Vacuum switching device for a circuit with main and secondary current paths

Description

Technical field of the present invention

[0001] The present invention relates to a vacuum switching device, in particular a vacuum interrupter, and a circuit having a main current path and a secondary current path parallel thereto, wherein a vacuum switching device is arranged in the secondary current path.

[0002] Fig. 9 shows a conventional vacuum switching device in the form of a vacuum interrupter. The conventional vacuum switching device has a housing body comprising an electrically insulating material such as a ceramic tube, a stationary electrical contact arranged stationary with respect to the housing body and within the housing body, and a movable electrical contact arranged movable with respect to the housing body and within the housing body such that it establishes electrical contact with the stationary electrical contact upon its movement toward the stationary electrical contact and breaks the electrical contact upon its movement away from the stationary electrical contact.

[0003] Vacuum interrupters must meet application-specific technical requirements during operation, particularly with regard to external dielectric strength. Due to the manufacturing process, a metallization edge or solder edge is present at the axial end of the ceramic tube, which is considered a potential weak point for the external dielectric strength U. In order to meet the external dielectric strength requirement in the operating environment, different design features on the tube (including installation situation) or insulation options (gas, oil, silicone, etc.) can be used. On the one hand, sufficient dielectric strength can be generated by sufficiently dimensioning the ceramic length in air or using gaseous insulating media such as SF6 (or other technical gases, even with increased pressure compared to the atmosphere). Other conventional measures include siliconizing entire tubes or partially insulating the metallization edge, e.g. using Pott tape.

[0004] A further requirement for the tube is sufficient contact pressure between the stationary electrical contact and the movable electrical contact. The current-carrying contacts of the vacuum switching device are held closed by external forces. These forces consist of the closing force due to the pressure difference from the inside to the outside and additional, externally applied closing forces, which are often implemented by springs (figs + spring). These forces prevent the contacts from lifting at high currents and reduce the internal resistance of the current path. Particularly in applications where only small currents need to be controlled, only small contact pressures are required due to the quadratic relationship to the current. If the intrinsic closing force of the tube itself is relatively small and also fluctuates due to component tolerances, defined conditions are created by additional externally applied forces.The generation of contact forces for vacuum interrupters is usually realized outside the tube in corresponding spring assemblies.

[0005] From GB 1 206 297 A a vacuum interrupter is known which has a moving contact guided in a bearing which is arranged to be movable by means of a bellows.

[0006] US2,981,813 discloses a vacuum switch in which the moving contact pin is guided in a bearing in a bellows.

[0007] EP 2479 769 A1 shows a switching device with a main current path and a secondary current path with a vacuum switch.

[0008] From WO 90 / 03657 A1 a circuit is known which has a main current path and a secondary current path with a vacuum switch.

[0009] EP 3 109 878 A1 discloses a vacuum interrupter with a bearing and a spring arrangement acting on the moving contact. Summary of the invention

[0010] There is a need for a vacuum switching device that meets the aforementioned requirements of sufficient external dielectric strength and sufficient contact pressure through a simplified design, and that can be integrated into a secondary current path. This need can be met by the subject matter of the independent claims. The present invention is further developed according to the dependent claims.

[0011] According to a first aspect of the invention, a vacuum switching device comprises a housing body comprising an electrically insulating material, a stationary electrical contact arranged stationary with respect to the housing body and within the housing body, a movable electrical contact arranged movable with respect to the housing body and within the housing body such that it establishes electrical contact with the stationary electrical contact upon movement toward the stationary electrical contact and breaks electrical contact upon movement away from the stationary electrical contact, and a sliding bearing connected to the housing body and slidably supporting the movable electrical contact for its movement toward and away from the stationary electrical contact. The sliding bearing comprises an electrically conductive material and at least partially dielectrically shields the housing body.The plain bearing has a spring support on which a spring element is supported, which presses the movable electrical contact towards the stationary electrical contact.

[0012] According to the present invention, the plain bearing performs a variety of functions, namely not only the plain bearing of the movable electrical contact, but also the function of dielectric control of the metallization edge and the counter bearing of the spring element (integrated, for example, in a bellows chamber) for building up the contact force. This means that many functions are already integrated in the assembly consisting of the plain bearing and the spring element. Furthermore, the housing body has a flange at one of its axial ends which comprises an electrically conductive material, wherein the plain bearing at least partially electrically shields the flange. The plain bearing made of electrically conductive material takes on ain conjunction with the flange) additionally performs the function of dielectric control of the metallization edge by homogenizing the electric field in the area of ​​the metallization edge in such a way that the dielectric strength can be increased there.

