Patent Description:
Furthermore, the invention relates to a gas-insulated high or medium voltage device comprising the above interrupter unit and further an arc extinguishing gas.

High or medium voltage devices, such as circuit breakers and switchgears are essential for the protection of technical equipment, especially in the high voltage range. For example, circuit breakers are predominantly used for interrupting a current, when an electrical fault occurs. As an example, circuit breakers have the task of opening arcing contacts, quench an arc, and keeping the arcing contacts apart from one another in order to avoid a current flow even in case of high electrical potential originating from the electrical fault itself. Circuit breakers may break medium to high short circuit currents of typically <NUM> kA to <NUM> kA at medium to high voltages of <NUM> kV to <NUM> kV and up to <NUM> kV. Thus, high or medium voltage devices accommodate high-voltage conductors such as conductors to which a high voltage is applied.

Some high or medium voltage devices, namely gas-insulated high or medium voltage devices comprise an insulation gas, for example sulphur hexafluoride, in order to shield and insulate the high-voltage conductor from other component and/or to improve quenching of an arc, when operating arcing contacts.

In particular the insulation gas is used for extinguishing the arc generated in an arcing region between the arcing contacts when a fault current is to be interrupted and is thus also called arc extinguishing gas. The arcing region is typically surrounded by an insulating nozzle. The nozzle typically also serves for guiding a stream of the insulation gas for extinguishing, or blowing off, the arc. Thereby, the arc extinguishing gas is typically guided by a dedicated passage in the nozzle, also called heating channel, which ends close to the arcing region. Thus, the arc extinguishing gas is guided directly onto the developing arc.

An electric arc is made up by a flux of electrons and a flux of ions which circulate in opposite directions between the arcing contacts. When the temperature of the arc decreases, ions and electrons recombine and the arc extinguishing gas resumes its electrical insulating properties. In a gas insulated circuit breaker, a cooler gaseous mantle surrounds the hot core of the arc. The temperature of the gaseous mantle decreases as the distance from the arc axis is increased. The current flow is interrupted when an efficient blast of arc extinguishing gas is applied to cool the arc and extinguish it. The capability of how efficient the arc is extinguished at the zero crossing of the alternating fault current by a high or medium voltage device is called thermal interruption performance.

Sulphur hexafluoride (SF<NUM>) is widely used as arc extinguishing gas, as it is known for its high dielectric strength and thermal interruption capability. However, SF<NUM> might have some environmental impact when released into the atmosphere, in particular due to its relatively high global warming potential and its relatively long lifetime in the atmosphere.

Thus, efforts have been made to substitute SF<NUM> with different more environmentally friendly arc extinguishing gases or to reduce the SF<NUM> content in the arc extinguishing gas mixture. For example, one candidate for substituting SF<NUM> as insulation gas is CO<NUM>. However, the arc extinguishing capability of CO<NUM> is inferior to that of SF<NUM>. Thus, for a circuit breaker of a conventional design, a sufficient interruption performance is thus often not achieved when CO<NUM> is used as a quenching gas instead of SF<NUM>. This is particularly the case for relatively high short-circuit currents and voltage ratings.

Document <CIT> describes a compressed gas switch with at least one switching path, which contains at least one hollow, nozzle-shaped contact piece, with the switching path being supplied with a flowing, gaseous extinguishing agent by means of a channel which is formed as an annular channel between the contact piece and a shell comprising the latter, using elements that disrupt the laminar flow and generate vortex flow, wherein the elements are arranged in the immediate vicinity of the mouth of the nozzle-shaped switching piece, viewed in the direction of flow.

Document <CIT> relates to an electrical switching device filled with a dielectric insulating medium. The switching device comprises a first erosion contact and an associated second erosion contact, an insulating nozzle, an auxiliary nozzle which is arranged concentrically in the interior of the insulating nozzle, an arc volume, a heating volume, and a heating channel which connects the arc volume to the heating volume. A stabilization arrangement for stabilizing the auxiliary nozzle is provided in the heating channel, which is arranged in such a way that it mechanically connects the insulating nozzle to the auxiliary nozzle and thus prevents a radial displacement of the auxiliary nozzle relative to the insulating nozzle and/or prevents an axial displacement of the auxiliary nozzle in the direction of the longitudinal axis beyond a predefined point.

