35kV dry-type transformer high-voltage winding structure

Abstract

The invention discloses a 35kV dry-type transformer high-voltage winding structure and relates to the technical field of dry-type transformers, the number of turns of a high-voltage winding is divided into n sections, n is an integer larger than or equal to 12, the n sections of the high-voltage winding are divided into reinforcing sections located at the head end and the tail end, and normal sections and tapping sections located between the reinforcing sections, compared with the normal section and the tapping section, the number of turn-dividing layers of the reinforcing section is reduced, and the thicknesses of the inner insulation and the outer insulation at the end part are increased. The number of turn layers of the end winding section is reduced, the internal and external insulation distance is increased, the end air field intensity is reduced, and air breakdown discharge is avoided. And the winding with low field intensity and high capacitance at the end part is beneficial to reducing the main insulation distance, so that the 35kV dry-type transformer can be tested and put into operation in a high-altitude area of 3000-5000 meters.

Description

Technical Field

[0001] The present application relates to the technical field of dry-type transformers, and in particular to a high-voltage winding structure of a 35kV dry-type transformer. Background Art

[0002] A dry-type transformer is a transformer that does not use insulating oil. Its core and winding are not immersed in insulating oil and rely on air convection for cooling. It is mainly composed of a core made of silicon steel sheets and a coil cast with epoxy resin. An insulating cylinder is placed between the high and low voltage coils to increase electrical insulation, and the coils are supported and constrained by pads. The fasteners of its parts have anti-loosening properties. Dry-type transformers are mainly cooled by natural air cooling and forced air cooling. When naturally cooled by air, the transformer can operate continuously for a long time at rated capacity; when forced air cooling is used, the output capacity of the transformer can be increased, which is suitable for intermittent overload operation or emergency overload operation.

[0003] The dry-type transformers used in high altitude areas of 3000-5000 meters have a modified insulation level that is 1.42-1.8 times higher than that of dry transformers in 1000-meter areas. 10kV dry transformers can adopt 20kV structure and insulation distance design. 35kV dry transformers do not have a higher insulation level product structure and insulation distance molded dry transformer support. The design and manufacture of 35kV dry transformers with high insulation levels have become a difficult problem in the industry. At 5000 meters above sea level, the air is thin and the air withstand voltage value of the dry transformer winding surface is low. Therefore, the winding surface of the high insulation level dry transformer needs to be designed with reduced field strength to avoid air breakdown discharge.

[0004] The insulation level of the traditional 35kV dry transformer in the 1000m area is LI200AC85kV, the modified insulation level of the 35kV dry transformer in the 3000m area is 1.42×LI200AC85kV, that is, LI285AC120kV, and the modified insulation level of the 35kV dry transformer in the 5000m area is 1.8×LI200AC85kV, that is, LI365AC155kV. Therefore, it is a technical problem to be solved in this field to design a 35kV dry transformer with high insulation level suitable for 3000-5000m altitude, and to realize the normal insulation level test and commissioning in high altitude areas. Summary of the invention

[0005] In order to solve the above technical problems, this application proposes the following technical solutions:

[0006] In the first aspect, an embodiment of the present application provides a 35kV dry-type transformer high-voltage winding structure, characterized in that the number of turns of the high-voltage winding is divided into n sections, n is an integer greater than or equal to 12, and the n sections of the high-voltage winding are divided into a reinforced section located at the head and end and a normal section and a tap section located between the reinforced sections. The reinforced section has a reduced number of turns compared to the normal section and the tap section, and the thickness of the inner insulation and the outer insulation at the end is increased.

[0007] In a possible implementation, when the insulation level of the 35kV dry-type transformer is designed to be LI285AC120kV, the first and last sections of the high-voltage winding are reinforced sections, and the rest are normal sections and tapping sections. The number of turns of the normal section and the tapping section is m, the number of turns of the reinforced section is m-2, and the maximum number of turns of the n-section high-voltage winding is the first number of turns.

