Capacitive bushing

Abstract

The present disclosure relates to a capacitive bushing comprising a capacitor core (1) and electrically conductive field grading layers (3) embedded in the insulating material of the capacitor core (1) and arranged around a central passage of a conductor (2) extending along an axis defining an axial direction, while an electrical connection (6) is provided to at least one of the field grading layers (3), wherein pairs of adjacent field grading layers (3) and the insulating material between the pairs of adjacent field grading layers form segments of the capacitor core having an axial length L1 to L n and a capacitance C1 to C n characterized in that the shape of at least one of the field grading layers (3) deviates from a cylindrical shape in order to reduce the inhomogeneity of the electric field stress of the capacitive bushing compared to a corresponding capacitive bushing with cylindrical field grading layers of the segments having an axial length L1 to L n and a capacitance C1 to C n ​

Description

Technical Field

[0001] The subject of this disclosure is a capacitor bushing suitable for power engineering. Background Technology

[0002] High-voltage bushings are primarily used to carry high-potential currents from the active portion of a first high-voltage component (such as a transformer, generator, or circuit breaker) through a barrier (e.g., the grounded casing of the first component) to a second high-voltage component (such as a high-voltage overhead line or high-voltage cable termination). These high-voltage bushings are used in switchgear installations (such as gas-insulated switchgear GIS or air-insulated switchgear AIS), power or distribution transformers, or in high-voltage rotating machinery (such as generators) for voltage levels ranging from a few kV to hundreds of kV and exceeding 1000 kV. To reduce and control the electric field, high-voltage bushings include capacitor cores that facilitate electric field stress control. Capacitive bushings can also be used as part of the high-voltage insulation system for cable terminations or instrument transformers or instrument transformers.

[0003] As shown in Figure 1, a typical capacitive bushing for medium- or high-voltage applications includes a capacitor core (1) having multiple concentric, cylindrical conductive field-grading layers (3) arranged around a central conductor (2) embedded in an insulating material. The innermost field-grading layer of the capacitor core is electrically connected to the bushing conductor via a high-voltage connection (5). One and / or the outermost field-grading layer is electrically connected to a ground potential via a ground connection (6). The connection to the ground potential is typically made via a metal flange (4) for mechanically securing the bushing to a grounding device. The insulating material between the field-grading layers (3) and the field-grading layers forms a capacitive voltage divider that applies a total voltage U to the capacitor core to fix and define a portion of U. i Distributed between field-grading layers. Each pair of adjacent field-grading layers (3) and the insulating material between that pair of adjacent field-grading layers form the capacitor core having a capacitance C. i The section. Each voltage section U i The reciprocal of the segment capacitance 1 / C i The voltages are proportional, and the sum of these parts equals the total voltage U. As a result, the electric field generated by the high voltage is distributed in a controlled manner along the axis of the bushing (axial field stress) on the inner side of the capacitor core in the radial direction (radial field stress) and on the outer side near the outer surface of the bushing. The capacitor core shown in Figure 1 has four segments, and any number of n segments can typically be applied.

[0004] Modern capacitive bushings are typically manufactured by winding spacer material around a mandrel or conductor and inserting conductive field-grading layers (foils) between the layers of spacer material. Alternatively, the field-grading layers can be printed directly onto the surface of the spacer material using conductive ink. This structure is then impregnated with a curable resin, which subsequently hardens. This method only allows for the production of cylindrical field-grading layers. However, additive manufacturing methods allow for improvements in the characteristics of capacitive bushings.

