Bushing type current transformer secondary winding winding method and bushing type current transformer

Abstract

The present application relates to a bushing type current transformer for a steam turbine generator set, comprising a secondary coil, a secondary terminal box and a mounting plate, wherein the mounting plate is circular in structure, the secondary coil is fixed on the mounting plate and concentric with the mounting plate, the secondary terminal box is fixed on the mounting plate and located outside the secondary coil, the secondary terminal box is provided with a secondary outgoing line plate, the secondary outgoing line plate is provided with secondary terminal studs, and the secondary coil is connected with the secondary terminal studs through secondary winding leads. The present application has the advantages of small volume, light weight, good heat dissipation condition, flexible installation, high insulation heat resistance grade, and long-term safe operation of the transformer under the condition of small space and high ambient temperature.

Description

Technical Field

[0001] This invention relates to the field of current transformer technology, specifically to a method for winding the secondary winding of a bushing-type current transformer and the bushing-type current transformer itself. Background Technology

[0002] Currently, the common method for winding the secondary windings of current transformers is subtractive polarity winding. This easily leads to excessively high temperatures in the secondary windings near the core during winding, resulting in excessive temperature rise and degraded product performance. Additionally, uneven distribution of enameled copper wire on the core causes uneven internal magnetic fields, leading to localized core saturation and a high rate of defective products. Furthermore, existing secondary coils are significantly affected by adjacent phase interference, which also contributes to a high defect rate.

[0003] Bushing-type current transformers for turbine generator sets are installed at the outgoing and neutral points of thermal power generator sets to measure current, energy, or provide relay protection. They are typically installed in sets of 4-5 units. Currently, these transformers face challenges such as limited installation space, strong adjacent-phase magnetic field interference, high ambient temperatures, poor heat dissipation, high insulation heat resistance, large size, heavy weight, and difficulty in disassembly and assembly. These issues have consistently plagued transformer designers and on-site power system maintenance personnel, becoming urgent problems to be solved in the development of dedicated current transformers for generator outgoing lines. Summary of the Invention

[0004] To address the aforementioned problems, the present invention aims to provide a method for winding the secondary winding of a bushing-type current transformer and a bushing-type current transformer, thereby solving the problems of low product performance and uneven internal magnetic field in existing current transformer secondary winding methods, as well as the problems of large size, heavy weight, difficult disassembly and assembly, strong magnetic field interference between adjacent phases, and easy local saturation of the iron core in existing generator-specific high current transformers.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] An embodiment of the present invention provides a method for winding the secondary winding of a bushing current transformer, comprising the following steps:

[0007] Multiple sets of shielded windings are interleaved and connected in series.

[0008] The secondary main winding is wound in series with the shielding winding at its beginning, and the secondary main winding is wound on the outside of the shielding winding.

[0009] Each set of shielding windings is a symmetrical structure consisting of two wires wound in opposite directions with the same number of turns.

[0010] The winding process of the shielding winding includes the following steps:

[0011] Welding the starting wires of two conductors together;

[0012] A wire is wound along the left half of the iron core in a leftward direction. After winding N1 turns, it is wound to 180°, then wound back to make N1-5 turns, and then wound back to the starting point.

[0013] Another wire is wound along the right half of the iron core in a right direction. After winding N1 turns, it is wound to 180°, then wound back N1-5 turns, and finally wound to the starting point.

[0014] The end wires of the two conductors are pulled counterclockwise along the outer diameter of the coil to a position 90° away from the starting wire, and the end wires of the two conductors are welded together to complete the first set of shielding windings.

[0015] One of the wires of the pull wire is wound to the right along the upper half of the iron core, making N3 turns, and then wound to the opposite 180° position, and then wound back N3-5 turns, until it reaches the starting point of the pull wire.

[0016] The other wire is wound to the left along the lower half of the iron core, with N3 turns, then wound to the opposite 180° position, and then wound back N3-5 turns, until the starting point of the wire is reached, completing the second set of shielding windings.

