Current transformer for electrified railways
By adopting a current transformer with epoxy resin vacuum casting and external shielding design, the insulation breakdown and flashover problems of electrified railway traction substations have been solved, the insulation stability and dynamic and thermal performance of the equipment have been improved, and the safe and reliable operation of railway substations has been ensured.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- DALIAN NORTH INSTR TRANSFORMER GROUP
- Filing Date
- 2024-12-09
- Publication Date
- 2026-06-09
Smart Images
Figure CN122177623A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to high-voltage measurement or relay protection equipment for power supply systems, specifically a current transformer for electrified railways. Background Technology
[0002] Electrified railway traction substations transform three-phase 110kV (or 220kV) high-voltage AC power into two single-phase 27.5kV AC power, which is then transmitted to the railway contact network to supply traction power. Current transformers within the substation are electrical devices connecting the primary lines and secondary equipment, primarily functioning as current measurement and monitoring devices, as well as relay protection devices. However, their design level is at the 1970s level in China, employing a semi-enclosed structure with exposed iron cores. These products suffer from small creepage distances, high temperature rises, and poor insulation reliability. Given the prevalence of pollution accumulation, moisture, condensation, frequent grounding faults, high overcurrents, high operating overvoltages, and frequent overvoltages in railway substations, faults such as flashover, excessive temperature rise, and insulation breakdown discharge are common. Therefore, to further improve the reliability of railway traction power supply, it is essential to develop a current transformer suitable for railway traction substations, comprehensively enhancing the safer and more reliable operation of railway substation equipment. Summary of the Invention
[0003] To address the aforementioned problems, the present invention aims to provide a current transformer for electrified railways, thereby solving the problems of flashover, excessive temperature rise, and insulation breakdown discharge that occur in existing high-voltage current transformers in railway traction substations due to the special environment.
[0004] To achieve the above objectives, the present invention adopts the following technical solution:
[0005] This invention provides a current transformer for electrified railways, comprising a casting body and a coil body encapsulated within the casting body. The coil body includes a secondary winding, a primary winding wound around the outside of the secondary winding, and a secondary winding support for supporting the secondary winding. The secondary winding includes multiple secondary winding units arranged side by side and forming an integral structure by wrapping the outer shielding layer of the secondary winding. The secondary terminals of the secondary winding are located at the bottom side of the casting body, and the primary terminals of the primary winding are located at the top of the casting body. The bottom of the casting body is provided with multiple mounting inserts.
[0006] The secondary winding unit includes an iron core, an iron core insulation layer, enameled round copper wire, and a secondary winding outer wrapping layer. The iron core is wrapped with an iron core insulation layer, and enameled round copper wire is wound around the outside of the iron core insulation layer. The outer wrapping layer of the secondary winding is wrapped around the outside of the enameled round copper wire.
[0007] The core insulation layer consists of, from the inside out, a layer of 0.5mm cardboard corner rings, a half-layer of plain weave tape, a half-layer of double-layer crepe paper, two half-layers of polyester film, and a half-layer of insulating self-adhesive tape.
[0008] The secondary winding outer wrapping layer comprises, from the inside out, a double layer of crepe paper half-overlapped with one layer and a polyester film half-overlapped with two layers.
[0009] The outer shielding layer of the secondary winding is semi-conductive crepe paper.
[0010] The secondary winding is connected to the secondary terminal via secondary winding leads. A primary equalizing mesh is provided between the primary winding and the secondary winding leads. The primary equalizing mesh has an arc structure and two legs extend from it to connect to the two mounting inserts near the secondary terminal.
[0011] The casting body is a one-piece rectangular structure cast with epoxy resin, with missing corners at the four corners and rounded corners at the transition points; the outer perimeter of the casting body is provided with umbrella skirt structures at equal intervals along the height direction.
[0012] The primary terminal block is a flat terminal block with threaded holes that is embedded in the casting body and partially exposed.
[0013] The outer side of the secondary wiring terminal is covered with a transparent secondary wiring cover.
[0014] The mounting insert at the bottom of the casting body is connected to the base plate by countersunk screws, and the base plate is provided with grounding bolts.
