Current transformer magnetic core heat treatment method for optimizing magnetic domain structure

Abstract

The invention relates to the technical field of current transformer magnetic cores, in particular to a current transformer magnetic core heat treatment method for optimizing a magnetic domain structure, which is characterized in that crystal grain nucleation and growth are completed in the heating process, a transverse magnetic field is applied in the cooling process to complete optimization of the magnetic domain structure, and the specific operation steps are as follows: 1) a pre-heating stage; 2) a coring stage; 3) an ultrafine grain growth stage; (4) a transverse magnetic field cooling stage: applying a transverse magnetic field under any one of the following three temperatures: applying the transverse magnetic field at the temperature of 300 DEG C, keeping the temperature for 30-40 minutes, and closing the magnetic field; when the magnetic core is cooled to 280 DEG C, a transverse magnetic field is applied, and heat preservation is conducted for 30-40 minutes; when the magnetic core is cooled to 250 DEG C, a transverse magnetic field is applied, heat preservation is conducted for 30-40 minutes, then the magnetic field is closed, and the magnetic core is discharged out of the furnace. The method has the advantages that the iron-based nanocrystalline strip iron core is subjected to continuous heat treatment, fine regulation and control of the magnetic domain structure are achieved under the economical and efficient condition, and the precision requirement of the current transformer for metering is met.

Description

Technical Field

[0001] The present invention relates to the technical field of current transformer cores, and in particular to a heat treatment method for a current transformer core with an optimized magnetic domain structure. Background Art

[0002] As a key device for power system monitoring and protection, the performance of current transformers is directly influenced by the soft magnetic properties of their core materials, which are closely related to the magnetic domain structure. Traditional heat treatment techniques have significant limitations in optimizing magnetic domain structure, such as low product precision, weak saturation resistance, and difficulty in achieving uniform microstructural control. While rapid thermal processing techniques (laser, microwave, flash annealing, etc.) have improved these issues to some extent, they still face challenges such as high equipment costs and complex processes.

[0003] Chinese invention patent application number 202410262224.3 discloses a nanocrystalline soft magnetic alloy, its preparation method, and application. The nanocrystalline soft magnetic alloy comprises Si, B, Cu, Nb, Ce, P, Zr, Co, and a balance of Fe. By adjusting the constituent elements in the nanocrystalline soft magnetic alloy, the present invention ensures that the final product possesses both excellent magnetic and mechanical properties, while also avoiding the adverse effects of excessive element doping on the performance of the nanocrystalline soft magnetic alloy. The preparation method enables uniform heating of the material, thereby controlling the orderly changes in the magnetic domains within the nanoscale soft magnetic alloy, resulting in excellent AC and DC performance. The resulting product is particularly suitable for Type A residual current transformers. Type A residual current transformers emphasize the sensitivity and reliability of leakage detection, focusing on safety protection, and placing greater emphasis on high sensitivity and anti-interference capabilities. They can detect even small leakage currents and accurately detect even in complex situations such as pulsating DC current. Key measurement indicators include performance fluctuation percentage and AC / DC ratio, making them unsuitable for metering current transformers.

[0004] The Chinese invention patent application number 202411399663.5 discloses an ultra-microcrystalline magnetic core and a processing method thereof. The magnetic core is composed of a dual-phase structure of amorphous and nanocrystalline with an average grain size of less than 25nm. It includes iron, copper, niobium, silicon and boron elements. The molecular formula of the magnetic core is FeaCubNbSidBe. The preparation method can simultaneously improve the induced potential and initial magnetic permeability of the ultra-microcrystalline magnetic core, reduce the core loss, and the production process is relatively simple and the cost is relatively low, which is easy to industrialize. The product has excellent soft magnetic properties and the initial magnetic permeability can reach 118,400. Under the condition of 50mA excitation current, the induced potential increased by 23.8%. Under the condition of 450mA excitation current, the induced potential increased by 4.27%. When the rated current percentage is 1% and 120%, the negative ratio difference is reduced by 0.05%, and the angular difference is reduced by 2.1min and 3min respectively.

