MAGNET CORE

Abstract

A magnet core has a linear B-H loop, a high modulability with alternating current and direct current, a relative permeability of more than 500 but less than 15,000, and a saturation magnetostriction lambdas of less than 15 ppm, and is made of a ferromagnetic alloy, at least 50 percent of which consist of fine crystalline parts having an average particle size of 100 nm or less (nanocrystalline alloy) and which is characterized by formula FeaCobNicCudMeSifBgXh, wherein M represents at least one of the elements V, Nb, Ta, Ti, Mo, W, Zr, Cr, Mn, and Hf, a, b, c, d, e, f, g are indicated in atomic percent, X represents the elements P, Ge, C and commercially available impurities, and a, b, c, d, e, f, g, h satisfy the following conditions: 0<=b<=40; 2<c<20; 0.5<=d<=2; 1<=e<=6; 6.5<=f<=18; 5<=g<=14; h<5 atomic percent; 5<=b+c<=45, and a+b+c+d+e+f=100.

Claims

1. A magnet core with a linear B-H loop and a high modulability in alternating current and direct current, comprising a relative permeability that is greater than 500 and less than 15,000, a saturation magnetostriction .sub.s whose amount is less than 15 ppm and consisting of a ferromagnetic alloy in which at least 50% of the alloy consists of fine crystalline particles with an average particle size of 100 nm or less and is characterized by the formula Fe.sub.aCo.sub.bNi.sub.cCu.sub.dM.sub.eSi.sub.fB.sub.gX.sub.h in which M is at least one of the elements from the group consisting of V, Nb, Ta, Ti, Mo, W, Zr, Cr, Mn and Hf, a, b, c, d, e, f, g are stated in atom %, X denotes elements P, Ge, C as well as commercial dopants and a, b, c, d, e, f, g, h satisfy the following conditions: 0b40; 2<c<20; 0.5d2; 1e6; 6.5f18; 5g14; h<5 atom % with 5b+c45, in which a+b+c+d+e+f=100.

2. A magnet core according to claim 1, wherein a, b, c, d, e, f, g, h satisfy the following conditions: 0b20; 2<c<15; 0.5d2; 1e6; 6.5f18; 5g14; h<5 atom % with 5b+c30, in which a+b+c+d+e+f=100.

3. A magnet core according to claim 1, wherein a, b, c, d, e, f, g, h satisfy the following conditions: 0b10; 2<c<15; 0.5d2; 1e6; 6.5f18; 5g14; h<5 atom % with 5b+c20, in which a+b+c+d+e+f=100.

4. A magnet core according to claim 1, wherein a, b, c, d, e, f, g, h satisfy the following conditions: 0.7d1.5; 2e4; 8f16; 6g12; with h<2.

5. A magnet core according to claim 1, wherein a Co content is less than or equal to a Ni content.

6. A magnet core according to claim 1, wherein the magnet core is in the form of an annular band core wound from a band with a thickness of less than 50 m.

7. A magnet core according to claim 1, wherein the amount of a coercitivity field intensity H.sub.c is less than 1 A/cm.

8. A magnet core according to claim 1, wherein a remanence ratio is less than 0.1.

9. A magnet core according to claim 1 having a relative permeability greater than 1000 and less than 10,000.

10. A magnet core according to claim 1 having a relative permeability greater than 1500 and less than 6000.

11. A magnet core according to claim 1, wherein a saturation magnetostriction .sub.s is less than 10 ppm.

12. A magnet core according to claim 1, wherein at least 50% of the alloy is accompanied by fine crystalline particles with an average particle size of 50 nm or less.

13. A magnet core according to claim 1, wherein the magnet core is configured as a closed toroidal core, oval core or rectangular core without air gap.

14. A magnet core according to claim 1, wherein the magnet core is fixed in a trough.

15. A magnet core according to claim 14, wherein for fixation of the core a soft elastic reaction adhesive and/or a soft plastic nonreactive paste is provided.