[0013] The sliding bearing also features a tubular sliding section that is coaxially mounted on the shaft section of the movable electrical contact, and a shielding section that extends radially outward from the sliding section and at least partially electrically shields the flange of the housing body as well as the soldering edge. This also results in a particularly compact design.

[0014] Furthermore, the shield section of the plain bearing has at least one spirally extending slot.

[0015] This gives the shield section a springy design, which also serves to mount and center the plain bearing with respect to an external device.

[0016] According to one embodiment, the movable electrical contact has a contact section and an axial shaft section connected thereto. The spring element is mounted coaxially on the shaft section and preloaded between the spring support of the sliding bearing and another spring support of the movable electrical contact. This results in a particularly compact design.

[0017] According to one embodiment, the plain bearing is attached to the housing body by a bayonet lock, a snap lock, an adhesive connection, or a thread. According to one embodiment, the bayonet lock, the snap lock, the adhesive connection, or the thread is provided on the sliding section of the plain bearing. The assembly and fixation of the plain bearing on / in the housing body are simplified by the integrated bayonet principle and / or the snap lock, an adhesive connection, and / or the thread.

[0018] According to one embodiment, the shielding section of the sliding bearing is axially inclined toward the housing body. According to one embodiment, the shielding section is arranged at an axial end of the sliding section. This achieves a compact design and, at the same time, effective dielectric control.

[0019] According to one embodiment, the shielding section of the plain bearing has a stop designed to center and axially support the plain bearing in its installed state. This integrates a further function into the plain bearing, namely the accommodation and centering of the plain bearing and / or the housing body in the vacuum switching device.

[0020] According to one embodiment, the shielding section is elastically deformable in the axial direction (for example, through the spirally extending slot). The resilient design of the shielding section enables installation in an undercut and ensures that the outer shielding section always rests against the solder edge and reliably deflects it. The counterforce of the spring element is transmitted via the plain bearing to the shielding section of the plain bearing, and from there to an external receiving body.

[0021] According to one embodiment, the vacuum switching device further comprises a bellows arranged coaxially over the spring element and coaxially over the tubular sliding portion of the sliding bearing and connected to the movable electrical contact on the one hand and the housing body on the other hand.

[0022] According to one embodiment, the vacuum switching device is a vacuum interrupter.

[0023] According to one embodiment, the shaft portion of the movable electrical contact projects axially beyond the sliding bearing and has a coupling portion at its axial end to which an external actuating element, such as a rocker, can be coupled in order to move the movable electrical contact toward or away from the stationary electrical contact.

[0024] According to a second aspect of the invention, a circuit is provided with a main current path and a secondary current path parallel thereto, wherein a vacuum switching device is arranged in the secondary current path, wherein the vacuum switching device is an embodiment of the first aspect of the invention described above, which has the following: a housing body which has an electrically insulating material; a stationary electrical contact which is arranged stationary with respect to the housing body and within the housing body; a movable electrical contact which is arranged movable with respect to the housing body and within the housing body such that it makes electrical contact with the stationary electrical contact when it moves towards it and breaks the electrical contact when it moves away from the stationary electrical contact;and a spring element that presses the movable electrical contact toward the stationary electrical contact. According to one embodiment, the vacuum switching device has a bellows that is arranged coaxially around the spring element or that is formed by the spring element.

[0025] Preferably, the vacuum switching device is an embodiment of the first aspect of the invention described above.

[0026] Preferably, at least one of the following features is met: a stroke of the movable electrical contact is 4 to 20 mm, preferably 6 to 10 mm; a load breaking current in the secondary current path is less than 1250 A, preferably 630 A ± 30 A; a current flow duration during a breaking operation of the vacuum switching device is 1 to 20 ms; the circuit is used in a voltage range that is greater than or equal to 1 kV, preferably in a range between 1 kV and 52 kV inclusive; a takeover current in a load-break switch-fuse combination in the secondary current path is less than 2500 A; a spring constant of the spring element is in a range between 1 and 15 N / mm inclusive.