[0015] The present invention has the following advantages and beneficial effects:
[0016] 1. Small size and flexible installation: The invention has an optimized structural design, making the structure more compact. The two primary terminals are flat terminal blocks with embedded threaded holes, which can be flexibly electrically and mechanically crimped with the main busbar and installed in the switch cabinet.
[0017] 2. Stable insulation and high pollution resistance: This invention uses epoxy resin vacuum casting to form an integral structure, which has stable and reliable insulation. The integral structure has uniformly distributed umbrella skirts with equal spacing from top to bottom, which effectively increases the creepage distance on the product surface. During long-term operation, it will not cause arc flash, discharge and insulation breakdown faults due to dust and dirt, and the insulation is more stable.
[0018] 3. High dynamic and thermal stability current and low temperature rise: The primary winding of this invention is made of wire with a larger diameter, which effectively increases the current-conducting cross section of the primary winding and improves the dynamic and thermal stability current. It can effectively avoid the overcurrent caused by system grounding faults, which can lead to excessive temperature rise of the transformer and insulation damage. The product has a lower operating temperature rise.
[0019] 4. The primary high-voltage winding and the secondary low-voltage winding of the present invention both adopt an external shielding wrapping scheme during wrapping, which makes the external electric field of the coil uniform, eliminates the risk of tip discharge, and greatly improves the partial discharge level of the product. Attached Figure Description
[0020] Figure 1 This is a schematic diagram of the internal structure of a current transformer for electrified railways according to the present invention;
[0021] Figure 2 for Figure 1 The left view;
[0022] Figure 3 for Figure 1 Top view;
[0023] Figure 4 for Figure 1 A schematic diagram of the K-line without a bottom;
[0024] Figure 5 for Figure 1 Enlarged view of a portion of point A in the middle;
[0025] Figure 6 This is a schematic diagram of the overall structure of a current transformer for electrified railways according to the present invention;
[0026] Figure 7 for Figure 6 The left view.
[0027] In the diagram: 1- Casting body; 2- Primary winding; 3- Iron core; 4- Iron core insulation layer; 5- Enameled round copper wire; 6- Secondary winding outer wrapping layer; 7- Primary winding wrapping layer; 8- Mounting insert; 9- Base plate; 10- Secondary winding bracket; 11- Secondary winding; 12- Secondary winding lead wire; 13- Primary equalizing mesh; 14- Secondary terminal block; 15- Secondary terminal cover; 16- Grounding bolt; 17- Primary terminal block; 18- Secondary winding outer shielding layer. Detailed Implementation
[0028] 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.
[0029] See Figures 1 to 7As shown, the present invention provides a current transformer for electrified railways, including a casting body 1 and a coil body encapsulated within the casting body 1. The coil body includes a secondary winding 11, a primary winding 1 wound around the outside of the secondary winding 11, and a secondary winding bracket 10 for supporting the secondary winding 11. The secondary winding 11 includes multiple secondary winding units, which are arranged side by side and formed into an integral structure by wrapping the outer shielding layer 18 of the secondary winding. The secondary terminals 14 of the secondary winding 11 are located at the bottom side of the casting body 1, and the primary terminals 17 of the primary winding 1 are located at the top of the casting body 1. The bottom of the casting body 1 is provided with multiple mounting inserts 8.
[0030] See Figure 1 , Figure 2 As shown, in an embodiment of the present invention, the mounting insert 8 at the bottom of the casting body 1 is connected to the base plate 9 with mounting holes by countersunk screws. The base plate 9 is provided with grounding bolts 16 to improve the safety of the system.
[0031] See Figure 1 , Figure 5 As shown, in an embodiment of the present invention, the secondary winding unit includes an iron core 3, an iron core insulation layer 4, an enameled round copper wire 5, and a secondary winding outer wrapping layer 6. The iron core 3 is wrapped with the iron core insulation layer 4, the enameled round copper wire 5 is wound around the outside of the iron core insulation layer 4, and the enameled round copper wire 5 is wrapped with the secondary winding outer wrapping layer 6.
