Autotransformer with medium-voltage regulating coil located at high-voltage coil

Abstract

The invention discloses an autotransformer with a medium-voltage regulating coil located at a high-voltage coil, and belongs to the technical field of transformer manufacturing, the winding directions of a high-voltage coil upper half phase and a high-voltage coil lower half phase are opposite, and the head ends of the high-voltage coil upper half phase and the high-voltage coil lower half phase are connected in parallel and then are led out through a high-voltage outgoing line; the medium-voltage regulating coil is embedded in the high-voltage coil, the head ends of the upper half phase of the medium-voltage regulating coil and the lower half phase of the medium-voltage regulating coil are connected in parallel and are connected with the tail end of the high-voltage coil, and the tail ends of the upper half phase of the medium-voltage regulating coil and the lower half phase of the medium-voltage regulating coil are connected with the head end of the medium-voltage coil; the medium-voltage regulating coil is provided with a plurality of taps including a first-stage tap to a last-stage tap; the head end of the first-stage tap is connected with the tail end of the high-voltage coil, the tail end of the last-stage tap is connected with the head end of the medium-voltage coil, and a medium-voltage outgoing line is led out from each tap through a tap selector of the tap switch; a neutral point outgoing line is arranged at the tail end of the medium-voltage coil.

Description

Technical Field

[0001] The invention belongs to the technical field of transformer manufacturing, and in particular relates to an autotransformer in which a medium-voltage regulating coil is located at a high-voltage coil. Background Art

[0002] As modern power systems continue to develop towards larger capacity and higher voltage levels, more stringent requirements are being placed on the performance, efficiency, and economy of power equipment. Traditional two- or three-winding transformers face problems such as high equipment costs and large size when transmitting electrical energy, making it difficult to meet the growing power transmission needs of the power grid. The emergence of autotransformers is precisely to effectively solve these problems. With its unique electrical connection structure, it achieves direct electrical connection between the primary and secondary circuits, allowing not only magnetic coupling but also electrical connection between the windings. Compared with ordinary transformers of the same capacity, it significantly reduces the number of winding turns and the amount of copper used, thereby reducing size and manufacturing costs. At the same time, it improves energy transmission efficiency and increases the maximum capacity, showing strong economic benefits and application potential in power grid construction and transformation.

[0003] With the widespread adoption of ultra-high voltage (UHV) transmission technology, 500 kV power grids have become a critical hub for power transmission. Voltage stability plays a crucial role in the safe operation of the power grid and the quality of power. As a core substation equipment, the proper placement of the autotransformer's tap changer is crucial. Placing the tap changer on the medium-voltage side allows for flexible adjustment of the medium-voltage output voltage while maintaining a constant high-voltage voltage, meeting the differentiated voltage requirements of different load areas. This design approach stems from the power system's demand for refined voltage quality control and the medium-voltage side's special role as a key link in power distribution and voltage conversion within the power grid. 500 kV autotransformers used in power grids typically have the tap changer placed on the medium-voltage side to ensure a constant high-voltage voltage while allowing for adjustable output voltage. This necessitates the installation of a voltage-regulating winding at the head of the medium-voltage coil.

[0004] After comprehensively considering the cost, impedance change trend and other factors, the layout is generally as follows: iron core (low voltage coil) - medium voltage regulating coil - medium voltage coil (common coil) - high voltage coil (series coil), such as Figure 1 As shown. Since the medium-voltage regulating winding 400 is placed between the medium-voltage winding 300 and the core 501 or the low-voltage winding (if any), this arrangement optimizes material usage and reduces costs to a certain extent. However, while placing the medium-voltage regulating winding 400 between the medium-voltage winding 300 and the core 501 or the low-voltage winding meets the basic voltage regulation requirements, it also brings a series of technical challenges.

[0005] Since the voltage regulating winding is located in an internal area with high electric field strength, high-strength insulation materials and complex insulation structures must be used to ensure insulation reliability, resulting in high insulation requirements. At the same time, the internal layout requires the lead wires of the voltage regulating winding to pass through multiple layers of coils. In an environment with a small space and complex electric field, the insulation design and mechanical fixation of the lead wires are greatly increased.

