Three-phase arc extinguishing device with two pistons

Abstract

The invention relates to a three-phase arc quenching apparatus having two pistons. The apparatus includes a first busbar, a second busbar, and a third busbar, each for a respective phase of a three-phase switchgear. The apparatus further includes a first piston and a second piston, each piston being made of an electrically conductive material. The apparatus further includes at least one pyrotechnic actuator arranged with the first piston and the second piston to axially move each of the first piston and the second piston when the at least one pyrotechnic actuator is activated. The first piston and the second piston are arranged relative to the first busbar, the second busbar, and the third busbar such that the axial movement brings the first piston into contact with both the first busbar and the second busbar, and brings the second piston into contact with both the first busbar and the third busbar.

Description

TECHNICAL FIELD

[0001] The present invention relates to an arc extinguishing device for a three-phase electrical switching device. BACKGROUND

[0002] In a switching device, an arc event can cause severe damage, even within a relatively short duration. The arc can be quenched by short-circuiting all phases to each other (and optionally, to ground). To protect the switching device components and avoid damage, the duration of the arc should be reduced. A circuit breaker can interrupt the fault current caused by the internal arc. However, the opening time of the circuit breaker can be relatively long, e.g. 30-60 ms. To quench the arc faster, e.g. within 2 ms of detecting the arc, a pyrotechnic actuator can be used.

[0003] EP 3 696 842 discloses a single-phase electrical closing switch that uses a pyrotechnic actuator to drive a movable piston to electrically connect a phase electrode and a ground electrode, thereby grounding one phase. SUMMARY

[0004] It is an object of the present invention to provide an arc extinguishing device for a three-phase electrical switching device using at least one pyrotechnic actuator.

[0005] According to an aspect of the invention, there is provided an arc extinguishing device for a three-phase electrical switching device. The device comprises a first busbar, a second busbar and a third busbar, each for a respective phase of the three-phase switching device. The device further comprises a first piston and a second piston, each made of an electrically conductive material. The device further comprises at least one pyrotechnic actuator arranged with the first piston and the second piston to axially move each of the first piston and the second piston when the at least one pyrotechnic actuator is activated. The first piston and the second piston are arranged relative to the first busbar, the second busbar and the third busbar such that said axial movement brings the first piston into contact with both the first busbar and the second busbar, thereby short-circuiting the first busbar and the second busbar via the first piston; and brings the second piston into contact with both the first busbar and the third busbar, thereby short-circuiting the first busbar and the third busbar via the second piston.

[0006] According to another aspect of the invention, there is provided a three-phase electrical switching device comprising the device according to any preceding claim and a fault clearing circuit breaker arranged to open the current of each of the three phases, the three phases being connected to the first busbar, the second busbar and the third busbar, respectively.

[0007] By allowing both the first piston and the second piston to be in electrical contact with the first busbar after the at least one pyrotechnic actuator has been initiated, it is possible to use only two pistons to cause all three phases to short, thereby reducing the cost and complexity of the arc extinguishing device.

[0008] It should be noted that any feature of any aspect of the aspects can be applied to any other aspect, where appropriate. Likewise, any advantage of any aspect of the aspects can be applied to any other aspect. Other objectives, features and advantages of the enclosed examples will be apparent from the following detailed description, from the appended claims as well as from the enclosed examples.

[0009] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined in the present document. All references to a / an / the item, apparatus, component, means etc. are to be interpreted openly as referring to at least one instance of whatever is being referred to unless indicated otherwise. The steps of any methods disclosed are not necessarily to be performed in the exact order disclosed unless explicitly stated as such. The use of “first”, “second” etc. does not connote any priority or order of importance, but rather the first named entity being treated as significant for identifying the second named entity. The use of “first”, “second” etc. does not connote any priority or order of importance, but rather the first named entity being treated as significant for identifying the second named entity. BRIEF DESCRIPTION OF DRAWINGS

[0010] The embodiments are described by way of example with reference to the accompanying drawings, wherein

[0011] Figure 1 is a schematic circuit diagram of a three-phase switchgear comprising an arc extinguishing device according to some embodiments of the present invention.

