WO2000058985A1

WO2000058985A1 - A switching device and the use thereof

Info

Publication number: WO2000058985A1
Application number: PCT/SE2000/000605
Authority: WO
Inventors: Ahmed Kaddani; Magnus Backman; Per Larsson; Said Zahrai; Jarmo KÄHKÖNEN; Gordon Kelly; Li Ming
Original assignee: Abb T&D Technology Ltd.
Priority date: 1999-03-30
Filing date: 2000-03-29
Publication date: 2000-10-05
Also published as: AU4160200A; SE9901150D0

Abstract

A switching device comprises two contact members (2, 3) at least one of which is movable such that they are movable relative to and from each other between a first position in which they are in electric contact with each other, and second position in which they are separated and have different potentials. It also comprises at least one insulating body (1) which electrically insulates the contact members (2, 3) from each other when they are in the second position. The insulating body (1) is arranged such that a main part of an electric field between said contact members (2, 3) is located within said insulating body (1).

Description

A SWITCHING DEVICE AND THE USE THEREOF

BACKGROUND OF THE INVENTION AND PRIOR ART

The present invention relates to a switching device for medium- or high-voltage applications. In particular, it relates to such a device comprising two contact members at least one of which is movable such that they are movable to and from each other between a first position in which they are in electric contact with each other, and a second position in which they are separated and have different potentials, and at least one insulating body which is arranged to electrically insulate the contact members from each other when they are in the second position.

The invention also relates to a method of breaking a current in medium- and high-voltage applications.

The invention is relevant to breaking devices for electric lines in general, but is particularly relevant to breaking switches in me- dium- or high-voltage applications. Medium voltages are referred to as voltages of 1 kV or more, while high voltages typically can be referred to as voltages of 72.5 kV and more according to the IEC Standards.

When breaking currents in medium- or high-voltage applications, phenomena that do not need to be considered in low-voltage applications appear. An electric arc will be generated between the separating contacts, almost immediately developing a huge amount of energy as heat and lightning. Hence, such an electric arc formed between the separating contacts must be extinguished as quickly as possible during the breaking phase, and must not be regenerated during the following insulating phase. Due to the high voltages involved, an electric discharge and a regeneration of the arc is much more likely to occur in medium- and high-voltage applications than in low-voltage applications.

In order to extinguish the arc quickly, the contacts have to be moved away from each other very rapidly, such that the arc is extended and weakened, making it possible to extinguish it by means of techniques well known per se, such as the puffer- technique or self blast-technique.

In order to shorten the distance needed between the separated contacts and to avoid an electrical breakdown, that is a regeneration of the arc, prior art uses pressurised gases, particularly SF₆, around and between the separated contacts. The higher the pressure, the less is the risk of having an electrical breakdown.

Hence, the equipment for moving the contacts and the equipment for generating and maintaining the gas pressure have to be quite powerful.

A number of breaking switching devices for electric lines which make use of solid insulating bodies between separated contacts have already been proposed in prior art. Almost without exception, such devices are related to low-voltage applications, while high-voltage switching devices make use of gas as the insulating medium between the contacts.

However, for improving the breaking performance of a medium- and high-voltage breaker, the international patent application WO 94/1 1 893 discloses a breaking switching device for electric lines, especially for medium- and high-voltage electric lines, said device having an electrically insulating screen adapted so as to be swiftly interposed between the two contacts during the separation thereof in order to stop the arc which could occur during opening. The device is characterised in that the screen is separated from the contacts in the open position of the device and that it acts by elongating and extinguishing the arc during the opening phase. Thereby, a somewhat slower separation of the contacts could be accepted, and a somewhat higher electrical breakdown voltage could be obtained due to the screen having a higher breakdown voltage than the pressurised gas.

However, the distribution of the electric field by a device as the one described in WO 94/1 1 893 will be such that important potential differences will appear between each contact and the adjacent insulating body surface. Such a potential difference might result in a discharge between contact and insulating body, which might in its turn result in the generation of a discharge all the way between the contacts. To be sure that no such discharges occur, the distances between the contacts and contacts and screen have to be large enough to ensure safety against such discharges, and there is still a need of pressurised gas, e.g. SF₆ for preventing such discharges and electrical breakdowns from being generated.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a switching device which reduces or even eliminates the need for high pressure gases during a breaking phase and a subsequent insulating phase and/or reduces the mechanical or electrical energy needed to separate the contact members during the breaking phase. The switching device should permit a short distance between the separated contact members while still presenting safety against electrical breakdowns.