16. A method for production of a magnet core comprising a relative permeability that is greater than 500 and less than 15,000, a saturation magnetostriction .sub.s whose amount is less than 15 ppm and consisting of a ferromagnetic alloy in which at least 50% of the alloy consists of fine crystalline particles with an average particle size of 100 nm or less and is characterized by the formula Fe.sub.aCo.sub.bNi.sub.cCu.sub.dM.sub.eSi.sub.fB.sub.gX.sub.h in which M is at least one of the elements from the group consisting of V, Nb, Ta, Ti, Mo, W, Zr, Cr, Mn and Hf, a, b, c, d, e, f, g are stated in atom %, X denotes the elements P, Ge, C as well as commercial dopants and a, b, c, d, e, f, g, h satisfy the following conditions: 0b40; 2<c<20; 0.5d2; 1e6; 6.5f18; 5g14; h<5 atom % with 5b+c45, in which a+b+c+d+e+f=100, the method comprising the step of performing a heat treatment in a magnetic transverse field of the magnet core.

17. A method according to claim 16, wherein a heat treatment is also performed in a magnetic longitudinal field.

18. A method according to claim 16, wherein a heat treatment is performed in the transverse field before a heat treatment in a longitudinal field.

19. A method according to claim 16, wherein a heat treatment is performed in the transverse field after heat treatment in a longitudinal field.

20. A current transformer for alternating power with a magnet core comprising a relative permeability that is greater than 500 and less than 15,000, a saturation magnetostriction .sub.s whose amount is less than 15 ppm and consisting of a ferromagnetic alloy in which at least 50% of the alloy consists of fine crystalline particles with an average particle size of 100 nm or less and is characterized by the formula Fe.sub.aCo.sub.bNi.sub.cCu.sub.dM.sub.eSi.sub.fB.sub.gX.sub.h in which M is at least one of the elements from the group consisting of V, Nb, Ta, Ti, Mo, W, Zr, Cr, Mn and Hf, a, b, c, d, e, f, g are stated in atom %, X denotes the elements P, Ge, C as well as commercial dopants and a, b, c, d, e, f, g, h satisfy the following conditions: 0b40; 2<c<20; 0.5d2; 1e6; 6.5f18; 5g14; h<5 atom % with 5b+c45, in which a+b+c+d+e+f=100, wherein the current transformer, in addition to the magnetic core as transformer core, has a primary winding and at least one secondary winding, wherein the secondary winding is low-resistance terminated by a load resistance and/or measurement electronics.

21. A current transformer according to claim 20 having a phase error of a maximum 7.5 C. in a circuit with a load resistance and/or measurement electronics according to a respective specification and dimension.

22. A current transformer according to claim 21 having a phase error of a maximum 5 C. in a circuit with a load resistance and/or measurement electronics according to a respective specification and dimension.

23. A current-compensated inductor with a magnet core according to claim 1, wherein the inductor has at least two windings in addition to the magnet core.

24. A current-compensated inductor according to claim 23, wherein the inductor has an insertion attenuation of at least 20 dB in the frequency range from 150 kHz to 1 MHz even during flow of a discharge current of at least 10% of the nominal current.

25. A current-compensated inductor according to claim 24, wherein the inductor has an insertion attenuation of at lest 20 dB in the frequency range from 150 kHz to 1 MHz even during flow of a discharge current of at least 20% of the nominal current.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0073] The invention is further explained below by means of the practical examples depicted in the figures of the drawing. In the drawing:

[0074] FIG. 1 shows a replacement circuit for a known current converter and the ranges of the different technical data that can occur in an operation,

[0075] FIG. 2 shows the trend of the magnetic fields in a current converter according to FIG. 1,

[0076] FIG. 3 shows the trend of the amplitude error (in %) and the phase error (in ) as a function of primary current (in A) for a nominal primary current I.sub.primN of 640 ,

[0077] FIG. 4 shows the trend of the amplitude error (in %) and the phase error (in ) as a function of primary current (in A) for a nominal primary current I.sub.primN of 400 and

[0078] FIG. 5 shows the hysteresis loop for a preferred alloy according to the invention.