It is an object of the invention to provide means to improve the thermal interruption performance of gas-insulated high or medium voltage devices, particularly for gas-insulated high or medium voltage devices comprising an arc extinguishing gas having a reduced SF<NUM> content or being free of SF<NUM>.

The object of the invention is solved by the features of the independent claims. Modified embodiments are detailed in the dependent claims.

Thus, the object is solved by an interrupter unit for a gas-insulated high or medium voltage device comprising a first arcing contact and a second arcing contact, wherein at least one of the arcing contacts is axially movable along a switching axis, a heating channel for guiding an arc extinguishing gas from a heating volume to an arcing region formed between the first arcing contact and the second arcing contact, wherein the interrupter unit comprises in a transition region of the heating volume to the heating channel a flow guiding element, and wherein a cross section of the flow guiding element along a plane comprising the switching axis comprises a closed shape, and wherein an aspect ratio of a convex hull of the closed shape is in between <NUM>:<NUM> to <NUM>:<NUM>.

The object is also solved by a gas-insulated high or medium voltage device comprising the above interrupter unit and wherein the high or medium voltage device further comprises an arc extinguishing gas.

Preferably the arc extinguishing gas is selected from CO<NUM>, mixtures comprising CO<NUM>, mixtures of CO<NUM> with a carrier gas and/or mixtures of fluoroketons and/or fluoronitriles with a carrier gas. The carrier gas for use with CO<NUM>, fluoroketons and/or fluoronitriles may comprise air, N<NUM>, CO<NUM>, and mixtures thereof. Further preferably the arc extinguishing gas may have a reduced fluorine content compared to SF<NUM> or may even be fluorine free.

According to another preferred embodiment of the invention the gas-insulated high or medium voltage device is preferably a circuit breaker and more preferably the gas-insulated high or medium voltage device is configured as a puffer-type circuit breaker, a self-blast circuit breaker, or a combined puffer-type and self-blast circuit breaker. In the context of this invention medium to high voltages means voltages of <NUM> kV to <NUM> kV (medium voltage) and up to <NUM> kV (high voltage).

An important parameter influencing the thermal interruption capability of an interruption unit is the flow of the arc extinguishing gas in the arcing region. The arcing region is typically surrounded by a nozzle for electrical insulation purpose. The nozzle preferably also serves for guiding the arc extinguishing gas from the heating volume to the arcing region. In other words, the heating channel connecting the heating volume with the arcing region is formed by the nozzle. According to the invention, the heating channel is formed in between an auxiliary nozzle at least partially surrounding one of the arcing contacts and an insulating nozzle. As the heating channel ends close to the arcing region, the arc extinguishing gas is preferably guided directly onto the developing arc during circuit breaking.

It has been found that a flow guiding element in the transition region from the heating volume to the heating channel, wherein the cross section of said flow guiding element along the plane comprising the switching axis comprises the closed shape, and wherein the aspect ratio of the convex hull of the closed shape is in between <NUM>:<NUM> to <NUM>:<NUM>, can aid in improving the thermal interruption capabilities of the interrupter unit.

Without being bound to a specific theory, it is believed that the increased interruption capability of the interruption unit is at least in part based on an increased polytetrafluorethylene (PTFE) vapor concentration of the arc extinguishing gas in the arcing region in a flow reversal phase, due to a decreased mixing of the arc extinguishing gas in the heating volume during a back heating phase of current interruption:.

During circuit breaking operation of the high or medium voltage device, by moving at least one of the arcing contacts along the switching axis, a direct contact between the arcing contacts is broken, such that an arc develops between the arcing contacts. In a high-current phase of the arcing period, the radiative energy of the burning arc induces PTFE evaporation at a nozzle surface surrounding the arcing region, which yields a rise of the pressure of the arc extinguishing gas in the region between the arcing contacts, for which the arc extinguishing gas expands in all available directions. In particular, the expanding arc extinguishing gas also streams from the arcing region to the heating volume, filling it at high pressure. This phase, where the arc extinguishing gas streams from the arcing region into the heating volume is called back heating phase or ablation-controlled arc phase. The described mechanism of pressure generation is typical for self-blast circuit breakers. In case of puffer-type circuit breakers, the pressure generated by the arc is further augmented by the shrinking of a compression volume.