[0005] Chinese invention patent application number 201710298580.0 discloses a heat treatment method for an amorphous iron core, comprising the following steps: placing the amorphous iron core in a heat treatment furnace; evacuating the heat treatment furnace; pre-filling the heat treatment furnace with nitrogen after evacuation; heating the amorphous iron core, during which a straight wire is energized to apply a transverse magnetic field to the amorphous iron core; holding the amorphous iron core, during which the transverse magnetic field continues to be applied to the amorphous iron core; cooling the amorphous iron core to room temperature along with the heat treatment furnace after the holding period. At the beginning of the cooling process, the straight wire is de-energized, and the magnetizing coil is energized to apply a longitudinal magnetic field to the amorphous iron core until the cooling process is complete, at which point the magnetic field is discontinued; and after the cooling process, removing the amorphous iron core and coating the surface of the amorphous iron core. This amorphous iron core heat treatment method is highly efficient and can effectively increase the saturation magnetization strength of the amorphous iron core, reduce stress in the amorphous iron core, and reduce losses in the amorphous iron core. Furthermore, the amorphous iron core is cured with epoxy resin, meeting the requirements for transformer applications.

[0006] Chinese invention patent application number 202110124958.1 discloses a heat treatment method for high-linearity current transformer cores. The resulting product is suitable for transformers operating at micro-gram levels and large ampere-turns. The method primarily focuses on optimizing linearity metrics and analyzes only from the perspective of angular difference. This differs from the metrics used in our research for measuring transformers operating at small ampere-turns in the 100-gram range. This linearity analysis is not applicable to metering current transformers.

[0007] Chinese invention patent application number 200510036133.5 discloses a nanocrystalline soft magnetic core, its heat treatment method, and its application. This method does not include a preheating and nucleation stage, resulting in weak soft magnetic properties. Furthermore, the applied transverse magnetic field ranges from 500 to 600 Gs, resulting in a relatively weak magnetic field. The prepared core samples were used in common-mode inductors and electromagnetic residual current transformers. The magnetic properties studied included initial and maximum permeability, which is different from the application of current transformers for measurement at 50 Hz power frequency.

[0008] The metering current transformer is a measuring instrument with a high level of precision. It is necessary to further optimize the heat treatment technology to finely control the magnetic domain structure so that the metering current transformer can more accurately measure the current in the power system, provide accurate signals for electric energy metering, and reduce the measurement error of the current transformer, namely "ratio error" and "angle error". Improving the soft magnetic properties of the current transformer core is a major issue that needs to be urgently addressed in this field. Summary of the Invention

[0009] The purpose of the present invention is to provide a current transformer core heat treatment method with optimized magnetic domain structure, overcoming the shortcomings of the existing technology. By continuously heat treating the iron-based nanocrystalline strip core, grain nucleation and growth are completed during the heating process, and a transverse magnetic field is applied during the cooling process to complete the magnetic domain structure optimization, the temperature gradient change of the magnetic core is fully utilized, energy loss is reduced, and processing efficiency is improved, so that the magnetic domain structure can be finely controlled under economical and efficient conditions.

[0010] To achieve the above object, the present invention is implemented through the following technical solutions:

[0011] A heat treatment method for a current transformer core with optimized magnetic domain structure is disclosed. The method completes grain nucleation and growth during the heating process, and applies a transverse magnetic field during the cooling process to optimize the magnetic domain structure. This method fully utilizes the temperature gradient change of the core, reduces energy loss, and improves treatment efficiency. The specific steps are as follows:

[0012] 1) Preheating stage: In a transverse magnetic furnace, heat the core from room temperature to 300°C at a heating rate of 2.75-2.9°C / min, and keep it at 300°C for 100-200 minutes;

[0013] 2) Nucleation stage: Raise the core temperature from 300°C to 480°C at a rate of 1.8°C / min to promote the formation of crystal nuclei, and keep it at 480°C for 100-200 minutes;

[0014] 3) Ultrafine grain growth stage: Raise the core temperature from 480°C to 550°C at a heating rate of 0.7°C / min to promote the growth of ultrafine grains and the formation of copper clusters. Keep the core temperature at 550°C for 100-200 minutes.