DETAILED DESCRIPTION

[0079] The area of application current transformers with dc tolerance for electric watt meters is treated as an example below. It was found in the pertinent investigations that, in the long known conventional current transformers with high-permeability cores, satisfaction of the requirements of the standard series IEC 62053 for dc tolerance is not possible. These standards, which apply for the requirements of electronic household meters with direct connection, require that even in the presence of half-wave-rectified (i.e., purely unipolar) sinusoidal currents power recording must be possible.

[0080] Conventional current transformers fail here because the high permeability cores are very quickly saturated by the unipolar flux that builds up. With diminishing permeability of the core material the time constant of the flux decline also drops with inductance so that the solution to the problem was sought in the use of more low-permeable amorphous alloys. However, a shortcoming here is the comparatively high price, which is mostly caused by the amorphous band of about 80% Co.

[0081] The starting point for the considerations is therefore defined in alternative very low-permeable ( preferably about 1500-6000) alloy variants suitable for replacing the amorphous low-permeability Co-based band with significant cost advantages.

[0082] Clarification of the question whether the attainable linearity approaches that of the excellent Co-based bands in this respect so that the requirements on accuracy of power measurement can be met is also important here. It can be accepted with some certain that the higher saturation induction can be transferred to the corresponding application on the way to optimization. A requirement is perfect functionality according to IEC 62053, which previously had a significant technical advantage relative to the use of cheaper ferrite cores.

[0083] Initially bands were investigated that are varied in Si content and Nb content. The experimental program included two cores each of each variant with two different temperatures in the transverse field heat treatment and three alloy compositions in the context of random experiments in alloy variation bands were cast from the experimental alloys with a width of 6.2 mm and processed to annular band cores. These were treated to achieve the flattest possible hysteresis loop in the transverse field at different temperatures. Initially the achieved average permeabilities .sub.av and other base parameters were determined (see Table 1).

TABLE-US-00001 TABLE 1 Alloys with V and Ni additives. Core T.sub.QF B.sub.max H.sub.c H.sub.a .sub.2 No. Fe Ni Cu Nb V Si B ( C.) (T) B.sub.r/B.sub.m (mA/cm) (A/cm) (av) (ppm) 1A Rem 10 1 3 0 15.9 6.6 540 1.12 0.008 13 1.75 5.083 4.4 1B Rem 10 1 3 0 15.9 6.6 470 1.13 0.009 15 2.01 4.463 2.8 2A Rem 10 1 3 0 12.5 8 540 1.19 0.008 19 2.95 3.198 7.7 2B Rem 10 1 3 0 12.5 8 570 1.20 0.011 35 3.49 2.735 6.7 3A Rem 10 1 1.5 1.5 12.5 8 540 1.20 0.016 59 3.71 2.578 6.5 3B Rem 10 1 1.5 1.5 12.5 8 570 1.20 0.057 216 3.94 2.425 5.8 Rem = remainder

[0084] At the beginning of the study all cores were inserted stress-free in troughs without filler, which were then suitably wound for the linearity measurements, in which the values at 25 C. were initially considered. The results are summarized in Table 2.

TABLE-US-00002 TABLE 2 Alloys with V and Ni additives and unfixed linearity (voltage stress-free in the trough). Core T.sub.QF /.sub.av No. Fe Ni Cu Nb V Si B ( C.) .sub.av (%) 1A-1 Remainder 10 1 3 0 15.9 6.6 540 5598 6.13 1A-2 Remainder 10 1 3 0 15.9 6.6 540 5605 6.24 1B-1 Remainder 10 1 3 0 15.9 6.6 570 4919 6.97 1B-2 Remainder 10 1 3 0 15.9 6.6 570 4888 6.79 2A-1 Remainder 10 1 3 0 12.5 8 540 3549 5.49 2A-2 Remainder 10 1 3 0 12.5 8 540 3523 5.52 2B-1 Remainder 10 1 3 0 12.5 8 570 3033 4.12 2B-2 Remainder 10 1 3 0 12.5 570 2981 3.48 3A-1 Remainder 10 1 1.5 1.5 12.5 8 540 2724 5.88 3A-2 Remainder 10 1 1.5 1.5 12.5 8 540 2714 5.46 3B-1 Remainder 10 1 1.5 1.5 12.5 8 570 2282 12.5 3B-2 Remainder 10 1 1.5 1.5 12.5 8 570 2300 12.5