When the fault alternating current decreases, the arc loses energy and, at some point, stops pumping mass and energy into the heating volume. The high-pressure gas stored in the heating volume consequently moves back towards the arc, thus quenching it. This phase is called flow reversal phase or axially blown arc phase.

As already mentioned, due to the high radiative energy of the arc in the high-current phase of the arcing period, ablation of the nozzle surrounding the arcing region takes place, influencing the chemical composition of the arc extinguishing gas in the arcing region. In particular nozzle ablation may increase the content of PTFE in the arc extinguishing gas being present in the arcing region during this phase.

It is believed that the flow guiding element in the transition region of the heating volume to the heating channel decreases the mixing of the arc extinguishing gas having a high PTFE content flowing into the heating volume with the arc extinguishing gas already present in the heating volume and having a low PTFE content in the back heating phase. As mixing in the heating volume is decreased in the back heating phase, arc extinguishing gas having a high PTFE content flows into the arcing region in the subsequent flow reversal phase, which in turn improves the thermal interruption performance of the interrupter unit.

As already mentioned, the cross section of the flow guiding element along the plane comprising the switching axis comprises the closed shape, and wherein the aspect ratio of the convex hull of the closed shape is in between <NUM>:<NUM> to <NUM>:<NUM>. The closed shape is a shape, whose boundary lines are connected and/or meet end to end. In other words, a closed shape starts and ends at the same point. In principle, the closed shape can have any form, as long as the aspect ratio of its convex hull is in between <NUM>:<NUM> to <NUM>:<NUM>. For example the closed shape can have the form of an ellipse with a wavy boundary line or the form of the letter D.

In case the closed shape is convex, the convex hull of the closed shape corresponds to the closed shape itself. In case the closed shape is concave, then the convex hull of the concave closed shape is the smallest convex shape that contains the concave closed shape.

The aspect ratio of the convex hull is a measure for the "circlishness" of the convex hull. In the context of this invention the aspect ratio is the ratio between the diameter of the minimum bounding circle of the convex hull and the diameter of the maximum inscribed circle of the convex hull. The minimum bounding circle is the smallest circle that contains all points of the boundary line of the convex hull. The maximum inscribed circle of the convex hull is the maximum circle within the convex hull. For example, when the cross section of the flow guiding element is a circle, the aspect ratio would be <NUM>:<NUM>.

In other words, the form of the flow guiding element preferably corresponds to a bluff body. In contrary to a streamlined body, which offers least resistance to a stream of gas in terms of pressure drag, a bluff body is such that boundary layers may separate to form unsteady vortex flows in a wake region of the bluff body. By using a flow guiding element whose cross-section is shaped as a bluff body, the mixing of the arc extinguishing gas having a high PTFE content with the arc extinguishing gas already present in the heating volume in the back heating phase is efficiently hindered.

According to a preferred embodiment of the invention, the closed shape is a regular polygon with at least three vertices, and preferably a regular convex polygon or a regular star polygon, or the closed shape is a circle. In other words, the cross section can comprise a regular triangle, a regular quadrangle, a regular pentagon, a regular pentagram, a regular hexagon, a regular hexagram, a regular heptagon, a regular heptagram, a regular octagon, a regular octagram, a regular nonagon, a regular nonagram, a regular decagon, a regular decagram, and so forth e.g. a regular dodecagon, a regular dodecagram, or a circle. Mathematically spoken the crosse section comprise a regular polygon with n vertices with n ≥ <NUM> and up to ∞, as the regular polygon with indefinite vertices corresponds to the circle.

In this context and according to another preferred embodiment of the invention, the polygon is a regular convex polygon or a regular star polygon. A regular polygon is convex if every line that does not contain any edge of the polygon intersects the polygon in at most two points. For example, the regular pentagon or hexagon are regular convex polygons. A regular star polygon is a non-convex regular polygon, such as a pentagram or hexagram. Regular star polygons have the same vertices as their corresponding regular convex polygons, but connect alternating vertices. Preferably, the cross-section of the flow guiding element comprises the regular convex polygon with n vertices with n ≥ <NUM>. This has the advantage that it is easier to manufacture than the star polygon. Further preferably, the cross-section of the flow guiding element comprises the circle.

