switching device
By designing the arc-initiating structure, permanent magnet, and magnetizing block, the arc problem in the low-speed contact system was solved, enabling rapid magnetic blow-out arc extinguishing, avoiding secondary and repeated breakdowns, and improving the arc extinguishing effect.
Patent Information
- Application Number
- CN202411793238.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-06
- Publication Date
- 2026-06-09
AI Technical Summary
In energy storage applications, the slow opening speed of pre-charged moving contacts leads to serious arcing problems, especially in low-speed contact systems where secondary and repeated breakdowns are prone to occur, affecting the dielectric strength of the arc-extinguishing chamber.
The design employs an arc-initiating structure, a permanent magnet, and a magnetizing block. The arc-initiating structure guides the electric arc to the arc-extinguishing chamber, while the permanent magnet and magnetizing block provide magnetic field force to move the electric arc to the arc-extinguishing chamber. The leakage magnetic phenomenon is used to form an effective magnetic field layout for arc guidance.
It achieves rapid magnetic blowout arc extinguishing, avoids secondary and repeated breakdowns, improves arc extinguishing effect, and is particularly suitable for low-speed contact systems.
Smart Images
Figure CN122177678A_ABST
Abstract
Description
Technical Field
[0001] This disclosure relates to a switching device with arc extinguishing capability. Background Technology
[0002] In energy storage applications, battery packs are typically charged using two parallel charging circuits. One circuit, called the "pre-charge circuit," is connected in series with a large resistor to limit the current at the moment of connection. The other circuit, called the "main circuit," carries the rated current for extended periods and will carry the current during normal charging and discharging when connected.
[0003] Due to limitations imposed by the mechanism's drive method and the energy matching of the main circuit mechanism, the opening speed of the pre-charged moving contact is relatively slow. It takes 40–50 ms from the separation of the moving and stationary contacts until they reach their maximum opening distance, significantly slower than the opening speed of typical unmanned switches. Therefore, a redesigned arc-extinguishing mechanism is necessary to achieve the required load-bearing breaking capacity (e.g., DC 1500V). Summary of the Invention
[0004] In response to the problems and needs mentioned above, this disclosure proposes a switching device with arc extinguishing capability. It adopts a design scheme including an arc ignition structure, a permanent magnet and a magnetizing block, which can cause the arc to move from the arc generation area toward the arc extinguishing chamber and enter the arc extinguishing chamber, thereby achieving a good arc extinguishing effect.
[0005] On one hand, this disclosure proposes a switching device, comprising: a stationary contact and a moving contact cooperating with the stationary contact; an arc-extinguishing chamber; an arc-initiating structure disposed on the stationary contact, the arc-initiating structure including two arc-initiating feet located on both sides of the stationary contact of the stationary contact, the two arc-initiating feet extending toward the arc-extinguishing chamber; a permanent magnet and a magnetizing block connected to the permanent magnet, the permanent magnet and the magnetizing block being located between the arc-generating region at the stationary contact and the moving contact and the arc-extinguishing chamber, wherein the permanent magnet and the magnetizing block are arranged such that the magnetizing block is closer to the arc-generating region than the permanent magnet.
[0006] According to the preferred embodiment, the permanent magnet and the magnetizing block are located on one side of the two arc-starting feet, and the height of the upper edge of the magnetizing block is higher than the height of the end of the arc-starting foot.
[0007] According to a preferred embodiment, the stacking direction and height direction of the permanent magnet and the magnetizing block are parallel to the extension direction of the two arc-inducing feet.
[0008] According to a preferred embodiment, both the permanent magnet and the magnetizing block are sheet-like structures, and in the thickness direction of the permanent magnet and the magnetizing block, the permanent magnet and the magnetizing block are located between the two arc-starting feet.
[0009] According to a preferred embodiment, the arc-initiating structure includes a first arc-initiating segment extending toward the arc-extinguishing chamber and a second arc-initiating segment extending from the first arc-initiating segment toward the direction away from the permanent magnet and the magnetizing block, and the two arc-initiating feet extend from the second arc-initiating segment.
