High-capacity on-load voltage regulating transformer

Abstract

The invention discloses a high-capacity on-load tap-changing transformer which comprises a body oil tank, a capsule type oil conservator is installed on the upper portion of one end of the body oil tank, an on-load tap-changing switch is installed at the other end of the body oil tank, and radiators are installed outside the two opposite sides of the body oil tank. A transformer body in the body oil tank is composed of windings and an iron core, the windings comprise a low-voltage winding, a high-voltage winding, a coarse voltage regulation winding and a fine voltage regulation winding which are sequentially arranged from inside to outside, and the high-voltage winding, the coarse voltage regulation winding and the fine voltage regulation winding are connected with the on-load tap-changer through leads. By adopting a coarse and fine voltage regulation structure, the coarse voltage regulation winding and the fine voltage regulation winding can be completely thrown away when the transformer operates at the most negative tap, so that stray loss caused by magnetic leakage can be effectively reduced, resistance loss caused by self resistance of the voltage regulation windings is reduced, and economical efficiency and reliability of operation of the transformer are greatly improved.

Description

Technical Field

[0001] The invention relates to the technical field of power transformers, in particular to a large-capacity on-load voltage-regulating transformer. Background Art

[0002] On-load tap-changing transformer plays an important role in the power system. It not only stabilizes the voltage at the load center, but is also an indispensable and important equipment for connecting the power grid, adjusting load current and improving reactive power distribution.

[0003] The basic methods of on-load voltage regulation are mainly linear voltage regulation, coarse and fine voltage regulation and positive-negative voltage regulation. Among them, linear voltage regulation is currently mostly used in off-excitation voltage regulation transformers, and on-load voltage regulation is rarely used. As far as the current operation status of my country's power system is concerned, due to the high stability of my country's power grid and the small voltage fluctuation, considering the economic performance of the product, most of the on-load voltage regulation transformers used in the market use the positive and negative voltage regulation method, which has a relatively simple structure and is currently a commonly used on-load voltage regulation method. Compared with the positive and negative voltage regulation method, the coarse and fine voltage regulation method has a higher transformer cost and is a rarely used voltage regulation method.

[0004] Transformers are large-scale equipment in the power system. They are customized products, just like tailoring clothes. Their design calculations must be analyzed based on the operating status of the transformer and the power grid, and a more appropriate design calculation scheme must be selected. For some countries with relatively backward economic development or vigorously developing the power industry, most of the power grids are currently in a biased negative tap operation for forward-looking considerations. Different targeted designs must be adopted for such situations.

[0005] For transformers that are in negative tap operation for a long time, although the positive and negative voltage regulation structure is relatively simple and the cost is relatively low, for long-term negative tap operation, the voltage regulating coil is always connected in reverse series, and the resulting stray losses caused by voltage regulating resistance and leakage magnetic field are high, which is not conducive to the economic operation of the transformer system. Summary of the invention

[0006] To solve the above problems, the present invention provides a large-capacity on-load voltage-regulating transformer with a reasonable structure, which can effectively reduce the stray loss caused by leakage magnetic flux, and at the same time reduce the resistance loss caused by the resistance of the voltage-regulating winding itself, thereby greatly improving the economy and reliability of the transformer operation.

[0007] The technical solution adopted by the present invention is as follows:

[0008] A large-capacity on-load voltage-regulating transformer comprises a main body oil tank, a capsule-type oil storage cabinet is installed on the upper part of one end of the main body oil tank, an on-load tap changer is installed at the other end of the main body oil tank, and radiators are installed on the opposite sides of the main body oil tank; the internal body of the main body oil tank is composed of windings and iron cores, and the windings include low-voltage windings, high-voltage windings, coarse voltage-regulating windings, and fine voltage-regulating windings arranged in sequence from the inside to the outside, and the high-voltage windings, coarse voltage-regulating windings, and fine voltage-regulating windings are connected to the on-load tap changer by using leads.

[0009] As a further improvement of the above technical solution:

[0010] The head end of the coarse voltage regulating winding is connected to the high-voltage winding, the tail end of the coarse voltage regulating winding is respectively connected to the K terminal and the positive terminal of the on-load tap changer, and the head end of the coarse voltage regulating winding is connected to the negative terminal of the on-load tap changer; the switch terminal of the on-load tap changer is connected to the terminal at the end of the fine voltage regulating winding, and the connection or disconnection switching between the high-voltage winding and the coarse voltage regulating winding is performed by connecting the switch terminal to the positive terminal or the negative terminal.