[0085] For a better overview the linearity of the current trends is expressed by the dimensions /.sub.av, in which the last two data points on reaching saturation were not included in the average value. The magnet cores mostly show a linearity that is suitable to ensure the required precision of power measurement over a wide current range during use of the cores for current transformers in electronic watt meters. An exception is variant 3B in which a relatively high value with 12.5% was achieved, which presumably was caused by overtempering in the transverse field.

[0086] To determine the applications of the related fixation effect a core of each variant was either coated with an insulating plastic layer or inserted into an adapted plastic trough with soft elastic adhesive and wound/measured again. Significantly different pictures for linearity behavior of the cores were obtained, which is apparent from the two following Tables 3 and 4.

TABLE-US-00003 TABLE 3 Linearity fixed close to production (plastic layer). Core / type/ T.sub.QF .sub.av no. Fe Ni Cu Nb V Si B ( C.) .sub.av (%) 1A-1 Remainder 10 1 3 0 15.9 6.6 540 10,170 151 1B-1 Remainder 10 1 3 0 15.9 6.6 570 8403 138 2A-1 Remainder 10 1 3 0 12.5 8 540 6555 161 2B-1 Remainder 10 1 3 0 12.5 8 570 4881 129 3A-1 Remainder 10 1 1.5 1.5 12.5 8 540 3696 82.9 3B-1 Remainder 10 1 1.5 1.5 12.5 8 570 2262 35.1

TABLE-US-00004 TABLE 4 Linearity fixed close to production (plastic trough with self-elastic adhesive). Core type/ T.sub.QF /.sub.av no. Fe Ni Cu Nb V Si B ( C.) .sub.av (%) 1A-1 Remainder 10 1 3 0 15.9 6.6 540 5716 13.2 1B-1 Remainder 10 1 3 0 15.9 6.6 570 4947 5.15 2A-1 Remainder 10 1 3 0 12.5 8 540 3587 5.46 2B-1 Remainder 10 1 3 0 12.5 8 570 3033 3.06 3A-1 Remainder 10 1 1.5 1.5 12.5 8 540 2699 6.74 3B-1 Remainder 10 1 1.5 1.5 12.5 8 570 2305 12.7

[0087] Table 3 shows a very distinct effect of the plastic layer of linearity of the characteristic via the magnetostriction caused by the Ni addition the material reacts so strongly to the shrinkage stress of the layer solidifying at about 120 C. and contracting during cooling that the resulting linearities no longer appear to be useful for use in a precision current transformer. The linearity deviations reach values that lie by a factor of 9 to more than 50 above the values of magnetostriction-free amorphous Co-based alloys used for comparison.

[0088] A much more favorable behavior is caused by trough fixation. Here, during use of a soft elastic adhesive the nonlinearities only rise by a maximum of a factor of 2. In each case the variants 1B, 2A, 2B and 3A appear to be useful at room temperature for use of high linear current transformers. For subsequent considerations concerning use over a broad (for example 40 to +70 C.) temperature range, the temperature properties of the complex permeability were also considered. For example, the trends for the core 2A-2 show a negative temperature coefficient of permeability that is almost linear between 40 and +85 C. and has a value of about 0.1%/K for core 2B-2. The value applies both for amplitude of the existing field of 4 mA/cm and for 15 mA/cm. It was found that a positive temperature coefficient for the current transformer is favorable to the extent that it behaves opposite the increasing resistance of the copper wire at increasing temperature and therefore reduces the phase error. During design of the current transformers, the resulting larger variation of errors with temperature must therefore be kept in mind. During use of the soft elastic adhesive it was found that a temperature change both at high and low temperatures leads to addition of linearity deviations of the converter errors. Tensile and compressive stresses occur here on the core, which are transferred because of the elastic behavior of the hardened adhesive from the trough material. A significant reduction of this effect could be achieved by using as filler a soft plastic nonreactive paste instead of a soft elastic reaction adhesive. Linearity values could therefore be kept almost constant within the temperature range from 40 to +85 C.