This object is achieved by means of a switching device as initially defined, characterised in that said insulating body is arranged such that the main part of an electric field between said contact members is located within the insulating body of the switching device.

According to a preferred embodiment, the switching device is characterised in that the insulating body mainly comprises an in- sulating material and at least two portions which have a substantially higher electrical conductivity than said insulating material, said portions being arranged such that the electric field is concentrated to the insulating body.

By arranging such portions in such a body the electric field distribution between the separated contact members can be effected and controlled in a favourable way, thereby preventing the generation of a discharge and an electrical breakdown during an insulating phase, as has been shown in experiments made by the inventors. For a given potential difference between the contact members, the distance between the adjacent ends of the contact members can be reduced while, at the same time, the breakdown resistance is maintained or even better than by prior art where no such portions with higher conductivity are used.

Hence, the distance that the contact members have to be moved from the first to the second position can be reduced. As a result thereof, the speed at which the contact members need to be moved and needed, the mechanical or electric power of the equipment accomplishing said movement is reduced.

As the field distribution between contact members and the insulating body can be controlled by the provision of said portions the risk of having discharges and electrical breakdowns can be reduced, whereby the need for high pressurised gas is also reduced.

By means of the invention, the switching device can be made less power consuming, and the need of gases that might be toxic when ignited, as is the case with SF₆, can be reduced or avoided.

According to another preferred embodiment, each of said portions has a potential which is approximately the same as or iden- tical with the potential of an adjacent one of the contact members in their second position. Hereby, a further concentration of the electric field to the insulating body is obtained. Thereby, the electric field distribution is further concentrated to the insulating body itself as there is little or no potential difference between the contact member in question and the corresponding, adjacent portion. The need of pressurised gas with high electrical break- down capacity between the contact member and the body is greatly reduced as the risk of a discharge occurring between the contact member and the body is reduced. As the insulating material of the insulating body preferably is a polymer or a composite material with a breakdown voltage which is up to approximately 5-10 times as high as the one of SF₆, it is easily realised that the distance between the contacting members can be far less than without such concentration of the field to the insulating body.

According to another preferred embodiment, at least one of said portions has the shape of a layer. Arranged as a layer, said portion may affect the electric field distribution favourably without occupying an unnecessarily large volume or part of the insulating body. The layer has a large width-thickness ratio, and may be generally planer or curved according to different applications.

According to another preferred embodiment, said portions are enclosed by the surrounding insulating material of said body. In this way, discharges emanating from an area or region between said portions and the insulating material, which could possibly give rise to a regeneration of an arc between the contact members, can be considerably reduced.

According to another preferred embodiment of the switching device, at least a part of said body is located between the adjacent ends of said contact members in the second position, said part comprising said portions. For most switching devices, and particularly switching devices in which the contact members are elongated rods in alignment with each other and separated by means of an axial movement from each other, this region is the one which is most susceptible to a voltage breakdown. Accordingly, the provision of said portions is particularly effective in this part of the body or region. According to another preferred embodiment, said insulating body defines a first solid insulating body, mainly located between the contact members in their second position, and the device com- prises at least one second body located very close to or even in contact with the first body and extending in the longitudinal direction of an adjacent contact member. Such a second body could easily be arranged so that it forms a barrier that prevents a discharge from being generated along a path which runs around the first insulating body. Said second body could, of course, be an integrated part of the first body, but should preferably be separate and movable in relation to said first body as well as the adjacent contact member for reasons that will be obvious when reading the rest of the description. Due to the provision of the second body, the need for pressurised gas is further reduced or even eliminated. Preferably, the second insulating body is also provided with a portion of significantly higher electrical conductivity than its insulating material, said portion being connected to an adjacent contact member for reasons similar to those already mentioned for the portions of the first body.

According to another preferred embodiment, the second body is arranged as a sleeve surrounding and running along a contact member and being located close to or in contact with the first body, as the contact members occupy their second position. Such an embodiment is favourable as it promotes the construction of a switching device which requires a minimum of space, a short distance between the contact members, and a high breakdown voltage, such that the need of a pressurised gas like SF₆ is reduced or even eliminated. Said sleeve is preferably movable in relation to its adjacent contact member in the longitudinal direction thereof, whereby it can be moved such that it does not prevent the contact member from reaching the second position in the shortest and fastest possible way. This embodiment takes full advantage of the high breakdown voltage of the insulating material, reducing the need of pressurised gases such as SF₆. Another object of the invention is to provide a method which reduces or even eliminates the need for high pressure gases during a breaking phase and a subsequent insulating phase and/or reduces the power needed to separate the contact members during the breaking phase. The method should permit a short distance between the separated contact members while still presenting safety against electrical breakdowns.