[0005] WO 1980000762 A1 discloses a high-voltage gas-filled insulating bushing having an outer ceramic weather-resistant shell with a central elongated conductor extending through the shell. The interior of the bushing is at least partially filled with modules, which may contain capacitance grading layers to classify dielectric stresses on the outer surface of the bushing, thereby allowing for a smaller bushing size for the same electrical load. GB 339227 A shows a capacitor-type insulator comprising a layer of metal foil embedded in an insulating material. The ends of the foil are folded once or multiple times to reduce the intensity of dielectric stresses near the foil edges. US4370514 A shows an insulating bushing with a central conductor. The insulator body is arranged concentrically around the conductor such that the capacitances of all segments formed by the field grading layers are equal. EP 0 085 966 ​​A1 relates to a bushing for gas-insulated electrical equipment, and includes a bushing in which a conductor passes through a ceramic tube having a mounting flange connected to a section of the ceramic tube, and wherein a main electrode concentric with the conductor is embedded between layers of an insulating member that isolates the outer periphery of the conductor. GB 953642 A shows an insulating bushing having a potential control plate embedded in a resin casting. The casting has a channel extending from the interior of the casting to the inner surface of the control plate to allow high-pressure gas to enter any gaps formed by differential expansion between the control plate and the resin of the casting. The control plate may have holes aligned with the ends of the channels in the resin casting, allowing the use of locating pins during the casting process, and has beaded reinforcing edges. US 2019 / 311822 A1 relates to the use of additive manufacturing to form articles, and more specifically, but not exclusively, to the use of additive manufacturing processes to form articles such as capacitive bushings, block-type bushings, or other articles. US 2019 / 389126 A1 discloses a method for producing an electrical device having an insulator by additive manufacturing, in which a polymer insulating material is applied to form a part of the device. The method further includes subjecting the insulator to high temperature and pressure for a predetermined time period in a subsequent consolidation step to solidify the insulator.

[0006] The main problem to be solved is reducing the diameter of the capacitor bushing.

[0007] Another problem is the electrical connections in the field-grading layers, each of which includes conductors bonded to the layer using conductive adhesive. These connections are complex in structure, prone to manufacturing errors, and generate relatively high inductance.

[0008] Another problem is the enhanced electric field at the surface of the capacitor core due to the sharp edges of the field grading layer near the surface. To minimize this enhancement, a thick over-build layer of insulating material is needed to cover the edges of the field grading layer over the entire axial distance adjacent to the edges. Due to the typically wide tolerances in both the radial and axial positions of the foil during capacitor core manufacturing, this over-build thickness must be even greater. Summary of the Invention

[0009] Figure 1 shows a capacitive bushing with cylindrical field-grading layers (foils). To generate potentially uniform gradations of the electric field in both the axial and radial directions, the interlayer spacing δ1' to δ... n 'and the axial length of the section L1 to L n They must be adjusted accordingly. For example, they are adjusted so that the capacitance C1 to C of the segment formed by the capacitor core is thus reduced. n Equal. This results in equal voltage distribution across the segments of the capacitor core, and when the axial length of the segments is linearly distributed, it leads to substantially uniform axial field stress across all segments. However, the interlayer spacing δ i 'They are usually not equal, and the field stress values ​​in the radial direction between the foils are also not equal. This field stress value is the segment voltage U.' i Interlayer spacing δ i The ratio of ' to ''. This means that only one or two segments can be stressed to the maximum permissible value. Other segments are understressed, meaning the capacitor core diameter is larger than the possible optimal value. The problem is concentrated at the sharp edges at the axial ends of the layers, which locally amplifies the field stress and makes the field in each individual segment highly non-uniform in distance between the edge of the foil and the adjacent foil in that segment. Due to this non-uniformity, the edge regions of the foil are most susceptible to electrical breakdown between layers. To avoid this breakdown, the capacitor core must be designed such that for each segment, the voltage U of that segment is ''. i The ratio of the radial width of the segment at its end (i.e., at the edge of the shorter layer along the axial direction of the segment) is less than the defined safety design limit. Throughout the description of this invention, this ratio will be referred to as the average edge field stress. For a capacitor core with cylindrical layers, the radial segment width at the layer edge (i.e., at the axial end of the segment) is equal to the interlayer spacing δ. i ', but usually not necessary, and throughout the description of this invention, we will use the name δ i 'or δ iThe radial width of the segment at its axial end is used to represent the width of the section. Typically, this width can differ at the two axial ends of the segment; in this description, we discuss only one end, but the invention equivalently relates to the second end. Due to the sharp edges of the layers, the safe design value for the average edge field stress is strongly limited, meaning that the design must have a relatively large δ. i ', and therefore the overall diameter of the casing is relatively large.

