EP2117015A1

EP2117015A1 - High voltage bushing and high voltage device comprising such bushing

Info

Publication number: EP2117015A1
Application number: EP08155697A
Authority: EP
Inventors: Thomas Eriksson; Fredrik Graas; Kerstin Ekeroth Reijm
Original assignee: ABB Technology AG
Current assignee: ABB Technology AG
Priority date: 2008-05-06
Filing date: 2008-05-06
Publication date: 2009-11-11
Also published as: BRPI0912527B8; BRPI0912527A2; CN101577154B; CN101577154A; WO2009135744A1; BRPI0912527B1

Abstract

The invention concerns a high voltage bushing comprising a hollow insulator housing (12), a high voltage conductor (10) provided inside the housing, a first connection arrangement (30) where the conductor can be connected to a first electric device and a second connection arrangement (32) where the conductor can be connected to a second electric device. The invention further has the features that at least one of said first connection arrangement and said second connection arrangement is designed as an external connection arrangement in which the conductor (10) has an extended end part (38), and the bushing comprises an exit opening (34) through which the extended end part (38) of the conductor exits from the bushing, in order for the extended end part of the conductor to be connectable to an electric device. The invention also concerns a high voltage device comprising such a bushing.

Description

Technical field of the invention

The present invention relates to the field of high voltage power systems, and in particular to high voltage bushings used in high voltage devices forming parts of such systems.

Background of the invention

It is known that high voltage equipment and devices, e.g. high voltage transformers, reactors, switchgear etc., are usually equipped with bushings that are adapted for carrying current at high potential through a grounded barrier, e.g. a wall or an enclosure of the electric device such as a transformer tank.
Conventional high voltage bushings comprise an insulator made of ceramic or composite material, which is normally provided with sheds and which is generally hollow. On the inside of the bushing, voltage grading is performed by a condenser core or some other type of voltage grading device, through which an electrical conductor passes. The electrical conductor connects one side of the bushing, where a high voltage electric device is connected, with the other side of the bushing where another electric device is connected. For example, when the first electric device is a transformer, the bushing is fitted on the transformer enclosure and the conductor of the bushing connects the inside of the transformer with the outside, where another electric device can be connected, e.g. a bus, surge arrester or DC-valve.
An example of a prior art bushing adapted for use with a high voltage transformer will now be described with reference to Fig. 1, showing a schematic cross sectional view of a bushing 1 mounted in a wall 18, such as the tank wall in the case of a transformer. A high voltage conductor 10 runs through the center of a hollow bushing insulator 12 that forms a housing around the high voltage conductor. A condenser core 14 is provided inside the insulator housing for voltage grading of voltage stress that is built up around the high voltage conductor 10. A flange 16 is provided on the outside of the housing 12, by means of which the housing of the bushing is connected to ground, via the transformer tank wall 18.
In Fig. 1 is also shown how the bottom end portion of the high voltage conductor 10 forms a bottom contact 20 that is arranged to be connected to the internal components of the transformer. For this purpose, a mating internal contact 22 is provided inside the transformer. An upper outer terminal 24 for the conductor 10 is provided at the upper end of the bushing, opposite the bottom contact 20 end. The outer terminal 24 is electrically connected to the conductor 10 through an interface, also forming a top cover of the bushing, in order to electrically connect the conductor and thus the transformer to an external source or device.
The term high voltage is conventionally used for voltages above approximately 50 kV. Today, the upper limit in commercial high voltage devices is generally 1100 kV, but higher voltages, such as 1200 kV or even more, are envisaged in the near future. Also, current levels are increasing and may be up to 4000-5000 A or even higher.
For high voltages in the region of 800 kV and more, and current ratings of 2000 A and above, the demands on the bushings are naturally increased, e.g. when it comes to heat dissipation and cooling, electric fields, electric insulation of the bushing etc. In this context, it becomes essential to have a low loss, in particular to be able to reach the target current. The losses in today's bushings mainly occur due to losses in the conductor and in each contact or joint in the current path between different parts of the bushing. The losses in the conductor itself can be optimized by selecting the material, the shape and the size of the conductor. When it comes to the losses in the outer terminal 24 of the prior art bushing illustrated in Fig. 1, the current is forced to flow from the conductor 10 to the top cover of the bushing via a contact area through the top cover itself, and then via another contact on the outside of the top cover to the outer terminal 24 and external connection. It is recognized that fewer joints would reduce losses which is advantageous in high voltage and high current applications.