This objective is achieved by means of a method of breaking a current in medium- and high-voltage applications, in which two contact members are moved from a first position, in which they are in electric contact with each other, to a second position, in which they are separated from each other, characterised in that an insulating body is arranged between the separated contact members such that a main part of an electric field between said contact members is located within said body.

According to a preferred embodiment, different voltages are applied to a pair of electrically conducting portions that form a part of said insulating body. Thereby, a further concentration of the electric field to the insulating body may be achieved, as has been shown in experiments made by the inventors.

The invention also relates to the use of the inventive switching device and method for breaking a current in medium- or high- voltage applications.

Further advantages and features of the present invention will be clear from the characteristic parts of the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the inventive switching device will be described by way of example with reference to the annexed drawings, wherein:

fig. 1 is a schematic perspective view of a first body according to one embodiment of the invention, fig. 2 is a cross-sectional view showing half the body of fig. 1 , fig. 3 is a schematic cross-sectional side view of one embodiment of the inventive switching device, including the body of figs. 1 and 2, and with its contact members in a first position, and fig. 4 is a view similar to the one of fig. 2, with the contact mem- bers located in a second position.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

One embodiment of the switching device according to the inven- tion is shown in figs. 1 -4. The switching device operates as a breaker of a medium- or high-voltage line. It comprises a first insulating, solid body 1 and two contact members 2, 3, each of which is surrounded by a respective second insulating, solid body 4, 5. The insulating material of said bodies 1 , 4, 5 may be any material having a high electrical breakdown resistance. A polymer or composite is preferred, particularly PTFE.

During a breaking phase, the contact members 2, 3 are to move from a first position, shown in fig. 3, to a second position in which they are separated, shown in fig. 4. As can be seen in figs. 2-4, the first body 1 comprises a passage or recess 6 to be penetrated by the contact members 3, 4 in their first position. Around the passage or recess 6 there is a chamber 7 arranged within the first body 1 . The chamber 7 communicates with the passage or recess 6 via a particular nozzle or opening 9. As the contact members are separated an electric arc will arise between the opposite contact ends, and, in a way known per se, pressurised gases will be created inside the chamber 7 due to the radiation from the arc causing ablation, i.e. an emission of gas, of the material of the insulating body 1 in the area of said nozzle 9 and chamber 7. As the contact members 2, 3 are retracted from each other the arc is extended and weakened, and finally the pressurised gas or gases in the chamber 7 will flow back towards the arc and blow it out, thereby completing the breaking phase. This technique is well known as "self-blasting".

The two contact members 2, 3 have an elongated shape and are arranged co-axially opposite to each other. They are separated in a co-axial movement in opposite directions accomplished by means of an equipment adapted thereto and not shown. As soon as the contact members are no longer in engagement with the passage or recess 6 the first body 1 is moved in a direction perpendicular to the direction of the moving contact members 2, 3. Accordingly, the passage 6 and the chamber 7 are displaced lat- erally in relation to the separated contact members 2, 3, thereby further extending and weakening the arc between the contacts, if there still is such an arc at this stage. During the lateral displacement of the first body 1 in relation to the contact members 2, 3, there is a spacing between the second bodies 4, 5 and the first body 1 at least as long as the arc still exists.

Eventually, the first body will reach the position shown in fig. 4. In this position, the second bodies 4, 5, which are movable generally co-axially in relation to the contact members 2, 3, are moved to a position in which they are very close to or in contact with the first body 1 , thereby preventing an arc from being regenerated along a path running around the first body 1 or through the passage 6. Further obstacles that are to prevent the arc from being regenerated are defined by flanges 1 1 , 12 pro- jecting from the first body 1 in the longitudinal direction of the contact members 2, 3 at opposite sides of each of the contact members 2, 3. Said flanges 1 1 , 12 also extend in the longitudinal direction of the first body 1 . Thereby, the main part of the first body 1 presents an H-profile cross-section.