[0017] The last wires of the second set of shielding windings are welded together.

[0018] Formula for selecting the number of turns of the first set of shielding windings:

[0019]

[0020] In the formula: C is the inner circumference of the coil before winding; D is the diameter of the wire gauge; K is the winding coefficient;

[0021] Formula for selecting the number of turns of the second set of shielding windings:

[0022]

[0023] In the formula: C1 is the inner circumference of the coil after the first set of shielding windings is wrapped; D1 is the diameter of the wire gauge; K1 is the winding coefficient.

[0024] The starting wire of the secondary main winding is welded to the ending wire of the second set of shielding windings, and the winding direction of the secondary main winding is left-hand winding.

[0025] Another embodiment of the present invention provides a bushing-type current transformer, including a secondary winding wound as described above, the secondary winding being wound on a ring-shaped iron core, and an insulating layer wrapped around the outside of the secondary winding.

[0026] The secondary winding includes a secondary main winding and multiple sets of shielding windings. The multiple sets of shielding windings are wound in multiple layers and each set of shielding windings is a symmetrical structure with two wires wound in opposite directions with the same number of turns.

[0027] The bushing-type current transformer also includes a mounting plate and a secondary junction box. The mounting plate has a circular structure. The secondary winding is concentrically mounted on the mounting plate by binding straps. The secondary junction box is set on the mounting plate. The secondary junction box has a secondary lead plate inside. The secondary lead plate has a secondary connection stud. The secondary winding is connected to the secondary connection stud through the secondary winding lead wire.

[0028] The secondary wiring stud is made of copper; the secondary output plate is made of epoxy resin, and the secondary wiring stud and the secondary output plate are cast as one piece.

[0029] The insulating layer comprises an insulating varnish and an insulating film arranged from the inside out.

[0030] The present invention has the following advantages and beneficial effects:

[0031] 1. Small size, light weight, good heat dissipation, and flexible installation: The optimized structural design of this invention makes the structure more compact, which can effectively save height space when multiple units are installed together; at the same time, the high insulation and heat resistance level ensures that the current transformer can operate safely for a long time in small spaces and high ambient temperatures.

[0032] 2. The secondary winding of the present invention is provided with N pairs of symmetrical shielding windings with a certain number of turns. The shielding windings are evenly wound in the inner layer of the secondary coil, and the magnetic field is evenly distributed, so that the local saturation of the transformer core will not occur, thus ensuring the product qualification rate.

[0033] 3. Stable insulation and safe operation: The secondary output board of this invention is made of epoxy resin, and the secondary wiring studs and the secondary output board are cast as one piece. When the user uses it, the insulation between the secondary wiring studs and the secondary junction box is good, ensuring safer operation.

[0034] 4. The secondary winding of the present invention is provided with N pairs of symmetrical shielding windings with a certain number of turns. The two wires in each pair of shielding windings are wound in opposite directions and uniformly in the inner layer of the secondary coil to cancel out the stray magnetic flux generated by the adjacent phase current and shield the magnetic field of the adjacent phase current from affecting it, so as to prevent the transformer core from being partially saturated and the transformer performance from deteriorating.

[0035] 5. The secondary winding of the present invention is provided with N pairs of symmetrical shielding windings with a certain number of turns. The current density of the shielding windings is very low, and the temperature of the shielding windings themselves will not be very high, which fully meets the temperature rise requirements of the transformer and will not generate heat. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the structure of the first set of shielding windings in one embodiment of the present invention;

[0037] Figure 2This is a schematic diagram of the structure of the second set of shielding windings in one embodiment of the present invention;

[0038] Figure 3 This is a schematic diagram of the structure of a bushing-type current transformer in another embodiment of the present invention;

[0039] Figure 4 for Figure 3 The left view;

[0040] Figure 5 This is a schematic diagram of the wire box structure in another embodiment of the present invention;

[0041] Figure 6 This is a schematic diagram of the junction box installation in another embodiment of the present invention;

[0042] Figure 7 for Figure 6 Rear view.