[0012] Figure 2a is a schematic view of a longitudinal section of a part of the arc extinguishing device according to some embodiments of the present invention when open (including one of the two pistons being in an open position).

[0013] Figure 2b is a schematic view of a longitudinal section of a part of the arc extinguishing device of Figure 2a when closed (the pistons being in a closed position) according to some embodiments of the present invention.

[0014] Figure 3 is a schematic perspective view of the first piston and the second piston of the arc extinguishing device arranged relative to the first busbar, the second busbar and the third busbar according to some embodiments of the present invention.

[0015] Figure 4 is a schematic perspective view of the first piston and the second piston of the arc extinguishing device arranged relative to the first busbar, the second busbar and the third busbar according to some embodiments of the present invention. Figure 3Fig. 1 is a schematic view of a longitudinal section of an arc extinguishing device arranged in an open position according to some embodiments of the application.

[0016] Figure 5 Fig. 2 is a schematic view of a longitudinal section of an arc extinguishing device arranged in an open position according to some embodiments of the application with respect to the first busbar, the second busbar and the third busbar and also with respect to the protective earth busbar.

[0017] Figure 6 Fig. 3 is a schematic view of a longitudinal section of an arc extinguishing device arranged in an open position according to some other embodiments of the application with respect to the first busbar, the second busbar and the third busbar.

[0018] Figure 7 Fig. 4 is a schematic view of a longitudinal section of an arc extinguishing device arranged in an open position according to some other embodiments of the application showing the first piston and the second piston with respect to the first busbar, the second busbar and the third busbar and also with respect to the protective earth busbar. DETAILED DESCRIPTION

[0019] Embodiments are now described in greater detail with reference to the figures. Such embodiments are presented by way of example only. Many different forms of other embodiments can be constructed without departing from the scope of the disclosure. Rather, the embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Throughout the specification, like reference numerals are used to designate like elements.

[0020] Figure 1 A three-phase electrical switching device 10 is illustrated, which comprises a circuit breaker 11, e.g. a fault clearing circuit breaker, arranged to interrupt the current of each of three phase / phase lines L1, L2 and L3. The switching device 10 can e.g. be arranged to interrupt the current to a load, in which case the switching device can be arranged between a power distribution system at the line side of the switching device and at least one load at the load side of the switching device. The switching device can be arranged for low voltage applications or medium voltage applications, meaning that the alternating current (AC) phase-to-phase voltage of the phases L1, L2 and L3 is in the medium voltage range or in the low voltage range, e.g. in the range 0.1 kV to 50 kV, or in the low voltage range 0.1 kV to 1 kV.

[0021] The circuit breaker 11 is typically able to clear an arc fault, i.e. to open the current in the phases L1, L2 and L3, within a time range of 30 ms to 60 ms after detection of the arc fault. This can be too slow to avoid damage caused by the arc fault. To quench the arc faster, the arc extinguishing device 1 is arranged in the switchgear 10 and is able to short-circuit all phases L1, L2 and L3 faster, e.g. within a time range of 0.1 ms to 5 ms, preferably within a time range of 0.1 ms to 2 ms, after detection of the arc. The arc extinguishing device 1 is connected via electrical conductors to each of the phases L1, L2 and L3 of the switchgear. In particular, the device 1 comprises phase busbars 5 (also referred to as busbars herein) which are electrically connected to the phase lines of the switchgear 10. In the example given herein, three busbars 5 connected to the phases L1, L2 or L3, respectively, are denoted as first busbar T, second busbar S and third busbar R, respectively. The arc extinguishing device 1 is configured to quench the arc by short-circuiting all three busbars T, S and R to each other (and optionally also to ground), thereby short-circuiting the three phases L1, L2 and L3 to each other.

