Preparation method of wide-range current transformer iron core

Abstract

The invention discloses a preparation method of a wide-range current transformer iron core, which comprises the following steps of: selecting a first ferromagnetic material strip with initial permeability mu i greater than 50,000 and a second ferromagnetic material strip with saturation flux density Bs greater than 1.8 T, the thickness of the first material being 15-30 microns, and the thickness of the second material being 0.10-0.30 mm; the strip is precisely cut, and the dimensional tolerance is controlled within + / -0.02 mm; the cut strip is subjected to surface insulation treatment, and an insulation coating of 1-3 microns is formed on the surface of the second material; the two materials are combined into an annular iron core in an alternate lamination mode, and an insulating layer smaller than 5 microns is arranged between layers; and carrying out multi-stage annealing treatment in a protective atmosphere, wherein the multi-stage annealing treatment comprises a 300-450 DEG C destressing stage, a recrystallization stage and a 400-500 DEG C magnetic field annealing stage. According to the iron core manufactured by the method, the ratio error is less than 0.5% and the angular difference is less than 20 minutes within the rated current range of 0.1-200%, so that wide-range and high-precision measurement is realized, and a reliable technical basis is provided for accurate measurement of a power system.

Description

Technical Field

[0001] This invention belongs to the field of power measurement equipment technology, specifically relating to a method for preparing a wide-range current transformer core. Background Technology

[0002] Traditional current transformer cores face significant technical bottlenecks in terms of measurement range and accuracy. When measuring small currents, conventional silicon steel or microcrystalline alloy cores exhibit finite initial permeability and nonlinear characteristics, leading to a significant increase in ratio and angle errors, resulting in a sharp decline in measurement accuracy. When measuring large currents, the core is prone to magnetic saturation, severely degrading accuracy and potentially damaging the equipment. This fundamental contradiction between accuracy and range has long constrained the performance improvement of current transformers. Pursuing high accuracy typically requires the use of high-permeability materials such as microcrystalline alloys, but these materials have relatively low saturation magnetic flux density, limiting the maximum measurement current range. Conversely, pursuing a wide range often involves using low-permeability materials such as silicon steel, but their accuracy is poor when measuring small currents. Furthermore, the inherent hysteresis and eddy current effects of ferromagnetic materials introduce non-negligible phase angle errors, especially under conditions of low current and frequency variation, which significantly impact the accuracy of power measurements.

[0003] While existing technological solutions alleviate the aforementioned problems to some extent, they still have many shortcomings. Multi-core or multi-winding current transformers, which handle different current ranges using different cores, can expand the measurement range, but they are structurally complex, bulky, and expensive to manufacture, requiring complex switching circuits for range conversion. Electronic current transformers and Rogowski coils, while offering wide ranges, require external power supplies, are susceptible to electromagnetic interference, and may not perform as well as high-performance electromagnetic current transformers in terms of long-term stability, temperature characteristics, and absolute accuracy, while also being relatively expensive. Some manufacturers have attempted to use combinations of cores made of different materials, but often lack a systematic design for material interface characteristics, magnetic circuit coupling efficiency, annealing process compatibility, and overall structural optimization, resulting in limited improvements in linearity and accuracy under wide range conditions, or the inability to achieve a compact structural design.

[0004] The current manufacturing process for current transformers lacks sufficient precision, further limiting the improvement of product performance. Insufficient control precision in key processes such as core cutting, lamination, winding, and annealing directly affects the magnetic properties of the materials and the electrical characteristics of the final product. Particularly in the annealing process, the lack of precise temperature control and magnetic field treatment technologies tailored to the characteristics of composite materials prevents the full utilization of the performance advantages of different materials. With the increasing demands for measurement accuracy in power systems and the deepening of smart grid construction, there is an urgent need to develop an innovative core manufacturing method that can effectively overcome the limitations of traditional technologies, achieving high-precision measurement across a wide dynamic range from extremely small to extremely large currents in a single, compact core structure, while also possessing low phase error, high temperature stability, and good adaptability for industrial production. Summary of the Invention

