A method for preparing nanocrystalline magnetic core of precision current transformer

Abstract

The invention discloses a method for preparing a nanocrystalline magnetic core of a precision current transformer, comprising the following steps: S100, mixing and smelting raw materials of a nanocrystalline strip to obtain an alloy melt; S200, spraying the alloy melt onto the roller surface of a cooling roller to obtain a nanocrystalline strip coil; S300, installing the nanocrystalline strip coil on a reverse rotation shaft; S400, passing the free end of the nanocrystalline strip coil through the upper end of a first supporting guide roller, the lower end of a metering roller and the upper end of a second supporting guide roller in sequence, and connecting with a winding shaft of a winding machine; S500, starting a reverse motor, a magnetic powder clutch and a winding machine, and the winding machine stops and cuts off the nanocrystalline strip after rotating a set number of circles to obtain a nanocrystalline magnetic core semi-finished product; S600, calculating the length of the used nanocrystalline strip and comparing it with a preset length to determine whether the semi-finished magnetic core is qualified; S700, performing equipment inspection if unqualified, and performing heat treatment on the qualified nanocrystalline magnetic core semi-finished product if qualified to obtain a nanocrystalline magnetic core finished product.

Description

Technical Field

[0001] The invention belongs to the technical field of nanocrystalline magnetic core preparation, and in particular relates to a method for preparing a nanocrystalline magnetic core of a precision current transformer. Background Art

[0002] In the power system, the current transformer is an important measuring device. The performance of the current transformer depends largely on the characteristics of its magnetic core. Traditional magnetic core materials have some limitations, such as insufficient magnetic permeability and large hysteresis loss, which will affect the measurement accuracy and stability of the transformer. Nanocrystalline magnetic cores have the advantages of high magnetic permeability, low coercivity, and low hysteresis loss, and are very suitable for the preparation of high-performance and high-precision current transformers.

[0003] In the prior art, the invention patent with patent number CN201710479922.9 discloses an iron-based nanocrystalline magnetic core and a preparation method thereof. In the technical scheme thereof, the preparation method of the iron-based nanocrystalline magnetic core mainly comprises the following steps: (1) smelting the iron-based nanocrystalline strip raw material to obtain an alloy melt; (2) spraying the alloy melt by a single-roller rapid cooling method to obtain an iron-based nanocrystalline strip; (3) winding the iron-based nanocrystalline strip into an annular nanocrystalline magnetic core; (4) placing the nanocrystalline magnetic core in a vacuum annealing furnace for heat treatment; (5) placing the heat-treated nanocrystalline magnetic core in a vacuum annealing furnace for heat treatment again; in the steps (4) and (5), the heat treatment steps are: a) subjecting the raw material to 110-13 0min to raise the temperature in the furnace from room temperature to 640-660K; b) keep it at 643-663K for 15-25min, and then use 32-40min to raise the temperature to 750-770K; c) keep it at 753-773K for 35-45min, and then use 11-15min to raise the temperature to 790-810K; d) keep it at 793-813K for 55-65min, and then use 10-14min to raise the temperature to 825-845K; e) keep it at 828-848K for 35-45min, then exit the furnace cover and use strong wind to cool the furnace body to 340-360K, open the furnace door and take out the nanocrystalline magnetic core; f) put the nanocrystalline magnetic core taken out of the furnace on a cooling rack and then use strong wind to cool it to room temperature. When making nanocrystalline magnetic cores in this patent solution, iron-based nanocrystalline strips are wound into ring-shaped nanocrystalline magnetic cores.

[0004] The invention patent with patent number CN202111240282.9 discloses a DC-resistant nanocrystalline dual-core current transformer core and its preparation method. In its technical scheme, the preparation method of the first nanocrystalline core includes the following steps: (1) winding an iron-based nanocrystalline alloy strip into a first magnetic ring; (2) annealing the first magnetic ring obtained in step (1) to obtain a first nanocrystalline core. The preparation method of the second nanocrystalline core includes the following steps: (a) tension crystallization annealing treatment of the iron-based nanocrystalline alloy strip and then winding to obtain a second magnetic ring; (b) the second magnetic ring obtained in step (a) is successively impregnated and solidified to obtain the second nanocrystalline core. When the patent scheme makes nanocrystalline cores, both the first nanocrystalline core and the second nanocrystalline core are obtained by winding the nanocrystalline alloy strip.

