WO2017162517A1

WO2017162517A1 - Electrical circuit breaker device

Info

Publication number: WO2017162517A1
Application number: PCT/EP2017/056261
Authority: WO
Inventors: Javier MANTILLA FLOREZ; Mahesh DHOTRE; Francesco Pisu; Stephan Grob; Xiangyang Ye; Oliver Cossalter
Original assignee: Abb Schweiz Ag
Priority date: 2016-03-24
Filing date: 2017-03-16
Publication date: 2017-09-28
Also published as: EP3433869B1; EP3433869A1; CN109196615B; CN109196615A

Abstract

An electric switching device (1) filled with a dielectric insulating medium comprises an arrangement of arcing contacts with a first arcing contact (3) and a second arcing contact (4), an insulating nozzle (2), an arcing volume (5) between the first arcing contact (3) and the second arcing contact (4), an exhaust volume (6) and an exhaust tube (7) arranged inside the exhaust volume (6). A diameter of the exhaust tube (7) increases in longitudinal direction (z) away from the arcing volume (5). Additionally or alternatively, the exhaust tube (7) comprises a plurality of exhaust tube openings (8) through its side wall (12), which connect the interior of the exhaust tube (7) with the exhaust volume (6), wherein at least a part of the exhaust tube openings (8) have different sizes.

Description

Electrical circuit breaker device

Technical field The invention resides in the field of medium and high voltage switching devices, particularly circuit breakers, and relates to an electrical switching device according to the independent claims. Background

Electrical switching devices are well known in the field of medium and high voltage switching applications. They are e.g. used for interrupting a nominal current as well as currents originating from an electrical fault occurs. For the purposes of this disclosure the term medium voltage refers to voltages from 1 kV to 72.5 kV and the term high voltage refers to voltages higher than 72.5 kV. The electrical switching devices, like said circuit breakers, may have to be able to carry high nominal currents of 3150 A to 6300 A and to switch very high short circuit currents of 31.5 kA to 80 kA at very high voltages of 72.5 kV to 1200 kV.

During interruption of a nominal or short circuit current within the electrical switching devices, the current commutates from the nominal contacts of the electrical switching device to its arcing contacts. They normally comprise as one arcing contact arcing contact fingers arranged around the longitudinal axis of the electrical switching device in a so- called arcing finger cage or tulip and, as a mating arcing contact, a rod which is driven into the finger cage. However, there are also arrangements with two rods as arcing contacts, which are driven towards one another and are connected via their front faces during a closing operation.

Tulip contacts are hollow and can connect to an exhaust tube. Pin contacts can also be hollow and may also connect to an exhaust tube.

During the opening or closing process of the electrical switching device an electric arc forms between the two arcing contacts. In order to interrupt the current, the electrical switching devices contain a dielectrically fluid used as an insulating medium (e.g. SF₆ gas) and for quenching the electric arc. Consequently, a part of the fluid located in the region where the electric arc is generated, called arcing volume, is considerably heated up (to around 20 ' 000-30 ' 000 °C) in a very short period of time. This part of the fluid builds up a pressure and is ejected from the arcing volume into so-called exhaust volumes .

Besides said gas pressure the axial gas flow acceleration in the nozzle system is another important parameter for cooling down the arc or for evacuating hot gas from the arcing volume as fast as possible. A way of influencing the flow acceleration away from the stagnation point is given by an optimized design of the nozzle system. This involves design of the so-called exhaust tube which serves to evacuate hot gas from the arcing volume into the exhaust volume and, as the case may be, further into a volume delimited by the enclosure of the circuit breaker.

In conventional circuit breakers the exhaust tube is a tube with openings, arranged following one of the arcing contacts of the circuit breaker in longitudinal direction (axial direction, i.e. in exhaust gas flow direction) . The hot gas flows through said arcing contact, then through the exhaust tube and subsequently it escapes into the exhaust volume through said openings of the exhaust tube. It may happen that evacuation of the hot gas from the arc zone is not optimal and results in lower switching performance.

In addition, due to the mass flow of the gas and the high speeds and pressures arising in the exhaust tube, the exhaust tube is subjected to erosion, which in turn may cause mechanical instability of the exhaust tube and may lead to particle generation, thereby reducing switching performance of the circuit breaker during normal operation, too. Description of the invention

It is an objective of the present invention to further improve an electrical switching device with respect to said disadvantages. In a first aspect of the invention this objective is solved by an electric switching device filled with a dielectric insulating medium and comprising at least an arrangement of arcing contacts with a first arcing contact and a corresponding second arcing contact. For opening and closing the electric switching device at least one of the arcing contacts are movable parallel to a longitudinal axis and cooperates with the other arcing contact. The switching device further comprises an insulating nozzle, an arcing volume between the first arcing contact and the second arcing contact, an exhaust volume and an exhaust tube. The exhaust tube is arranged in extension to the first arcing contact along the longitudinal axis and connects the exhaust volume with the arcing volume for evacuating at least a part of hot dielectric insulating medium into the exhaust tube.