[0015] 4) Transverse magnetic gradient cooling stage: The transverse magnetic furnace is evacuated to ensure that the vacuum degree in the furnace reaches -0.1Mpa. Subsequently, inert gas is filled into the transverse magnetic furnace to make the pressure in the transverse magnetic furnace reach 0.1Mpa; a transverse magnetic field is applied under any of the following three temperature conditions: a transverse magnetic field is applied at 300°C, kept warm for 30-40 minutes, and then the magnetic field is turned off; when the core is cooled to 280°C, a transverse magnetic field is applied, kept warm for 30-40 minutes, and then the magnetic field is turned off; a transverse magnetic field is applied at 250°C, kept warm for 30-40 minutes, and then the magnetic field is turned off. The core temperature drops below 250°C and the core is taken out of the furnace.

[0016] Furthermore, the room temperature range is 10-35°C.

[0017] Furthermore, the specification model of the transverse magnetic furnace is DY4-66-6, the magnetic field control current is set to 48A, and the magnetic field strength is 1000Gs.

[0018] Furthermore, the inert gas is nitrogen or argon.

[0019] Furthermore, in the transverse magnetic gradient cooling process, the cooling method is furnace cooling or fan cooling, and the cooling rate should not be higher than 2.5°C / minute.

[0020] Furthermore, the temperature of the magnetic core out of the furnace should not be lower than 200°C.

[0021] Furthermore, the magnetic core is composed of a dual-phase structure of amorphous and nanocrystalline, with an average grain size of less than 20 nm. The molecular formula of the magnetic core is FeaCubNbcSidBe, wherein a, b, c, d and e are the atomic ratios of the corresponding elements in the alloy, wherein: 0.6≤b≤1; 2.5≤c≤3.5; 0.5≤d≤3; 13≤e≤15, a+b+c+d+e=100.

[0022] Furthermore, the strip used for the magnetic core is prepared by a single-roller rapid cooling method. The ejected strip is divided into a free surface and a roller-attached surface. The cooling roller speed is 1550-1650 r / min, the strip width is 25 mm, and the strip thickness is 34-36 μm.

[0023] Furthermore, the magnetic core is a ring-shaped magnetic core with an inner diameter of 100 mm, an outer diameter of 123±0.5 mm, a height of 25 mm, and a single body weight of 600 g.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1) By continuously heat treating the iron-based nanocrystalline ribbon core, grain nucleation and growth are completed during the heating process, and a transverse magnetic field is applied during the cooling process to optimize the magnetic domain structure. This fully utilizes the temperature gradient change of the magnetic core, reduces energy loss by 15%, shortens processing time, improves efficiency, and achieves fine control of the magnetic domain structure under economical and efficient conditions;

[0026] 2) The treatment process is simple, low-cost, easy to industrialize and mass-produce, and has good application prospects;

[0027] 3) The optimized magnetic core exhibits better "ratio difference" and "angle difference" performance in power system monitoring and protection, and can better meet the needs of high-precision current transformers for measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The magnetic domain structure of Inventive Example 1;

[0029] Figure 2 The magnetic domain structure of Inventive Example 2;

[0030] Figure 3 The magnetic domain structure of Inventive Example 3;

[0031] Figure 4 is the magnetic domain change of the comparative example;

[0032] Figure 5 XRD diffraction profiles of Examples 1 to 3 of the invention and the comparative example;

[0033] Figure 6 AC BH curves measured in Examples 1 to 3 of the invention and the comparative example;

[0034] Figure 7 AC loss angle ψ-H curves measured for Examples 1 to 3 of the invention and the comparative example. DETAILED DESCRIPTION

[0035] The technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments.