[0010] According to the preferred embodiment, the arc-initiating structure is integrally formed with the stationary contact.
[0011] According to a preferred embodiment, the permanent magnet and the magnetizing block have uniform thicknesses, and the thickness of the permanent magnet is greater than or equal to the thickness of the magnetizing block.
[0012] According to a preferred embodiment, the thickness of the magnetizing block decreases in the direction away from the permanent magnet.
[0013] According to a preferred embodiment, the height of the magnetizing block decreases in the direction away from the stationary contact.
[0014] According to a preferred embodiment, the permanent magnet and the magnetizing block are enclosed by an insulating shell, and the end of the insulating shell near the arc generation region has a tapered shape.
[0015] According to a preferred embodiment, the insulating housing has a first inclined wall and a second inclined wall defining a tapered shape, and the included angle between the two inclined walls is an acute angle.
[0016] According to a preferred embodiment, the insulating housing further comprises a first body wall and a second body wall extending from the first inclined wall and the second inclined wall respectively and parallel to each other, wherein the first inclined wall and the first body wall and the second inclined wall and the second body wall both form an obtuse angle.
[0017] The preferred embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings so that the features and advantages of the present disclosure can be readily understood. Attached Figure Description
[0018] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings of the embodiments of this disclosure will be briefly described below. The drawings are merely illustrative of some embodiments of this disclosure and are not intended to limit all embodiments of this disclosure to them.
[0019] Figure 1A A partial view of a switching device according to a preferred embodiment of the present disclosure is shown, wherein the stationary contact and the moving contact are in an engaged state;
[0020] Figure 1B A partial view of a switching device according to a preferred embodiment of the present disclosure is shown, wherein the stationary contact and the moving contact are in an open state;
[0021] Figure 2The structure and arrangement of the arc-starting structure, permanent magnet, and magnetizing block according to a preferred embodiment of the present disclosure are shown;
[0022] Figure 3 A partial view of a switching device according to a preferred embodiment of the present disclosure is shown, with particular emphasis on the arrangement of the arc-inducing structure, the permanent magnet, and the magnetizing block;
[0023] Figure 4 Shown from another perspective Figure 3 A partial view of the switching device;
[0024] Figure 5 Shown from another perspective Figure 3 A partial view of the switching device;
[0025] Figure 6A and 6B This diagram illustrates the magnetic field lines generated by a permanent magnet and the forces acting on an electric arc.
[0026] Figures 7A-7D Various exemplary embodiments of the permanent magnet and the magnetizing block are shown;
[0027] Figure 8 A schematic diagram of the insulating housing of the permanent magnet and the magnetizing block is shown.
[0028] List of reference numerals
[0029] 10 stationary contacts
[0030] 20 Moving contacts
[0031] 11 Arc-starting structure
[0032] 111 First Arc Segment
[0033] 112 Second arc segment
[0034] 113 Arc Foot
[0035] 30 permanent magnet
[0036] 40 magnetizing blocks
[0037] 50 Insulating Housing
[0038] 51 First inclined wall
[0039] 52 Second inclined wall
[0040] 53 First body wall
[0041] 54 Second body wall Detailed Implementation
[0042] To make the objectives, technical solutions, and advantages of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. The same reference numerals in the drawings represent the same components. It should be noted that the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.
[0043] Compared to the embodiments shown in the accompanying drawings, feasible embodiments within the scope of this disclosure may have fewer components, other components not shown in the drawings, different components, components arranged differently, or components with different connections, etc. Furthermore, two or more components in the drawings may be implemented in a single component, or a single component shown in the drawings may be implemented as multiple separate components.
[0044] Unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning understood by one of ordinary skill in the art to which this disclosure pertains. The terms “first,” “second,” and similar terms used in this patent application specification and claims do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, “an” or “a” and similar terms do not necessarily indicate a quantity limitation. Terms such as “comprising” or “including” mean that the element or object preceding the word encompasses the element or object listed following the word and its equivalents, without excluding other elements or objects. Terms such as “connected” or “linked” are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as “upper,” “lower,” “left,” and “right” are used only to indicate relative positional relationships, which may change accordingly when the absolute position of the described object changes.
