Three-phase three-element combined mutual inductor for state grid

Abstract

This utility model discloses a three-phase three-element combined instrument transformer for State Grid, relating to the field of instrument transformer technology. It includes a main insulator integrally cast with epoxy resin, comprising current transformer body A, current transformer body B, current transformer body C, and voltage transformer body A, voltage transformer body B, and voltage transformer body C. The outer surface of the main insulator is fitted with a silicone rubber sleeve. The upper part of the primary high-voltage conductors of current transformer bodies A, B, and C extends out of the main insulator, while the lower part is located within the main insulator and connected to the first high-voltage terminal of the corresponding voltage primary winding of voltage transformer bodies A, B, and C. The second high-voltage terminals of the voltage primary windings of voltage transformer bodies A, B, and C are twisted together to form a Y-connection and then connected to the primary N terminal. This invention uses epoxy resin and silicone rubber composite insulation, which has advantages such as small size, resistance to flashover, high dynamic and thermal stability current, large secondary capacity, resistance to ultraviolet radiation and wind erosion, long maintenance cycle, and convenient installation.

Description

Technical Field

[0001] This utility model relates to the field of instrument transformer technology, specifically to a three-phase three-element combined instrument transformer for State Grid. Background Technology

[0002] In power systems, combined instrument transformers are key devices for energy metering and protection, widely used in substations, distribution networks, and other applications. Traditional outdoor combined instrument transformers mostly employ oil-immersed insulation structures, which suffer from problems such as large size, susceptibility to oil leakage, and high maintenance costs. Furthermore, oil-immersed instrument transformers are prone to flashover in harsh environments, leading to decreased insulation performance, and have lower dynamic and thermal stability current and secondary capacity, making it difficult to meet the high precision and high reliability requirements of smart grids.

[0003] While existing three-phase two-element V / V type combined instrument transformers simplify the structure to some extent, they still suffer from drawbacks such as high electromagnetic interference, insufficient metering accuracy, and poor weather resistance. Especially in outdoor environments, factors like ultraviolet radiation and wind erosion accelerate equipment aging and shorten its lifespan. Furthermore, traditional instrument transformers lack adequate anti-theft measures, and their transformation ratio markings are easily tampered with, posing challenges to electricity consumption supervision. Utility Model Content

[0004] The purpose of this utility model is to provide a three-phase three-element combined instrument transformer for State Grid, which uses epoxy resin and silicone rubber composite insulation and has the advantages of small size, resistance to pollution flashover, high dynamic and thermal stability current, large secondary capacity, resistance to ultraviolet wind erosion, long maintenance cycle and convenient installation.

[0005] To achieve the above objectives, the technical solution of this application is as follows: a three-phase three-element combined instrument transformer for State Grid, comprising: a main insulator in which current transformer body A, current transformer body B, current transformer body C, voltage transformer body A, voltage transformer body B, and voltage transformer body C are cast together using epoxy resin, and a silicone rubber sleeve is fitted on the outer surface of the main insulator.

[0006] The upper part of the primary high-voltage conductor of current transformer body A, current transformer body B, and current transformer body C extends out of the main insulator, and the lower part is located inside the main insulator and connected to the first high-voltage terminal of the primary voltage winding of the corresponding voltage transformer body A, voltage transformer body B, and voltage transformer body C.

[0007] The second high-voltage terminals of the primary windings of voltage transformer bodies A, B, and C are twisted together to form a Y-type connection and then connected to the primary N terminal, which is located between phases A and B of the main insulator.

[0008] The secondary leads of current transformer body A, current transformer body B, current transformer body C, voltage transformer body A, voltage transformer body B, and voltage transformer body C are connected to the secondary terminals according to their corresponding markings.

[0009] The secondary n-terminals of voltage transformer body A, voltage transformer body B, and voltage transformer body C are twisted together as a common terminal to form a Y-type connection, which is then connected to the n-terminal of the secondary terminal.

[0010] The current transformer body A and voltage transformer body A, current transformer body B and voltage transformer body B, and current transformer body C and voltage transformer body C are all arranged in a one-to-one correspondence in the main insulator, resulting in a compact structure.