[0036] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the specific embodiments required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the specific embodiments described below are some implementation methods of the present invention. For ordinary technicians in this field, other specific embodiments can be obtained based on these specific embodiments without paying any creative work.

[0037] The components of the embodiments of the present invention generally described and shown in the specific embodiments herein can be arranged and designed in countless different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the specific embodiments is not intended to limit the scope of the claimed invention, but is merely representative of selected embodiments of the present invention.

[0038] The magnetic cores used in the following examples and comparative examples are made from iron-based nanocrystalline ribbon. The cores consist of a dual-phase structure of amorphous and nanocrystalline materials, with an average grain size of less than 25 nm. The molecular formula of the cores is FeaCubNbcSidBe, where a, b, c, d, and e represent the atomic ratios of the corresponding elements in the alloy, with the following characteristics: 0.1 ≤ b ≤ 2; 0.5 ≤ c ≤ 5; 0.5 ≤ d ≤ 3; and 6 ≤ e ≤ 12. The cores are produced using a single-roller quenching method. The ejected ribbon has a free surface and a roller-applied surface. The cooling roller rotates at a speed of 1500-1650 rpm, and the ribbon width is 25 mm, with a thickness of 32-36 μm. The cores are toroidal, with an inner diameter of 100 mm, an outer diameter of 123 ± 0.5 mm, a height of 25 mm, and a weight of 600 g. The room temperature range is 10-35°C. The transverse magnetic furnace is DY4-66-6. The inert gas is nitrogen or argon.

[0039] Example 1

[0040] A heat treatment method for a current transformer core with optimized magnetic domain structure is disclosed. The method completes grain nucleation and growth during the heating process, and applies a transverse magnetic field during the cooling process to optimize the magnetic domain structure. This method fully utilizes the temperature gradient change of the core, reduces energy loss, and improves treatment efficiency. The specific steps are as follows:

[0041] 1) Preheating stage:

[0042] In a transverse magnetic furnace, the core was heated from room temperature (10°C) to 300°C at a rate of 2.9°C / min and kept at 300°C for 100 minutes.

[0043] 2) Nucleation stage:

[0044] The core temperature was raised from 300°C to 480°C at a rate of 1.8°C / min to promote the formation of crystal nuclei, and then kept at 480°C for 100 minutes.

[0045] 3) Ultrafine grain growth stage:

[0046] The core temperature was raised from 480°C to 550°C at a rate of 0.7°C / min to promote the growth of ultrafine grains and the formation of copper clusters. The core was kept at 550°C for 100 minutes.

[0047] 4) Transverse Magnetic Gradient Cooling Stage: The transverse magnetic furnace is evacuated to a vacuum of -0.1 MPa. Subsequently, inert gas is introduced into the furnace to a pressure of 0.1 MPa. The magnetic field control current is set to 48A, and the magnetic field strength is 1000 Gs. A transverse magnetic field is applied at 300°C for 30 minutes, after which the magnetic field is removed. When the core cools to 250°C, it is removed from the furnace. During the transverse magnetic gradient cooling process, the core cools as it cools along with the furnace.

[0048] Example 2

[0049] A heat treatment method for a current transformer core with optimized magnetic domain structure is disclosed. The method completes grain nucleation and growth during the heating process, and applies a transverse magnetic field during the cooling process to optimize the magnetic domain structure. This method fully utilizes the temperature gradient change of the core, reduces energy loss, and improves treatment efficiency. The specific steps are as follows:

[0050] 1) Preheating stage:

[0051] In a transverse magnetic furnace, the core was heated from room temperature (25°C) to 300°C at a rate of 2.75°C / min and held at 300°C for 100 minutes.