In embodiments of this, the first arcing contact is a tulip contact or a hollow pin contact, the interior of which extends into the exhaust tube. This is for guiding the exhaust gases from the arcing volume through the first hollow arcing contact to the exhaust tube and therefrom into the exhaust volume.

In this aspect of the invention a diameter (i.e. a cross-sectional diameter) of the exhaust tube increases, at least along a section of the exhaust tube, in longitudinal direction away from the arcing volume (in other words in flow direction of the insulating medium or in exhaust gas flow direction) .

Increasing the diameter of the exhaust tube in the way stated above has a beneficial effect on controlled evacuation of the hot gas from the arcing zone in order to improve the switching performance. In particular, in the case of the diameter of the exhaust tube increasing at least along the section (i.e. increase-section LI) of the exhaust tube in longitudinal direction away from the arcing volume, the diameter of the exhaust tube is chosen to increase such that during a switching operation under operating conditions of the electric switching device a mass flow of the hot dielectric insulating medium to be evacuated through the exhaust tube is maximized.

In a second aspect of the invention, instead of providing an exhaust tube with an increasing diameter, the exhaust tube comprises a plurality of openings through its wall, which connect the interior of the exhaust tube with the exhaust volume, wherein at least a part of the openings have different sizes .

By providing holes of different sizes it is possible to optimize the circuit breaker depending on different parameters and/or depending on the circuit breaker construction. For example it is possible to take into account supersonic or subsonic gas flow in the exhaust tube. In other words, it is possible to optimize gas flow between the exhaust tube and the exhaust volume in order to control the material stress and hence erosion .

In a third aspect of the invention a combination of both measures mentioned above is used. Hence, the diameter of the exhaust tube is increased in longitudinal direction away from the arcing volume and the exhaust tube is provided with openings of different sizes along its longitudinal or axial extension .

By combining the first and the second aspect of the invention the combined advantages mentioned above are achieved.

In a fourth aspect of the invention the objective is solved by an electric switching device filled with a dielectric insulating medium and comprising at least an arrangement of arcing contacts with a first arcing contact and a corresponding second arcing contact. For opening and closing the electric switching device at least one of the arcing contacts is movable parallel to a longitudinal axis and cooperates with the other arcing contact. The switching device further comprises an insulating nozzle, an arcing volume between the first arcing contact and the second arcing contact, an exhaust volume and an exhaust tube. The exhaust tube is arranged in extension to the first arcing contact, in particular hollow tulip contact or hollow pin contact, along the longitudinal axis and connects the exhaust volume with the arcing volume for evacuating at least a part of hot dielectric insulating medium into the exhaust tube. The exhaust tube comprises a plurality of openings on its surface, which connect the interior of the exhaust tube with the exhaust volume. In this aspect of the invention a barrier element is arranged inside the exhaust tube in a region defined by a distal end of the exhaust tube with respect to the arcing volume and by a closest opening with respect to the distal end. A position, in particular a position along a longitudinal direction or axis z of the electric switching device, of the barrier element in said region is adjustable.

The fourth aspect of the invention makes it possible to eliminate "dead" volumes inside the exhaust tube by redirecting the gas towards the openings connecting the exhaust tube with the exhaust volume. In this way losses at the stagnation point are reduced, while heat transfer is increased due to the more effective redirection of the gas towards the openings (particularly the last openings) and consequently into the exhaust volume where the hot gas originating from the arcing volume mixes with cold gas. This again leads to the advantages mentioned in the context of the first aspect of the invention. Particularly by making the position (i.e. longitudinal or axial position) of the barrier element adjustable within said prescribed range, it is possible to account for different exhaust tube dimensions and designs of the exhaust tube openings, more specifically for the position of the last opening.

In an advantageous embodiment, a cross-section of each opening is chosen such that during a switching operation a substantially equal amount of mass (i.e. mass of of exhaust gas) is flowing through each opening from the exhaust tube into the exhaust volume.

In embodiments, the electrical switching device according to the invention may be used as an earthing device, a fast-acting earthing device, a circuit breaker, a generator circuit breaker, a switch disconnector, a combined disconnector and earthing switch, or a load break switch.

In further embodiments, the dielectric insulation medium used inside the circuit breaker is SF₆ or comprises an organofluorine compound selected from the group consisting of: fluoroethers , in particular hydrofluoromonoethers , a fluoro- amine, a fluorooxirane, fluoroketones , in particular perfluoro- ketones, fluoroolefins , in particular hydrofluoroolefins , fluoronitriles , in particular perfluoronitriles , and mixtures thereof, in particular in a mixture with a background gas.

