Miniature current transformer

Abstract

The utility model relates to a miniature current transformer, which comprises a shell and a coil arranged in the shell, the coil comprises an iron core and a secondary winding wound on the surface of the nanocrystalline iron core, and the iron core is manufactured by performing heat treatment on nanocrystalline materials in a magnetic field; the shell is provided with a center channel which is arranged in a penetrating mode, a primary side wire can penetrate through the center channel, and the number of penetrating turns of the primary side wire is one. The miniature current transformer can realize output current at the secondary side when muA-level small current is input, fills the blank of a traditional transformer in the field of low-current measurement, improves the monitoring capability of a power system on a small current signal, is helpful for more accurately mastering the change condition of weak current in the power system, and improves the measurement accuracy. Accurate data support can be provided for electric leakage monitoring of some precise electronic equipment, current detection of a low-power-consumption circuit and the like, so that the safety and the reliability of a power system are improved.

Description

Technical Field

[0001] This utility model relates to the field of current transformer technology, and in particular to a miniature current transformer. Background Technology

[0002] As an extremely important measurement and protection device in the power system, the main function of the current transformer is to convert the large primary current into a small secondary current according to a certain ratio based on the principle of electromagnetic induction, so as to facilitate the accurate monitoring and control of the operating parameters of the power system by measurement, metering, protection and control equipment.

[0003] Traditional miniature current transformers struggle to simultaneously guarantee normal operation under both low-current input (e.g., μA level) and normal-current conditions (e.g., 6A). On one hand, at low currents, due to the low initial permeability of the core and the small μA-level input current on the primary side, almost all the current is used for excitation, resulting in an inability to generate an effective current output on the secondary side. On the other hand, the original core has a narrow linear region, making it prone to saturation under rated or higher current inputs. This leads to decreased measurement accuracy and unstable operation, making it unsuitable for the complex requirements of wide-range current measurement in modern power systems. This limits its widespread application in power engineering and warrants improvement. Utility Model Content

[0004] In order to overcome at least one of the defects of the prior art, according to one aspect of the present invention, a miniature current transformer is provided, including a housing and a coil disposed in the housing, the coil including an iron core and a secondary winding wound on the surface of the nanocrystalline iron core, the iron core being made by heat treatment of nanocrystalline material under a magnetic field;

[0005] The housing has a through-hole central channel for the primary side conductor to pass through, and the number of turns of the primary side conductor through the center is one.

[0006] In one embodiment of this application, the coil further includes an upper protective shell and a lower protective shell assembled on the upper and lower sides, the iron core is disposed inside the upper and lower protective shells, and the secondary winding is wound on the surface of the upper and lower protective shells.

[0007] In one embodiment of this application, a lower buffer pad is provided between the iron core and the bottom wall of the lower protective shell.

[0008] In one embodiment of this application, an upper buffer pad is provided between the iron core and the top wall of the upper protective shell.

[0009] In one embodiment of this application, the housing includes a bottom shell, the bottom shell having a bottom wall, an annular sidewall disposed on the top circumferential edge of the bottom wall, and a flange disposed in the middle of the top side of the bottom wall. The central channel passes through the flange and the bottom wall, and an assembly cavity is formed between the bottom wall, the annular sidewall, and the flange. The coil is disposed in the assembly cavity and sleeved on the circumferential outer side of the flange. The assembly cavity between the coil and the housing is filled with epoxy resin.

[0010] In one embodiment of this application, the top side surface of the bottom shell, the top side surface of the flange, and the top side surface of the epoxy resin are flush.

[0011] In one embodiment of this application, the bottom shell includes a semi-circular portion and a rectangular portion connected together, the shape of the semi-circular portion being adapted to the shape of the coil.

[0012] In one embodiment of this application, the semi-circular portion and the rectangular portion are integrally formed.

[0013] In one embodiment of this application, the magnetic permeability μ1 of the iron core is in the range of 80000H / m≤μ1≤200000H / m.

[0014] In one embodiment of this application, the coil and the flange are annular, and the inner diameter of the coil is larger than the outer diameter of the flange.

