CONDENSER BUSHING

Abstract

The present disclosure relates to a condenser bushing including a condenser core and electrically conductive field-grading layers, which are embedded in insulating material of the condenser core and arranged around a central channel for conductor extending along an axis defining an axial direction, while an electric connection is provided to at least one of the field-grading layers, wherein pairs of neighbouring field-grading layers with the insulation material between them form sections of the condenser core of axial lengths L.sub.1 through L.sub.n and with capacitances C.sub.1 through C.sub.n, characterized in that a shape of at least one of the field-grading layers deviates from cylindricality in order to reduce non-uniformity of electric field stress of the condenser bushing compared to a corresponding condenser bushing with the cylindrical field-grading layers forming sections of the axial lengths L.sub.1 through L.sub.n and with capacitances C.sub.1 through C.sub.n.

Claims

1. A condenser bushing comprising: a condenser core and electrically conductive field-grading layers, which are embedded in insulating material of the condenser core and arranged around a central channel for conductor extending along an axis defining an axial direction, an electric connection being provided to at least one of the field-grading layers, pairs of neighbouring field-grading layers with the insulation material between them forming sections of the condenser core of axial lengths L.sub.1 through L.sub.n and with capacitances C.sub.1 through C.sub.n, a shape of at least one of the field-grading layers deviating from cylindricality to reduce non-uniformity of electric field stress of the condenser bushing compared to a corresponding condenser bushing with the cylindrical field-grading layers forming sections of the axial lengths L.sub.1 through L.sub.n and with capacitances C.sub.1 through C.sub.n, and at least one of the field-grading layers being shaped such that the diameter of said field-grading layer varies along the axial direction, the diameter of said field grading layer having at least one maximum between the edges of the field-grading layer.

2. The condenser bushing according to claim 1, wherein the mean edge field stress level, defined as the ratio of the voltage U.sub.i of the section and the radial width δ.sub.i of the section at its end in at least one section formed by a non-cylindrical field-grading layer is smaller than in the corresponding section of a condenser bushing with cylindrical field-grading layers forming sections of identical capacitances C.sub.1 through C.sub.n and identical axial lengths L.sub.1 through L.sub.n.

3. The condenser bushing according to claim 2, wherein the absolute value of $\left(\frac{U_i}{\delta i}/\frac{U_j}{\delta j}-1\right)$ is at least 20% smaller than the absolute value of $\left(\frac{U_i}{{\delta }_i^{\prime }}/\frac{U_j}{{\delta }_j^{\prime }}-1\right),$ where $\frac{U_i}{\delta i}\mathrm{and}\frac{U_j}{\delta j}$ are the mean edge field stress levels of two neighbouring sections, wherein at least one section is formed by a non-cylindrical field-grading layer and $\frac{U_i}{{\delta }_i^{\prime }}\mathrm{and}\frac{U_j}{{\delta }_j^{\prime }}$ are the mean edge field stress levels of two corresponding neighbouring sections the corresponding condenser bushing with the cylindrical field-grading layers.

4. The condenser bushing according to claim 1, wherein the radial widths of the sections at their axial ends are substantially equal.

5. The condenser bushing according to claim 1, wherein the innermost and/or the outermost field-grading layer is cylindrical.

6. The condenser bushing according to claim 1, wherein the capacitances of all the sections formed by the field-grading layers are equal.

7. The condenser bushing according to claim 1, wherein at least one edge of at least one of the field-grading layers is bent outwards with respect to the axis.

8. The condenser bushing according to claim 7, wherein the radius of curvature of the bent edge of the field-grading layer is equal to at least three layer thicknesses.

9. The condenser bushing according to claim 1, wherein at least one potential connection is an integral part of a field-grading layer and has a substantially axially symmetric shape, with the conductive material volume reaching from the field-grading layer to the outer or inner surface of the condenser core.

10. The condenser bushing according to claim 1, wherein the condenser core is shaped in such a way that the thickness of an insulating material between the each of the edges of adjacent field-grading layers and the outer surface of the condenser core is greater than the thickness of an insulating material between the middle point between the edges of the field-grading layers and the outer surface of the condenser core.

11. An additive manufacturing method to manufacture the condenser bushing according to claim 1.

12. The condenser bushing according to claim 7, wherein the radius of curvature of the bent edge of the field-grading layer is equal to at least five layer thicknesses.

