The core has an exciting power less than 1 VA/kg when measured at 60 Hz and an operating induction of 1.40 to 1.45 Tesla, the measurement being carried out at ambient temperature. Such cores can be run at higher operating induction than those annealed to minimize core loss. The physical size of the transformer's magnetic components, including the core, is significantly reduced.

Description

- H01F 1153, C21D 600 Al (43) Ijoleraatiml PnlJlcatíon Date: 12 Augun 1999 (12.08.99) WD-Tiortty? Fc--: 09/01 * 01 4 FWWtt? 199 »(04? 2J») ALLOY AMORPHA WITH INDUCTION OF INCREASED OPERATION CROSS REFERENCE TO RELATED REQUESTS It is a continuation in part of the North American Application > Serial No. 08 / 796,011, filed on February 5, 1997, entitled "Amorphous Alloy it Increased Operating Induction" (Amorphous Alloy with Increased Operation Induction). BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION (10) This invention relates to amorphous metal transformer cores that have an increased induction of operation, and more particularly to a magnetic field annealing process that markedly increases the induction of large-scale operation. transformer cores 15 2. DESCRIPTION OF THE PREVIOUS TECHNIQUE Soft magnetic properties of amorphous metal alloys for transformer core develop as a result of the annealing at suitable temperature and time conditions in the presence of a magnetic field. The purpose of said annealing is to reduce the negative effects of the residual stresses resulting from the rapid cooling rate associated with the manufacturing processes of amorphous alloys Another purpose is to define the "easy magnetic axis" in the body in the process of annealing; say, define a preferred orientation of magnetization which could ensure less loss of core and excitation power of the body in the process of annealing. Historically, said magnetic field annealing has been performed to minimize core loss of the annealed body, in accordance with what is disclosed in US Patents 4,116,728 and 528,481, for example. In addition to the magnetic field annealing, the annealing of amorphous alloys while in a state of tension results in improved soft magnetic properties, as shown, for example, in US Patent Nos. 4,05,1331 and 4,053,332. A sample configuration for tension annealing has invariably been a flat strip. The use of tension annealing for the production of large amorphous alloy transformer cores is not practicable. The two most important magnetic properties of a transformer core are the core loss and excitation power of the core material. When the annealed metallic glass magnetic cores receive energy (that is, they are magnetized by the application of a magnetic field), a certain amount of the input energy is consumed in the core and irrevocably lost as heat. This energy consumption is typically caused by the energy required to align the magnetic domains in the amorphous metal alloy in the direction of the field. The Lost energy is known as core loss, and is represented quantitatively as the area circumscribed by the B-H loop generated during a complete magnetization cycle of the material. Core loss is usually reported in units of W / kg, which in fact represents the loss of energy in one second per one kilogram of material in the reported conditions of frequency, core induction level, and temperature. Core loss is affected by the history of annealing of the amorphous metal alloy. In simple terms, the core loss depends on whether the alloy is undercooked, optimally annealed or overcooked. Overcooked alloys have residual voltages that require additional energy during magnetization and exhibit greater core loss and excitation power during the magnetic cycle. Overrecoated alloys are believed to exhibit maximum atomic "packaging" and / or may contain crystalline phases, the result of which is a loss of ductility and / or lower magnetic properties such as increased core loss caused by increased resistance to movement. of the magnetic domains. Optimally annealed alloys present a fine balance between ductility and magnetic properties. It is difficult to achieve an optimally annealed condition in a large transformer core, that is, a core that weighs approximately 40 to 400 kg. The large thermal mass of the core prevents uniform heating during the annealing process. Specifically, the outer layers of a large core tend to overcook while the inner sections of the core tend to become overcooked. Given these conditions, transformer manufacturers currently augment the cores to minimize core loss; but they do not optimize the induction of operation of the nucleus. With processes of this type, core loss values of less than 0.37 W / kg (60 Hz and 1.4 T) and induction of operation are typically achieved within a range of approximately 1.26 to 1.4 Tesla. The excitation power is the electrical energy required to produce a magnetic field of sufficient force to achieve a given level of induction in the metallic glass (B). The excitation power is proportional to the magnetic field required (H), and therefore, to the electric current in the primary coil. An amorphous metal alloy rich in iron in the state in which it is emptied has a B-H loop that is relatively cut. During annealing, amsotropies are released from the emptying and stresses from the emptying, the B-H loop becomes more squared and narrower in relation to the shape of the loop in the state in which it was emptied until optimal annealing. When overcooking occurs, the B-H loop tends to widen as The result of a reduced tolerance to deformation and, depending on the degree of overcooking, the existence of crystalline phases. Thus, as the annealing process for a given alloy progresses from overcooking through optimal recoil to overcooking, the value of the excitation power for a given level of magnetization decreases micially, then reaches an optimum value (the lowest ba ), and then it rises. However, the annealing conditions that produce an optimal (lower) value of excitation power in an amorphous metal alloy do not match the conditions that result in a smaller core loss. As a result, amorphous, annealed metal alloys to minimize core loss do not exhibit optimal excitation power. It should be apparent that the optimum conditions of annealing are different for amorphous alloys of different compositions, and for each required property. Therefore, an "optimal" annealing is generally recognized as the annealing process that produces the best balance between the combination of characteristics needed for a given application. In the case of the manufacture of a large transformer core, the manufacturer determines a specific time and a specific temperature for annealing that are "optimal" for the alloy used, and does not deviate from this time / temperature scheme.