[0011] The fine voltage regulating winding adopts a linear structure, and the outlet of the fine voltage regulating winding tapped according to the voltage ratio is connected one by one to multiple terminals of the on-load tap changer, and the connection or disconnection of the fine voltage regulating winding is adjusted by sliding the sliding contact on the on-load tap changer.

[0012] The fine voltage regulating winding adopts radial outlets, and the high voltage winding, the low voltage winding and the coarse voltage regulating winding adopt axial outlets.

[0013] An electrostatic plate is placed in the 220kV high-voltage area at the upper end of the high-voltage winding. The electrostatic plate has rounded corners, and the size of the rounded corners is consistent with the angle of divergence of the electromagnetic wires at the end; two formed angle rings 1 are placed on the inner and outer diameter sides above the electrostatic plate, and the rounded corners of the formed angle ring 1 are consistent with the angle of divergence of the electromagnetic wires at the end; adjacent formed angle rings 1 and formed angle ring 1 and the electrostatic plate are separated by oil gap gaskets; a formed angle ring 2 is placed on the inner diameter of the lower end of the high-voltage winding.

[0014] The upper end of the high-voltage winding is covered with two layers of insulating molded parts on one side, and three layers of paperboard are further covered on the outer side of the insulating molded parts.

[0015] The iron core adopts a three-phase five-column structure, including three main columns in the middle and side columns on both sides, and the side columns on both sides are D-shaped structures arranged facing each other; an oil channel is opened in the iron core; the upper iron yoke and the lower iron yoke located at both ends of the iron core adopt a T-shaped structure arranged back to back, and lung-shaped magnetic shields are installed in the upper iron yoke and the lower iron yoke.

[0016] The current of the on-load tap changer is selected to be 1.2 times the rated current of the high-voltage winding, and three on-load tap changers are selected to form three phases.

[0017] The radiators are arranged in order and divided into groups, and the oil inlet and outlet of a single group of radiators are installed with butterfly valves; a fan for blowing air upwards is installed under the radiator.

[0018] Ladders are respectively arranged on the side of the main body oil tank and the side of the oil storage cabinet.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] By adopting a coarse and fine voltage regulating structure, the present invention can completely discard the coarse voltage regulating winding and the fine voltage regulating winding when the transformer is operating at the most negative tap, thereby effectively reducing the stray loss caused by leakage magnetic flux, and at the same time reducing the resistance loss caused by the voltage regulating winding's own resistance, thereby greatly improving the economy and reliability of the transformer operation.

[0021] The present invention also includes the following advantages:

[0022] The capacity of the large-capacity on-load tap-changing transformer reaches 525,000 kVA, the voltage ratio reaches 232±10×1.25% / 21 kV, and the short-circuit impedance is 28%. At the same time, corresponding settings are made according to the high leakage magnetic characteristics brought by the large capacity to reduce the diffusion of leakage magnetic, reduce stray losses, and avoid local overheating. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is the front view of the present invention.

[0024] Figure 2 for Figure 1 Left view of .

[0025] Figure 3 for Figure 1 Top view of the .

[0026] Figure 4 It is a wiring diagram of the low voltage winding of the present invention.

[0027] Figure 5 This is a wiring diagram of the high voltage winding and the voltage regulating winding of the present invention.

[0028] Figure 6 Schematic diagram of the arrangement of the windings of the present invention.

[0029] Figure 7 It is a side view of the upper iron yoke and the lower iron yoke of the present invention.

[0030] Figure 8 It is a schematic structural diagram of the iron core of the present invention.

[0031] Among them: 1. Main body oil tank; 2. High-voltage neutral point bushing; 3. High-voltage bushing; 4. Low-voltage bushing; 5. Oil storage cabinet; 6. Radiator; 7. On-load tap changer; 8. Coarse voltage regulating winding; 9. Fine voltage regulating winding;

[0032] 10. Ladder; 11. Upper fuel tank; 12. Lower fuel tank; 13. Upper iron yoke; 14. Lung-shaped magnetic shield; 15. Upper clamp; 16. Lower iron yoke; 17. Lower clamp; 18. Side column;

[0033] 30. High-voltage booster seat; 31. High-voltage winding; 32. Electrostatic plate; 33. Forming angle ring 1; 34. Insulation forming part; 35. Paperboard; 36. Forming angle ring 2;

[0034] 40. Low voltage booster; 41. Low voltage winding;

[0035] 60. Fan. DETAILED DESCRIPTION

[0036] The specific implementation of the present invention will be described below in conjunction with the accompanying drawings.

