ELECTRICAL BUSHING AND METHODS OF PRODUCING AN ELECTRICAL BUSHING

Abstract

An electrical bushing is specified, the bushing including a flange with a lower part and an upper part affixed to one another and further including a core surrounded by the flange, wherein the flange is affixed to the core by a locking compound disposed in a volume of a joint between the flange and the core, and wherein the volume of the joint further includes a compressible material, the compressible material being configured to compress or expand in response to a change in the volume of the joint.

Furthermore, a method of producing an electrical bushing is specified.

Claims

1. An electrical bushing, comprising: a flange comprising a lower part and an upper part affixed to one another, and a core surrounded by the flange, wherein: the flange is affixed to the core by a locking compound disposed in a volume of a joint between the flange and the core, and the volume of the joint further comprises a compressible material, the compressible material being configured to compress or expand in response to a change in the volume of the joint.

2. The electrical bushing according to claim 1, wherein the core has a first section with a diameter that is larger than a diameter of a second section and a diameter of a third section, wherein the first section is arranged between the second section and the third section along an axial direction of the bushing, wherein the flange forms a seat for a first transition between the first section and the second section and wherein the volume of the joint is located at a second transition between the first section and the third section.

3. The electrical bushing according to claim 2, wherein the seat is located at the lower part of the flange and the joint is located at least in part at the upper part of the flange or vice versa.

4. The electrical bushing according to claim 1, wherein the compressible material is compressible by at least 10% with respect to its unloaded volume.

5. The electrical bushing according to claim 1, wherein the compressible material comprises at least one of: an elastomer, a gel, a compressible filler, expancels.

6. The electrical bushing according to claim 1, wherein the joint is an annular joint spanning a circumference of the core.

7. The electrical bushing according to claim 1, wherein the locking compound is an Epoxy-type resin, an Epoxy-type adhesive, a Silicone-type adhesive or a Polyurethane-type adhesive.

8. The electrical bushing according to claim 1, wherein the bushing is a capacitance graded bushing.

9. A method for producing an electrical bushing, the method comprising: providing a core and a flange with a lower part and an upper part; arranging the upper part and the lower part of the flange around the core; affixing the upper part and the lower part to one another; forming a joint between the flange and the core, comprising the steps of: injecting a locking compound filling a second portion of the volume of the joint, wherein a compressible material is provided in a first portion of the volume of the joint, and curing the locking compound while it is in contact with the compressible material.

10. The method according to claim 9, wherein the locking compound is injected into the joint after affixing the upper part and the lower part to one another.

11. The method according to claim 10, wherein the injection is performed with hand-held equipment or mixing equipment, and wherein the joint is sealed after injection.

12. The method according to claim 9, wherein the locking compound is hardened by heating it to a temperature of at least 50° C.

13. The method according to claim 9, wherein a bushing is produced comprising: a flange comprising a lower part and an upper part affixed to one another, and a core surrounded by the flange, wherein: the flange is affixed to the core by a locking compound disposed in a volume of a joint between the flange and the core, and the volume of the joint further comprises a compressible material, the compressible material being configured to compress or expand in response to a change in the volume of the joint.

14. The method according claim 13, wherein the bushing is a capacitance graded bushing.

15. The method according to claim 13, wherein the locking compound is an Epoxy-type resin, an Epoxy-type adhesive, a Silicone-type adhesive or a Polyurethane-type adhesive.

16. The method according to claim 13, wherein the joint is an annular joint spanning a circumference of the core.

17. The method according to claim 13, wherein the compressible material comprises at least one of: an elastomer, a gel, a compressible filler, expancels.

18. The method according to claim 13, wherein the compressible material is compressible by at least 10% with respect to its unloaded volume.

