Double-high-voltage conversion transformer and control method thereof

Abstract

A double-high-voltage conversion transformer comprises a transformer iron core, a low-voltage coil, a high-voltage coil, a voltage regulating coil, an on-load tap-changer, a reverse breaking switch and a Y-D conversion switch, when the reverse breaking switch is arranged at a position I, a third contact is electrically connected with a first contact, and when the reverse breaking switch is arranged at a position II, the third contact is electrically connected with a second contact; the high-voltage coil comprises a first split coil, a second split coil and a third split coil. Compared with the prior art, the voltage regulation range, the voltage regulation level difference and the impedance value under the two voltage levels before and after voltage conversion are approximately equal, so that the power supply quality is improved. On the other hand, the voltage regulation coil is always subjected to on-load voltage regulation in the middle of the coil before and after voltage conversion, so that the problem that relatively high oscillation voltage is generated when line end regulation is adopted to directly enter the wave regulation coil from the on-load voltage regulation coil in an all-insulation system of 110kV and above is solved; and the problem that a neutral point is not suitable to be led out when neutral point voltage regulation is adopted in a 110kV and above Y-connection all-insulation system is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of transformers, and in particular to a dual high-voltage conversion transformer and a control method thereof. Background Art

[0002] A dual high-voltage conversion transformer is a transformer that can realize two voltage levels on the high-voltage side that can be converted to each other, and then combined with the low voltage to operate with dual windings. Generally, there are two main application scenarios. One is the mobile vehicle-mounted substation that has emerged in foreign countries in recent years; the other is the transition period between the transformation of old and new lines of substations. After the construction of new lines is completed, the old lines will be decommissioned. The high-voltage voltage of the transformer will be fixed at a certain voltage in the later stage, and the other set of high-voltage voltages will lose their function. In both application scenarios, the high-voltage side of the substation transformer needs to be connected to a line of a certain voltage level for a period of time, and after a period of time, the high-voltage side of the same transformer needs to be connected to a line of another voltage level, that is, the transformer needs to achieve dual high-voltage conversion.

[0003] The Chinese utility model patent with announcement number CN213935896U discloses a dual high-voltage conversion transformer, which realizes dual high-voltage conversion through a series-parallel wiring technical solution. Its disadvantage is that the voltage regulation range and voltage regulation level difference under the two voltage levels before and after the voltage conversion are quite different, resulting in low power supply quality. Summary of the invention

[0004] The present invention provides a dual high-voltage conversion transformer to solve the technical problem that the voltage regulation range and voltage regulation level difference of the existing dual high-voltage conversion transformer at two voltage levels before and after the dual high-voltage conversion are greatly different, resulting in low power supply quality.

[0005] To achieve the above object, the present invention adopts the following technical solution.

[0006] On the one hand, the present invention provides a dual high-voltage conversion transformer, including a transformer core, a low-voltage coil, a high-voltage coil, a voltage regulating coil, an on-load tap changer and a YD conversion switch, and also includes a reverse switch, the reverse switch includes a first contact, a second contact and a third contact, when the reverse switch is placed in position I, the third contact is electrically connected to the first contact, when the reverse switch is placed in position II, the third contact is electrically connected to the second contact; the high-voltage coil includes a first split coil, a second split coil and a third split coil; the YD conversion switch includes a YD conversion contact, a D contact and a Y contact; the Y contacts of the three phases are respectively led to the neutral point bushing;

[0007] Taking phase A as an example, and phases B and C are analogous, the head end of the first split coil is connected to the tail end of the third split coil; the head end of the third split coil is respectively connected to the second contact and the tail end of the second split coil, and the head end of the second split coil is connected to the first contact; the tail end of the first split coil is connected to the voltage regulating coil through the K terminal of the on-load tap changer, and the K terminal is also a + and - switching terminal. The voltage regulating coil is connected to the head end of a high-voltage basic coil through the moving contact of the on-load tap changer, and all taps of the voltage regulating coil are connected to the static contact of the on-load tap changer; the tail end of the high-voltage basic coil is connected to the YD conversion contact, and the third contact is connected to the D contact point and led to the high-voltage A-phase bushing; the YD conversion switch switches between the D contact point and the Y contact point as needed to realize the YD conversion of the dual high-voltage conversion transformer.

