380kV large-impedance high-voltage on-load voltage regulation autotransformer

Abstract

The utility model relates to a 380kV large-impedance high-voltage on-load voltage regulation autotransformer, which comprises an iron core, and a medium-voltage winding, a high-voltage winding, a voltage regulation winding and a low-voltage winding which are sequentially wound on the iron core from inside to outside, the heights of the medium-voltage winding and the high-voltage winding are both L, the distance between the two ends of the low-voltage winding and the corresponding end of the high-voltage winding is both H, h is equivalent to 20%-40% of L, and the height of the voltage regulating winding is smaller than L. According to the utility model, by changing the arrangement mode of the coils and the design of the windings with different heights, the equivalent magnetic flux leakage area is increased, and the impedance can be improved by means of transverse magnetic flux leakage generated by ampere-turn imbalance, so that the requirements of foreign users on short-circuit current are met.

Description

Technical Field

[0001] This utility model relates to the field of transformer technology, specifically a 380kV high-impedance high-voltage on-load tap-changing autotransformer. Background Technology

[0002] In many national power grids, considering the breaking capacity of circuit breakers on the lines, the short-circuit current on each voltage side of the transformer is required not to exceed the system short-circuit current. However, for high-voltage on-load tap-changing autotransformers, the low-voltage side capacity is relatively small, sometimes as small as 1 / 200 of the rated capacity. In this case, the impedance on the low-voltage side is also relatively low. To reduce the low-voltage side short-circuit current, very high medium-low and high-low impedances are required. Currently, the most common method to increase medium-low and high-low impedances is to connect a current-limiting reactor in series with the low-voltage winding. However, some overseas users do not accept this approach. In such cases, other methods or structures to increase impedance need to be considered.

[0003] Patent CN103050260A discloses a 330kV three-phase three-winding on-load tap-changing autotransformer with high impedance. The transformer has a three-phase five-limb core with a low-voltage winding, a common winding, a series winding and a tap-changing winding concentrically mounted outside. The transformer uses a series reactor in the low-voltage winding to achieve short-circuit impedance between the high-low and medium-low windings.

[0004] The patent CN218274211U discloses an on-load autotransformer that places the low-voltage winding on two side posts, thereby increasing the distance between the low-voltage winding and the medium-voltage and high-voltage windings. This increases the medium-low impedance and high-low impedance on the low-voltage winding, thus enhancing the short-circuit withstand capability of the low-voltage winding. Utility Model Content

[0005] The purpose of this invention is to provide a 380kV high-impedance high-voltage on-load tap-changing autotransformer. By changing the coil arrangement and the design of unequal-height windings, it can increase the equivalent leakage magnetic area and improve the impedance by utilizing the transverse leakage magnetic field generated by the ampere-turn imbalance, thereby meeting the requirements of foreign users for short-circuit current.

[0006] The objective of this utility model is achieved through the following technical solution:

[0007] A 380kV high-impedance on-load tap-changing autotransformer includes an iron core and a medium-voltage winding, a high-voltage winding, a tap-changing winding, and a low-voltage winding wound sequentially from the inside to the outside of the iron core. The height of the medium-voltage winding and the high-voltage winding is L. The distance between the two ends of the low-voltage winding and the corresponding ends of the high-voltage winding is H, and H is equivalent to 20% to 40% of L. The height of the tap-changing winding is less than L.

[0008] The outermost low-voltage winding has an upper coil end ring at the upper end and a lower coil end ring at the lower end. The upper coil end ring has an upper insulating end ring on its upper side and an insulating cylinder on its upper side. The lower coil end ring has multiple lower insulating end rings stacked sequentially along the height direction on its lower side.

[0009] The innermost medium-voltage winding end is equipped with an electrostatic plate and a corner ring.

[0010] An insulating plate and support bars are provided between the medium-voltage winding and the high-voltage winding.

[0011] The advantages and positive effects of this utility model are as follows:

[0012] 1. This utility model, by changing the coil arrangement and the design of unequal height windings, can increase the equivalent leakage magnetic area and improve the impedance by using the transverse leakage magnetic field generated by the ampere-turn imbalance, thereby meeting the requirements of foreign users for short-circuit current.

[0013] 2. The height of the low-voltage winding of this utility model is greatly reduced. Its relatively small capacity will not cause a significant increase in load loss or overheating of structural components due to the lateral leakage flux. At the same time, it can also reduce the amount of materials used in the transformer, such as copper wire, silicon steel sheets, and transformer oil, thereby achieving the goal of comprehensive cost reduction of the transformer and improving the competitiveness of the transformer. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the structure of this utility model.