13. An electrical insulation system comprising: an active part comprising a conductor; a condenser bushing disposed around the conductor, the condenser bushing comprising: a condenser core and electrically conductive field-grading layers, which are embedded in insulating material of the condenser core and arranged around a central channel for conductor extending along an axis defining an axial direction, an electric connection being provided to at least one of the field-grading layers, pairs of neighbouring field-grading layers with the insulation material between them forming sections of the condenser core of axial lengths L.sub.1 through L.sub.n and with capacitances C.sub.1 through C.sub.n, a shape of at least one of the field-grading layers deviating from cylindricality to reduce non-uniformity of electric field stress of the condenser bushing compared to a corresponding condenser bushing with the cylindrical field-grading layers forming sections of the axial lengths L.sub.1 through L.sub.n and with capacitances C.sub.1 through C.sub.n, and at least one of the field-grading layers being shaped such that the diameter of said field-grading layer varies along the axial direction, the diameter of said field grading layer having at least one maximum between the edges of the field-grading layer.

14. The electrical insulation system according to claim 13, wherein the active part is part of a high voltage component of one of a transformer, a generator, and a circuit breaker.

15. The electrical insulation system according to claim 13, wherein the mean edge field stress level, defined as the ratio of the voltage U.sub.i of the section and the radial width δ.sub.i of the section at its end in at least one section formed by a non-cylindrical field-grading layer is smaller than in the corresponding section of a condenser bushing with cylindrical field-grading layers forming sections of identical capacitances C.sub.1 through C.sub.n and identical axial lengths L.sub.1 through L.sub.n.

16. The electrical insulation system according to claim 14, wherein the absolute value of $\left(\frac{U_i}{\delta i}/\frac{U_j}{\delta j}-1\right)$ is at least 20% smaller than the absolute value of $\left(\frac{U_i}{{\delta }_i^{\prime }}/\frac{U_j}{{\delta }_j^{\prime }}-1\right),$ where $\frac{U_i}{\delta i}\mathrm{and}\frac{U_j}{\delta j}$ are the mean edge field stress levels of two neighbouring sections, wherein at least one section is formed by a non-cylindrical field-grading layer and $\frac{U_i}{{\delta }_i^{\prime }}\mathrm{and}\frac{U_j}{{\delta }_j^{\prime }}$ are the mean edge field stress levels of two corresponding neighbouring sections the corresponding condenser bushing with the cylindrical field-grading layers.

17. The electrical insulation system according to claim 13, wherein the radial widths of the sections at their axial ends are substantially equal.

18. The electrical insulation system according to claim 13, wherein the innermost and/or the outermost field-grading layer is cylindrical.

19. The electrical insulation system according to claim 13, wherein the capacitances of all the sections formed by the field-grading layers are equal.

20. The electrical insulation system according to claim 13, wherein at least one edge of at least one of the field-grading layers is bent outwards with respect to the axis.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0029] Condenser bushing is depicted in exemplary embodiments, wherein figures present in a cross section:

[0030] FIG. 1—prior art condenser bushing,

[0031] FIG. 2—first embodiment,

[0032] FIG. 3—second embodiment,

[0033] FIGS. 4 and 5—condenser bushing comprising potential connections,

[0034] FIG. 6—condenser bushing comprising insulation material surface following field-grading layer edges

DETAILED DESCRIPTION

[0035] Manufacturing of a bushing using additive manufacturing methods allows for manufacturing the field-grading layers (3) of an arbitrary shape. An example of such a bushing is shown in FIG. 2. In this embodiment the field-grading layers are shaped so that the radial width of all sections at their ends, δ.sub.i, are equal. The innermost and the outermost layers are cylindrical. The other layers are shaped so that the capacitances of all the sections are also equal. This makes the mean edge field stress values of all the sections equal, all reaching the safe design limit, and allows for making the overall diameter of the condenser core significantly smaller than in an equivalent design with cylindrical layers in which the mean edge field stress value reaches the safe design limit only in one or two sections.