[0008] In a possible implementation, when the insulation level of the 35kV dry-type transformer is designed to be LI365AC155kV, the first three sections and the last three sections of the high-voltage winding are reinforced sections, and the rest are normal sections and tapping sections. The number of turns of the first section and the last section is m-2 layers, the number of turns of the two sections adjacent to the first section and the two sections adjacent to the last section is m or m-2 layers, and the maximum number of turns of each layer of the reinforced section is greater than the first number of turns; the number of turns of the normal section and the tapping section is m layers, the maximum number of turns of each layer is less than the first number of turns, and the maximum number of turns of each layer of the tapping section is 1-3 turns more than that of the normal section.

[0009] In a possible implementation, the high-voltage winding uses enameled round wire and is stacked with z mesh cloths, with wide wires falling outside the mesh and narrow wires and round wires falling inside the mesh; when measuring the layer insulation thickness, the double-sided turn insulation thickness of the wire is calculated as the difference between the maximum narrow side size of the insulated wire with turns and the nominal narrow side size of the bare wire.

[0010] In a possible implementation, the working field strength between the layers of the reinforcement section is controlled to reach a preset range, and the number of mesh sheets is selected according to the working field strength to determine the layer insulation thickness.

[0011] In a possible implementation, when the main insulation structure without the main air gap is adopted, a ground screen is provided at the end of the winding, and when the insulation level is LI365AC155kV, an umbrella skirt is provided at the end.

[0012] In a possible implementation, the insulation level is designed to be LI285AC120kV. When the segmented and layered design is performed, the working field strength between the winding layers is controlled to be less than or equal to the first working field strength, the layer insulation thickness is selected and the interlayer capacitance is determined, the working field strength between the winding junction sections is controlled to be less than or equal to the second working field strength, the working field strength between normal sections is less than or equal to the third working field strength, the inter-segment insulation distance is selected, and the inter-segment capacitance is determined; the normal section is filled with mesh cloth so that the inner and outer insulation thickness reaches the first thickness; after the inner and outer insulation of the reinforced section is filled with mesh cloth to reach a preset thickness, the mesh cloth is filled again so that the inner and outer insulation of the reinforced section winding is thicker than the normal section.

[0013] In a possible implementation, the insulation level is designed to be LI365AC155kV. When the segmented and layered design is performed, the working field strength between the winding connection sections is controlled to be less than or equal to the fourth working field strength, and the working field strength between the normal sections is less than or equal to the fifth working field strength. The insulation distance between sections is selected, and the capacitance between sections is determined. The normal section of the winding is filled with mesh cloth so that the inner and outer insulation thickness reaches the second thickness, and the inner and outer insulation of the reinforced section is filled with mesh cloth to reach the third thickness, and then the mesh cloth is filled so that the inner and outer insulation of the reinforced section is thicker than the normal section.

[0014] In a possible implementation, the high and low main air gaps are eliminated in a small-capacity dry-type transformer. When the insulation level is designed to be LI285AC120kV, the high and low voltage resin air gaps are selected according to the power frequency withstand voltage field strength level, the main air gap is greater than or equal to the first spacing, the winding height and heat dissipation capacity are maintained, and the phase distance is greater than or equal to the second spacing; an end ground screen is provided to eliminate the influence of the high voltage of the high-voltage winding on the external electrode, and no umbrella skirt is provided from the end to the ground screen surface. The end insulation distance is selected according to the field strength level during the power frequency withstand voltage, the high-voltage end insulation is greater than or equal to the third spacing, the low-voltage end insulation is greater than or equal to the fourth spacing, the end insulation top to the iron yoke air gap is greater than or equal to the fifth spacing, a pressure block is installed to compact the winding, and the first and last sections of the high-voltage winding are flush with the inner diameters of other sections;

[0015] The insulation level is designed to be LI365AC155kV. The high and low voltage resin air channels are selected according to the power frequency withstand voltage field strength level. The main air channel is greater than or equal to the sixth spacing to maintain the winding height and heat dissipation capacity, and the phase distance is greater than or equal to the seventh spacing. An end ground screen is set to eliminate the influence of the high voltage of the high-voltage winding on the external electrode. The end insulation distance is selected according to the field strength level during power frequency withstand voltage. The high voltage end insulation is greater than or equal to the eighth spacing, and the low voltage end insulation is greater than or equal to the ninth spacing. The ground screen is evenly slotted in the main air channel and the middle of the high voltage to reduce the eddy current loss of the leakage magnetic field during load operation. The air gap from the top of the end insulation to the iron yoke is greater than or equal to the tenth spacing. The first and last sections of the high voltage winding are flush with the inner diameters of other sections. Continuous umbrella skirts are made on the upper and lower ends of the insulation surface to increase the air surface creepage distance from the end to the ground screen.