[0015] Figure 2 This is a schematic diagram illustrating the structural principle of this utility model.

[0016] Figure 3 This is a schematic diagram of the leakage magnetic flux distribution during medium- to low-voltage operation simulated using ANDERSON software.

[0017] Figure 4 This is a schematic diagram of the leakage magnetic flux distribution during high-voltage-low-voltage operation simulated using ANDERSON software, according to this invention.

[0018] Figure 5 This is a schematic diagram illustrating the structural principle of a high-voltage on-load tap-changing autotransformer in existing technology.

[0019] Figure 6 This is a schematic diagram of the leakage flux distribution of an existing high-voltage on-load tap-changing autotransformer under medium- to low-voltage operation, simulated using ANDERSON software.

[0020] Figure 7 This is a schematic diagram of the leakage flux distribution of an existing high-voltage on-load tap-changing autotransformer during high-voltage-low-voltage operation, simulated using ANDERSON software.

[0021] Among them, 1 is the iron core, 2 is the medium voltage winding, 3 is the high voltage winding, 4 is the voltage regulating winding, 5 is the low voltage winding, 6 is the pressure plate, 701 is the upper insulating end ring, 702 is the lower insulating end ring, 8 is the electrostatic plate, 9 is the corner ring, 10 is the insulating plate, 11 is the support bar, 12 is the insulating cylinder, 1301 is the upper coil end ring, 1302 is the lower coil end ring, 14 is the iron yoke pad, 15 is the iron yoke insulation, 16 is the enclosure, 17 is the oil tank wall, 18 is the first leakage magnetic area, 19 is the second leakage magnetic area, 20 is the third leakage magnetic area, and 21 is the fourth leakage magnetic area. Detailed Implementation

[0022] The present invention will now be described in further detail with reference to the accompanying drawings.

[0023] like Figures 1-7 As shown, this utility model includes an iron core 1 and a medium-voltage winding 2, a high-voltage winding 3, a voltage-regulating winding 4, and a low-voltage winding 5 wound sequentially on the iron core 1 from the inside out. The height of the medium-voltage winding 2 and the high-voltage winding 3 is L. The distance between the two ends of the low-voltage winding 5 and the corresponding ends of the high-voltage winding 3 is H, and H is equivalent to 20% to 40% of L. The height of the voltage-regulating winding 4 is less than L.

[0024] The design concept of this utility model is as follows: When a load current flows through the transformer winding, leakage flux is generated around the winding. The magnitude of the leakage flux depends on the load current, and the leakage flux can be divided into two components: axial leakage flux and transverse leakage flux. The axial leakage flux is vertically upward, while the transverse leakage flux is a horizontal component generated by the outward divergence of the leakage flux at the upper end of the winding and the inward convergence of the leakage flux at the lower end of the winding. Figure 5 As shown, the existing high-voltage on-load tap-changing autotransformer has a structure comprising, from the inside out, a low-voltage winding 5, a medium-voltage winding 2, a high-voltage winding 3, and a tap-changing winding 4 wound sequentially on the core 1, and as... Figures 6-7 As shown, under the existing structure, the leakage flux is mostly axial within the winding height range, with only a transverse component at the winding ends and in the ampere-turn imbalance section.

[0025] In addition, leakage flux generates eddy current losses at the conductors and stray losses in ferromagnetic structural components such as core clamps, core tie plates, and tank walls 17. In severe cases, this can cause localized overheating and the generation of fault gases. To avoid localized overheating and reduce eddy current and stray losses, current technologies generally design the transformer windings to be concentric and at the same height, with a balanced ampere-turn distribution. This reduces the lateral leakage flux component. When the transformer windings are designed to be concentric and at the same height, the ampere-turn distribution between the windings is balanced, and the influence of lateral leakage flux between the windings can be ignored. The empirical formula for calculating transformer impedance in this case is:

[0026] Uk =49.6×f×IW×∑D×ρ / (et× Hk ×107) (1);

[0027] In the above formula (1), Uk is the percentage of impedance voltage; f is the rated frequency; IW is the rated ampere-turns, which is related to the transformer capacity; ∑D is the equivalent leakage magnetic area, an important factor of short-circuit impedance; ρ is the Rockwell coefficient, the correction coefficient of short-circuit impedance; et is the turn potential, the voltage per turn of the winding; Hk is the average reactance height of the winding.

[0028] As can be seen from equation (1) above, the short-circuit impedance of the transformer is mainly changed by adjusting ∑D and Hk.