[0008] Through the above scheme, the voltage regulation range, voltage regulation level difference and impedance value at two voltage levels before and after voltage conversion are nearly equal, thereby improving the power supply quality. On the other hand, the voltage regulating coil of the present invention always belongs to the on-load voltage regulation in the middle of the coil before and after voltage conversion, which not only solves the problem of high oscillation voltage generated by directly entering the wave regulating coil from the on-load voltage regulating coil in the fully insulated system of 110kV and above by using the line end regulation, but also solves the problem that it is not suitable to lead out the neutral point when using the neutral point voltage regulation in the Y-connected fully insulated system of 110kV and above.

[0009] In some embodiments, the low-voltage coil, high-voltage basic coil, high-voltage coil, and voltage regulating coil are respectively sleeved on the transformer core from the inside to the outside.

[0010] In some embodiments, the low voltage coil is right-winding, the first split coil is left-winding, the second split coil and the third split coil are right-winding, and the high voltage basic coil is right-winding.

[0011] In some embodiments, the voltage regulating coil is connected in parallel in two groups, the upper half is wound in the left direction, and the lower half is wound in the right direction.

[0012] Based on the same inventive concept, the present invention also provides a dual high-voltage conversion transformer, comprising a transformer core, a low-voltage coil, a high-voltage coil, a voltage regulating coil, an on-load tap changer and a YD conversion switch, and also comprising a reverse switch, the reverse switch comprising a first contact, a second contact and a third contact, the third contact being electrically connected to the first contact when the reverse switch is placed in position I, and the third contact being electrically connected to the second contact when the reverse switch is placed in position II; the high-voltage coil comprises a first split coil, a second split coil and a third split coil; the YD conversion switch comprises a YD conversion contact, a D contact and a Y contact; the Y contacts of the three phases are respectively led to the neutral point bushing;

[0013] Taking phase A as an example, and phases B and C are analogous, the tail end of the first split coil is connected to the voltage regulating coil through the K terminal of the on-load tap changer, and the K terminal is also a + and - switching terminal. The voltage regulating coil is connected to the third contact through the moving contact of the on-load tap changer, and all taps of the voltage regulating coil are connected to the static contact of the on-load tap changer; the first end of the first split coil is connected to the D contact point and led to the high-voltage A phase bushing, and the tail end of the third split coil is connected to the YD conversion contact; the YD conversion switch switches between the D contact point and the Y contact point as needed to realize the YD conversion of the dual high-voltage conversion transformer; the first end of the second split coil is connected to the first contact, and the tail end is connected to the first end of the second contact and the third split coil respectively.

[0014] In some embodiments, the low-voltage coil, high-voltage coil, and voltage regulating coil are respectively sleeved on the transformer core from the inside to the outside.

[0015] In some embodiments, the low voltage coil is wound in the right direction, the first split coil is wound in the left direction, and the second split coil and the third split coil are wound in the right direction.

[0016] In some embodiments, the voltage regulating coil is connected in parallel in two groups, the upper half is wound leftward and the lower half is wound rightward. Based on the same inventive concept, the present invention also provides a control method for the above dual high-voltage conversion transformer, the method comprising:

[0017] If the voltage transformation ratio before and after the dual high voltage conversion is less than When the dual high-voltage conversion transformer is switched to D connection, the reverse switch is placed in position Ⅰ; when the dual high-voltage conversion transformer is switched to Y connection, the reverse switch is placed in position Ⅱ;

[0018] If the voltage transformation ratio before and after the dual high voltage conversion is greater than When the dual high-voltage conversion transformer is switched to D connection, the reverse switch is placed in position II. When the dual high-voltage conversion transformer is switched to Y connection, the reverse switch is placed in position I.