COMPENDIUM OF THE INVENTION The present invention offers a method to obtain a maximum operation induction in a large transformer composed of magnetic amorphous alloys. Generally speaking, the magnetic amorphous alloy is annealed to optimize the induction of operation, rather than to minimize core loss. The method of the present invention minimizes the excitation power, significantly reducing the likelihood of a "thermal runaway" at the highest operating induction. The use of said higher operation induction, in turn, notably decreases the transformer core size and, consequently, its cost. It has been surprisingly found that the induction of core operation is optimized when the core is annealed using a thermal impregnation time significantly greater than that required to minimize core loss. In general terms, the annealing process comprises the steps of (a) heating the core in the presence of a magnetic field applied at a peak temperature; (b) maintaining the core at the peak temperature in the presence of the magnetic field during a thermal impregnation time at least 50% longer than the thermal impregnation time required to minimize the loss of power; and (c) cooling the core to a temperature about 100 ° C lower than the peak temperature at a cooling rate within a range of about 0.1 to 10 ° C / m? n. The invention also provides a large amorphous metal alloy magnetic core having an excitation power of less than 1 VA / kg when measured at 60 Hz and an induction of operation that is within a range of 1.40 to 1.45 Tesla. A ferromagnetic amorphous metal alloy core having a power loss of less than about 0.25 W / Kg is further provided. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be more fully understood and its additional advantages will be apparent with reference to the following detailed description and the accompanying drawings in which: the figure is a graph showing the loss of core as a function of temperature, the graph illustrates the dependence of the loss of nucleus of laboratory samples of straight strips in isochronic observations of 2 hours made in a magnetic field at various temperatures; Figure Ib is a graph showing the power of illustration as a function of temperature, the graph shows the dependence of the excitation power of laboratory samples of straight strips in isochronic observations of 2 hours carried out in a magnetic field at various temperatures; g Figure 2a is a graph representing the loss of core as a function of temperature, the graph illustrating the dependence of the loss of nucleus of real nuclei of transformers in isochronic observations of 2 hours made in a magnetic field at various temperatures; Figure 2b is a graph showing the excitation power as a function of temperature, the graph illustrates the dependence of the excitation power of real transformer cores in isochronic 2-hour isolations performed in a magnetic field at various temperatures; Figure 3 is a graph showing the excitation power as a function of induction, the graph illustrates the dependence of the induction level of the excitation power of samples of annealed straight strips in three different conditions; Figure 4 is a graph showing the excitation power as a function of the test temperature, the graph illustrates the dependence of the excitation power of the test temperature for samples of straight strips that have been annealed using three different conditions; Figure 5 is a graph showing the excitation power as a function of the thermal impregnation time, the graph illustrates the dependence of the thermal impregnation time of the transformer core of the excitation power; Figure 6 is a graph showing the excitation power as a function of induction, the graph illustrates the dependence of the induction level of excitation power for real transformer cores that have been annealed in a magnetic field using thermal impregnation times different DETAILED DESCRIPTION OF THE INVENTION As used herein, the term "amorphous metal alloys" refers to a metal alloy which lacks substantially long range order and is characterized by X-ray diffraction intensity maxima which are qualitatively similar to those observed for liquids or glasses of inorganic oxides. As used herein, the term "strip" refers to a thin body whose transverse dimensions are much smaller than its length. Accordingly a strip includes wire, ribbon, and sheets, of regular or irregular cross section.