[0006] Therefore, overcoming the complex lead-out problem of the autotransformer's voltage-regulating coil has become a core technical bottleneck restricting the performance improvement and structural optimization of the autotransformer. Finding an effective solution can not only optimize the structural design of the autotransformer and reduce operation and maintenance costs, but also further explore its application potential in power systems and meet the urgent requirements of modern power grids for high reliability, high economy, and intelligent operation and maintenance of equipment. To solve the above problems, a voltage-regulating design on the side pole came into being. By transferring the voltage-regulating winding to the side pole, this structure simplifies the lead-out design and reduces the complexity of internal insulation. However, since the side pole needs to be equipped with excitation and voltage-regulating coils, the overall volume and material cost of the transformer are increased, resulting in poor economic efficiency. Summary of the Invention

[0007] The purpose of the present invention is to overcome the problem of complex lead-out wires of an autotransformer coil, and proposes an autotransformer in which a medium-voltage regulating coil is located between a high-voltage coil.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions: In a first aspect, an autotransformer in which a medium voltage regulating coil is located above a high voltage coil comprises a high voltage coil, a medium voltage regulating coil, and a medium voltage coil; The high-voltage coil is composed of an upper half phase of the high-voltage coil and a lower half phase of the high-voltage coil. The winding directions of the upper half phase of the high-voltage coil and the lower half phase of the high-voltage coil are opposite, and the head ends of the upper half phase of the high-voltage coil and the lower half phase of the high-voltage coil are connected in parallel and then led out through a high-voltage lead wire; The medium voltage regulating coil is embedded in the high voltage coil, and includes an upper half phase of the medium voltage regulating coil and a lower half phase of the medium voltage regulating coil. The head ends of the upper half phase of the medium voltage regulating coil and the lower half phase of the medium voltage regulating coil are connected in parallel and connected to the end of the high voltage coil, and the ends of the upper half phase of the medium voltage regulating coil and the lower half phase of the medium voltage regulating coil are connected to the head end of the medium voltage coil. The medium voltage regulating coil is provided with a plurality of taps, including a first-stage tap to a last-stage tap; the first end of the first-stage tap is connected to the end of the high voltage coil, and the end of the last-stage tap is connected to the first end of the medium voltage coil, and each tap leads to a medium voltage lead wire through the tap selector of the tap changer; A neutral point lead wire is provided at the end of the medium voltage coil.

[0009] Furthermore, the upper half phase of the high-voltage coil is connected in series with the second part of the upper half phase of the high-voltage coil through an external lead, and the lower half phase of the high-voltage coil is connected in series with the second part of the lower half phase of the high-voltage coil through an external lead, and the two parts have symmetrical structures.

[0010] Furthermore, the tail ends of the second portion of the upper half phase of the high-voltage coil and the second portion of the lower half phase of the high-voltage coil are connected through external leads to form the end of the high-voltage coil.

[0011] Furthermore, the series connection point between the second portion of the upper half phase of the high-voltage coil and the second portion of the lower half phase of the high-voltage coil is located in the middle of the axial height of the high-voltage coil.

[0012] Furthermore, the upper half phase of the medium voltage regulating coil and the lower half phase of the medium voltage regulating coil are connected in parallel to form a multi-stage symmetrically distributed voltage regulating section.

[0013] Furthermore, each stage of the voltage regulation section corresponds to a tap.

[0014] Furthermore, the taps are evenly distributed along the axial direction of the medium voltage regulating coil and are connected to the moving contact of the tap changer via external leads.

[0015] Furthermore, the number of turns of each voltage regulating section of the medium voltage regulating coil is equal, and the voltage difference between adjacent taps is a fixed value.

[0016] Furthermore, the tap selector of the tap changer is located outside the high-voltage coil and is connected to the tap of the medium-voltage regulating coil through an insulating bushing.

[0017] In a second aspect, a method for regulating voltage of an autotransformer in which a medium voltage regulating coil is located within a high voltage coil comprises the following steps: Switch the tap changer to the target tap, so that the corresponding tap of the medium voltage regulating coil is connected to the medium voltage lead through the tap selector; By adjusting the number of connected sections of the medium voltage regulating coil and changing the turns ratio between the medium voltage coil and the high voltage coil, the output voltage on the medium voltage side is adjusted; The tap of the medium voltage regulating coil is embedded in the high voltage coil, and the head end is directly connected to the end of the high voltage coil, and the end is directly connected to the head end of the medium voltage coil.