[0032] Specifically, the core insulation layer 4 consists of, from the inside out, a layer of 0.5mm cardboard corner rings, a half-layer of plain weave tape, a half-layer of double-layer crepe paper, two half-layers of polyester film, and a half-layer of insulating self-adhesive tape. The core insulation layer 4 increases the buffering force, resulting in better electrical safety performance for the entire secondary winding.
[0033] Specifically, the secondary winding outer wrapping layer 6 includes two layers of double-layered crepe paper and two layers of polyester film wrapped sequentially from the inside out.
[0034] Preferably, the outer shielding layer 18 of the secondary winding is a semi-conductive corrugated paper layer stacked on top of each other. The primary winding 1 is wrapped with a primary winding wrapping layer 7. Both the primary winding 1 and the secondary winding 11 adopt an outer shielding wrapping scheme, which provides strong protection for the internal electric field of the uniform transformer.
[0035] See Figure 1As shown, in this embodiment of the invention, the secondary winding 11 is connected to the secondary terminal 14 via the secondary winding lead 12. A primary equalizing mesh 13 is provided between the primary winding 1 and the secondary winding lead 12. The primary equalizing mesh 13 has an arc structure, and two legs extend from the primary equalizing mesh 13 to connect with two mounting inserts 8 near the secondary terminal 14. In this embodiment, the bottom of the casting body 1 is provided with four or more mounting inserts 8. The primary equalizing mesh 13 effectively prevents the phenomenon of tip discharge under high voltage, providing a good guarantee for improving the partial discharge level of the product.
[0036] In the embodiments of the present invention, the casting body 1 is an integral structure in the shape of a cuboid cast with epoxy resin, and the four corners are missing. The transition is rounded, which optimizes the structural design and ensures that the primary and secondary coils inside have a uniform and sufficient insulation distance. The outer perimeter of the casting body 1 is provided with umbrella skirt structures at equal intervals along the height direction, which ensures that the product has a large surface creepage distance between high voltage and ground, making the insulation more reliable. The optimized shape design will not accumulate too much dust and dirt during operation.
[0037] Specifically, the primary terminal 17 is a flat terminal block with threaded holes embedded in the casting body 1 and partially exposed, which effectively ensures electrical and mechanical crimping with the busbar inlet and outlet in the main busbar chamber, increasing the effective contact area. The overall structure is made of epoxy resin vacuum casting, making the structure more compact.
[0038] Furthermore, the outer side of the secondary terminal block 14 is covered with a transparent secondary terminal cover 15. The secondary terminal cover 15 is equipped with lead-sealed screws, which provides excellent dustproof and anti-theft protection. During use, it will not cause secondary short circuits or monitoring failures due to environmental condensation or moisture. The secondary winding support 10 has a bridge-shaped structure with an arc-shaped bridge surface and two through holes on the base. The secondary winding support 10 supports the secondary winding inside the casting body 1.
[0039] The present invention provides a current transformer for electrified railways, the manufacturing process of which is as follows:
[0040] Multiple secondary winding units are integrated into a single unit to form a secondary winding 11. A primary winding 2 is wound using a special tool, and an insulating wrapping layer 7 is added to the primary winding. The secondary winding 11 is then bound and cushioned using a secondary winding bracket 10 to form a coil body with a primary terminal 17, a primary winding 2, a secondary winding 11, and a secondary terminal 14. The secondary winding 11 is fixed to the mold using the secondary winding bracket 10, and the primary winding 2 is positioned and fixed to the mold using the primary terminal 17. After adjusting the distance, epoxy resin is vacuum cast and cured to form an integrated structure. The integrated structure features evenly spaced umbrella skirts distributed from top to bottom, ensuring a large surface creepage distance between the high voltage and ground, resulting in more reliable insulation. The casting body 1 has a rectangular shape with missing corners, optimizing the structural design and ensuring a uniform and ample insulation distance around the internal coils. It also prevents excessive dust and dirt accumulation during use. The two primary terminals 17 are flat terminal plates with threaded holes, embedded in the casting body 1 and partially exposed, effectively ensuring electrical and mechanical crimping with the busbar inlet and outlet in the main busbar compartment. The overall structure is vacuum-cast using epoxy resin, resulting in a more compact design. A primary equalizing mesh 13 is provided between the primary winding 2 and the secondary winding lead 12, effectively preventing tip discharge under high voltage. The secondary terminal 14 is located at the lower front of the integrated structure. The secondary terminal cover 15 is made of transparent flame-retardant material and has lead-sealed screws, providing dust and water protection. It prevents secondary short circuits and monitoring failures due to environmental condensation or moisture during use. Both the primary winding 2 and the secondary winding 11 were wrapped with external shielding, which made the external electric field of the coil uniform, eliminated the risk of tip discharge, and greatly improved the partial discharge level of the product.