The term "annealing", as used in the specification and in the claims, refers to the heating of a material, in the presence of a magnetic field for example, to provide thermal energy which, in turn, allows the development of properties tools. Several techniques of annealing are available to develop these properties.

As used herein, the term "straight strip" refers to the configuration of a sample subjected to measurements of magnetic properties. The sample can be truly tested as a straight strip, in which case its length is much longer than that of the detection / field coils. Alternatively, a more reasonable sample length can be employed if the material to be tested is employed as the fourth section in a single trans-pipeline core. In any case, the test material is in the form of a straight strip. The term "large magnetic core", as used herein, refers to a magnetic component used in any number of electrical applications and electrical devices and having a weight that is within a range of approximately 40 to 400 kg. A magnetic core is usually constructed of magnetic strip or powder. The term "peak temperature", as used herein, refers to the maximum temperature reached by any part of the transformer core during the annealing cycle. The term "thermal impregnation time", as used herein, refers to the duration during which the core is in fact at the annealing temperature, and does not include heating and cooling times of the core. The terms "saturation induction" and "operation induction" refer to two levels of magnetic induction vant to the transformer core materials and the operation of it. Saturation induction is the maximum amount of induction available in a material. The induction of operation is the amount of magnetic induction used in the operation of a transformer core. In the case of amorphous metal alloys, the induction of saturation is determined by the chemistry of the alloys and by the temperature. The saturation induction decreases as the temperature rises. The induction of operation of a magnetic material determined by the induction of saturation. Transformers are designed to operate at lower magnetic induction levels than saturation induction.