[0005] It can be seen from the above patents that an indispensable step in preparing annular nanocrystalline magnetic cores is to wind or wrap nanocrystalline alloy strips. For precision current transformers, the structure of the nanocrystalline magnetic cores used has higher precision requirements, such as size and number of winding layers. These structures are related to the tightness during winding, the thickness of the nanocrystalline strip, and the length of the nanocrystalline strip used. In the prior art, the invention patent with patent number CN201811518848.8 proposes how to control the thickness of the nanocrystalline strip. However, the preparation methods of nanocrystalline magnetic cores provided by the above patents do not have technical solutions for controlling the tightness during winding and measuring the length of the nanocrystalline strip used. In order to solve this problem, the applicant proposes a method for preparing nanocrystalline magnetic cores for precision current transformers. Summary of the invention

[0006] The object of the present invention is to provide a method for preparing a nanocrystalline magnetic core of a precision current transformer, aiming to improve the problem that the existing methods for preparing nanocrystalline magnetic cores do not have a technical solution for controlling the tightness during winding and measuring the length of the nanocrystalline strip used.

[0007] In order to achieve the above object, the present invention provides a method for preparing a nanocrystalline magnetic core of a precision current transformer, comprising the following steps:

[0008] S100, mixing and smelting the raw materials of the nanocrystalline strip according to the process ratio to obtain an alloy melt;

[0009] S200, spraying the alloy melt onto the roller surface of the cooling roller to obtain a nanocrystalline strip coil;

[0010] S300, installing the obtained nanocrystalline ribbon roll onto a reverse rotation shaft, wherein the reverse rotation shaft is connected to a reverse rotation motor via a magnetic powder clutch, and a first supporting guide roller, a metering roller, and a second supporting guide roller are sequentially arranged between the reverse rotation shaft and the winding machine, wherein the first supporting guide roller, the metering roller, and the second supporting guide roller are arranged in a V shape, and the metering roller is connected to a counter, and the counter is electrically connected to the winding machine;

[0011] S400, passing the free end of the nanocrystalline ribbon roll through the upper end of the first supporting guide roller, the lower end of the metering roller and the upper end of the second supporting guide roller in sequence, and connecting to the winding shaft of the winder;

[0012] S500, starting the reverse motor, the magnetic powder clutch and the winding machine, the reverse motor and the winding machine rotate in opposite directions, the winding machine stops and cuts off the nanocrystalline strip after rotating for a set number of turns, and obtains a semi-finished nanocrystalline magnetic core;

[0013] S600, calculating the length of the nanocrystalline ribbon used in the nanocrystalline magnetic core semi-finished product, and comparing it with the preset length to determine whether the magnetic core semi-finished product is qualified;

[0014] S700, if the equipment is unqualified, the equipment is inspected; if the equipment is qualified, the qualified semi-finished nanocrystalline magnetic core is heat treated to obtain a finished nanocrystalline magnetic core.

[0015] Furthermore, in step S200, the nanocrystalline ribbon is subjected to fixed-width roller shearing to obtain a nanocrystalline ribbon roll having the same width as the desired nanocrystalline magnetic core.

[0016] Furthermore, in the step S600, the preset length is L0, and the calculated length L1 of the nanocrystalline strip used for the semi-finished magnetic core is, if |L0-L1|÷L0×100%≤M%, the semi-finished magnetic core is judged to be qualified; if |L0-L1|÷L0×100%>M%, the semi-finished magnetic core is judged to be unqualified, wherein 0<M≤5.

[0017] Furthermore, in the step S600, the length L1 of the nanocrystalline ribbon used in the semi-finished magnetic core is calculated by the following formula: L1 = N × πd, where N is the number of revolutions of the metering roller measured by the counter, and d is the diameter of the metering roller.

[0018] Furthermore, a first limiting roller is arranged at the upper end of the first supporting guide roller, and the distance between the first supporting guide roller and the first limiting roller is greater than the thickness of the nanocrystalline strip; a second limiting roller is arranged at the upper end of the second supporting guide roller, and the distance between the second supporting guide roller and the second limiting roller is greater than the thickness of the nanocrystalline strip; the nanocrystalline strip passes between the first supporting guide roller and the first limiting roller and between the second supporting guide roller and the second limiting roller.