[0043] In the diagram: 1-Iron core; 2-Secondary winding; 3-Secondary junction box; 4-Rear cover; 5-Front cover; 6-Secondary wiring stud; 7-Secondary outlet plate; 8-Label; 9-Binding strap; 10-Mounting plate; 11-Insulating varnish; 12-Insulating film; 13-Counterhead hole; 14-Plug; 15-Secondary winding lead; 16-Cap screw; 17-Inlet port; 18-Grounding bolt; 19-Grounding mark; 20-Warning sign; 21-Primary mark; 201-First conductor; 202-Second conductor; 203-End wire of the first shielding winding; 204-Start wire of the second shielding winding; 205-Third conductor; 206-Fourth conductor; 207-End wire of the second shielding winding. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0045] An embodiment of the present invention provides a method for winding the secondary winding of a bushing current transformer, the method comprising the following steps:

[0046] Multiple sets of shielding windings are interleaved and connected in series.

[0047] The secondary main winding is wound in series with the shielding winding at its beginning, and the secondary main winding is wound on the outside of the shielding winding.

[0048] In embodiments of the present invention, each set of shielding windings is a symmetrical structure consisting of two wires (first wire 201 and second wire 202) wound in opposite directions with the same number of turns. See also Figure 1-2 As shown, the winding process of the shielding winding includes the following steps:

[0049] The first ends of the first conductor 201 and the second conductor 202 are welded together to form the first set of shielding winding start line S1;

[0050] Winding the first set of shielding windings: The first conductor 201 is wound leftward along the left half of the iron core, winding N1 turns and then to the 180° position (opposite to the starting line), then backwinding N1-5 turns, ensuring insulation between layers, and winding to the starting line S1, at which point a total of 2N1-5 turns are made; The second conductor 202 is wound rightward along the right half of the iron core, winding N1 turns and then to the 180° position (opposite to the starting line), then backwinding N1-5 turns, ensuring insulation between layers, and winding to the starting line, at which point a total of 2N1-5 turns are made; The last wires of the first conductor 201 and the second conductor 202 are then pulled counterclockwise along the outer diameter of the coil to a position 90° from the starting line, ensuring insulation during the pulling process, and the two last wires are welded together, requiring a firm weld without false soldering, forming the last wire 203 of the first set of shielding windings. These two windings constitute the first set of shielding windings, and the winding of the first set of shielding windings is now complete, with insulation between the windings.

[0051] Winding the second set of shielding windings: The end wire 203 of the first set of shielding windings also serves as the starting wire 204 of the second set of shielding windings. Two wires are defined as the third wire 205 and the fourth wire 206. The third wire 205 is wound along the upper half of the iron core to the right, with N3 turns, wound to the opposite 180° position, and then wound back N3-5 turns to the starting wire of the pull wire. Insulation is done between layers, for a total of 2N3-5 turns. The fourth wire 206 is wound along the lower half of the iron core to the left, with N3 turns, wound to the opposite 180° position, and then wound back N3-5 turns to the starting wire of the pull wire. Insulation is done between layers, for a total of 2N3-5 turns. The two end wires are welded together, ensuring a firm weld without false welds, to form the end wire 207 of the second set of shielding windings, thus completing the second set of shielding windings.

[0052] The starting line of the secondary main winding is welded to the ending line 207 of the second set of shielding windings. It is led out by a single wire. The winding direction of the secondary main winding is left-hand and does not pass through the line. The ending line of the secondary main winding is S2.

