Anti-short-circuit three-winding transformer winding structure and design method

Abstract

The invention relates to an anti-short-circuit three-winding transformer winding structure and a design method. The anti-short-circuit three-winding transformer winding structure comprises an iron core, a medium-voltage winding, a high-voltage winding, a voltage regulating winding and a low-voltage winding, wherein voltage regulating outgoing lines at the upper end and the lower end of the voltage regulating winding adopt an axial outgoing line mode and are led out from the outer side of the end part of the low-voltage winding to be connected with the on-load voltage regulating switch. By changing the arrangement sequence of the windings, the purposes of ensuring high-voltage-low-voltage impedance and simultaneously improving medium-voltage-low-voltage impedance are achieved, the production cost of products is reduced, and the competitiveness of the products is improved.

Description

Technical Field

[0001] The invention relates to the field of transformers, in particular to a winding structure and a design method of a short-circuit resistant three-winding transformer. Background Art

[0002] Improving the short-circuit resistance of transformers is one of the key factors to ensure the reliable operation of power grids. Therefore, when designing transformers, short-circuit force calculations need to be performed on loaded windings to ensure that the transformer can withstand the short-circuit force assessment during operation. At present, in many exported three-winding high-voltage on-load tap-changing transformers, the capacity of the high-voltage and medium-voltage sides is the rated capacity, while the capacity of the low-voltage side is only 1 / 3 of the rated capacity or less. Users have clear requirements for the impedance of high-voltage-medium voltage, but no clear requirements for the impedance of high-voltage-low voltage and medium-voltage-low voltage. In this case, if the conventional winding arrangement is used, the impedance of the medium-voltage-low voltage winding is relatively small during operation, which will cause the short-circuit force of the low-voltage winding and the medium-voltage winding to fail to meet the requirements. Summary of the invention

[0003] The purpose of the present invention is to provide a short-circuit resistant three-winding transformer winding structure and design method, which achieves the purpose of ensuring high-voltage-low-voltage impedance while improving medium-voltage-low-voltage impedance by changing the arrangement order of each winding, and reduces product production costs and improves product competitiveness.

[0004] The objective of the present invention is achieved through the following technical solutions:

[0005] A short-circuit resistant three-winding transformer winding structure comprises an iron core and a medium voltage winding, a high voltage winding, a voltage regulating winding and a low voltage winding which are sequentially sleeved on the iron core from the inside to the position, wherein the voltage regulating outgoing wires at the upper and lower ends of the voltage regulating winding adopt an axial outgoing wire method and are led out from the outside of the low voltage winding end to be connected to an on-load voltage regulating switch.

[0006] A design method for a short-circuit resistant three-winding transformer winding structure comprises the following steps:

[0007] Step 1: Determine the method to improve the short-circuit resistance of the transformer in medium-low voltage operation, according to the transformer impedance calculation formula:

[0008] Uk=49.6×f×IW×∑D×ρ / (et×Hk×10 7 );

[0009] Among them, Uk is the impedance voltage percentage; f is the rated frequency; IW is the rated ampere-turn, 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 factor 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;

[0010] When Hk cannot be changed, the impedance between medium voltage and low voltage can be increased by adjusting the equivalent magnetic leakage area ∑D;

[0011] Step 2: Determine the arrangement of each winding, specifically: iron core-medium voltage winding-high voltage winding-voltage regulating winding-low voltage winding, where the voltage regulating winding is placed between the high voltage winding and the low voltage winding to increase the main distance between high voltage and low voltage, and at the same time the main distance between medium voltage and low voltage is also increased;

[0012] Step 3: Determine the voltage regulating winding outlet mode. The voltage regulating outlet adopts the axial outlet mode and is horizontally led out from the outside of the low-voltage winding end;

[0013] Step 4: Use software to simulate and verify the change of winding leakage magnetic area.