[0011] As a preferred embodiment of this utility model, the current transformer body A, current transformer body B, and current transformer body C have the same structure, each including, from the inside to the outside, an insulating cardboard corner ring, a twill cloth insulating layer, a polyurethane board buffer layer, and a half-layer of self-adhesive tape arranged on the current core. Enamelled round copper wire is wound on the half-layer of self-adhesive tape to form a secondary current winding. A polyester film is half-layered outside the secondary current winding, and a molded copper foil or molded aluminum foil is added. A secondary support is provided on the outside of the molded copper foil or molded aluminum foil. A semi-conductive crepe paper shielding layer is half-layered on the secondary support. The primary current winding passes through the current core and is wound. A high-voltage conductive busbar is welded to both ends of the primary current winding. From the inside to the outside, a twill cloth, a crepe paper, and a semi-conductive crepe paper are half-layered on the primary current winding.

[0012] In a preferred embodiment of this utility model, the voltage transformer bodies A, B, and C have identical structures, each including a basic insulation layer. A secondary voltage winding is wound around the basic insulation layer, with PMP composite paper added between the winding layers as interlayer insulation. A low-voltage shielding layer is formed by winding semi-conductive crepe paper around the outer layer of the secondary voltage winding. A resin skeleton is provided between the low-voltage shielding layer and the inner shielding layer. The inner shielding layer includes shaped copper foil and semi-conductive crepe paper. Multiple layers of DMD insulating paper are first wound onto the inner shielding layer, and then the primary voltage winding is wound. After fabrication, an outer shaped copper foil is added as a shielding layer, and semi-conductive crepe paper is wrapped around the shielding layer to form a high-voltage shielding layer; the voltage secondary winding is fitted into the resin skeleton, and the voltage core is fitted into the voltage secondary winding; the exposed part of the voltage core has a multi-layer insulation structure, specifically including, from the inside out, a half-layer of self-adhesive tape insulation layer, a shaped polyurethane board buffer layer, a half-layer of self-adhesive tape insulation layer, and then an outer shaped copper foil or aluminum foil, and a half-layer of semi-conductive crepe paper. Semi-conductive paint is applied to both sides of the wrapped voltage core to form a low-voltage shielding layer.

[0013] As a preferred embodiment of this utility model, multiple rainproof umbrella skirts are distributed on the upper outer wall of the main insulator, and the multiple rainproof umbrella skirts are distributed around the lower outer periphery of the primary high voltage conductor; silicone umbrella skirts are distributed in the middle and lower parts of the main insulator.

[0014] As a preferred embodiment of this utility model, the secondary support for current phase A and the secondary support for current phase C have the same structure, both including symmetrically arranged angular legs. The top of each angular leg is connected to the side of the first arc-shaped support plate and the connection points are symmetrically arranged. The bottom of each angular leg is connected to a first fixing plate.

[0015] As a preferred embodiment of this utility model, the current B-phase secondary support includes asymmetrically arranged irregularly shaped legs, the top of each irregularly shaped leg is connected to the side of the second arc-shaped support plate and the connection points are not symmetrically arranged, and the bottom of each irregularly shaped leg is connected to a second fixing plate.

[0016] In a preferred embodiment of this invention, auxiliary secondary windings are added outside the voltage secondary windings of voltage transformer bodies A, B, and C. The end wire of the auxiliary secondary winding of voltage transformer body A is connected to the beginning wire of the auxiliary secondary winding of voltage transformer body B, and the end wire of the auxiliary secondary winding of voltage transformer body B is connected to the beginning wire of the auxiliary secondary winding of voltage transformer body C. The beginning wire of the auxiliary secondary winding of voltage transformer body A and the end wire of the auxiliary secondary winding of voltage transformer body C are respectively connected to the corresponding terminals of the auxiliary secondary winding of the main insulator. Before the silicone rubber sleeve is encapsulated, these two terminals are connected with bare copper wire to form a closed suppression circuit, which can effectively prevent the occurrence of ferroresonance and make the product safer to operate.

[0017] As a preferred embodiment of this utility model, the primary high-voltage conductors of each phase are tilted at an angle and arranged in a V-shape to optimize the electric field distribution, and are also equipped with a protective cover for sealing.