[0019] Furthermore, in step S700, the heat treatment includes annealing, and the annealing includes the following steps:

[0020] S710, placing the nanocrystalline magnetic core material in a heat treatment furnace;

[0021] S720, heating the heat treatment furnace to 475°C-485°C and keeping the temperature for a first time T1;

[0022] S730, continue to heat up the heat treatment furnace to 530°C-550°C, and keep the temperature for a second time T2;

[0023] S740, continue to heat the heat treatment furnace to 570°C-590°C, and keep the temperature for a third time T3;

[0024] S750, cool naturally to room temperature.

[0025] Furthermore, the annealing process is performed in a vacuum environment or an inert gas atmosphere or a nitrogen atmosphere, and the inert gas includes helium and argon.

[0026] Furthermore, in step S720, the heating rate is controlled at 3°C / min-5°C / min, and the first time T1 is between 40 minutes and 50 minutes.

[0027] Furthermore, in step S730, the heating rate is controlled between 1°C / min-2°C / min, and the second time T2 is between 60 minutes and 90 minutes.

[0028] Furthermore, in step S740, the heating rate is controlled between 1°C / min-2°C / min, and the third time T3 is between 30 minutes and 40 minutes.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. The present invention can control the tightness of the nanocrystalline strip when winding it, so as to prepare the high-precision nanocrystalline magnetic core required for the precision current transformer. At the same time, the length of the nanocrystalline strip used to prepare the high-precision nanocrystalline magnetic core can be measured to check whether the wound magnetic core is qualified, so as to effectively ensure the preparation of the required high-precision nanocrystalline magnetic core.

[0031] 2. The present invention uses a magnetic powder clutch to control the tightness of the wound nanocrystalline strip. The magnetic powder clutch has the advantages of stepless adjustment and slip-differential operation, and is reliable in adjustment and has strong applicability.

[0032] 3. The first supporting guide roller, metering roller and second supporting guide roller used in the present invention are arranged in a V shape, which can ensure that the metering roller can be driven to rotate when the nanocrystalline strip is wound, so as to ensure the accuracy of the calculation results. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a layout diagram of the reverse rotation shaft, the first supporting guide roller, the metering roller, the second supporting guide roller and the winding machine described in the embodiment of the present invention;

[0034] Figure 2 is a flow chart of a method for preparing a nanocrystalline magnetic core of a precision current transformer provided in an embodiment of the present invention;

[0035] Figure 3 It is a flow chart of heat treatment of the semi-finished nanocrystalline magnetic core provided in an embodiment of the present invention.

[0036] In the figure: 1. Nanocrystalline ribbon coil; 2. Counter-rotation axis; 3. First supporting guide roller; 4. Measuring roller; 5. Second supporting guide roller; 6. Winding axis; 7. First limiting roller; 8. Second limiting roller. DETAILED DESCRIPTION

[0037] The following is a further description with reference to the accompanying drawings and specific embodiments:

[0038] Example 1

[0039] This embodiment provides a method for preparing a nanocrystalline magnetic core of a precision current transformer, such as Figure 1 As shown, the method requires the use of the following mechanisms: a counter-rotating shaft 2, a first supporting guide roller 3, a metering roller 4, a second supporting guide roller 5 and a winding shaft 6. Among them, the winding shaft 6 is the output shaft of the winding machine, and the counter-rotating shaft 2 is used to install the nanocrystalline strip roll 1. The counter-rotating shaft 2 is connected to the counter-rotating motor through a magnetic powder clutch, that is, the counter-rotating motor drives the counter-rotating shaft 2 to rotate through the magnetic powder clutch, and the rotation direction of the counter-rotating motor and the counter-rotating shaft 2 is opposite to the rotation direction of the winding shaft 6. The first supporting guide roller 3, the metering roller 4 and the second supporting guide roller 5 are arranged in sequence between the counter-rotating shaft 2 and the winding machine. The first supporting guide roller 3, the metering roller 4 and the second supporting guide roller 5 are arranged in a V shape. The metering roller 4 is connected to a counter for recording the number of revolutions of the metering roller 4, which can be a complete integer number of revolutions or a number of revolutions with a decimal.