[0015] In summary, the miniature current transformer provided by this utility model has the following technical effects:

[0016] The miniature current transformer of this application can achieve output current on the secondary side when a small current input of μA is achieved, filling the gap of traditional transformers in the field of low current measurement, improving the power system's ability to monitor small current signals, and helping to more accurately grasp the weak current changes in the power system. For example, it can provide accurate data support in leakage current monitoring of some precision electronic equipment and current detection of low power circuits, thereby improving the safety and reliability of the power system.

[0017] Furthermore, it can simultaneously guarantee normal operation at a normal current of 6A, and through the optimized design of the nanocrystalline core, the core saturation problem is effectively solved, widening the linear operating range of the instrument transformer. This allows it to adapt to a wide range of measurement needs, from small currents in the μA range to normal currents and even certain overload currents. Under different operating conditions of the power system, whether it is a small current under low load or a large current under normal operation or overload, it can stably and accurately measure and convert current, providing strong support for the comprehensive monitoring and protection of the power system, and reducing the cost and complexity of equipping multiple instrument transformers of different specifications due to the range limitations of the instrument transformer. Attached Figure Description

[0018] Figure 1This is a schematic diagram of the structure of the miniature current transformer according to an embodiment of the present invention;

[0019] Figure 2 This is a schematic diagram of the internal structure of the miniature current transformer according to an embodiment of the present invention;

[0020] Figure 3 This is an exploded view of the miniature current transformer according to an embodiment of the present invention.

[0021] Figure 4 This is another exploded view of the miniature current transformer according to an embodiment of the present invention;

[0022] Figure 5 This is a cross-sectional view of a miniature current transformer according to an embodiment of the present invention;

[0023] Attached Figures: 1-Shell, 11-Central Channel, 12-Bottom Shell, 121-Bottom Wall, 122-Annular Side Wall, 123-Flange, 124-Assembly Cavity, 13-Epoxy Resin, 2-Wire Coil, 21-Iron Core, 22-Upper Protective Shell, 23-Lower Protective Shell, 24-Lower Buffer Pad Detailed Implementation

[0024] To better understand and implement this invention, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings.

[0025] In the description of this utility model, it should be noted that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0027] Embodiments of this application disclose a current transformer, specifically a miniature current transformer. For example, the overall height is between 30mm and 80mm, and the overall length or width is between 20mm and 50mm.

[0028] Specifically, this application can identify small currents in the μA range, and can also work normally under larger current conditions, thus well adapting to the requirements of remote control and smart home devices.

[0029] The following is in conjunction with the appendix Figures 1-5 This paper describes the specific scheme of the miniature current transformer of this application.

[0030] Specifically, this miniature current transformer includes a housing 1 and a coil 2 disposed inside the housing 1. The coil 2 includes an iron core 21 and a secondary winding wound on the surface of the nanocrystalline iron core 21. The iron core 21 is made by heat treatment of nanocrystalline material under a magnetic field. The wound secondary winding extends outward through the through hole of the housing 1.

[0031] The housing 1 has a through-hole central channel 11 for the primary side conductor to pass through, and the number of through-hole turns of the primary side conductor is one.

[0032] Traditional miniature current transformers cannot generate an effective output current on the secondary side when the primary input current is as small as μA, for example, 75μA. To address this, the miniature current transformer in this application employs a single-turn design to identify μA-level currents in practical applications. This design is highly advantageous for identifying μA-level currents, making it sensitive to changes in the magnetic field generated by such currents. It effectively converts these changes into a detectable induced electromotive force on the secondary side, thus enabling the identification of μA-level currents.

[0033] Further research and development revealed that while the single-turn design can identify small currents at the μA level, when this miniature current transformer is applied to normal current operation, such as 6A, the low initial permeability and narrow linear region of the nanocrystalline core 21 cause it to saturate easily at rated current or higher input current. This leads to decreased measurement accuracy and unstable operation of the transformer, making it unsuitable for the complex requirements of wide-range current measurement in modern power systems and limiting its widespread application in power engineering.