[0022] To detect an arc fault, the switchgear 10 comprises an arc fault detector 13 which is connected to an arc fault sensor 12, e.g. an optical sensor, a current sensor, a pressure sensor and / or a thermal sensor, which is configured to detect an arc in the switchgear, e.g. between two of the phases L1, L2 and L3, between a phase and ground, or generally within the switchgear 10. When the arc fault detector 13 detects an arc via the sensor 12, the detector 13 sends an activation signal 14 to the arc extinguishing device 1, thereby causing at least one pyrotechnic actuator 3 (see Fig. 2) of the device 1 to activate.

[0023] Figure 2a and Figure 2b The open position and the closed position of one of the pistons P of the arc extinguishing device 1 are illustrated in Figs. 2 and 3, respectively. The piston has a rear end 24 (as indicated by the downward pointing arrow in Fig. 2) facing away from the axial movement direction, a front end 23 facing the axial movement direction, and a lateral surface 21. The discussion of the piston P shown in Figs. 2 and 3 also applies to the other piston P of the device 1. Figure 2a Figure 2a and Figure 2b The discussion of the piston P shown in Figs. 2 and 3 also applies to the other piston P of the device 1.

[0024] The piston P (in particular, its lateral surface 21 ) is made of an electrically conductive material, such that the piston is able to short-circuit the busbars 5 via the piston by the lateral surface 21 of the piston making electrical contact with the busbars 5. The piston P typically has a circular cross-section. The piston is arranged with a pyrotechnic actuator 3 which, when activated, forms an expanding gas which pushes the previously stationary piston P along its longitudinal axis 20 in a direction away from the actuator 3 (in the direction indicated by the axial arrow in the figures, below the piston).​

[0025] The actuator 3 is arranged to axially move the piston P from its open position (e.g. as shown in Figure 2a , Figure 2b and Figure 6 illustrated) or a plurality of axially arranged openings 6 (e.g. as illustrated in the examples of Figures 3 to 5 and Figure 7 ) through the opening 6 (as illustrated in Figure 2a and Figure 2b ) to its closed position (e.g. as illustrated in Figure 2a and Figure 2b ). The opening 6 or each of the openings 6 can be a hole, a through-hole or a blind hole in the busbar 5, or an opening between different and mutually electrically insulated busbars 5a and 5b (as illustrated in the examples of

[0026] To facilitate the axial movement of the piston P by the actuator 3 when activated, the housing 4 can be arranged around the piston P, thereby preferably providing an enclosed chamber 7 between the rear end 24 of the piston P and the interior of the housing 4 during the entire axial movement of the piston. Thus, when the actuator 3 is activated, a gas can be formed within the chamber 7, which pushes the rear end 24 of the piston P, thereby moving the piston axially and expanding the chamber 7.

[0027] Additionally or alternatively, the actuator itself can comprise a moving part which, when the pyrotechnic actuator is activated, axially presses against the piston P in physical contact therewith to cause the axial movement of the piston. In this case, the gas expansion can take place in a chamber within the actuator 3, rather than in the chamber 7 between the actuator 3 and the rear end 24 of the piston P.

[0028] Preferably, the piston P has a tapered shape, e.g. tapering towards the front end 23 of the piston at an angle θ within a range of 3° to 12°, preferably 4° to 8°, e.g. 5.5° to 6.5° from the longitudinal axis 20. This allows the piston P to wedge into the one or more openings 6, which at their closed position at the end of the axial movement of the piston typically correspond in size and shape to the tapered shape of the piston, thereby improving the electrical connection between the piston P and the busbar 5. Preferably, the piston has a conical shape, e.g. a truncated shape or a truncated-cone shape as illustrated in the drawings. The conical piston typically has a circular base, thereby forming an end surface of the rear end 24 of the piston. Typically, the cone is a right circular cone. In a right conical piston P which is truncated or not truncated, the angle θ between the generatrix line of the lateral surface 21 and the central longitudinal axis 20 can thus be within a range of 3° to 12°, preferably 4° to 8°, e.g. 5.5° to 6.5°.