[0037] like Figure 1 , Figure 2 and Figure 3 As shown, a large-capacity on-load voltage-regulating transformer of the present embodiment comprises a main body oil tank 1, a capsule-type oil storage cabinet 5 is installed on the upper part of one end of the main body oil tank 1, an on-load tap changer 7 is installed at the other end of the main body oil tank 1, and a radiator 6 is installed on the opposite sides of the main body oil tank 1; the internal body of the main body oil tank 1 is composed of windings and iron cores, and the windings comprise a low-voltage winding 41, a high-voltage winding 31, a coarse voltage-regulating winding 8, and a fine voltage-regulating winding 9 which are arranged in sequence from the inside to the outside, and the high-voltage winding 31, the coarse voltage-regulating winding 8, and the fine voltage-regulating winding 9 are connected to the on-load tap changer 7 by using leads.

[0038] In this embodiment, by adopting a coarse and fine voltage regulating structure, the coarse voltage regulating winding 8 and the fine voltage regulating winding 9 can be completely discarded when the transformer is operating at the most negative tap, thereby effectively reducing the stray loss caused by leakage magnetic flux and reducing the resistance loss caused by the voltage regulating winding's own resistance.

[0039] like Figure 5 As shown, the head end of the coarse voltage regulating winding 8 is connected to the high voltage winding 31, and the tail ends of the coarse voltage regulating winding 8 are respectively connected to the K terminal and the positive terminal (+) of the on-load tap changer 7, and the head end of the coarse voltage regulating winding 8 is connected to the negative terminal (-) of the on-load tap changer 7; the switch terminal (O) of the on-load tap changer 7 is connected to the terminal at the end of the fine voltage regulating winding 9, and the connection or disconnection switching between the high voltage winding 31 and the coarse voltage regulating winding 8 is performed by connecting the switch terminal (O) to the positive terminal (+) or the negative terminal (-).

[0040] In this embodiment, the number of turns of the high-voltage winding 31 is the total number of turns of the high-voltage most negative tap, the number of turns of the coarse voltage regulating winding 8 is the same as the total number of turns of the fine voltage regulating winding 9, and the three windings are connected to each other through the on-load tap changer 7 using leads.

[0041] The fine voltage regulating winding 9 adopts a linear structure, and the outlet of the fine voltage regulating winding 9 tapped according to the voltage ratio is connected one by one to multiple terminals of the on-load tap changer 7. The connection or disconnection of the fine voltage regulating winding 9 is adjusted by sliding the sliding contact on the on-load tap changer 7.

[0042] In one embodiment, the fine voltage regulating winding 9 is provided with ten taps according to the voltage ratio, and eleven outlets are led out, and the eleven outlets are respectively connected to the (1)-(11) terminals of the on-load tap changer 7; the switch terminal is always connected to the terminal (11); when the sliding contact slides to the terminal (11), the fine voltage regulating winding 9 is completely disconnected, and when the sliding contact slides to the terminal (1), the fine voltage regulating winding 9 is completely connected.

[0043] In this embodiment, the connection of the low voltage winding 41 adopts YNd1, such as Figure 4 shown.

[0044] In this embodiment, the high voltage winding 31 adopts an inner-screen continuous winding structure, and the low voltage winding 41, the coarse voltage regulating winding 8, and the fine voltage regulating winding 9 all adopt a spiral winding structure.

[0045] The fine voltage regulating winding 9 adopts radial outlets, and the high voltage winding 31, the low voltage winding 41 and the coarse voltage regulating winding 8 adopt axial outlets.

[0046] like Figure 6 As shown, an electrostatic plate 32 is placed in the 220kV high voltage area at the upper end of the high-voltage winding 31. The electrostatic plate 32 has rounded corners, and the size of the rounded corners is basically consistent with the angle of divergence of the end electromagnetic wires to avoid electric field concentration, improve the end electric field, and enhance insulation performance.

[0047] Two formed angle rings 33 are placed on the inner and outer diameter sides above the electrostatic plate 32. The rounded corners of the formed angle rings 33 are basically consistent with the divergence angle of the end electromagnetic wires to improve the high-voltage field strength at the end and at the same time cut off the discharge channel between high and low voltages, playing a good insulating role.