[0034] To address this, the miniature current transformer in this application specifically employs a high-permeability nanocrystalline core 21. Due to the high permeability of the nanocrystalline core 21, even with a small primary input current in the μA range, it can generate a relatively strong change in magnetic flux. This magnetic flux passes through the secondary winding wound on the surface of the nanocrystalline core 21. According to the law of electromagnetic induction, an electromotive force is induced in the secondary winding, thereby generating a secondary current output. Furthermore, when a normal current (e.g., 6A) is input, through special treatment of the nanocrystalline core 21 (e.g., heat treatment under a magnetic field), it possesses a wide linear operating region, capable of withstanding large magnetic flux density changes without saturation. This ensures a stable proportional relationship between the secondary current output and the primary current, enabling accurate measurement and monitoring of large currents.

[0035] In summary, the miniature current transformer of this application can achieve output current on the secondary side when a small current input of μA is achieved, filling the gap of traditional transformers in the field of low current measurement, improving the power system's ability to monitor small current signals, and helping to more accurately grasp the weak current changes in the power system. For example, it can provide accurate data support in areas such as leakage current monitoring of some precision electronic equipment and current detection of low-power circuits, thereby improving the safety and reliability of the power system.

[0036] Furthermore, it can ensure normal operation under normal current conditions, and through the optimized design of the nanocrystalline core 21 (e.g., heat treatment under a magnetic field), the saturation problem of the core 21 is effectively solved, widening the linear operating range of the transformer and enabling it to adapt to a wide range of measurement needs, from small currents in the μA range to normal currents and even certain overload currents. Under different operating conditions of the power system, whether it is a small current under low load or a large current under normal operation or overload, it can stably and accurately measure and convert current, providing strong support for the comprehensive monitoring and protection of the power system, and reducing the cost and complexity of equipping multiple transformers of different specifications due to the range limitation of the transformer.

[0037] It should be noted that the iron core 21 is made by heat-treating nanocrystalline materials under a magnetic field, which is a prior art. Since the iron core 21 after such treatment has high permeability and a wide linear operating range, the miniature current transformer of this application uses the nanocrystalline iron core 21 after heat treatment under a magnetic field to achieve both output current on the secondary side when there is a small current input in the μA range and normal operation when the normal current is 6A.

[0038] Specifically, heat treatment under a magnetic field refers to a strong magnetic field in the range of 1-10 Tesla (T), such as magnetic field strengths of 1T, 2T, 4T, 6T, 8T, or 10T. Of course, in other embodiments, other magnetic field strengths in the range of 1-10T can also be used. If the magnetic field strength is below 1T, it may not be able to sufficiently drive the rearrangement and growth of magnetic domains, failing to achieve the expected effect of expanding the linear working region; while if the magnetic field strength is above 10T, it may cause excessive changes in the internal structure of the nanocrystalline iron core 21, such as lattice defects or local overheating damage, affecting the performance stability of the iron core 21. Therefore, within this intensity range, the microstructure and magnetic domain state of the nanocrystalline iron core 21 can be effectively altered.

[0039] Specifically, the heat treatment temperature can typically be set between 300 and 600 degrees Celsius. Within this temperature range, processes such as atomic diffusion and domain wall migration in nanocrystalline materials can be effectively controlled. If the temperature is below 300 degrees Celsius, the thermal motion of atoms is not intense enough, making it difficult to fully homogenize the magnetic phase inside the iron core 21 and failing to effectively improve linearity. On the other hand, if the temperature is above 600 degrees Celsius, it may cause undesirable phenomena such as grain growth and grain boundary migration in nanocrystalline materials, destroying the advantages of the nanocrystalline structure and leading to problems such as a decrease in initial permeability.

[0040] Specifically, the heat treatment time is generally around 1-5 hours. If the time is too short, such as less than 1 hour, the microstructure adjustment inside the iron core 21 will not be sufficient, and the effective expansion of the linear working area cannot be achieved; while if the time is too long, such as more than 5 hours, it will not only increase production costs and energy consumption, but may also cause the material performance of the iron core 21 to deteriorate due to the long-term high temperature and magnetic field, such as accelerated oxidation and magnetic property decay.