[0016] In the embodiment of the present application, the number of turns of the end winding segment is reduced, the internal and external insulation distance is increased, the air field strength of the end is reduced, and air breakdown discharge is avoided. The low field strength and high capacitance winding at the end is conducive to reducing the main insulation distance, thereby realizing that the 35kV dry-type transformer can be tested and put into operation in areas with an altitude of 3000-5000 meters. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic diagram of the specifications and dimensions of the mesh cloth provided in the embodiment of the present application;

[0018] Figure 2 A schematic diagram of the stacking thickness of the mesh cloth provided in an embodiment of the present application;

[0019] Figure 3 A schematic diagram of insulation thickness of different wire mesh cloth layers provided in an embodiment of the present application;

[0020] Figure 4 A schematic diagram of a 35kV high-voltage winding arrangement structure with an insulation level of LI285AC120kV provided in an embodiment of the present application;

[0021] Figure 5 A main insulation structure diagram of a 35kV dry-type transformer provided in an embodiment of the present application;

[0022] Figure 6 A main insulation structure diagram of a 35kV dry-type transformer provided in an embodiment of the present application;

[0023] Figure 7 The insulation level provided for the embodiment of the present application is a 35kV high-voltage winding arrangement structure of LI365AC155kV. DETAILED DESCRIPTION

[0024] The present solution is described below in conjunction with the accompanying drawings and specific implementation methods.

[0025] In this embodiment, the 35kV dry-type transformer is improved to meet the normal insulation level test and commissioning at an altitude of 3000-5000 meters. The number of turns of the high-voltage winding is divided into n sections, n is an integer greater than or equal to 12, and the n sections of the high-voltage winding are divided into a reinforcement section located at the head and end, and a normal section and a tapping section located between the reinforcement sections. The number of turns of the reinforcement section is reduced compared to the normal section and the tapping section, and the thickness of the inner insulation and the outer insulation of the end is increased.

[0026] See also Figure 1-Figure 3When 0.4mm thick mesh cloth is used for 35kV dry-type transformer high-voltage winding winding, z mesh cloths are selected as layer insulation. The stacking thickness of z mesh cloths is (z-1)×0.4×0.7+0.4mm. When the outermost layer of mesh cloth is wound around a wide flat conductor, the conductor cannot fall into the mesh cloth groove, and the layer insulation thickness is (z-1)×0.4×0.7+0.4mm. Narrow flat conductors or round conductors can fall into the mesh cloth groove, and the layer insulation thickness is z×0.4×0.7mm.

[0027] When the number of insulation mesh sheets of 35kV dry transformer high-voltage winding layer is z=2, the enameled round wire film thickness is 0.12mm, the interlayer insulation distance is 2×0.4×0.7+0.12=0.68mm, the inner radius of the winding is Rn=250mm, the radial direction is B=36mm, and the wire diameter is 1.5mm, the number of turns per inner diameter layer is designed to be W n 、Number of turns of outer diameter layer W w , layer insulation capacitance C = 2πε0ε r h / Ln(R2 / R1), the inner and outer diameters of the layer insulation are R1 and R2, the layer insulation height h is proportional to the number of wire turns W, and the dielectric constant is a constant value, then the layer insulation capacitance on the outer diameter side and the inner diameter side is [W w / Ln(284.5 / 283.82)]:[W n / Ln(252.18 / 251.5)]=1.128W w / W n ; then design W w =W n / 1.128, the inner and outer layers of the winding have equal capacitance, in this case W n =16 turns, W w =14, 16 / 14=1.143 is close to 1.128.