Particular preferably the flow guiding element is formed such that a flow of a back streaming arc extinguishing gas from the arcing region into the heating volume is split into at least two sub streams. Further preferably the flow guiding element is formed such that the flow of the back streaming arc extinguishing gas from the arcing region separates into at least two sub streams. Hence, mixing of the back streaming arc extinguishing gas from the arcing region with the arc extinguishing gas within the heating volume is efficiently decreased.

As already mentioned, the flow guiding element is arranged within the transition region of the heating volume to the heating channel. The transition region is formed around the connection of the heating channel to the heating volume. The heating channel as well as the heating volume are preferably enclosed by sidewalls, wherein the heating channel extends essentially along the direction of the switching axis. At the connection of the heating channel to the heating volume the sidewalls of the heating channel and the heating volume merge. The transition region is the region around the connection where a significant increase or decrease of a distance between the sidewalls enclosing the heating channel and/or the sidewalls enclosing the heating volume takes place in the course of the direction of the switching axis.

According to a preferred embodiment of the invention, a sidewall of the heating channel and/or heating volume in the transition region comprises a fillet. Particular preferably, the sidewall of the heating channel and/or heating volume at a connection of the heating channel to the heating volume comprises the fillet. A fillet is a rounding of an interior or exterior corner. As already mentioned above, at the connection of the heating channel to the heating volume the distance between the sidewalls enclosing the heating channel and the sidewalls enclosing the heating volume changes. In case the transition region does not comprise the fillet, the distance change in an abrupt manner. However, with the fillet the connection of the of the heating channel to the heating volume is more gradual and also the distance between the opposing sidewalls changes more gradually. Preferably the flow guiding element is arranged with respect to the switching axis in the region of the fillet of the transition region. The fillet has the effect of slowing down and deflecting the arc extinguishing gas entering in the heating volume sideways. As a consequence, during the back heating phase the mixing of the arc extinguishing gas having high PTFE content with the arc extinguishing gas already present in the heating volume is even more hindered, and thus arc extinguishing gas having a high PTFE content flows back to the arcing region in the subsequent flow reversal phase, which in turn further improves the thermal interruption performance of the interrupter unit.

According to a preferred embodiment of the invention, the interrupter unit comprises the nozzle, wherein the nozzle at least partially encloses the arcing region and wherein the nozzle comprises PTFE. As already mentioned, the arcing region is preferably surrounded by the nozzle for electrical insulation purpose. Preferably a material of the nozzle comprises PTFE. Ablation of the nozzle during current interruption vaporizes some of the PTFE and increases the content of PTFE in the arc extinguishing gas being present in the arcing region.

According to another preferred embodiment of the invention, the the flow guiding element is at least partially revolving around the switching axis. Preferably the nozzle and thus the heating channel formed within the nozzle is rotationally symmetric around the switching axis. Hence, it is preferable to have a flow guiding element, that at least partially revolves around the switching axis. Further preferably, the flow guiding element is a circumferential flow guiding element and/or is ring shaped.

In connection to this and according to another preferred embodiment, the flow guiding element is preferably rotationally symmetric around the switching axis. The ring-shaped flow guiding element is preferably rotationally symmetric. It has been found that the interruption performance is increased if the symmetry of the flow guiding element matches the symmetry of the nozzle and/or heating channel of the interrupter unit. It is also possible that the rotational symmetry of the flow guiding element around the switching axis is a discrete rotational symmetry, for example a three-fold rotational symmetry. In the example of the <NUM>-fold rotational symmetry the shape of the flow guiding element would correspond to a ring made from three distinct segments that are separated by small gaps circumferentially.

With regard to the arrangement of the flow guiding element, and as already stated the flow guiding element is arranged in the transition region of the heating volume to the heating channel. For example, the flow guiding element can be arranged in the heating volume in front of the opening into the heating channel. In this regard and according to a preferred embodiment of the invention, the flow guiding element is at least partially arranged within the heating channel and/or the flow guiding element is at least partially arranged within the heating volume.

Different arrangement of the flow guiding element in the transition region are possible. Preferably the arrangement of the flow guiding element and a diameter of the polygon or circle of the cross section of the flow guiding element is such that a part of the flow guiding element is located within the heating channel - preferably meaning that this part of the flow guiding element is located in a region of the heating channel, where the distance between the opposing sidewalls of the heating channel is preferably constant over the extent of the flow guiding element.