Short description of the drawings

Embodiments, advantages and applications of the invention result from the dependent claims and from the now following description by means of the figures. It is shown in:

Fig. 1 a longitudinal sectional view of a part of a known electrical switching device;

Fig. 2 a schematized side view of a first embodiment of the exhaust tube according to the first aspect of the invention ;

Fig. 3 a schematized side view of a first embodiment of the exhaust tube according to the second aspect of the invention ;

Fig. 4 a schematized side view of a second embodiment of the exhaust tube according to the second aspect of the invention ;

Fig. 5 a schematized side view of an embodiment of the exhaust tube according to the third aspect of the invention;

Fig. 6 a schematized side view of an embodiment of the exhaust tube according to the fourth aspect of the invention;

Fig. 7 a diagram showing an influence of the position of a barrier element according to Fig. 6;

Fig. 8 and 9 a schematized side view of alternative embodiments of the exhaust tube according to the second aspect of the invention; and

Fig. 10 a schematized side view of a particular embodiment of the openings of the exhaust tube according to the invention .

In the drawings same references denote same or similarly components of the electrical switching device.

Ways of carrying out the invention

The term „last" in connection with openings is to be understood as farthest away from the arcing volume in longitudinal (axial) direction of the switching device, in the following exemplarily referred to as circuit breaker. Accordingly, the term "first" in connection with openings is to be understood as closest to the arcing volume in longitudinal (axial) direction of the exemplary circuit breaker. In the same way, the term "distal" or "proximal" is understood as relating to the arcing volume.

A "closed configuration" as used herein means that the nominal contacts and/or the arcing contacts of the circuit breaker are mutually engaged. Accordingly, an "opened configuration" as used herein means that the nominal contacts and/or the arcing contacts of the circuit breaker are opened, therefore not mutually engaged.

Fig. 1 shows a longitudinal sectional view of a part of a known embodiment of a circuit breaker 1 in an opened configuration. The device is rotationally symmetric about a longitudinal axis z. Not all elements of the circuit breaker 1 are described herein, as the principle and the variants of such circuit breakers are known to the skilled person in high voltage electrical engineering, e.g. nominal contacts, enclosure, etc., are not shown in the figures for clarity reasons.

The circuit breaker 1 comprises an arcing contact arrangement formed by a first arcing contact 3 and a second arcing contact 4. The first arcing contact 3 comprises multiple fingers arranged in a finger cage (tulip configuration) . For the sake of clarity only two fingers of the first arcing contact are shown in Fig. 1. The second arcing contact 4 is rod-shaped in this embodiment.

It is assumed that an insulating fluid of the type mentioned above is present inside the circuit breaker 1.

For the explanatory purposes of the present invention it is assumed that only the first arcing contact 3 is movable along the z-axis and the second arcing contact 4 is stationary. However, the invention is not limited to this configuration. Other configurations, e.g. double-motion interrupters, are known and are useful for implementing the invention disclosed and claimed herein, in which interrupters also the second arcing contact 4 is movable.

An insulating element 2 is arranged partly around the second arcing contact 4. In other words the insulating element 2 encloses the second arcing contact 4 concentrically and protrudes beyond it, as can be seen in the figure. This element is also known as insulating nozzle 2. A main purpose of this insulating nozzle 2 is to form a constriction or flow path, in combination with other elements of the circuit breaker 1, for guiding the insulating fluid into and out of an arcing volume 5.

The arcing volume 5 is a region in which the first arcing contact 3 is moved back and forth for closing or opening an arcing circuit. As known, in this region an electric arc L develops during an opening and closing procedure between the first contact 3 and the second contact 4, which heats up the fluid located in the arcing volume 5. This arcing region 5 is defined by an inner wall of the insulating nozzle 2 and by the front extremity of the second arcing contact 4 and the frontal extremities of the fingers of the first arcing contact 3. The arcing volume 5 is connected, amongst others, with a heating volume 9 by a channel in such a way that the insulating fluid may travel between the heating volume 9 and the arcing volume 5 (illustrated by the arrows a) .

Furthermore, the arcing volume 5 is also connected to an exhaust volume 6, the purpose of which has been described above, via an exhaust tube 7. The exhaust tube 7 can be a prolongation of the first arcing contact 3, as can be seen in the Fig. 1. The hot gas travels through the exhaust tube 7, as shown by the arrows a, and escapes into the exhaust volume 6 through openings 8. The passage of the hot gas into the exhaust volume 6 is indicated by arrow b. Subsequently, mixed hot gas from the arcing volume 5 and cold gas from the exhaust volume 6 escape into a volume (not shown) delimited by an enclosure of the circuit breaker 1 (not shown) via exhaust volume holes 10.

As illustrated in Fig. 1, previously known exhaust tubes 7 are tubular (i.e. with constant cross-section or cylindrical) and comprise openings 8 with same cross-sections. The present invention focuses on the exhaust tube 7 for reaching the above mentioned objectives. Therefore, for clarity reasons, the following figures only show the exhaust tube 7 and not the entire circuit breaker 1. It is understood that the exhaust tube 7 of Fig. 1 shall be replaced by an exhaust tube 7 according to one of the aspects of the invention. In the following, some general aspects of the exhaust tube 7 according to all of its following embodiments shall be mentioned. The orientation of the exhaust tube 7 inside the circuit breaker 1 is indicated by the arrow z. The exhaust gas flow direction of relevance herein is shown in embodiments to be anti-parallel to the arrow z.