[0029] Preferably, the inner surface of the one or more openings 6 is arranged to fit against the tapered shape of the piston P to improve the electrical connection. If the opening 6 is a hole in the busbar 5, the hole can be tapered at the same angle Θ to the longitudinal axis 20 as the piston P to fit against the lateral surface 21 at the end of the axial movement of the piston (corresponding to the closed position of the piston P and the closed state of the device 1). Additionally or alternatively, the shape (typically circular) and size (in a plane perpendicular to the longitudinal axis 20) of the hole 6 corresponds to the cross section of the piston such that the inner surface of the hole contacts the lateral surface 21 of the piston around the entire circumference of the piston when the piston has reached its closed position.

[0030] Likewise, if the opening 6 is located between two busbars 5a and 5b, each of the respective end surfaces 22 of the two busbars 5a and 5b can be inclined at the same angle Θ to the axis 20 as the piston P to fit against the lateral surface 21 at the end of the axial movement of the piston (corresponding to the closed position of the piston P and the closed state of the device 1). Additionally or alternatively, each of the respective end surfaces 22 of the two busbars 5a and 5b can be curved in a plane perpendicular to the longitudinal axis 20 to continuously contact around a section of the circumference of the piston when the piston has reached its closed position.

[0031] To guide the piston P into and / or through the opening 6 or the plurality of axially arranged openings 6, the piston can be provided with a guide 8 extending axially from the front end 23 of the piston. The guide 8 is made of electrically insulating material. The guide 8 is typically cylindrical, e.g. has a circular cross section.

[0032] Figure 3 and Figure 4 An embodiment of the arc extinguishing device 1 is illustrated, wherein the first piston P1 and the second piston P2 are each arranged to axially move through a respective opening 6 in the form of a first or second through hole in the first busbar T. Each of the second and third busbars S and R is arranged with an opening 6 in the form of a hole (through hole or blind hole) axially aligned with a respective one of the through holes of the first busbar T to receive the first piston P1 or the second piston P2.

[0033] Hence, when the arc extinguishing device 1 is open, each of the pistons P1 and P2 is in its open position in which all three busbars T, S and R are electrically insulated from each other at the one or more openings 6, e.g. by an electrically insulating gas (such as air) in the one or more openings 6 or by another electrically insulating gas / gas mixture (like (pure) nitrogen). In Figure 3 and Figure 4In embodiments of the application, the first busbar T and the first and second holes 6 therein are each associated with axial movement of the piston arranged before (above in the figures) the holes of the second and third busbars S and R, respectively. Then, the piston P1 and / or P2 can be in contact with the first busbar T but not with any of the second and third busbars S and R, or the piston P1 and / or P2 can not be in contact with any of the busbars T, S or R. However, in other embodiments, the first busbar T and the first and second holes 6 therein can be arranged after (below in the figures) the holes of the second and third busbars S and R, respectively, with respect to axial movement of the piston. Figure 3 and Figure 4 below).

[0034] When the at least one pyrotechnic actuator 3 is initiated, the first piston P1 and the second piston P2 are simultaneously moved axially until each of the first and second pistons P1 and P2 reaches its closed position, thereby closing the arc extinguishing device 1. In its closed position, the first piston P1 is in physical (and thus electrical) contact with the first and second busbars T and S. Specifically, the lateral surface 21 of the first piston P1 is in physical contact with the inner surface of the first hole 6 through the first busbar T and with the inner surface of the hole 6 through or in the second busbar S. Likewise, in its closed position, the second piston P2 is in physical (and thus electrical) contact with the first and third busbars T and R. Specifically, the lateral surface 21 of the second piston P2 is in physical contact with the inner surface of the second hole 6 through the first busbar T and with the inner surface of the hole 6 through or in the third busbar R.