[0014] The advantages and positive effects of the present invention are:

[0015] 1. The present invention changes the arrangement of each winding into: iron core-medium voltage winding-high voltage winding-voltage regulating winding-low voltage winding, wherein the voltage regulating winding is placed between the high voltage winding and the low voltage winding to increase the main distance between the high voltage and the low voltage, thereby ensuring the equivalent magnetic leakage area between the high voltage and the low voltage, and further ensuring the impedance between the high voltage and the low voltage. At the same time, the main distance between the medium voltage and the low voltage is also increased, thereby increasing the equivalent magnetic leakage area between the medium voltage and the low voltage, and further improving the impedance between the medium voltage and the low voltage. Figure 5 and Figure 8 In comparison, the leakage magnetic area (trapezoidal C) of the present invention during medium voltage-low voltage operation is significantly larger than the leakage magnetic area under the conventional winding arrangement, while the leakage magnetic area (trapezoidal D) of the present invention during high voltage-low voltage operation does not change much compared with the leakage magnetic area under the conventional winding arrangement. Therefore, the present invention can simultaneously meet the short-circuit requirements of the transformer high voltage-low voltage and medium voltage-low voltage operation.

[0016] 2. The present invention eliminates the need for current limiting reactors and other structures, and under the premise of satisfying load loss, the present invention reduces the volume of the oil tank and the amount of various materials used, thereby reducing the manufacturing cost and making the product more competitive. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The following is a schematic diagram of the winding arrangement and terminal position of the low-voltage winding of the three-winding high-voltage on-load voltage-regulating transformer in the prior art,

[0018] Figure 2 The following is a schematic diagram of the wiring principle of a three-winding high-voltage on-load voltage regulating transformer with a low-voltage winding connected in series with a current-limiting reactor in the prior art.

[0019] Figure 3 It is a top view of the structure arrangement of the low voltage winding of the three-winding high voltage on-load voltage regulating transformer in the prior art,

[0020] Figure 4 This is the wiring schematic diagram of a single-phase switch of a high-voltage on-load voltage-regulating transformer in the prior art.

[0021] Figure 5 It is a schematic diagram of magnetic leakage analysis of a three-winding high-voltage on-load tap-changing transformer in the prior art.

[0022] Figure 6 This is a schematic diagram of the magnetic leakage distribution of the three-winding high-voltage on-load tap-changing transformer in the prior art simulated by ANDERSEN software during medium-voltage-low-voltage operation with conventional winding arrangement.

[0023] Figure 7 This is a schematic diagram of the magnetic leakage distribution of the three-winding high-voltage on-load tap-changing transformer in the prior art simulated by ANDERSEN software under high-voltage-low-voltage operation with conventional winding arrangement.

[0024] Figure 8 The following is a schematic diagram of the winding arrangement and the position of the lead-out terminal and a schematic diagram of the magnetic leakage analysis of the present invention.

[0025] Fig. 9 It is a top view of the structure arrangement of the present invention.

[0026] Fig.10 This is a schematic diagram of the magnetic flux leakage distribution during medium-low voltage operation simulated by ANDERSEN software.

[0027] Fig.11 This is a schematic diagram of the magnetic leakage distribution when the ANDERSEN software simulates the high-voltage-low-voltage operation of the present invention.

[0028] Among them, 1 is the iron core, 2 is the low voltage winding, 3 is the medium voltage winding, 4 is the high voltage winding, 5 is the voltage regulating winding, 6 is the oil tank, 7 is the current limiting reactor, 8 is the on-load voltage regulating switch, and 9 is the voltage regulating output line. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with the accompanying drawings.

[0030] like Figures 1 to 5 As shown, the winding structure adopted by the oil-immersed transformer in the prior art is a core structure, and each winding is sequentially mounted on the core 1. Since the core 1 is in a grounded state during the operation and insulation test of the transformer, the three-winding high-voltage on-load tap-changing transformer in the prior art usually places the low-voltage winding 2 close to the core 1 when arranging the windings, and the low-voltage winding 2, the medium-voltage winding 3 and the high-voltage winding 4 are arranged from the inside to the outside, and considering that the on-load tap-changing transformer has many voltage regulating leads, such as Figure 4As shown in FIG. 1 , the high-voltage side ±8×1.25% on-load voltage-regulating transformer has 9 lead wires from the upper and lower ends of the voltage-regulating winding 5 to the on-load voltage-regulating switch 8. Considering the convenience of wiring the voltage-regulating winding 5 to the on-load voltage-regulating switch 8, the voltage-regulating winding 5 is usually placed on the outermost side in the prior art. Figures 1 to 5 As shown, the arrangement of the windings of the three-winding high-voltage on-load voltage-regulating transformer in the prior art is: iron core 1 - low-voltage winding 2 - medium-voltage winding 3 - high-voltage winding 4 - voltage-regulating winding 5.