[0053] In an embodiment of the present invention, the formula for selecting the number of turns of the first set of shielding windings is as follows:

[0054]

[0055] In the formula: C is the inner circumference of the coil before winding, in mm; D is the diameter of the wire gauge, in mm; K is the winding coefficient;

[0056] Formula for selecting the number of turns of the second set of shielding windings:

[0057]

[0058] In the formula: C1 is the inner circumference of the coil after the first set of shielding windings is wrapped, in mm; D1 is the wire gauge diameter, in mm; K1 is the winding coefficient. In general design, D and D1 are equal, and K and K1 are equal.

[0059] Specifically, the diameter of the coil before winding is D1mm, and the total number of turns in the first layer of winding is N. 1总 = Coil circumference ÷ Secondary wire gauge ÷ Winding coefficient = π × D1 ÷ 2.12 ÷ 1.05. The distance increased by wrapping for each layer of winding is 5mm. Therefore, the coil diameter at the start of the second layer is (D1-5)mm. The total number of turns in the second layer is N. 2总 = Coil circumference ÷ Secondary wire gauge ÷ Winding coefficient = π × (D1 - 5) ÷ 2.12 ÷ 1.05, First layer N 1总 -Second layer N 2总 The difference N 差 =π×D1÷2.12÷1.05-π×(D1-5)÷2.12÷1.05=π÷2.12÷1.05×{D1-(D1-5)}=7, the actual difference of half a cycle is 3.5 turns. In actual production, the difference between the two layers of half cycles is taken as 5, that is, the second layer is N1-5 turns.

[0060] In this embodiment, the secondary current of the bushing-type current transformer used in this type of steam turbine generator set is 5A. The secondary wire gauge is generally φ2.12mm wire. The wire gauge is thick enough to minimize the secondary current density and ensure that the secondary current temperature rise is kept to a minimum. In addition, φ2.12mm wire is more convenient to produce, avoiding situations where the wire gauge is too thick and cannot be handled.

[0061] An embodiment of the present invention provides a method for winding the secondary winding of a bushing-type current transformer. The secondary winding contains N pairs of symmetrical shielding windings with a certain number of turns. These shielding windings are uniformly wound within the inner layer of the secondary coil, resulting in a uniform magnetic field distribution and preventing localized saturation of the transformer core. The two wires in the shielding windings are wound in opposite directions and uniformly within the inner layer of the secondary coil to cancel out stray magnetic flux generated by adjacent phase currents, shielding the magnetic field of adjacent phase currents from their influence. This prevents localized saturation of the transformer core and deterioration of transformer performance, ensuring a high product qualification rate. The shielding windings wound using this method have a very low current density, and the temperature of the shielding windings themselves is not very high, fully meeting the temperature rise requirements of the transformer and preventing overheating.

[0062] See Figure 3-4 As shown, another embodiment of the present invention provides a bushing-type current transformer, including a secondary winding 2 wound as described above. The secondary winding 2 is wound on a circular iron core 1, and an insulating layer is wrapped around the outside of the secondary winding 2.

[0063] In embodiments of the present invention, the secondary winding 2 includes a secondary main winding and multiple sets of shielding windings. The multiple sets of shielding windings are multi-layered and interleaved, with each set of shielding windings being a symmetrical structure consisting of two conductors wound in opposite directions with the same number of turns. The shielding windings are used to shield the magnetic field of adjacent phase currents from their influence, preventing local saturation of the transformer core and deterioration of the transformer's performance.

[0064] Furthermore, the bushing-type current transformer provided by the present invention also includes a mounting plate 10 and a secondary junction box 3. The mounting plate 10 has a circular structure, and the secondary winding 2 is concentrically mounted on the mounting plate 10 by a binding strap 9. The secondary junction box 3 is disposed on the mounting plate 10, and a secondary lead plate 7 is provided inside the secondary junction box 3. A secondary lead plate 7 is provided on the secondary lead plate 7, and a secondary connection stud 6 is provided on the secondary lead plate 7. The secondary winding 2 is connected to the secondary connection stud 6 through a secondary winding lead wire 15.

