EP2117014A1

EP2117014A1 - High voltage bushing contact, high voltage bushing comprising such contact and high voltage device comprising bushing with such contact

Info

Publication number: EP2117014A1
Application number: EP08155694A
Authority: EP
Inventors: David Emilsson; Thomas Eriksson
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
Anticipated expiration: 2028-05-06
Also published as: EP2117014B1; WO2009135743A1; ATE521069T1; CN101577375A; CN101577375B; BRPI0912526A2

Abstract

The invention concerns a high voltage bushing contact, comprising a first contact part (14) for connection with an electric device and a second contact part (16) for connection with a conductor (10) of the bushing, wherein the second contact part has an inner bore (18) with an opening for receiving an end of the conductor. The contact also comprises a set of mounting holes (22, 42) and a set of mounting members (24) adapted to be inserted through the mounting holes and by means of which both contact parts (14, 16) are secured to the end of the conductor (10), and that each mounting hole (22, 42) has a first opening inside the inner bore (18) of the second contact part (16). The invention also concerns a high voltage bushing comprising such a contact, and 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 contacts for 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 provided with sheds and which is generally hollow. On the inside of the bushing, voltage grading is performed by a condenser body 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, such as the tank wall, 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.
In prior art bushings, the bottom end portion of the high voltage conductor forms a bottom contact that is arranged to be connected to a first electric device, which in the case of a transformer will be the internal components of the transformer. For this purpose, a mating internal contact is provided inside the transformer. At the upper end of the bushing, opposite the bottom contact end, the conductor is provided with an upper outer terminal, or external connection contact, by means of which the conductor is connected to a second electric device or external source. Traditionally, the external connection contact is electrically connected to the conductor through an essentially planar 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 electric device.
In another type of prior art bushings where the outer terminal may not be attached directly to the top cover of the bushing, the connection between the outer terminal and the conductor is achieved by means of a conducting intermediate part. This intermediate part is mounted over the end of the conductor, it stretches through the top cover of the bushing, and the outer terminal is screwed onto this intermediate part on the outside of the bushing. In order to fasten the intermediate part to the conductor, it has to be screwed into a steel draw ring or similar located inside the conductor. This draw ring is in turn screwed into the conductor, thereby reducing the wall thickness of the conductor due to the necessary internal threads. This draw ring arrangement also requires that a sealing is provided.
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. When it concerns the conductor, it therefore becomes increasingly important to minimize every type of arrangement that leads to reductions in the conducting material in the conductor, such as threads, for example. It is also 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 contact that improves prior bushing contacts, 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 bushing comprising such a contact and a high voltage device comprising such a high voltage bushing.
These objects, among others, are achieved by a high voltage bushing contact, a high voltage bushing and a high voltage device as defined in the independent claims.
Accordingly is defined a high voltage bushing contact, comprising a first contact part for connection with an electric device and a second contact part for connection with a conductor of the bushing, wherein the second contact part has an inner bore with an opening for receiving an end of the conductor, characterized in that the contact also comprises a set of mounting holes and a set of mounting members adapted to be inserted through the mounting holes and by means of which both contact parts are secured to the end of the conductor, and that each mounting hole has a first opening inside the inner bore of the second contact part. By securing both contact parts to the end of the conductor with the same set of mounting holes and mounting screws the advantage of a simpler construction with fewer parts is achieved.
According to a further feature, the first contact part has a maximum external cross sectional measure, perpendicular to the axis of the conductor, and the mounting holes are located within the maximum external cross sectional measure of the first contact part. By locating the mounting holes according to this feature is offered the possibility of having a first external contact part with a larger cross section than in prior art, for example when the mounting holes are located externally of the contact part on a flange. A larger diameter on the external contact makes it possible to increase the current capability without making a huge top contact.
According to a first embodiment, the first contact part is hollow and each mounting hole has a second opening inside the hollow portion of the first contact part, for insertion of the mounting members. The mounting members can therefore be inserted into the mounting holes from inside the hollow interior of the first contact part, i.e. the contact part that is connected to an external electrical device. Through this arrangement, the mounting holes and the mounting members may be made shorter than in the second embodiment described below.
According to a second embodiment, the first contact part is a solid body and each mounting hole stretches through the solid body and further through a bottom of the inner bore. This embodiment is simple to manufacture and sturdy.
In this embodiment, each mounting hole has a second opening at a free end of the first contact part.
According to another feature of contact of the present invention, it is made in one piece. This provides for favourable current paths, with a minimum of losses due to joints, for example. It is also easy to manufacture. For example, it can be manufactured from a solid rod by using a lathe, or from a pipe.
In a variant of the first embodiment, the inner bore of the second contact part may be separated from the hollow portion of the first contact part by a separate intermediate wall and the mounting holes are made in the intermediate wall.
According to the present invention is also defined a high voltage bushing comprising an external connection contact in accordance with any one of the claims defining the contact, and a high voltage device comprising such a high voltage bushing.

Brief description of the drawings

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

Fig. 1 illustrates schematically, in cross section, an end part of a high voltage bushing provided with an external connection contact in accordance with a first embodiment of the present invention,
Fig. 2 illustrates schematically, a perspective view in cross section and in a larger scale, the contact according to the first embodiment of the present invention,
Fig. 3 illustrates schematically, in cross section, a variant of the first embodiment of the contact, and
Fig. 4 illustrates schematically, in cross section, a second embodiment of a contact according to the present invention.

