WALL BUSHING

Abstract

A wall bushing for high voltage application is presented. The wall bushing includes a grounded shield. The grounded shield includes a grading ring in a distal end thereof. The grading ring has an elliptic cross section with conjugate diameters, wherein a major diameter of the conjugate diameters is arranged in an axial direction of the grounded shield and a minor diameter of the conjugate diameters is arranged in a radial direction of the grounded shield. The major diameter is larger than the minor diameter.

Claims

1. A wall bushing for high voltage application, the wall bushing comprising a grounded shield, the grounded shield comprising a grading ring in a distal end thereof, the grading ring having an elliptic cross section with conjugate diameters, wherein a major diameter of the conjugate diameters is arranged in an axial direction of the grounded shield and a minor diameter of the conjugate diameters is arranged in a radial direction of the grounded shield, wherein the major diameter is larger than the minor diameter, wherein the major diameter is between 10 and 55% longer than the minor diameter.

2. The high voltage wall bushing according to claim 1, wherein the major diameter is between 15 and 40% longer than the minor diameter.

3. The high voltage wall bushing according to claim 2, wherein the major diameter is between 18 and 34% longer than the minor diameter.

4. The high voltage wall bushing according to claim 1, wherein the shield is elongated and concentric around a longitudinal axis.

5. The high voltage wall bushing according to claim 1, wherein the wall bushing is a gas insulated wall bushing.

6. The high voltage wall bushing according to claim 1, wherein the grading ring is made of Aluminium.

7. The high voltage wall bushing according to claim 1, wherein the wall bushing is configured to be arranged with the shield concentrically arranged around a high voltage tube.

8. A high voltage wall bushing comprising: a grounded shield that includes a grading ring in a distal end thereof, wherein a major diameter of conjugate diameters is arranged in an axial direction of the grounded shield and a minor diameter of conjugate diameters is arranged in a radial direction of the grounded shield, wherein the major diameter is larger than the minor diameter, wherein the major diameter is between 10 and 55% longer than the minor diameter.

9. The high voltage wall bushing according to claim 8, wherein the grading ring includes an elliptic cross section with the conjugate diameters.

10. The high voltage wall bushing of claim 8, wherein the major diameter is between 15 and 40% longer than the minor diameter.

11. The high voltage wall bushing according to claim 8, wherein the major diameter is between 18 and 34% longer than the minor diameter.

12. The high voltage wall bushing according to claim 8, wherein the shield is elongated and concentric around a longitudinal axis.

13. The high voltage wall bushing according to claim 8, wherein the wall bushing is a gas insulated wall bushing.

14. The high voltage wall bushing according to claim 8, wherein the grading ring comprises Aluminium.

15. The high voltage wall bushing according to claim 8, wherein the wall bushing is configured to be arranged with the shield concentrically arranged around a high voltage tube.

16. The high voltage wall bushing according to claim 8, wherein the wall bushing comprises a gas insulated wall bushing, and wherein the grading ring comprises Aluminium.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Aspects and embodiments are now described, by way of example, with reference to the accompanying drawings, in which:

[0017] FIG. 1 is a diagram schematically illustrating a wall bushing;

[0018] FIG. 2 is a diagram schematically illustrating a detail of the wall bushing shown in FIG. 1 with a circular cross section of a grading ring;

[0019] FIG. 4 is a diagram schematically illustrating a detail of a wall bushing with an elliptic cross section;

[0020] FIG. 3 is a diagram schematically illustrating a cross section of part of FIG. 2;

[0021] FIG. 5 is a diagram schematically illustrating a cross section of part of FIG. 4; and

[0022] FIG. 6 is a diagram schematically illustrating how the electric stress in a grading ring is affected by the shape of the cross section of the grading ring.

DETAILED DESCRIPTION

[0023] The aspects of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown.

[0024] These aspects may, however, be embodied in many different forms and should not be construed as limiting; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and to fully convey the scope of all aspects of invention to those skilled in the art. Like numbers refer to like elements throughout the description.

[0025] A wall bushing grading ring with an elliptic cross section is according to an aspect presented with reference to FIGS. 4 and 5. FIGS. 4 and 5 show a typical grounded shield 2 in a wall bushing similar to the one illustrated in FIGS. 1-3. The same reference numbers have been used for other parts then the grading ring 6 and its cross section 7. An elliptic shape of the cross section 7 of the grading ring 6 enables the wall bushing to be rated for higher voltage and/or to be designed in a more compact design than for wall bushings with traditional grading rings of circular cross section. The configuration of the grading ring is presented, and other details of the wall bushing is within the knowledge of a person skilled in the art of wall bushings.