[0028] The above calculation takes into account the ratio of reduced turns and rounds up. 1.128 is set as 1.14. Figure 4 In the 35kV high-voltage winding arrangement structure diagram shown in the figure, the high-voltage winding is designed to reduce turns from the inner layer to the outer layer, and the maximum number of turns of a single layer can be reduced by 14%. The first three layers are arranged as W i , after the 3rd level, reduce 7% W i Round to [0.93W i ] turns, outer 3-5 layers reduce 14% W i The turns are rounded to [0.86W i ] turns, and statistics are given for other winding radii and radial dimensions. The winding turn reduction design is related to the radial and single-layer maximum number of turns. The dry-type transformer winding design also takes equal capacitance design as the goal. When the radial is too large or the single-layer maximum number of turns is too much, a larger proportional coefficient can be selected to reduce the turns.

[0029] See also Figure 4, LI285AC120kV 35kV high-voltage winding arrangement structure with high insulation level, adopts equal height design for each section, the winding is divided into n sections, n is 12 sections, small capacity is 14 sections, each section is divided into m layers, the first and last sections are m-2 layers, and the maximum number of turns of each section is W i To meet the LI285AC120kV insulation level, combined Figure 5 The main insulation structure of the 35kV dry-type transformer is designed according to the following requirements, which increases the insulation distance and attenuates the gradient value at the beginning and end.

[0030] When designing by sections and layers, the working field strength between winding layers is controlled to be ≤700V / mm, the thickness of layer insulation is selected, and the capacitance between layers is determined; the working field strength between winding junction sections is controlled to be ≤170V / mm, and the working field strength between normal sections is ≤150V / mm, the insulation distance between sections is selected, and the capacitance between sections is determined; the normal section of the winding is m layers, and 0.5mm mesh cloth is filled to make the inner and outer insulation thickness reach 4.4mm; the first and last sections of the winding are m-2 layers, and the inner and outer insulation is filled with mesh cloth to reach 1 layer of "conductor + layer insulation" thickness, and then 0.5mm mesh cloth is filled 4.4mm, so that the inner and outer insulation of the first and last sections of the winding are 2~3mm thicker than the normal section. The inner and outer insulation of the low-voltage winding is designed to reach 2~3mm.

[0031] For high and low main air channels, consider the air withstand voltage field strength of the factory test power frequency test 0.75-0.85kV / mm, the main air channel air gap A≥120 / 0.85=141mm, set the casing to divide the air gap, increase the power frequency withstand voltage by 30%, consider the 15% margin, the main air channel air gap A≥141×0.85=120mm, take into account the thickness of the winding surface insulation, the main air channel ≥127mm. Correspondingly, the winding air channel air gap E≥120+10mm=130 between high-voltage adjacent phases, take into account the insulation thickness, the phase spacing ≥138mm; the low-voltage winding to the core air gap A0≥10mm, calculate the winding temperature rise correction. Correspondingly, at a site at an altitude of 3,000 meters, the power frequency 85kV test air withstand voltage is (0.75-0.85) / 1.42kV / mm, that is, 0.53-0.6kV / mm, and the main air duct air gap distance is checked to be ≥85 / 0.6×0.85=120mm.

[0032] In the end insulation design, the allowable compressive strength of glass fiber is 1.75kV / mm, and the lightning impulse is converted to the power frequency voltage 255 / 2.5=102kV. The insulation distance of the high-voltage end is Hc1≈102 / 1.75=60mm. Considering the air withstand voltage limit of the upper yoke bare electrode at the power frequency withstand voltage of 0.45kV / mm, the air gap H1 of the high-voltage end insulation to the upper yoke is ≥120 / 0.45-Hc1=210mm. The air gap H2=H1 of the low-voltage end insulation to the upper yoke, and the low-voltage end insulation distance Hc2=Hc2-15=45mm in the structural design.

[0033] Figure 6The main insulation structure design scheme for small-capacity dry-type transformers to cancel the air gaps between high and low main air ducts is as follows: when LI285AC is 120kV, high and low voltage resin air ducts are selected according to the field strength level of 1.4kV / mm during power frequency withstand voltage, the main air duct ≥120 / 1.4=86mm, the winding height and heat dissipation capacity are maintained, and the phase distance is ≥138mm; an end ground screen is set to eliminate the influence of the high voltage of the high-voltage winding on the external electrode, and no umbrella skirt is set from the end to the ground screen surface. The end insulation distance is selected according to the field strength level of 0.6kV / mm during power frequency withstand voltage, the high-voltage end insulation ≥120 / 0.6=200mm, the low-voltage end insulation ≥200-50=150mm, the air gap from the top of the end insulation to the iron yoke ≥85mm, and a pressure block is installed to compact the winding. The outer insulation thickness of the high-voltage winding is 3mm, the first and last sections of the high-voltage winding are flush with the inner diameter of other sections, and the outer insulation thickness of the end section is about 8mm.