[0019] The present invention has at least the following technical effects or advantages: the voltage regulation range, voltage regulation step difference and impedance value at two voltage levels before and after voltage conversion are nearly equal, thereby improving the power supply quality. On the other hand, the voltage regulating coil of the present invention always belongs to the on-load voltage regulation in the middle of the coil before and after voltage conversion, which not only solves the problem that a higher oscillation voltage will be generated when the line end regulation is directly input from the on-load voltage regulating coil into the wave regulating coil in the 110kV and above fully insulated system, but also solves the problem that the neutral point should not be drawn out when the neutral point voltage regulation is used in the 110kV and above Y-connected fully insulated system. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1A schematic diagram of the arrangement of the A-phase coils of the dual high-voltage conversion transformer and the circuit connection between the YD conversion switch and the reverse switch in one embodiment of the present invention;

[0021] Figure 2 A wiring schematic diagram of a dual high-voltage conversion transformer in one embodiment of the present invention;

[0022] Figure 3 A schematic diagram of the arrangement of the A-phase coils of the dual high-voltage conversion transformer and the circuit connection between the YD conversion switch and the reverse switch in one embodiment of the present invention;

[0023] Figure 4 The figure is a wiring schematic diagram of a dual high-voltage conversion transformer in one embodiment of the present invention. DETAILED DESCRIPTION

[0024] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0025] Embodiment 1

[0026] Figure 1 The present application discloses a schematic diagram of the arrangement of the A-phase coils of a dual high-voltage conversion transformer and the circuit connection of a YD conversion switch and a reverse trip switch, including a transformer core 1, a low-voltage coil 2, a high-voltage coil, a high-voltage basic coil 3, a voltage regulating coil 4, a reverse trip switch 6, an on-load tap changer and a YD conversion switch 7.

[0027] The reverse switch 6 includes a first contact 61, a second contact 62 and a third contact 63. When the reverse switch 6 is placed in position I, the third contact 63 is electrically connected to the first contact 61. When the reverse switch 6 is placed in position II, the third contact 63 is electrically connected to the second contact 62. The high-voltage coil includes a first split coil 31, a second split coil 32 and a third split coil 33. The YD conversion switch includes a YD conversion contact, a D contact and a Y contact O. The YD conversion contact includes three contacts X, Y and Z, and the D contact includes three contacts A, B and C. The Y contacts O of the three phases are respectively led to the neutral point bushing.

[0028] Taking phase A as an example, and phases B and C are analogous, the head end of the first split coil 31 is connected to the tail end of the third split coil 33, the head end of the third split coil 33 is respectively connected to the second contact 62 and the tail end of the second split coil 32, and the head end of the second split coil 32 is connected to the first contact 61. The tail end of the first split coil 31 is connected to the voltage regulating coil 4 through the K terminal 51 of the on-load tap changer, and the K terminal 51 is also a + and - switching terminal. The voltage regulating coil 4 is connected to the head end of a high-voltage basic coil through the moving contact 52 of the on-load tap changer, and all taps of the voltage regulating coil 4 are connected to the static contact of the on-load tap changer. The tail end of the high-voltage basic coil 3 is connected to the X contact of the YD conversion contact, and the third contact 63 is connected to the A contact of the D contact and is led to the high-voltage A phase bushing; the YD conversion switch 7 switches between the D contact and the Y contact as needed to realize the YD conversion of the dual high-voltage conversion transformer.

[0029] The low-voltage coil 2, high-voltage coil, and voltage regulating coil 4 are respectively sleeved on the transformer core 1 from the inside to the outside, and the high-voltage basic coil 3 is sleeved between the low-voltage coil 2 and the high-voltage coil. Among them, the low-voltage coil 2 is right-wound, the first split coil 31 is left-wound, the second split coil 32 and the third split coil 33 are right-wound, and the voltage regulating coil 4 adopts two groups of upper and lower parallel connections, the upper half is left-wound, the lower half is right-wound, and the high-voltage basic coil 3 is right-wound. The voltage regulating coil 4 adopts a dedicated outlet structure similar to the high-voltage middle incoming line in the insulation structure and is placed on the outermost side.