[0035] Thus, in some embodiments of the application, the device 1 is arranged such that, upon axial movement of the first and second pistons P1 and P2, the lateral surface 21 of the first piston P1 contacts the respective inner surfaces of the first hole 6 in the first busbar T and of the hole 6 in the second busbar S, and the lateral surface 21 of the second piston P2 contacts the respective inner surfaces of the second hole 6 in the first busbar T and of the hole 6 in the third busbar R.

[0036] As discussed above, the holes 6 of the busbars T, S and R are preferably shaped to fit against the pistons P1 and P2 when the pistons P1 and P2 are in their closed positions, such that the pistons wedge against the busbars by their axial movement to create a good electrical contact. For instance, if each of the first and second pistons P1 and P2 has a right conical shape tapering towards its front end 23 (downwards in the figures), then each of the holes 6 in the first, second and third busbars T, S and R can be circular and have an inner surface with a corresponding tapering (i.e. tapering in the axial movement direction). Due to the conical shape of the pistons P1 and P2, when the first and second holes 6 of the first busbar T are arranged before the axially arranged holes 6 of the second and third busbars S and R, respectively (as in the figures), the pistons P1 and P2 will wedge against the busbars T, S and R by their axial movement. Figure 4 Likewise, if each of the first and second pistons P1 and P2 has a right conical shape tapering towards its back end 25 (upwards in the figures), then each of the holes 6 in the first, second and third busbars T, S and R can be circular and have an inner surface with a corresponding tapering (i.e. tapering in the axial movement direction). Due to the conical shape of the pistons P1 and P2, when the first and second holes 6 of the first busbar T are arranged after the axially arranged holes 6 of the second and third busbars S and R, respectively (as in the figures), the pistons P1 and P2 will wedge against the busbars T, S and R by their axial movement.Figure 4 The first and second holes in the first busbar T preferably each have a larger diameter than the axially later arranged holes of the second busbar S or the third busbar R, respectively.

[0037] Figure 5 Fig. 1 illustrates an embodiment of the arc extinguishing device 1 according to the present invention. Figure 3 Fig. 2 illustrates an embodiment of the arc extinguishing device 1 according to the present invention. Figure 4 Fig. 3 illustrates an embodiment of the arc extinguishing device 1 according to the present invention, similar to the embodiment of Figs. 1 and 2 but also having a protective earth (PE) busbar. In this embodiment, in addition to the two busbar layers in Figs. 1 and 2, the PE busbar forms a third busbar layer. For instance, as illustrated in Fig. 3, the PE busbar can be arranged (in the axial movement direction) before the first busbar T (above in Fig. 3). Figure 3 Fig. 4 illustrates an embodiment of the arc extinguishing device 1 according to the present invention, similar to the embodiment of Fig. 3 but having a different arrangement of the PE busbar. Figure 4 Fig. 5 illustrates an embodiment of the arc extinguishing device 1 according to the present invention, similar to the embodiment of Fig. 3 but having a different arrangement of the PE busbar. Figure 5 Fig. 6 illustrates an embodiment of the arc extinguishing device 1 according to the present invention, similar to the embodiment of Fig. 3 but having a different arrangement of the PE busbar. Figure 5 Fig. 7 illustrates an embodiment of the arc extinguishing device 1 according to the present invention, similar to the embodiment of Fig. 3 but having a different arrangement of the PE busbar. Figure 5 Fig. 8 illustrates an embodiment of the arc extinguishing device 1 according to the present invention, similar to the embodiment of Fig. 3 but having a different arrangement of the PE busbar. Figure 3 Fig. 9 illustrates an embodiment of the arc extinguishing device 1 according to the present invention, similar to the embodiment of Fig. 3 but having a different arrangement of the PE busbar. Figure 4 Fig. 10 illustrates an embodiment of the arc extinguishing device 1 according to the present invention, similar to the embodiment of Fig. 3 but having a different arrangement of the PE busbar. Fig. 11 illustrates an embodiment of the arc extinguishing device 1 according to the present invention, similar to the embodiment of Fig. 3 but having a different arrangement of the PE busbar.