[0034] See also Figure 7 , the 35kV high-voltage winding arrangement structure of LI365AC155kV with high insulation level adopts the design of unequal height of each section. The winding is divided into n sections, n is 12 sections, each section is divided into m layers, the first and last 3 sections are m-2 layers, and the number of turns evenly divided by n sections is the maximum number of turns per layer of the normal section. The first and last 3 sections are insulation-reinforced sections, and the maximum number of turns per layer is W1~W3, W n-2 ~W n Close to 1.2 times of the maximum number of turns per layer of the normal section, control the working field strength between winding layers to ≤900V / mm, select the insulation thickness of the reinforced section layer, and determine the capacitance between the reinforced sections; if necessary, only the first and last ends are m-2 layers, and the remaining reinforced sections are also m layers, further increasing the capacitance of the winding end; the maximum number of turns per layer of the middle joint section and other non-reinforced sections is close to 0.8 times of the maximum number of turns per layer of the normal section, and the maximum number of turns per layer of the middle joint section is W h , W h+1 The maximum number of turns per layer of the non-reinforced section can be 1 to 3 more turns than the maximum number of turns per layer of the non-reinforced section to reduce the gap between the tapped current-carrying turns, improve the ampere-turn balance, control the working field strength between the winding layers to ≤600V / mm, select the insulation thickness of the non-reinforced section, and determine the capacitance between the non-reinforced sections; when the capacity is small and n is 14 sections, a normal section transition layer capacitance can be set between the reinforced section and the non-reinforced section, control the working field strength between the winding layers to ≤700V / mm, select the insulation thickness of the normal section, and determine the capacitance between the normal section. In order to meet the LI365AC155kV insulation level, combined with Figure 5 The main insulation structure of the 35kV dry-type transformer shown in the figure is designed according to the following requirements.

[0035] When designing by sections and layers, control the working field strength between the winding connection sections to ≤150V / mm, the working field strength between the normal sections to ≤120V / mm, select the insulation distance between sections, and determine the capacitance between sections; the normal section of the winding is m layers, filled with 0.5mm mesh cloth so that the inner and outer insulation thickness reaches 5, 6mm; the first and last three sections of the winding are m-2 layers, the inner and outer insulation is filled with mesh cloth to reach 1 layer of "conductor + layer insulation" thickness, and then filled with 0.5mm mesh cloth 5, 6mm, so that the inner and outer insulation of the first and last sections of the winding is 2 to 3mm thicker than the normal section. Design the inner and outer insulation of the low-voltage winding to 3 to 4mm.

[0036] For high and low main air channels, consider the air withstand voltage field strength of the factory test power frequency test 0.75-0.85kV / mm, the main air channel air gap A≥155 / 0.85=182mm, set the casing to divide the air gap, increase the power frequency withstand voltage by 30%, consider the 15% margin, the main air channel air gap A≥182×0.85=155mm, take into account the insulation thickness of the winding surface, the main air channel ≥164mm. Correspondingly, the winding air channel air gap E≥155+10mm=165 between high-voltage adjacent phases, take into account the insulation thickness, and the phase spacing ≥178mm; the low-voltage winding to the core air gap A0≥10mm, calculate the winding temperature rise correction. Correspondingly, at a site at an altitude of 5000 meters, the power frequency 85kV test air withstand voltage is (0.75-0.85) / 1.8kV / mm, that is, 0.42-0.47kV / mm, and the main air duct air gap distance is checked to be ≥85 / 0.47×0.85=153mm.