[0065] In this embodiment of the invention, the secondary wiring stud 6 is made of copper; the secondary output plate 7 is made of epoxy resin. The secondary wiring stud 6 and the secondary output plate 7 are cast as one piece, ensuring good insulation between the secondary wiring stud 6 and the secondary junction box 3 during user use, thus ensuring safer operation. The secondary junction box 3 is made of cast aluminum to ensure mechanical strength. The top and side walls of the secondary junction box 3 are respectively provided with a warning sign 20 and a grounding bolt 18. Specifically, the grounding bolt 18 is located on the left side of the secondary junction box 3, pressing down the grounding sign 19. The warning sign 20 is affixed to the top of the secondary junction box 3 with anaerobic adhesive. The left and right side walls of the secondary junction box 3 are provided with wire-passing holes, and hollow rubber plugs 14 are provided inside the wire-passing holes to seal the cables passing through the holes.

[0066] See Figure 5-7 As shown in the embodiment of the present invention, the secondary junction box 3 includes a box body, a rear cover 4, and a front cover 5. The box body is a rectangular frame structure with openings at both ends. The box body is fixedly connected to the mounting plate 10. The rear cover 4 and the front cover 5 are respectively sealed to the openings at both ends of the box body. The left and right side walls of the box body are provided with wire-passing holes, and rubber plugs 14 are placed in the wire-passing holes to allow cables to pass through. The rear cover 4 is provided with an inlet 17 for the secondary winding lead wires 15 to pass through. The secondary winding lead wires 15 are all welded with a 6mm diameter. 2 The high-temperature conductor is introduced into the secondary junction box 3 through the inlet 17 on the rear cover 4. The secondary winding lead 15 is connected to the secondary terminal stud 6. The secondary outlet plate 7 is set parallel to the rear cover 4 and the front cover 5.

[0067] Specifically, the rear cover 4 is fixed to the rear end of the secondary junction box 3 using a set of cover screws 16 with lead-sealed holes, ensuring that the secondary winding lead 15 is introduced from the inlet 17 of the rear cover 4. The front cover 5 is fixed to the front end of the secondary junction box 3 using another set of cover screws 16 with lead-sealed holes.

[0068] Further, see Figure 3-4 As shown, a square boss is provided radially on one side of the mounting plate 10, and a countersunk hole 13 is provided on the boss. The secondary junction box 3 is fixed to the countersunk hole 13 on the boss by an Allen head bolt. A nameplate frame and a nameplate 8 installed on the nameplate frame are installed on the mounting plate 10 by bolts, and the primary identification 21 is sprayed on the mounting plate 10.

[0069] In embodiments of the present invention, the insulating layer comprises an insulating varnish 11 and an insulating film 12 arranged from the inside out. Specifically, the secondary winding 2 is wrapped with insulating varnish 11 that is impregnated with an insulation heat resistance class of H, and then dried before being wrapped with an insulating film 12. This insulating layer provides good heat dissipation and improves the insulation heat resistance class of the transformer. The wires and insulating materials used in the transformer are all of class F or above, and some materials have an insulation heat resistance class of H, ensuring that the transformer can operate safely for a long time in confined spaces and high ambient temperatures. The secondary coil is bound to a high-strength, high-temperature resistant class F insulating laminate mounting plate 10 with binding straps 9. Installation is convenient and quick for users, and the transformer is smaller and lighter than traditional transformers cast in epoxy resin in cast aluminum or copper shells, with significantly improved heat dissipation.

[0070] The bushing-type current transformer for steam turbine generator sets provided by this invention is small in size, light in weight, easy to dissipate heat, has a high insulation and heat resistance rating, and strong resistance to adjacent phase magnetic field interference. The transformer is dry-type, without an outer cast aluminum or copper shell and without epoxy resin casting. The primary conductor of the generator output terminal or neutral point terminal passes through the inner cavity of the transformer, and the secondary lead of the secondary winding 2 is led out from the secondary junction box 3, resulting in a compact overall structure. When the user is wiring, the front cover 5 is removed, the user's secondary output is connected to the secondary wiring stud 6, and the user's secondary output is led out from the rubber plug 14. Then, the front cover 5 is fixed to the secondary junction box 3.