[0038] Fig. 12 illustrates an embodiment of the arc extinguishing device 1 according to the present invention, similar to the embodiment of Fig. 3 but having a different arrangement of the PE busbar. Fig. 13 illustrates an embodiment of the arc extinguishing device 1 according to the present invention, similar to the embodiment of Fig. 3 but having a different arrangement of the PE busbar.

[0039] Fig. 14 illustrates an embodiment of the arc extinguishing device 1 according to the present invention, similar to the embodiment of Fig. 3 but having a different arrangement of the PE busbar. Fig. 15 illustrates an embodiment of the arc extinguishing device 1 according to the present invention, similar to the embodiment of Fig. 3 but having a different arrangement of the PE busbar.

[0040] The above discussion relating to the inner surfaces of the holes 6 in the first busbar T, the second busbar S, and the third busbar R also relates to the inner surfaces of the holes 6 in the PE busbar, which are shaped to fit against pistons P1 and P2 when in their respective closed positions.

[0041] For reference Figure 2a and Figure 2b As mentioned, the piston P may be provided with a guide 8 made of electrically insulating material to help the piston pass through the opening 6. For example... Figure 5 As shown, this is such that each piston is arranged with more than two axially aligned openings 6 (e.g., holes through the PE busbar, the first busbar T, the second busbar S, or the third busbar R, as shown). Figure 5 This is particularly advantageous in cases where the busbars (as shown in the example) are in electrical contact. The guide 8 can then ensure that the piston has both physical and electrical contact with all the busbars that are arranged to simultaneously contact it in its closed position. If the piston P only contacts two busbars, for example, Figure 5 The T and S in the figure present a risk of delaying or preventing the piston from contacting all the busbars that are arranged to contact it in its closed position, for example, by welding the two busbars that first come into contact.

[0042] To ensure controlled, straight axial movement of piston P during axial movement of actuator 3, piston guide 8 can be arranged through guide hole 51 in insulator 50 made of electrically insulating material, disposed on the other side of opening 6, as seen in the direction of piston axial movement. For example, when piston is in its open position, the tip of guide 8 can extend into guide hole 51 in insulator 50, and can then further penetrate or pass through guide hole during axial movement until piston has reached its closed position. Therefore, piston movement or tilting at an angle to the longitudinal axis during its axial movement can be prevented.

[0043] Figure 6 Another embodiment of the invention is illustrated, wherein the lateral surfaces 21 of pistons P1 and P2 are not arranged to contact the inner surfaces of the holes 6 in the first generatrix T, the second generatrix S, and the third generatrix R (the inner surfaces of each hole completely surround the piston in the closed position), but are arranged to contact the end surfaces 22 of each of the first generatrix T, the second generatrix S, and the third generatrix R (each end surface 22 extends only along a section of the circumference of the piston in the closed position / contacts a portion of the circumference of the piston in the closed position).

[0044] Therefore, in some embodiments of the invention, the device 1 is arranged such that after axial movement of the first piston P1 and the second piston P2, the lateral surface 21 of the first piston P1 contacts the corresponding end surfaces 22 of the first generatrix T and the second generatrix S, and the lateral surface 21 of the second piston P2 contacts the corresponding end surfaces 22 of the first generatrix T and the third generatrix R. The first generatrix T, the second generatrix S, and the third generatrix R, or at least their end components including the end surfaces 22, can be arranged in the same plane perpendicular to the longitudinal axis 20 of the pistons.

