Transformer winding and method for constructing transformer winding

Abstract

The invention provides a transformer winding and a method for constructing the transformer winding, the transformer winding comprises a leading-out terminal, and the leading-out terminal comprises a leading-out wire of a winding conductor of the transformer winding; the insulating layer wraps the lead-out wire; the grounding shielding layer covers one side, close to the winding conductor, of the insulating layer; the stress slow-release material layer is made of a semi-conductive material, covers one side, far away from the winding conductor, of the insulating layer, and is electrically connected with the grounding shielding layer; wherein the stress sustained-release material layer is matched with the impedance of the insulating layer.

Description

Technical Field

[0001] The present invention relates to the field of transformers, and in particular to a transformer winding and a method for constructing a transformer winding. Background Art

[0002] Compared with the conventional large-volume power frequency transformers that it can replace, medium-voltage high-frequency transformers have higher power density, efficiency and lighter weight. For example, for a 100kW transformer at 50Hz, when its frequency is increased to 20kHz, its volume can be reduced to one percent of the original (reaching the cubic decimeter level), the power density is increased by about one hundred times, and the efficiency will also be slightly improved. These advantages make it have a good prospect in the market of medium-voltage power conversion systems. However, with the increase in power density and the reduction in size of the transformer, its reliability problem has become more prominent, and there is a problem of greatly reduced service life. Since the medium-voltage transformer is the core component of the system and bears almost all the insulation stress of the system, when its power density is increased by a hundred times, the high-voltage winding and the low-voltage winding cannot form an air flash distance due to the reduction in overall size, and a grounding shielding layer must be used, the electrical stress generated at the terminal of the high-voltage winding surges, and its insulation layer is more likely to fail due to electrical aging caused by partial discharge, which eventually becomes the main factor leading to long-term failure of the transformer. Therefore, it is necessary to control the electrical stress of the insulation layer of the transformer to reduce the occurrence of partial discharge and increase the service life of the transformer. Summary of the invention

[0003] Based on the above problems in the prior art, the present invention provides a transformer winding, which includes an output terminal, and the output terminal includes:

[0004] Lead wires of winding conductors of the transformer winding;

[0005] An insulating layer covering the lead wire;

[0006] a grounded shielding layer covering a side of the insulating layer close to the winding conductor; and

[0007] A stress relief material layer, which is a semi-conductive material, covers a side of the insulating layer away from the winding conductor and is electrically connected to the ground shielding layer;

[0008] Wherein, the stress relief material layer and the insulation layer are impedance matched.

[0009] In one embodiment, the stress relief material layer is made of a nonlinear resistance material, a high dielectric material or a medium resistance semiconductive material.

[0010] In one embodiment, the material of the stress relief material layer is a nonlinear resistor material, and the characteristic conductivity range of the nonlinear resistor material is 10 -12-10 -8 S / m, and the nonlinear coefficient range is 1-15mm / kV.

[0011] In one embodiment, the stress relief material layer is made of a high dielectric material with a dielectric constant ranging from 20 to 30.

[0012] In one embodiment, the material of the stress relief material layer is a medium-resistance semiconductive material, and the conductivity range of the medium-resistance semiconductive material is 10 -8 -10 -5 S / m.

[0013] In one embodiment, the stress relief material layer overlaps the ground shielding layer.

[0014] In one embodiment, the overlap length is not less than 5 mm.

[0015] In one embodiment, the outlet terminal further comprises an insulating tape which is bound to the end of the stress relief material layer away from the winding conductor to fix the stress relief material layer.

[0016] In one embodiment, the outlet terminal further includes a protective layer, which is coated on the outermost side of the outlet terminal.

[0017] In one embodiment, the protective layer has an umbrella skirt structure.

[0018] In one embodiment, the protective layer is an insulating tape or a cold shrink protective sleeve.

[0019] In one embodiment, the stress relief material layer is a stress relief tape or a stress relief coating.

[0020] The present invention also provides a method for constructing the above transformer winding, the method comprising:

[0021] Determine the minimum length of the outgoing terminal based on the minimum creepage distance under the design voltage;

[0022] Based on the finite element analysis method, the surface electric field intensity distribution of the outgoing line end under different stress relief material layer lengths is obtained based on the characteristic conductivity, nonlinear coefficient, dielectric constant, thickness of the stress relief material layer, and the thickness of the insulating layer;

[0023] The shortest length of the stress relief material layer is obtained so that the surface electric field intensity at the outlet end is less than the upper limit threshold.