[0018] Compared with the prior art, the present invention has the following beneficial technical effects: This invention proposes an autotransformer with a medium-voltage regulator coil located within the high-voltage coil. By embedding the medium-voltage regulator coil within the high-voltage coil, this reduces copper usage, simplifies the lead-out structure, and eases insulation design. The ends of the high-voltage coil and the medium-voltage regulator coil form a single unit, exhibiting a well-defined electrode shape. The voltages of the two coils are similar, without significantly increasing insulation design requirements. In traditional structures, the regulator coil lead-out wires must pass through multiple windings, complicating insulation and mechanical design. This invention routes the tap changer tap directly through the outside of the high-voltage coil, eliminating the need for the lead-out wires to pass through other coils, significantly improving assembly efficiency. The high-voltage coil utilizes a parallel structure with the upper and lower half phases wound in opposite directions. The high-voltage lead-out terminal is located in the middle, facilitating connection between the high-voltage coil and the high-voltage bushing. Furthermore, the reduced radial dimension of the coil reduces the total copper wire length. Combined with the efficiency advantages of the autotransformer, this reduces overall losses. By integrating the regulator coil with the high-voltage coil, the autotransformer's insulation design is simplified, losses are reduced, and efficiency is improved, adapting to the needs of new power systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0020] Figure 1 Schematic diagram of the structure of an existing autotransformer.

[0021] Figure 2 This is a structural schematic diagram of an autotransformer in which a medium-voltage regulating coil is located between high-voltage coils according to the present invention.

[0022] Figure 3 This is a schematic diagram of the electrical connections of an autotransformer with a medium-voltage regulating coil located within a high-voltage coil.

[0023] Among them, 101 represents the upper half phase of the high-voltage coil; 102 represents the lower half phase of the high-voltage coil; 201 represents the second part of the upper half phase of the high-voltage coil; 202 represents the second part of the lower half phase of the high-voltage coil; 301 represents the medium-voltage coil; 401 represents the upper half phase of the medium-voltage regulating coil; 402 represents the lower half phase of the medium-voltage regulating coil; 501 represents the iron core; 601 represents the high-voltage lead wire; 602 represents the medium-voltage lead wire; 603 represents the neutral point lead wire, 200 represents the high-voltage winding, 300 represents the medium-voltage winding, and 400 represents the medium-voltage regulating winding. DETAILED DESCRIPTION

[0024] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0025] Reference will now be made in detail to specific embodiments of the present application, examples of which are illustrated in the accompanying drawings. Although the present application will be described in conjunction with specific embodiments, it will be understood that the present application is not intended to be limited to the described embodiments. On the contrary, it is intended to cover variations, modifications, and equivalents within the spirit and scope of the present application. It should be noted that the method steps described herein can be implemented by any functional block or functional arrangement, and any functional block or functional arrangement can be implemented as a physical entity or a logical entity, or a combination of the two.

[0026] It should be noted that when an element is referred to as being "disposed on" another element, it may be directly on the other element or there may be an element centered thereon. When an element is referred to as being "connected to" another element, it may be directly connected to the other element or there may be an element centered thereon. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only embodiments.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one skilled in the art to which this invention pertains. The terms used in this specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0028] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0029] Example 1 See also Figure 2 , a medium voltage regulating coil is located in the autotransformer of the high voltage coil, including a high voltage coil, a medium voltage regulating coil, and a medium voltage coil 301; the high voltage coil is composed of an upper half phase 101 of the high voltage coil and a lower half phase 102 of the high voltage coil, the winding directions of the upper half phase 101 of the high voltage coil and the lower half phase 102 of the high voltage coil are opposite, and the head ends of the upper half phase 101 of the high voltage coil and the lower half phase 102 of the high voltage coil are connected in parallel and then led out through a high voltage lead-out line 601; the medium voltage regulating coil is embedded in the interior of the high voltage coil, including an upper half phase 401 of the medium voltage regulating coil and a lower half phase 402 of the medium voltage regulating coil, The half-phase 401 and the head end of the lower half-phase 402 of the medium-voltage regulating coil are connected in parallel and connected to the end of the high-voltage coil. The ends of the upper half-phase 401 of the medium-voltage regulating coil and the lower half-phase 402 of the medium-voltage regulating coil are connected to the head end of the medium-voltage coil 301. The medium-voltage regulating coil is provided with multiple taps, including the first-stage tap to the last-stage tap. The head end of the first-stage tap is connected to the end of the high-voltage coil, and the end of the last-stage tap is connected to the head end of the medium-voltage coil 301. Each tap leads to a medium-voltage lead-out line 602 through the tap selector of the tap changer. A neutral point lead-out line 603 is provided at the end of the medium-voltage coil 301.