[0045] This disclosure relates to switching devices with arc-extinguishing capabilities, and in particular to the arrangement of arc-extinguishing structures in the switching devices. The switching devices include, but are not limited to, circuit breakers.
[0046] The switching device includes a stationary contact 10 as a core component and a moving contact 20 that cooperates with the stationary contact 10. The stationary and moving contacts work together to control the on / off state of the circuit. When on / off occurs, the stationary contact 10 remains stationary, while the moving contact 20 moves relative to the stationary contact 10. For example, the moving contact 20 can rotate about its own axis of rotation to engage or disengage from the stationary contact 10, thereby connecting or disconnecting the circuit. Figure 1A The stationary contact 10 and the moving contact 20 of the switching device are in the engaged state. Figure 1BIn a switching device, the stationary contact 10 and the moving contact 20 are in an open state. During the separation of the moving contact 20 from the stationary contact 10, an electric arc is easily generated between them. In this paper, the area near the moving and stationary contacts where an electric arc is formed is referred to as the arc generation region. The generation of an electric arc can damage the contacts and other components of the switching device.
[0047] To extinguish the electric arc, the switching device also includes an arc-extinguishing chamber. The arc-extinguishing chamber is not shown in the accompanying drawings, but it is understood that it is located downstream of the arc-generating region. Figure 1A , 1B , Figure 3 , Figure 4 In terms of orientation, the arc-extinguishing chamber is located approximately below the permanent magnet 30 and the magnetizing block 40. The electric arc can enter the arc-extinguishing chamber through its front end. The arc-extinguishing chamber can stretch the arc length, thus extinguishing it.
[0048] In typical breaking unit designs, the contact opening speed is set to a relatively fast value. This is to quickly lengthen the arc and rapidly increase the arc voltage within a short time, while also allowing the arc to enter the arc-extinguishing chamber as quickly as possible, reducing contact erosion. However, in some applications, a slow contact opening speed leads to more severe arcing problems, resulting in secondary and repeated breakdowns. For example, when a low-speed contact system is used in DC applications, after the first arc is extinguished, the power supply voltage remains, the opening distance is still small, and the dielectric strength in the arc-extinguishing chamber decreases after arc extinguishing, leading to secondary and repeated breakdowns. Secondary and repeated breakdowns significantly worsen the dielectric strength in the arc-extinguishing chamber and drastically prolong the total arcing time. The arc-extinguishing scheme disclosed in this paper, through the design of a static contact arc-initiating structure 11, a permanent magnet 30, and a magnetizing block 40, can achieve rapid magnetic blow-out arc extinguishing, avoiding secondary and repeated breakdowns caused by excessively slow contact speeds. It has a good arc-extinguishing effect and is particularly suitable for low-speed contact systems.
[0049] Figures 2-5 Partial views of the switching device according to a preferred embodiment of the present disclosure are shown from different perspectives and in different formats, particularly the arrangement of the arc-initiating structure 11, the permanent magnet 30, and the magnetizing block 40.
[0050] For clarity, see reference. Figure 2 and Figure 4 The coordinate system described in this disclosure is as follows. Here, the x-direction corresponds to the length direction of the switching device, the y-direction corresponds to the height direction of the switching device, and the z-direction corresponds to the thickness direction of the switching device. It is understood that in actual use of the switching device, the horizontally shown x-direction is not necessarily parallel to the ground.
[0051] This disclosure primarily enhances the arc initiation and extinguishing effects through an arc-initiating structure 11 on the stationary contact, a specially arranged permanent magnet 30, and a magnetizing block 40. Generally, the arc-initiating structure 11 on the stationary contact guides the arc root, allowing it to move away from the stationary contact along the structure 11. This reduces the temperature in the contact area of the stationary contact, facilitating arc extinguishing and preventing secondary breakdown. The permanent magnet 30 and the magnetizing block 40 exert a force on the arc through magnetic field lines, causing the arc to move towards the arc-extinguishing chamber, further enhancing the arc initiation and extinguishing effects.