[0048] In this embodiment, the formed corner ring 33 is formed by extrusion of pulp with excellent insulating properties in a specially designed mold.

[0049] Adjacent formed angle rings 33 and formed angle rings 33 and electrostatic plates 32 are separated by oil gap pads; while ensuring insulation, the heat generated during the operation of the winding is brought out through the thermal convection performance of the oil, thereby playing a heat dissipation role.

[0050] In this embodiment, the oil gap pad between the electrostatic plate 32 and the formed angle ring 33 is stacked with paper tape and pasted on the electrostatic plate 32. The oil gap pad is also made into a rounded corner form on the inner and outer diameter sides to improve the end field strength and improve the insulation performance.

[0051] A molded angle ring 36 is placed on the inner diameter of the lower end of the high-voltage winding 31 to improve the electric field in the lower part between the high and low voltages and improve the insulation performance.

[0052] The potential of the lower end of the high-voltage winding 31 is equal to that of the coarse voltage regulating winding 8, so there is no need to add protective measures such as a formed angle ring between the lower ends of the high-voltage winding 31 and the coarse voltage regulating winding 8.

[0053] The upper end of the high-voltage winding 31 is covered with two layers of insulating molded parts 34 on one side, and three layers of paperboard 35 are further covered on the outer side of the insulating molded parts 34 .

[0054] In actual operation, considering the high voltage (i.e. 220 kV) at the upper end of the high-voltage winding 31 , 10 mm insulation is firstly wrapped on one side, and then the insulating molded part 34 and the paperboard 35 are wrapped.

[0055] In this embodiment, the insulating molded parts 34 and the paperboard 35 are separated by stays or corrugated paperboards to leave oil gaps and improve the insulation performance. The head molded parts are made from the coil head to provide comprehensive protection.

[0056] like Figure 7 As shown, the upper iron yoke 13 and the lower iron yoke 16 located at the two ends of the iron core adopt a T-shaped structure arranged back to back, and lung-shaped magnetic shields 14 are installed in the upper iron yoke 13 and the lower iron yoke 16.

[0057] In this embodiment, the low-voltage current reaches 14434A. In order to reduce the loss caused by the high current of the product, lung-shaped magnetic shields 14 of the device body are placed above and below the coil to effectively introduce the coil leakage magnetic field into the iron core and reduce the leakage magnetic field entering the steel parts to cause local overheating.

[0058] In this embodiment, by providing an upper iron yoke 13 and a lower iron yoke 16 of a T-shaped structure arranged back to back, the leakage magnetic field attracted by the lung-shaped magnetic shielding 14 of the upper and lower body can be conveniently introduced into the iron yoke at the T-shaped notch; in addition, the cross-sectional area of ​​the upper and lower iron yokes is appropriately enlarged to reduce the magnetic density of the iron yoke and ensure that there is no local overheating in the magnetic path of the magnetic shielding of the body.

[0059] At the same time, a tank magnetic shield is welded on the inner side of the tank wall of the main body tank 1 to prevent the tank from overheating.

[0060] like Figure 8 As shown, the core adopts a three-phase five-column structure, including three main columns in the middle and side columns 18 on both sides. The side columns 18 on both sides are D-shaped structures arranged opposite to each other. An oil channel is opened in the core.

[0061] By adopting the D-shaped side column 18, compared with the conventional elliptical structure, the center distance with the main column is shortened, the weight of the silicon steel sheet is reduced, and the cost is reduced. According to calculations, the weight of the silicon steel sheet is reduced by about 500kg.

[0062] In this embodiment, the temperature rise inside the core is reduced by appropriately adding oil passages in the core.

[0063] In this embodiment, the iron limb plates extending from the upper clamp 15 and the lower clamp 17 are made of non-magnetic steel plates to avoid local overheating. The core plate is also made of non-magnetic steel plates because it is close to the low-voltage coil, and the magnetic isolation gap is increased to reduce the eddy current loss on the plate surface.

[0064] A high-voltage neutral point bushing 2, a high-voltage bushing 3, and a low-voltage bushing 4 are sequentially installed on the top surface of the main oil tank 1. The bushing current is selected to be greater than or equal to 1.2 times the rated current of the winding, and the bushings are all installed on corresponding elevated seats.

[0065] The current of the on-load tap changer 7 is selected to be 1.2 times the rated current of the high-voltage winding 31. Since the current is too large, three on-load tap changers 7 are selected to form three phases.