In embodiments, a cross-section of each opening 8 connecting the interior of the exhaust tube 7 with the exhaust volume 6 is chosen such that all openings 8 have a substantially equal mass flow of the insulating medium or hot gas through them. As the hot gas enters the exhaust tube 7 with high pressure, the first openings 8 are particularly stressed, as large amounts of the gas tend to escape through them. The more the hot gas travels towards the distal end of the exhaust tube 7, the more the pressure decreases, such that the last openings 8 experience very low pressure. Accordingly, the first openings 8 erode much faster than the last openings 8. This may change the behavior of the circuit breaker 1 in an undesired manner, as gas mixing behavior is influenced by the cross-section of the openings 8 and by the amount of the hot gas evacuated from arcing zone 5. It is therefore desired that the mass flow m(t) of the gas is as evenly distributed as possible for all exhaust tube openings 8. This can be achieved by varying size and shape of the exhaust tube openings 8. Therefore, many of the following embodiments of the exhaust tube 7 deal with different sizes or arrangements of the exhaust tube openings 8. Generally, it is preferred that the exhaust tube openings 8 of the exhaust tube 7 are arranged in rows extending in longitudinal direction z, wherein the rows are distributed on an entire circumference of the exhaust tube 7. It is preferred to choose a number of rows between 2 and 6 rows. Furthermore, it is preferred that all exhaust tube openings 8 of one row are distributed uniformly in longitudinal direction z, except for the embodiment of Fig. 8. All rows may have a same alignment, meaning that centers of circumferentially adjacent exhaust tube openings 8 are arranged on a same circumference line. In other embodiments (not shown) each row may be shifted by an offset in z-direction with respect to its adjacent rows. However, it is also possible to arrange the exhaust tube openings 8 in no recognizable pattern, i.e. such that no row pattern is distinguishable .

Additionally to the discussion of the exhaust tube openings 8, the shape of the exhaust tube 7 itself may contribute to an optimized gas flow for reducing erosion and achieving better gas mixing and for increasing the amount of hot gas evacuated from the arcing zone, as mentioned. Such an embodiment is shown in Fig. 2.

Fig. 2 shows a schematized side view of a first embodiment of the exhaust tube 7 according to the first aspect of the invention. In this embodiment the diameter of the exhaust tube 7 increases linearly along a section of the exhaust tube 7, the length of which is denoted by the reference LI in Fig. 2. The length of a preceding tubular section of the exhaust tube 7 is denoted by L2. In other words, the section LI has the shape of a conical frustum. In another embodiment said section LI of the exhaust tube 7 may be substantially trumpet-shaped. Other shapes may also be used.

In this embodiment the length of the section LI of the exhaust tube 7 is in the range between 0.1 and 2 times the length of the rest or remainder of the exhaust tube 7, i.e. of the section L2 in longitudinal direction z.

Preferably, a maximum diameter of the exhaust tube 7 is greater than a minimum diameter of the exhaust tube 7, i.e. the diameter of the tubular section L2, by a factor ranging between 1.05 and 1.5, wherein a preferred factor is ranging from 1.24 to 1.5 or is 1.24, a more preferred factor is ranging from 1.34 to 1.5 or is 1.34, and a most preferred factor is ranging from 1.44 to 1.5 or is 1.44.

In the shown embodiment the exhaust tube openings 8 have equal diameters, however they may also have the different shapes and alignments discussed in connection with following embodiments of the exhaust tube 7.

Fig. 3 shows a schematized side view of a first embodiment of the exhaust tube 7 according to the second aspect of the invention. In this embodiment the cross-section of the exhaust tube openings 8 attributed to one row increase for all rows in longitudinal direction z away from the arcing volume 5, wherein the exhaust tube openings 8 of a row are equidistant (distance d between centers of two adjacent openings is constant) . In this way the mass flow is equalized for all exhaust tube openings 8 along the z-axis (under operating conditions of the switching device) . Little gas can flow out through the first exhaust tube openings 8. Due to the pressure drop experienced after having passed the first exhaust tube openings 8, less gas would exit the second exhaust tube openings 8 and so forth. Hence, if the second exhaust tube openings 8 are designed with a larger cross-section than the first exhaust tube openings 8, the pressure drop after the first exhaust tube openings 8 is "compensated" by larger (second and subsequent) exhaust tube openings 8, such that substantially the same gas throughput is achieved for the first and the second openings, and so forth.

It is preferred that the increase rate of the opening diameter of the exhaust tube openings 8 is constant (in particular as a function of increasing distance from the arcing zone 5) , for at least a part of the rows, and preferably for all rows .

