Flexible current transformer and manufacturing method thereof

Abstract

The invention provides a flexible current transformer which comprises an iron core, the iron core has a long-strip-shaped first state and an annular second state, when the iron core is in the second state, the two ends of the iron core in the length direction abut against each other in a matched mode, a connecting component is arranged at the abutting matching position, the outer wall of the iron core is sleeved with a heat shrink tube, and the outer wall of the heat shrink tube is sleeved with a coil; the coil extends in the length direction of the iron core, and a silicon rubber case is further arranged on the outer wall of the iron core and used for wrapping the coil. The flexible current transformer can be installed at a cable to be detected through simple steps, and can be better installed at a position with a narrow space, so that current data of the cable at the position can be detected.

Description

Technical Field

[0001] The present invention relates to the technical field of mutual inductors, and in particular to a flexible current mutual inductor and a manufacturing method thereof. Background Art

[0002] Driven by the current modernization of the Internet of Things and smart grids, the demand for current measurement equipment is increasing. At present, open-type current transformers have become an important option in the field of current measurement because they can be installed without destroying the original cable structure, significantly saving manpower and material resources. However, open-type current transformers are usually large in size and difficult to install in some complex environments.

[0003] Rogowski coils, as a current measurement technology that does not require an iron core, began to be used. Rogowski coils use their own coil structure for electromagnetic induction and can be flexibly used in a smaller space, solving the problem of installation in complex environments. However, the test accuracy of Rogowski coils is obviously limited, especially when measuring small currents. The lack of induction caused by the lack of an iron core medium affects its reliability and accuracy in practical applications. This limits the widespread use of Rogowski coils, especially in situations where high-precision current measurement is required.

[0004] In addition, the production process of traditional current transformers usually includes multiple complex steps such as dipping, winding and cutting, which not only increases production costs but also leads to reduced production efficiency.

[0005] Therefore, a simpler and more efficient current transformer solution is urgently needed. Summary of the invention

[0006] The present invention provides a flexible current transformer, which includes an iron core. The iron core has a first state of being a long strip and a second state of being a ring. When the iron core is in the second state, the two ends of the iron core in the length direction are abutted against each other, and a connecting component is provided at the abutting position. The outer wall of the iron core is provided with a heat shrinkable tube, and the outer wall of the heat shrinkable tube is provided with a coil. The coil extends along the length direction of the iron core. The outer wall of the iron core is also provided with a silicone sleeve, and the silicone sleeve is used to wrap the coil.

[0007] Preferably, the iron core includes a first lamination, a second lamination and a third lamination of increasing lengths, the first lamination, the second lamination and the third lamination are sequentially bonded, a first through hole is provided at one end of the first lamination, a second through hole is provided at the end of the second lamination away from the first through hole, and a third through hole is provided at the end of the third lamination close to the first through hole.

[0008] Preferably, the shortest distance between the first through hole and the end face of the first laminate in the length direction is 5mm, and the radius of the first through hole is 2.5mm; the shortest distance between the second through hole and the end face of the second laminate in the length direction is 5mm, and the radius of the second through hole is 2.5mm; the shortest distance between the third through hole and the end face of the third laminate in the length direction is 5mm, and the radius of the third through hole is 2.5mm. The thickness of the first laminate, the second laminate, and the third laminate are all 0.35mm.

[0009] Preferably, the number of the first laminations, the second laminations and the third laminations are all 2.

[0010] Preferably, the first stack has two ends in the width direction through which a first slot is formed, the second stack has two ends in the width direction through which a second slot is formed, and the third stack has two ends in the width direction through which a third slot is formed. The first slot, the second slot, and the third slot correspond to each other to form positioning slots when the first stack, the second stack, and the third stack are sequentially fitted together.

[0011] Preferably, the first laminations, the second laminations and the third laminations are all made of annealed silicon steel sheets.

[0012] Preferably, one end of the coil has a lead wire that passes through the silicone sleeve and extends away from the iron core, and the outer wall of the lead wire is provided with an epoxy resin soft shell.