[0030] The autotransformer in this embodiment reduces the use of copper by sharing some windings between the high-voltage and medium-voltage windings. The design of the medium-voltage regulating coil embedded in the high-voltage coil eliminates the need for an independent regulating winding and reduces the volume. The graded voltage regulating tap is directly set on the medium-voltage regulating coil, and the voltage regulating range can be selected in conjunction with the tap changer. The high-voltage coil adopts double-half-phase reverse winding to reduce the end insulation distance. At the same time, the insulation withstand voltage strength is improved. The medium-voltage regulating coil and the high-voltage coil share the main insulation structure, which simplifies the insulation design and improves the pass rate of the power frequency withstand voltage test. Through electromagnetic-structural coordinated optimization, while maintaining the inherent advantages of the autotransformer, the voltage regulation flexibility, operational reliability and economy are particularly enhanced. It is especially suitable for scenarios such as urban power grid upgrades and renovations that require high equipment compactness and control accuracy.

[0031] The high-voltage coil upper phase 101 is connected in series with the high-voltage coil upper phase second portion 201 via external leads. The high-voltage coil lower phase 102 is also connected in series with the high-voltage coil lower phase second portion 202 via external leads. The two portions are symmetrically structured. The tail ends of the high-voltage coil upper phase second portion 201 and the high-voltage coil lower phase second portion 202 are connected via external leads, forming the end of the high-voltage coil. The series connection point between the high-voltage coil upper phase second portion 201 and the high-voltage coil lower phase second portion 202 is located midway along the axial height of the high-voltage coil.

[0032] The upper phase 401 of the medium-voltage regulating coil and the lower phase 402 of the medium-voltage regulating coil are connected in parallel to form a multi-stage symmetrically distributed regulating section. Each regulating section corresponds to a tap. The taps are evenly distributed along the axial direction of the medium-voltage regulating coil and connected to the moving contact of the tap changer via external leads. Each regulating section of the medium-voltage regulating coil has an equal number of turns, and the voltage difference between adjacent taps is fixed. The tap selector of the tap changer is located outside the high-voltage coil and is connected to the taps of the medium-voltage regulating coil via an insulating sleeve.

[0033] Example 2 See also Figure 3 A voltage regulating method for an autotransformer in which a medium voltage regulating coil is located at a high voltage coil comprises the following steps: Switch the tap changer to the target tap, so that the corresponding tap of the medium voltage regulating coil is connected to the medium voltage lead wire 602 through the tap selector; By adjusting the number of connected sections of the medium voltage regulating coil, the turns ratio between the medium voltage coil 301 and the high voltage coil is changed, and the output voltage on the medium voltage side is adjusted; The tap of the medium voltage regulating coil is embedded in the high voltage coil, and its head end is directly connected to the end of the high voltage coil, and the end is directly connected to the head end of the medium voltage coil.

[0034] In this embodiment, the medium-voltage voltage-regulating coil is embedded within the high-voltage coil, eliminating the need for a separate winding structure. This significantly reduces the size and weight of the transformer, making it suitable for space-constrained scenarios. The "embedded series" design, with the head end directly connected to the end of the high-voltage coil and the end directly connected to the head end of the medium-voltage coil, simplifies the winding layout and reduces the complexity of interlayer insulation. By adjusting the number of connected sections of the voltage-regulating coil, the high-voltage to medium-voltage turns ratio is directly adjusted, achieving voltage regulation on the medium-voltage side. The autotransformer structure inherently features low losses, and combined with tapped voltage regulation, energy efficiency can be further optimized. Sharing the insulation system of the high-voltage coil reduces the use of additional insulation materials and reduces manufacturing costs.