Summary of the invention

It is an object of the present invention to provide a high voltage bushing that improves prior art bushings, and which makes it possible to reach the high voltage levels and high current ratings described above.
It is also an object of the present invention to provide a high voltage device comprising such a high voltage bushing.
These objects, among others, are achieved by a high voltage bushing and a high voltage device as defined in the independent claims.
According to the present invention, a high voltage bushing is defined comprising a hollow insulator housing, a high voltage conductor provided inside the housing, a first connection arrangement where the conductor can be connected to a first electric device and a second connection arrangement where the conductor can be connected to a second electric device, characterized in that at least one of said first connection arrangement and said second connection arrangement is designed as an external connection arrangement in which the conductor has an extended end part, and the bushing comprises an exit opening through which the extended end part of the conductor exits from the bushing, in order for the extended end part of the conductor to be connectable to an electric device.
An advantage of this invention is that the losses are reduced since the contact surfaces and joints are reduced. With the present invention, at least one of the contact areas of the prior art external terminal is made redundant since the current does not have to flow through the top cover, but can flow directly from the conductor to a contact mounted on the conductor, outside the housing. An example of a suitable contact is described in a European patent application filed by the same applicant and on the same day as the present application, entitled "High voltage bushing contact, high voltage bushing comprising such contact and high voltage device comprising bushing with such contact". Reduced losses will reduce the need for cooling of the bushing.
Another advantage is that the cooling of the conductor is improved by direct heat transfer to the surrounding air, which is made possible when the conductor extends outside the bushing. Improved cooling will make it possible to transfer higher power through the bushing, i.e., increase voltage and/or current.
A further advantage is increased robustness for high currents since fewer parts need to have a current contact function.
According to another aspect of the invention, the high voltage bushing comprises a holder device for fixating the conductor in relation to the housing, at the exit opening. Such a holder device may be mounted either outside of the housing or inside the housing, if wanted.
According to one feature, the holder device may comprise at least one clamping member for providing rotational locking by radial clamping pressure to the extended end part of the conductor.
The clamping member may comprise at least one wedge element adapted to be mounted on the conductor, outside the exit opening, a locking ring mounted over the wedge element, and fastening elements, such as screws, for fixating the wedge element and the locking ring to the housing, outside the exit opening. The housing, the at least one wedge element and the locking ring are provided with holes adapted for the screws, and the holes in the housing are provided with internal threads for cooperation with external threads on the screws.
As a further feature, the housing and the at least one wedge element are in thermal and electrical contact with each other. This helps cooling of the inside of the bushing, since heat from the conductor can be transferred through the housing and the wedges to the surrounding air. This also has the advantage that the conductor and the housing have the same potential, by means of the contact through the wedge elements.
In order to position the conductor in relation to the housing, the conductor is provided with first axial positioning elements on its outer circumference for cooperation with corresponding second axial positioning elements on the internal circumference of the at least one clamping member in order to achieve a predefined axial position of the conductor in relation to the housing.
Either one of the first axial positioning elements and the second axial positioning elements are designed as at least one annular groove and the other axial positioning elements are designed as at least one projecting profile.
An example of axial positioning elements is at least one annular groove in the extended end part of the conductor and corresponding projecting profile along the internal circumference of the at least one clamping member. Through this design there are no demands on correct angular orientation of the end of the conductor, which is required in prior art when the conductor is connected to the top cover.
According to a further aspect of the invention, the bushing includes a cover forming part of the housing and the exit opening for the conductor is designed as a hole in the cover through which hole the extended end part of the conductor exits from the bushing. The cover may be made as a separate part, similar to what is mostly the case in prior art. By letting the conductor go through the cover, the number of joints are reduced compared to prior art, and the losses are reduced.
The inventive high voltage bushing finds its applicability primarily as a DC bushing. However, it may also be an AC bushing.
The inventive high voltage bushing may be a gas insulated bushing.
The external connection arrangement of the inventive bushing may be an external air contact, i.e. the inventive details of the bushing are applied to a contact of the bushing, which contact is located at an end of the bushing that is in contact with the surrounding air, for example corresponding to the outer terminal of prior art in Fig. 1.
The bushing may also be a bushing where the housing is a sealed housing whereby the interior of the bushing is sealed off from the surroundings of the bushing. This is required when there is an insulation medium inside the bushing that must not leak out into the surroundings.
Finally, according to the present invention is defined a high voltage device comprising a bushing in accordance with any one of the claims defining a bushing, and said high voltage device being either one of the first electric device or the second electric device to which the conductor can be connected.
Further features, advantages and objects will become apparent from the following detailed description of the invention.