[0013] Preferably, the connecting component includes a component shell in the form of an elongated strip, and the component shell forms a through plug-in slot along the length direction, and both ends of the plug-in slot are used for inserting the two ends of the iron core in the length direction; a first fitting portion in the form of a circular tube is formed at one end of the component shell in the height direction, and a first connecting hole connected to the plug-in slot is formed at the bottom of the first fitting portion; a second fitting portion is formed at one end of the component shell away from the first fitting portion, and a second connecting hole connected to the plug-in slot is formed at the second fitting portion; a bolt is provided at the end of the first connecting hole away from the plug-in slot, and the bolt has a bolt head and a threaded rod formed in sequence, and the threaded rod is used to pass through the first connecting hole, the first through hole, the second through hole, the third through hole, and the second connecting hole to be detachably matched with the second fitting portion, and the bolt head is used to abut against the side of the first connecting hole away from the plug-in slot.

[0014] Preferably, the second matching portion forms a first threaded hole along the height direction, and the first threaded hole is used for threaded matching with the threaded rod.

[0015] The present invention also provides a method for manufacturing a flexible current transformer, which comprises the following steps: The diameter data of the cable to be measured are collected to determine the lengths of the first laminate, the second laminate and the third laminate; the first laminate, the second laminate and the third laminate are stacked in sequence to form an iron core, the first slot, the second slot and the third slot are aligned in sequence to form a positioning slot, and the adjacent first laminate, the second laminate and the third laminate are combined by welding or bonding, at which time the first through hole and the third through hole are coaxial; a heat shrink tube is sleeved on the outer wall of the iron core, and the heat shrink tube is heated to reduce its volume and fit the iron core; a coil is wound on the outer wall of the heat shrink tube and a lead wire is provided at one end in the length direction of the coil; a silicone sleeve is wrapped on the outer wall of the iron core by a die-casting method.

[0016] Beneficial effects: First, the iron core can be bent, so it is more convenient for users to install it, and it has better environmental adaptability and can be installed and used in a smaller space.

[0017] Second, by switching between two states of the iron core, the installation of the iron core at the cable to be tested is achieved. When the iron core is in the first state, it is in the shape of a long strip, which is convenient for storage and transportation. Compared with the ring-shaped open-and-closed current transformer, it occupies less space when stacked, making it easier for users to carry.

[0018] Third, by adding a flexible iron core to the coil, the magnetic field can be effectively enhanced, thereby improving the sensitivity and accuracy of the mutual inductor and significantly improving the ability to capture weak current signals.

[0019] Fourth, the flexible current transformer has only one opening, so there is less magnetic leakage during use, higher measurement accuracy, better stability, and can be used for a long time, thereby reducing maintenance and lowering the cost of use.

[0020] Fifth, by wrapping the heat shrink tube outside the iron core, insulation can be effectively achieved. Then, a silicone sleeve is installed outside the coil to effectively protect the internal coil, heat shrink tube and iron core. Silicone has good ductility and sealing properties, which can prevent the heat shrink tube from aging and the coil from moisture corrosion, thereby greatly improving the service life of the flexible mutual inductor.

[0021] Sixth, by providing notches at both ends of each lamination, a matching structure is formed to ensure that each lamination can be accurately positioned during assembly, thereby ensuring the integrity and consistency of the core interior, thereby enhancing the stability of the transformer in measuring the cable current.

[0022] Seventh, through the design of the multi-layer laminate structure, when one or several layers of laminates are damaged, the damaged laminates can be removed and replaced, so that maintenance can be carried out more conveniently without scrapping the mutual inductor. Therefore, the present invention can further reduce maintenance costs and reduce material waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of a flexible current transformer in at least one embodiment of the present invention; Figure 2 for Figure 1 Schematic diagram of explosion of medium flexible current transformer; Figure 3 It is a schematic diagram of the installation of a flexible current transformer in at least one embodiment of the present invention; Figure 4 It is an axonometric schematic diagram of a connecting member in at least one embodiment of the present invention; Figure 5A is a cross-sectional schematic diagram of a connecting member in Example 1; Figure 5B is a cross-sectional schematic diagram of a connecting member in Example 2; Fig. 6A This is a schematic diagram of the axonometric measurement of the bolt in Example 1; Figure 6B This is a schematic diagram of the axonometric measurement of the nut in Example 1; Figure 7 It is a schematic diagram of the axonometric measurement of the core; Figure 8 This is a schematic diagram of the iron core explosion; Fig. 9 This is a schematic diagram of the core flattening; Fig.10 This is a schematic diagram of the iron core winding ring. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] Unless otherwise defined, the technical or scientific terms used herein shall have the usual meanings understood by persons of ordinary skill in the field to which the invention belongs. The words "first", "second" and similar terms used in the patent application specification and claims of the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Words such as "include" or "comprise" mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Inside", "outside", "upper", "lower" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0026] The drawings in this disclosure are not drawn strictly according to the actual scale, and the number of the first laminate 11, the second laminate 12 and the third laminate 13 is not limited to the number shown in the drawings. The specific size and number of each structure can be determined according to actual needs. The drawings described in this disclosure are only schematic diagrams of the structures.