19. An electrical bushing, comprising: a flange comprising a lower part and an upper part affixed to one another, and a core surrounded by the flange, wherein: the flange is affixed to the core by a locking compound disposed in a volume of a joint between the flange and the core, and the volume of the joint further comprises a compressible material, the compressible material being configured to compress or expand in response to a change in the volume of the joint, wherein the core has a first section with a diameter that is larger than a diameter of a second section and a diameter of a third section, wherein the first section is arranged between the second section and the third section along an axial direction of the bushing, wherein the flange forms a seat for a first transition between the first section and the second section and wherein the volume of the joint is located at a second transition between the first section and the third section, wherein the seat is located at the lower part of the flange and the joint is located at least in part at the upper part of the flange or vice versa, wherein the compressible material comprises at least one of: an elastomer, a gel, a compressible filler, expancels, and wherein the locking compound is an Epoxy-type resin, an Epoxy-type adhesive, a Silicone-type adhesive or a Polyurethane-type adhesive.

20. The electrical bushing according to claim 19, wherein the bushing is a capacitance graded bushing.

Description

BRIEF DRAWING DESCRIPTION

[0032] FIG. 1 shows a cutaway view of an example embodiment of a bushing according to some embodiments of the disclosure;

[0033] FIG. 2 shows a cutaway view of a further example embodiment of a bushing according to some embodiments of the disclosure; and

[0034] FIG. 3. shows an example embodiment of a method for producing a bushing.

DETAILED DESCRIPTION

[0035] In the example embodiments and figures similar or similarly acting constituent parts are provided with the same reference signs. Generally, only the differences with respect to the individual embodiments are described. Unless specified otherwise, the description of a part or aspect in one embodiment applies to a corresponding part or aspect in another embodiment as well.

[0036] The elements illustrated in the figures and their size relationships among one another are not necessarily true to scale. Rather, individual elements or layer thicknesses may be represented with an exaggerated size for the sake of better representability and/or for the sake of better understanding.

[0037] FIG. 1 is a schematic view of a bushing according to an embodiment disclosed herein. The bushing 1 has a core 2 seated in a flange 3. The flange comprises a lower part 31 and an upper part 32. The lower part 31 forms a mounting face 30 for mounting the flange 3 to an appliance.

[0038] The flange 3, for example the lower part 31 and the upper part 32 may be made from a metal or a metal alloy, for instance from an aluminum alloy or stainless steel.

[0039] The core 2 is a machined resin impregnated paper condenser core, for example. Along an axial direction of the bushing 1, the core comprises a first section 21 arranged between a second section 22 and a third section 23, wherein a diameter of the first section 21 is larger than that of the second section 22 and the third section 23. The lower part 31 of the flange 3 has a tapered section that forms a seat 6 that fits a first transition 26 between the first section 21 and the second section 22 of the core. In the example embodiment shown, the first transition 26 is a tapered section of the core 2, thereby providing means for aligning and fixing the core 2 within the lower part 31 of the flange 3. However, other shapes may be used for the first transition 26 as well.

[0040] The upper part 32 of the flange 3 is connected to the lower part 31 of the flange 3, for instance clamped or bolted (not explicitly shown), and sealed via O-ring gaskets 5a. The gaskets are arranged in annular axial grooves formed in at least one of the upper part 32 and the lower part 31, for instance in the lower part as shown in FIG. 1. Furthermore, the flange 3, for example the upper part 32, is sealed against the core 2 by three O-ring gaskets 5b. These gaskets are located within recesses on the inner surface of the upper part 32 of flange 3. The gaskets 5a, 5b prevent ingress of contaminants and moisture and prevent the loss of liquid locking compound during injection.

[0041] The upper part 32 of flange 3 further has a recess that, when mounted on the core 2, forms the volume of joint 10. The groove forming the joint volume is annular and consists of a first portion 11 and a second portion 12 adjacent to the first portion.

[0042] When seen along the axial direction, the volume of the joint 10 is delimited by a flange transition 15 on one side and by the tapered second transition 27 between the first section 21 and the third section 23 of the core 2 on the opposite side. This arrangement provides the core 2 to be secured in position with respect to the flange 3 after locking. In the embodiment shown, the flange transition 15 is embodied as a step forming a flange surface extending perpendicular to the axial direction. However, angles other than 90° may also be used.

