A transformer core and an oil-immersed transformer

Abstract

This invention relates to the field of three-phase transformer technology, and more particularly to a transformer core and an oil-immersed transformer. The oil-immersed transformer of this invention includes a transformer core comprising a high-voltage coil and a low-voltage coil mounted on the same iron core. The high-voltage coil is located outside the low-voltage coil, and an insulating layer is provided between them. The transformer core is axially split into an upper coil assembly and a lower coil assembly. The upper coil assembly includes an upper high-voltage coil and an upper low-voltage coil, and the lower coil assembly includes a lower high-voltage coil and a lower low-voltage coil. An insulating structure is provided between the upper and lower coil assemblies to achieve insulation isolation between them. The upper and lower coil assemblies are connected in parallel. This split parallel arrangement reduces the short-circuit current during short-circuit faults, preventing the transformer from burning out due to short circuits and causing property damage.

Description

Technical Field

[0001] This invention relates to the field of three-phase transformer technology, and more particularly to a transformer core and an oil-immersed transformer. Background Technology

[0002] Due to environmental issues and the need for sustainable development, an energy structure based on clean and renewable energy is being established to replace the energy structure based on heavily polluting and resource-limited fossil fuels. Among these, solar and wind energy are the most ideal alternative energy sources due to their almost unlimited energy reserves.

[0003] In photovoltaic and wind power generation systems, photovoltaic cells convert solar energy into direct current (DC), eddy current generators convert wind energy into DC, and then inverters convert DC into alternating current (AC). After that, transformers are used to raise the voltage of the AC output from the inverter to a voltage level suitable for long-distance transmission. After transmission, the high voltage is converted back to a voltage level suitable for power consumption. Transformers also serve to isolate the main power grid from distributed power sources, ensuring the stable operation of the power grid.

[0004] Wind power capacity has grown rapidly in recent years. Wind power plants are typically located in remote areas, with installations scattered across harsh environments. Onshore wind turbines usually have box-type transformers at the base for voltage boosting and current collection. Figure 9 As shown, the output line of the turbine generator at the top of the wind turbine 21 is connected to the transformer substation 22. After the voltage is stepped up by the transformer substation 22, the current from multiple wind turbines is combined and then input to the medium voltage bus 24. The voltage level is further increased by the step-up transformer 23. After the voltage is stepped up to 110kV or higher, the wind turbine outputs to the high voltage bus 25 and connects to the power grid.

[0005] With the ever-increasing demand for electricity, the capacity requirements for transformers are also increasing. Currently, the applied capacity is 12500kVA, while the voltage on the low-voltage side is usually 0.4kV, 0.63kV, 0.69kV, 0.8kV, and 1.14kV. The cross-sectional area of ​​the low-voltage conductor used in such low-voltage, high-capacity transformers increases with the increase in capacity, making the processing of coil supports difficult. Furthermore, as the capacity increases, the rated current on the low-voltage side increases while the rated voltage remains unchanged. If a short circuit occurs during the operation of the transformer, the short-circuit current is usually ten to thirty times the rated current, which can cause the transformer to burn out and result in property damage.

[0006] Chinese invention patent CN111933431B, authorized on July 6, 2021, discloses an axially split transformer coil structure, a low-voltage coil lead-out structure, and a transformer. This coil structure employs a dual-winding design, with a low-voltage coil wound on the iron core. An insulation layer is provided on the outside of the low-voltage coil, and a high-voltage coil is wound on the outside of the insulation layer. The low-voltage coil adopts an axially split design, divided into an upper low-voltage coil and a lower low-voltage coil, with an insulation structure between them. By using this axially split design for the low-voltage coil, the cross-sectional area of ​​the low-voltage conductor is reduced for the same transformer capacity, which can reduce the processing difficulty of the coil support. However, in the event of a short-circuit fault, the short-circuit current supplied by the power grid flowing through the split transformer may cause the transformer to burn out, resulting in irreparable losses to users and enterprises. Summary of the Invention

[0007] The purpose of this invention is to provide a transformer core to solve the problem of transformer burnout caused by short circuit faults.

[0008] Another objective of this invention is to provide an oil-immersed transformer to solve the above-mentioned problems.

[0009] The transformer core of this invention adopts the following technical solution: A transformer core includes an iron core and a coil assembly mounted on the iron core. The coil assembly is a segmented structure with axially segmented sections. Each segment includes a low-voltage coil on the inner side and a corresponding high-voltage coil on the outer side. The low-voltage coil and the high-voltage coil of each segment have their own terminals.

[0010] Furthermore, the terminals of the high-voltage coils of each segment and / or the terminals of the low-voltage coils of each segment are connected in parallel.