[0005] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0006] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0007] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing a wide-range current transformer core.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing a wide-range current transformer core, characterized in that it includes: A first ferromagnetic material strip with an initial magnetic permeability μi greater than 50,000 and a second ferromagnetic material strip with a saturation magnetic induction intensity Bs greater than 1.8T were selected. The first and second ferromagnetic material strips are precision cut, with dimensional tolerances controlled within ±0.02mm; The cut strip is subjected to surface insulation treatment to form an insulating coating with a thickness of 1~3μm on the surface of the second ferromagnetic material strip; The first ferromagnetic material strip and the second ferromagnetic material strip are combined in an alternating stacking manner to form a ring core, and an insulating layer with a thickness of less than 5μm is set between the layers. The assembled toroidal core is subjected to multi-stage annealing under a protective atmosphere, including: a stress relief stage with the temperature raised to 300~450℃, a recrystallization stage with the temperature raised to the optimal annealing temperature of the first ferromagnetic material, and a magnetic field annealing stage in which a longitudinal magnetic field with an intensity of 1000~5000 A / m is applied in the temperature range of 400~500℃ during the cooling process.

[0009] In a preferred embodiment of the preparation method described in this invention, the thickness of the first ferromagnetic material strip is 15~30μm, and the thickness of the second ferromagnetic material strip is 0.10~0.30mm.

[0010] As a preferred embodiment of the preparation method described in this invention, the first ferromagnetic material is any one of iron-based nanocrystalline alloy strip, cobalt-based amorphous alloy strip, or permalloy strip with a nickel content greater than 80%; the second ferromagnetic material is any one of high magnetic induction oriented silicon steel strip, iron-based amorphous alloy strip, or permalloy strip with high saturation magnetic induction intensity.

[0011] In a preferred embodiment of the preparation method described in this invention, the volume ratio of the first ferromagnetic material strip to the second ferromagnetic material strip is 1:2 to 2:5.

[0012] As a preferred embodiment of the preparation method described in this invention, the alternating layering method includes simple alternating layering, grouped alternating layering, or gradual transition layering.

[0013] As a preferred embodiment of the preparation method described in this invention, the multi-stage annealing process further includes a controlled cooling stage performed after the magnetic field annealing stage is completed, wherein the cooling rate from the annealing temperature to 300°C is controlled at 20~50°C / h, and the cooling rate from 300°C to room temperature is controlled at 50~100°C / h.

[0014] As a preferred embodiment of the preparation method described in this invention, the longitudinal magnetic field applied during the magnetic field annealing stage is a DC magnetic field or an AC magnetic field with a frequency of 50~60Hz, the deviation angle between the magnetic field direction and the magnetic circuit direction of the iron core does not exceed ±5°, and the magnetic field application time is 2~5 hours.

[0015] As a preferred embodiment of the preparation method described in this invention, the method further includes a step of combining a first ferromagnetic material strip and a second ferromagnetic material strip in a layered winding manner. The layered winding manner involves first winding the first ferromagnetic material strip to form an inner core, and then winding the second ferromagnetic material strip around its outer side to form an outer ring. The winding tension is controlled within the range of 30% to 60% of the material's yield strength.

[0016] As a preferred embodiment of the preparation method described in this invention, when the first ferromagnetic material is an iron-based nanocrystalline alloy strip, the annealing temperature during the recrystallization stage is 540~560℃, and the holding time is 30~90 minutes; when the first ferromagnetic material is a permalloy strip, the annealing temperature during the recrystallization stage is 1100~1200℃, and the holding time is 2~6 hours.

[0017] Another objective of this invention is to overcome the shortcomings of the prior art and provide a current transformer core, wherein the ratio difference of the core within the range of 0.1% to 200% of the rated current is less than 0.5% and the phase difference is less than 20 minutes.

[0018] Beneficial effects of this invention: (1) Significantly expands the measurement range and greatly improves measurement accuracy. By scientifically combining a first ferromagnetic material with ultra-high initial permeability (μi > 50,000) with a second ferromagnetic material with high saturation magnetic induction (Bs > 1.8T), this invention effectively solves the fundamental contradiction between accuracy and range in traditional single-material cores. The composite laminate structure enables the core to maintain high-precision measurement over an extremely wide current range of 0.1%-200%, with the ratio difference controlled within 0.5% and the angle difference less than 20 minutes. This represents a qualitative breakthrough compared to the problem of a sharp drop in accuracy when measuring small currents with traditional cores. Verification by examples shows that the ratio difference is only 0.08% under 0.1% rated current conditions and the saturation degree is less than 5% under 200% rated current conditions, fully meeting the accuracy requirements of 0.2S or even 0.1S levels, providing a reliable technical foundation for accurate measurement in power systems and the construction of smart grids.