[0027] Example 1 See Figure 1-4 The present embodiment provides a flexible current transformer, which includes an iron core 1. The iron core 1 has a first state of being a long strip and a second state of being a ring. When the iron core 1 is in the second state, the two ends of the iron core 1 in the length direction abut against each other to form an annular sleeve arranged at the cable to be tested. The abutting position is provided with a connecting member 2. The outer wall of the iron core 1 is provided with a heat shrink tube 3. The outer wall of the heat shrink tube 3 is provided with a coil 4. The coil 4 extends along the length direction of the iron core 1. The outer wall of the iron core 1 is also provided with a silicone sleeve 5. The silicone sleeve 5 is used to wrap the coil 4. One end of the coil 4 has a lead wire 41 extending through the silicone sleeve 5 to a direction away from the iron core 1. The outer wall of the lead wire 41 is provided with an epoxy resin soft shell.

[0028] According to the flexible current transformer provided in this embodiment, the iron core 1 is switched between two states to achieve its installation at the cable to be tested. When the iron core 1 is in the first state, it is in the shape of a long strip, which is convenient for storage and transportation. Compared with the ring-shaped open and close current transformer, it occupies less space when stacked, which is convenient for users to carry. When the iron core 1 is in the second state, the two ends of the iron core 1 are connected by a connecting member 2 to form a ring shape, which can be sleeved on the cable to be tested. The coil 4 sleeved on the iron core 1 can generate an induced current, and the lead wire 41 is used to connect to the measuring instrument to measure the current value at the cable. Since the iron core 1 can be bent, it is more convenient for users to install it, and it has better environmental adaptability and can be installed and used in a smaller space.

[0029] Furthermore, the traditional coil 4 relies on its own electromagnetic induction to measure the current of the cable, and it is difficult to sense the cable with a smaller current. By adding a flexible iron core 1 to the coil 4, the magnetic field can be effectively enhanced, thereby improving the sensitivity and accuracy of the mutual inductor, and significantly improving the ability to capture weak current signals, thereby overcoming the defects of the traditional coil 4. In addition, because the flexible iron core 1 allows the mutual inductor to be installed on cables of different shapes and sizes, especially when used in space-constrained and complex environments, compared with the rigid iron core 1 made of ferrite particles and the iron core 1 made of ferrite cloth, the installation process is more convenient and the measurement accuracy is higher, which better expands the scope of application of the coil 4.

[0030] Moreover, by wrapping the heat shrink tube 3 outside the iron core 1, insulation can be effectively achieved. Then, a silicone sleeve 5 is arranged outside the coil 4, which can effectively protect the internal coil 4, the heat shrink tube 3 and the iron core 1. The silicone has good ductility and sealing properties, which can prevent the heat shrink tube 3 from aging and the coil 4 from moisture corrosion, thereby greatly improving the service life of the flexible mutual inductor.

[0031] In addition, the flexible current transformer provided in this embodiment has only one opening, so there is less magnetic leakage during use, the measurement accuracy is higher, the stability is better, and it can be used for a long time, thereby reducing maintenance and reducing the cost of use.