Alternatively or additionally and further preferably the arrangement of the flow guiding element and the diameter of the polygon or circle of the cross section of the flow guiding element is such that a part of the flow guiding element is located within the heating volume - preferably meaning that this part of the flow guiding element is located in a region of the heating volume, where the distance between the sidewalls of the heating volume is preferably constant over the extent of the flow guiding element.

Further preferably the arrangement of the flow guiding element and the diameter of the polygon or circle of the cross section of the flow guiding element is such that the flow guiding element is located in the transition region, where the distance between the sidewalls of the heating channel and/or the sidewalls of the heating volume is changing over an extent of the flow guiding element, and preferably over the whole extent of the flow guiding element.

According to another preferred embodiment of the invention, the heating channel comprises a portion that extends parallel to the switching axis and wherein the flow guiding element is at least partially arranged within said portion of the heating channel. It has been found that such an arrangement of the flow guiding element and such a configuration of the heating channel is advantageous for the interruption performance of the interrupter unit. Further preferably, said portion of the heating channel that is parallel to the switching axis preferably also has a constant distance between the opposing sidewalls of the heating channel. Also, this embodiment is most advantageous together with the fillet region in the transition region.

With regard to the connection of the heating channel to the heating volume it is further preferred if one sidewall of the heating channel merges with one sidewall of the heating volume without forming a corner. This means in other words, that preferably a continuous sidewall is formed by one of the sidewalls of the heating channel and one of the sidewalls of the heating volume. Preferably the sidewall of the heating channel that merges with one sidewall of the heating volume without forming a corner, is the sidewall of the heating channel that is closer to the switching axis.

According to another preferred embodiment of the invention, the flow guiding element is not entirely arranged within the heating channel. This means in other words, that the arrangement of the flow guiding element and the diameter of the polygon or circle of the cross section of the flow guiding element is preferably not such that the entire flow guiding element is located in a region of the heating channel, where the distance between the sidewalls of the heating channel is constant over the whole extent of the flow guiding element.

According to another preferred embodiment of the invention, the flow guiding element is arranged spaced apart from opposing walls of the heating channel. With regard to the preferable arrangement of the flow guiding element partially within the heating channel it is preferred that a distance from the flow guiding element towards the opposing walls of the heating channel is the same ± <NUM>%. In other words, the flow guiding element is located essentially on a central axis of the heating channel.

According to another preferred embodiment a diameter of a minimum bounding circle of the convex hull is at least <NUM> % of the distance between opposing sidewalls of the heating channel. In case the closed shape is the circle this also means that the diameter of the circle is preferably at least <NUM> % of the distance between opposing sidewalls of the heating channel. For the regular convex polygon, the minimum bounding circle is the same as the circumcircle. The circumcircle (also called circumscribed circle) of a polygon is a circle that passes through all the vertices of the polygon. It has been found that the above given relationship between the distance of the opposing sidewalls of the heating channel and the minimum bounding circle of the convex hull or the diameter of the circle improves the interruption performance of the interrupter unit. Furthermore, the diameter of the minimum bounding circle of the convex hull is preferably not more than <NUM> % of the distance between opposing sidewalls of the heating channel. This preferably also means that the diameter of the circle is preferably not more than <NUM> % of the distance between opposing sidewalls of the heating channel.

According to another preferred embodiment of the invention, the flow guiding element is attached to at least one of two opposing sidewalls of the heating channel and/or heating volume. Preferably the flow guiding element is attached by multiple spacers to at least one of the two opposing sidewalls. Further preferably the flow guiding element is attached by multiple spacers to the sidewall of the heating channel and/or heating volume closer to the switching axis. Further preferably, the spacers are arranged rotationally symmetric around the switching axis for attachment of the flow guiding element. This improves the flow of the arc extinguishing gas through the heating channel compared to a non-symmetrical arrangement of the spacers.