[0037] In the end insulation design, the allowable compressive strength of glass fiber is 1.75kV / mm, and the lightning impulse is converted to the power frequency voltage of 330 / 2.5=132kV. The insulation distance of the high-voltage end is Hc1≈132 / 1.75=75mm. Considering the air withstand voltage limit of the upper yoke bare electrode at the power frequency withstand voltage of 0.45kV / mm, the air gap H1 of the high-voltage end insulation to the upper yoke is ≥155 / 0.45-Hc1=270mm. The air gap H2=H1 of the low-voltage end insulation to the upper yoke, and the low-voltage end insulation distance Hc2=Hc2-20=55mm in the structural design.

[0038] by Figure 6The main insulation structure design scheme for small-capacity dry-type transformers when the air gaps between high and low main air ducts are cancelled, when LI365AC155kV, high and low voltage resin air ducts are selected according to the field strength level of 1.4kV / mm during power frequency withstand voltage, the main air duct ≥155 / 1.4=110mm, maintaining the winding height and heat dissipation capacity, and the phase-to-phase distance ≥138mm. An end ground screen is provided to eliminate the influence of the high voltage of the high-voltage winding on the external electrode. The end insulation distance is selected according to the field strength level of 1.25kV / mm during power frequency withstand voltage. The high-voltage end insulation is ≥155 / 1.25=124mm, and the low-voltage end insulation is ≥124-34=90mm. The ground screen is evenly slotted in the main airway and the middle of the high voltage to reduce the eddy current loss of the leakage magnetic field during load operation. The air gap from the top of the end insulation to the iron yoke is ≥85mm. The outer insulation thickness of the high-voltage winding is 4mm. The first and last sections of the high-voltage winding are flush with the inner diameter of other sections. The outer insulation thickness of the end section is about 10mm. Continuous umbrella skirts are made at the upper and lower ends of the insulation surface to increase the air surface creepage distance from the end to the ground screen by ≥400mm.

[0039] In the embodiments of the present application, "at least one" refers to one or more, and "plurality" refers to two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent the existence of A alone, the existence of A and B at the same time, and the existence of B alone. Among them, A and B can be singular or plural. The character " / " generally indicates that the previous and subsequent associated objects are in an "or" relationship. "At least one of the following" and similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one of a, b and c can be represented by: a, b, c, ab, ac, bc, or abc, where a, b, c can be single or multiple.

[0040] The above is only a specific implementation of the present application. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. The protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A 35kV dry-type transformer high voltage winding structure, characterized in that: The number of turns of the high-voltage winding is divided into n sections, where n is an integer greater than or equal to 12. The n sections of the high-voltage winding are divided into a reinforced section located at the head and end, and a normal section and a tapping section located between the reinforced sections. The number of turns of the reinforced section is reduced compared to the normal section and the tapping section, and the thickness of the inner insulation and the outer insulation of the end is increased.

2. The 35kV dry-type transformer high-voltage winding structure according to claim 1 is characterized in that: When the insulation level of the 35kV dry-type transformer is designed to be LI285AC120kV, the first and last sections of the high-voltage winding are reinforced sections, and the rest are normal sections and tapping sections. The number of turns of the normal section and the tapping section is m, the number of turns of the reinforced section is m-2, and the maximum number of turns of the n-section high-voltage winding is the first number of turns.

3. The 35kV dry-type transformer high-voltage winding structure according to claim 1 is characterized in that: When the insulation level of the 35kV dry-type transformer is designed to be LI365AC155kV, the first three sections and the last three sections of the high-voltage winding are reinforced sections, and the rest are normal sections and tapping sections. The number of turns of the first section and the last section is m-2 layers, the number of turns of the two sections adjacent to the first section and the two sections adjacent to the last section is m or m-2 layers, and the maximum number of turns of each layer of the reinforced section is greater than the first number of turns; the number of turns of the normal section and the tapping section is m layers, the maximum number of turns of each layer is less than the first number of turns, and the maximum number of turns of each layer of the tapping section is 1-3 turns more than that of the normal section.

4. The 35kV dry-type transformer high-voltage winding structure according to any one of claims 1 to 3, characterized in that: The high-voltage winding adopts enameled round wire and is stacked with z sheets of mesh cloth. The wide wire falls outside the mesh, and the narrow wire and round wire fall inside the mesh. When measuring the thickness of the layer insulation, the double-sided turn insulation thickness of the wire is calculated according to the difference between the maximum narrow side size of the insulated wire with turns and the nominal narrow side size of the bare wire.