[0024] The transformer winding and the method for constructing the transformer winding in the present invention electrically connect the stress relief material layer at the ground shielding layer of the outlet terminal, so that the surface potential of the outer surface of the outlet terminal changes more slowly and the surface electric field intensity is smaller, thereby reducing the electric field distortion. When used, the stress relief material can be directly wrapped or painted on the surface of the insulation layer without the need for a complex geometric structure, and the power density loss is small. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Shown is a schematic diagram of the triple junction effect in an insulating system.

[0026] Figure 2A A schematic diagram of a transformer winding in the prior art is shown.

[0027] Figure 2B Shows Figure 2A Schematic diagram of the cross section of the transformer winding along line AA'.

[0028] Figure 2C Shows Figure 2B Schematic diagram of the cross section in the figure.

[0029] Figure 3 A schematic diagram of the electric field distortion at the ground shielding layer is shown.

[0030] Figure 4 The one-dimensional equivalent link model of the outgoing line end is shown.

[0031] Figure 5 The transformer winding according to one embodiment of the present invention is shown along Figure 2A A schematic plan view of a cross section along line AA' is shown.

[0032] Figure 6 A cross-sectional schematic diagram of a transformer winding according to a second embodiment of the present invention is shown.

[0033] Figure 7 A cross-sectional schematic diagram of a transformer winding output terminal according to a third embodiment of the present invention is shown.

[0034] Figure 8 A cross-sectional schematic diagram of a transformer winding output terminal according to a fourth embodiment of the present invention is shown.

[0035] Fig. 9 A flow chart of a method for constructing a transformer winding output terminal according to an embodiment of the present invention is shown.

[0036] Fig.10 The electric field distribution at the outlet end without stress relief material and two typical stress relief materials at 18 kV is shown.

[0037] Fig.11The potential distribution of the outlet terminal without stress relief material and containing two typical stress relief materials at 18 kV is shown.

[0038] Fig.12 The electric field distribution at the outlet of two typical stress relief materials at 35 kV is shown.

[0039] Fig.13 The potential distribution of the outlet terminals of two typical stress relief materials at 35 kV is shown. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention will be further described in detail below through specific embodiments in conjunction with the accompanying drawings. It should be noted that the embodiments given in the present invention are only for illustration and do not limit the scope of protection of the present invention.

[0041] The main components of the transformer are high-voltage windings, low-voltage windings and iron cores. Partial discharge generally occurs in the high-voltage winding part, including partial discharge in the insulation layer and air corona discharge at the interface of the insulation layer. Among them, partial discharge in the insulation layer is mainly caused by defects in the casting process. Generally, a shielding layer of semiconductor material is added to the insulation layer to reduce the electric field strength in the insulation layer to avoid partial discharge caused by bubbles in the insulation layer. Air corona discharge at the interface of the insulation layer is mainly caused by the triple junction effect of the insulation system, such as Figure 1 As shown, when the medium at the interface of the insulating structure has a large difference in dielectric constant, the equipotential lines at the interface will bend. When the curvature of the bend is too large, that is, the electric field strength exceeds the corona triggering threshold of the air, corona discharge will occur. The generated heat and electrochemical changes will damage the insulating layer and accelerate the aging and failure of the insulating layer.

[0042] In order to prevent corona discharge, the common practice is to attach a grounded semi-conductive material layer to the outside of the insulating layer interface, thereby reducing the difference in dielectric constant at the interface and shielding the electric field of the main insulating layer, reducing the electric field strength at the interface to zero. Figure 2A shows a schematic diagram of a transformer winding in the prior art, Figure 2B Shows Figure 2A Schematic diagram of the cross section of the transformer winding along line AA', Figure 2C Shows Figure 2B Schematic diagram of the cross section in the figure. Figure 2A-2CAs shown, the transformer winding includes an annular winding portion 201, an outlet terminal 202 and a connection terminal 203. The annular winding portion 201 includes a winding conductor 204, an insulating layer 206 covering the winding conductor 204, and a grounding shielding layer 207 covering the insulating layer 206. The outlet terminal 202 includes a lead wire 205, an insulating layer 206 covering the lead wire 205, and a grounding shielding layer 207 partially covering the insulating layer 206. The connection terminal 203 is used to connect to an external power source or a load.

[0043] However, at the outlet terminal 202, since a suitable distance must be maintained between the ground shielding layer 207 and the terminal 203 to prevent terminal discharge, there is still electric field distortion due to the triple junction effect at the interface of the insulating layer exposed to the air at the end of the ground shielding layer 207, such as Figure 3 shown.