[0043] In radial direction, the second transition 27 adjoins a tapered section 14 of the flange resulting in a volume of the joint 10 that symmetrically tapers in axial direction towards the mounting face 30.

[0044] The first portion 11 is the portion of the joint 10 that is filled with the compressible material 4, and the second portion 12 is filled with the locking compound 45. For instance, the compressible material comprises a foam such as a closed-cell silicone foam and the locking compound is a thermoset epoxy-type resin. However, other materials, for example those mentioned herein may also be used.

[0045] The first portion 11 is arranged on that side of the second portion that faces away from the seat 6.

[0046] If the core 2 expands more strongly than the flange 3 in axial direction due to different coefficients of thermal expansion, the volume of joint 10 decreases and the compressible material 4 is elastically compressed. In this case, the second transition 27 axially moves in a direction away from the mounting face 30 thereby exerting force on the locking compound 45 which is transferred to the flange transition 15 via the compressible material 4. By means of this configuration, the flange transition 15 provides sufficient securing to make the bushing 1 rigid enough for its functionality, while very small movement is enabled to compensate for differential thermal expansion by means of the compressible material 4. Thus, the mechanical load on the further elements of the bushing 1, for example on the locking compound 45 and the flange 3 is reduced, in particular when compared to the case where the volume of the joint is completely filled with a stiff locking compound.

[0047] In the example embodiment of FIG. 1 the seat 6 is located at the lower part 31 of the flange 3 and the joint 10 is located at the upper part 32 of the flange 3. For example, the entire volume of the joint is located in one part of the flange 3, namely in the upper part 32. However, the arrangement may also be inverted so that the seat 6 is provided by the upper part 32 of the flange 3.

[0048] FIG. 2 is a schematic view of a bushing according to further embodiments disclosed herein.

[0049] This further example embodiment essentially corresponds to that of the previously described embodiment.

[0050] Unlike in the previously described embodiment, the volume of joint 10 is at least partly formed adjacent to the same part of the flange 3 as the seat 6, namely in the lower part 31 of the flange 31. In other words, the volume is located at an interface between the lower part 31 of the flange 3 and the upper part 32 of the flange. For instance, the first portion 11 of the volume is located adjacent to the upper part 32 and the second portion 12 is adjacent to the lower part 31 of the flange 3. For instance, the volume of the joint 10 is formed by an annular groove within the upper part 32 and a further annular groove within the lower part 31, so that when both parts are mounted around the core 2 each form part of the volume of joint 10.

[0051] As in the previous embodiment, the lower part 31 of the flange 3 is sealed against the core by three O-ring gaskets 5a. The lower part 31 of the flange is bolted or clamped to the upper part 32 of the flange 3. The upper part 32 of the flange 3 is sealed against the core by an O-ring gasket 5b. The gaskets 5a, 5b are located within recesses on the inner surface of the upper part and the lower part of the flange 3.

[0052] The upper part 32 has an annular recess 325 configured to receive an end of an insulator (not shown in the Figure).

[0053] As in the previous embodiment, the first section 21 of the core 2 is delimited by a first transition 26 and a second transition 27, wherein the first transition is located at the seat 6 and the second transition is located at the joint 10. The diameter of the core 2 outside of the first section 21 is smaller than in the first section, so that the core can be easily inserted into the lower part 31 of the flange during production of the bushing 1. However, the diameter of the first section 21 does not have to be constant throughout the entire axial extent of the first section as shown in FIG. 2.

[0054] FIG. 3 illustrates a method for producing a bushing 1 which may be configured as described in connection with FIGS. 1 and 2, for instance. For better understanding, the same reference signs are used for the constituents of the bushing as in FIGS. 1 and 2 even though the individual constituents are not drawn in FIG. 3.