[0040] In some exemplary embodiments, a first limiting roller 7 is disposed at the upper end of the first supporting guide roller 3, and the distance between the first supporting guide roller 3 and the first limiting roller 7 is greater than the thickness of the nanocrystalline ribbon. A second limiting roller 8 is disposed at the upper end of the second supporting guide roller 5, and the distance between the second supporting guide roller 5 and the second limiting roller 8 is greater than the thickness of the nanocrystalline ribbon. The nanocrystalline ribbon passes between the first supporting guide roller 3 and the first limiting roller 7 and between the second supporting guide roller 5 and the second limiting roller 8. The first limiting roller 7 and the second limiting roller 8 can reduce the jumping of the nanocrystalline ribbon between the first supporting guide roller 3 and the second supporting guide roller 5 to ensure that the nanocrystalline ribbon can drive the metering roller 4 to rotate.

[0041] like Figure 2 As shown, the method for preparing the nanocrystalline magnetic core comprises the following steps:

[0042] S100, mixing and smelting the raw materials of the nanocrystalline strip according to the process ratio to obtain an alloy melt.

[0043] S200, spraying the alloy melt onto the roller surface of the cooling roller to obtain a nanocrystalline strip coil 1. The thickness of the produced nanocrystalline strip can be adjusted by adjusting the spraying speed of the alloy melt and the rotation speed of the cooling roller. In addition, the nanocrystalline strip needs to be roll-cut to a fixed width to obtain a nanocrystalline strip coil 1 having the same width as the desired nanocrystalline magnetic core.

[0044] S300, installing a nanocrystalline ribbon roll 1 having the same width as the nanocrystalline magnetic core to be manufactured onto a counter-rotation shaft 2, and the counter-rotation shaft 2 is connected to a counter-rotation motor via a magnetic powder clutch.

[0045] S400, the free end of the nanocrystalline strip roll 1 passes through between the first supporting guide roller 3 and the first limiting roller 7, the lower end of the metering roller 4, and between the second supporting guide roller 5 and the second limiting roller 8 in sequence, and is connected to the winding shaft 6 of the winder.

[0046] S500, starting the reversing motor, the magnetic powder clutch and the winding machine, the reversing motor and the winding machine rotate in opposite directions, the winding machine stops and cuts off the nanocrystalline strip after rotating for a set number of turns, and obtains a nanocrystalline magnetic core semi-finished product.

[0047] S600, calculate the length of the nanocrystalline ribbon used in the nanocrystalline magnetic core semi-finished product, and compare it with the preset length to determine whether the semi-finished magnetic core is qualified. The preset length is L0, and the calculated length L1 of the nanocrystalline ribbon used in the semi-finished magnetic core is, if |L0-L1|÷L0×100%≤M%, then the semi-finished magnetic core is determined to be qualified, if |L0-L1|÷L0×100%>M%, then the semi-finished magnetic core is determined to be unqualified, where 0<M≤5. Specifically, M can be any number among 1, 1.5, 2, 2.78, 3.45, 4, 4.3, and 5. The length L1 of the nanocrystalline ribbon used in the semi-finished magnetic core is calculated by the following formula: L1=N×πd, where N is the number of revolutions of the metering roller 4 measured by the counter, and d is the diameter of the metering roller 4.

[0048] S700, if the equipment is unqualified, the equipment is inspected; if the equipment is qualified, the qualified semi-finished nanocrystalline magnetic core is heat treated to obtain a finished nanocrystalline magnetic core.

[0049] The heat treatment includes annealing, which includes the following steps:

[0050] S710, placing the nanocrystalline magnetic core material in a heat treatment furnace, wherein the heat treatment furnace is a vacuum environment or an inert gas atmosphere or a nitrogen atmosphere, wherein the inert gas includes helium and argon.

[0051] S720, heating the heat treatment furnace to 475°C, controlling the heating rate at 3°C / min, and maintaining the temperature for a first time T1, which is 40 minutes, to ensure that the nanocrystalline magnetic core is fully heat treated.

[0052] S730, continue to heat up the heat treatment furnace to 530°C, control the heating rate at 1°C / min, and keep the temperature for a second time T2, which is 60 minutes, to ensure the annealing effect of the nanocrystalline magnetic core.

[0053] S740, continue to heat up the heat treatment furnace to 570°C, control the heating rate at 1°C / min, and keep the temperature for a third time T3, which is 30 minutes, to ensure the adequacy and stability of the heat treatment.

[0054] S750, cool naturally to room temperature.