Fig. 4 shows a schematized side view of a second embodiment of the exhaust tube 7 according to the second aspect of the invention. In this embodiment the cross-section of the exhaust tube openings 8 attributed to one row decrease for at least a part of the rows, preferably for all rows in longitudinal direction z away from the arcing volume 5.

Fig. 5 shows a schematized side view of an embodiment of the exhaust tube 7 according to the third aspect of the invention. This embodiment shows exemplarily a combination of the first and the second aspect of the invention, that is, an expanding exhaust tube 7 according to the first aspect combined with exhaust tube openings 8 of different sizes according to the second aspect. In this particular example, exhaust tube openings 8 with increasing diameter towards the last exhaust tube opening 8 have been chosen. However, all other embodiments of the exhaust tube openings 8 can be used for expanding exhaust tubes 7. Here, the expanding exhaust tube 7 has been chosen to have an increasing diameter in flow direction for its entire length and not only for a section, as it is the case for the embodiment of Fig. 2. In the context of Fig. 5 it is noted that the exhaust tube 7 may also be formed such that its cross-section gets narrower towards its distal end (not shown) .

Fig. 6 shows a schematized side view of an embodiment of the exhaust tube 7 according to the fourth aspect of the invention. As for the other embodiments, the exhaust tube 7 comprises a plurality of exhaust tube openings 8 in its wall or side wall, which fluidly connect the interior of the exhaust tube 7 with the exhaust volume 6. In this particular example the openings 8 have the same cross-section and diameter. But of course, all types of exhaust tube openings 8 discussed herein may be applied to this embodiment, as well.

A barrier element 11 is arranged inside the exhaust tube 7 in a region defined by a distal end of the exhaust tube 7 with respect to the arcing volume 5 (see Fig. 1) and by a closest exhaust tube opening 8 with respect to the distal end (reference c) . The barrier element 11 avoids gas accumulating in the "dead" space following the last exhaust tube opening 8 and redirects the gas towards the exhaust tube openings 8. It is particularly advantageous that a position of the barrier element 11 in said region is adjustable. This makes it possible to account for different gas pressures and flow patterns, e.g. subsonic or supersonic gas flow.

The barrier element 11 is preferably cone-shaped, as shown in the present example, or frustoconical , pointing towards the arcing volume 5. The conicity given by angle a ranges between 20° and 80°, being preferably of 35°, more preferred of 45°, most preferred of 55°, with respect to the longitudinal axis z. It is furthermore preferred that a tip of the cone or edges of the small base of the frustum, respectively, is or are rounded in order to avoid increased erosion and enhance a smooth gas flow. Due to the same reason the barrier element 11 in a cone- embodiment tapers by a constant rate or a non-constant rate from its base to the apex, or the barrier element 11 in a frustum- embodiment tapers by a constant rate or a non-constant rate from its large base to its small base.

Fig. 7 shows a diagram illustrating an influence of the position of a barrier element 11 according to Fig. 6. The diagram shows the total mass flow in kg/s of the insulating gas as a function of time t for two cases (under relevant operating conditions of the switching device) . The curve 20 describes the total mass flow m(t) for a configuration with a barrier element arranged close to the last openings 8 of the exhaust tube 7, and the curve 21 shows the total mass through holes m(t) for a configuration with a barrier element 11 arranged far (200 mm) from the last openings 8 of the exhaust tube 7. The vertical line illustrates a typical arc interruption instant. It has been found that an arrangement of the barrier element 11 far away from the last exhaust tube openings 8 leads to a strong fluctuation of the mass flow through the openings 8 due to Helmholtz resonances. The time integral illustration in Fig. 7 reflects this fact in that it shows a clear lower total mass flow through the openings 8 at the instant of arc interruption. As compared to the close arrangement of curve 20 it has been found for the tested case that the mass flow was 23% lower than with an arrangement of the barrier element 11 close to the last exhaust tube openings 8.

Fig. 8 and 9 show a schematized side view of alternative embodiments of the exhaust tube 7 according to the second aspect of the invention.

In Fig. 8 the exhaust tube openings 8 of one row are not distributed uniformly in longitudinal direction, i.e. their centers are not at same distances to the ones of adjacent exhaust tube openings 8. For example, it is conceivable to implement groups of exhaust tube openings 8, wherein the exhaust tube openings 8 of one group are closer to one another than to the exhaust tube openings 8 of another group.

In Fig. 9 the exhaust tube openings 8 have different shapes, like oval, rectangular and/or circular. It is understood that differently shaped exhaust tube openings 8 may be arranged on the same exhaust tube 7.