[0041] It should be noted that heat treatment under a magnetic field specifically refers to a heat treatment performed on the nanocrystalline iron core after it has been initially prepared or shaped; it is essentially a secondary heat treatment. Its main purpose is to optimize the magnetic properties of the nanocrystalline iron core, especially under strong magnetic field conditions, by altering the internal microstructure and magnetic domain state of the core to improve its permeability, broaden its linear working region, and enhance its resistance to saturation.

[0042] The initial heat treatment is usually carried out during the preparation of nanocrystalline iron cores. For example, the initial heat treatment is carried out during the process of making nanocrystalline strips from raw materials (such as alloy materials containing elements such as iron, nickel, boron, and silicon). The heat treatment at this stage is mainly to promote the transformation of amorphous alloys into nanocrystalline states. This is existing technology and will not be elaborated further.

[0043] Specifically, the permeability μ1 of the nanocrystalline iron core 21 ranges from 80000H / m to 200000H / m. Through numerous experiments, the nanocrystalline iron core 21 with a permeability of 80000H / m to 200000H / m significantly improves the detection capability of miniature current transformers for small currents. For example, when a small current (e.g., in the μA range) is input to the primary side, the high permeability of the iron core 21 generates a sufficiently strong magnetic field change. According to the law of electromagnetic induction, a relatively large electromotive force can be induced in the secondary winding, thereby generating a detectable output current. This high sensitivity enables the transformer to accurately measure minute current changes in power systems, performing exceptionally well in applications such as leakage current detection and current monitoring of low-power devices, contributing to improved power system safety and refined management.

[0044] Furthermore, within this permeability range, the nanocrystalline core 21 maintains good linearity over a wide current range. This means that there is a stable proportional relationship between the secondary output current and the primary input current. For example, as the primary current varies from a few milliamps to a few amps, the measurement error of the transformer can be controlled within a small range (e.g., within ±1%). This high linearity and accuracy provide reliable data support for current measurement in power systems, which is beneficial for accurate metering, fault analysis, and protection control operations in power systems.

[0045] Specifically, the coil 2 also includes an upper protective shell 22 and a lower protective shell 23, which are assembled on the upper and lower sides. The nanocrystalline iron core 21 is disposed inside the upper protective shell 22 and the lower protective shell 23, and the secondary winding is wound on the surface of the upper protective shell 22 and the lower protective shell 23. During the winding process of the coil 2 of the miniature current transformer, the winding operation will apply a certain stress to the iron core 21. Especially in precision miniature transformers, due to the small size of the iron core 21 and the extremely high requirements for magnetic performance, this winding stress may cause deformation or damage to the internal microstructure of the iron core 21. For example, it may cause lattice distortion of the nanocrystalline strip, thereby affecting its magnetic domain structure and key magnetic performance parameters such as permeability. This change in the performance of the iron core 21 caused by winding stress will reduce the measurement accuracy and stability of the transformer, causing a deviation in the ratio between the secondary side output current and the primary side input current. In long-term operation or high-precision measurement scenarios, the accumulation of errors may lead to errors in power system monitoring and control.

[0046] To address this, a split upper and lower sheath structure is adopted, which effectively disperses and reduces the stress applied to the iron core 21 during winding. The upper and lower sheaths enclose the nanocrystalline iron core 21, ensuring that the tensile and compressive stresses during winding primarily act on the upper and lower sheaths rather than directly on the iron core 21. For example, when the secondary winding is wound on the surfaces of the upper and lower sheaths, the sheaths bear the mechanical force of the winding, preventing problems such as lattice distortion and magnetic domain destruction in the iron core 21 caused by winding stress. This maintains the structural integrity of the iron core 21, ensuring its stable and reliable magnetic performance, and is beneficial for improving the measurement accuracy and long-term stability of the transformer.