[0010] Using additive manufacturing technology, in which the insulating material forming the capacitor core and the conductive material forming the field hierarchical layer can be deposited layer by layer in a controlled manner at defined locations on the accumulated surface of the manufactured capacitor core, the problems of unequal stress across all sections and strong limitations on average edge field stress are solved by providing a capacitor core with a sheath of non-cylindrical, curved field hierarchical layers. In this way, additive manufacturing allows for optimized field stress distribution in the capacitor core, potentially leading to a reduction in the capacitor core diameter and correspondingly reducing material usage, processing time, and component costs.

[0011] In one example, the shape of the field grading layer is configured such that the difference between the average edge field stress values ​​of the segments is reduced, or that all average edge field stress values ​​are equal. For example, one field grading layer is formed in a segment of a cylindrical layer in an optimized design where the stress is set to the maximum, reaching the safety design limit. The shape of this field grading layer is configured such that the interlayer spacing of this segment is maintained over most of the layer surface area, but the interlayer spacing increases in the region near the edge of the second layer forming this segment. In this way, the voltage of this segment remains substantially constant, but the average edge field stress of this segment decreases. Simultaneously, the average edge field stress of adjacent segments increases, but does not reach the safety design limit. This change allows all interlayer spacings of the capacitor core to be reduced proportionally, and thereby reduces the total diameter of the capacitor core until the maximum average edge field stress again reaches the safety design limit. In this way, optimization of all layers can also make the average edge field stress substantially equal for all segments, thereby allowing a significant reduction in the total diameter of the capacitor core.

[0012] In another example, the edges of the field-grading layers curve outward, reducing the concentration of the electric field at the axial ends of the segment and making the field stress values ​​more uniform along the paths between layers near the edges. As the field stress becomes more uniform, the breakdown voltage of the segment becomes greater, and therefore the safe design limit for the average edge field stress value can be set at a higher point. This allows for a significant reduction in the interlayer spacing, and thus allows for a reduction in the overall diameter of the capacitor core.

[0013] Furthermore, additive manufacturing technology can provide electrical connections that are integral parts of the field-grading layer, formed into a substantially axially symmetrical shape, with a volume of conductive material extending from the layer to the outer or inner surface of the capacitor core. This simplifies the connection's structure because it uses fewer components and requires no additional manufacturing processes compared to those used to produce the insulating layer and field-grading layer of the core. It also results in a significantly lower inductance compared to connections made at a single point using wires.

[0014] Furthermore, additive manufacturing allows for the shaping of the outer surface of the capacitor core, enabling the over-construction thickness of the insulating material at the edges of the field-grading layers to be greater than the thickness in the sections between the edges. In contrast to current spacer winding, impregnation, and curing manufacturing techniques, additive manufacturing allows for precise synchronization of the position of the layer edges and the position of the protruding portions of the capacitor core's external shape. Therefore, the problem of electric field enhancement at the surface of the capacitor core can be addressed using a minimal amount of insulating material, applied only where a reduction in the surface electric field is desired.

[0015] This disclosure relates to a capacitive bushing comprising a capacitor core (1) and conductive field-grading layers (3), the conductive field-grading layers being embedded in an insulating material of the capacitor core (1) and arranged around a central channel of a conductor (2) extending along an axis defining an axial direction, while an electrical connection (6) is provided to at least one of the field-grading layers (3), wherein an insulating material between a pair of adjacent field-grading layers (3) and the pair of adjacent field-grading layers forms an axial length L1 to L2. n And has capacitors C1 to C n The capacitor core section wherein at least one of the field grading layers (3) has a shape deviating from a cylindrical shape in order to have a forming axial length L1 to L n And has capacitors C1 to C n Compared to the corresponding capacitive bushing of the cylindrical field grading layer in the section, the non-uniformity of the electric field stress of the capacitive bushing is reduced, wherein the shape of at least one field grading layer in the field grading layer (3) is configured such that the diameter of the field grading layer (3) varies along the axial direction, characterized in that the diameter of the field grading layer (3) has at least one maximum value between the edges of the field grading layer (3).