[0044] The peak value of the electric field along the surface of the insulation layer at the outgoing line end is located near the end of the grounded shield layer, which is caused by the rapidly rising surface potential. Figure 4 FIG. 4 shows a one-dimensional equivalent link model of the outgoing line end, showing a ground shielding layer 407, an insulating layer 406 and an outgoing line 405. test is the test or operating voltage value, C iso is the volume capacitance of the insulating layer per unit length, Z air is the impedance of the thin layer of air per unit length. The relative dielectric constant of air is about 1, and the resistivity is about 3×10 13 Ω·m, so the impedance of air is Z air It can be equivalent to its capacitance C air The relative dielectric constant of the insulating layer 406 is about 4, and the resistivity is more than 10 16 Ω·m, can also be simplified into a capacitor structure, and compared to air, C iso >C air Therefore, the impedance of the thin air layer with a smaller capacitance in the series capacitor structure is larger, which causes the voltage along the surface of the insulating layer 406 to rise rapidly, resulting in the distortion of the electric field distribution and a sudden increase in the field strength. Therefore, the inventors found that in order to relieve the electrical stress along the surface of the insulating layer, on the one hand, the equivalent impedance of the insulating layer can be increased, that is, the insulating layer capacitance C can be reduced. iso On the other hand, the impedance of the surface layer (i.e., the layer in contact with the insulating layer, such as the air layer) can be reduced to achieve impedance matching between the two, thereby reducing the speed of potential drop, reducing the electric field strength along the surface, and reducing electric field distortion.

[0045] Figure 5 The transformer winding according to one embodiment of the present invention is shown along Figure 2AA schematic plan view of the cross section of line AA' shown. The transformer winding includes a ring-shaped winding portion 501, an outlet terminal 502 and a terminal 503. The ring-shaped winding portion 501 includes a winding conductor 504, an insulating layer 506 covering the winding conductor 504 and a grounding shielding layer 507 covering the insulating layer 506. The outlet terminal 502 includes a lead wire 505 of the winding conductor 504; an insulating layer 506 covering the lead wire 505; a grounding shielding layer 507 covering a side of the insulating layer close to the winding conductor; a stress relief material layer 508 covering a side of the insulating layer away from the winding conductor and electrically connected to the grounding shielding layer 507, wherein the stress relief material layer is impedance matched with the insulating layer. The terminal 503 is used to connect to an external power supply or a load. By means of the stress relief material layer 508 electrically connected to the ground shielding layer 507, the impedance of the surface layer can be effectively reduced, and impedance matching between the stress relief material layer and the ground shielding layer can be achieved, thereby reducing the speed of change of the surface potential of the insulating layer, reducing the surface electric field strength, and reducing the electric field distortion. In the present invention, the term "along the surface" is used to describe the outer surface of the outlet terminal 502. The term "impedance matching" in the present invention is used to describe the impedance matching between the stress relief material layer and the insulating layer so as to avoid the electric field distortion caused by the triple junction effect at the interface of the insulating layer.

[0046] The stress relief material layer includes electrical stress relief (Stress Grading, SG) material, which is a semi-conductive material, including but not limited to non-linear resistance material, high dielectric material, medium resistance semi-conductive material.

[0047] The electrical conductivity of the stress relief material can be described as:

[0048] σ SG (E) = σ * ×e |E|×β (1)

[0049] where σ SG (E) is the conductivity of the stress relief material when the electric field strength is E, |E| is the modulus of the electric field strength, the characteristic conductivity σ* is the conductivity when the external electric field is 0, and β is the nonlinear coefficient. For nonlinear resistance materials, the nonlinear coefficient β is not zero, and the conductivity of the stress relief material increases with the increase of the electric field. For high dielectric materials and medium resistance semiconductive materials, the nonlinear coefficient β is equal to zero, and the conductivity of the material does not change with the electric field environment.

[0050] In one embodiment, the characteristic conductivity σ* of the nonlinear resistor material is in the range of 10 -12 -10 -8 S / m, nonlinear coefficient β ranges from 1-15mm / kV, such as silicon carbide and zinc oxide.

[0051] In one embodiment, the dielectric constant of the high dielectric material is in the range of 20-30.

[0052] In one embodiment, the conductivity σ of the medium-resistance semiconducting material is SG Range is 10 -8 -10 -5 S / m.