[0018] As a preferred embodiment of this utility model, a secondary wiring platform is cast in the lower part of the main insulator. The secondary wiring platform has built-in secondary wiring terminals. The secondary wiring terminals are sealed by a secondary rubber gasket and a secondary cover plate. The screws used to fix the secondary cover plate are equipped with lead-sealed holes and lead seals, which can prevent the theft of electricity by replacing or changing the transformer ratio of the nameplate, and also facilitate the supervision and inspection work of the electricity consumption department. The State Grid special electronic tag is attached to the secondary wiring terminals with silicone and is located above the secondary wiring terminals for easy remote identification.

[0019] As a preferred embodiment of this utility model, the current ratio is permanently marked on the surface of the main insulator by laser etching, which can prevent the theft of electricity by replacing or changing the label ratio, and also facilitates the supervision and inspection work of the electricity user department.

[0020] By adopting the above technical solution, this utility model can achieve the following technical effects:

[0021] 1. Compact size, strong anti-interference, and high metering accuracy: Through optimized structural design, a compact layout with the current converter on top and the voltage converter below effectively saves space, achieving a small size and large capacity. The coil uses copper foil or non-magnetic aluminum foil combined with shielding materials such as semi-conductive crepe paper, significantly reducing electromagnetic interference between current and voltage, as well as between adjacent phases, ensuring high metering accuracy, especially suitable for harsh outdoor environments.

[0022] 2. Easy installation, remote identification, and easy maintenance: During installation, only the current transformer needs to be fixed and the primary and secondary wirings completed according to the phase sequence, significantly saving assembly time. During maintenance, product information can be quickly and remotely queried by scanning the electronic tag code at a distance, requiring no special maintenance and making operation simple and efficient.

[0023] 3. Stable insulation and safe operation: Utilizing epoxy resin inner insulation and an outer silicone rubber coating, it boasts a high withstand voltage rating and reliable insulation performance. The surface skirt design effectively increases the creepage distance, mitigating potential quality issues from the outset and ensuring operational safety.

[0024] 4. Large creepage distance and strong anti-pollution flashover performance: The primary A, B, and C three-phase current terminals extend to both sides, and the high-voltage end is equipped with a protective cover for sealing, effectively preventing leakage and flashover, and ensuring operational safety.

[0025] 5. Anti-ferromagnetic resonance, more stable operation: The secondary windings of the three-phase voltage coils A, B, and C are all equipped with auxiliary windings, and the Y / Y0 type end-to-end connection method can effectively suppress ferroresonance and further improve the safety of product operation. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a front view of the internal structure of this utility model;

[0028] Figure 2 This is a front view of the external structure of this utility model;

[0029] Figure 3 This is a side view of the external structure of this utility model;

[0030] Figure 4 This is a top view of the external structure of this utility model;

[0031] Figure 5 These are the three-view and three-dimensional views of the AC phase secondary support structure of this utility model;

[0032] Figure 6 The following are the three-view and three-dimensional views of the current B-phase secondary support structure of this utility model;

[0033] Figure 7 This is a schematic diagram of the wiring principle for a single current transformer of this utility model.

[0034] The components include: 1. Primary high-voltage conductor busbar; 2. Primary current winding; 3. Current core; 4. Secondary current winding; 5. A-phase secondary support; 6. Primary connecting wire; 7. Primary voltage winding; 8. Voltage core; 9. Secondary voltage winding; 10. Voltage transformer body clamp; 11. Secondary terminal block; 12. Main insulator; 13. Silicone rubber sleeve; 14. Base; 15. Secondary cover plate; 16. Secondary rubber pad; 17. Electronic tag; 18. B-phase secondary support; 19. Resin skeleton; 20. Primary N-terminal; 21. Silicone umbrella skirt; 22. Auxiliary secondary platform; 23. First arc-shaped support plate; 24. Angular support leg; 25. First fixing plate; 26. Second arc-shaped support plate; 27. Irregularly shaped support leg; 28. Second fixing plate. Detailed Implementation

[0035] It should be noted that, where there is no conflict, the embodiments and features in the embodiments of this utility model can be combined with each other. The present utility model will now be described in detail with reference to the accompanying drawings and embodiments.