[0055] In a method step 701 a core 2 and a flange 3 with an upper part 32 and a lower part 31 are provided. The upper part and the lower part are separate elements of the flange configured to be affixed to one another in a subsequent step. The upper part and the lower part may be formed by means of casting, for instance.

[0056] In a method step 702, the upper part 32 and the lower part 31 of the flange 3 are arranged around the core 2. For instance, the core 2 is inserted into the lower part 31. This can be performed by lowering the core 2 into the lower part 31 of flange 3 either manually or by a hoist or crane. At this stage, the core 2 may rest on a seat 6 of the lower part 31. After lowering the core 2, the correct seating of the core 2 may be inspected and an adjustment of the position of the core may be performed.

[0057] Afterwards, the upper part 32 may be lowered over the core 2 in a similar manner. Alternatively, the seat 6 may also be provided by the upper part 32 of the flange 3. In this case, the core is inserted into the upper part 32 of the flange.

[0058] For example, a compressible material 4 is provided in a first portion of a volume of a joint 10 that is to be formed between the core 2 and the flange 3. For instance, the compressible material 4 is a prefabricated annular element that rests in one of the flange parts.

[0059] In a method step 703, the upper part 32 and the lower part 31 are fixed to one another, for example mechanically, for instance by clamping or bolting. A seal between the upper part 32 and the lower part 31 may be obtained by one or more gaskets between the two parts, for instance. At this stage, the core 2 is already held within the flange 3.

[0060] In a method step 704, a joint 10 between the flange and the core is formed. For this purpose a locking compound 45 is injected into a second portion 12 of the volume of the joint 10. For example, the locking compound 45 fills the entire remaining volume of the joint 10 that has not been filled with the compressive material 4 before. Typically, the locking compound 45 is injected through one or more injection channels by a technician, but the process can also be automated. After the injection, the injection channels are sealed, e.g. by plugging.

[0061] After the injection, the locking compound 45 is cured while it is in direct contact with the compressible material 4 until the locking compound has hardened. The curing step can involve heating the bushing 1 or part of the bushing 1, e.g. by utilizing an oven or heating mats. The temperature and time of the curing step typically are dependent on the locking compound, e.g. a thermoset polymer may require a temperature of 80° C. for a period of 4 hours.

[0062] Once the locking compound has hardened, the core 2 is aligned within the flange 3 and held in place in radial as well as in axial direction. However, if the volume of the joint 10 decreases during operation of the bushing 1 due to an axial thermal expansion of the core that is larger than that of the flange 3, the compressive material 4 is elastically compressed, thereby mitigating the mechanical stress on the further elements of the bushing 1, for example on the locking compound 45 and the flange 3.

[0063] The bushing 1 has been described in connection with a condenser core bushing, but the inventive concept may also be used for any other kind of electrical bushing, such as a solid bushing, also known as a bulk type bushing. The skilled technician is aware that the components of the bushing may be made from a number of available materials and composites, such that the mention of one specific material must not be understood as a limitation. The core 2 of the bushing can be made from any suitable material or compound, such as resin impregnated paper, resin impregnated synthetic or solid epoxy.

[0064] The embodiments are not restricted to the example embodiments by the description on the basis of said example embodiments. Rather, the embodiments encompass any new feature and also any combination of features, which in particular comprises any combination of features in the patent claims and any combination of features in the example embodiments, even if this feature or this combination itself is not explicitly specified in the patent claims or example embodiments.

LIST OF REFERENCE SIGNS

[0065] 1 bushing [0066] 10 joint [0067] 11 first portion [0068] 12 second portion [0069] 14 tapered section [0070] 15 flange transition [0071] 2 core [0072] 21 first section [0073] 22 second section [0074] 23 third section [0075] 26 first transition [0076] 27 second transition [0077] 3 flange [0078] 30 mounting face [0079] 31 lower part [0080] 32 upper part [0081] 325 recess [0082] 4 compressible material [0083] 45 locking compound [0084] 5a, 5b gasket [0085] 6 seat [0086] 701 step [0087] 702 step [0088] 703 step [0089] 704 step