[0053] In one embodiment, the stress relief material layer can be a stress relief tape or a stress relief coating. The stress relief tape is half-wound on the surface of the insulation layer of the outlet terminal or the stress relief coating is coated on the surface of the insulation layer of the outlet terminal and is electrically connected to the ground shielding layer. For the non-sticky stress relief tape, after winding, the gap is filled with epoxy resin vacuum impregnation. In one embodiment, the length of the stress relief material layer ranges from 5 to 15 cm.

[0054] In one embodiment, the winding conductor is a Litz wire, a copper foil or an enameled rectangular wire.

[0055] In one embodiment, the ground shield layer is a semi-conductive coating or a semi-conductive tape with a resistivity in the range of 10 -1 -10 4 Ω*m.

[0056] In one embodiment, the insulating layer comprises an inter-turn insulating layer of the winding conductor, and an insulating tape wrapping layer and an insulating casting layer outside the winding conductor.

[0057] In the above embodiments, the transformer winding only shows an insulating layer and a grounding shielding layer, but those skilled in the art should understand that in actual applications, the transformer may include other layers. For example, in patent CN114792598A, the annular winding portion and the outlet terminal of the transformer winding include a first insulating layer, a first semi-conductive layer, a second insulating layer and a second semi-conductive layer (i.e., a grounding shielding layer), and such an annular winding portion and the outlet terminal structure are also within the protection scope of the present invention. That is, in the present invention, the term "coating" includes direct coating and indirect coating through other layers.

[0058] Figure 6 FIG. 4 shows a cross-sectional schematic diagram of a transformer winding according to a second embodiment of the present invention. Figure 5 The same parts are not repeated here. In this embodiment, the stress relief material layer 608 covers the side of the insulating layer 606 away from the winding conductor, and overlaps with the ground shielding layer 607 to ensure electrical connection. The stress relief material layer 608 can be overlapped on the outside of the ground shielding layer 607, or overlapped between the ground shielding layer 607 and the insulating layer 606. In one embodiment, the overlap length is not less than 5 mm, preferably not less than 1 cm.

[0059] Figure 7A cross-sectional schematic diagram of a transformer winding output terminal according to a third embodiment of the present invention is shown.

[0060] The lead-out terminal includes a lead-out wire 705 of a winding conductor; an insulating layer 706 covering the lead-out wire 705; a grounding shielding layer 707 covering the side of the insulating layer close to the winding conductor; a stress relief material layer 708 covering the side of the insulating layer away from the winding conductor and overlapping the grounding shielding layer 707 to ensure electrical connection; an insulating tape 709 tightly bound to the end of the stress relief material layer 708 away from the winding conductor for fixing the stress relief material layer 708; and a protective layer 710 covering the outside of the stress relief material layer 708 and the insulating tape 709 for protecting the stress relief material layer 708 to prevent wear and aging. In one embodiment, the protective layer is an insulating tape or a shrink protective sleeve. In an embodiment where the stress relief material layer 708 can be fixed to the insulating layer 706, the insulating tape 709 can also be omitted.

[0061] Figure 8 A cross-sectional schematic diagram of a transformer winding output terminal according to a fourth embodiment of the present invention is shown.

[0062] Among them, Figure 7 The same parts are not repeated here. In this embodiment, the protective layer 810 has an umbrella skirt structure to increase the creepage distance between the ground shielding layer and the wiring terminal of the transformer winding. The creepage distance is the shortest path between two conductive parts or between a conductive part and the protective interface of the equipment measured along the insulation surface.

[0063] Fig. 9 A flow chart of a method for constructing a transformer winding outlet terminal according to an embodiment of the present invention is shown, the method comprising:

[0064] Step 901: Determine the minimum length of the outlet terminal based on the minimum creepage distance under the design voltage.

[0065] Step 902: Based on the finite element analysis method, the characteristic conductivity σ*, nonlinear coefficient β, dielectric constant ε, thickness D of the stress relief material layer sg , and the thickness of the insulation layer D iso , obtain different stress relief material layer lengths L sg The electric field intensity distribution along the surface of the outgoing line end.

[0066] Step 903: Obtain the shortest length of the stress relief material layer so that the electric field intensity along the surface of the outlet end is less than the upper limit threshold.

[0067] Specifically, the maximum value of the electric field strength along the surface of the outlet end is compared with the upper limit threshold of the field strength. If the maximum value of the electric field strength is greater than the upper limit threshold, the length L of the stress relief layer needs to be further increased.sg , until the maximum value of the surface electric field intensity is less than the upper threshold value, and the shortest length of the stress relief material layer is obtained.