Fig. 10 shows a schematized side view of a particular embodiment of the openings 8 of the exhaust tube 7 according to the invention. In this embodiment a wall 12 of each exhaust tube opening 8 is not perpendicular relative to the longitudinal axis z. Depending on the gas flow and its degree of turbulence and gas pressure it may be advantageous to design the walls 12 of exhaust tube openings 8 obliquely (i.e. under non-vertical angles wrt to z-axis) in order to facilitate gas passage and avoid increased erosion of edges of the exhaust tube openings 8. The figure shows a combination of exhaust tube openings 8 with walls inclined towards the arcing volume 5 and/or towards the distal end of the exhaust tube 7. This configuration may be particularly useful when using a barrier element 11. In such a configuration it may be preferred to provide exhaust tube openings 8 with walls inclined towards the distal end of the exhaust tube 7, except for the last exhaust tube openings 8, which are inclined towards the arcing volume 5. As the gas flows in a direction against the arrow z, it will pass through the exhaust tube openings 8 easier when these are inclined in flow direction, leading to a faster evacuation, however also to less turbulence in the region of the exhaust tube openings 8. As a result, the gas can be evacuated faster. At the end of the exhaust tube 7 the gas which has not yet flown into the exhaust volume 6 impacts the barrier element 11 (not shown in Fig. 10), thereby causing increased turbulence in the respective area. The gas flows towards the exhaust tube wall, as it is deflected by the cone-shaped barrier element 11, and tends to flow back in z- direction. Therefore, if the last exhaust tube openings 8 are inclined in this new flow direction (i.e. towards the arcing volume 5, as induced by the barrier element 11) they facilitate that this remaining gas flows into the exhaust volume 6 due to their special wall orientation.

It is noted that the configuration of exhaust tube openings 8, in particular their sizes and positions, may not only be chosen in relation to the gas flow from the exhaust tube 7 into the exhaust volume 6. Another factor which may influence their arrangement is given by the configuration of gas passage from the exhaust volume into a volume existing between the outer shell and the exhaust volume 6. This passage is indicated in Fig. 1 by the exhaust volume openings 10.

For the purposes of this disclosure the fluid used in the encapsulated or non-encapsulated electric apparatus can be SF₆ gas or any other dielectric insulation medium, may it be gaseous and/or liquid, and in particular can be a dielectric insulation gas or arc quenching gas. Such dielectric insulation medium can for example encompass media comprising an organo- fluorine compound, such organofluorine compound being selected from the group consisting of: fluoroethers , in particular hydrofluoromonoethers , a fluoroamine, a fluorooxirane, fluoro- ketones, in particular perfluoroketones , fluoroolefins , in particular hydrofluoroolefins , and fluoronitriles , in particular perfluoronitriles , and mixtures thereof; and preferably being a fluoroketone and/or a fluoroether, more preferably a perfluoroketone and/or a hydrofluoroether . Herein, the terms "fluoroether", "fluoroamine", "fluoroketone", fluorolefins and fluoronitrils refer to at least partially fluorinated compounds. In particular, the term "fluoroether" encompasses both hydrofluoroethers and perfluoroethers , the term "fluoroamine" encompasses both hydrofluoroamines and perfluoroamines , and the term "fluoroketone" encompasses both hydrofluoroketones and perfluoroketones . It can thereby be preferred that the fluoroether, the fluoroamine, the fluoroketone and the oxirane are fully fluorinated, i.e. perfluorinated .

In particular, the term "fluoroketone" as used in the context of the present invention shall be interpreted broadly and shall encompass both fluoromonoketones and fluorodiketones or generally fluoropolyketones . The term shall also encompass both saturated compounds and unsaturated compounds including double and/or triple bonds between carbon atoms. The at least partially fluorinated alkyl chain of the fluoroketones can be linear or branched and can optionally form a ring.

In particular, the fluoroketone can be a fluoromonoketone and/or may also comprise heteroatoms, such as at least one of a nitrogen atom, oxygen atom and sulphur atom, replacing one or more carbon atoms. More preferably, the fluoromonoketone, in particular perfluoroketone, shall have from 3 to 15 or from 4 to 12 carbon atoms and particularly from 5 to 9 carbon atoms. Most preferably, it may comprise exactly 5 carbon atoms and/or exactly 6 carbon atoms and/or exactly 7 carbon atoms and/or exactly 8 carbon atoms.

The dielectric insulation medium can further comprise a background gas or carrier gas different from the organofluorine compound, in particular different from the fluoroether, the fluoroamine, the fluoroketone, the oxirane, the olefin or hydrofluorolefin and the fluoronitril, and preferably can be selected from the group consisting of: air, N₂, 0₂ , CO₂, a noble gas, ¾; NO₂, NO, ₂O, fluorocarbons and in particular perfluorocarbons and preferably CF₄, CF₃I, SF₆, and mixtures thereof.