Brief description of the drawings

The present invention will now be described with reference to the enclosed drawings, illustrating an embodiment of the invention, by way of example only, and in which:

Fig. 1 illustrates schematically, in cross section, a high voltage bushing according to prior art,
Fig. 2a illustrates schematically, in cross section, an embodiment of a high voltage bushing according to the present invention,
Fig. 2b illustrates schematically, in cross section, a variant of the embodiment illustrated in Fig. 2a,
Fig. 3 shows a schematic, partial view of a bushing according to the present invention, in cross section,
Fig. 4 shows details of the inventive bushing of Figs. 2a , 2b and 3 provided with an inventive holder device according to the present invention, and
Fig. 5 illustrates the details of a holder device in a bushing according to the present invention.

Detailed description of the invention

In this description, the term "high voltage" (HV) will be used for voltages of 50 kV and higher. The present upper limit for commercial high voltage is 1100 kV, but it is foreseen that the invention can be used also for higher voltages, up to 1200 kV or even more. Generally, the present invention will find its applicability from about 200 kV and upwards.
An embodiment of a bushing according to the present invention is schematically illustrated in Fig. 2a. In principle, the bushing of this embodiment has the same main parts as the prior art bushing in Fig. 1, with the exception of the upper part with the outer terminal 24, and the fact that the present invention is not limited to a bushing with a condenser 14. In the following description, the same reference numerals are used for the same or corresponding parts in the different figures, whenever applicable.
The inventive bushing in Fig. 2a comprises a hollow bushing insulator that forms a housing 12. A high voltage conductor 10 runs through the center of the housing. There is a flange 16 provided around the housing in order to connect the housing of the bushing to ground potential through contact with the wall 18. The wall 18 may be a wall of any type of high voltage electric device where high voltage bushings are used. For example, when the electric device is a transformer, the wall 18 would be the transformer tank wall. Inside the bushing, surrounding the conductor 10, there is also arranged some type of voltage grading device 14. However, it should be noted that the wall and flange are not a requirement for the inventive bushing.
At the bottom end of the bushing there is a first connection arrangement 30 in the form of a contact for connecting the conductor with a corresponding contact 22 of an electric device located on this side of the bushing. The electric device on this first side of the bushing will be referred to as a first electric device. In the case of the first electric device being a transformer, the first connection arrangement 30 in the form of the contact would be inside the transformer and the transformer would have a mating internal contact 22. At the upper end of the bushing, on the other side of the wall 18, there is provided a second connection arrangement 32, in the form of an external connection arrangement comprising an exit opening 34 in the housing 12, through which the conductor 10 exits from the bushing. This is illustrated in more detail in Fig. 3. In the illustrated embodiment, the housing 12 includes a top cover 35 which has a hole 36 through which the conductor 10 runs to the outside of the bushing. This will in the following be referred to as the second side of the bushing. In the illustrated embodiment, the hole 36 actually forms the exit opening 34. The conductor 10 may be described as being extended outside the housing of the bushing by means of the conductor having an extended end part 38 forming an extended free end of the conductor. The conductor end part 38 extending outside the bushing is adapted for contact with a second electric device. In the case of the bushing being fitted to a transformer, the second side of the bushing could for instance be connected to an external device, bus or cable.
In Fig. 2b is illustrated a variant of the embodiment in Fig. 2a and the same reference numerals are used. The variant in Fig. 2b differs from the embodiment in Fig. 2a in that the wall of the housing 12 stretches beyond the extended free end part 38 of the conductor 10. Another way of describing the variant in Fig. 2b is that the cover 35 with the protruding extended end part 38 of the conductor is arranged as being recessed in the upper end of the housing 12 of the bushing. The details of Figs. 3, 4 and 5 are equally applicable to both variants.
According to the present invention, the conductor 10 is positioned and fixated, i.e. held steady, in relation to the housing, at the exit opening 34, by means of a holder device 40 mounted on the housing, i.e. the cover 35 in the illustrated embodiment. The holder device is illustrated in Fig. 4 and in further detail in Fig. 5. The holder device is intended to provide radial clamping pressure to the conductor, resulting in rotational friction locking of the conductor with respect to the cover. This radial clamping pressure can be achieved by clamping members 42, 43 that in combination with a locking ring 46 exert radial pressure on the conductor. In the presented embodiment, the clamping members 42, 43 are designed as two conical, wedge shaped members. The locking ring 46 and the wedges 42, 43 are provided with holes 47, 48 for fastening elements 44, in the present case screws. The fastening elements 44 are intended to provide axial clamping force between the locking ring 46 and the top cover 35 when secured in holes 49 in the locking ring. By means of the conical wedges 42, 43 the axial clamping force results in radial pressure on the conductor's end part 38.