[0019] (2) Achieving a compact structural design and significantly improving manufacturing process stability. This invention achieves performance indicators that traditional multi-core systems can only achieve on a single compact core structure through precise alternating lamination technology and multi-stage annealing process, avoiding complex switching circuits and large structural designs. The multi-stage annealing process includes precise control of stress relief, recrystallization, and magnetic field annealing stages. In particular, the innovative process of applying a longitudinal magnetic field of 1000-5000 A / m in the temperature range of 400~500℃ effectively orients the magnetic domain structure and significantly reduces coercivity and hysteresis loss. During the manufacturing process, dimensional tolerances are controlled within ±0.02mm, and the insulation layer thickness control accuracy reaches ±0.5μm, ensuring a high degree of consistency in product quality. Temperature stability tests show that the initial permeability change rate is less than ±0.15% in the full temperature range of -40℃ to 85℃, providing a reliable guarantee for long-term stable operation in harsh environments. At the same time, the process is mature and has good prospects for industrial application. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein: Figure 1 This is a schematic diagram of the overlapping composite laminated core structure of the present invention; Figure 2 This is a schematic diagram of the temperature curve for the multi-stage annealing process of the present invention; Figure 3 This is a schematic diagram comparing the material selection and performance parameters of the present invention; Figure 4 This is a schematic diagram comparing the wide-range accuracy performance of the present invention. Detailed Implementation

[0021] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0022] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0023] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0024] The first type of materials in this invention mainly includes iron-based nanocrystalline alloys (Fe73.5Cu1Nb3Si13.5B9, Fe73.5Si13.5B9Nb3Cu1, etc.), cobalt-based amorphous alloys, and high-nickel permalloy (1J85 series with Ni content greater than 80%). These materials have extremely high initial permeability, low coercivity, and excellent small-signal linearity, ensuring extremely high measurement accuracy even under weak current conditions. The second type of materials uses high-magnetic-induction oriented silicon steel (30ZH105, 27ZH095, etc.), iron-based amorphous alloys (Fe78Si9B13, Fe80B20, etc.), or permalloy with high saturation magnetic induction. The saturation magnetic induction of these materials is usually greater than 1.8T, and some can reach more than 2.0T, which can withstand the strong magnetic field generated by large current without saturation.

[0025] In the structural design and implementation of this invention, the composite laminated structure employs a precisely controlled alternating lamination technique, participating in... Figure 1The first type of material strips and the second type of material strips are stacked according to a preset ratio and sequence. Typical stacking patterns include simple alternating pattern (ABABA), grouped alternating pattern (AA-BB-AA-BB), and gradual transition pattern (A-AB-B-BA-A), each optimized for specific application requirements. Interlayer insulation uses an inorganic insulating coating with a thickness of 2-5 micrometers, such as silicon dioxide, alumina, or a specially made composite insulating film, to ensure effective isolation of eddy current paths without affecting magnetic flux conduction. The core design of the invention, featuring complementary materials and a compact structure, is visually presented and serves as the basic structural carrier for achieving wide range and high precision. The ring shape is a standard design for current transformer cores, ensuring an uninterrupted magnetic flux closed path, avoiding accuracy loss due to magnetic leakage, and adapting to the magnetic circuit requirements of medium and low voltage power system transformers.

[0026] The precision machining stage of this invention requires high-precision cutting of all strips, with dimensional tolerances controlled within ±0.01mm and a surface roughness Ra value of less than 0.8μm. Laser cutting is the preferred method, and the cutting parameters need to be precisely adjusted according to the material properties. For nanocrystalline alloys, the laser power density is controlled at 10... 6 -10 7 Within the W / cm² range, the pulse frequency is 1~10kHz; for silicon steel, continuous laser cutting is used, and the power density is appropriately increased to ensure cutting quality. Wire cutting and precision stamping are alternative options, but processing stress needs to be strictly controlled to avoid adverse effects on the material's magnetic properties.