[0031] The winding structure of the present invention is as follows Figures 8-9 As shown, from inside to outside, it is iron core 1-medium voltage winding 3-high voltage winding 4-voltage regulating winding 5-low voltage winding 2. The theoretical analysis of this structure is as follows:

[0032] Improving the short-circuit resistance of the transformer during medium-low voltage operation can be achieved by increasing the impedance of the medium-low voltage. Therefore, in the prior art, connecting a current-limiting reactor 7 in series with the low-voltage winding 2 is one of the methods for increasing the impedance. Figure 3 As shown, the transformer needs to increase the size of the oil tank 6 to place the current limiting reactor 7. The increase of materials such as the current limiting reactor 7, insulating oil and the steel plate of the oil tank 6 will greatly increase the manufacturing cost of the transformer. In addition, three current limiting reactors 7 need to be connected in series to each phase low-voltage winding 2 through leads, and its structure is relatively complicated. The specific wiring principle diagram is as follows Figure 2 As shown, this structure cannot be adopted by the present invention.

[0033] In addition, the short-circuit resistance of the transformer in medium-low voltage operation can be improved by theoretically reducing the electric density of the low-voltage winding 2 and increasing the medium-low voltage main distance to increase the medium-low voltage impedance. Taking the SFSZ-80000 / 220 transformer as an example, the specific parameters of the transformer are as follows:

[0034] Transformer voltage ratio: 220±8×1.25% / 23 / 13.8kV;

[0035] Transformer capacity: 80 / 80 / 26.67MVA;

[0036] Connectivity group: YNyn0d11;

[0037] Transformer insulation level: SI850LI1050AC460 (high voltage);

[0038] LI170AC70 (high voltage neutral point);

[0039] LI150AC50 (medium voltage);

[0040] LI150AC50 (medium voltage neutral point);

[0041] LI110AC34

[0042] Impedance: 12.5% ​​(high voltage-medium voltage), no requirement for high voltage-low voltage and medium voltage-low voltage impedance;

[0043] No-load loss: 40kW;

[0044] Load loss: 300kW (high voltage-medium voltage), no requirements for high voltage-low voltage and medium voltage-low voltage load loss;

[0045] Considering the voltage of each winding and the convenience of voltage regulation, if the conventional winding arrangement is adopted: core-low voltage-medium voltage-high voltage-voltage regulation, Figure 6 The leakage magnetic distribution of the above transformer simulated by ANDERSEN software under the conventional winding arrangement in medium voltage-low voltage operation can be known ( Figure 6 A refers to the winding involved in the operation, and B refers to the winding not involved in the operation). The leakage magnetic flux is mainly distributed in the medium voltage, low voltage winding and the main air path between the medium voltage and low voltage. According to the total current law, the magnetic motive force is distributed in a trapezoidal shape along the radial direction of the winding. Since the magnetic resistance is a constant, Figure 5 As shown in Figure 2, the distribution of leakage flux density is also trapezoidal, and Figure 7 The leakage magnetic distribution of the above transformer simulated by ANDERSEN software under the conventional winding arrangement during high-voltage-low-voltage operation can be known ( Figure 7 Similarly, A refers to the winding involved in the operation, and B refers to the winding not involved in the operation). At this time, the leakage magnetic field is mainly distributed in the high-voltage and low-voltage windings, as well as the main air path between high-voltage and low-voltage and the medium-voltage winding. Figure 6 The equivalent leakage magnetic area of ​​medium-low pressure operation is shown as Figure 5 As shown in trapezoid C, Figure 7 The equivalent leakage magnetic area of ​​high-pressure-low-pressure operation is shown as Figure 5 As shown by the trapezoid D in the figure. From the above analysis, it can be seen that if the low-voltage winding 2 is arranged close to the iron core 1, and the low-voltage-medium-voltage main distance is increased while the low-voltage winding 2 electric density is reduced, the wire cross-section needs to be increased to reduce the low-voltage winding 2 electric density, which will increase the diameter of the low-voltage winding 2. At the same time, increasing the low-voltage-medium-voltage main distance will cause the diameter of the coil sleeved on the outside of the low-voltage winding 2 to increase, and the amount of copper wire used will increase. Therefore, in addition to increasing the cost of the low-voltage winding 2, this method will also increase the cost of the medium-voltage winding 3 and the high-voltage winding 4 sleeved on the outside of the low-voltage winding 2, which will greatly increase the manufacturing cost of the transformer, and the present invention cannot be adopted.