[0011] Furthermore, the coil structure is identical for each segment.

[0012] Furthermore, the coil assembly includes two segments, which are arranged symmetrically vertically.

[0013] Furthermore, the two segments have equal capacity.

[0014] Beneficial Effects: The transformer core of this invention is a pioneering creation. The transformer core of this invention includes an iron core and a coil assembly mounted on the iron core. The coil assembly has a segmented structure with axially segmented sections. The two parts are electrically insulated and isolated, distributing capacity to each segment. This avoids the high production difficulty of the low-voltage conductor due to excessive capacity, and also reduces the hazards of short-circuit current during short circuits. Each segment includes an inner low-voltage coil and a corresponding outer high-voltage coil. Each segment's low-voltage and high-voltage coils have their own terminals. The independent terminal design for each segment allows for more flexible configuration. This split design reduces the short-circuit current during short-circuit faults, preventing the transformer from burning out due to short circuits and causing property damage.

[0015] The oil-immersed transformer of the present invention adopts the following technical solution: An oil-immersed transformer includes a transformer core, which comprises an iron core and a coil assembly mounted on the iron core. The coil assembly is a segmented structure with axially segmented sections. Each segment includes an inner low-voltage coil and a corresponding outer high-voltage coil. Each segment's low-voltage coil and high-voltage coil have their own terminals.

[0016] Furthermore, the terminals of the high-voltage coils of each segment and / or the terminals of the low-voltage coils of each segment are connected in parallel.

[0017] Furthermore, the coil structure is identical for each segment.

[0018] Furthermore, the coil assembly includes two segments, which are arranged symmetrically vertically.

[0019] Furthermore, the two segments have equal capacity.

[0020] Beneficial Effects: The oil-immersed transformer of this invention is an improved invention. The oil-immersed transformer of this invention includes a transformer core, which comprises an iron core and a coil assembly mounted on the iron core. The coil assembly has a segmented structure with axially segmented sections. The two parts are electrically insulated and isolated, distributing capacity to each segment. This avoids the high production difficulty of the low-voltage conductor due to excessive capacity, and also reduces the hazards of short-circuit current during short circuits. Each segment includes an inner low-voltage coil and a corresponding outer high-voltage coil. Each segment's low-voltage and high-voltage coils have their own terminals. The independent terminal design for each segment allows for more flexible configuration. This split configuration reduces the short-circuit current during short-circuit faults, preventing the transformer from burning out due to short circuits and causing property damage. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of an embodiment of the oil-immersed transformer of the present invention; Figure 2 for Figure 1 Top view; Figure 3 This is a schematic diagram of the structure of one embodiment of the transformer core of the present invention; Figure 4 for Figure 3 Schematic diagram of the structure of medium and low voltage coils; Figure 5 for Figure 3 Top view; Figure 6 for Figure 3 Schematic diagram of the middle corner ring; Figure 7 for Figure 6 Top view; Figure 8 for Figure 3 Schematic diagram of the structure of the middle insulating end ring; Figure 9 For existing photovoltaic and wind power generation systems; Figure 10 This invention relates to the application of the invention in power systems. Figure 11 for Figure 1 Diagram showing the lead distribution of medium and high voltage coils.

[0022] In the diagram: 1. Iron core; 2. Upper high-voltage coil; 3. Upper low-voltage coil; 4. Lower high-voltage coil; 5. Lower low-voltage coil; 6. Insulating end ring; 7. Angle ring; 8. Tap changer lead; 9. Oil passage; 10. Oil tank; 11. Radiator; 12. Oil conservator; 13. Voltage regulating tap changer; 14. Gas relay; 15. Oil level indicator; 16. Pad; 17. High-voltage bushing; 18. Low-voltage bushing; 19. Lead wire; 20. Lead-out copper busbar; 21. Fan; 22. Box-type substation; 23. Step-up transformer; 24. Medium-voltage busbar; 25. High-voltage busbar. Detailed Implementation

[0023] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0024] As transformer capacity increases, the damage caused by transformer short-circuit faults also increases, easily leading to transformer burnout. The concept of this invention is to reduce the magnitude of the short-circuit current through a split design, thus preventing the short-circuit circuit from burning out the transformer.

[0025] The specific embodiments of the transformer core of the present invention are as follows: Based on the above ideas, such as Figure 3 , 4As shown, in a basic embodiment, the transformer core of the present invention includes an iron core 1 and a coil assembly mounted on the iron core 1. The coil assembly is a segmented structure with axially segmented sections, each section sharing the same iron core. Each section is electrically insulated and isolated, distributing capacity to each section to avoid increasing the cross-sectional area of ​​the low-voltage conductor due to excessive capacity, thus reducing production difficulty. At the same time, it reduces the harm of short-circuit current during short circuits. Each section includes an inner low-voltage coil and a corresponding outer high-voltage coil. The low-voltage coil and high-voltage coil of each section have their own terminals. The independent terminal design of each section allows for more flexible configuration. Through the split configuration, the short-circuit current during short-circuit faults is reduced, preventing the transformer from burning out due to short circuits and causing property damage.