[0027] Surface treatment and insulation processes have a decisive impact on the final performance. For silicon steel, an improved phosphating process is used for surface insulation, with specific organic modifiers added to the phosphating solution to significantly improve the adhesion and temperature resistance of the insulation layer. The C6 environmentally friendly coating is applied using electrostatic spraying technology, ensuring that the coating thickness uniformity is controlled within ±0.5μm. For nanocrystalline alloys, because their surfaces easily form a natural oxide layer, surface cleaning is required in a vacuum or inert gas environment, and plasma cleaning technology is used to remove surface contaminants when necessary.

[0028] The assembly process utilizes specialized precision stacking equipment equipped with force and displacement sensors to monitor stacking pressure and interlayer thickness in real time. Stacking pressure is typically controlled within the range of 0.5–2.0 MPa to ensure tight adhesion between layers without generating excessive mechanical stress. For wound structures, a CNC winding machine is used for precise control. The winding tension needs to be adjusted according to the material's mechanical properties and thickness, typically controlled within 30–50% of the material's yield strength.

[0029] The effect of the annealing process in this invention directly determines the final magnetic properties of the iron core. The stress-relief annealing temperature in the first stage needs to be precisely set according to the characteristics of different materials. For composite iron cores containing nanocrystalline alloys, the temperature is usually controlled at 350~400℃, the holding time is 1~3 hours, and the heating and cooling rates do not exceed 50℃ / h to ensure that the stress is fully released without causing unnecessary structural changes.

[0030] The second stage, recrystallization annealing, is a crucial step in restoring the material's magnetic properties. For nanocrystalline alloys, precise control is required near their crystallization temperature, typically 540–560°C, with a holding time of 30–90 minutes. Temperature control accuracy in this stage must be ±2°C, and the holding time needs to be adjusted based on the material's specific composition and thickness. For permalloys, the annealing temperature is typically 1100–1200°C, and it must be carried out under a hydrogen protective atmosphere to prevent oxidation and decarburization.

[0031] The third stage, magnetic field annealing, is the key innovation of this invention. During the cooling process, when the temperature drops to the range of 400~500℃, a longitudinal magnetic field with an intensity of 1500~3000 A / m is applied. The direction of the magnetic field must be strictly consistent with the magnetic circuit direction of the iron core, and the deviation angle must not exceed ±5°. The magnetic field is typically applied for 2~4 hours, during which the temperature remains constant. This process can effectively orient the magnetic domain structure, significantly reduce coercivity and hysteresis loss, and improve the initial permeability and maximum permeability.

[0032] The cooling rate needs to be strictly controlled during the controlled cooling stage, especially when passing through the Curie point temperature of various materials. The cooling rate from the magnetic field annealing temperature to 300°C should be controlled at 20~40°C / h, and the cooling rate from 300°C to room temperature can be appropriately increased to 50~80°C / h. The entire cooling process must be carried out under a protective atmosphere with a purity of 99.9% or higher.

[0033] The completed iron core undergoes a rigorous quality inspection process. Magnetic performance testing employs specialized magnetic performance measuring equipment, measuring key parameters including initial permeability, maximum permeability, saturation magnetic induction, coercivity, remanent magnetic induction, and power loss. Testing conditions are strictly implemented according to relevant international standards, and testing frequencies cover common power frequencies such as 50Hz, 60Hz, and 400Hz.

[0034] Dimensional accuracy is checked using a coordinate measuring machine or laser measuring equipment to ensure that the geometric dimensions of the core meet design requirements. Insulation resistance testing is conducted under specified temperature and humidity conditions, and the insulation resistance value should not be less than 100MΩ. Mechanical strength testing includes bending strength, compressive strength, and impact resistance testing to ensure that the core is not damaged during transportation and installation.

[0035] Figure 2 This is a schematic diagram of the temperature curve of the multi-stage annealing process of the present invention. It is a key process carrier for activating the magnetic properties of composite iron cores. Through precise temperature control and magnetic field synergy, the magnetic domain structure of the material is optimized in a directional manner, reducing hysteresis loss and coercivity.