[0052] 2) Nucleation stage:

[0053] The core temperature was raised from 300°C to 480°C at a rate of 1.8°C / min to promote the formation of crystal nuclei, and then kept at 480°C for 100 minutes.

[0054] 3) Ultrafine grain growth stage:

[0055] The core temperature was raised from 480°C to 550°C at a rate of 0.7°C / min to promote the growth of ultrafine grains and the formation of copper clusters. The core was kept at 550°C for 100 minutes.

[0056] 4) Transverse Magnetic Gradient Cooling Stage: The transverse magnetic furnace is evacuated to a vacuum of -0.1 MPa. Subsequently, inert gas is introduced into the furnace to a pressure of 0.1 MPa. The magnetic field control current is set to 48A, and the magnetic field strength is 1000 Gs. A transverse magnetic field is applied at 280°C for 30 minutes, after which the magnetic field is removed. When the core cools to 250°C, it is removed from the furnace. During the transverse magnetic gradient cooling process, fans are used for cooling, and the cooling rate should not exceed 2.5°C / minute.

[0057] Example 3

[0058] A heat treatment method for a current transformer core with optimized magnetic domain structure is disclosed. The method completes grain nucleation and growth during the heating process, and applies a transverse magnetic field during the cooling process to optimize the magnetic domain structure. This method fully utilizes the temperature gradient change of the core, reduces energy loss, and improves treatment efficiency. The specific steps are as follows:

[0059] 1) Preheating stage: In a transverse magnetic furnace, the core is heated from room temperature (10°C) to 300°C at a heating rate of 2.9°C / min, and then kept at 300°C for 100 minutes;

[0060] 2) Nucleation stage: Raise the core temperature from 300°C to 480°C at a rate of 1.8°C / min to promote the formation of crystal nuclei, and keep the temperature at 480°C for 100 minutes;

[0061] 3) Ultrafine grain growth stage: the core temperature is increased from 480°C to 550°C at a heating rate of 0.7°C / min to promote the growth of ultrafine grains and the formation of copper clusters. The core is kept at 550°C for 100 minutes.

[0062] 4) Transverse Magnetic Gradient Cooling Stage: The transverse magnetic furnace is evacuated to a vacuum of -0.1 MPa. Subsequently, inert gas is introduced into the furnace to a pressure of 0.1 MPa. The magnetic field control current is set to 48A, and the magnetic field strength is 1000 Gs. A transverse magnetic field is applied at 250°C for 30 minutes, after which the magnetic field is removed. When the core cools to 250°C, it is removed from the furnace. During the transverse magnetic gradient cooling process, the core cools as it cools along with the furnace.

[0063] Comparative Example

[0064] Grain nucleation and growth are completed during the heating process. The specific steps are as follows:

[0065] 1) Preheating stage: In a transverse magnetic furnace, the core is heated from room temperature (10°C) to 300°C at a heating rate of 2.9°C / min, and then kept at 300°C for 100 minutes;

[0066] 2) Nucleation stage: Raise the core temperature from 300°C to 480°C at a rate of 1.8°C / min to promote the formation of crystal nuclei, and keep the temperature at 480°C for 100 minutes;

[0067] 3) Ultrafine grain growth stage: The core temperature is raised from 480°C to 550°C at a heating rate of 0.7°C / min to promote the growth of ultrafine grains and the formation of copper clusters. The core is kept at 550°C for 100 minutes. When the core is cooled to 250°C with the furnace, the core is taken out of the furnace.