[0047] Specifically, a lower buffer pad 24 is provided between the iron core 21 and the bottom wall 121 of the lower protective shell 23. In actual operation, when a miniature current transformer experiences vibration, temperature changes, and other conditions, friction and wear can easily occur due to the difference in hardness between the materials of the iron core 21 and the lower protective shell 23, as well as any possible small gaps or uneven surfaces. For example, during long-term operation, periodic temperature changes can cause relative displacement between the iron core 21 and the lower protective shell 23 due to thermal expansion and contraction. Without a buffer layer, this relative movement can lead to gradual wear on the surface of the iron core 21 and the bottom wall 121 of the lower protective shell 23, damaging the structural integrity of the iron core 21, affecting its magnetic properties, and consequently reducing the measurement accuracy and reliability of the transformer.

[0048] To address this, the lower buffer pad 24 effectively prevents direct contact and friction between the iron core 21 and the bottom wall 121 of the lower protective shell 23. The lower buffer pad 24 is typically made of a material with a certain degree of elasticity and wear resistance, such as rubber or a special flexible polymer. When this miniature current transformer is exposed to vibration or temperature changes, the lower buffer pad 24 can elastically deform with the relative movement of the iron core 21 and the lower protective shell 23, absorbing and buffering the frictional force between them. This prevents the surface of the iron core 21 from being scratched or worn, maintaining the flatness and smoothness of the iron core 21 surface, thereby maintaining the original magnetic properties of the iron core 21 and ensuring that the accuracy and stability of the measurement of this miniature current transformer are not affected by changes in the performance of the iron core 21 caused by wear.

[0049] Specifically, an upper buffer pad is provided between the iron core 21 and the top wall of the upper protective shell 22. Similarly, under certain operating conditions, such as being subjected to pressure or impact from above, such as accidental collisions with other components during installation or accidental falling and crushing of equipment above, the top of the iron core 21 will directly bear a large external force. Since the material of the iron core 21 is usually brittle, such a direct and strong impact may cause cracks, damage, or even shattering at the top of the iron core 21, seriously damaging the structural integrity of the iron core 21, and thus greatly affecting its magnetic properties, causing the current transformer to malfunction, resulting in the interruption of power monitoring and measurement, and affecting the operational stability and reliability of the entire power system.

[0050] In response, the upper buffer pad effectively cushions various external forces from above. When pressure or impact acts on the upper protective shell 22, the upper buffer pad absorbs and disperses energy through its elastic deformation characteristics, preventing the iron core 21 from directly bearing excessive impact force. For example, in the event of a minor collision with an upper component, the upper buffer pad can convert the impact force into its own elastic potential energy and gradually release it, preventing damage to the top of the iron core 21, maintaining the structural stability of the iron core 21, and ensuring the normal operation of the instrument transformer. This helps improve the shock resistance of the instrument transformer in complex installation and operating environments, reduces equipment failures and maintenance costs caused by unexpected external forces, and ensures the continuous and stable operation of the power system.

[0051] Specifically, the housing 1 includes a bottom shell 12, which has a bottom wall 121, an annular sidewall 122 disposed on the top circumferential edge of the bottom wall 121, and a flange 123 disposed in the middle of the top side of the bottom wall 121. A central channel 11 passes through the flange 123 and the bottom wall 121. An assembly cavity 124 is formed between the bottom wall 121, the annular sidewall 122, and the flange 123. The coil 2 is disposed in the assembly cavity 124 and sleeved on the circumferential outer side of the flange 123. Epoxy resin 13 is filled between the coil 2 and the assembly cavity 124 of the housing. Without a suitable assembly structure and filling material, the coil 2 is difficult to securely and reliably within the housing 1. During the transportation, installation, and long-term operation of the miniature current transformer, the coil 2 may shift due to vibration, shaking, and other factors, causing a change in the relative position of the secondary winding and the primary conductor, affecting the electromagnetic coupling efficiency, and consequently reducing the measurement accuracy of the transformer. Meanwhile, coil 2 lacks sufficient protection and is easily invaded by external dust, moisture and other impurities. These impurities may accumulate on the surface of coil 2 or seep into the interior, causing a decrease in the insulation performance between windings, increasing the risk of leakage, and even causing short circuit faults, seriously threatening the safe operation of the transformer.