[0036] Figure 3 This diagram illustrates the comparison of material selection and performance parameters in this invention. It shows that the combination of two types of materials covers the full range of current requirements from 0.1% to 200% of the rated current. At low currents, the high μi material dominates magnetic conduction, ensuring accuracy; at high currents, the high Bs material dominates magnetic load-bearing, preventing saturation. The complementary advantages of these two types of materials provide material-level support for the performance breakthrough of the composite core.

[0037] Example 1 This embodiment addresses the high-precision measurement requirements within a range of 0.1% to 20%. A 20μm thick Fe73.5Cu1Nb3Si13.5B9 nanocrystalline alloy is selected as the first material, and a 0.15mm thick 27ZH095 high-magnetic-induction silicon steel is selected as the second material. The volume ratio of the first to the second material is 2:3, employing a grouped alternating layered structure, i.e., every two layers of nanocrystalline material are followed by three layers of silicon steel. Interlayer insulation uses a 3μm thick polyimide film, which exhibits excellent temperature resistance and insulation properties.

[0038] The specific preparation process is as follows: (1) Perform laser precision cutting on nanocrystalline alloy strip. The cutting parameters are laser power 800W, cutting speed 15m / min, and pulse frequency 5kHz to ensure that the cutting edge is smooth and burr-free.

[0039] The silicon steel strip is precision stamped and cut, with the stamping gap controlled within 8-12% of the material thickness. In the surface treatment stage, the silicon steel sheet is treated with an improved phosphating process, with the phosphating solution temperature controlled at 65-70℃ and the treatment time at 8-12 minutes, forming a dense phosphating film with a thickness of 1-2μm.

[0040] The surface of the nanocrystalline ribbon is cleaned with plasma to remove the surface oxide layer and contaminants.

[0041] (2) The stacking process is carried out in a constant temperature and humidity environment, with the temperature controlled at 20±2℃ and the relative humidity controlled at 45~55%. A special stacking fixture is used to stack the layers one by one according to the design sequence. An intermediate inspection is carried out every 10 layers to ensure the uniformity of the interlayer thickness. After the stacking is completed, a clamping force of 1.5MPa is applied and held for 30 minutes to eliminate the interlayer air gaps.

[0042] (3) The annealing process adopts a four-stage precision control: The first stage involves heating to 380℃ and holding for 2 hours to relieve stress. The second stage involves heating to 550℃ and holding for 1 hour to induce nanocrystallization. In the third stage, when the temperature is reduced to 420℃, a longitudinal DC magnetic field of 2500A / m is applied, and the temperature is maintained for 3 hours for magnetic annealing. The fourth stage involves cooling to 200°C at a rate of 25°C / h, followed by furnace cooling to room temperature. The entire annealing process is conducted under a vacuum of less than 10... -3 The process is carried out in a vacuum furnace.

[0043] (4) The completed iron core was tested. The ratio difference was 0.08% and the angle difference was 1.8 minutes under the condition of 0.1% rated current. The ratio difference was 0.05% and the angle difference was 1.2 minutes under the condition of 20% rated current. It fully meets the 0.2S level accuracy requirement, and some performance indicators reach the 0.1S level.

[0044] Example 2 This embodiment addresses the high-current measurement requirements within the 100%-200% measurement range. A 25μm thick Fe78Si9B13 iron-based amorphous alloy is selected as the first material, and a 0.23mm thick 30ZH105 ultra-high magnetic induction silicon steel is selected as the second material. Considering the anti-saturation requirements for high current, the volume ratio of the two materials is adjusted to 1:4, employing an inner core-outer ring winding structure. Specifically, the iron-based amorphous alloy is first wound to form the inner core, and then the silicon steel strip is wound around the outer ring to form the outer ring.

[0045] The specific preparation process is as follows: (1) The iron-based amorphous alloy strip is surface treated by using a weak acid cleaning solution to remove the surface oxide layer, and then a silicon dioxide insulating film with a thickness of 0.5 μm is formed on the surface.