[0030] Specifically, the head end of the first split coil 31 is led out through a dedicated upper and lower parallel coil outlet structure and connected in series to the tail end of the third split coil 33. The head end of the third split coil 33 and the tail end of the second split coil 32 are led out together through a dedicated outlet structure in the middle of the upper and lower parallel coils and connected in series to the second contact 62. The head end of the second split coil 32 is led out through a dedicated outlet structure in the middle of the upper and lower parallel coils and connected to the first contact 61. The third contact 63 of the trip switch 6 is led out with a high-voltage cable and connected to the high-voltage A-phase bushing; the structures of the B-phase and C-phase are the same as those of the A-phase. This insulation structure ensures the safety and reliability of the outlet structure.

[0031] Figure 1 In the figure, A1 and Xk are the head end and tail end of the first split coil 31 respectively, X2 is the tail end of the third split coil 33, A3 and X are the head end and tail end of the high-voltage basic coil 3 respectively, and a and x are the head end and tail end of the low-voltage coil 2 respectively.

[0032] by Figure 1Taking the SZ-20000 / U1 (U2) dual high-voltage conversion transformer as an example, the turn voltage = et V, the number of turns of the voltage regulating coil stage is Nt turns, and the on-load voltage regulating stage phase voltage = Nt x et = Ut V. The number of turns of the high-voltage basic coil is Ng turns, the first split coil 31 and the third split coil 33 are both Nf turns, and the second split coil 32 is Nd turns. When switching to D connection, the second split coil 32 is connected in series on the U2kV side. The total number of turns of the high-voltage rated gear = Ng + Nf + Nf + Nd = N2 turns, the D-connection phase voltage = N2 x et = U2 V, the D-connection U2kV line-level voltage percentage = Ut / U2 = 1.11%, the theoretical value is 1.13%, and the voltage ratio error is only 0.08%; when switching to Y connection, the second split coil 32 is removed on the U1kV side, the total number of turns of the high-voltage rated gear = Ng + Nf + Nf-Nd = N1 turns, the Y-connection phase voltage = N1 xet = U1 / √3V, the Y-connection U1kV line-level voltage percentage = (Ut x√3) / U1 = 1.23%, the theoretical value is 1.25%, and the voltage ratio error is only 0.12%. This shows that the voltage regulation range and voltage regulation step difference of the transformer of the present invention at two voltage levels before and after voltage conversion are nearly equal.

[0033] by Figure 1 For example, even if the second split coil 32 is removed when switching to Y connection at U1kV, since the structures of the first split coil 31 and the third split coil 33 are symmetrically distributed up and down, although no current passes through the second split coil 32, the system ampere-turns, equivalent leakage magnetic area, coil reactance height, Rockwell coefficient and other parameters that affect the impedance do not change much compared to when the second split coil 32 is connected in series at U2kV when switching to D connection. Therefore, the impedance values ​​of the transformer of the present invention at the two voltage levels before and after the voltage conversion are almost equal.

[0034] by Figure 1 For example, when switching to D connection, the turn split ratio of the high-voltage coil and the high-voltage basic coil 3 = (Nf+Nf+Nd):Ng=0.5:0.5; when switching to Y connection, the turn split ratio of the high-voltage coil and the high-voltage basic coil 3 = (Nf+Nf):Ng=0.448:0.552, and the voltage regulating coil 4 is connected in series between the high-voltage coil and the high-voltage basic coil 3. Such a high-voltage coil turn split ratio ensures that the voltage regulating coil 4 always belongs to the on-load voltage regulation in the middle of the coil before and after voltage conversion.

[0035] Figure 2 : is the wiring schematic diagram of the dual high-voltage conversion transformer in this embodiment. Taking phase A as an example, in the figure, A1 and Xk are the head end and tail end of the first split coil 31, An and Xr are the head end and tail end of the second split coil 32, A2 and X2 are the head end and tail end of the third split coil 33, and A3 and X are the head end and tail end of the high-voltage basic coil 3. The same is true for phases B and C.

[0036] Embodiment 2

[0037] Figure 3 This is a schematic diagram of the arrangement of the A-phase coil of another dual high-voltage conversion transformer and the circuit connection of the YD conversion switch and the reverse switch of the present application, including a transformer core 1, a low-voltage coil 2, a high-voltage coil, a voltage regulating coil 4, a reverse switch 6, an on-load tap changer and a YD conversion switch 7.