[0046] In order to improve the short-circuit resistance of the transformer in medium-low voltage operation, the present invention finally improves the medium-low voltage impedance by adjusting the winding arrangement to meet the short-circuit force requirements, specifically:

[0047] According to the transformer impedance calculation formula:

[0048] Uk=49.6×f×IW×∑D×ρ / (et×Hk×10 7 );

[0049] Among them, Uk is the impedance voltage percentage; 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.

[0050] It can be seen from the above formula that the short-circuit impedance of the transformer is related to several parameters, and the short-circuit impedance is mainly changed by adjusting ∑D and Hk. In order to reduce the lateral leakage flux of the transformer, the reactance height Hk of the other windings of the transformer except the voltage regulating winding 5 is basically the same. Therefore, for the three-winding transformer, if there is a requirement for the high-voltage-medium-voltage impedance, if you want to increase the medium-voltage-low-voltage impedance, you can only adjust the equivalent leakage flux area ∑D.

[0051] Therefore, Figures 8-9 As shown, the present invention adjusts the low-voltage winding 2 from a position close to the core 1 to the outermost side. The improved winding arrangement of the present invention is: core 1-medium-voltage winding 3-high-voltage winding 4-voltage regulating winding 5-low-voltage winding 2. The voltage regulating winding 5 has many protruding leads, and considering the convenience of switch wiring, the voltage regulating winding 5 is placed between the high-voltage winding 4 and the low-voltage winding 2. This can also increase the main distance between high voltage and low voltage, ensure the equivalent leakage magnetic area of ​​high voltage and low voltage, and further ensure the impedance of high voltage and low voltage. At the same time, the main distance between medium voltage and low voltage is also increased, which increases the equivalent leakage magnetic area of ​​medium voltage and low voltage, and further improves the impedance of medium voltage and low voltage.

[0052] In addition, Figures 3-4 As shown, when the voltage regulating winding 5 in the prior art is located at the outermost side, it is convenient to lead out the voltage regulating winding 5, so it is usually directly connected to the on-load voltage regulating switch 8 in a radial leading way. The voltage regulating position of the high-voltage winding 4 is at the neutral point, so the insulation level of the voltage regulating winding 5 is considered according to the insulation level of the neutral point of the high-voltage winding 4, and the high-voltage neutral point insulation level of the above transformer listed in the present invention is LI170AC70. The voltage regulating winding 5 needs to consider an appropriate oscillation coefficient during the insulation test, so as Figures 8-9 As shown, when the low-voltage winding 2 of the present invention is mounted on the outside of the voltage regulating winding 5, the voltage regulating outlet line 9 is horizontally led out from the outside of the end of the low-voltage winding 2 in an axial outlet manner, and the insulation thickness of all lead-out ends is ensured according to insulation calculation, thereby ensuring the insulation distance and creepage distance of the voltage regulating outlet line 9 to the low-voltage winding 2 and surrounding structural parts, while meeting the wiring requirements of the on-load voltage regulating switch 8.