[0016] The capacitive bushing may also include any of the following features or any technically feasible combinations of these features:

[0017] • The shape of at least one field classification layer in the field classification layer (3) is configured such that the diameter of the field classification layer varies along the axial direction;

[0018] The diameter of the field grading layer (3) has at least one maximum value between the edges of the field grading layer (3).

[0019] The average edge field stress level is limited to the voltage U of the section. i The radial width δ of the section at the end of the section, i.e. at the edge of the shorter axial field-grading layer of the section. i The ratio; the average edge field stress level in at least one segment formed by a non-cylindrical field gradation layer is less than that of segments having the same capacitance C1 to C2. n and the same axial length L1 to L n The average edge field stress level in the corresponding section of the capacitive bushing of the cylindrical field grading layer in the section;

[0020] · absolute value ratio The absolute value is at least 20% smaller, of which and It is the average edge field stress level of two adjacent sections, where at least one section is formed by a non-cylindrical field hierarchy; and and It is the average edge field stress level of two corresponding adjacent sections of the corresponding capacitive bushing with a cylindrical field grading layer;

[0021] • The radial widths of the sections at their axial ends are substantially equal;

[0022] • The innermost grading layer and / or the outermost grading layer are cylindrical;

[0023] • The capacitance of all segments formed by the field-grading layer (3) is equal;

[0024] • At least one edge of at least one field grading layer (3) is bent outward relative to the axis;

[0025] • The radius of curvature of the curved edge of the field grading layer is equal to at least three layer thicknesses, preferably at least five layer thicknesses;

[0026] • At least one potential connection (5, 6, 7) is an integral part of the field hierarchical layer (3) and has a substantially axially symmetrical shape, wherein the volume of conductive material extends from the field hierarchical layer to the outer or inner surface of the capacitor core (1).

[0027] • The shape of the capacitor core (1) is configured such that the thickness of the insulating material between each edge of the adjacent field leveling layer (3) and the outer surface of the capacitor core (1) is greater than the thickness of the insulating material between the midpoint between the edges of the adjacent field leveling layer (3) and the outer surface of the capacitor core (1).

[0028] This disclosure also relates to the use of additive manufacturing methods to manufacture capacitor bushings. Attached Figure Description

[0029] The exemplary embodiment depicts a capacitive bushing, wherein the figures are presented in cross-section:

[0030] Figure 1 – Existing capacitor bushing;

[0031] Figure 2 —First embodiment;

[0032] Figure 3 —Second embodiment;

[0033] Figure 4 and Figure 5 —Including capacitor bushings for electrical connections,

[0034] Figure 6 —Including capacitive sleeves on the surface of insulating material at the edge of the field gradation layer. Detailed Implementation

[0035] Using additive manufacturing methods to manufacture casings allows for the fabrication of field-grade layers of arbitrary shapes (3). Figure 2 An example of such a sleeve is shown. In this embodiment, the shape of the field grading layer is configured such that the radial width δ of all segments at their ends is... i The innermost and outermost layers are cylindrical. The shapes of the other layers are configured such that the capacitance of all segments is also equal. This makes the average edge field stress value equal in all segments, all reaching the safety design limit, and allows the overall diameter of the capacitor core to be significantly smaller than an equivalent design with cylindrical layers, in which the average edge field stress value reaches the safety design limit only in one or two segments.