<FIG> schematically shows an interrupter unit <NUM> for a gas-insulated high or medium voltage device, according to a preferred embodiment. The interrupter unit <NUM> comprises a first arcing contact <NUM> and a second arcing contact <NUM>. In this embodiment the first arcing contact <NUM> has the form of a plug contact <NUM> and the second arcing contact <NUM> is configured as tulip contact <NUM>. The plug contact <NUM> is axially movable along a switching axis <NUM>. The tulip contact <NUM> is also axially movable along the switching axis <NUM> and is further configured to engage around a proximal portion of the plug contact <NUM>, in the closed position of the contacts <NUM>, <NUM> (not shown in <FIG>). The interrupter unit <NUM> further comprises a heating channel <NUM> for guiding an arc extinguishing gas from a heating volume <NUM> to an arcing region <NUM> formed between the first arcing contact <NUM> and the second arcing contact <NUM>.

Furthermore, as can be seen in <FIG>, the interrupter unit <NUM> comprises in a transition region <NUM> of the heating volume <NUM> to the heating channel <NUM> a flow guiding element <NUM>. With regard to the form of the flow guiding element <NUM>, and as can be seen in <FIG>, a cross section of the flow guiding element <NUM> along a plane comprising the switching axis <NUM>, comprises a circle.

Furthermore, in this embodiment the flow guiding element <NUM> has a ring-shaped form and is rotationally symmetric around the switching axis <NUM>. As can also be seen, the flow guiding element <NUM> is partially arranged within the heating channel <NUM> and also partially arranged within the heating volume <NUM>. In this embodiment the connection of the heating channel <NUM> to the heating volume <NUM> is designed such that a sharp corner <NUM> is formed at the connection. Furthermore, the flow guiding element <NUM> is spaced apart from two opposing sidewalls <NUM>,<NUM> forming the heating channel <NUM>.

With regard to the sidewalls <NUM>,<NUM> it can be seen in <FIG> that in this embodiment the sidewall <NUM> closer to the switching axis <NUM> extends parallel to the switching axis <NUM> and forms a continuous wall with a sidewall <NUM> of the heating volume <NUM>.

The heating channel <NUM> is formed by a nozzle system <NUM> of the interrupter unit <NUM> and in particular by an insulating nozzle <NUM> and an auxiliary nozzle <NUM>. The nozzle system <NUM> comprises PTFE for insulation purpose.

<FIG> schematically shows a portion of an interrupter unit <NUM> of a high or medium voltage device, according to another preferred embodiment of the invention. The interrupter unit <NUM> of this embodiment is similar to the interrupter unit <NUM> of the embodiment in <FIG>, hence in the following only the differences are described:.

In the embodiment shown in <FIG>, the connection of the heating channel <NUM> to the heating volume <NUM> is not designed such that a sharp corner <NUM> is formed. Instead, a fillet <NUM> is formed at the connection. Furthermore, the flow guiding element <NUM> is partially arranged within the heating channel <NUM> and also partially arranged within the region of the fillet <NUM>.

<FIG> schematically shows a portion of an interrupter unit <NUM> of a high or medium voltage device, according to another preferred embodiment of the invention. The interrupter unit <NUM> of this embodiment is also similar to the interrupter unit <NUM> of the embodiment in <FIG>, hence in the following only the differences are described:.

In the embodiment shown in <FIG>, the connection of the heating channel <NUM> to the heating volume <NUM> is not designed such that a sharp corner <NUM> is formed. Instead, and similar to the embodiment shown in <FIG>, the transition region comprises the fillet <NUM>. Furthermore, the cross section of the flow guiding element <NUM> is not a circle, but a regular convex polygon. In this case the polygon is a heptagon. Furthermore, the flow guiding element <NUM> is entirely arranged within the fillet region.

<FIG> schematically shows a cross section of a flow guiding element <NUM> of an interrupter unit <NUM> (not shown) according to a further preferred embodiment. In this embodiment the cross section of the flow guiding element <NUM> is a closed concave shape, similar to a distorted C. A convex hull <NUM> of the closed shape is also depicted in <FIG> by dashed lines. Furthermore, also a minimum bounding circle <NUM> and a maximum inscribed circle <NUM> of the convex hull <NUM> is shown in <FIG>. As can be seen, the aspect ratio, i.e. the ratio of the diameter of the minimum bounding circle <NUM> to the diameter of the maximum inscribed circle <NUM> for this flow guiding element is around <NUM>,<NUM>:<NUM>.

<FIG> schematically shows in a) a portion of an interrupter unit <NUM> of a high or medium voltage device according to preferred embodiment of the invention, and in b) a portion of an interrupter unit <NUM>' of a high or medium voltage device according to prior art.