Further, the conductor needs to be fixated in relation to the housing 12 and the cover 35 both in the axial direction and the rotational direction. In order to position and fixate the conductor 10 in the axial direction, the extended end part 38 of the conductor is provided with axial positioning elements 50 for cooperation with corresponding axial positioning elements 51 on the conical wedges 42, 43. The axial positioning elements 50 on the end part 38 of the conductor 10 are designed as at least one external annular groove. The axial positioning elements 51 on the conical wedges 42, 43 are designed as at least one corresponding projecting profile, such as a ring or part of a ring along the internal circumference of the respective wedge. It should be noted that naturally each wedge comprises only a part of each projecting ring along the internal circumference and it is only when the wedges are mounted together that a more complete projecting ring is obtained. The number of grooves and projecting profiles, such as rings, is three in the illustrated embodiment, but may of course be varied.
The holder device is mounted on the extended free end part 38 of the conductor 10 by first placing the conical wedges 42, 43 against the conductor. By means of the cooperating grooves 50 and the projecting rings 51 the correct axial positioning of the wedges is achieved. Then the locking ring 46 is mounted over the wedges, and the screws 44 are inserted through the holes 48 in the locking ring, further through the holes 47 in the wedges 42, 43, and finally screwed into the holes 49 in the cover 35, thereby securing the parts of the holder device to the cover 35. When the screws are tightened, the conductor is positioned and locked by the wedges in the axial direction by means of the engaging grooves 50 and the projecting rings 51, and the conductor is also locked in the rotational direction by friction force. This locking is obtained irrespective of how the conductor is oriented in the rotational direction in relation to the cover 35.
There are of course other alternatives for the cooperating grooves and the corresponding projecting profile, for example a groove and a separate, loose ring, or a pin cooperating with a corresponding hole.
It would of course also be possible to have an arrangement with radially arranged pins or screws adapted to exert a radial force on the conductor from several directions, thereby achieving locking.
When the holder device is mounted, the wedges are pressed against the conductor and the cover. This helps cooling of the inside of the bushing, since heat can be transferred from the conductor through the wedges and further to the cover, the housing and the surrounding air. It also ensures electrical contact between the cover, the housing and the conductor. These two advantages are achieved when choosing an electrical and thermal conductive material. However, other materials may be used to obtain these features of the holder device.
Naturally, the number of wedges may be varied, as long as they, when assembled to the conductor, form a ring or at least the major part of a ring, in order to obtain symmetrical clamping distribution. However, it should be mentioned that it would also be possible to have a conical wedge shaped element that only covers part of the circumference of the conductor. For example it is possible to use only one conical wedge that covers half the circumference.
It would also be conceivable to use a slit wedge shaped ring that is pulled over the end of the conductor, by means of the slit providing the necessary resiliency to the ring. The wedge shaped ring can then be snapped into position on the conductor by means of the cooperating grooves and projecting profiles.
Since the bushing has a space between the conductor 10 and the housing 12 normally filled with insulating medium, e.g. a gas, there is provided a sealing 52 between the conductor 10 and the cover 35, such as radial sealing.
In the illustrated embodiment of Figs. 2a and 2b, the bushing is only provided with one external connection arrangement in accordance with the present invention, namely the second connection arrangement 32 at the upper end. The first connection arrangement 30 is illustrated as a regular contact used in prior art. However, it should be perfectly clear that also the first connection arrangement 30 may be designed in the same way as the illustrated second connection arrangement 32, whenever suitable. This may for example be the case when the bushing is a wall bushing between valve halls.
Further, in the illustrated embodiment, the bushing includes a separate cover 35 of the housing 12. Alternatively, the cover can be integrated in the housing and be made in one piece with the housing. The housing can then be described as having an inwards directed flange or possibly flanges, and the exit opening 34 for the conductor 10 is then provided between the edges of the flange or flanges.
The housing and the cover are traditionally made of metal in order to be electrically and thermically conducting. However, there may be applications where at least one of them is made from non-conductive material, e.g. epoxy material.
The conductor 10 may be a solid conductor or a hollow conductor.
The described bushing may be used both for DC and AC applications.
In the illustrative embodiment, it has been indicated that a transformer may be a high voltage device on which the inventive high voltage bushing is used. However, it is emphasized that the inventive high voltage bushing may also be used with other types of high voltage devices, such as reactors, breakers, generators, switchgear or any other suitable device finding an application in high voltage systems. Further, the terms electric device and high voltage device should also be interpreted as including cables, buses, surge arresters, DC valves and the like, within the context of the present invention.
When the inventive bushing is used in a transformer, oil is used as insulating medium inside the transformer and on the other side of the bushing the medium is air, for example in an HVDC valve hall. This type of bushing is generally referred to as an air-oil bushing. However, as indicated above, the bushing according to the invention is suitable for use in many electric devices, irrespective of the media on the respective sides of the bushing, such as air-air (wall bushing), air-gas (gas switchgear), etc. It should also be mentioned that the present invention bears no restriction as to the choice of insulation medium inside the bushing. It may for example be gas, oil, gel, or combinations thereof.
The present invention is not limited to the described embodiment, given as example only, but may be varied and modified in many ways within the scope of the appended claims, as will be realized by a person skilled in the art.