[0036] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this utility model or its application or use. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this utility model.

[0037] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to the present invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0038] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of this invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0039] In the description of this utility model, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is usually based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this utility model and simplifying the description. Unless otherwise stated, these directional terms 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, and therefore should not be construed as a limitation on the scope of protection of this utility model. The directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0040] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the device as described in the figures. For example, if the device in the figures were inverted, a device described as "above" or "on top of" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0041] It should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0042] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore cannot be construed as limiting the scope of protection of this utility model.

[0043] Example 1

[0044] This embodiment provides a method for manufacturing a three-phase three-element combined instrument transformer for State Grid, including:

[0045] S1. Body fixing process

[0046] S1.1 Position the current transformer body A, current transformer body B, and current transformer body C in the casting mold through the corresponding secondary brackets for current phase A, current phase B, and current phase C, respectively.

[0047] S1.2 The voltage transformer body A, voltage transformer body B, and voltage transformer body C are fixed in the predetermined position of the casting mold using voltage transformer body clamps.

[0048] S2. Electrical connection process

[0049] S2.1 Connect the first high-voltage terminal of the primary voltage winding to the corresponding phase's primary high-voltage busbar via a primary connection line. The exposed part at the connection point is sealed with semi-conductive rubber tape to achieve effective shielding of the high-voltage electric field.

[0050] S2.2 The second high-voltage terminals of the primary windings of each phase are twisted together to form a Y-type connection and then connected to the primary N terminal.

[0051] S3. Secondary wiring process

[0052] S3.1 Connect the secondary leads of current transformer body A, B, C and voltage transformer body A, B, C to the secondary terminals according to their corresponding markings;

[0053] S3.2 Connect the secondary n terminals of voltage transformer bodies A, B, and C as common terminals by twisting them together to form a Y-type connection, and then connect it to the n terminal of the secondary terminal block.

[0054] S4. Insulation forming process

[0055] S4.1 After adjusting the spacing between each component, high-quality epoxy resin is used for vacuum casting to form the main insulator;

[0056] S4.2 A high-temperature vulcanized silicone rubber sleeve is molded onto the outer surface of the main insulator, and the two are bonded and fixed together by a single-component silicone rubber adhesive.

[0057] S4.3 Place the assembled product in a constant temperature and humidity treatment chamber to complete the curing process.

[0058] Preferably, the manufacturing method of current transformer body A, current transformer body B, and current transformer body C may include:

[0059] Iron core insulation treatment: The current iron core is subjected to multi-layer insulation treatment, which consists of wrapping the insulation layer cardboard corner ring, twill cloth tape insulation layer, polyurethane board buffer layer, and then half-lapping a layer of self-adhesive tape from the inside out.

[0060] Secondary winding fabrication: Enamelled round copper wire is wound on the current core after insulation treatment to form a secondary current winding, and a polyester film is half-lapped on the outer layer, and then shaped copper foil or aluminum foil is added on top.

[0061] Bracket installation: After fixing the secondary brackets for phases A, B, and C of the current-carrying device, a semi-conductive corrugated paper shielding layer is half-lapped on top;

[0062] Primary winding fabrication: The primary current winding is wound through the current core, and a high-voltage busbar is welded to both ends;

[0063] Primary winding insulation treatment: The primary winding is subjected to multi-layer insulation treatment, with a layer of twill tape, crepe paper, and semi-conductive crepe paper stacked sequentially from the inside to the outside.

[0064] Body forming: After completing the above processes, the current transformer body is formed into three phase units A, B, and C.

[0065] Preferably, the manufacturing method of voltage transformer body A, voltage transformer body B, and voltage transformer body C may include:

[0066] Insulation layer preparation: A layer of insulating paperboard is rolled on the skeleton substrate, and multiple layers of PMP composite paper are stacked to form a basic insulation layer;

[0067] Secondary winding fabrication: A voltage secondary winding is wound outside the basic insulation layer, with PMP composite paper insulation added between layers, and semi-conductive corrugated paper is wrapped around the outer layer to form a low-voltage shielding layer.

[0068] Skeleton assembly: The resin skeleton is fixed on a CNC parallel winding machine, and an inner shielding layer is formed by adding molded copper foil and semi-conductive crepe paper.