[0027] The conventional vacuum tubes previously used in switchgear were always used in circuit breakers in the main current path. An important and demanding requirement for vacuum tubes in this conventional application was their ability to withstand short-circuit currents. Relatively high forces are at work here, requiring correspondingly large and strong springs. Due to the size of the spring, positioning the spring in the bellows was not feasible.

[0028] The present invention uses a vacuum switching device for use in a bypass current path. This eliminates the requirement for short-circuit current carrying capacity. The spring element used serves as a mechanical support. It is comparatively weak and compact. Therefore, the spring element can be arranged within a bellows for use in a vacuum interrupter. Brief description of the drawings

[0029] The above-defined aspects and further aspects of the present invention will become apparent from the following exemplary embodiments. The invention will be described in more detail below with reference to the exemplary embodiments, to which, however, the invention is not limited. Fig. 1 shows a longitudinal section through a vacuum switching device according to an embodiment of the present invention; Fig. 2 shows a perspective view of an assembly consisting of a sliding bearing and a spring element according to the embodiment; Fig. 3 shows a perspective view of an assembly consisting of the sliding bearing, the spring element, a movable electrical contact, and a shield according to the embodiment; Fig. 4 shows a perspective view of an assembly consisting of a ceramic tube, a flange, and the movable electrical contact; Fig. 5 shows a perspective view of an assembly consisting of the flange, the movable electrical contact, and the sliding bearing; Fig. 6 shows a perspective longitudinal section through the vacuum switching device according to the embodiment of the present invention;Fig. 7 shows a longitudinal section through the vacuum switching device according to the embodiment of the present invention; Fig. 8 shows an equivalent circuit diagram of a circuit with a main current path and a parallel auxiliary current path, wherein a vacuum switching device is arranged in the auxiliary current path; and Fig. 9 shows a conventional vacuum switching device. Character description

[0030] The drawings are schematic. It should be noted that similar or identical elements in different figures are designated by the same reference numerals.

[0031] Fig. 1 shows a longitudinal section through a vacuum switching device 1 according to an embodiment of the present invention. The vacuum switching device 1 is a vacuum interrupter and has a cylindrical housing body 2, which comprises an electrically insulating material or is formed from an electrically insulating material. The electrically insulating material can be a ceramic. The electrically insulating material can be formed by a tube, as in the illustrated embodiment, in particular by a cylindrical ceramic tube 19.Within the housing body 2, a stationary electrical contact 3, which is arranged stationary with respect to the housing body 2, and a movable electrical contact 4 are arranged, which is arranged movable with respect to the housing body 2 such that it makes electrical contact with the stationary electrical contact 3 when it moves towards it and breaks the electrical contact when it moves away from the stationary electrical contact 3.

[0032] The vacuum switching device 1 further comprises a sliding bearing 5, which is connected to the housing body 2 and slidingly supports the movable electrical contact 4 for its movement to and from the stationary electrical contact 3. The sliding bearing 5 comprises an electrically conductive material or is formed from an electrically conductive material, and it at least partially electrically shields the housing body 2. A spring support 6 is provided on the sliding bearing 5, on which a spring element 7 in the form of a compression spring is supported, which presses the movable electrical contact 4 toward the stationary electrical contact 3. The spring element 7 is mounted coaxially on the shaft section 10 and preloaded between the spring support 6 of the sliding bearing 5 and another spring support 11 of the movable electrical contact 4.

[0033] The movable electrical contact 4 has a contact section 9 and an axial shaft section 10 connected thereto.

[0034] The housing body 2 has at one of its axial ends (at the right end in the Fig. 1 ) a flange 8 which comprises an electrically conductive material or is formed from an electrically conductive material, wherein the plain bearing 5 at least partially electrically shields the flange 8. The housing body 2 further has at its other axial end (at the left end in the Fig. 1 ) a further flange 18, which comprises an electrically conductive material or is formed from an electrically conductive material. In the illustrated embodiment, the housing body 2 is therefore formed by the cylindrical ceramic tube 19, the flange 8, and the further flange 18.

[0035] The shaft portion 10 of the movable electrical contact 4 projects axially beyond the sliding bearing 5 and has at its axial end a coupling portion 16 to which an external actuating element such as a rocker can be coupled in order to move the movable electrical contact 4 toward or away from the stationary electrical contact 3.