[0045] As discussed above, regarding Figure 2a and Figure 2b The respective end surfaces 22 of the two generatrices T and S (for the first piston P1) and T and R (for the second piston P2) may be inclined at the same angle θ as the taper of piston P1 or P2 to fit against the lateral surface 21 in the closed position of the piston. Additionally or alternatively, each end surface 22 of the two generatrices T and S (for the first piston P1) and T and R (for the second piston) may be bent in a plane perpendicular to the longitudinal axis 20 to continuously contact a portion of the piston circumference when the piston has reached its closed position.

[0046] Therefore, in some embodiments of the present invention, each of the end surfaces 22 of the first busbar T, the second busbar S and the third busbar R is bent to fit against the lateral surface 21 of the first piston P1 or the second piston P2, the lateral surface 21 of the first piston P1 or the second piston P2 being arranged to contact the end surface.

[0047] At least one pyrotechnic actuator 3 is used to drive the first piston P1 and the second piston P2 to move axially. The advantage of the pyrotechnic actuator is that it reduces the time required for a three-phase short circuit, for example, within 5ms, 4ms, or 2ms after an arc fault is detected.

[0048] In some embodiments, at least one pyrotechnic actuator 3 may include two actuators 3, one actuator 3 for each of the first piston P1 and the second piston P2. Therefore, in some embodiments of the invention, at least one pyrotechnic actuator 3 includes or is composed of a first actuator and a second actuator, the first actuator being arranged to move the first piston P1 but not the second piston, while the second actuator is arranged to move the second piston P2 but not the first piston. When more than one actuator 3 is used, it is desirable to simultaneously activate the actuators to rapidly and simultaneously short-circuit all three phases. Therefore, the first actuator and the second actuator 3 can be synchronized. However, it should be noted that because the increase in gas pressure may vary slightly, the first piston P1 and the second piston P2 may move at slightly different times (e.g., within 1 μs to 10 μs of each other) and / or speeds.

[0049] Alternatively, in some other embodiments of the invention, the at least one pyrotechnic actuator 3 consists of only one actuator arranged to move both the first piston P1 and the second piston P2. For example, the first piston P1 and the second piston P2 may be rigidly mechanically connected to each other such that the first piston P1 and the second piston P2 do not move relative to each other during axial movement of the actuator 3.

[0050] Figure 7 An example embodiment is illustrated with only one actuator 3 for both the first piston P1 and the second piston P2. The first piston P1 and the second piston P2 are rigidly mechanically connected to each other and are arranged to be driven together axially (upwards in the figure) by a single actuator 3 to contact the first busbar T, the second busbar S, and the third busbar R via end surfaces 22, optionally through first and second through-holes 6 of the PE busbar. The end surfaces 22 and the through-holes 6 can be as discussed above with respect to the other figures.

[0051] The present invention has been described above primarily with reference to several embodiments. However, those skilled in the art will appreciate that other embodiments besides those disclosed above are also possible within the scope of this disclosure as defined by the appended claims.

Claims

1. An arc-extinguishing device (1) for a three-phase electrical switchgear (10), the arc-extinguishing device comprising: The first busbar (T), the second busbar (S), and the third busbar (R) are each used for the corresponding phases (L1, L2, L3) of the three-phase electrical switchgear. The first piston (P1) is characterized in that the arc-extinguishing device further includes a second piston (P2), each piston being made of a conductive material; and At least one pyrotechnic actuator (3) is arranged together with the first piston and the second piston to axially move each of the first piston and the second piston when the at least one pyrotechnic actuator is activated; The first piston (P1) and the second piston (P2) are arranged relative to the first busbar (T), the second busbar (S), and the third busbar (R) such that the axial movement causes the first piston (P1) to contact both the first busbar (T) and the second busbar (S), thereby short-circuiting the first busbar and the second busbar via the first piston; and causes the second piston (P2) to contact both the first busbar (T) and the third busbar (R), thereby short-circuiting the first busbar and the third busbar via the second piston.