[0038] The reverse switch 6 includes a first contact 61, a second contact 62 and a third contact 63. When the reverse switch 6 is placed in position I, the third contact 63 is electrically connected to the first contact 61. When the reverse switch 6 is placed in position II, the third contact 63 is electrically connected to the second contact 62. The high-voltage coil includes a first split coil 31, a second split coil 32 and a third split coil 33. The YD conversion switch includes a YD conversion contact, a D contact and a Y contact O. The YD conversion contact includes three contacts X, Y and Z, and the D contact includes three contacts A, B and C. The Y contacts O of the three phases are respectively led to the neutral point bushing.

[0039] Taking phase A as an example, and phases B and C are analogous, the tail end of the first split coil 31 is connected to the voltage regulating coil 4 through the K terminal 51 of the on-load tap changer, and the K terminal 51 is also a + and - switching terminal. The voltage regulating coil 4 is connected to the third contact 63 through the moving contact 52 of the on-load tap changer, and all taps of the voltage regulating coil 4 are connected to the static contact of the on-load tap changer. The head end of the first split coil 31 is connected to the A contact of the D contact point and is led to the high-voltage A phase bushing, and the tail end of the third split coil 33 is connected to the X contact of the YD conversion contact; the YD conversion switch 7 switches between the D contact point and the Y contact point as needed to realize the YD conversion of the dual high-voltage conversion transformer; the head end of the second split coil 32 is connected to the first contact 61, and the tail end is connected to the second contact 62 and the head end of the third split coil 33 respectively.

[0040] The low-voltage coil 2, high-voltage coil, and voltage regulating coil 4 are respectively sleeved on the transformer core 1 from the inside to the outside. Among them, the low-voltage coil 2 is right-winding, the first split coil 31 is left-winding, the second split coil 32 and the third split coil 33 are right-winding, and the voltage regulating coil 4 adopts two groups of upper and lower parallel connection, the upper half is left-winding, and the lower half is right-winding. The voltage regulating coil 4 adopts a dedicated outlet structure similar to the high-voltage middle incoming line in the insulation structure and is placed on the outermost side.

[0041] Figure 4 : is the wiring schematic diagram of the dual high-voltage conversion transformer in this embodiment. Taking phase A as an example, in the figure, A1 and Xk are the head end and tail end of the first split coil 31, An and Xr are the head end and tail end of the second split coil 32, and A2 and X2 are the head end and tail end of the third split coil 33. The same is true for phases B and C.

[0042] Embodiment 3

[0043] A control method applicable to the dual high-voltage conversion transformer in Embodiment 1 or Embodiment 2, the method comprising:

[0044] If the voltage transformation ratio before and after the dual high voltage conversion is less than When the dual high-voltage conversion transformer is switched to D connection, the reverse switch is placed in position Ⅰ; when the dual high-voltage conversion transformer is switched to Y connection, the reverse switch is placed in position Ⅱ;

[0045] If the voltage transformation ratio before and after the dual high voltage conversion is greater than When the dual high-voltage conversion transformer is switched to D connection, the reverse switch is placed in position II. When the dual high-voltage conversion transformer is switched to Y connection, the reverse switch is placed in position I.

[0046] In the description provided herein, a large number of specific details are described. However, it is understood that embodiments of the present invention can be practiced without these specific details. In some instances, well-known methods, structures and techniques are not shown in detail so as not to obscure the understanding of this description.

[0047] Similarly, it should be understood that in order to streamline the present disclosure and aid in understanding one or more of the various inventive aspects, in the above description of exemplary embodiments of the present invention, various features of the present invention are sometimes grouped together into a single embodiment, figure, or description thereof. However, this disclosed method should not be interpreted as reflecting the intention that the claimed invention requires more features than those expressly recited in each claim. Rather, as reflected in the claims, inventive aspects lie in less than all of the features of the individual embodiments previously disclosed. Therefore, the claims that follow the detailed description are hereby expressly incorporated into the detailed description, with each claim itself serving as a separate embodiment of the present invention.

[0048] Those skilled in the art will appreciate that the modules or units or groups of the devices in the examples disclosed herein may be arranged in the device as described in the embodiment, or alternatively may be located in one or more devices different from the devices in the example. The modules in the foregoing examples may be combined into one module or may be divided into multiple submodules.