[0029] In this invention, when there are requirements for high-voltage to medium-voltage impedance, if we want to increase the impedance between medium-voltage and low-voltage and between high-voltage and low-voltage, we can only increase the equivalent leakage magnetic area ∑D under medium-voltage to low-voltage and high-voltage to low-voltage conditions and decrease the average reactance height Hk. However, due to insulation reasons, transformers of different voltage levels have minimum requirements for winding reactance height. Therefore, when the average reactance height Hk reaches the minimum value, this invention can only increase the leakage magnetic area ∑D. Changing the coil arrangement and increasing the distance between coils are common methods, but this will increase the main body spacing of the transformer, thereby increasing the no-load and load losses of the transformer and the manufacturing cost, which will make the transformer uncompetitive.

[0030] Compared to Figure 5 The winding arrangement of the existing high-voltage on-load tap-changing autotransformer shown is core-low voltage-medium voltage-high voltage, as follows: Figure 2 As shown, in this invention, the low-voltage winding 2 is moved from the position closest to the core 1 to the outermost position, that is, the winding arrangement becomes: core-medium voltage-high voltage-adjusting voltage-low voltage. The reason for this arrangement is as follows:

[0031] Figure 6 The diagram shows the leakage flux distribution of an existing high-voltage on-load tap-changing autotransformer during medium- to low-voltage operation, simulated using ANDERSEN software. Solid lines represent the operating windings, and dashed lines represent the non-operating windings. The diagram shows that the leakage flux is mainly distributed in the medium- and low-voltage windings, as well as in the main channel between the medium and low voltage sections. According to the current law, the magnetomotive force is distributed in a trapezoidal pattern along the winding radial direction. Since the magnetic reluctance is constant, the leakage flux density distribution is also trapezoidal. Figure 5 The third leakage magnetic area 20 is shown in the figure.

[0032] Figure 7The diagram shows the leakage flux distribution of an existing high-voltage on-load tap-changing autotransformer during high-voltage-to-low-voltage operation, simulated using ANDERSEN software. The diagram shows that the leakage flux is mainly distributed in the high-voltage, medium-voltage, low-voltage, and tap-changing windings, as well as in the main open channels between these windings. Furthermore, since the transformer's tap-changing range is off-center, the tap-changing winding also participates in operation during all rated taps. The equivalent leakage flux area during high-voltage-to-low-voltage operation is shown below. Figure 5 The fourth leakage magnetic area 21 is shown in the figure.

[0033] And such Figure 2 As shown, in one embodiment of this utility model, the winding arrangement is core-medium voltage-high voltage-regulating voltage-low voltage, and the reactance height of the low voltage winding 5 is 24% of the reactance height L of the high voltage winding 3 and the medium voltage winding 2 (that is, H is 38% of L). Figure 3 The diagram shows the leakage flux distribution during medium-voltage-low-voltage operation simulated using ANDERSON software in this embodiment. Solid lines represent windings involved in operation, and dashed lines represent windings not involved in operation. It can be seen from the diagram that the leakage flux is mainly distributed in the medium-voltage, low-voltage windings, the main open channel between medium-voltage and low-voltage, the high-voltage winding, and the voltage regulating winding. The equivalent leakage flux area during medium-voltage-low-voltage operation is shown below. Figure 2 The first leakage magnetic area is shown in Figure 18. Figure 4 The diagram shown illustrates the leakage flux distribution during high-voltage-low-voltage operation as simulated using ANDERSON software in this embodiment. It can be seen that the leakage flux is mainly distributed in the high-voltage, medium-voltage, and low-voltage windings, the voltage regulating winding, and the main channels between these windings. The equivalent leakage flux area during high-voltage-low-voltage operation is shown below. Figure 2 The second leakage magnetic area is shown in Figure 19.

[0034] Depend on Figure 2 and Figure 5 The comparison shows that after the winding arrangement of this utility model is changed to core-medium voltage-high voltage-voltage regulation-low voltage, its leakage magnetic area is significantly larger than that of the existing transformer winding arrangement. Therefore, this utility model selects the above arrangement.

[0035] However, after determining the above winding arrangement, another problem still exists in this invention: the above empirical formula (1) for impedance calculation is only applicable to transformers with concentric windings of equal height, and all methods to increase impedance are based on the axial leakage flux direction. In addition to axial leakage flux, there is also transverse leakage flux inside the transformer. For transformers with very small low-voltage winding capacity like this invention, the transverse leakage flux caused by the ampere-turn imbalance in the medium-low voltage and high-voltage-low voltage states will not cause significant increase in losses or overheating of structural components. Impedance can be increased from the direction of transverse leakage flux. However, when the ampere-turn distribution between windings is unbalanced, the transverse leakage flux will also increase sharply. Therefore, the above empirical formula (1) for impedance calculation is no longer applicable. Therefore, this invention needs to use software and the finite element method of winding leakage magnetic field to calculate the vector magnetic potential and magnetic flux density of each unit, and then further apply the energy method to calculate the per-unit value of short-circuit leakage reactance, and then calculate the impedance.