The switching device has now passed from the breaking phase to the insulating phase, as shown in fig. 4. The part of the first body located between the ends of the contact members 2, 3 is provided with disc-like portions 13, 14 of a material which has a substantially higher electrical conductivity than the insulating material which surrounds them and forms the main part of the in- sulating body 1 . These portions 13, 14 are preferably made of metal or a semiconducting material. They are provided such that they counteract a regeneration of an arc by affecting the distribution of the electric field between the two separated contact members 2, 3. The portions 13, 14 are opposite to each other and opposite an adjacent contact member 2, 3. Each portion 13, 14 defines a curved plate or layer, at least a part of which generally follows an equipotential line of the electric field between said contact members 2, 3, as the equipotential lines would run under free conditions, i.e. without being affected by said portions. Each portion 13, 14 is therefore slightly cup-shaped.

A first position 1 3 of these two portions may have a potential which is between zero and the potential of the adjacent contact member 2 or equal to the potential of the contact member 2. Also, the second portion 14 of said portions may have a potential which is between zero and a potential of its adjacent contact member 3, or equal to the potential of said contact member 3. Here, the respective portion 13, 14 has the same potential or voltage as its adjacent contact member 2 and 3, respectively, as it is connected to said contact member 2 and 3, respectively, through a particular connecting member 15, 16, schematically shown in fig. 4. Thereby, a very favourable distribution of the electric field between the contact members is accomplished, making it possible to have a very short distance between the separated contact members 2, 3 without running the risk of having a regeneration of the arc. Preferably, the connecting member 15, 16 is covered by some insulating material (not shown) in or- der to minimise the risk of having an arc generated between the connecting members 15, 16.

Also the second bodies 4, 5 are provided with portions 17, 18 having a substantially better conductivity than the insulating material of each second body 4, 5, respectively. Also these portions may be made of a metal or a semiconducting material. Here, the second bodies 4, 5 are arranged as sleeves around each contact member 2, 3, respectively, and said portions 17, 18 are provided as generally cylindrical layers, here, complete cylinders, inside each body 4 and 5 respectively, running in the longitudinal direction and co-axially with the latter ones. In the second position of the contact members 2 during the insulating phase, the portion 17, 18 of each second body 4, 5 may have a potential between zero and the voltage of the adjacent contact member 2, 3, respectively. Here, each portion 17, 18 has a potential equal to the one of its adjacent contact member 2, 3 due to a connection 20, 21 being established between the contact members 2, 3 and portions 17, 18 at this stage. Here, said connections 20, 21 are con- stantly present, but could, as an alternative, be established as the second bodies 4, 5 are moved to their final position which they occupy during the insulating phase. Also the portions 17, 18 counteract the regeneration of an electrical arc by affecting the distribution of the electric field between the contact members 2, 3.

There are also action members 22, 23, here springs, provided in order to push the second bodies 4, 5 against the first body 1 for improving the insulation behaviour. In the zone where the first body 1 and a respective second body 4, 5 face each other, at least one of said bodies 1 , 4, 5 comprises a material prone to ablation when subjected to an electric arc. Thanks to such an ablation, a pressure increase may be achieved in said zone, thereby counteracting the generation of discharges in said zone. Hence, the second bodies 4, 5, together with the first body 1 , define a means for squeezing an arc and extinguishing an arc. Due to the provision of the first body 1 with its flanges 1 1 , 12, the second bodies 4, 5 and said portions 13, 14, 17, 18 of electrically conducting material inside said bodies 1 , 4, 5, a very reliable breaker is accomplished. The arrangement provides for a very rapid and effective extinction of the arc during the breaking phase, and the need for a pressurised gas such as SF₆ during the breaking and insulating phase is greatly reduced or even eliminated.

Of course, a plurality of alternative embodiments will be obvious for a man skilled in the art without departing from the scope of the invention, as defined in the enclosed patent claims supported by the description and the drawings.

For example, the relative dimensions of the different bodies and contact members may differ from the ones shown, as well as the positioning, shapes and dimensions of said portions 13, 14, 17, 18.

Moreover, the width of the disc-like portions 13, 14 should correspond to, i.e. be approximately the same as, the diameter of the cylindrical shape of the portions 17, 18 in the second body in order to obtain a favourable field distribution.

The first insulating body 1 could also be divided into a number of sub-bodies, each of which could be provided with one or more portions like portions 13, 14. Such embodiments should still be regarded as falling within the scope of the invention as defined in the following claims.

Claims

Patent claims

1 . A switching device for medium- or high-voltage applications, comprising - two contact members (2, 3) at least one of which is movable such that they are movable to and from each other between a first position in which they are in electric contact with each other, and a second position in which they are separated and have different potentials, - at least one insulating body (1 ) which mainly comprises an insulating material and which is arranged to electrically insulate the contact members (2, 3) from each other when they are in the second position, characterised in that - said insulating body (1 ) is arranged such that a main part of an electric field between said contact members (2, 3) is located within said insulating body (1 ).