[0089] A distinct advantage of the nanocrystalline material is the variability of permeability, which curing use of trough fixation must also be transported with satisfactory linearity into application. Because of the expanded useful level control range a de-tolerant current transformer can easily be tuned to an optimum of preloadability. To improve linearities, the magnetostriction can also be reduced if the percentage of added nickel is reduced by 10% in order to arrive at permeabilities of 4000 or 6400.

[0090] FIGS. 3 and 4 show the trend of the amplitude error (in %) and the phase error (in ) as a function of primary current (in A) for different nominal primary currents I.sub.primN of 640 A (FIG. 3) and 400 A (FIG. 4).

[0091] FIG. 5 finally shows the hysteresis loop (magnetic flux B in T over the field intensity H in A/cm) for an alloy with 65.2 atom % Fe, 12 atom % Ni, 0.8 atom % Cu, 2:5 atom % Nb, 11.5 atom % Si and 8 atom % B. This alloy is compared with other alloys according to the invention in Table 5, in which QF stands for the transverse field treatment and LF for longitudinal field treatment. The alloys marked with an * are comparison alloys that do not belong to the invention.

[0092] Heat treatment in the transverse field (transverse field treatment QF) is always necessary, in which the permeability can be arbitrarily adjusted with additional heat treatment in the longitudinal field (longitudinal field treatment LF) which can occur before or after transverse field treatment. This has the advantage that cores with different properties can be produced from the same alloy and therefore different classes of current transformers (current classes). The combination of temperature and duration of transverse field treatment should always have a stronger effect than temperature and duration of longitudinal field treatment.