[0035] Example 3 See also Figure 2 and Figure 3 A medium voltage regulating coil is located in the autotransformer of the high voltage coil, which consists of a high voltage coil, a medium voltage regulating coil embedded in the high voltage coil, a medium voltage coil 301, and lead wires of each coil.

[0036] The high-voltage coil is composed of an axially symmetrical upper half phase 101 and a lower half phase 102 of the high-voltage coil. The two are spirally wound in opposite directions and connected in parallel at the head end through a copper busbar to lead out a high-voltage lead wire 601.

[0037] The second half of the upper phase 101 of the high-voltage coil is connected in series with the second part 201 of the upper phase of the high-voltage coil through a lead wire. The two parts are located at the same axial height of the iron core column, with an insulation gap reserved in the middle; the structure of the lower phase 102 is symmetrical with it.

[0038] The tail ends of the second parts 201 and 202 of the upper and lower half phases of the high voltage coil are connected through external leads to form the end of the high voltage coil and are directly connected to the head end of the medium voltage regulating coil.

[0039] The medium voltage regulating coil is embedded in the high voltage coil. The upper half phase 401 and the lower half phase 402 adopt a pancake structure. The first ends of the two are connected in parallel to form five taps from the first to the fifth level.

[0040] Each tap is arranged along the coil axis, and the tap lead is connected to the static contact of the tap changer. The first tap is directly welded to the end lead of the high-voltage coil, and the fifth tap is connected to the first end of the medium-voltage coil 301 through a lead.

[0041] The medium voltage coil 301 is wound in layers, with a neutral point 603 at the end being connected to the ground together with the core 501 via a lead wire.

[0042] Example 4 An autotransformer with a medium-voltage regulating coil located within the high-voltage coil. The medium-voltage regulating coil has five taps, each with equal turns, and a voltage difference of 2.5% of the rated voltage between adjacent taps. The end of the seventh tap is connected to the head end of the medium-voltage coil 301 via a lead wire. The first tap at the head end is connected to the end of the high-voltage coil via a lead wire. The middle tap is connected to multiple static contacts of the tap selector via leads.

[0043] When the voltage on the medium voltage side needs to be increased, the tap changer is controlled to switch from the third level to the first and second level taps, increasing the turns ratio of the medium voltage coil 301 to the high voltage coil; when the voltage needs to be reduced, it is switched to the fourth and fifth level taps to reduce the turns ratio; during the voltage regulation process, the system potential balance is maintained by grounding the neutral point 603.

[0044] Many embodiments and applications beyond the examples provided will be apparent to those skilled in the art upon reading the foregoing description. Therefore, the scope of the present teachings should be determined not with reference to the foregoing description, but rather with reference to the preceding claims, along with the full scope of equivalents to which such claims are entitled. For the purpose of completeness, all articles and references, including the disclosures of patent applications and publications, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein from the preceding claims is not a disclaimer of such subject matter, nor should it be interpreted that the applicants did not consider such subject matter to be part of the disclosed inventive subject matter.

[0045] Note that the advantages, strengths, and effects mentioned in this disclosure are merely examples and not limitations, and should not be construed as necessarily possessed by each embodiment of this application. Furthermore, the specific details disclosed above are provided for illustrative purposes and to facilitate understanding, not limitations, and the details do not necessarily limit this application to the use of the specific details.

[0046] The above content is a further detailed description of the present invention, and it cannot be considered that the specific implementation methods of the present invention are limited to these. For ordinary technicians in the technical field to which the present invention belongs, they can make several simple deductions or substitutions without departing from the concept of the present invention, which should be regarded as belonging to the determined protection scope of the present invention submitted.