[0068] Core performance test

[0069] The performance tests were conducted on the nanocrystalline soft magnetic alloys provided in the embodiments and comparative examples. The testing instrument was the MATS-2010SA soft magnetic AC measuring device of Hunan Lianzhong Technology Co., Ltd. The test conditions were AC 50Hz, 60 turns of primary winding, and 2 turns of secondary winding. The remanence, coercive force and loss performance results of the magnetic core are shown in Table 1. The electrical performance test of the magnetic core was conducted using the HD-1 iron core magnetic performance measuring instrument of Jingjiang Zhicheng Measuring Instrument Co., Ltd. In the experiment, the primary winding of the magnetic core was 1 turn and the secondary winding was 1 turn. The induced potential results are shown in Table 2, in mV. The error test of the magnetic core was conducted using the SZCP-2 current transformer calibration equipment of Shenyang Shanzhong Technology Co., Ltd. The ratio difference comparison of the magnetic core is shown in Table 3, and the angular difference comparison of the magnetic core is shown in Table 4. The magnetic domain test was conducted using the soft magnetic material testing magneto-optical Kerr system of Zhizhen Precision Instrument (Qingdao) Co., Ltd. The XRD diffraction test used the D8 Advance X-ray diffractometer produced by Bruker, Germany, with a scanning range of 30° to 90°. The AC BH curve and ψ-H curve were tested under the impedance function conditions using the SZCP-2 mutual inductor calibration equipment of Shenyang Shanzhong Technology Co., Ltd.

[0070] Table 1

[0071] Serial number Remanence T Coercive force A / m <![CDATA[Loss × 10 -3 W / kg]]> Example 1 0.4237 1.026 11.23 Example 2 0.4113 0.997 10.95 Example 3 0.4024 0.976 10.67 Comparative Example 0.4450 1.124 12.62

[0072] Table 1 shows the AC magnetic properties of the core samples, including remanence, coercivity, and loss measurements, tested at Bm = 0.5 T. Examples 1-3 exhibit reduced remanence, loss, and coercivity, with Example 3 exhibiting the lowest loss, a 14.45% reduction compared to the comparative example. Example 3 also exhibits the lowest coercivity, a 13.17% reduction compared to the comparative example. These examples demonstrate lower core losses.

[0073] Table 2

[0074] Serial number 10mA 50mA 250mA 300mA 450mA 500mA 600mA Example 1 0.2 1.5 29.9 44.2 52.3 50.8 52.5 Comparative Example 2 0.2 1.5 30.7 46.4 53.2 52.7 54.2 Example 3 0.2 1.5 31.9 47.7 54.6 55.3 56.3 Comparative Example 0.2 1.5 28.4 37.1 47.4 48.9 50.9

[0075] Table 2 shows the changes in the induced potential of the magnetic core samples. Within the 10 to 50 mA range, the induced potential of Examples 1-3 remained essentially unchanged. Within the 250 mA to 600 mA range, the induced potential of Examples 1-3 increased. At 450 mA, approaching 120% of the rated current, the induced potential of Example 3 increased from 47.4 mV in the comparative example to 54.6 mV, a 14.47% increase. This demonstrates excellent anti-saturation performance.

[0076] Table 3

[0077] Current percentage 1％ 5％ 20％ 100％ 120％ Example 1 -0.13 -0.10 -0.04 0.02 0.04 Example 2 -0.11 -0.09 -0.04 0.01 0.03 Example 3 -0.10 -0.08 -0.03 0.03 0.05 Comparative Example -0.14 -0.13 -0.07 -0.02 0.02

[0078] Table 3 shows the ratio difference results of the current transformer; it shows the ratio difference under 10VA secondary load conditions. The ratio differences of the magnetic cores of Comparative Examples 1 to 3 at 1% and 5% of the rated current are all reduced. The ratio differences of the magnetic cores after treatment in Example 3 at 1% and 5% of the rated current are -0.1% and -0.08%, respectively, and the angular difference values are reduced by 0.04% and 0.05%, respectively. It is obvious that the ratio difference of the magnetic cores after treatment in the examples is closer to the zero axis, showing excellent measurement accuracy, and the measurement accuracy of Example 3 is more accurate.