[0032] See Figure 7-10 In this embodiment, the iron core 1 includes two first laminations 11, two second laminations 12 and two third laminations 13 with increasing lengths. The first laminations 11, the second laminations 12 and the third laminations 13 are sequentially bonded together. One end of the first lamination 11 is provided with a first through hole 111 penetrating therethrough, the end of the second lamination 12 away from the first through hole 111 is provided with a second through hole 121 penetrating therethrough, and the end of the third lamination 13 close to the first through hole 111 is provided with a third through hole 131.

[0033] Among them, the shortest distance between the first through hole 111 and the end face of the first laminate 11 in the length direction is 5mm, and the radius of the first through hole 111 is 2.5mm; the shortest distance between the second through hole 121 and the end face of the second laminate 12 in the length direction is 5mm, and the radius of the second through hole 121 is 2.5mm; the shortest distance between the third through hole 131 and the end face of the third laminate 13 in the length direction is 5mm, and the radius of the third through hole 131 is 2.5mm. The thickness of the first laminate 11, the second laminate 12, and the third laminate 13 are all 0.35mm.

[0034] Furthermore, the first lamination 11 is formed with a first slot 112 at both ends in the width direction, the second lamination 12 is formed with a second slot 122 at both ends in the width direction, and the third lamination 13 is formed with a third slot 132 at both ends in the width direction. The first slot 112, the second slot 122 and the third slot 132 correspond to each other to form a positioning slot 14 when the first lamination 11, the second lamination 12 and the third lamination 13 are sequentially fitted together.

[0035] Through the above structure, by setting notches at both ends of each lamination, a matching structure is formed to ensure that each lamination can be accurately positioned during assembly, thereby ensuring the integrity and consistency of the core 1, and further enhancing the stability of the transformer in measuring the cable current. Specifically, when the ring is used, the second lamination 12 is inserted between the first lamination 11 and the third lamination 13, so that the transformer has a stronger integrity and less leakage magnetic field, so the measurement accuracy is higher.

[0036] In addition, through the design of the multi-layer laminate structure, when one or several layers of laminates are damaged, the damaged laminates can be removed and replaced, so that maintenance can be carried out more conveniently without scrapping the mutual inductor. Therefore, the present invention can further reduce maintenance costs and reduce material waste.

[0037] The flexible iron core 1 provided in the present solution can be manufactured by simply stacking, pasting and combining the iron core 1. Compared with the iron core 1 manufactured by dipping, winding and cutting, the process of the present solution is simple. The first laminate 11, the second laminate 12 and the third laminate 13 can be manufactured by only stamping or cutting (wire cutting, laser cutting, etc.). The production cost is low and can be mass-produced to reduce the production cost, which is convenient for wide promotion and use.

[0038] It can be understood that the materials of the first laminate 11 , the second laminate 12 and the third laminate 13 are all annealed silicon steel sheets.

[0039] Among them, annealed silicon steel undergoes specific heat treatment during the manufacturing process, which can significantly improve the magnetic permeability of the material, allowing the laminate to focus and conduct the magnetic field more effectively, improving the sensitivity and accuracy of current measurement. In addition, the annealing process can reduce the stress and defects inside the material, thereby reducing the iron loss (eddy current loss and hysteresis loss) generated under the action of the alternating magnetic field. Therefore, annealed silicon steel has good toughness and plasticity, which can reduce breakage when processed into laminates, ensuring the smooth progress of the production process, not only improving production efficiency, but also extending its service life.

[0040] See Figure 5A , 6A 6B, in this embodiment, the connecting member 2 includes a component shell 21 in the form of an elongated strip, the component shell 21 is formed with a through insertion groove 211 along the length direction, and the two ends of the insertion groove 211 are used for inserting the two ends of the core 1 in the length direction, and the component shell 21 is formed with a first tubular matching portion 22 at one end in the height direction, and a first connecting hole 221 connected to the insertion groove 211 is formed at the bottom of the first matching portion 22, and a second matching portion 23 is formed at the end of the component shell 21 away from the first matching portion 22, and a second connecting hole 231 connected to the insertion groove 211 is formed at the second matching portion 23, and the first connecting hole 221 is formed at the bottom of the first matching portion 22. A bolt 6 is provided at one end away from the plug-in slot 211, and the bolt 6 has a bolt head 61 and a threaded rod 62 formed in sequence. The threaded rod 62 is used to pass through the first connecting hole 221, the first through hole 111, the second through hole 121, the third through hole 131 and the second connecting hole 231 and detachably cooperate with the second matching portion 23. The bolt head 61 is used to abut against the side of the first connecting hole 221 away from the plug-in slot 211. The second matching portion 23 forms a mounting groove 233 along the height direction. A nut 7 is provided in the mounting groove 233. The nut 7 forms a second threaded hole 71 along the axial direction. The second threaded hole 71 is used to threadably cooperate with the bolt 6.