In the embodiment shown in <FIG>), the connection of the heating channel <NUM> to the heating volume <NUM> is not designed such that a sharp corner <NUM> is formed. Instead, the transition region comprises the fillet <NUM>. Furthermore, the cross section of the flow guiding element <NUM> comprises a circle and the flow guiding element <NUM> is entirely arranged within the fillet region.

The prior art interrupter unit <NUM>' shown in <FIG>) neither comprises a flow guiding element nor comprise a fillet. Instead, a sharp corner <NUM>' is formed.

With reference to <FIG> the effect of the flow guiding element <NUM> is described. During the opening operation of the interrupter unit <NUM>, a distance between the plug contact <NUM> and tulip contact <NUM> increases an and arc forms between the arcing contacts <NUM>,<NUM>. In a first phase of the circuit breaking operation the axial movement of at least one of the arcing contacts <NUM>,<NUM> leads to contact separation between the arcing contacts <NUM>,<NUM> and an arc establishes in the arcing region <NUM>. During this high-current phase of the breaking operation, ablation of the nozzle system <NUM> surrounding the arcing region <NUM> takes place, increasing the content of PTFE in the arc extinguishing gas present in the arcing region <NUM>. Due to the energy of the burning arc, the arc extinguishing gas expands, the pressure rises, and the arc extinguishing gas streams into the heating volume <NUM>. This phase, where the arc extinguishing gas streams from the arcing region <NUM> into the heating volume <NUM> is called back heating phase and shown in <FIG>.

As already mentioned, due to the ablation of the nozzle system <NUM> in the high current phase, during the back heating phase arc extinguishing gas having a high PTFE content, which is indicated in <FIG> with the dotted region, flows to the heating volume <NUM>, where arc extinguishing gas is present having a low PTFE content, as indicated in <FIG> with the hatched region.

As is schematically illustrated in <FIG>, the flow guiding element <NUM> bypasses part of the high PTFE content arc extinguishing gas entering in the heating volume <NUM>, deflecting it towards an outer surface of the heating volume <NUM>. Consequently, the part of the high PTFE content arc extinguishing gas traveling along the sidewall <NUM> closer to the switching axis <NUM> penetrates less into the heating volume <NUM> thus reducing its mixing with the arc extinguishing gas already present therein and having a low PTFE content. As mixing in the heating volume <NUM> is decreased in the back heating phase, arc extinguishing gas having a high PTFE content flows into the arcing region <NUM> in the subsequent flow reversal phase, which in turn improves the thermal interruption performance of the interrupter unit <NUM>.

Claim 1:
Interrupter unit (<NUM>) for a gas-insulated high or medium voltage device comprising
a first arcing contact (<NUM>) and a second arcing contact (<NUM>), wherein at least one of the arcing contacts (<NUM>,<NUM>) is axially movable along a switching axis (<NUM>),
a heating channel (<NUM>) for guiding an arc extinguishing gas from a heating volume (<NUM>) to an arcing region (<NUM>) formed between the first arcing contact (<NUM>) and the second arcing contact (<NUM>),
wherein the heating channel (<NUM>) is formed in between an auxiliary nozzle (<NUM>) and an insulating nozzle (<NUM>), the auxiliary nozzle (<NUM>) at least partially surrounding one of the arcing contacts (<NUM>, <NUM>),
wherein the interrupter unit (<NUM>) comprises a transition region (<NUM>) of the heating volume (<NUM>) to the heating channel (<NUM>),
characterised by a flow guiding element (<NUM>) in the transition region (<NUM>) of the heating volume (<NUM>) to the heating channel (<NUM>),
wherein the transition region (<NUM>) is formed around the connection of the heating channel (<NUM>) to the heating volume (<NUM>) and is a region comprising a change of a distance between sidewalls (<NUM>, <NUM>) enclosing the heating channel (<NUM>) and/or sidewalls (<NUM>) enclosing the heating volume (<NUM>) in the course of the direction of the switching axis (<NUM>),
wherein a cross section of the flow guiding element (<NUM>) along a plane comprising the switching axis (<NUM>) comprises a closed shape, and wherein an aspect ratio of a convex hull (<NUM>) of the closed shape is in between <NUM>:<NUM> to <NUM>:<NUM>.