2. The arc extinguishing device according to claim 1 further includes a protective grounding bus (PE), the protective grounding bus being arranged such that when the at least one pyrotechnic actuator (3) is activated, the first piston (P1) and the second piston (P2) are each axially moved until each of the pistons also contacts the protective grounding bus, such that each of the first bus (T), the second bus (S) and the third bus (R) is also short-circuited to the protective grounding bus via at least one of the first piston and the second piston.

3. The arc extinguishing device according to claim 1 or 2, wherein the at least one pyrotechnic actuator (3) comprises a first actuator and a second actuator or is composed of the first actuator and the second actuator, wherein the first actuator is arranged to move the first piston (P1) but not the second piston, and the second actuator is arranged to move the second piston (P2) but not the first piston.

4. The arc extinguishing device according to claim 3, wherein the first actuator and the second actuator (3) are synchronized to start simultaneously.

5. The arc extinguishing device according to claim 1 or 2, wherein the at least one pyrotechnic actuator (3) comprises only one actuator arranged to move the first piston (P1) and the second piston (P2).

6. The arc extinguishing device according to claim 5, wherein the first piston (P1) and the second piston (P2) are rigidly mechanically connected to each other such that when the first piston (P1) and the second piston (P2) are axially moved by the actuator (3), the first piston (P1) and the second piston (P2) do not move relative to each other.

7. The arc extinguishing device according to claim 1 or 2, wherein each of the first piston (P1) and the second piston (P2) has a tapered shape that tapers toward its front end (23).

8. The arc-extinguishing device according to claim 7, wherein each of the first piston (P1) and the second piston (P2) has a conical shape.

9. The arc-extinguishing device according to claim 8, wherein each of the first piston (P1) and the second piston (P2) has a truncated conical shape.

10. The arc extinguishing device according to claim 1 or 2, wherein the arc extinguishing device (1) is arranged such that after the axial movement of the first piston (P1) and the second piston (P2), the lateral surface (21) of the first piston (P1) contacts the corresponding inner surfaces of the first hole (6) in the first busbar (T) and the hole (6) in the second busbar (S), and the lateral surface (21) of the second piston (P2) contacts the corresponding inner surfaces of the second hole (6) in the first busbar (T) and the hole (6) in the third busbar (R).

11. The arc extinguishing device according to claim 10, wherein each of the first hole (6) and the second hole (6) of the first busbar (T), the hole (6) of the second busbar (S) and the hole (6) of the third busbar (R) is tapered to fit against the lateral surface (21) of the first piston (P1) or the second piston (P2), the lateral surface (21) of the first piston (P1) or the second piston (P2) being arranged to contact the hole (6).

12. The arc extinguishing device according to claim 1 or 2, wherein the arc extinguishing device (1) is arranged such that after the axial movement of the first piston (P1) and the second piston (P2), the lateral surface (21) of the first piston (P1) contacts the corresponding end surfaces (22) of the first busbar (T) and the second busbar (S), and the lateral surface (21) of the second piston (P2) contacts the corresponding end surfaces (22) of the first busbar (T) and the third busbar (R).

13. The arc extinguishing device according to claim 12, wherein each of the end surfaces (22) of the first busbar (T), the second busbar (S) and the third busbar (R) is bent to fit against the lateral surface (21) of the first piston (P1) or the second piston (P2), the lateral surface (21) of the first piston (P1) or the second piston (P2) being arranged to contact the end surface (22).

14. The arc extinguishing device according to claim 7, wherein each of the first piston (P1) and the second piston (P2) is provided with a guide (8) made of an electrically insulating material, the guide (8) extending axially from the front end (23) of the piston.

15. A three-phase electrical switchgear (10) comprising an arc-extinguishing device (1) according to any one of the preceding claims and a fault-clearing circuit breaker (11), the fault-clearing circuit breaker (11) being arranged to disconnect the current of each of the three phases (L1, L2, L3), the three phases (L1, L2, L3) being respectively connected to a first bus (T), a second bus (S) and a third bus (R).

16. The switching device according to claim 15, configured for low-voltage or medium-voltage applications.

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