5. The 35kV dry-type transformer high-voltage winding structure according to claim 4 is characterized in that: The working field strength between the layers of the reinforcement section is controlled to reach a preset range, the number of grid cloth sheets is selected according to the working field strength, and the insulation thickness of the layer is determined.

6. The 35kV dry-type transformer high-voltage winding structure according to claim 5, characterized in that: When the main insulation structure without main air gap is adopted, a ground screen is installed at the end of the winding. When the insulation level is LI365AC155kV, an umbrella skirt is installed at the end.

7. The 35kV dry-type transformer high-voltage winding structure according to claim 5, characterized in that: The insulation level is designed to be LI285AC120kV. When designing in sections and layers, the working field strength between winding layers is controlled to be less than or equal to the first working field strength, the layer insulation thickness is selected and the interlayer capacitance is determined, the working field strength between winding junction sections is controlled to be less than or equal to the second working field strength, the working field strength between normal sections is less than or equal to the third working field strength, the inter-segment insulation distance is selected, and the inter-segment capacitance is determined; the normal section is filled with mesh cloth so that the inner and outer insulation thickness reaches the first thickness; after the inner and outer insulation of the reinforced section is filled with mesh cloth to reach the preset thickness, the mesh cloth is filled again so that the inner and outer insulation of the reinforced section winding is thicker than the normal section.

8. The 35kV dry-type transformer high-voltage winding structure according to claim 5, characterized in that: The insulation level is designed to be LI365AC155kV. When designing in sections and layers, control the working field strength between the winding connection sections to be less than or equal to the fourth working field strength, and the working field strength between the normal sections to be less than or equal to the fifth working field strength. Select the insulation distance between sections and determine the capacitance between sections. Fill the normal section of the winding with mesh cloth so that the inner and outer insulation thickness reaches the second thickness, and fill the inner and outer insulation of the reinforced section with mesh cloth so that the thickness reaches the third thickness. Then fill the mesh cloth so that the inner and outer insulation of the reinforced section is thicker than that of the normal section.

9. The 35kV dry-type transformer high-voltage winding structure according to claim 1, characterized in that: When the small-capacity dry-type transformer cancels the high and low main air gaps and the insulation level is designed to LI285AC120kV, the high and low voltage resin air gaps are selected according to the power frequency withstand voltage field strength level, the main air gap is greater than or equal to the first spacing, the winding height and heat dissipation capacity are maintained, and the phase distance is greater than or equal to the second spacing; the end ground screen is set to eliminate the influence of the high voltage of the high-voltage winding on the external electrode, and no umbrella skirt is set from the end to the ground screen surface. The end insulation distance is selected according to the field strength level during the power frequency withstand voltage, the high-voltage end insulation is greater than or equal to the third spacing, the low-voltage end insulation is greater than or equal to the fourth spacing, and the air gap from the end insulation top to the iron yoke is greater than or equal to the fifth spacing. The pressure block is installed to compact the winding, and the first and last sections of the high-voltage winding are flush with the inner diameter of other sections; The insulation level is designed to be LI365AC155kV. The high and low voltage resin air channels are selected according to the power frequency withstand voltage field strength level. The main air channel is greater than or equal to the sixth spacing to maintain the winding height and heat dissipation capacity, and the phase distance is greater than or equal to the seventh spacing. An end ground screen is set to eliminate the influence of the high voltage of the high-voltage winding on the external electrode. The end insulation distance is selected according to the field strength level during power frequency withstand voltage. The high voltage end insulation is greater than or equal to the eighth spacing, and the low voltage end insulation is greater than or equal to the ninth spacing. The ground screen is evenly slotted in the main air channel and the middle of the high voltage to reduce the eddy current loss of the leakage magnetic field during load operation. The air gap from the top of the end insulation to the iron yoke is greater than or equal to the tenth spacing. The first and last sections of the high voltage winding are flush with the inner diameters of other sections. Continuous umbrella skirts are made on the upper and lower ends of the insulation surface to increase the air surface creepage distance from the end to the ground screen.

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