[0036] The sliding bearing 5 has a tubular sliding portion 12 which is coaxially slidingly mounted on the shaft portion 10 of the movable electrical contact 4, and a shielding portion 13 which extends radially outward from the sliding portion 12 and at least partially electrically shields the flange 8 of the housing body 2.

[0037] At the interface between the ceramic tube 19 and the flange 8, there is a solder edge or a metallization edge of the housing body 2, which is typically considered a weak point with regard to the dielectric strength or external dielectric strength. However, in the present invention, the plain bearing 5 and, in particular, its shielding section 5 ensure dielectric control or smoothing of the electric field in the area of ​​the metallization edge, so that the dielectric strength there can be significantly improved.

[0038] The vacuum switching device 1 further includes a bellows 15 arranged coaxially above the spring element 7 and coaxially above the tubular sliding section 12 of the sliding bearing 5, and connected to the movable electrical contact 4 on the one hand and the housing body 2 (i.e., the flange 8) on the other. This achieves a particularly compact design. The bellows 15 is protected by a pot-shaped shield 17 arranged on the movable electrical contact 4.

[0039] The spring element 7 does not necessarily have to be designed as a separate compression spring. In one embodiment, the bellows 15 can additionally assume the function and properties of the spring element 7. In another embodiment, the spring element 7 and the plain bearing 5 can be formed integrally, wherein the spring support 6 can be realized, for example, by a material, form-fitting, or force-fitting coupling between the spring element 7 and the plain bearing 5.

[0040] The shield portion 13 of the sliding bearing 5 is arranged at one axial end of the sliding portion 12 and is axially inclined toward the housing body 2. A plurality of spirally extending slots 14 are formed in the shield portion 13 of the sliding bearing 5, so that the shield portion 13 is elastically deformable in the axial and radial directions.

[0041] Fig. 2 shows a perspective view of an assembly consisting of the plain bearing 5 and the spring element 7 according to the embodiment. Fig. 2 shows in particular the spring support 6 for the spring element 7, the sliding section 12, the shielding section 13 and the plurality of slots 14 in the shielding section 13 of the sliding bearing 5. The Fig. 2 also shows a bayonet lock 20, by which the plain bearing 5 is attached to the housing body 2. The bayonet lock 20 is formed on an outer surface of the sliding section 12 and engages with a complementary inner contour of the flange 8. The sliding section 12 of the plain bearing 5 is inserted into a central through-opening in the flange 8, and by rotating the plain bearing 5, the bayonet lock 20 engages or closes.

[0042] Fig. 3 shows a perspective view of an assembly consisting of the sliding bearing 5, the spring element 7, the movable electrical contact 4, which has the contact section 9 and the shaft section 10, and the shield 17 according to the exemplary embodiment. The slots 14 in the shield section 13 of the sliding bearing 5 are also shown.

[0043] Fig. 4 shows a perspective view of an assembly consisting of the ceramic tube 19, the flange 8 and the movable electrical contact 4. The shaft section 10 of the movable electrical contact 4 projects axially beyond the sliding bearing 5 located behind the flange 8 (not shown in the Fig. 4 shown) and has at its axial end the coupling section 16 to which the external actuating element such as the rocker can be coupled in order to move the movable electrical contact 4 towards or away from the stationary electrical contact 3.

[0044] Fig. 5 shows a perspective view of an assembly consisting of the flange 8 located behind the sliding bearing 5, the movable electrical contact 4 and the sliding bearing 5. The Fig. 5 shows in comparison with the Fig. 4 the state in which the plain bearing 5 is arranged above the flange 8.

[0045] Figuren 6 und 7 1 and 2 each show perspective longitudinal sections through the vacuum switching device 1 according to the exemplary embodiment of the present invention. The various components and functions of the sliding bearing 5 are indicated again. Reference symbol A denotes the bearing function for the sliding bearing of the movable electrical contact 4 by the sliding section 12 of the sliding bearing 5. Reference symbol B denotes the function of the sliding bearing 5 for dielectric control or for smoothing the electric field by means of the shielding section 13, which shields the metallization edge or solder edge of the housing body 2.

[0046] Reference symbol C denotes the previously mentioned function for centering the plain bearing 5. Centering is achieved by a stop 22. The stop 22 is formed by a raised, annular contour of the shield portion 13 and engages in a complementary recess of an external receiving body 21 according to the tongue-and-groove principle.