[0052] To address this, the unique structural design of the base shell 12, including the assembly cavity 124 formed by the bottom wall 121, the annular side wall 122, and the flange 123, provides precise installation space for the coil 2. This allows the coil 2 to be tightly fitted onto the circumferential outer side of the flange 123 and located within the assembly cavity 124, achieving precise positioning. The epoxy resin 13 filling the assembly cavity 124 further enhances the fixing effect of the coil 2. During the curing process, the epoxy resin 13 fills the tiny gaps between the coil 2 and the shell 1, firmly bonding the coil 2 to the shell 1 and effectively preventing displacement under various operating conditions. This ensures the relative positional stability between the secondary winding and the primary conductor, maintains a good electromagnetic coupling relationship, guarantees the accuracy and reliability of the transformer measurements, and enables it to operate stably in the monitoring and control circuit of the power system for a long period.

[0053] Furthermore, epoxy resin 13, as a filler material, possesses excellent insulation properties. It forms a continuous and dense insulating layer between the coil 2 and the outer casing, effectively preventing external dust, moisture, and other impurities from entering the coil 2, thus avoiding a decline in winding insulation performance and significantly reducing the risk of leakage and short circuits. Simultaneously, this insulating layer can also resist a certain degree of electromagnetic interference, reducing the influence of external electric and magnetic fields on the electromagnetic induction process inside the coil 2, further improving the transformer's anti-interference capability and signal quality. This excellent insulation and protection performance helps improve the safety and stability of the transformer, extends its service life, reduces maintenance and replacement costs due to environmental factors, and ensures the safe and stable operation of the power system.

[0054] Specifically, the top side of the base shell 12, the top side of the flange 123, and the top side of the epoxy resin 13 are flush. In actual use, if the top side of the base shell 12, the top side of the flange 123, and the top side of the epoxy resin 13 are not flush, stress concentration points will occur at the connection points between the components when the miniature current transformer is subjected to external mechanical forces (such as vibration, collision, or compression). These stress concentration points may cause local deformation, cracking, or even damage to the components.

[0055] Therefore, when the top side of the base shell 12, the top side of the flange 123, and the top side of the epoxy resin 13 are flush, the force can be evenly distributed across the entire plane when the miniature current transformer is subjected to external mechanical forces, avoiding stress concentration. This allows the shell 1 structure to better withstand various external forces, maintaining structural integrity and stability. Whether under slight vibration during normal operation or under significant impact during transportation and installation, the risk of component damage can be effectively reduced, ensuring that key components such as the coil 2 and the core 21 inside the transformer are always in their normal working position and condition. This ensures reliable operation and long-term stability of the transformer, reduces maintenance and replacement costs due to structural damage, and improves the economic efficiency of power system operation.

[0056] Specifically, the base shell 12 includes a connected semi-circular portion and a rectangular portion, the shape of which matches the shape of the coil 2. This design, with the semi-circular portion of the base shell 12 matching the shape of the coil 2, allows the coil 2 to be precisely placed within the base shell 12, making the assembly process smoother and more efficient. The high degree of fit between the coil 2 and the base shell 12 reduces the possibility of shaking and displacement, effectively improving the overall structural stability of the current transformer. On the production line, this good fit reduces assembly difficulty, increases assembly speed and quality consistency, reduces product defects caused by poor assembly, lowers production costs, and facilitates the large-scale production and widespread application of current transformers.

[0057] Specifically, the semi-circular and rectangular portions are molded as a single piece. In actual manufacturing, if the bottom shell 12 adopts a non-one-piece molding structure, and instead the semi-circular and rectangular portions are manufactured separately and then assembled, then multiple sets of molds need to be designed and manufactured during the production process. For example, a corresponding mold is needed for each of the semi-circular and rectangular portions, which undoubtedly increases the design cost, manufacturing cost, and management cost of the molds. Moreover, multiple sets of molds will increase the production process and production cycle, reduce production efficiency, and are not conducive to large-scale production and cost control.