To summarize, the different aspects of the invention may be used alone or in combination in order to improve switching performance of the circuit breaker during normal operation and to control erosion of the exhaust tube 7 and of the exhaust tube openings 8. As poor switching performance can occur due to different reasons, the effects of each aspect of the invention may address same or different causes. For example, one cause is poorly mixed gas, meaning that the hot gas from the arcing zone has not been cooled effectively. Another cause is erosion, leading to distribution of particles of the circuit breaker material, e.g. of the exhaust tube, in the gas. Whether the different aspects of the invention are used alone or in combinations depends on the circuit breaker design, its ratings, etc.. A choice of the optimum configuration can be made by conducting simulations using said different configurations and different ratings. Such simulations typically show e.g. heat distribution in the gas along the travel path of the gas throughout the entire inner space of the circuit breaker or in designated sections. Based on such simulations it is possible to identify critical conditions at known sensitive locations inside the circuit breaker. Based upon this it is possible to choose the best alternative for exhaust tube design out of the variety of combinations described above.

While there are shown and described presently preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may otherwise variously be embodied and practised within the scope of the following claims. Therefore, terms like "preferred" or "in particular" or "particularly" or "advantageously", etc. signify optional and exemplary embodiments only. Reference list

1 = circuit breaker

2 = insulating nozzle

3 = first arcing contact

4 = second arcing contact

5 = arcing volume

6 = exhaust volume

7 = exhaust tube

8 = openings of exhaust tube

9 = heating volume

10 = exhaust volume openings

11 = barrier element

12 = wall of openings of exhaust tube

20 = mass transfer with barrier element close to last opening

21 = mass transfer with barrier element far from the last opening

a = flow of insulating gas towards exhaust tube b = flow of insulating gas towards exhaust volume c = shifting range for barrier element

d = distance between adjacent openings 8

L = electric arc

LI = length of non-tubular exhaust tube section L2 = length of tubular exhaust tube section

a = conicity angle of barrier element

z = longitudinal axis

Claims

1. An electric switching device (1), filled with a dielectric insulating medium, comprising

at least an arrangement of arcing contacts with a first arcing contact (3) and a corresponding second arcing contact (4), wherein for opening and closing the electric switching device (1) at least one of the arcing contacts (3, 4) is movable parallel to a longitudinal axis (z) and cooperates with the other arcing contact (4, 3),

further comprising an insulating nozzle (2), an arcing volume (5) between the first arcing contact (3) and the second arcing contact (4), an exhaust volume (6) and an exhaust tube (7), wherein the exhaust tube (7) is arranged in extension to the first arcing contact (3) , in particular hollow tulip contact (3) or hollow pin contact, along the longitudinal axis (z) and connects the exhaust volume (6) with the arcing volume (5) for evacuating at least a part of hot dielectric insulating medium into the exhaust tube (7),

characterized in that a diameter of the exhaust tube

(7) increases, at least along a section of the exhaust tube (7), in longitudinal direction (z) away from the arcing volume (5), and/or

in that the exhaust tube (7) comprises a plurality of exhaust tube openings (8) through its wall, which connect the interior of the exhaust tube (7) with the exhaust volume (6), wherein at least a part of the exhaust tube openings (8) have different sizes.

2. The electric switching device according to claim

1, wherein, in the case of the diameter of the exhaust tube (7) increasing at least along the section (LI) of the exhaust tube (7) in longitudinal direction (z) away from the arcing volume (5), the diameter of the exhaust tube (7) is chosen to increase such that during a switching operation under operating conditions of the electric switching device (1) a mass flow of the hot dielectric insulating medium to be evacuated through the exhaust tube (7) is maximized.

3. The electric switching device according to any one of the preceding claims, wherein the diameter of the exhaust tube (7) increases linearly along said section of the exhaust tube (7), or the diameter of the exhaust tube (7) increases in such a way that said section of the exhaust tube (7) is substantially trumpet-shaped, particularly wherein the diameter of the exhaust tube (7) increases along the entire exhaust tube (7) in direction of flow of the insulating medium away from the arcing volume (5) .

4. The electric switching device according to any one of the preceding claims, wherein a length of a section (LI) of the exhaust tube (7) having increasing diameter in direction of flow of the insulating medium away from the arcing volume (5) is in the range between 0.1 to 2 times a length of the section (L2) of the remainder of the exhaust tube (7) in longitudinal direction ( z ) .

5. The electric switching device according to claim 1, wherein, in the case of the exhaust tube (7) comprising a plurality of exhaust tube openings (8) having increasing cross- sections in longitudinal direction (z) away from the arcing volume (5), the diameter of the exhaust tube (7) decreases, in particular decreases linearly, along said section of the exhaust tube (7), particularly along the entire length of the exhaust tube (7) .

6. The electric switching device according to any one of the preceding claims, wherein a maximum diameter of the exhaust tube (7) is greater than a minimum diameter of the exhaust tube (7) by a factor ranging between 1.05 and 1.5, preferably is ranging from 1.24 to 1.5 or is 1.24, more preferred is ranging from 1.34 to 1.5 or is 1.34, most preferred is ranging from 1.44 to 1.5 or is 1.44.