[0036] In the design shown in the attached figure, the equivalent grading system formed by the cylindrical field grading layers has all segments with the same capacitance C1 to C4 and the same axial length L1 to L4 of the layers. Segment C4 will be the only segment with an average edge field stress level that reaches the safety design limit. In the grading system, by forming the inner layer of segment C4 into a non-cylindrical shape, the edge width δ4 of this segment is increased compared to the cylindrical design. In this way, the average edge field stress level of this segment is reduced, and the radial dimension of the set of all layers can be scaled down to a smaller diameter, thereby bringing the average edge field stress value of segment C4 back to the safety design limit. In this way, the diameter of the capacitor core can be made smaller than the diameter of the capacitor core manufactured according to known technology. The diameter of the field grading layer (3) has at least one maximum value between the edges of the field grading layer (3). Therefore, the capacitance between adjacent field grading layers (3) can be changed by adjusting the position, width, or amplitude of the maximum value of each field grading layer (3). In this way, the distance between adjacent field hierarchical layers can be adjusted, and thus the capacitance and average edge field stress are also adjusted. Since the maximum value of the field hierarchical layer (3) reduces the distance between adjacent field hierarchical layers (3), a stronger electric field is stored at this maximum value, thus reducing the electric field strength at the edges. Figure 2 In the illustrated embodiment, the maximum value of the field grading layer (3) has been designed such that, with increasing distance from the capacitor core (1), the maximum value of the field grading layer (3) becomes larger in amplitude but narrower in width. Figure 2 In the example, all layers are optimized in the manner described, such that the average edge field stress is equal in all segments compared to a design with cylindrical layers, and a significantly reduced diameter is provided.

[0037] exist Figure 3 Another embodiment is shown. The edges of the field grading layers are curved outward, thereby reducing electric field stress near the edges. Compared to capacitor cores with cylindrical layers, this results in more uniform field stress across the distance between layers at the ends of the segments and allows for setting safe design limits for the average edge field stress level at higher values.

[0038] Figure 4 and Figure 5The diagram shows an electrical connection (5), a high-voltage connection (6), and a voltage-tap connection (7), which are formed as axially symmetrical, blocky conductive material objects produced by an additive manufacturing process, parallel to the insulating material of the capacitor core. The diameter of the inner field grading layer (3) has a maximum value between its edges. Therefore, the electric field accumulates at the maximum value, and the electric field decreases at the edges of the field grading layer (3). The capacitance between the field grading layers is adjusted and balanced by correspondingly forming the maximum value.

[0039] Figure 6 The shape of a capacitor core (1) is shown, the outer surface of which follows the edge of the field grading layer (3). The thickness of the insulating material increases near the edge of the layer. The surface of the capacitor core (1) is stepped, such that the thickness of the insulating material between each edge of an adjacent field grading layer (3) and the outer surface of the capacitor core (1) is greater than the thickness of the insulating material between the midpoint between the edges of the field grading layer (3) and the outer surface of the capacitor core (1). Therefore, the corners of the stepped outer surface of the capacitor core (1) are positioned horizontally between adjacent field grading layers (3). In this way, excessive electric field between the edge of the field grading layer (3) and the outer surface of the capacitor core (1) is omitted. Both the insulating material and the conductive layer can be fabricated in an additive manufacturing process, thus allowing for a precise correlation between the position of the layer and the position of the protruding portion of the insulating material.

[0040] The potential connection portions (5, 6, 7) are also applicable to other types of capacitive bushings, such as those for capacitive bushings with cylindrical field grading layers. Therefore, this disclosure also relates to a capacitive bushing comprising a capacitor core (1) and a conductive field grading layer (3) embedded in the insulating material of the capacitor core (1) and arranged around a central channel of a conductor (2) extending along an axis defining an axial direction, while an electrical connection portion (6) is provided to at least one layer of the field grading layer (3), the connection portion being an integral part of the field grading layer (3) and having a substantially axially symmetrical shape, wherein the volume of conductive material extends from the field grading layer to the outer or inner surface of the capacitor core (1).

[0041] This also applies to the outer surface following the edge of the field grading layer (3). This disclosure also relates to a capacitive bushing comprising a capacitor core (1) and a conductive field grading layer (3), the conductive field grading layer (3) being embedded in the insulating material of the capacitor core (1) and arranged around a central channel of a conductor (2) extending along an axis defining an axial direction, while providing electrical connections (6) to at least one layer of the field grading layer (3), wherein the shape of the capacitor core (1) is configured such that the thickness of the insulating material between the edge of the field grading layer (3) and the outer surface of the capacitor core (1) is greater than the thickness of the insulating material between the section between the edges of the field grading layer (3) and the outer surface of the capacitor core (1).