[0069] Primary winding fabrication: After adding multiple layers of DMD insulating paper to the inner shielding layer, the voltage primary winding is wound. After the winding is completed, shaped copper foil is added (with gaps left at the beginning and end), and semi-conductive crepe paper is wrapped around the outer layer to form a high-voltage shielding layer.

[0070] Component assembly: The voltage secondary winding is fitted into the resin frame, and the voltage core is fitted into the voltage secondary winding;

[0071] Core fixing: A metal hose clamp is used to pass through the gap between the outer side of the core and the secondary voltage winding, and the voltage core and voltage transformer body clamp are fastened by the positioning thread.

[0072] Iron core insulation treatment: The exposed part of the voltage iron core is subjected to multi-layer insulation treatment, from the inside to the outside, in the following order: half-layer of self-adhesive tape, polyurethane board buffer layer, half-layer of self-adhesive tape, shaped copper foil or aluminum foil, and half-layer of semi-conductive crepe paper.

[0073] Surface treatment: Apply a semi-conductive varnish of appropriate width to both sides of the wrapped voltage core;

[0074] Body forming: After completing the above processes, the voltage transformer body is formed into three phase units A, B, and C.

[0075] Preferably, the current and voltage transformer bodies are dried in the layered drying chamber of the cluster vacuum drying equipment, then grouped, fixed, and sealed for preservation to prevent moisture absorption before molding.

[0076] This embodiment achieves standardized production of three-phase three-element combined instrument transformers for State Grid through the above steps. The product features a compact structure, anti-resonance, and anti-theft characteristics, and is particularly suitable for power metering and protection in three-phase three-wire neutral point ungrounded systems.

[0077] Example 2

[0078] Please see Figure 1-7 This embodiment provides a three-phase three-element combined instrument transformer for State Grid, which is manufactured by the method described in Embodiment 1. Specifically, it includes: casting a main insulator, consisting of current transformer body A, current transformer body B, current transformer body C, voltage transformer body A, voltage transformer body B, and voltage transformer body C, into a single unit using epoxy resin, and then fitting a silicone rubber sleeve onto the outer surface of the main insulator to form a composite insulation.

[0079] The upper part of the primary high-voltage conductor of current transformer body A, current transformer body B, and current transformer body C extends out of the main insulator, and the lower part is located inside the main insulator and connected to the first high-voltage terminal of the primary voltage winding of the corresponding voltage transformer body A, voltage transformer body B, and voltage transformer body C. The exposed part of the connection is wrapped with semi-conductive rubber tape.

[0080] The second high-voltage terminals of the primary windings of voltage transformer bodies A, B, and C are twisted together to form a Y-type connection and then connected to the primary N terminal. This primary N terminal is located between phases A and B on the upper rear side of the main insulator.

[0081] The secondary leads of current transformer body A, current transformer body B, current transformer body C, voltage transformer body A, voltage transformer body B, and voltage transformer body C are connected to the secondary terminals according to their corresponding markings.

[0082] The secondary n-terminals of voltage transformer bodies A, B, and C are twisted together as a common terminal to form a Y-type connection, which is then connected to the n-terminal of the secondary terminal block.

[0083] In this embodiment, multiple rainproof skirts are distributed on the upper outer wall of the main insulator, and these skirts surround the lower outer periphery of the primary high-voltage conductor. Silicone skirts are also distributed in the middle and lower parts of the main insulator. This multi-segment umbrella-shaped structure effectively increases the creepage distance, improves insulation performance, and disperses electric field stress through the geometric shape of the skirts, avoiding electric field concentration and improving the overall operational reliability of the equipment.

[0084] In this embodiment, the lower part of the main insulation is recessed inward to form a stepped shape, and the bottom center is a square boss.

[0085] In this embodiment, the primary voltage winding is insulated from the secondary voltage winding by passing through a resin skeleton.

[0086] In this embodiment, the current transformer body A and voltage transformer body A, the current transformer body B and voltage transformer body B, and the current transformer body C and voltage transformer body C are all arranged in a one-to-one correspondence in the main insulator and are electrically connected through a primary connecting line.