The primary reason for this design requirement includes the permeability (μ) of the magnetic core material. Permeability is defined as the ratio between the magnetic induction (B) and the magnetic field (H) required to propel the material to this induction; that is, μ = B / H. The permeability decreases as the magnetic induction rises to levels approaching the induction of saturation. If a transformer core is operated on a magnetic induction too close to the saturation induction of the core material, a disproportionately large magnetic field will be required to achieve additional magnetic induction. In transformers, the magnetic field is applied by passing the current electrical through the primary coil. Thus, a large increase in the required magnetic field requires a large increase in current through the primary coil. A large increase in the primary current of a transformer is undesirable for numerous reasons. Large current variations through a simple transformer can degrade the quality of electrical energy through the nearby electrical power distribution system. An increase in the primary current will also result in an increased July (I2R) heating within the primary coil. This loss of electrical energy due to heat conversion affects the efficiency of the transformer. In addition, excessive current will cause excessive heating of the primary coil which can cause physical deterioration and failure of the electrical insulation used inside the coil. The failure of the electrical insulation will directly cause the transformer to fail. The heat generated in the primary coil can also heat the magnetic core of the transformer. This last effect described above, the heating of the magnetic core of the transformer, can cause a condition known as "exhaust term". As the temperature of the magnetic core rises, the saturation induction of the magnetic material decreases. For a transformer that performs at an induction level of fixed operation, the thermally induced decrease in saturation induction creates the same effect as a further increase in the induction of operation. Additional electric current is drawn through the primary coil, creating an additional July effect heating. The temperature of the magnetic core of the transformer rises further, exacerbating the situation. This uncontrolled increase in transformer temperature associated with "thermal runaway" is another frequent reason for transformer core failures in the field. To avoid these undesirable conditions, the transformers are typically designed in such a way that the induction of operation of the core or standard conditions is no greater 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 metal alloys which allows increased operation induction and decreased excitation power without inducing thermal runaway. It is desirable to operate a large magnetic core at an induction level as high as possible so that the cross section of the core can be minimized. That is, a transformer core operates based on the number of magnetic flux lines, not based on the flux density (induction). The ability to increase the density of flow of operation allows the use of smaller cross-sections of the magnetic core, while a given flow is employed. Substantial benefits are consequently derived from the manufacture of smaller magnetic core sizes for given capacitor transformers. As described above, the optimum temperature of annealing and the time for the amorphous metal alloys currently employed in the manufacture of the transformer is a temperature within a range of 140 ° C to 100 ° C below the crystallization temperature of the alloy during a period of time that is within a range of 1.5 to 2. 5 hours for a minimized core loss. The dependence of the loss of magnetic core of the annealing temperature for samples of straight strips of alloy 2605SA-1 METLAS®, after having been annealed for 2 hours is shown in Figure la. At lower temperatures, core loss is high due to insufficient recoil resulting in an easy and not well defined magnetic e. In contrast, core loss is high at higher temperatures due to the initiation of crystallization in the amorphous metal alloy. The lowest core loss is observed at approximately 360 ° C in the case of straight strip samples. Figure Ib shows the dependence of the excitation power on the annealing temperature for samples of straight strips of alloy 2605SA-1 METLAS®, after annealing for 2 hours. In this case, the optimum (minimum) excitation power is observed when an annealing process is applied for 2 hours at a temperature of about 375 ° C. The difference in optimization temperatures is very significant since both the technical literature and the patent literature have indicated the recoction of amorphous celestial alloys only to optimize the core loss while the reason for the transformer core failure is the power of high excitement. The data in figures 2a and 2b are similar to the data appearing in figures la and Ib, except that they now refer to magnetic cores for electric power service transformers. It is significant that the benefit of the collection of samples of straight strips at higher temperatures is also realized for these magnetic cores. This demonstrates the commercial utility of the present invention. Another way in which the results of the present invention can be illustrated is shown in Figure 3. The curves in Figure 3 show the dependence of the induction level of the excitation power for samples of straight strips that were annealed according to the times and indicated temperatures. The benefits of higher temperature annealing are evident. For example, if a level is selected of given excitation power, a higher operating induction may be employed for samples that have been annealed at a higher temperature. The data in figure 3 indicate that an increase of up to 5% in the induction of operation can be achieved. A further advantage of the present invention is illustrated in Figure 4, in which the dependence of the straight strip sample excitation power of the sample test temperature is shown. It is readily apparent from FIG. 4 that the benefits derived from the invention are greater at higher sample temperature. This is important because the transformers operate at temperatures higher than the ambient temperature and can achieve even higher temperatures when they are in an overload condition. Thus, the teachings of the present invention present an especially useful benefit. Annealing is a time / temperature process. Thus, Figure 5 shows the dependence of the excitation power of the "thermal impregnation time" during the annealing of a magnetic core. It is significant that, again, the excitation power decreases with an increased thermal impregnation time. This illustrates the option of using either the thermal impregnation time of the annealing cycle or temperature to develop the method of the present invention on a commercial scale. As figure 3, the Figure 6 shows the dependence of the magnetic core excitation power of the induction for cores that have been annealed using different times of thermal impregnation. EXAMPLE 1 Sixteen single phase coiled magnetic cores for use in commercial distribution transformers were manufactured using 6.7"wide METGLAS® SA-1 alloys with a nominal FeßoBuSig chemistry Each core had a weight of approximately 75 kg These sixteen cores were divided into groups of four, each group was annealed at a temperature of about 355 ° C with a different thermal impregnation time.The thermal impregnation time of basal line annealing, to achieve a minimum core loss, is approximately 20 The other three groups were annealed using thermal impregnation times of 30, 40, and 60 minutes, these times of thermal impregnation represented an increase of 50%, 100%, and 150% respectively The results for all these nuclei have already appeared in Figures 5 and 6. A significant decrease in excitation power was observed for each of the increased thermal impregnation times. In addition it was found that longer thermal impregnation times resulted in a lower excitation power.

EXAMPLE 2 Three single phase coiled magnetic cores for use in commercial distribution transformers were manufactured using a 6.7"wide METGLAS® SA-1 alloy with a nominal FeßoB ?? Si9 chemistry Each core had a weight of approximately 118 kg, and care was taken to minimize the effects of thermal gradient on the cores during heating and cooling.These three cores were annealed using a thermal impregnation time of 20 minutes and a peak temperature of approximately 370CC instead of the peak temperature The results of the excitation power and core loss measurements in these cores, which were annealed at a higher temperature, appear in comparison with the data corresponding to the cores that were conventionally annealed in the figure. 2a and 2b, respectively.