[0053] Fig.10This is a schematic diagram of the magnetic flux leakage distribution during medium-low voltage operation of the present invention simulated by ANDERSEN software ( Fig.10 A refers to the winding involved in the operation, and B refers to the winding not involved in the operation). Fig.10 It can be seen that the leakage magnetic flux is mainly distributed in the medium voltage, low voltage windings, the main air path between medium voltage and low voltage, the high voltage winding and the voltage regulating winding. Fig.11 This is a schematic diagram of the magnetic flux leakage distribution during high-voltage-low-voltage operation of the present invention simulated by ANDERSEN software ( Fig.11 A refers to the winding involved in the operation, and B refers to the winding not involved in the operation). Fig.11 It can be seen that the leakage magnetic flux is mainly distributed in the high-voltage and low-voltage windings, as well as the main air path and voltage regulating winding between high-voltage and low-voltage. Fig.10 The equivalent magnetic leakage area during the medium-low pressure operation of the present invention is as follows: Figure 8 As shown in trapezoid C, Fig.11 The equivalent magnetic leakage area during high-pressure-low-pressure operation of the present invention is as follows: Figure 8 As shown in the trapezoid D in Figure 5 and Figure 8 In comparison, the leakage magnetic area (trapezoidal C) of the present invention during medium voltage-low voltage operation is significantly larger than the leakage magnetic area under the conventional winding arrangement, while the leakage magnetic area (trapezoidal D) of the present invention during high voltage-low voltage operation does not change much compared with the leakage magnetic area under the conventional winding arrangement. Therefore, the medium voltage-low voltage impedance is greatly improved while the high voltage-low voltage impedance does not change much, which can simultaneously meet the short-circuit requirements of the transformer high voltage-low voltage and medium voltage-low voltage operation, producing unexpected technical effects.

[0054] Furthermore, the present invention only has requirements for the load loss under high-voltage-medium voltage operation. When the medium-voltage winding 3 and the high-voltage winding 4 are arranged close to the core 1, the size of the medium-voltage winding 3 and the high-voltage winding 4 is reduced, and the length of the copper wire of the medium-voltage winding 3 and the high-voltage winding 4 is shortened. Under the premise of meeting the load loss, the winding density can be improved, and the amount of copper wire can be reduced, saving costs. Taking the above-mentioned transformer as an example, the impedance, weight of each material and size comparison under the operating conditions of the existing conventional winding structure and the winding structure arrangement of the present invention are shown in Table 1 below:

[0055] Table 1

[0056]

[0057] The working principle of the present invention is:

[0058] like Figures 8-9As shown, the structure of the present invention includes an iron core 1 and a medium voltage winding 3, a high voltage winding 4, a voltage regulating winding 5 and a low voltage winding 2 which are sequentially sleeved on the iron core 1 from the inside to the position, wherein the voltage regulating outgoing wires 9 at the upper and lower ends of the voltage regulating winding 5 are led out from the outer side of the end of the low voltage winding 2 in an axial outgoing wire manner and are connected to the on-load voltage regulating switch 8.

[0059] The design method of the present invention comprises the following steps:

[0060] Step 1: Determine a method to improve the short-circuit resistance of the transformer in medium-low voltage operation, wherein the first method is to connect a current-limiting reactor 7 in series with the low-voltage winding 2 to increase the impedance, and the second method is to increase the medium-low voltage impedance by reducing the electric density of the low-voltage winding 2 and increasing the medium-low voltage main distance. Both methods will greatly increase the manufacturing cost of the transformer. Therefore, the present invention adopts the third method: according to the transformer impedance calculation formula: Uk = 49.6 × f × IW × ∑ D × ρ / (et × Hk × 10 7 ), when there is a requirement for high voltage-medium voltage impedance, the impedance of medium voltage-low voltage can be improved by adjusting the equivalent leakage magnetic area ∑D.