[0047] In the Fig. 7 Force flows are also shown. The arrow designated by reference symbol D shows the force flow of the spring force of the spring element 7 between the stop 22 and the additional spring support 11 formed on the movable electrical contact 4. The arrow designated by reference symbol E shows the force flow of a force between the flange 8 and the contact section 9. This force is composed of a bellows force applied by the bellows 15 and an externally applied gas pressure differential force.

[0048] Fig. 8 shows an equivalent circuit diagram of a circuit 100 with a main current path 30 and a parallel auxiliary current path 40, wherein a vacuum switching device 1 is arranged in the auxiliary current path 40. The main current path 30 and the auxiliary current path 40 each have a common node P at one end, which is connected to a first line 60. The other ends of the main current path 30 and the auxiliary current path 40 can be selectively connected to a second line 70 via a switching device 50.

[0049] Preferably, but not necessarily, the Fig. 1The vacuum switching device 1 shown can be arranged in the bypass current path. Such a vacuum switching device 1 has a housing body 2 which comprises an electrically insulating material, a stationary electrical contact 3 which is arranged stationary with respect to the housing body 2 and within the housing body 2, a movable electrical contact 4 which is arranged movable with respect to the housing body 2 and within the housing body 2 such that it makes electrical contact with the stationary electrical contact 3 when it moves towards it and breaks the electrical contact when it moves away from the stationary electrical contact 3, and a spring element 7 which presses the movable electrical contact 4 towards the stationary electrical contact 3.

[0050] The spring element 7 is preferably designed as a compression spring. The vacuum switching device 1 can have a bellows 15 arranged coaxially around the spring element 7. Alternatively, the bellows can be formed by the spring element 7 itself.

[0051] Preferably, at least one of the following features is met: a stroke of the movable electrical contact 4 is 4 to 20 mm, preferably 6 to 10 mm; a load breaking current in the auxiliary current path 40 is less than 1250 A, preferably 630 A ± 30 A; a current flow duration during a breaking operation of the vacuum switching device 1 is 1 to 20 ms; the circuit 100 is used in a voltage range that is greater than or equal to 1 kV, preferably in a range between 1 kV and 52 kV inclusive; a spring constant of the spring element is in a range between 1 and 15 N / mm inclusive; a transfer current in a load break switch-fuse combination in the auxiliary current path 40 is less than 2500 A. In the load break switch-fuse combination, a fuse (not shown), such as a melting fuse, can be arranged in series with the vacuum switching device 1 in the second line 70.The fuse can be arranged at the output of the vacuum switching device 1. The fuse, in turn, can be connected, for example, to a transformer connected to the output of the second line 70.

[0052] It should be noted that the term "comprising" does not exclude other elements or steps. Elements described in connection with different embodiments may also be combined. It should also be noted that reference signs in the claims should not be interpreted to reflect the scope of the claims. List of reference symbols

[0053] 1Vacuum switching device 2Housing body 3Fixed electrical contact 4Movable electrical contact 5Sliding bearing 6Spring support 7Spring element 8Flange 9Contact section 10Shaft section 11Further spring support 12Sliding section 13Shield section 14Slot 15Bellows 16Coupling section 17Shield 18Further flange 19Ceramic tube 20Bayonet lock 21External receptacle 22Stop 30Main current path 40Sub-current path 50Switching device 60First line 70Second line 100Circuit

Claims

1. Vacuum switching device (1) having: a housing body (2) that comprises an electrically insulating material; a spatially fixed electrical contact (3), which is arranged in a spatially fixed manner in relation to the housing body (2) and within the housing body (2); and a movable electrical contact (4), which is arranged in a movable manner in relation to the housing body (2) and within the housing body (2) such that, when it is moved toward the spatially fixed electrical contact (3), it establishes electrical contact therewith and, when it is moved away from the spatially fixed electrical contact (3), it interrupts the electrical contact; wherein a sliding bearing (5) that is connected to the housing body (2) and supports the movable electrical contact (4) in a sliding manner for the movement thereof toward and away from the spatially fixed electrical contact (3); wherein the sliding bearing (5) comprises an electrically conductive material and at least partially electrically shields the housing body (2); and has a spring support (6) that supports a spring element (7) that presses the movable electrical contact (4) in the direction toward the spatially fixed electrical contact (3), wherein the housing body (2), on one of its axial ends, has a flange (8) that comprises an electrically conductive material, wherein the sliding bearing (5) at least partially electrically shields the flange (8), wherein the sliding bearing (5) has a tubular sliding section (12) that is seated so as to slide coaxially on the shaft section (10) of the movable electrical contact (4), and a shielding section (13) that extends radially externally from the sliding section (12) and at least partially electrically shields the flange (8) of the housing body (2) and characterized in that the shielding section (13) of the sliding bearing (5) has at least one slot (14) extending in a spiral shape.