[0049] Those skilled in the art will appreciate that the modules in the devices in the embodiments may be adaptively changed and arranged in one or more devices different from the embodiments. The modules or units or groups in the embodiments may be combined into one module or unit or group, and in addition they may be divided into a plurality of submodules or subunits or subgroups. Except that at least some of such features and / or processes or units are mutually exclusive, all features disclosed in this specification (including the accompanying claims, abstracts and drawings) and all processes or units of any method or device disclosed in this manner may be combined in any combination. Unless otherwise expressly stated, each feature disclosed in this specification (including the accompanying claims, abstracts and drawings) may be replaced by an alternative feature providing the same, equivalent or similar purpose.

[0050] Furthermore, those skilled in the art will appreciate that although some embodiments described herein include certain features included in other embodiments but not other features, the combination of features from different embodiments is meant to be within the scope of the present invention and to form different embodiments.

[0051] In addition, some of the embodiments are described herein as methods or combinations of method elements that can be implemented by a processor of a computer system or by other devices that perform the functions. Therefore, a processor with necessary instructions for implementing the method or method elements forms a device for implementing the method or method elements. In addition, the elements described herein of the device embodiments are examples of devices for implementing the functions performed by the elements for the purpose of implementing the invention.

[0052] The various techniques described herein may be implemented in combination with hardware or software, or a combination thereof. Thus, the method and apparatus of the present invention, or some aspects or portions of the method and apparatus of the present invention may be in the form of program codes (i.e., instructions) embedded in a tangible medium, such as a floppy disk, a CD-ROM, a hard disk drive, or any other machine-readable storage medium, wherein when the program is loaded into a machine such as a computer and executed by the machine, the machine becomes a device for practicing the present invention.

[0053] In the case where the program code is executed on a programmable computer, the computing device generally includes a processor, a storage medium readable by the processor (including volatile and non-volatile memory and / or storage elements), at least one input device, and at least one output device. The memory is configured to store the program code; the processor is configured to execute the method of the present invention according to the instructions in the program code stored in the memory.

[0054] By way of example and not limitation, computer readable media include computer storage media and communication media. Computer readable media include computer storage media and communication media. Computer storage media stores information such as computer readable instructions, data structures, program modules or other data. Communication media generally embodies computer readable instructions, data structures, program modules or other data in a modulated data signal such as a carrier wave or other transmission mechanism, and includes any information delivery medium. Any combination of the above is also included within the scope of computer readable media.

[0055] As used herein, unless otherwise specified, the use of ordinal numbers "first," "second," "third," etc. to describe common objects merely indicates that different instances of similar objects are involved, and is not intended to imply that the objects so described must have a given order in time, space, order, or in any other manner.

[0056] Although the present invention has been described according to a limited number of embodiments, it will be apparent to those skilled in the art, with the benefit of the above description, that other embodiments may be envisioned within the scope of the invention thus described. In addition, it should be noted that the language used in this specification is selected primarily for readability and teaching purposes, rather than for explaining or defining the subject matter of the present invention. Therefore, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the present invention is illustrative, not restrictive, with respect to the scope of the present invention, which is defined by the appended claims.

[0057] Finally, it should be noted that the present invention does not explain in detail the common knowledge recognized by technicians in this field. The above is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A dual high-voltage conversion transformer, comprising a transformer core, a low-voltage coil, a high-voltage coil, a voltage regulating coil, an on-load tap changer and a YD conversion switch, characterized in that: It also includes a reverse switch, which includes a first contact, a second contact and a third contact. When the reverse switch is placed in position I, the third contact is electrically connected to the first contact, and when the reverse switch is placed in position II, the third contact is electrically connected to the second contact; the high-voltage coil includes a first split coil, a second split coil and a third split coil; the YD conversion switch includes a YD conversion contact, a D contact point and a Y contact point, and the Y contacts O of the three phases are respectively led to the neutral point bushing; Taking phase A as an example, and phases B and C are analogous, the head end of the first split coil is connected to the tail end of the third split coil; the head end of the third split coil is respectively connected to the second contact and the tail end of the second split coil, and the head end of the second split coil is connected to the first contact; the tail end of the first split coil is connected to the voltage regulating coil through the K terminal of the on-load tap changer, and the K terminal is also a + and - switching terminal. The voltage regulating coil is connected to the head end of a high-voltage basic coil through the moving contact of the on-load tap changer, and all taps of the voltage regulating coil are connected to the static contact of the on-load tap changer; the tail end of the high-voltage basic coil is connected to the YD conversion contact, and the third contact is connected to the D contact point and led to the high-voltage A-phase bushing; the Y contacts of the three phases are respectively led to the neutral point bushing; the YD conversion switch switches between the D contact point and the Y contact point as needed to realize the YD conversion of the dual high-voltage conversion transformer.