[0055] Example 2

[0056] This embodiment provides an annealing method for a semi-finished nanocrystalline magnetic core, comprising the following steps:

[0057] S710, placing the nanocrystalline magnetic core material in a heat treatment furnace, wherein the heat treatment furnace is a vacuum environment or an inert gas atmosphere or a nitrogen atmosphere, wherein the inert gas includes helium and argon.

[0058] S720, heating the heat treatment furnace to 480°C, controlling the heating rate at 4°C / min, and maintaining the temperature for a first time T1, which is 45 minutes, to ensure that the nanocrystalline magnetic core is fully heat treated.

[0059] S730, continue to heat up the heat treatment furnace to 540°C, control the heating rate at 1.5°C / min, and keep the temperature for a second time T2, which is 80 minutes, to ensure the annealing effect of the nanocrystalline magnetic core.

[0060] S740, continue to heat up the heat treatment furnace to 585°C, control the heating rate at 1.6°C / min, and keep the temperature for a third time T3, which is 35 minutes, to ensure the adequacy and stability of the heat treatment.

[0061] S750, cool naturally to room temperature.

[0062] Example 3

[0063] This embodiment provides an annealing method for a semi-finished nanocrystalline magnetic core, comprising the following steps:

[0064] S710, placing the nanocrystalline magnetic core material in a heat treatment furnace, wherein the heat treatment furnace is a vacuum environment or an inert gas atmosphere or a nitrogen atmosphere, wherein the inert gas includes helium and argon.

[0065] S720, heating the heat treatment furnace to 485°C, controlling the heating rate at 5°C / min, and maintaining the temperature for a first time T1, which is 50 minutes, to ensure that the nanocrystalline magnetic core is fully heat treated.

[0066] S730, continue to heat up the heat treatment furnace to 550°C, control the heating rate at 2°C / min, and keep the temperature for a second time T2, which is 90 minutes, to ensure the annealing effect of the nanocrystalline magnetic core.

[0067] S740, continue to heat up the heat treatment furnace to 590°C, control the heating rate at 2°C / min, and keep the temperature for a third time T3, which is 40 minutes, to ensure the adequacy and stability of the heat treatment.

[0068] S750, cool naturally to room temperature.

[0069] The principle of controlling the tightness during winding and measuring the length of the nanocrystalline ribbon used in the present invention is as follows: the nanocrystalline ribbon coil 1 is installed on the counter-reversal shaft 2, the counter-reversal shaft 2 is connected to the counter-reversal motor through a magnetic powder clutch, and the rotation direction of the counter-reversal motor and the counter-reversal shaft 2 is opposite to the rotation direction of the winding shaft 6. Therefore, when the winding machine is winding the nanocrystalline ribbon, the counter-reversal shaft 2 and the magnetic powder clutch apply a force in the opposite direction to the nanocrystalline ribbon, and the magnitude of the force can be adjusted and controlled by the controller of the magnetic powder clutch, so that the control of the tightness during winding can be achieved. Under the condition of the given winding tightness, the size of the nanocrystalline magnetic core and the thickness of the nanocrystalline ribbon, the length of the nanocrystalline ribbon used is also determined. The present invention arranges the first supporting guide roller 3, the metering roller 4 and the second supporting guide roller 5 in a V-shape. When the winding shaft 6 rotates to wind the nanocrystalline strip, the metering roller 4 is driven to rotate. Since the metering roller 4 is connected to a counter, the number of revolutions of the metering roller 4 can be recorded by the counter, and then the length L1 of the nanocrystalline strip used can be calculated by the formula: L1 = N × πd. In this way, it can be compared with the length of the nanocrystalline strip to be used, that is, the preset length L0, to verify whether the wound magnetic core semi-finished product is qualified. If it is unqualified, the equipment is inspected to find out the cause, and if it is qualified, production continues.

[0070] In summary, the present invention can control the tightness when winding the nanocrystalline strip to prepare the high-precision nanocrystalline magnetic core required for the precision current transformer. At the same time, the length of the nanocrystalline strip used to prepare the high-precision nanocrystalline magnetic core can be measured to check whether the wound magnetic core is qualified. This can effectively ensure that the required high-precision nanocrystalline magnetic core is prepared.