[0046] After degreasing and cleaning, the silicon steel strip is treated with a C6 environmentally friendly insulating coating, with the coating thickness controlled at 2±0.3μm.

[0047] (2) The winding process uses a CNC precision winding machine. The tension is controlled at 150N and the winding speed is 2m / min to ensure that the strip is tightly fitted without gaps.

[0048] During outer ring winding, the tension is increased to 200N, and the winding speed is reduced to 1.5m / min to ensure good bonding with the inner core. Tension is monitored every turn during winding, and automatic adjustment is made when the deviation exceeds ±5%.

[0049] (3) The annealing process has been optimized for high-current applications: The first stage involves heating to 400℃ and holding for 1.5 hours. The second stage involves heating to the optimal annealing temperature of the iron-based amorphous alloy, 380°C, and holding for 2 hours. At this temperature, the iron-based amorphous alloy remains in an amorphous state, but the stress is fully released. In the third stage, when the temperature is reduced to 400℃, an alternating magnetic field with a frequency of 50Hz and an effective value of 2000A / m is applied for magnetic annealing for 4 hours. The alternating magnetic field can further optimize the magnetic domain structure. The fourth stage involves controlled cooling, with the cooling rate maintained at 30°C / h as it passes the Curie point.

[0050] (4) The obtained iron core was tested under 200% rated current conditions and showed that the saturation degree was less than 5%, the specific difference was kept within 0.4%, and the angle difference was less than 12 minutes, demonstrating excellent anti-saturation performance. Under 100% rated current conditions, the specific difference was 0.2% and the angle difference was 8 minutes, meeting the 0.5 grade accuracy requirements.

[0051] Example 3 This embodiment is designed for harsh environment applications, with an operating temperature range of -40℃ to +85℃. 1J85 permalloy (85% Ni content), with an extremely low temperature coefficient, is selected as the primary material, with a thickness of 30μm. It is paired with a special-composition silicon steel (3.5% Si content, with trace amounts of Al added) with a thickness of 0.20mm as the secondary material. To ensure stability over a wide temperature range, both materials undergo a special pretreatment process.

[0052] The specific preparation process is as follows: (1) The pretreatment of the permalloy strip includes pre-annealing in a hydrogen atmosphere at a temperature of 900°C for 4 hours, followed by rapid cooling to room temperature. This process can eliminate internal stress in the strip and optimize the crystal structure.

[0053] Silicon steel strip undergoes decarburization annealing, which involves holding it at 850℃ for 6 hours in dry hydrogen to remove carbon and impurities from the steel and improve the stability of its magnetic properties.

[0054] (2) The stacked structure adopts a symmetrical design, that is, from the center of the iron core outward, it is silicon steel-permalloy-silicon steel-permalloy, forming a symmetrical magnetic property distribution, which is beneficial to reduce the impact of temperature changes on the overall performance.

[0055] The interlayer insulation uses an inorganic silica coating, which is prepared by the sol-gel method with a thickness controlled at 2 μm and has excellent temperature resistance and chemical stability.

[0056] (3) The annealing process has added a temperature cycling stage to the original four stages: After magnetic field annealing, a three-cycle treatment is performed, heating to 300℃ and then cooling to 100℃, with each heating and cooling rate of 50℃ / h, and holding at 300℃ and 100℃ for 2 hours each. This temperature cycling treatment effectively eliminates residual internal stress, improves the microstructure stability of the material, and thus improves the temperature coefficient.

[0057] (4) To verify temperature stability, the completed iron core underwent performance testing across the entire temperature range. The test results showed that within the temperature range of -40℃ to 85℃, the rate of change of initial permeability was less than ±0.15%, the rate of change of saturation magnetic induction was less than ±0.1%, and the temperature coefficients of specificity difference and angle difference were less than ±0.002% / ℃ and ±0.02 min / ℃, respectively, fully meeting the application requirements under harsh environments.

[0058] Comparative Example 1 This comparative example provides a traditional method for preparing silicon steel cores, specifically as follows: 27ZH095 high magnetic silicon steel with a thickness of 0.15mm was selected as the raw material. The shearing kerf gap was 0.01mm, the overlap was 0.8mm, and the strip tension was 0.30MPa. The winding tension control range was 0.10MPa. The annealing temperature was 450℃, the holding time was 10h, the annealing atmosphere was nitrogen or inert gas, the heating rate was 150℃ / h, the cooling rate was 50℃ / h, and the strip was cold rolled to 150℃ and then cooled to room temperature in the furnace.