[0058] Therefore, by adopting a one-piece molded base shell 12 structure, which includes a one-piece molded semi-circular part and a rectangular part, only one set of molds is needed to manufacture the base shell 12. This greatly simplifies the mold design, manufacturing, and management process, and reduces mold-related costs. At the same time, it reduces production steps, improves production efficiency, and enables faster, large-scale production, which helps to reduce product manufacturing costs and enhance the product's competitiveness in the market. For example, in the mass production of miniature current transformers, the one-piece molded base shell 12 structure can significantly shorten the production cycle, reduce the consumption of human and material resources, and make the product more advantageous in terms of price and delivery speed.

[0059] Specifically, coil 2 and flange 123 are annular, with the inner diameter of coil 2 being larger than the outer diameter of flange 123. In actual assembly, it was found that when the dimensional difference between the inner diameter of coil 2 and the outer diameter of flange 123 is inappropriate, it may lead to positioning problems during installation. For example, coil 2 may easily collide or rub against flange 123, potentially damaging the winding of coil 2 and affecting its insulation or electromagnetic properties.

[0060] To address this, a design was adopted where the inner diameter of coil 2 is larger than the outer diameter of flange 123, facilitating the installation of coil 2. This dimensional relationship allows coil 2 to easily fit around the circumferential outer side of flange 123, reducing the risk of collision and friction during installation and effectively protecting the windings of coil 2. In mass production, this ease of installation improves assembly efficiency and reduces production costs. Simultaneously, it reduces the possibility of damage to coil 2 during installation, improving product quality and reliability.

[0061] The technical means disclosed in this utility model are not limited to those disclosed in the above embodiments, but also include technical solutions composed of any combination of the above technical features. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of this utility model, and these improvements and modifications are also considered within the scope of protection of this utility model.

Claims

1. A miniature current transformer, characterized in that, It includes a housing (1) and a coil (2) disposed inside the housing (1). The coil (2) includes an iron core (21) and a secondary winding wound around the surface of the nanocrystalline iron core (21). The iron core (21) is made by heat-treating nanocrystalline material under a magnetic field. The housing (1) has a through-hole central channel (11) for the primary side conductor to pass through, and the number of through-hole turns of the primary side conductor is one.

2. A miniature current transformer according to claim 1, characterized in that, The coil (2) also includes an upper protective shell (22) and a lower protective shell (23) assembled on the upper and lower sides. The iron core (21) is disposed inside the upper protective shell (22) and the lower protective shell (23). The secondary winding is wound on the surface of the upper protective shell (22) and the lower protective shell (23).

3. A miniature current transformer according to claim 2, characterized in that, A lower buffer pad (24) is provided between the iron core (21) and the bottom wall (121) of the lower protective shell (23).

4. A miniature current transformer according to claim 2, characterized in that, An upper buffer pad is provided between the iron core (21) and the top wall of the upper protective shell (22).

5. A miniature current transformer according to any one of claims 1-4, characterized in that, The housing (1) includes a bottom shell (12), the bottom shell (12) having a bottom wall (121), an annular sidewall (122) disposed on the top circumferential edge of the bottom wall (121), and a flange (123) disposed in the middle of the top side of the bottom wall (121). The central channel (11) passes through the flange (123) and the bottom wall (121). An assembly cavity (124) is formed between the bottom wall (121), the annular sidewall (122), and the flange (123). The coil (2) is disposed in the assembly cavity (124) and sleeved on the circumferential outer side of the flange (123). Epoxy resin (13) is filled between the coil (2) and the assembly cavity (124) of the housing.

6. A miniature current transformer according to claim 5, characterized in that, The top side of the bottom shell (12), the top side of the flange (123), and the top side of the epoxy resin (13) are flush.

7. A miniature current transformer according to claim 5, characterized in that, The bottom shell (12) includes a semi-circular portion and a rectangular portion connected together, the shape of which is adapted to the shape of the coil (2).

8. A miniature current transformer according to claim 7, characterized in that, The semi-circular part and the rectangular part are integrally formed.

9. A miniature current transformer according to any one of claims 1-4, characterized in that, The permeability μ1 of the core (21) is in the range of 80000H / m≤μ1≤200000H / m.

10. A miniature current transformer according to claim 5, characterized in that, The coil (2) and the flange (123) are annular, and the inner diameter of the coil (2) is larger than the outer diameter of the flange (123).

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