[0036] In this embodiment, the low-voltage side short-circuit current is required to be ≤25kA. Calculations show that the minimum impedance of the transformer in both the medium-low and high-low states must be ≥84% (500MVA). This calculation is well-known in the art. This invention calculates the impedance under two winding arrangements using ANDERSEN software, CUR software, and impedance calculation formulas. The comparison results are shown in Table 1 below. The conventional structure refers to the existing transformer winding arrangement, while the improved structure is the winding arrangement of this invention.

[0037]

[0038] Table 1

[0039] As shown in Table 1 above, when operating in the high-medium voltage state, the winding reactance heights are the same, and the impedance values ​​calculated by the three methods for the conventional and improved structures are similar. However, when operating in the medium-low and high-low voltage states, the impedance calculation formula does not consider the lateral leakage flux caused by the difference in winding reactance height, resulting in a larger deviation in the calculated impedance values. This also proves that the empirical impedance calculation formula (1) is only applicable to transformers with equal winding heights. The impedance calculated by ANDERSEN and CUR software through finite element analysis is closer to the measured values. In addition, as shown in the table above, under the medium-low voltage and high-low voltage operating conditions, the impedances of both the conventional and improved structures meet the requirements, but the impedance improvement under the improved structure is more significant. This not only achieves the purpose of limiting the short-circuit current on the low-voltage side but also better improves the short-circuit withstand capability of the low-voltage winding. The ANDERSEN and CUR software mentioned above are well-known technologies in this field and are commercially available software.

[0040] Furthermore, it can be seen from the magnetic leakage diagram that the direction of the transverse magnetic leakage is perpendicular to the tank wall 17. This invention has also performed relevant calculations on the magnetic field and structural components such as the tank. Since the current of the low-voltage winding is small, the transverse magnetic leakage generated is relatively controllable. Through calculation, it can be seen that if magnetic shielding is installed on the tank, the overheating of the tank can be avoided.

[0041] like Figure 2 As shown, the height of both the medium-voltage winding 2 and the high-voltage winding 3 in this utility model is L. The distance between the two ends of the low-voltage winding 5 and the corresponding ends of the high-voltage winding 3 is H. H is equivalent to 20% to 40% of L. This range value is obtained by repeated calculations using the ANDERSEN or CUR software mentioned above to ensure that the impedance meets the project requirements.

[0042] The comparison of the no-load loss, material usage, and dimensions of the improved structure of this utility model and the conventional structure of existing transformers is shown in Table 2 below:

[0043]

[0044] Table 2

[0045] As shown in Table 2 above, this invention significantly improves the impedance under medium-low and high-low load conditions by improving the winding arrangement of the transformer body, while maintaining the short-circuit withstand performance of the low-voltage winding while increasing its electrical density. Furthermore, with the improved transformer body structure, the medium-voltage and high-voltage windings are closer to the core, and the winding conductor length is shortened. Given a fixed high-medium load loss, the electrical density of the high-voltage and medium-voltage windings can be further improved. The table also shows that with the improved transformer body structure, the amount of copper wire, silicon steel sheets, insulating oil, and other materials used in the transformer, as well as the transformer's transport weight and total weight, are significantly reduced, greatly lowering the manufacturing and transportation costs of the transformer and enhancing its market competitiveness.

[0046] like Figure 1 As shown, each winding of this invention has a pressure plate 6 at its upper and lower ends to clamp and fix the windings. The outermost low-voltage winding 5 has an upper coil end ring 1301 at its upper end and a lower coil end ring 1302 at its lower end. An upper insulating end ring 701 is located on the upper side of the upper coil end ring 1301, and an insulating cylinder 12 is located on the upper side of the upper insulating end ring 701. Multiple lower insulating end rings 702 are stacked sequentially along the height direction on the lower side of the lower coil end ring 1302. This invention ensures... Figure 2 The height of H shown meets the requirements, thus ensuring that the height of the low-voltage winding 5 meets the requirements. The coil end ring, insulating cylinder, and insulating end ring are all technologies known in the art.

[0047] like Figure 1As shown, in this embodiment, the innermost medium-voltage winding 2 is provided with an electrostatic plate 8 and a corner ring 9. The electrostatic plate 8 and the corner ring 9 are both technologies known in the art.