[0026] In a preferred embodiment, the terminals of the high-voltage coils and / or the terminals of the low-voltage coils of each segment can be directly connected in parallel at the transformer to form a set of external connection ports. The high-voltage coils of each segment are connected in parallel and output to the busbar, or the power is input to the transformer via the transmission line and then shunted and connected in parallel to the low-voltage coils of each segment. Figure 10 As shown, a transformer comprising two sets of low-voltage connection ports and one set of high-voltage connection ports is illustrated. This transformer uses the aforementioned coil combination and includes a two-segment transformer core. Compared to existing technologies, the wind turbine's transmission circuit is divided into two circuits, each connected to the two segments of the low-voltage coils of the phase coil combination of the transformer 22 corresponding to the wind turbine 21. The two segments of each phase coil combination are arranged in a parallel manner on the circuit from the wind turbine's output circuit to the medium-voltage busbar, and then flow through the step-up transformer 23 for further voltage boosting before being output to the high-voltage busbar 25 and entering the power grid. In the event of a fault in one branch, due to the parallel arrangement of the two branches, the change in busbar voltage is small, ensuring the stability of the power system.

[0027] In a preferred embodiment, the coil structures of each segment are identical, reducing the manufacturing process and simplifying production. Furthermore, the identical coil structure minimizes interference between segments during operation, thus reducing the impact on power transmission. In other embodiments, each segment may employ a different structural design.

[0028] In a preferred embodiment, the coil assembly includes two segments: an upper coil assembly and a lower coil assembly. The upper coil assembly includes an upper high-voltage coil 2 and an upper low-voltage coil 3, and the lower coil assembly includes a lower high-voltage coil 4 and a lower low-voltage coil 5. This design reduces the cross-sectional area of ​​the low-voltage conductor and lowers the processing difficulty. Too many segments, on the other hand, increase the processing difficulty and the complexity of the power system, which is detrimental to ensuring the stable operation of the transformer. Furthermore, the two segments are symmetrically arranged, facilitating wiring at the terminals and resulting in a more rational layout. In other embodiments, the coil assembly may also include three or more segments, which similarly reduces the cross-sectional area of ​​the low-voltage conductor.

[0029] In a preferred embodiment, the two segments have equal capacities. Compared to an unevenly distributed capacity, this results in a smaller maximum short-circuit current flowing through the transformer core during a short circuit, reducing the damage caused by short circuits. Furthermore, the structure is simpler, allowing for a halving of the cross-sectional area of ​​the low-voltage conductor. The two segments can also employ the same design, facilitating mass production. In other embodiments, the two segments have unevenly distributed capacities.

[0030] When one segment fails, the short-circuit current supplied by the grid passes through the transformer core. Because the semi-through reactance is larger than the through reactance, the supplied short-circuit current is smaller than that of the unsegmented transformer core. At the same time, the feedback current supplied to the short-circuit point by the other branch of the transformer core will also be reduced, thus preventing the transformer from burning out due to a short circuit. Furthermore, when one branch of the transformer core fails, the other branch can still operate normally and will not fail due to the fault. The bus voltage drop is relatively small, thus ensuring the operational stability of the electrical equipment on the bus. Through the axial split setting of the low-voltage coil, the cross-sectional area of ​​the low-voltage conductor is reduced for the same transformer capacity. For increasingly larger photovoltaic and wind power transformers, this avoids the difficulty in selecting low-voltage conductors and also avoids the problem of the winding machine's winding shaft length not meeting the coil height requirements when selecting a single foil winding.

[0031] like Figure 10 As shown, the above-mentioned coil combination includes two segmented voltage cores. Compared with the prior art, the power transmission circuit of the wind turbine is divided into two circuits, which are respectively connected to the two segmented low-voltage coils of each phase coil combination of the transformer 22 corresponding to the wind turbine 21. The two segments of each phase coil combination are set in a similar parallel manner on the circuit between the output circuit of the wind turbine 21 and the medium-voltage bus 24. Then, the power flows through the step-up transformer 23 for further voltage boosting and output to the high-voltage bus 25, entering the power grid.

[0032] In a preferred embodiment, the high-voltage coil is provided with a tap changer 8 for adjusting the voltage level. The tap changer 8 is connected to a voltage regulating tap switch 13 on the transformer casing. The voltage regulating tap switch 13 controls the winding ratio of the transformer, thereby controlling the output voltage level of the transformer.