7. The electric switching device according to claim 1, wherein, in the case of the exhaust tube (7) comprising a plurality of exhaust tube openings (8), a total area of all exhaust tube openings (8) of the exhaust tube (7) is greater than a cross-section, in particular an average cross-section or a constant cross-section, of the exhaust tube (7) by a factor ranging between 1 and 6, particularly ranging between 3 and 6.

8. The electric switching device according to any one of the preceding claims, wherein, in the case of the exhaust tube (7) comprising a plurality of exhaust tube openings (8), a cross-section of each exhaust tube opening (8) is chosen such that during a switching operation a substantially equal amount of mass is flowing through each exhaust tube opening (8) from the exhaust tube (7) into the exhaust volume (6) under operating conditions of the electric switching device (1) .

9. The electric switching device according to any one of the preceding claims, wherein the exhaust tube openings (8) of the exhaust tube (7) are arranged in rows extending in longitudinal direction (z), wherein the rows are distributed on an entire circumference of the exhaust tube (7), particularly wherein a number of rows ranges between 2 and 6 rows.

10. The electric switching device according to claim 8, wherein all exhaust tube openings (8) of one row are distributed uniformly in longitudinal direction (z), or wherein at least a part of the exhaust tube openings (8) of one row are not distributed uniformly in longitudinal direction (z).

11. The electric switching device according to claim 9 or 10, wherein all rows have a same alignment or wherein each row is shifted by an offset with respect to its adjacent rows.

12. The electric switching device according to any one of the claims 9 to 11, wherein a cross-section of the exhaust tube openings (8) attributed to one row increase for all rows in longitudinal direction (z) away from the arcing volume (5); or wherein, in the case of the diameter of the exhaust tube (7) increasing, at least along a section (LI) of the exhaust tube (7), in longitudinal direction (z) away from the arcing volume (5), the cross-section of the exhaust tube openings (8) attributed to one row decrease for all rows in longitudinal direction (z) away from the arcing volume (5) .

13. The electric switching device according to any one of the claims 1 to 11, wherein, in the case of the diameter of the exhaust tube (7) increasing at least along a section (LI) of the exhaust tube (7) in longitudinal direction (z) away from the arcing volume (5), all exhaust tube openings (8) have equal cross-sections with respect to their shape and area.

14. The electric switching device according to any one of the preceding claims, wherein a wall (12) of each exhaust tube opening (8) is not perpendicular to the longitudinal axis (z) .

15. The electric switching device, particularly according to any one of the preceding claims, wherein the electric switching device (1) is filled with a dielectric insulating medium and comprises

at least an arrangement of arcing contacts with a first arcing contact (3) and a corresponding second arcing contact (4), wherein for opening and closing the electric switching device (1) at least one of the arcing contacts (3, 4) is movable parallel to a longitudinal axis (z) and cooperates with the other arcing contact (4, 3), and comprises

an insulating nozzle (2), an arcing volume (5) between the first arcing contact (3) and the second arcing contact (4), an exhaust volume (6) and an exhaust tube (7), wherein the exhaust tube (7) is arranged in extension to the first arcing contact (3) , in particular hollow tulip contact (3) or hollow pin contact, along the longitudinal axis (z) and connects the exhaust volume (6) with the arcing volume (5) for evacuating at least a part of hot dielectric insulating medium into the exhaust tube (7),

wherein the exhaust tube (7) comprises a plurality of exhaust tube openings (8) on its surface, which fluidly connect the interior of the exhaust tube (7) with the exhaust volume ( 6) , characterized in that a barrier element (11) is arranged inside the exhaust tube (7) in a region (c) defined by a distal end of the exhaust tube (7) with respect to the arcing volume (5) and by a closest exhaust tube opening (8) with respect to the distal end, wherein a position of the barrier element (11) in said region is adjustable.

16. The electric switching device according to claim 14, wherein the barrier element (11) is cone-shaped or frustoconical and points towards the arcing volume (5) , particularly with a conicity ranging between 20° and 80°, being preferably of 35°, more preferred of 45°, most preferred of 55°, with respect to the longitudinal axis (z), particularly wherein an apex of the cone or edges of a small base of the frustum, respectively, is or are rounded, particularly wherein the cone tapers by a constant rate or a non-constant rate from its base to the apex or wherein the frustum tapers by a constant rate or a non-constant rate from its large base to its small base.

17. The electrical device according to one of the preceding claims, wherein a dielectric insulation medium, in particular dielectric insulation gas, is present that comprises an organofluorine compound selected from the group consisting of: fluoroethers , in particular hydrofluoromonoethers , a fluoro- amine, a fluorooxirane, fluoroketones , in particular perfluoro- ketones, fluoroolefins , in particular hydrofluoroolefins , fluoronitriles , in particular perfluoronitriles , and mixtures thereof, in particular in a mixture with a background gas; and/or wherein the switching device (1) is selected from the group consisting of: earthing device, fast-acting earthing device, circuit breaker, generator circuit breaker, switch disconnector, combined disconnector and earthing switch, or load break switch.