[0059] Comparative Example 2 This comparative example provides a method for preparing a traditional microcrystalline alloy core, specifically as follows: Fe73.5Cu1Nb3Si13.5B9 nanocrystalline alloy with a thickness of 20μm was selected as the raw material. The raw material was cut into square alloy sheets using a cross-cutting device. These square alloy sheets were then subjected to magnetic field annealing under nitrogen protection: nitrogen was introduced into the electric furnace as a protective gas; the temperature was increased to 250℃ at a heating rate of 20℃ / min, and a DC magnetic field with an intensity of 100mT was applied, with the magnetic field direction perpendicular to the casting direction of the alloy strip. The temperature was held at 250℃ for 120min, and then increased to 390℃ at the same heating rate; the magnetic field direction and intensity were kept unchanged, and the temperature was held at 390℃ for 120min; then the temperature was decreased at a rate of 10℃ / min, and the magnetic field was removed when the temperature dropped to 250℃. The temperature was then reduced to room temperature at the same cooling rate.

[0060] Figure 4This diagram illustrates a performance comparison between the composite core of this invention and traditional silicon steel cores and microcrystalline alloy iron. It shows that traditional cores rely on a single material and cannot cover the entire measurement range. This invention achieves a synergistic effect of high precision at low current and anti-saturation at high current through material composite and multi-stage annealing. The curve trend directly proves that the technical solution of this invention solves the contradiction between accuracy and range in traditional technologies, providing reliable support for accurate measurement in power systems.

[0061] In actual production, the main problems that may be encountered include interlayer short circuits, uneven magnetic properties, and dimensional deviations. Interlayer short circuits are usually caused by insulation layer damage or uneven thickness. The solution is to strengthen the quality control of the insulation layer, adopt a multi-layer composite insulation structure, and add insulation detection points at critical locations. Specific measures include online insulation resistance monitoring, real-time detection of insulation layer thickness, and the use of higher-performance insulation materials.

[0062] Non-uniform magnetic properties mainly stem from improper control of the annealing process, particularly uneven temperature distribution and inaccurate cooling rate control. Improvement measures include optimizing the annealing furnace temperature control system, increasing the density of temperature monitoring points, employing multi-zone independent temperature control technology, and improving the furnace airflow circulation system to ensure temperature uniformity. Furthermore, establishing a mathematical model of the annealing process and optimizing process parameters through simulation can further improve the process controllability and reproducibility.

[0063] Dimensional deviations mainly occur during the cutting and stacking processes. Improving cutting accuracy requires regular calibration of the cutting equipment, optimization of cutting parameters, and enhanced monitoring of tool wear. Dimensional control during the stacking process requires improved design of the stacking fixture, the addition of a real-time monitoring system, and the establishment of a feedback control mechanism.

[0064] To further improve product quality, it is recommended to adopt statistical process control methods, establish control charts for key process parameters, and monitor the stability of the production process in real time. By collecting and analyzing a large amount of production data, key factors affecting product quality can be identified, and preventative quality control strategies can be established. Simultaneously, a comprehensive traceability system should be established to record the material batches, process parameters, and testing data for each iron core, providing data support for subsequent quality analysis and process improvement.

[0065] The main technological innovation of this invention lies in achieving complementary advantages in material properties. Through precise structural design and process control, a single iron core can maintain high precision over an extremely wide current range. Specific innovations include: employing a scientific combination scheme of multiple materials, forming a series of material selection systems; developing composite structure design methods to meet different application requirements; establishing a precise multi-stage annealing process, particularly the application of magnetic field annealing technology; and forming a complete quality control and performance testing system.

[0066] Through the implementation of the above detailed technical solution, this invention can produce current transformer cores that maintain high accuracy across a wide measurement range of 0.1% to 200%, providing a reliable technical foundation for precise measurement and protection of power systems. This manufacturing method is not only technologically advanced but also possesses mature and reliable processes, showing promising prospects for industrial application. As the requirements for measurement accuracy in power systems continue to increase and the application environment becomes increasingly complex, the technical solution provided by this invention will play an increasingly important role.