[0048] like Figure 1 As shown, in this embodiment, an insulating plate 10 and a support bar 11 are provided between the medium-voltage winding 2 and the high-voltage winding 3, which are of the same height, to achieve separation. The insulating plate 10 and the support bar 11 are both technologies known in the art.

[0049] like Figure 1 As shown, in this embodiment, a yoke pad 14 is provided below the lower pressure plate 6, and a yoke insulation 15 is provided between the lower pressure plate 6 and the yoke pad 14.

[0050] like Figure 1 As shown, the outer side of this utility model is surrounded by a screen 16.

[0051] The design method of this utility model includes the following steps:

[0052] Step 1: Determine the adjustment parameters based on the following empirical formula (1) for transformer impedance:

[0053] Uk =49.6×f×IW×∑D×ρ / (et× Hk ×107) (1);

[0054] In equation (1) above, Uk is the percentage of impedance voltage; f is the rated frequency; IW is the rated ampere-turns; ∑D is the equivalent leakage magnetic area; ρ is the Rockwell coefficient; et is the turn potential; and Hk is the average reactance height of the winding.

[0055] Based on the above formula (1), adjust ∑D and Hk to change the short-circuit impedance.

[0056] Step Two: Further determine the adjustment parameters based on the transformer impedance requirements, specifically:

[0057] If there are requirements for the high-voltage to medium-voltage impedance, and if we want to increase the impedance of medium-voltage to low-voltage and high-voltage to low-voltage, we can only increase the equivalent leakage magnetic area ∑D in the medium-voltage to low-voltage and high-voltage to low-voltage states and decrease the average reactance height Hk. However, there is a minimum requirement for the winding reactance height. Therefore, when the average reactance height Hk reaches the minimum value, we can only increase the adjustment leakage magnetic area ∑D.

[0058] Step 3: By simulating the leakage magnetic area of ​​the transformer during medium-low voltage operation and high-low voltage operation using software, the coil winding arrangement and the distance H range between the two ends of the low-voltage winding 5 and the corresponding ends of the high-voltage winding 3 are determined. The winding arrangement becomes: core-medium voltage-high voltage-voltage regulation-low voltage, and H is equivalent to 20% to 40% of L.

[0059] like Figure 2 and Figure 5 As shown, this step can increase the leakage magnetic area by changing the winding arrangement.

[0060] Step 4: Verify by calculating the impedance using software.

[0061] In this step, due to the significant reduction in the height of the low-voltage winding 5, the ampere-turn distribution between windings becomes unbalanced, and the transverse leakage flux increases sharply. The above-mentioned empirical impedance calculation formula (1) is no longer applicable. As shown in Table 1 above, this utility model calculates the impedance under two winding arrangements using ANDERSEN software, CUR software, and impedance calculation formula respectively. While verifying that formula (1) is no longer applicable, it also verifies that the structural change of this utility model can meet the requirements.

[0062] The improved transformer body structure of this utility model has been tested and verified in the field in projects such as the Saudi Electricity Company's Riyadh Arid Station Project, Riyadh Nazim Station Project, Dammam Thuqbah Station Project, and Dammam Rames Station Project, and can meet the special requirements of foreign customers for transformer equipment.

Claims

1. A 380 kV high impedance high voltage on-load tap changer autotransformer, characterized in that: The transformer comprises a core (1), a medium-voltage winding (2), a high-voltage winding (3), a voltage-regulating winding (4) and a low-voltage winding (5) which are sequentially arranged on the core (1) from inside to outside, wherein the medium-voltage winding (2) and the high-voltage winding (3) have a height L, the distance between the low-voltage winding (5) and the corresponding end of the high-voltage winding (3) is H, and H is equivalent to 20-40% of L, and the height of the voltage-regulating winding (4) is less than L.

2. The 380 kV high impedance on-load tap changing autotransformer according to claim 1, characterized in that: The outermost low-voltage winding (5) is provided with an upper coil end ring (1301) at the upper end and a lower coil end ring (1302) at the lower end, the upper coil end ring (1301) is provided with an upper insulating end ring (701) on the upper side, the upper insulating end ring (701) is provided with an insulating cylinder (12) on the upper side, and the lower coil end ring (1302) is provided with a plurality of lower insulating end rings (702) which are sequentially stacked along the height direction on the lower side.

3. The 380 kV high impedance on-load tap changing autotransformer according to claim 1, characterized in that: The innermost medium-voltage winding (2) is provided with an electrostatic plate (8) and an angle ring (9) at the end.

4. The 380 kV high impedance on-load tap changing autotransformer according to claim 1, characterized in that: The medium-voltage winding (2) and the high-voltage winding (3) are provided with an insulating plate (10) and a support strip (11) therebetween.

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