2. The dual high voltage conversion transformer according to claim 1, characterized in that: The low-voltage coil, high-voltage basic coil, high-voltage coil and voltage regulating coil are respectively sleeved on the transformer core from the inside to the outside.

3. The dual high voltage conversion transformer according to claim 1 or 2, characterized in that: The low-voltage coil is wound in the right direction, the first split coil is wound in the left direction, the second split coil and the third split coil are wound in the right direction, and the high-voltage basic coil is wound in the right direction.

4. The dual high voltage conversion transformer according to claim 1 or 2, characterized in that: The voltage regulating coil is connected in parallel in two groups, the upper half is wound in the left direction and the lower half is wound in the right direction.

5. A dual high-voltage conversion transformer, comprising a transformer core, a low-voltage coil, a high-voltage coil, a voltage regulating coil, an on-load tap changer and a YD conversion switch, characterized in that: It also includes a reverse switch, which includes a first contact, a second contact and a third contact. When the reverse switch is placed in position I, the third contact is electrically connected to the first contact, and when the reverse switch is placed in position II, the third contact is electrically connected to the second contact; the high-voltage coil includes a first split coil, a second split coil and a third split coil; the YD conversion switch includes a YD conversion contact, a D contact point and a Y contact point, and the Y contacts O of the three phases are respectively led to the neutral point bushing; Taking phase A as an example, and phases B and C are analogous, the tail end of the first split coil is connected to the voltage regulating coil through the K terminal of the on-load tap changer, and the K terminal is also a + and - switching terminal. The voltage regulating coil is connected to the third contact through the moving contact of the on-load tap changer, and all taps of the voltage regulating coil are connected to the static contact of the on-load tap changer; the first end of the first split coil is connected to the D contact point and led to the high-voltage A phase bushing, and the tail end of the third split coil is connected to the YD conversion contact; the Y contacts of the three phases are respectively led to the neutral point bushing; the YD conversion switch switches between the D contact point and the Y contact point as needed to realize the YD conversion of the dual high-voltage conversion transformer; the first end of the second split coil is connected to the first contact, and the tail end is respectively connected to the second contact and the first end of the third split coil.

6. The dual high voltage conversion transformer according to claim 5, characterized in that: The low-voltage coil, the high-voltage coil and the voltage regulating coil are respectively sleeved on the transformer core from the inside to the outside.

7. The dual high voltage conversion transformer according to claim 5 or 6, characterized in that: The low-voltage coil is wound in the right direction, the first split coil is wound in the left direction, and the second split coil and the third split coil are wound in the right direction.

8. The dual high voltage conversion transformer according to claim 5 or 6, characterized in that: The voltage regulating coil is connected in parallel in two groups, the upper half is wound in the left direction and the lower half is wound in the right direction.

9. A control method for a dual high voltage conversion transformer according to any one of claims 1 to 8, characterized in that: The method includes: If the voltage transformation ratio before and after the double high-voltage conversion is less than √3, when the double high-voltage conversion transformer is switched to D connection, the reverse switch is placed in position Ⅰ, and when the double high-voltage conversion transformer is switched to Y connection, the reverse switch is placed in position Ⅱ; If the voltage transformation ratio before and after the dual high-voltage conversion is greater than √3, when the dual high-voltage conversion transformer is switched to D connection, the reverse switch is placed in position II; when the dual high-voltage conversion transformer is switched to Y connection, the reverse switch is placed in position I.

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