[0071] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a nanocrystalline magnetic core of a precision current transformer, characterized in that: The steps include: S100, mixing and smelting the raw materials of the nanocrystalline strip according to the process ratio to obtain an alloy melt; S200, spraying the alloy melt onto the roller surface of the cooling roller to obtain a nanocrystalline strip coil (1); S300, installing the obtained nanocrystalline ribbon roll (1) onto a reverse reversing shaft (2), wherein the reverse reversing shaft (2) is connected to a reverse reversing motor via a magnetic powder clutch, and a first supporting guide roller (3), a metering roller (4) and a second supporting guide roller (5) are sequentially arranged between the reverse reversing shaft (2) and the winding machine, wherein the first supporting guide roller (3), the metering roller (4) and the second supporting guide roller (5) are arranged in a V shape, and the metering roller (4) is connected to a counter; S400, passing the free end of the nanocrystalline ribbon roll (1) through the upper end of the first supporting guide roller (3), the lower end of the metering roller (4), and the upper end of the second supporting guide roller (5) in sequence, and connecting to the winding shaft (6) of the winding machine; S500, starting the reverse motor, the magnetic powder clutch and the winding machine, the reverse motor and the winding machine rotate in opposite directions, the winding machine stops and cuts off the nanocrystalline strip after rotating for a set number of turns, and obtains a semi-finished nanocrystalline magnetic core; S600, calculating the length of the nanocrystalline ribbon used in the nanocrystalline magnetic core semi-finished product, and comparing it with the preset length to determine whether the magnetic core semi-finished product is qualified; S700, if the equipment is unqualified, perform equipment inspection, and if the equipment is qualified, perform heat treatment on the qualified semi-finished nanocrystalline magnetic core to obtain a finished nanocrystalline magnetic core; In the step S600, the preset length is L0, and the calculated length L1 of the nanocrystalline strip used in the semi-finished magnetic core is, if |L0-L1|÷L0×100%≤M%, the semi-finished magnetic core is determined to be qualified, and if |L0-L1|÷L0×100%>M%, the semi-finished magnetic core is determined to be unqualified, wherein 0<M≤5; In the step S600, the length L1 of the nanocrystalline ribbon used in the semi-finished magnetic core is calculated by the following formula: L1 = N × πd, wherein N is the number of revolutions of the metering roller (4) measured by the counter, and d is the diameter of the metering roller (4).

2. The method for preparing a nanocrystalline magnetic core of a precision current transformer according to claim 1, characterized in that: In the step S200, the nanocrystalline ribbon is subjected to fixed-width roller shearing to obtain a nanocrystalline ribbon roll (1) having a width that is the same as the width of the nanocrystalline magnetic core to be manufactured.

3. The method for preparing a nanocrystalline magnetic core of a precision current transformer according to claim 1, characterized in that: A first limiting roller (7) is arranged at the upper end of the first supporting guide roller (3), and the distance between the first supporting guide roller (3) and the first limiting roller (7) is greater than the thickness of the nanocrystalline strip; a second limiting roller (8) is arranged at the upper end of the second supporting guide roller (5), and the distance between the second supporting guide roller (5) and the second limiting roller (8) is greater than the thickness of the nanocrystalline strip; the nanocrystalline strip passes between the first supporting guide roller (3) and the first limiting roller (7), and between the second supporting guide roller (5) and the second limiting roller (8).

4. The method for preparing a nanocrystalline magnetic core of a precision current transformer according to claim 1, characterized in that: In step S700, the heat treatment includes annealing, and the annealing includes the following steps: S710, placing the nanocrystalline magnetic core material in a heat treatment furnace; S720, heating the heat treatment furnace to 475°C-485°C, and keeping the temperature for a first time T1; S730, continue to heat up the heat treatment furnace to 530°C-550°C, and keep the temperature for a second time T2; S740, continue to heat the heat treatment furnace to 570°C-590°C, and keep the temperature for a third time T3; S750, naturally cool to room temperature; In the step S720, the heating rate is controlled at 3°C / min-5°C / min, and the first time T1 is between 40 minutes and 50 minutes; In the step S730, the heating rate is controlled between 1°C / min and 2°C / min, and the second time T2 is between 60 minutes and 90 minutes; In the step S740, the heating rate is controlled between 1°C / min-2°C / min, and the third time T3 is between 30 minutes and 40 minutes.

5. The method for preparing a nanocrystalline magnetic core of a precision current transformer according to claim 4, characterized in that: The annealing process is performed in a vacuum environment or an inert gas atmosphere or a nitrogen atmosphere, and the inert gas includes helium and argon.

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