[0079] Table 4

[0080] Current percentage 1％ 5％ 20％ 100％ 120％ Example 1 16.6 9.3 5.5 1.3 1.1 Example 2 16.3 9.0 5.3 1.2 1.0 Example 3 15.9 8.5 5.1 1.0 0.9 Comparative Example 18.4 11 7.2 4.4 3.5

[0081] Table 4 shows the angular difference results of the current transformer; it shows the angular difference under 10VA secondary load conditions. The angular difference of the magnetic cores treated in Examples 1 to 3 at 120% of the rated current percentage is greatly reduced, and the angular difference value is closer to zero, indicating that the embodiments have better anti-saturation performance. In particular, the angular difference value of Example 3 at 120% of the rated current percentage is reduced to 25.71% of the original, and the phase deviation value is even lower. The angular differences at 1% and 5% of the rated current are 15.9 minutes and 8.5 minutes, respectively, which are 2.5 minutes less than the control example. It is obvious that the angular difference of the magnetic core after treatment in the embodiment is closer to the zero axis, showing excellent accuracy performance;

[0082] Figure 1 The magnetic domain structure of Example 1 shows a striped domain structure with a certain orientation. The overall arrangement is relatively orderly, but not uniform. The domain walls are relatively flat, with many uneven areas at the edges. There are a large number of 180° domain walls between adjacent domains, with a small number of 90° domain walls.

[0083] Figure 2 The magnetic domain structure of Example 2 shows multiple discontinuous, oriented strip-shaped domains. While the overall arrangement is relatively orderly, the domain walls are not perfectly aligned. The flatness of the domain walls is relatively poor, with numerous uneven areas at the edges. The majority of adjacent domains still have 180° domain walls, with a few 90° domain walls present.

[0084] Figure 3 The magnetic domain structure of Example 3 of the invention shows a neatly arranged strip domain structure in the figure, which is mainly composed of 180° domain walls. The flatness of the magnetic domain walls is relatively good, the morphology of the magnetic domain walls is regular, and they show a highly ordered feature. Therefore, the defect density is lower, the pinning effect of the magnetic domain walls is smaller, and the magnetic properties are better.

[0085] Figure 4 For the comparative magnetic domain structure, the distribution of magnetic domains presents block characteristics, the 180° domain wall and the 90° domain wall account for a similar proportion, the distribution is relatively disordered, the flatness of the magnetic domain wall is poor, and there are a large number of uneven areas, which will lead to higher magnetic loss of the iron core and worse magnetic properties.

[0086] Figure 5 The XRD diffraction patterns of Examples 1 to 3 and the comparative example show that the ribbon samples have crystallized, with sharp crystallization diffraction peaks appearing near 2θ = 45°, 65°, and 85°. Comparison with PDF cards reveals that these peaks are α-Fe(Si) phases, with corresponding crystal plane indices of (110), (200), and (211), demonstrating that the ribbons prepared by all schemes have a nanocrystalline phase structure.

[0087] Figure 6 The AC BH curves for Examples 1-3 and the comparative example show that the magnetic flux density (B) of the example samples decreases when the magnetic field strength is below approximately 8.7 mA / cm. However, the magnitude of the magnetic flux density increases instantaneously around 7 mA / cm. After exceeding 8.7 mA / cm, the magnetic flux density (B) exceeds that of the comparative example. This phenomenon demonstrates that the treatments in Examples 1-3 significantly improve the magnetic flux density of the magnetic core at specific magnetic field strengths, further optimizing its magnetic properties and increasing its resistance to saturation.

[0088] Figure 7AC loss angle ψ-H curves measured for the inventive examples and comparative examples. The core loss angle of the samples in Examples 1-3 changed from a peak to an arched shape, with the peak maximum loss angle decreasing from approximately 70° to approximately 50°. The peak magnetic field intensity corresponding to the maximum loss angle also decreased, from approximately 10 mA / cm to approximately 8 mA / cm. These changes demonstrate that Examples 1-3 effectively reduce core losses and improve magnetic properties.