[0036] In the design shown in the drawing, the equivalent grading system formed by cylindrical field-grading layers, having all sections of the same capacitances C.sub.1 through C.sub.4 and the same axial lengths of the layers L.sub.1 through L.sub.4, the section C.sub.4 would be the only one with the mean edge field stress level reaching the safe design limit. In the grading system, by non-cylindrical shaping of the inner layer of the section C.sub.4, the edge width δ.sub.4 of that section is increased compared to the cylindrical design. In that way, the mean edge field stress level of this section is reduced and the radial dimension of the set of all layers can be proportionally scaled down to a smaller diameter, bringing back the mean edge field stress value of the section C.sub.4 to the safe design limit. In such a way the diameter of the condenser core can be made smaller than that of the one made according to known art. The diameter of the field-grading layer (3) has at least one maximum between the edges of the field-grading layer (3). Therefore, a capacitance between adjacent field-grading layers (3) can be altered by adjusting the position, the width or the amplitude of the maximum of each of field grading layer (3). In this way the distance between adjacent field-grading layers, and thereby also the capacitance and the mean edge field stress, can be adapted. As the maximum of the field-grading layer (3) reduces the distance of between adjacent field-grading layers (3) a stronger electric field is stored at the maximum, hence, reducing the electric field strength at the edges. In the embodiment shown in FIG. 2 the maximums of the field-grading layers (3) have been designed such that the maximums of the field-grading layers (3) become bigger in amplitude, but narrower in width, with increasing distance from the condenser core (1). In the example in FIG. 2 all the layers are optimized in the described way, bringing the mean edge field stress to an equal value in all the sections and providing a significant reduction of the diameter compared to the design with cylindrical layers.

[0037] Another embodiment is shown in FIG. 3. The edges of the field-grading layers are bent outwards thus reducing the electric field stress close to the edges, making the field stress more uniform over the distance between the layers at the end of the section and allowing for setting the safe design limit of the mean edge field stress level at a higher value compared to a condenser core with cylindrical layers.

[0038] FIGS. 4 and 5 show the potential connections, high-voltage (5), ground (6), and voltage-tap (7), made in a form of an axially symmetric bulk conductive material objects, produced in an additive manufacturing process in parallel with the insulation material of the condenser core. The diameter of the inner field-grading layers (3) have a maximum between the edges of the field-grading layer (3). Hence, the electric field is accumulated at the maximums and the electric field at the edges of the field-grading layers (3) is reduced. The capacitance between field-grading layers is adjusted and levelled by forming the maximums accordingly.

[0039] FIG. 6 shows the shape of the condenser core (1) with its outer surface following the edges of the field-grading layers (3). The insulation material thickness is enlarged close to the edges of the layers. The surface of the condenser core (1) is stepped such that the thickness of the insulating material between the each of the edges of adjacent field-grading layers (3) and the outer surface of the condenser core (1) is greater than the thickness of an insulating material between the middle point between the edges of the field-grading layers (3) and the outer surface of the condenser core (1). Hence, the corner of step-shaped outer surface of the condenser core (1) is positioned at a level between adjacent field-grading layers (3). In this way excessive electric fields between the edge of the field-grading layers (3) and the outer surface of the condenser core (1) are omitted. Both the insulation material and the conductive layers can be made in an additive manufacturing process allowing for a precise correlation of the positions of the layers and the positions of the protruding parts of the insulating material.

[0040] Potential connection (5, 6, 7) are suitable also for other types of condenser bushing, for example for a condenser bushing with a cylindrical field-grading layers. Therefore a present disclosure relates also to a condenser bushing comprising a condenser core (1) and electrically conductive field-grading layers (3) which are embedded in insulating material of the condenser core (1) and arranged around a central channel for conductor (2) extending along an axis defining an axial direction, while an electric potential connection (6) is provided to at least one layer of the field-grading layers (3), the connection being an integral part of a field-grading layer (3) and having a substantially axially symmetric shape, with the conductive material volume reaching from the field-grading layer to the outer or inner surface of the condenser core (1).

[0041] The same applies to the outer surface following the edges of the field-grading layers (3). The present disclosure relates also to a condenser bushing comprising a condenser core (1) and electrically conductive field-grading layers (3) which are embedded in insulating material of the condenser core (1) and arranged around a central channel for conductor (2) extending along an axis defining an axial direction, while an electric potential connection (6) is provided to at least one layer of the field-grading layers (3), wherein the condenser core (1) is shaped in such a way that the thickness of an insulating material between the edges of the field-grading layers (3) and the outer surface of the condenser core (1) is greater than the thickness of an insulating material between the section between the edges of the field-grading layers (3) and the outer surface of the condenser core (1).

REFERENCE NUMBERS LIST

[0042] 1—condenser core

[0043] 2—conductor

[0044] 3—field-grading layers

[0045] 4—flange

[0046] 5—high-voltage connection

[0047] 6—ground connection

[0048] 7—voltage tap connection

[0049] 8—curvature of field-grading layer

[0050] 9—edges of field-grading layers bent outwards

[0051] 10—curvature of outer surface of condenser core, where the insulation material surface follows the field-grading layer edges