It is clear that a substantial decrease in the excitation power is achieved when the peak temperature used during nucleation of the core is increased while only a small increase in core loss is incurred. The results of Example 2, produced by the increased peak temperature annealing, are comparable to the results produced in Example 1 by the annealing during extended thermal impregnation times.

EXAMPLE 3 Laboratory samples of straight strips were made using an SA-1 alloy of METGLAS® 6.7"wide, with a nominal FeßoBuSig chemistry, These samples of straight strips were subjected to 2-hour isochronic isolations performed in a magnetic field at Various temperatures The results of excitation and core loss measurements on these laboratory samples of straight strips are plotted as a function of temperature in Figures la and Ib It is clear that a substantial decrease in excitation power is realized when the peak temperature of the annealing rises by at least 5 ° C. EXAMPLE 4 Laboratory samples of straight strips were made using a 6.7"wide METGLAS® SA-1 alloy with a nominal FeßoBuSig chemistry. These samples of straight strips were subjected to two-hour isochronic isolations made in a magnetic field at various temperatures. Figure 4 shows the excitation power measured at the indicated temperature after annealing. The results indicate an even greater reduction of the excitation power at elevated temperatures at which the transformer cores operate, compared to what is observed at room temperature. Having thus described the invention in a detailed manner, It will be understood that it is not necessary to strictly comply with these details, but that the person skilled in the art can make changes and modifications that all fall within the scope of the invention defined in the appended claims.

Claims (1)

CLAIMS A magnetic core of amorphous metal alloy having an excitation power of less than 1 VA / kg when measured at 60 Hz and an operation induction of 1.40 to about 1.45 Tesla, said measurement being carried out at room temperature. A magnetic core in accordance with the claim 1, which has a core loss of less than about 0.25 W / kg. A magnetic core in accordance with the claim 2, said core has been annealed using a thermal impregnation time at least 50% longer than required to minimize said core loss. A magnetic core according to claim 2, said core has been annealed using a thermal impregnation time at least 100% longer than required to minimize said core loss. A magnetic core according to claim 2, said core has been annealed using a thermal impregnation time at least 150% longer than required to minimize said core loss. A magnetic core according to claim 2, said core has been annealed using a peak temperature at least 5 ° C higher than the temperature required to minimize said core loss. 7. A magnetic core according to claim 2, said core has been annealed employing a peak temperature at least 15 ° C higher than the temperature required to minimize said core loss. 8. In a method for making a magnetic core of amorphous metal alloy, the improvement where said core is annealed to minimize its excitation power. 9. A method for annealing an amorphous metallic alloy magnetic core, comprising the steps of: a. heating said core in the presence of a magnetic field applied at a peak temperature; b. maintaining said core at said peak temperature in the presence of said magnetic field during a thermal impregnation time at least 50% longer than required to minimize core loss thereof; and c. cooling said core to a temperature of about 100 ° C below said peak temperature at a cooling rate that is within a range of about 0.1 to 10 ° C / m? n. A method of annealing an amorphous metallic alloy magnetic core, as claimed in claim 9, wherein the thermal impregnation time for said step of maintaining said core at said peak temperature is at least 100% greater than which is required to minimize core loss. 11. A method for annealing an amorphous metallic alloy magnetic core, according to claim 9, wherein the thermal impregnation time for said step of maintaining said core at said peak temperature is at least 150% longer than what is said. requires to minimize the loss of the core. 12. A method for annealing an amorphous metallic alloy magnetic core, comprising the steps of: a. heating said core in the presence of a magnetic field applied at a peak temperature at least 5 ° C higher than the temperature required to minimize core loss; b. maintaining said core at said peak temperature in the presence of said magnetic field during a time of thermal impregnation; and c. cooling said core to a temperature of about 100 ° C lower than said peak temperature at a cooling rate which is within a range of about 0.1 to 10 ° C / m? n. A method for annealing an amorphous metallic alloy magnetic core, as claimed in claim 12, wherein said peak temperature is at least 15 ° C higher than the temperature that is required to minimize said core loss. 14. A magnetic core of amorphous metal alloy, of according to claim 1, said core has a composition consisting essentially of about 11% boron atoms and about 9% silicon atoms, the remainder being iron and incidental impurities. . A magnetic core of amorphous metal alloy having an excitation power of less than 1 VA / kg when measured at 60 Hz and an induction of operation greater than

1. 40 to about 1.45 Tesla, said measurement is carried out at room temperature.