[0041] That is, when in use, both ends of the core 1 are inserted into the insertion slot 211, and the second laminate 12 is inserted between the first laminate 11 and the third laminate 13, so as to form a ring-shaped mutual inductor. The first through hole 111, the second through hole 121, the third through hole 131, the first connecting hole 221 and the second connecting hole 231 are all coaxial. At this time, the threaded rod 62 of the bolt 6 is inserted into the first connecting hole 221 and passed out from the second connecting hole 231. The practical nut 7 is threadedly matched with the passed threaded rod 62, and the nut 7 is abutted against the second connecting hole 231, thereby better realizing the installation of the mutual inductor.

[0042] As a specific embodiment, the composition and production method of annealed silicon steel sheet are provided below: The chemical composition of annealed silicon steel sheet is: Iron (Si) ≥ 96.32% Silicon (Si): 2.5% - 3.5% Carbon (C): ≤0.03% Manganese (Mn): ≤0.1% Phosphorus (P) ≤ 0.03% Sulfur (S): ≤0.02% The production process is as follows: The cold-rolled silicon steel strip with uniform thickness and smooth surface is annealed under nitrogen protection, with the temperature set at 800-900°C and the holding time being 1.35h. The grain growth is uniform by slowly cooling down, thereby achieving the purpose of improving the magnetic properties.

[0043] Afterwards, the silicon steel sheets are cut into shape by a high-precision laser cutting machine, and then punched by a punching machine to obtain the first laminate 11, the second laminate 12 and the third laminate 13.

[0044] Example 2 See Figure 5B This embodiment provides a flexible current transformer, which is different from the flexible current transformer in Embodiment 1 in that: the second mating portion 23 forms a first threaded hole 232 along the height direction, and the first threaded hole 232 is used for threaded mating with the threaded rod 62. The above structure can realize the installation of the current transformer without using the nut 7, which preferably reduces the difficulty of installation.

[0045] Example 3 This embodiment provides a method for manufacturing a flexible current transformer, which includes the following steps: S1: collecting diameter data of the cable to be measured to determine the lengths of the first laminate 11, the second laminate 12 and the third laminate 13; S2: stacking the first lamination 11, the second lamination 12 and the third lamination 13 in sequence to form the iron core 1, aligning the first notch 112, the second notch 122 and the third notch 132 in sequence to form the positioning groove 14, and combining the adjacent first lamination 11, the second lamination 12 and the third lamination 13 by welding or bonding, at this time, the first through hole 111 and the third through hole 131 are coaxial; S3: a heat shrink tube 3 is sheathed on the outer wall of the iron core 1, and the heat shrink tube 3 is heated to reduce its volume so as to fit the iron core 1; S4: Winding the coil 4 on the outer wall of the heat shrink tube 3 and setting the lead wire 41 at one end of the coil 4 in the length direction; S5: Wrap the silicone sleeve 5 on the outer wall of the iron core 1 by die-casting.

[0046] It is easy to understand that those skilled in the art can combine, split, reorganize, etc. the embodiments of the present application to obtain other embodiments based on one or several embodiments provided in the present application, and these embodiments do not exceed the protection scope of the present application.

[0047] The present invention and its implementation methods are described schematically above, and the description is not restrictive. The embodiments shown in the embodiments are only part of the implementation methods of the present invention, and the actual structure is not limited thereto. Therefore, if a person skilled in the art is inspired by the embodiments and designs a structure and an implementation method similar to the technical solution without creativity without departing from the purpose of the invention, they should all fall within the protection scope of the present invention.