[0068] Fig.10 The electric field distribution of the outlet end without stress relief material and two typical stress relief materials at 18kV is shown. It shows the electric field intensity along the surface of the outlet end, which is Fig.10 It can be seen that the electric field intensity along the surface of the outlet end including the stress relief material layer is smaller. Fig.11 The figure shows the potential distribution of the output terminal without stress relief material and containing two typical stress relief materials at 18kV. Fig.11 It can be seen that the rate of change of the surface potential of the outlet end including the stress relief material layer is slower and the electric field distortion is smaller.

[0069] Fig.12 The figure shows the electric field distribution of the outlet end of two typical stress relief materials at 35kV. It shows the electric field intensity along the surface of the outlet end. Fig.12 It can be seen that the electric field intensity along the surface of the outlet end including the stress relief material layer is very small. Fig.13 The figure shows the potential distribution of the outlet terminals of two typical stress relief materials at 35kV. Fig.13 It can be seen that the rate of change of the surface potential of the outlet end including the stress relief material layer is very slow, and the electric field distortion is smaller.

[0070] In one embodiment, the transformer winding outlet terminal and the method for constructing the transformer winding outlet terminal in the present invention are mainly applied to a voltage range of 10-35KV.

[0071] The transformer winding and the method for constructing the transformer winding in the present invention electrically connect the stress relief material layer at the ground shielding layer of the outlet terminal, so that the surface potential of the outer surface of the outlet terminal changes more slowly and the surface electric field intensity is smaller, thereby reducing the electric field distortion. When used, the stress relief material can be directly wrapped or painted on the surface of the insulation layer without the need for a complex geometric structure, and the power density loss is small.

[0072] Although the present invention has been described through preferred embodiments, the present invention is not limited to the embodiments described herein but includes various changes and modifications that may be made without departing from the scope of the present invention.

Claims

1. A transformer winding, comprising an output terminal, wherein the output terminal comprises: Lead wires of winding conductors of the transformer winding; An insulating layer covering the lead wire; A grounded shielding layer covering a side of the insulating layer close to the winding conductor; as well as A stress relief material layer, which is a semi-conductive material, covers a side of the insulating layer away from the winding conductor and is electrically connected to the ground shielding layer; Wherein, the stress relief material layer and the insulation layer are impedance matched.

2. The transformer winding according to claim 1, wherein: The material of the stress relief material layer is a nonlinear resistance material, a high dielectric material or a medium resistance semiconductive material.

3. The transformer winding according to claim 2, wherein: The material of the stress relief material layer is a nonlinear resistor material, and the characteristic conductivity range of the nonlinear resistor material is 10 -12 -10 -8 S / m, and the nonlinear coefficient range is 1-15mm / kV.

4. The transformer winding according to claim 2, wherein: The material of the stress relief material layer is a high dielectric material, and the dielectric constant thereof is in the range of 20-30.

5. The transformer winding according to claim 2, wherein: The material of the stress relief material layer is a medium-resistance semi-conductive material, and the conductivity range of the medium-resistance semi-conductive material is 10 -8 -10 -5 S / m.

6. The transformer winding according to claim 1, wherein: The stress relief material layer overlaps the ground shielding layer.

7. The transformer winding according to claim 6, wherein: The overlap length is not less than 5 mm.

8. The transformer winding according to claim 1, wherein: The outlet terminal also includes an insulating tape, which is bound to the end of the stress relief material layer away from the winding conductor and is used to fix the stress relief material layer.

9. The transformer winding according to claim 1 or 8, wherein: The outlet terminal also includes a protective layer, which is coated on the outermost side of the outlet terminal.

10. The transformer winding according to claim 9, wherein: The protective layer has an umbrella skirt structure.

11. The transformer winding according to claim 9, wherein: The protective layer is an insulating tape or a cold shrink protective sleeve.

12. The transformer winding according to claim 1, wherein: The stress relief material layer is a stress relief tape or a stress relief coating.

13. A method for constructing a transformer winding according to any one of claims 1 to 12, the method comprising: Determine the minimum length of the outgoing terminal based on the minimum creepage distance under the design voltage; Based on the finite element analysis method, the surface electric field intensity distribution of the outgoing line end under different stress relief material layer lengths is obtained based on the characteristic conductivity, nonlinear coefficient, dielectric constant, thickness of the stress relief material layer, and the thickness of the insulating layer; The shortest length of the stress relief material layer is obtained so that the surface electric field intensity at the outlet end is less than the upper limit threshold.

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