[0066] The current of the low-voltage bushing 4 reaches 20000A. Due to the large current, the leakage magnetic flux is also large. The low-voltage booster seat 40 located below the low-voltage bushing 4 is made of non-magnetic steel plate as a whole. A copper plate is also welded on the upper surface of the cover of the low-voltage booster seat 40 to block the leakage magnetic flux formed by the low-voltage current and prevent the low-voltage booster seat 40 from overheating.

[0067] In this embodiment, the connection between the low-pressure booster seat 40 and the flange uses non-magnetic stainless steel bolts to avoid overheating of the bolts.

[0068] The high-voltage bushing 3 adopts an oil-SF6 bushing, and the high-voltage bushing 3 is installed on a high-voltage riser 30. The lower part of the high-voltage bushing 3 is immersed in transformer oil, and the upper part of the high-voltage bushing 3 is in the SF6 gas of the GIS.

[0069] The radiators 6 are arranged in order and divided into groups. The oil inlet and outlet of each group of radiators 6 are installed with butterfly valves so that the radiators 6 can be disassembled and installed individually when oil leakage and other faults occur during years of operation. A fan 60 for blowing air upwards is installed under the radiator 6.

[0070] In one embodiment, the radiators 6 are installed in four groups and are arranged in order on two opposite sides of the main body oil tank 1 .

[0071] In this embodiment, the fan 60 blows air upwards, so that hot air flows upwards, thereby improving the heat dissipation efficiency.

[0072] In this embodiment, the fan power line is connected to the air cooling control cabinet, and the transformer temperature signal is connected to the air cooling control cabinet. The air cooling control cabinet controls the opening and closing of the fans 60 in groups according to the designed temperature information to reduce the fan energy consumption as much as possible. In practice, the air cooling control cabinet is installed separately on the ground.

[0073] A ladder 10 is provided on the side of the main body oil tank 1 and the side of the oil storage cabinet 5 respectively. The ladder 10 is installed at an angle to facilitate corresponding operations by personnel during installation and maintenance.

[0074] In this embodiment, the main oil tank 1 is composed of an upper oil tank 11 and a lower oil tank 12 connected by bolts; an oil filling valve and an oil drain valve are installed at the end of the lower oil tank 12.

[0075] The capacity of the large-capacity on-load tap-changing transformer in this embodiment reaches 525000 kVA, the voltage ratio reaches 232±10×1.25% / 21 kV, and the short-circuit impedance is 28%. At the same time, corresponding settings are made for the high leakage magnetic characteristics brought by the large capacity to reduce the diffusion of leakage magnetic, reduce stray losses, and avoid local overheating.

[0076] The working principle of the present invention is:

[0077] When the tap is at the most negative value, only the low voltage winding 41 and the high voltage winding 31 are in operation, that is, the switch terminal (O) of the on-load tap changer 7 is connected to the negative terminal (-), and the sliding contact is connected to the terminal (11), so that the coarse voltage regulating winding 8 and the fine voltage regulating winding 9 can be disconnected. At this time, the product has low magnetic leakage, small loss, and high operating economy.

[0078] Since the capacity of this 220kV product is 525000kVA, it is a typical large-capacity product. The result of large capacity is large leakage magnetic flux. Therefore, appropriately reducing leakage magnetic flux has a great effect on the economic efficiency of operation.

[0079] When the voltage can be stabilized at the rated tapping, it can be achieved by simply connecting the switch terminal (O) of the on-load tap changer 7 to the positive terminal (+) and hitting the sliding contact to the terminal (11).

[0080] If the voltage needs to be adjusted to a positive tap, the switch terminal (O) of the on-load tap changer 7 is connected to the positive terminal (+), and the sliding contact is hit to the corresponding terminal (one of 1-11). At this time, if the sliding contact is connected to the terminal (1), it is in the most positive tap, that is, +10 tap.

[0081] The present invention adopts a coarse and fine voltage regulation structure, thereby being able to effectively reduce stray losses caused by magnetic leakage, while reducing resistance losses caused by the resistance of the voltage regulation winding itself, thereby greatly improving the economy and reliability of transformer operation.

[0082] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0083] The above description is an explanation of the present invention, not a limitation of the present invention. The scope of the present invention is defined in the claims. Any form of modification may be made within the scope of protection of the present invention.