[0071] The bushing-type current transformer provided by this invention is manufactured as follows:

[0072] The secondary winding 2 is evenly wound on a circular iron core 1. A dedicated winding machine is used to wind the shielding winding and the secondary winding 2, with auxiliary insulation material wrapping and impregnation with H-class insulating varnish 11. The coil is then dried, wrapped with an insulating film 12, and secured to the mounting plate 10 with binding tape 9. The entire coil is then dried again. The binding tape 9 has good flexibility and adhesion, unfolds into a mesh structure, is easy to unwind, does not fray, and has no overlapping marks. The binding tape 9 used in this product exhibits excellent properties such as high strength, impact resistance, high modulus, low elongation, no hysteresis, and no eddy current loss.

[0073] The secondary junction box 3 is fixed to the countersunk hole 13 of the mounting plate 10 with hex head bolts. The secondary output plate 7 is fixed to the inner cavity of the secondary junction box 3 with hex head bolts. Rubber plugs 14 are installed at both ends of the secondary junction box 3. The secondary winding lead 15 is introduced from the rear end of the secondary junction box 3 and soldered to the secondary wiring stud 6. The rear cover 4 is fixed to the rear end face of the secondary junction box 3 with a sealing screw 16 with a lead-sealed hole. The front cover 5 is fixed to the front end face of the secondary junction box 3 with a sealing screw 16 with a lead-sealed hole, protecting the secondary wiring stud 6 at the front end of the secondary junction box 3 from being touched and also serving as a dustproof function. A grounding bolt 18 and a grounding mark 19 are installed on the left end of the secondary junction box 3. A warning sign 20 is affixed to the top of the secondary junction box 3. First, rivet the nameplate 8 onto the nameplate frame, and then use hex bolts and nuts to fix the nameplate frame onto the mounting plate 10. The nameplate 8 is located on the left side of the secondary junction box 3, with the front of the nameplate 8 facing outwards. Then, spray a primary marking 21 on the right side of the mounting plate 10.

[0074] The bushing-type current transformer provided by this invention is mainly used in steam turbine generator sets. Its installation positions are primarily at the generator output terminal and neutral point terminal. It is installed in a package configuration, with multiple transformers of various stages and combinations secured together using limit screws, branch pipes, and matching fasteners (all made of non-magnetic materials) through dedicated mounting holes on the mounting plate. Sufficient gaps are maintained between each transformer for heat dissipation. The entire unit is then mounted on the primary conductors at the output terminal and neutral point terminal. For user wiring, the front cover 5 of the secondary junction box 3 is removed, and the user's secondary output wire is connected to the secondary wiring stud 6. The user's secondary output wire is led out from the rubber plug 14. The front cover 5 is then fixed to the secondary junction box 3, and the grounding bolt 18 on the secondary junction box 3 is reliably grounded, thus completing the installation.

[0075] The bushing-type current transformer for steam turbine generator sets provided by this invention is a new product designed entirely in accordance with national standards. It adopts a rolled iron core and utilizes the electromagnetic conversion principle to enable the secondary current to accurately reflect the changes in the primary current and transmit it to the secondary metering and control device. The product can be directly installed at the generator output terminal and neutral point terminal for use as current and energy measurement and relay protection.

[0076] This invention utilizes a dry-type coil vacuum impregnation process, which is then bound to a mounting plate. It is small in size, lightweight, facilitates heat dissipation, boasts high insulation and heat resistance, strong resistance to adjacent phase magnetic field interference, offers comprehensive functions, large capacity, convenient installation, easy maintenance, stable insulation, and safe operation. It can be widely used for installation at the output and neutral point terminals of thermal power generators. The optimized structural design of this invention results in a more compact structure, effectively saving height space when multiple units are combined for installation.