[0033] like Figure 6 , 7 In the embodiment shown in 8, the insulation structure includes an angle ring 7 and an insulating end ring 6. A pad 16 is adhered to the insulating end ring 6. The angle ring 7 includes an annular horizontal part for isolating each segment of the high-voltage coil and a cylindrical vertical part for clamping and fixing. The angle ring 7 is formed by overlapping and bending multiple layers of slotted cardboard in an arc direction. As the axial insulation structure of the high-voltage coil, the angle ring 7 mainly functions to limit the relaxation voltage of the high-voltage coil and prevent the relaxation voltage from spreading along the axial direction of the high-voltage coil. At the same time, it can also protect the insulation structure of the coil and extend the service life of the transformer.

[0034] The specific embodiments of the oil-immersed transformer of the present invention are as follows: In one basic embodiment, the oil-immersed transformer of the present invention includes a transformer core, the specific implementation of which is described above and will not be repeated here.

[0035] like Figure 1 , 2 As shown, the oil-immersed transformer of the present invention is a three-phase transformer, including an oil tank 10. One or more radiators 11 are reasonably arranged on the side of the oil tank 10 according to the temperature rise during operation. An oil conservator 12 for storing transformer oil is provided at the upper end of the oil tank 10. An oil level indicator 15 is provided on the oil conservator 12. The oil conservator 12 and the oil tank 10 are connected by an oil pipe. A gas relay 14 is provided on the oil pipe. A voltage regulating tap changer 13 is provided on the top of the outer shell of the oil tank 10. A low-voltage sleeve 18 and a high-voltage sleeve 17 are also provided on the outer shell of the oil tank 10. A transformer core is provided inside the oil tank 10.

[0036] like Figure 5 As shown, the adjacent side of the core 1 is the upper low-voltage coil 3. An oil passage 9 is provided between the adjacent layers of the upper low-voltage coil 3 according to the temperature rise of the transformer. The upper high-voltage coil 2 is wound outside the upper low-voltage coil 3. An oil passage 9 is arranged between the upper high-voltage coil 2 and the upper low-voltage coil 3. An oil passage 9 is provided between the adjacent layers of the upper high-voltage coil 2. The oil passage 9 is the flow channel of transformer oil, which transfers the heat generated by the coil to the surface of the radiator 11 and the oil tank 10 for heat dissipation.

[0037] like Figure 11As shown, high-voltage coils of the same phase are connected in parallel by leads, and the ends of the three-phase high-voltage coils are connected sequentially by leads to form a delta connection. The delta connection helps to reduce line losses and has a compact and stable structure, which can improve voltage stability. Current can flow through multiple coils, reducing coil resistance and harmonic generation, thus improving circuit stability.

[0038] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. The scope of patent protection of the present invention shall be determined by the claims. Similarly, any equivalent structural changes made based on the description and drawings of the present invention shall also be included within the scope of protection of the present invention.

Claims

1. A transformer core, characterized in that, It includes an iron core and a coil assembly mounted on the iron core. The coil assembly is a segmented structure with segments arranged axially upwards. Each segment includes a low-voltage coil on the inner side and a corresponding high-voltage coil on the outer side. Each segment's low-voltage coil and high-voltage coil have their own terminals.

2. The transformer core according to claim 1, characterized in that, The terminals of the high-voltage coils of each segment and / or the terminals of the low-voltage coils of each segment are connected in parallel.

3. The transformer core according to claim 1 or 2, characterized in that, The coil structures of each segment are identical.

4. The transformer core according to claim 1 or 2, characterized in that, The coil assembly includes two segments, which are arranged symmetrically vertically.

5. The transformer core according to claim 4, characterized in that, The two segments have equal capacity.

6. An oil-immersed transformer, comprising a transformer core, characterized in that, The transformer core includes an iron core and a coil assembly mounted on the iron core. The coil assembly is a segmented structure with axially segmented sections. Each segment includes a low-voltage coil on the inner side and a corresponding high-voltage coil on the outer side. Each segment's low-voltage coil and high-voltage coil have their own terminals.

7. The oil-immersed transformer according to claim 6, characterized in that, The terminals of the high-voltage coils of each segment and / or the terminals of the low-voltage coils of each segment are connected in parallel.

8. The oil-immersed transformer according to claim 6 or 7, characterized in that, The coil structures of each segment are identical.

9. The oil-immersed transformer according to claim 6 or 7, characterized in that, The coil assembly includes two segments, which are arranged symmetrically vertically.

10. The oil-immersed transformer according to claim 9, characterized in that, The two segments have equal capacity.

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