[0089] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A heat treatment method for a current transformer core with optimized magnetic domain structure, characterized in that: During the heating process, grain nucleation and growth are completed. During the cooling process, a transverse magnetic field is applied to optimize the magnetic domain structure. This fully utilizes the temperature gradient change of the magnetic core, reduces energy loss, and improves processing efficiency. The specific operation steps are as follows: 1) Preheating stage: In a transverse magnetic furnace, heat the core from room temperature to 300°C at a heating rate of 2.75-2.9°C / min, and keep it at 300°C for 100-200 minutes; 2) Nucleation stage: Raise the core temperature from 300°C to 480°C at a rate of 1.8°C / min to promote the formation of crystal nuclei, and keep it at 480°C for 100-200 minutes; 3) Ultrafine grain growth stage: Raise the core temperature from 480°C to 550°C at a heating rate of 0.7°C / min to promote the growth of ultrafine grains and the formation of copper clusters. Keep the core temperature at 550°C for 100-200 minutes. 4) Transverse magnetic gradient cooling stage: The transverse magnetic furnace is evacuated to ensure that the vacuum degree in the furnace reaches -0.1Mpa. Subsequently, inert gas is filled into the transverse magnetic furnace to make the pressure in the transverse magnetic furnace reach 0.1Mpa; a transverse magnetic field is applied under any of the following three temperature conditions: a transverse magnetic field is applied at 300°C, kept warm for 30-40 minutes, and then the magnetic field is turned off; when the core is cooled to 280°C, a transverse magnetic field is applied, kept warm for 30-40 minutes, and then the magnetic field is turned off; a transverse magnetic field is applied at 250°C, kept warm for 30-40 minutes, and then the magnetic field is turned off. The core temperature drops below 250°C and the core is taken out of the furnace.

2. The method for heat treating a current transformer core with optimized magnetic domain structure according to claim 1, characterized in that: The room temperature range is 10-35°C.

3. The heat treatment method for a current transformer core with optimized magnetic domain structure according to claim 1, characterized in that: The specification model of the transverse magnetic furnace is DY4-66-6, the magnetic field control current is set to 48A, and the magnetic field strength is 1000Gs.

4. The method for heat treating a current transformer core with optimized magnetic domain structure according to claim 1, characterized in that: The inert gas is nitrogen or argon.

5. The method for heat treating a current transformer core with optimized magnetic domain structure according to claim 1, characterized in that: During the transverse magnetic gradient cooling process, the cooling method is furnace cooling or fan cooling, and the cooling rate should not be higher than 2.5°C / minute.

6. The method for heat treating a current transformer core with optimized magnetic domain structure according to claim 1, characterized in that: The temperature of the magnetic core out of the furnace should not be lower than 200°C.

7. The method for heat treating a current transformer core with optimized magnetic domain structure according to claim 1, characterized in that: The magnetic core is composed of an amorphous and nanocrystalline dual-phase structure with an average grain size of less than 20 nm. The molecular formula of the magnetic core is FeaCubNbcSidBe, wherein a, b, c, d and e are the atomic ratios of the corresponding elements in the alloy, wherein: 0.6≤b≤1; 2.5≤c≤3.5; 0.5≤d≤3; 13≤e≤15, and a+b+c+d+e=100.

8. The method for heat treating a current transformer core with optimized magnetic domain structure according to claim 1, characterized in that: The strip used for the magnetic core is prepared by a single-roller rapid cooling method, with a cooling roller speed of 1550-1650 r / min, a strip width of 25 mm, and a strip thickness of 34-36 μm.

9. The method for heat treating a current transformer core with optimized magnetic domain structure according to claim 1, characterized in that: The magnetic core is a ring-shaped magnetic core with an inner diameter of 100 mm, an outer diameter of 123±0.5 mm, a height of 25 mm, and a single body weight of 600 g.

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