Detailed description of the invention

In Fig. 1 is shown one end of a high voltage bushing provided with a contact according to a first embodiment of the present invention. The high voltage bushing comprises a hollow bushing insulator 2 that forms a housing around the high voltage conductor 10. The end of the bushing is closed by a top cover 4. The cover is provided with a hole 6 through which the conductor 10 runs to the outside of the bushing. An example of such an arrangement is described in the European patent application entitled "High voltage bushing and high voltage device comprising such bushing" which is filed on the same date as the present application and by the same applicant.
The conductor 10 is hollow and it is provided with some kind of end plug 12 at its end, which end plug is only schematically illustrated. There may also be other devices or arrangement inside the conductor, such as a draw rod arrangement, which are not shown. Alternatively, the conductor may be solid, in which case the contact may be attached to the conductor by the screws 24 being screwed into corresponding mounting holes provided in the end of the conductor.
The contact according to the first embodiment illustrated in Fig. 1 and Fig. 2 comprises a first contact part 14 for connection with an electric device outside the bushing, and a second contact part 16 for connection with the conductor 10. For this purpose, the second contact part has an inner bore 18 with an opening for receiving the conductor 10. The end of the conductor is inserted into the inner bore and electrical connection with the contact is ascertained by an electrical connection device 20 (electrical connection devices are not shown in fig 2). The contact also comprises mounting holes 22 and mounting members 24, such as screws in the illustrated example, by means of which the contact is secured to the end of the conductor. The arrangement with a first contact part and a second contact part ensures redundancy of electrical contact between conductor 10 and contact 14 and should one contact part fail the other is sufficient for carrying the currency from conductor to contact.
The first contact part 14, in the following also called the external contact part, is hollow in the illustrated embodiment. The second contact part 16, also referred to as the conductor contact part in the following, has a bottom part, formed by the bottom of the inner bore 18. This bottom part can also be described as an intermediate wall 26 that separates the external contact part from the conductor contact part. In the illustrated embodiment, the external contact part 14, the conductor contact part 16 and the intermediate wall 26 are all formed in one piece.
The mounting holes 22 are formed in the intermediate wall 26, with one opening in the hollow interior of the external contact part 14 and one opening in inner bore 18 of the conductor contact part 16. When the contact is mounted on the conductor, the screws 24 are inserted in the holes 22 and are screwed into the end of the conductor, which is provided with some appropriate device for receiving the screws. This may be a simple end plug or some other suitable device.
A variant of the first embodiment is shown in Fig. 3. In this figure, elements that are the same or similar to elements in Fig. 1 or Fig. 2 have been given the same reference number. The contact according to this variant comprises an external contact part 14 and conductor contact part 16 with an inner bore 18. The external contact part is hollow. The difference between this variant and Fig. 2 is that the intermediate wall 38 is made as a separate element that is inserted in the contact. Consequently the mounting holes 22 are made in this separate element.
A second embodiment of the present invention is illustrated in Fig. 4. According to this embodiment the external contact part 14 is not hollow, but is made as a solid body. The mounting holes 42 stretches all the way through the solid body 14, from the free external end of the external contact part 14 to the inner bore 18 inside the conductor contact part 16.
The external shape as well as the internal shape of the external contact part 14 may vary. In Figs. 2 the external contact part is illustrated as being cylindric. However, it may very well be square, hexagonal or any other shape that is adapted to the contact of the electric device to which it is going to be connected. For example, in the case of the second embodiment, a hexagonal shape may be suitable.
In all embodiments, the first, external, contact part has a maximum external cross sectional measure, perpendicular to the axis of the conductor, and the mounting holes are located within the maximum external cross sectional measure of the first contact part. This is irrespective of the external shape or internal shape of the external contact part.
In this description, the term "high voltage" (HV) is 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.
The described high voltage bushing contact may be used in a bushing both for DC and AC applications.
The inventive contact and high voltage bushing may also be used in many types of high voltage devices, such as transformers, 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 arrestors, DC valves etc., within the context of the present invention.
Furthermore, the present invention bears no restriction as concerns the media on the respective sides of the bushing, such as air-oil, air-air (wall bushing), air-gas (gas switchgear), etc. Nor does it involve any 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

High voltage bushing contact, comprising a first contact part (14) for connection with an electric device and a second contact part (16) for connection with a conductor (10) of the bushing, wherein the second contact part has an inner bore (18) with an opening for receiving an end of the conductor, characterized in that the contact also comprises a set of mounting holes (22, 42) and a set of mounting members (24) adapted to be inserted through the mounting holes and by means of which both contact parts (14, 16) are secured to the end of the conductor (10), and that each mounting hole (22, 42) has a first opening inside the inner bore (18) of the second contact part (16).
Contact according to claim 1, characterized in that the first contact part (14) has a maximum external cross sectional measure, perpendicular to the axis of the conductor (10), and that the mounting holes (22, 42) are located within the maximum external cross sectional measure of the first contact part.
Contact according to claim 1 or claim 2, characterized in that the first contact part (14) is hollow and that each mounting hole (22) has a second opening inside the hollow portion of the first contact part, for insertion of the mounting members (24).
Contact according to claim 1 or claim 2, characterized in that the first contact part (14) is a solid body and that each mounting hole (42) stretches through the solid body and further through a bottom of the inner bore (18).
Contact according to claim 4, characterized in that each mounting hole (42) has a second opening at a free end of the first contact part (14).
Contact according to any one of the preceding claims, characterized in that it is made in one piece.
Contact according to claim 3, characterized in that the inner bore (18) of the second contact part (16) is separated from the hollow portion of the first contact part by a separate intermediate wall (36) and that the mounting holes (22) are made in the intermediate wall.
High voltage bushing comprising an external connection contact in accordance with any one of claims 1-7.
High voltage device comprising a high voltage bushing according to claim 8.