Claims

1. An autotransformer with a medium voltage regulating coil located on a high voltage coil, characterized in that: It includes a high-voltage coil, a medium-voltage regulating coil, and a medium-voltage coil (301); The high-voltage coil is composed of a high-voltage coil upper half phase (101) and a high-voltage coil lower half phase (102), the winding directions of the high-voltage coil upper half phase (101) and the high-voltage coil lower half phase (102) are opposite, and the head ends of the high-voltage coil upper half phase (101) and the high-voltage coil lower half phase (102) are connected in parallel and then led out through a high-voltage lead wire (601); The medium-voltage regulating coil is embedded in the interior of the high-voltage coil, and includes an upper half phase (401) of the medium-voltage regulating coil and a lower half phase (402) of the medium-voltage regulating coil. The head ends of the upper half phase (401) of the medium-voltage regulating coil and the lower half phase (402) of the medium-voltage regulating coil are connected in parallel and connected to the end of the high-voltage coil. The ends of the upper half phase (401) of the medium-voltage regulating coil and the lower half phase (402) of the medium-voltage regulating coil are connected to the head end of the medium-voltage coil (301). The medium voltage regulating coil is provided with a plurality of taps, including a first-stage tap to a last-stage tap; the first end of the first-stage tap is connected to the end of the high voltage coil, and the end of the last-stage tap is connected to the first end of the medium voltage coil (301); each tap leads to a medium voltage lead wire (602) through a tap selector of a tap changer; A neutral point lead wire (603) is provided at the end of the medium voltage coil (301).

2. The autotransformer with a medium voltage regulating coil located at a high voltage coil according to claim 1, characterized in that: The upper half phase (101) of the high-voltage coil is connected in series with the second part (201) of the upper half phase of the high-voltage coil via an external lead, and the lower half phase (102) of the high-voltage coil is connected in series with the second part (202) of the lower half phase of the high-voltage coil via an external lead, and the two parts have symmetrical structures.

3. The autotransformer with a medium voltage regulating coil located at a high voltage coil according to claim 2, characterized in that: The tail ends of the second portion (201) of the upper half phase of the high-voltage coil and the second portion (202) of the lower half phase of the high-voltage coil are connected via external leads to form the end of the high-voltage coil.

4. The autotransformer with a medium voltage regulating coil located at a high voltage coil according to claim 3, characterized in that: The series connection point of the second portion (201) of the upper half phase of the high-voltage coil and the second portion (202) of the lower half phase of the high-voltage coil is located at a middle position of the axial height of the high-voltage coil.

5. The autotransformer with a medium voltage regulating coil located at a high voltage coil according to claim 1, characterized in that: The upper half phase (401) of the medium voltage regulating coil and the lower half phase (402) of the medium voltage regulating coil are connected in parallel to form a multi-stage symmetrically distributed voltage regulating section.

6. The autotransformer with a medium voltage regulating coil located between high voltage coils according to claim 5, characterized in that: Each level of the voltage regulating section corresponds to a tap.

7. The autotransformer with a medium voltage regulating coil located between high voltage coils according to claim 6, characterized in that: The tapping terminals are evenly distributed along the axial direction of the medium voltage regulating coil and are connected to the moving contact of the tap changer through external leads.

8. The autotransformer with a medium voltage regulating coil located between high voltage coils according to claim 6, characterized in that: The number of turns of each voltage regulating section of the medium voltage regulating coil is equal, and the voltage difference between adjacent taps is a fixed value.

9. The autotransformer with a medium voltage regulating coil located between high voltage coils according to claim 6, characterized in that: The tap selector of the tap changer is located outside the high-voltage coil and is connected to the tap of the medium-voltage regulating coil through an insulating bushing.

10. A voltage regulating method for an autotransformer in which a medium voltage regulating coil is located between high voltage coils, characterized in that: The following steps are involved: Switching the tap changer to the target tap, so that the corresponding tap of the medium voltage regulating coil is connected to the medium voltage lead wire (602) through the tap selector; By adjusting the number of access sections of the medium voltage regulating coil, the turns ratio between the medium voltage coil (301) and the high voltage coil is changed, thereby adjusting the output voltage on the medium voltage side; The tap of the medium voltage regulating coil is embedded in the high voltage coil, and the head end is directly connected to the end of the high voltage coil, and the end is directly connected to the head end of the medium voltage coil.

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