Claims

A high voltage bushing comprising
a hollow insulator housing (12),
a high voltage conductor (10) provided inside the housing,
a first connection arrangement (30) where the conductor can be connected to a first electric device and a second connection arrangement (32) where the conductor can be connected to a second electric device,
characterized in that at least one of said first connection arrangement and said second connection arrangement is designed as an external connection arrangement
in which
the conductor (10) has an extended end part (38), and
the bushing comprises an exit opening (34) through which the extended end part (38) of the conductor exits from the bushing, in order for the extended end part of the conductor to be connectable to an electric device.
A high voltage bushing according to claim 1, characterized in that it comprises a holder device (40) for fixating the conductor (10) in relation to the housing (12), at the exit opening (34).
A high voltage bushing according to claim 2, characterized in that the holder device (40) comprises at least one clamping member (42, 43) for providing rotational locking by radial clamping pressure to the extended end part (38) of the conductor (10).
A high voltage bushing according to claim 3, characterized in that the holder device (40) comprises at least one wedge element (42, 43) forming a clamping member and adapted to be mounted on the extended end part (38) of the conductor (10), a locking ring (46) mounted over the wedge element, and fastening elements (44) for fixating the wedge element and the locking ring to the housing (12), outside the exit opening (34).
A high voltage bushing according to claim 4, characterized in that the fastening elements are screws (44), and that the housing (12), the at least one wedge element (42, 43) and the locking ring (46) are provided with holes (47, 48, 49) adapted for the screws, and that the holes in the housing are provided with internal threads for cooperation with external threads on the screws.
A high voltage bushing according to any one of claims 4-5, characterized in that the housing (12) and the at least one wedge element (42,43) are in thermal and electrical contact with each other.
A high voltage bushing according to any one of claims 3-6, characterized in that the extended end part (38) of the conductor (10) is provided with first axial positioning elements (50) on its outer circumference for cooperation with corresponding second axial positioning elements (51) on the internal circumference of the at least one clamping member (42, 43) in order to achieve a predefined axial position of the conductor (10) in relation to the housing (12).
A high voltage bushing according to claim 7, characterized in that either one of the first axial positioning elements and the second axial positioning elements are designed as at least one annular groove (50), and that the other axial positioning elements are designed as at least one projecting profile (51).
A high voltage bushing according to any one of claims 1-8, characterized in that the bushing includes a cover (35) forming part of the housing (12), that the exit opening (34) for the conductor (10) is designed as a hole (36) in the cover through which hole the extended end part (38) of the conductor (10) exits from the bushing.
A high voltage bushing according to claim 9, characterized in that the cover (35) is made as a separate part.
A high voltage bushing according to any one of claims 1-10, characterized in that it is a DC bushing.
A high voltage bushing according to any one of claims 1-10, characterized in that it is a gas insulated bushing.
A high voltage bushing according to any one of claims 1-10, characterized in that the external connection arrangement is an external air contact.
A high voltage bushing according to any one of claims 1-10, characterized in that the housing is a sealed housing whereby the interior of the bushing is sealed off from the surroundings of the bushing.
A high voltage device comprising a bushing in accordance with any one of claims 1-14, and said high voltage device being either one of the first electric device or the second electric device to which the conductor can be connected.