[0041] The present invention provides a current transformer for electrified railways, which is a new product designed in full accordance with national standards and railway traction substation technology. 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 is used for current measurement and relay protection.
[0042] This invention is made by vacuum casting of epoxy resin. The product has the characteristics of small size, flexible installation, reliable insulation, high pollution resistance, high dynamic and thermal stability current, and low temperature rise. It is perfectly suitable for use in railway traction substation environments and improves the overall manufacturing level of railway substation equipment.
[0043] 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 current transformer for electrified railways, comprising a cast body (1) and a coil former housed in the cast body (1), characterized in that, The coil body includes a secondary winding (11), a primary winding (1) wound around the outside of the secondary winding (11), and a secondary winding bracket (10) for supporting the secondary winding (11). The secondary winding (11) includes multiple secondary winding units, which are arranged side by side and formed into an integral structure by wrapping the outer shielding layer (18) of the secondary winding. The secondary terminals (14) of the secondary winding (11) are located at the bottom side of the casting body (1), and the primary terminals (17) of the primary winding (1) are located at the top of the casting body (1). The bottom of the casting body (1) is provided with multiple mounting inserts (8).
2. The current transformer for electrified railways according to claim 1, characterized in that, The secondary winding unit includes an iron core (3), an iron core insulation layer (4), an enameled round copper wire (5), and a secondary winding outer wrapping layer (6). The iron core (3) is wrapped with the iron core insulation layer (4), the enameled round copper wire (5) is wound around the outside of the iron core insulation layer (4), and the enameled round copper wire (5) is wrapped with the secondary winding outer wrapping layer (6) on the outside of the enameled round copper wire (5).
3. The current transformer for electrified railways according to claim 2, characterized in that, The core insulation layer (4) consists of, from the inside out, a layer of 0.5mm cardboard corner ring, a half-layer of plain weave tape, a half-layer of double-layer crepe paper, two half-layers of polyester film, and a half-layer of insulating self-adhesive tape.
4. The current transformer for electrified railways according to claim 2, characterized in that, The secondary winding outer wrapping layer (6) includes two layers of double-layered crepe paper and two layers of polyester film wrapped sequentially from the inside out.
5. The current transformer for electrified railways according to claim 1, characterized in that, The outer shielding layer (18) of the secondary winding is semi-conductive crepe paper.
6. The current transformer for electrified railways according to claim 1, characterized in that, The secondary winding (11) is connected to the secondary terminal (14) through the secondary winding lead (12). A primary equalizing mesh (13) is provided between the primary winding (1) and the secondary winding lead (12). The primary equalizing mesh (13) has an arc structure and two legs extend from the primary equalizing mesh (13) to connect with the two mounting inserts (8) near the secondary terminal (14).
7. The current transformer for electrified railways according to claim 1, characterized in that, The casting body (1) is a rectangular prism-shaped integral structure cast with epoxy resin, and the four corners are missing corners with rounded transition corners; the outer perimeter of the casting body (1) is provided with umbrella skirt structures at equal intervals along the height direction.
8. The current transformer for electrified railways according to claim 1, characterized in that, The primary terminal (17) is a flat terminal block with threaded holes that is embedded in the casting body (1) and partially exposed.
9. The current transformer for electrified railways according to claim 1, characterized in that, The outer side of the secondary terminal (14) is covered with a transparent secondary terminal cover (15).
10. The current transformer for electrified railways according to claim 1, characterized in that, The mounting insert (8) at the bottom of the casting body (1) is connected to the base plate (9) by countersunk screws, and the base plate (9) is provided with grounding bolts (16).