[0042] List of reference numerals in the attached diagram:

[0043] 1-Capacitor core

[0044] 2-Conductor

[0045] 3-Field Classification Layer

[0046] 4-Flange

[0047] 5-High voltage connection part

[0048] 6-Grounding connection part

[0049] 7-Voltage tap connection part

[0050] 8-Field graded layer bending section

[0051] 9-Field graded layer outward curved edge

[0052] 10 - The curved portion of the outer surface of the capacitor core, wherein the surface of the insulating material follows the edge of the field gradation layer.

Claims

1. A capacitive bushing comprising a capacitor core (1) and conductive field-grading layers (3), the conductive field-grading layers (3) being embedded in an insulating material of the capacitor core (1) and arranged around a central channel of a conductor (2) extending along an axis defining an axial direction, while an electrical connection (6) is provided to at least one of the field-grading layers (3), wherein the insulating material between a pair of adjacent field-grading layers (3) and the pair of adjacent field-grading layers forms an axial length L1 to L2. n And has capacitors C1 to C n The section of the capacitor core, wherein at least one of the field grading layers (3) is deviated from a cylindrical shape in order to have a forming axial length L1 to L n And has capacitors C1 to C n Compared to the corresponding capacitive bushing of the cylindrical field grading layer in the section, the non-uniformity of the electric field stress of the capacitive bushing is reduced, and the shape of at least one field grading layer in the field grading layer (3) is set such that the diameter of the field grading layer (3) varies along the axial direction, characterized in that, The diameter of the field grading layer (3) has at least one maximum value between the edges of the field grading layer (3), wherein, as the distance from the capacitor core (1) increases, the magnitude of the maximum value of the field grading layer (3) becomes larger in the radial direction but narrower in the axial direction, and wherein the terminal portion of each field grading layer (3) is straight in the axial direction.

2. The capacitive bushing according to claim 1, wherein, The average edge field stress level is limited to the voltage U of the section. i The radial width δ of the segment at the end of the segment. i That is, the radial width δ at the edge of the shorter field-grading layer along the axial direction in this section. i The ratio; the average edge field stress level in at least one segment formed by a non-cylindrical field gradation layer is less than that of segments having the same capacitance C1 to C2. n and the same axial length L1 to L n The average edge field stress level in the corresponding section of the capacitive bushing of the cylindrical field grading layer of the section.

3. The capacitive bushing according to claim 2, wherein, absolute value ratio The absolute value is at least 20% smaller, of which and It is the average edge field stress level of two adjacent sections, where at least one section is formed by a non-cylindrical field hierarchy; and and It is the average edge field stress level of two corresponding adjacent sections of the corresponding capacitive bushing with a cylindrical field gradation layer.

4. The capacitive bushing according to any one of claims 1-3, wherein, The radial width of the section at its axial end is equal.

5. The capacitive bushing according to any one of claims 1-3, wherein, The innermost grading layer and / or the outermost grading layer are cylindrical.

6. The capacitive bushing according to any one of claims 1-3, wherein, The capacitance of all segments formed by the field-level layer (3) is equal.

7. The capacitive bushing according to any one of claims 1-3, wherein, At least one electrical connection (5, 6, 7) is an integral part of the field grading layer (3) and has a substantially axially symmetrical shape, wherein the volume of conductive material extends from the field grading layer to the outer or inner surface of the capacitor core (1).

8. The capacitive bushing according to any one of claims 1-3, wherein, The shape of the capacitor core (1) is configured such that the thickness of the insulating material between each edge of the adjacent field grading layer (3) and the outer surface of the capacitor core (1) is greater than the thickness of the insulating material between the midpoint between the edges of the field grading layer (3) and the outer surface of the capacitor core (1).

9. Use of additive manufacturing methods to manufacture the capacitor bushing according to any one of the preceding claims.

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