[0077] The above description is merely an embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, extensions, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A method for winding the secondary winding of a bushing-type current transformer, characterized in that, Includes the following steps: Multiple sets of shielded windings are interleaved and connected in series. The secondary main winding is wound in series with the shielding winding, and the secondary main winding is wound on the outside of the shielding winding. Each set of shielding windings is a symmetrical structure consisting of two wires wound in opposite directions with the same number of turns; The winding process of the shielding winding includes the following steps: Welding the starting wires of two conductors together; A wire is wound along the left half of the iron core in a leftward direction. After winding N1 turns, it is wound to 180°, then wound back to make N1-5 turns, and then wound back to the starting point. Another wire is wound along the right half of the iron core in a right direction. After winding N1 turns, it is wound to 180°, then wound back N1-5 turns, and finally wound to the starting point. The end wires of the two conductors are pulled counterclockwise along the outer diameter of the coil to a position 90° away from the starting wire, and the end wires of the two conductors are welded together to complete the first set of shielding windings. One of the wires of the pull wire is wound to the right along the upper half of the iron core, making N3 turns, and then wound to the opposite 180° position, and then wound back N3-5 turns, until it reaches the starting point of the pull wire. The other wire is wound to the left along the lower half of the iron core, with N3 turns, then wound to the opposite 180° position, and then wound back N3-5 turns, until the starting point of the wire is reached, completing the second set of shielding windings. The last wires of the second set of shielding windings are welded together.

2. The method for winding the secondary winding of a bushing-type current transformer according to claim 1, characterized in that, Formula for selecting the number of turns of the first set of shielding windings: N1= ； In the formula: C is the inner circumference of the coil before winding; D is the diameter of the wire gauge; K is the winding coefficient; Formula for selecting the number of turns of the second set of shielding windings: N3= ； In the formula: C1 is the inner circumference of the coil after the first set of shielding windings is wrapped; D1 is the diameter of the wire gauge; K1 is the winding coefficient.

3. The method for winding the secondary winding of a bushing-type current transformer according to claim 1, characterized in that, The starting wire of the secondary main winding is welded to the ending wire of the second set of shielding windings, and the winding direction of the secondary main winding is left-hand winding.

4. A bushing-type current transformer, characterized in that, Includes a secondary winding (2) wound by the method described in any one of claims 1-3, the secondary winding (2) being wound on a ring-shaped iron core (1), and the outer side of the secondary winding (2) being wrapped with an insulating layer.

5. The bushing-type current transformer according to claim 4, characterized in that, The secondary winding (2) includes a secondary main winding and multiple sets of shielding windings, wherein the multiple sets of shielding windings are wound in multiple layers and each set of shielding windings is a symmetrical structure with the same number of turns wound in opposite directions by two wires.

6. The bushing-type current transformer according to claim 4, characterized in that, It also includes a mounting plate (10) and a secondary junction box (3), wherein the mounting plate (10) is a circular ring structure, the secondary winding (2) is concentrically mounted on the mounting plate (10) by a binding strap (9), the secondary junction box (3) is set on the mounting plate (10), the secondary junction box (3) is provided with a secondary output plate (7), the secondary output plate (7) is provided with a secondary connection stud (6), and the secondary winding (2) is connected to the secondary connection stud (6) through a secondary winding lead (15).

7. The bushing-type current transformer according to claim 6, characterized in that, The secondary wiring stud (6) is made of copper; the secondary output plate (7) is made of epoxy resin, and the secondary wiring stud (6) and the secondary output plate (7) are cast together.

8. The bushing-type current transformer according to claim 4, characterized in that, The insulating layer comprises an insulating varnish (11) and an insulating film (12) arranged from the inside out.

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