[0026] The wall bushing is configured for high voltage application. The wall bushing comprises a grounded shield 2. The grounded shield 2 comprises a grading ring 6 in a distal end thereof. The grading ring 6 has an elliptic cross section 7 with conjugate diameters. A major diameter of the conjugate diameters is arranged in an axial direction of the grounded shield 2 and a minor diameter of the conjugate diameters is arranged in a radial direction of the grounded shield 2. The major diameter is larger than the minor diameter. The shortest distance between the grading ring 6 and the grounded flange 5 is x, which is about the same distance as the between the grounded shield 2 and the grounded flange 5.

[0027] The major diameter may be between 10 and 55% longer than the minor diameter. The major diameter may further be between 15 and 40% longer than the minor diameter. The major diameter may yet further be between 18 and 34% longer than the minor diameter.

[0028] The grounded shield 2 may be elongated and concentric around a longitudinal axis, as illustrated with a dot-dashed line.

[0029] The wall bushing may be a gas insulated wall bushing. A typical gas insulated wall bushing for high power DC bushings uses SF6 gas for isolation. For the highest voltages, about 150 kV-1500 kV, SF6 gas is particularly useful for its electrical isolation properties.

[0030] The wall bushing may be configured to be arranged with the grounded shield 2 concentrically arranged around the high voltage tube 1.

[0031] FIG. 6 shows a test of electric stress for wall bushings as presented with reference to FIGS. 4 and 5, with different shapes of the elliptic cross section 7. Tests have been made for a wall bushing configured for a high voltage, in this case 1100 kV DC, with a grading ring 6 with an elliptic cross section 7 diameter of 50 mm. The grading ring 6 is arranged about 200 mm from the conductor tube 1 and about 200 mm (x in this example) from the grounded flange 5. In FIG. 6 the AC stress in arbitrary units is plotted against an elliptic grading ring with different cross section shapes. The cross section of the grading ring has a major axis along the axial direction of the wall bushing and a minor axis along the radial direction of the wall bushing. For wall bushing configured for higher voltage the distances are longer between the grading ring and the conductor tube and the grounded flange, respectively. Correspondingly, the distances are shorter for lower voltages.

[0032] The elliptic offset is distance in mm that the major axis is longer than the minor axis. For zero offset, i.e., for a circular cross section, the electric stress is 0.83. With a major axis of 55 mm (the minor axis is constantly 50 mm) the electric stress is 0.81. With a major axis of 60 mm the electric stress is 0.79. With a major axis of 62 mm the electric stress is 0.79. With a major axis of 65 mm the electric stress is 0.79. With a major axis of 70 mm the electric stress is 0.80. With a major axis of 75 mm the electric stress is 0.81. With a major axis of 80 mm the electric stress is 0.82.

[0033] The elliptic profile in this embodiment comprises aluminium, but may be made of other electrically conductive materials. The elliptic profile may further be made by a ring with an electrically conductive surface. Other parts of the grounded shield may also comprise aluminium of other electrically conductive materials.

[0034] The lowest electric stress is achieved with a cross section having the major axis being about 20-30% longer than the minor axis. A substantially lower electric stress is achieved with a cross section having the major axis being about 15-40% longer than the minor axis. A clearly usefully lower electric stress is achieved with a cross section having the major axis being about 15-55% longer than the minor axis.

[0035] Embodiments of the present invention may be described in any one of the following points. [0036] 1. A wall bushing for high voltage application, the wall bushing comprising a grounded shield 2, the grounded shield comprising a grading ring 6 in a distal end thereof, the grading ring having an elliptic cross section 7 with conjugate diameters, wherein a major diameter of the conjugate diameters is arranged in an axial direction of the grounded shield and a minor diameter of the conjugate diameters is arranged in a radial direction of the grounded shield, wherein the major diameter is larger than the minor diameter. [0037] 2. The high voltage wall bushing according to point 1, wherein the major diameter is between 10 and 55% longer than the minor diameter. [0038] 3. The high voltage wall bushing according to point 2, wherein the major diameter is between 15 and 40% longer than the minor diameter. [0039] 4. The high voltage wall bushing according to point 3, wherein the major diameter is between 18 and 34% longer than the minor diameter. [0040] 5. The high voltage wall bushing according to any one of points 1 to 4, wherein the shield is elongated and concentric around a longitudinal axis. [0041] 6. The high voltage wall bushing according to any one of points 1 to 5, wherein the wall bushing is a gas insulated wall bushing. [0042] 7. The high voltage wall bushing according to any one of points 1 to 6, wherein the grading ring is made of Aluminium. [0043] 8. The high voltage wall bushing according to any one of points 1 to 7, wherein the wall bushing is configured to be arranged with the shield concentrically arranged around a high voltage tube 1.

[0044] The aspects of the present disclosure have mainly been described above with reference to a few embodiments and examples thereof. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.