Claims

1. A flexible current transformer, comprising an iron core, characterized in that: The iron core has a first state in the shape of a long strip and a second state in the shape of a ring. When the iron core is in the second state, the two ends of the iron core in the length direction are abutted against each other, and a connecting component is provided at the abutting position. The outer wall of the iron core is provided with a heat shrink tube, and the outer wall of the heat shrink tube is provided with a coil. The coil extends along the length direction of the iron core. The outer wall of the iron core is also provided with a silicone sleeve, which is used to wrap the coil.

2. The flexible current transformer according to claim 1, characterized in that: The iron core includes a first lamination, a second lamination and a third lamination with increasing lengths. The first lamination, the second lamination and the third lamination are sequentially bonded. A first through hole is provided at one end of the first lamination, a second through hole is provided at the end of the second lamination away from the first through hole, and a third through hole is provided at the end of the third lamination close to the first through hole.

3. The flexible current transformer according to claim 2, characterized in that: The shortest distance between the first through hole and the end face of the first laminate in the length direction is 5mm, and the radius of the first through hole is 2.5mm; the shortest distance between the second through hole and the end face of the second laminate in the length direction is 5mm, and the radius of the second through hole is 2.5mm; the shortest distance between the third through hole and the end face of the third laminate in the length direction is 5mm, and the radius of the third through hole is 2.5mm. The thickness of the first laminate, the second laminate, and the third laminate are all 0.35mm.

4. The flexible current transformer according to claim 2, characterized in that: The first lamination is formed by passing through both ends in the width direction to form a first slot, the second lamination is formed by passing through both ends in the width direction to form a second slot, and the third lamination is formed by passing through both ends in the width direction to form a third slot. The first slot, the second slot and the third slot correspond to each other to form positioning slots when the first lamination, the second lamination and the third lamination are sequentially fitted together.

5. The flexible current transformer according to claim 2, characterized in that: The first lamination, the second lamination and the third lamination are all made of annealed silicon steel sheets.

6. The flexible current transformer according to claim 1, characterized in that: One end of the coil is provided with a lead wire which passes through the silicone sleeve and extends in a direction away from the iron core, and the outer wall of the lead wire is provided with an epoxy resin soft shell.

7. The flexible current transformer according to claim 2, characterized in that: The connecting component includes a component shell in the form of an elongated strip, and the component shell forms a through plug-in slot along the length direction, and both ends of the plug-in slot are used for inserting the two ends of the iron core in the length direction. A first matching portion in the form of a circular tube is formed at one end of the component shell in the height direction, and a first connecting hole connected to the plug-in slot is formed at the bottom of the first matching portion. A second matching portion is formed at one end of the component shell away from the first matching portion, and a second connecting hole connected to the plug-in slot is formed at the second matching portion. A bolt is provided at the end of the first connecting hole away from the plug-in slot, and the bolt has a bolt head and a threaded rod formed in sequence. The threaded rod is used to pass through the first connecting hole, the first through hole, the second through hole, the third through hole and the second connecting hole and be detachably matched with the second matching portion, and the bolt head is used to abut against the side of the first connecting hole away from the plug-in slot.

8. The flexible current transformer according to claim 7, characterized in that: The second matching portion forms a first threaded hole along the height direction, and the first threaded hole is used for threaded matching with the threaded rod.

9. The flexible current transformer according to claim 7, characterized in that: The second matching portion forms a mounting groove along the height direction, a nut is arranged in the mounting groove, and the nut forms a second threaded hole along the axial direction, and the second threaded hole is used to match with the bolt thread.

10. A method for manufacturing a flexible current transformer, comprising the following steps: The diameter data of the cable to be measured are collected to determine the lengths of the first laminate, the second laminate and the third laminate; the first laminate, the second laminate and the third laminate are stacked in sequence to form an iron core, the first notch, the second notch and the third notch are aligned in sequence to form a positioning groove, and the adjacent first laminate, the second laminate and the third laminate are combined by welding or bonding, at which time the first through hole and the third through hole are coaxial; a heat shrink tube is sleeved on the outer wall of the iron core, and the heat shrink tube is heated to reduce its volume and fit the iron core; a coil is wound on the outer wall of the heat shrink tube and a lead wire is arranged at one end of the length direction of the coil; a silicone sleeve is wrapped on the outer wall of the iron core by a die-casting method.

Images