Claims

1. A large-capacity on-load voltage-changing transformer, comprising a main body oil tank (1), characterized in that: A capsule-type oil storage cabinet (5) is installed on the upper part of one end of the main body oil tank (1), an on-load tap changer (7) is installed at the other end of the main body oil tank (1), and radiators (6) are installed on the opposite sides of the main body oil tank (1). The internal body of the main body oil tank (1) is composed of windings and iron cores, and the windings include a low-voltage winding (41), a high-voltage winding (31), a coarse voltage regulating winding (8), and a fine voltage regulating winding (9) arranged in sequence from the inside to the outside, and the high-voltage winding (31), the coarse voltage regulating winding (8), and the fine voltage regulating winding (9) are connected to the on-load tap changer (7) by using lead wires.

2. A large-capacity on-load voltage-changing transformer as claimed in claim 1, characterized in that: The head end of the coarse voltage regulating winding (8) is connected to the high voltage winding (31), the tail end of the coarse voltage regulating winding (8) is respectively connected to the K terminal and the positive terminal of the on-load tap changer (7), and the head end of the coarse voltage regulating winding (8) is connected to the negative terminal of the on-load tap changer (7); the switch terminal of the on-load tap changer (7) is connected to the terminal at the end of the fine voltage regulating winding (9), and the high voltage winding (31) and the coarse voltage regulating winding (8) are connected or disconnected by connecting the switch terminal to the positive terminal or the negative terminal.

3. A large-capacity on-load voltage-changing transformer as claimed in claim 1, characterized in that: The fine voltage regulating winding (9) adopts a linear structure, and the outlet of the fine voltage regulating winding (9) tapped according to the voltage ratio is connected one by one to multiple terminals of the on-load tap changer (7), and the connection or disconnection of the fine voltage regulating winding (9) is adjusted by sliding the sliding contact on the on-load tap changer (7).

4. A large-capacity on-load voltage-changing transformer as claimed in claim 1, characterized in that: The fine voltage regulating winding (9) adopts radial outlets, while the high voltage winding (31), the low voltage winding (41) and the coarse voltage regulating winding (8) adopt axial outlets.

5. A large-capacity on-load voltage-changing transformer as claimed in claim 4, characterized in that: An electrostatic plate (32) is placed in the 220 kV high voltage area at the upper end of the high voltage winding (31), and the electrostatic plate (32) has rounded corners, the size of which is consistent with the angle at which the electromagnetic wires at the end diverge; two formed angle rings (33) are placed on the inner and outer diameter sides above the electrostatic plate (32), respectively, and the rounded corners of the formed angle rings (33) are consistent with the angle at which the electromagnetic wires at the end diverge; adjacent formed angle rings (33) and formed angle rings (33) and the electrostatic plate (32) are separated by oil gap gaskets; and a formed angle ring (36) is placed on the inner diameter of the lower end of the high voltage winding (31).

6. A large-capacity on-load voltage-changing transformer as claimed in claim 4, characterized in that: The upper end of the high-voltage winding (31) is covered on one side with two layers of insulating molded parts (34), and the outer side of the insulating molded parts (34) is further covered with three layers of paperboard (35).

7. A large-capacity on-load voltage-changing transformer as claimed in claim 1, characterized in that: The iron core adopts a three-phase five-column structure, including three main columns in the middle and side columns (18) on both sides, and the side columns (18) on both sides are D-shaped structures arranged opposite to each other; an oil channel is opened in the iron core; an upper iron yoke (13) and a lower iron yoke (16) located at both ends of the iron core adopt a T-shaped structure arranged opposite to each other, and a lung-shaped magnetic shield (14) is installed in the upper iron yoke (13) and the lower iron yoke (16).

8. A large-capacity on-load voltage-changing transformer as claimed in claim 1, characterized in that: The current of the on-load tap changer (7) is selected to be 1.2 times the rated current of the high-voltage winding (31), and three on-load tap changers (7) are selected to form three phases.

9. A large-capacity on-load voltage-changing transformer as claimed in claim 1, characterized in that: The radiators (6) are arranged in order and divided into groups, and the oil inlet and outlet of a single group of radiators (6) are installed with butterfly valves; and a fan (60) for blowing air upwards is installed below the radiator (6).

10. A large capacity on-load voltage-changing transformer as claimed in claim 1, characterized in that: Ladders (10) are respectively arranged on the side of the main body oil tank (1) and the side of the oil storage cabinet (5).

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