[0067] This invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of this invention. To provide the public with a thorough understanding of this invention, specific details are described in detail in the following preferred embodiments; however, those skilled in the art will fully understand the invention even without these details. Furthermore, to avoid unnecessary misunderstanding of the essence of this invention, well-known methods, processes, procedures, components, and circuits are not described in detail.

[0068] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the present invention.

Claims

1. A method for preparing a wide-range current transformer core, characterized in that: include, A first ferromagnetic material strip with an initial magnetic permeability μi greater than 50,000 and a second ferromagnetic material strip with a saturation magnetic induction intensity Bs greater than 1.8T were selected. The first and second ferromagnetic material strips are precision cut, with dimensional tolerances controlled within ±0.02mm; The cut strip is subjected to surface insulation treatment to form an insulating coating with a thickness of 1~3μm on the surface of the second ferromagnetic material strip; The first ferromagnetic material strip and the second ferromagnetic material strip are combined in an alternating stacking manner to form an iron core, and an insulating layer with a thickness of less than 5μm is set between the layers; The assembled core is subjected to multi-stage annealing under a protective atmosphere, including: a stress relief stage with the temperature raised to 300~450℃, a recrystallization stage with the temperature raised to the optimal annealing temperature of the first ferromagnetic material, and a magnetic field annealing stage in which a longitudinal magnetic field with an intensity of 1000~5000A / m is applied in the temperature range of 400~500℃ during the cooling process.

2. The preparation method according to claim 1, characterized in that: The thickness of the first ferromagnetic material strip is 15~30μm, and the thickness of the second ferromagnetic material strip is 0.10~0.30mm.

3. The preparation method according to claim 1, characterized in that: The first ferromagnetic material is any one of iron-based nanocrystalline alloy strip, cobalt-based amorphous alloy strip, or permalloy strip with a nickel content greater than 80%; the second ferromagnetic material is any one of high magnetic induction oriented silicon steel strip, iron-based amorphous alloy strip, or permalloy strip with high saturation magnetic induction intensity.

4. The preparation method according to claim 1, characterized in that: The volume ratio of the first ferromagnetic material strip to the second ferromagnetic material strip is 1:2 to 2:

5.

5. The preparation method according to claim 1, characterized in that: The alternating stacking method includes simple alternating stacking, grouped alternating stacking, or gradual transition stacking.

6. The preparation method according to claim 1, characterized in that: The multi-stage annealing process also includes a controlled cooling stage after the magnetic field annealing stage is completed, wherein the cooling rate from the annealing temperature to 300°C is controlled at 20~50°C / h, and the cooling rate from 300°C to room temperature is controlled at 50~100°C / h.

7. The preparation method according to claim 1, characterized in that: The longitudinal magnetic field applied during the magnetic field annealing stage is a DC magnetic field or an AC magnetic field with a frequency of 50~60Hz. The deviation angle between the magnetic field direction and the magnetic circuit direction of the iron core does not exceed ±5°, and the magnetic field is applied for 2~5 hours.

8. The preparation method according to claim 1, characterized in that: It also includes the step of combining the first ferromagnetic material strip and the second ferromagnetic material strip in a layered winding manner. The layered winding manner is to first wind the first ferromagnetic material strip to form an inner core, and then wind the second ferromagnetic material strip around it to form an outer ring. The winding tension is controlled within the range of 30% to 60% of the material yield strength.

9. The preparation method according to claim 1, characterized in that: When the first ferromagnetic material is an iron-based nanocrystalline alloy strip, the annealing temperature during the recrystallization stage is 540~560℃, and the holding time is 30~90 minutes; when the first ferromagnetic material is a permalloy strip, the annealing temperature during the recrystallization stage is 1100~1200℃, and the holding time is 2~6 hours.

10. A current transformer core, characterized in that, The core is manufactured using the preparation method described in any one of claims 1 to 9, wherein the ratio difference within the range of 0.1% to 200% of the rated current is less than 0.5%, and the angle difference is less than 20 minutes.

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