[0061] Step 2: Determine the arrangement of each winding, wherein the present invention adjusts the low-voltage winding 2 from the position close to the iron core 1 to the outermost side, and the improved winding arrangement is: iron core 1-medium voltage winding 3-high voltage winding 4-voltage regulating winding 5-low voltage winding 2, wherein the voltage regulating winding 5 is placed between the high voltage winding 4 and the low voltage winding 2 to increase the main distance between the high voltage and the low voltage, thereby ensuring the equivalent leakage magnetic area of ​​the high voltage and the low voltage, and further ensuring the impedance of the high voltage and the low voltage. At the same time, the main distance between the medium voltage and the low voltage is also increased, which increases the equivalent leakage magnetic area of ​​the medium voltage and the low voltage, and further improves the impedance of the medium voltage and the low voltage.

[0062] Step 3: Determine the outlet method of the voltage regulating winding 5. The voltage regulating outlet line 9 is horizontally led out from the outside of the end of the low-voltage winding 2 in an axial manner. All lead-out ends are insulated according to insulation calculations to ensure insulation thickness, ensure insulation distance and creepage distance of the voltage regulating outlet line 9 to the low-voltage winding 2 and surrounding structural parts, and meet the wiring requirements of the on-load voltage regulating switch 8.

[0063] Step 4: Use software to simulate and verify the change of winding leakage magnetic area, in which the existing conventional winding Figures 5 to 7 and the present invention Figure 8 and Figures 10-11 As shown in Table 1 above, the leakage magnetic area (trapezoidal C) of the present invention during medium voltage-low voltage operation is significantly larger than the leakage magnetic area under the conventional winding arrangement, while the leakage magnetic area (trapezoidal D) of the present invention during high voltage-low voltage operation does not change much compared with the leakage magnetic area under the conventional winding arrangement. Therefore, the medium voltage-low voltage impedance of the present invention is greatly improved while the high voltage-low voltage impedance does not change much, and can simultaneously meet the short-circuit requirements of the transformer high voltage-low voltage and medium voltage-low voltage operation.

[0064] The connection method between the windings of the present invention is the same as that of the prior art, but the present invention achieves the purpose of ensuring the high-voltage-low-voltage impedance and improving the medium-voltage-low-voltage impedance by simply changing the winding arrangement order, and saves the structure such as the current limiting inductor 7. At the same time, it can be seen from Table 1 above that, under the premise of meeting the load loss, the volume of the oil tank 6 and the amount of various materials used in the present invention are reduced, thereby reducing the manufacturing cost, producing unexpected technical effects, and making the product more competitive.

Claims

1. A short-circuit resistant three-winding transformer winding structure, characterized in that: The invention comprises an iron core (1) and a medium voltage winding (3), a high voltage winding (4), a voltage regulating winding (5) and a low voltage winding (2) which are sequentially sleeved on the iron core (1) from the inside to the inside, wherein the voltage regulating outlets (9) at the upper and lower ends of the voltage regulating winding (5) are axially led out from the outside of the end of the low voltage winding (2) and connected to an on-load voltage regulating switch (8).

2. A design method for the winding structure of a short-circuit resistant three-winding transformer according to claim 1, characterized in that: The steps include: Step 1: Determine the method to improve the short-circuit resistance of the transformer in medium-low voltage operation, according to the transformer impedance calculation formula: Uk=49.6×f×IW×∑D×ρ / (et×Hk×10 7 ); Among them, Uk is the impedance voltage percentage; f is the rated frequency; IW is the rated ampere-turn, 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 factor 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; When Hk cannot be changed, the impedance between medium voltage and low voltage can be increased by adjusting the equivalent magnetic leakage area ∑D; Step 2: Determine the arrangement of each winding, specifically: iron core (1) - medium voltage winding (3) - high voltage winding (4) - voltage regulating winding (5) - low voltage winding (2), wherein the voltage regulating winding (5) is placed between the high voltage winding (4) and the low voltage winding (2) to increase the main distance between the high voltage and the low voltage, and at the same time the main distance between the medium voltage and the low voltage is also increased; Step 3: Determine the outlet mode of the voltage regulating winding (5), and the voltage regulating outlet line (9) is horizontally led out from the outer side of the end of the low-voltage winding (2) in an axial outlet mode; Step 4: Use software to simulate and verify the change of winding leakage magnetic area.

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