2. A switching device according to claim 1 , characterised in that the insulating body (1 ) mainly comprises an insulating mate- rial and at least two portions (13, 14) which have a substantially higher electrical conductivity than said insulating material, said portions (13, 14) being arranged such that the electric field is concentrated to the insulating body (1 ).

3. A switching device according to claim 2, characterised in that each of said portions (13, 14) has a potential which is approximately the same as or identical with the potential of an adjacent contact member (2, 3) in its second position.

4. A switching device according to claim 2 or 3, characterised in that said contact members (2, 3) are electrically connected to one of said portions (13, 14) respectively when being in the second position.

5. A switching device according to claim 4, characterised in that, as the contact members (2, 3) occupy the second position, said portions (13, 14) are located at different distances from each of the contact members (2, 3), said contact members (2, 3) being electrically connected to the most adjacent one of said portions (13, 14).

6. A switching device according to any one of claims 2-5, characterised in that said portions (13, 14) comprise a metal or a semiconducting material.

7. A switching device according to any one of claims 2-6, char- acterised in that at least one of said portions (13, 14) has the shape of a layer.

8. A switching device according to any one of claims 2-7, characterised in that at least one of said portions (13, 14), or at least a part thereof, generally follows an equipotential line of an electric field between said contact members (2, 3) under free field conditions.

9. A switching device according to any one of claims 2-8, char- acterised in that said portions (13, 14) are enclosed by the surrounding insulating material of said body (1 ).

10. A switching device according to any one of claims 2-9, characterised in that at least a part of said body (1 ) is located be- tween the adjacent ends of said contact members (2, 3) in the second position, said part comprising said portions (13, 14).

1 1. A switching device according to any one of claims 1 -10, characterised in that said insulating body (1 ) defines a first body (1 ), mainly located between the contact members (2, 3) in the second position, and that the device comprises at least one second insulating body (4, 5), mainly comprising an insulating material and extending in the longitudinal direction of an adjacent contact member (2, 3).

12. A switching device according to claim 1 1 , characterised in that said second insulating body (4, 5) comprises a portion (17, 18) which has a substantially higher electrical conductivity than the insulating material of that body (4, 5).

13. A switching device according to claim 12, characterised in that said portion (17, 18) of said second insulating body (4, 5) has a potential which is approximately the same as or identical with the potential of an adjacent contact member (2, 3).

14. A switching device according to claims 12 and 13, charac- terised in that said portion (17, 18) of said second insulating body (4, 5) is connected to its adjacent contact member (2, 3).

15. A switching device according to any one of claims 1 1 -13, characterised in that the second body (4, 5) is arranged as a sleeve surrounding and running along a contact member (2, 3) and located in proximity to or in contact with the first body (1 ), as the contact member is in its second position.

16. A switching device according to any on of claims 1 1 -15, characterised in that at least one of the first and second insulating bodies (1 , 4, 5) comprises a material prone to ablation when subjected to an electric arc, said material being located in a region where said bodies face each other.

17. A switching device according to any one of claims 1 -15, characterised in that the potential difference between said contact members (2, 3), when being in their second position, is of the order of 1 kV or more.

18. A method of breaking a current in medium- and high-voltage applications, in which two contact members (2, 3) are moved from a first position, in which they are in electric contact with each other, to a second position, in which they are separated from each other, characterised in that an insulating body (1 ) is arranged between the separated contact members (2, 3) such that a main part of an electric field between said contact members (2, 3) is located within said body (1 ).

19. A method according to claim 18, characterised in that different voltages are applied to a pair of electrically conducting portions (13, 14) that form a part of said insulating body (1 ).

20. A method according to claim 19, characterised in that the voltage applied to the respective portion (13, 14) corresponds to the potential of the respective adjacent contact member (2, 3).

21. A method according to claim 20, characterised in that the respective voltages are applied to the respective portion (13, 14) by connecting the respective portion to a corresponding, adjacent contact member (2, 3).

22. A method according to any one of claims 19-21 , characterised in that a voltage corresponding to the potential of the respective contact member is also applied to a further electrically conducting portion (17, 18) located in a further insulating body (4, 5) located adjacent to said respective contact member (2, 3).

23. A method according to any one of claims 18-22, characterised in that it is applied by means of a switching device according to any one of claims 1 -21 .

24. Use of a switching device according to any one of claims 1 - 17 and a method according to any one of claims 18-23 for breaking a current in medium- or high-voltage applications.