TABLE-US-00005 TABLE 5 B.sub.m H.sub.c TK .sub.s Nr Fe Co Ni Cu Nb V Si B WB (T) B.sub.r/B.sub.m (A/cm) (%/ C.) (ppm) 1 75.5 0 1 3 12.5 8 0.5 h 550 C. QF 1.32 0.006 0.005 10600 0.25 4.4 2 70.5 5 1 3 12.5 8 0.5 h 550 C. QF 1.28 0.001 0.008 5020 0.18 3a 65.5 10 1 3 12.5 8 0.5 h 570 C. QF 1.23 0.006 0.019 2630 0.13 3b 65.5 10 1 3 12.5 8 0.5 h 550 C. QF 1.21 0.001 0.005 2837 0.17 3c 65.5 10 1 3 12.5 8 0.5 h 540 C. QF 1.19 0.008 0.019 3200 0.16 7.7 3d 65.5 10 1 3 12.5 8 0.5 h 550 C. LF + 1.21 0.001 0.015 6080 0.05 3 h 500 C. QF 3e 65.5 10 1 3 12.5 8 0.5 h 550 C. LF + 1.20 0.003 0.030 7140 0.01 3 h 460 C. QF 3f 65.5 10 1 3 12.5 8 0.5 h 550 C. LF + 1.20 0.002 0.018 8360 0.03 3 h 423 C. QF 4 65.5 10 1 1.5 1.5 12.5 8 0.5 h 540 C. QF 1.20 0.016 0.059 2578 0.16 6.5 5a 60.5 15 1 3 12.5 8 0.5 h 550 C. QF 1.12 0.005 0.026 1860 0.12 5b 60.5 15 1 3 12.5 8 0.5 h 550 C. LF + 1.12 0.036 0.073 4590 0.03 3 h 500 C. QF 5c 60.5 15 1 3 12.5 8 0.5 h 550 C. LF + 1.12 0.036 0.061 5420 0.001 3 h 460 C. QF 5d 60.5 15 1 3 12.5 8 0.5 h 550 C. LF + 1.12 0.044 0.031 6490 0.02 3 h 423 C. QF 6 55.5 20 1 3 12.5 8 0.5 h 550 C. QF 0.18 0.140 1.14 1.75 7 64.5 10 1 3 14 7.5 0.5 h 550 C. QF 1.10 0.005 0.012 3520 0.15 8 66 10 1 3 11 9 0.5 h 550 C. QF 1.25 0.001 0.003 2617 0.15 8.7 9a 63.5 10 1 3 15.9 6.6 0.5 h 550 C. QF 1.14 0.002 0.003 4307 0.12 9b 63.5 10 1 3 15.9 6.6 0.5 h 540 C. QF 1.12 0.008 0.013 5080 0.09 4.4 10 63.5 10 1 1.5 1.5 15.9 6.6 0.5 h 540 C. QF 1.12 0.011 0.026 3400 0.12 3.1 11 66.7 10 0.8 3 11.5 8 0.5 h 550 C. QF 1.23 0.000 0.002 2610 0.14 8.1 12 67 10 0.8 2.7 11.5 8 0.5 h 550 C. QF 1.27 0.001 0.003 2610 0.13 13 69.2 8 0.8 2.5 11.5 8 0.5 h 550 C. QF 1.32 0.012 0.041 3090 0.12 7.6 14 67.2 10 0.8 2.5 11.5 8 0.5 h 550 C. QF 1.29 0.006 0.022 2650 0.12 15 65.2 12 0.8 2.5 11.5 8 0.5 h 550 C. QF 1.26 0.004 0.019 2230 0.11 8.8 16 63.2 14 0.8 2.5 11.5 8 0.5 h 550 C. QF 1.16 0.110 0.620 1720 0.09 17 67.4 10 0.8 2.3 11.5 8 0.5 h 550 C. QF 1.30 0.016 0.063 2610 0.09 18 67.6 10 0.8 2.1 11.5 8 0.5 h 550 C. QF 1.30 0.064 0.253 2600 0.04 19 66.8 10 0.8 2.9 11.5 8 0.5 h 550 C. QF 1.25 0.012 0.041 2787 0.14 7.9 20 61.8 5 10 0.8 2.9 11.5 8 0.5 h 550 C. QF 1.25 0.008 0.039 2045 0.13 10.7 21 56.8 10 10 0.8 2.9 11.5 8 0.5 h 550 C. QF 1.24 0.012 0.073 1627 0.15 12.5 22 46.8 20 10 0.8 2.9 11.5 8 0.5 h 550 C. QF 1.22 0.015 0.127 1097 0.16 20.5 23 36.8 30 10 0.8 2.9 11.5 8 0.5 h 550 C. QF 1.17 0.018 0.208 845 0.17 23.5 24 26.8 40 10 0.8 2.9 11.5 8 0.5 h 550 C. QF 1.03 0.040 0.519 582 0.46 22

[0093] The values listed in the above Table 5 mean: [0094] 1. QF=heat treatment in magnetic transverse field, LF=heat treatment in magnetic transverse field. [0095] 2. Bm was measured at a maximum field intensity of Hm=8 A/cm for examples 1 to 21 and Hm=32 A/cm for examples 22 to 24. [0096] 3. denotes the average permeability, defines the average slope of the hysteresis curve. [0097] 4. No. 1 and No. 6 are comparative examples NOT according to the invention.

[0098] The numbering of the alloys from Table 5 differs from that in Tables 1-4. The permeability values between Table 5 and the other tables can therefore easily differ, since different experimental series are involved.

[0099] With the magnet cores according to the invention current transformers can be produced in Which the maximum undistorted amplitude of a half-wave electrified sinusoidal primary current has a numerical value at least 10%, better 20% of the effective value of the maximum undistorted bipolar sinusoidal primary current.