[0087] This utility model provides a three-phase, three-element combined instrument transformer for State Grid applications. It employs an epoxy resin-silicone rubber composite insulation structure, optimizing the electric field distribution through double-layer insulation. The coils are made using copper foil or non-magnetic aluminum foil combined with semi-conductive crepe paper and other shielding materials, effectively suppressing electromagnetic interference between current and voltage units and between adjacent phases, fundamentally solving the technical defects of traditional equipment. The product adopts a Y / Y0 type winding design to achieve a compact structure. Overall, it possesses comprehensive advantages such as excellent resistance to flashover, high dynamic and thermal stability current, large secondary capacity, resistance to UV erosion, long maintenance cycle, and convenient installation, fully meeting the stringent requirements of smart grid outdoor applications. The use of semi-conductive crepe paper and semi-conductive paint on the current and voltage transformer bodies is intended to shield or equalize the electric field, thereby reducing the partial discharge of the combined instrument transformer. The use of copper foil fully considers the mutual influence of electromagnetic fields between current and voltage during operation, ensuring higher stability, reliability, and accuracy in product metering.

[0088] During installation and use, only one or two wirings need to be performed according to the phase sequence. Finally, protective covers are installed on the A, B, and C high-voltage terminals for sealing. It has the advantages of small size, large creepage distance, strong anti-interference, high metering accuracy, convenient installation, easy maintenance, stable insulation, and safe operation, which further improves the design and manufacturing level of combined instrument transformers.

[0089] During operation, grounding of the primary neutral (N) terminal is strictly prohibited. Taking a single current transformer as an example, the secondary terminals n, aS2, bS2, and cS2 must be reliably grounded. Open circuits are strictly prohibited on the secondary side of current transformers, and short circuits are strictly prohibited on the secondary side of voltage transformers. The current ratio is laser-etched in a prominent position on the transformer surface. This prevents electricity theft by replacing or tampering with the transformer ratio label and facilitates supervision and inspection by electricity users.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A three-phase, three-element combined instrument transformer for State Grid applications, characterized in that, include: The main insulator is made by casting the current transformer body A, current transformer body B, current transformer body C, voltage transformer body A, voltage transformer body B, and voltage transformer body C into one piece using epoxy resin, and the outer surface of the main insulator is covered with a silicone rubber sleeve. The upper part of the primary high-voltage conductor of current transformer body A, current transformer body B, and current transformer body C extends out of the main insulator, and the lower part is located inside the main insulator and connected to the first high-voltage terminal of the primary voltage winding of the corresponding voltage transformer body A, voltage transformer body B, and voltage transformer body C. The second high-voltage terminals of the primary windings of voltage transformer bodies A, B, and C are twisted together to form a Y-type connection and then connected to the primary N terminal, which is located between phases A and B of the main insulator. The secondary leads of current transformer body A, current transformer body B, current transformer body C, voltage transformer body A, voltage transformer body B, and voltage transformer body C are connected to the secondary terminals according to their corresponding markings. The secondary n-terminals of voltage transformer body A, voltage transformer body B, and voltage transformer body C are twisted together as a common terminal to form a Y-type connection, which is then connected to the n-terminal of the secondary terminal. The current transformer body A and voltage transformer body A, current transformer body B and voltage transformer body B, and current transformer body C and voltage transformer body C are all arranged in a one-to-one correspondence in the main insulator.

2. The State Grid three-phase three-element combined instrument transformer according to claim 1, characterized in that, The current transformer bodies A, B, and C have the same structure, each including, from the inside out, an insulating cardboard corner ring, a twill cloth insulating layer, a polyurethane board buffer layer, and a half-layer of self-adhesive tape arranged on the current core. Enamelled round copper wire is wound on the half-layer of self-adhesive tape to form a secondary current winding. A polyester film is half-layered outside the secondary current winding, and a molded copper foil or molded aluminum foil is added. A secondary support is provided outside the molded copper foil or molded aluminum foil, and a semi-conductive crepe paper shielding layer is half-layered on the secondary support. The primary current winding passes through the current core and is wound with a high-voltage conductive busbar welded to both ends. From the inside out, a twill cloth, a crepe paper, and a semi-conductive crepe paper are half-layered on the primary current winding.