2. Vacuum switching device (1) according to one of the preceding claims, wherein the movable electrical contact (4) has a contact section (9) and an axial shaft section (10) connected thereto, and the spring element (7) is seated coaxially on the shaft section (10) and is pretensioned between the spring support (6) of the sliding bearing (5) and a further spring support (11) of the movable electrical contact (4).

3. Vacuum switching device (1) according to one of the preceding claims, wherein the sliding bearing (5) is attached to the housing body (2) by way of a bayonet connection (20), a snap-in connection, an adhesive bond or a thread.

4. Vacuum switching device (1) according to the two preceding claims, wherein the bayonet connection (20) or the snap-in connection, or the adhesive bond or the thread is provided on the sliding section (12) of the sliding bearing (5).

5. Vacuum switching device (1) according to one of Claims 1 to 4, wherein the shielding section (13) of the sliding bearing (5) is inclined axially toward the housing body (2).

6. Vacuum switching device (1) according to one of Claims 1 to 5, wherein the shielding section (13) is arranged on an axial end of the sliding section (12).

7. Vacuum switching device (1) according to one of Claims 1 to 6, wherein: the shielding section (13) of the sliding bearing (5) has a stop (22) that is configured so as to centre the sliding bearing (5) in its installed state.

8. Vacuum switching device (1) according to one of Claims 1 to 7, wherein the shielding section (13) is elastically deformable in the axial direction.

9. Vacuum switching device (1) according to one of Claims 1 to 8, furthermore having: a bellows (15) that is arranged coaxially above the spring element (7) and coaxially around the tubular sliding section (12) of the sliding bearing (5) and is connected to the movable electrical contact (4), on the one hand, and to the housing body (2), on the other hand.

10. Vacuum switching device (1) according to one of the preceding claims, wherein the vacuum switching device (1) is a vacuum switching tube.

11. Vacuum switching device (1) according to one of Claims 2 to 10, wherein the shaft section (10) of the movable electrical contact (4) protrudes axially beyond the sliding bearing (5) and, on its axial end, has a coupling section (16) to which an external actuation element is able to be coupled in order to move the movable electrical contact (4) toward the spatially fixed electrical contact (3) or away therefrom.

12. Circuit (100) having a main current path (30) and an auxiliary current path (40) in parallel therewith, wherein a vacuum switching device (1) according to one of Claims 1 to 11 is arranged in the auxiliary current path (40) and comprises the following: a housing body (2) that comprises an electrically insulating material; a spatially fixed electrical contact (3), which is arranged in a spatially fixed manner in relation to the housing body (2) and within the housing body (2); a movable electrical contact (4), which is arranged movably with respect to the housing body (2) and within the housing body (2) in such a way that it makes an electrical contact with it when it moves to the stationary electrical contact (3) and interrupts the electrical contact when it moves from the stationary electrical contact (3); and a spring element (7) that presses the movable electrical contact (4) in the direction toward the spatially fixed electrical contact (3).

13. Circuit (100) according to the preceding claim, furthermore comprising: a bellows (15) that is arranged coaxially around the spring element (7) or is formed by the spring element (7).

14. Circuit (100) according to one of Claims 12 and 13, wherein at least one of the following features is achieved: a lift of the movable electrical contact (4) is 4 to 20 mm, preferably 6 to 10 mm; a load deactivation current in the auxiliary current path (40) is less than 1250 A, preferably 630 A ± 30 A; a current flow duration during a deactivation process of the vacuum switching device (1) is 1 to 20 ms; the circuit (100) is used in a voltage range that is greater than or equal to 1 kV, preferably in a range between 1 kV and 52 kV inclusive; a takeover current in the case of a load circuit breaker / fuse combination in the auxiliary current path (40) is less than 2500 A; a spring constant of the spring element (7) is in a range between 1 and 15 N / mm inclusive.