3. The State Grid three-phase three-element combined instrument transformer according to claim 1, characterized in that, The voltage transformer bodies A, B, and C have identical structures, all including a basic insulation layer. A secondary voltage winding is wound around the basic insulation layer, with PMP composite paper added between the winding layers as interlayer insulation. A low-voltage shielding layer is formed by winding semi-conductive corrugated paper around the outer layer of the secondary voltage winding. A resin skeleton is provided between the low-voltage shielding layer and the inner shielding layer. The inner shielding layer includes shaped copper foil and semi-conductive corrugated paper. Multiple layers of DMD insulating paper are first wound onto the inner shielding layer, followed by the winding of the primary voltage winding. After the primary voltage winding is completed, a shaped copper foil is added. Copper foil serves as a shielding layer, and semi-conductive crepe paper is wrapped around the shielding layer to form a high-voltage shielding layer. The voltage secondary winding is fitted into a resin skeleton, and the voltage core is fitted into the voltage secondary winding. The exposed part of the voltage core has a multi-layer insulation structure, specifically including, from the inside out, a half-stacked layer of self-adhesive tape insulation layer, a molded polyurethane board buffer layer, a half-stacked layer of self-adhesive tape insulation layer, and then an outer molded copper foil or aluminum foil, and a half-stacked layer of semi-conductive crepe paper. Semi-conductive paint is applied to both sides of the wrapped voltage core to form a low-voltage shielding layer.

4. The State Grid three-phase three-element combined instrument transformer according to claim 1, characterized in that, Multiple rainproof skirts are distributed on the upper outer wall of the main insulator, and these multiple rainproof skirts are distributed around the lower outer periphery of the primary high voltage conductor; silicone skirts are distributed in the middle and lower parts of the main insulator.

5. A three-phase three-element combined instrument transformer for State Grid as described in claim 2, characterized in that, The secondary support for phase A current and the secondary support for phase C current have the same structure, both including symmetrically arranged angular legs. The top of each angular leg is connected to the side of the first arc-shaped support plate, and the connection points are symmetrically arranged. The bottom of each angular leg is connected to the first fixing plate.

6. A three-phase three-element combined instrument transformer for State Grid as described in claim 2, characterized in that, The B-phase secondary support includes asymmetrically arranged irregularly shaped legs. The top of each irregularly shaped leg is connected to the side of the second arc-shaped support plate, and the connection points are not symmetrically arranged. The bottom of each irregularly shaped leg is connected to a second fixing plate.

7. A three-phase three-element combined instrument transformer for State Grid as described in claim 3, characterized in that, An auxiliary secondary winding is added outside the voltage secondary windings of the voltage transformer body A, voltage transformer body B, and voltage transformer body C. The end line of the auxiliary secondary winding of voltage transformer body A is connected to the beginning line of the auxiliary secondary winding of voltage transformer body B, and the end line of the auxiliary secondary winding of voltage transformer body B is connected to the beginning line of the auxiliary secondary winding of voltage transformer body C. The beginning line of the auxiliary secondary winding of voltage transformer body A and the end line of the auxiliary secondary winding of voltage transformer body C are respectively connected to the corresponding terminals of the auxiliary secondary winding of the main insulator. Before the silicone rubber sleeve is encapsulated, the two terminals are connected with bare copper wire to form a closed suppression circuit.

8. A three-phase three-element combined instrument transformer for State Grid as described in claim 1, characterized in that, Each phase's primary high-voltage conductor is tilted at an angle in a V-shape and is sealed with a protective cover.

9. A three-phase three-element combined instrument transformer for State Grid as described in claim 1, characterized in that, A secondary wiring platform is cast in the lower part of the main insulator. The secondary wiring platform has built-in secondary wiring terminals. The secondary wiring terminals are sealed by secondary rubber gaskets and secondary cover plates. The screws used to fix the secondary cover plates are equipped with lead sealing holes and lead seals are installed. The State Grid special electronic tag is attached to the secondary wiring terminals with silicone.

10. A three-phase three-element combined instrument transformer for State Grid as described in claim 1, characterized in that, The current ratio is permanently marked on the surface of the main insulator by laser etching.

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