[0052] A preferred embodiment of the arc-starting structure 11 can be found in [reference needed]. Figures 2-4 The arc-initiating structure 11 first includes two arc-initiating feet 113 located on both sides of the stationary contact of the stationary contact 10. The two arc-initiating feet 113 guide the arc away from the stationary contact of the stationary contact 10 and extend towards the arc-extinguishing chamber. The presence of the two arc-initiating feet 113 facilitates guiding the arc root towards the arc-extinguishing chamber.
[0053] Two arc-initiating feet 113 are spaced apart in the z-direction. Each arc-initiating foot 113 is a rod-shaped or strip-shaped structure of a certain length, extending a certain distance in the y-direction to guide the arc to a farther position in that direction. The length of the arc-initiating foot 113 provides more movement space for the arc root of the stationary contact, keeping it away from the area where the moving and stationary contacts are prone to secondary breakdown, thereby reducing the temperature in that area and reducing the possibility of secondary breakdown.
[0054] Preferably, as shown in the figure, the arc-initiating structure 11 further includes a first arc-initiating segment 111 and a second arc-initiating segment 112. The first arc-initiating segment 111 is arranged generally in the y-direction and extends toward the arc-extinguishing chamber. The second arc-initiating segment 112 extends from the first arc-initiating segment 111 and is arranged generally in the x-direction, extending away from the permanent magnet 30 and the magnetizing block 40. The first arc-initiating segment 111 and the second arc-initiating segment 112 may have an angle of approximately 90°. The two arc-initiating feet 113 extend from the second arc-initiating segment 112. The two arc-initiating feet 113 may also have an angle of approximately 90° with the second arc-initiating segment 112.
[0055] In an alternative embodiment, a separate arc-inducing segment may also be provided, which extends obliquely, i.e., simultaneously extending in a direction away from the permanent magnet 30 and the magnetizing block 40 and in a direction towards the arc-extinguishing chamber.
[0056] Preferably, the arc-initiating structure 11 is integral with the stationary contact. For example, the arc-initiating structure 11 and the stationary contact can be integrally manufactured from a conductor material.
[0057] For a preferred arrangement of the permanent magnet 30 and the magnetizing block 40, please refer to [reference needed]. Figures 2-4 ,and Figures 7A to 7DSeveral exemplary structures of the permanent magnet 30 and the magnetizing block 40 are shown. In the y-direction, the permanent magnet 30 and the magnetizing block 40 are located between the arc-generating region at the stationary contact and the moving contact and the arc-extinguishing chamber. The permanent magnet 30 and the magnetizing block 40 are connected to each other, and the permanent magnet 30 and the magnetizing block 40 are arranged such that the magnetizing block 40 is closer to the arc-generating region than the permanent magnet 30. The N pole and S pole of the permanent magnet 30 are arranged along the direction from the arc-generating region toward the arc-extinguishing chamber, i.e., along the y-direction, and the N pole and S pole can be interchanged.
[0058] Figure 6A and 6B The diagram illustrates the magnetic field lines generated by the permanent magnet 30 and the forces acting on the electric arc. The magnetizing block 40 can be made of a soft magnetic material with high magnetic permeability. Due to the presence of the magnetizing block 40, the magnetic field lines generated by the permanent magnet 30 can be further guided upwards in the y-direction, expanding the range of the magnetic field lines. Moreover, due to the presence of the magnetizing block 40 in contact with the permanent magnet 30, two parts of the magnetic field lines are formed based on magnetic leakage. In the diagram, A represents the magnetic field lines that do not pass through the magnetizing block 40, and B represents the magnetic field lines guided by the magnetizing block 40, including both cases where the entire length of the magnetizing block is passed and cases where only a portion of the length of the magnetizing block is passed. Furthermore, the diagram uses several discrete dots to represent the trajectory of the electric arc, with the topmost dot representing the initial position of the arc. Due to... Figure 6A and 6B The directions of the current in the electric arcs are different, therefore the trajectories of the arcs are different.
[0059] This arrangement utilizes the unique magnetic field lines formed by magnetic leakage to guide the electric arc: in the initial stage of arc generation, the arc is primarily driven by the force of magnetic field line B, moving along the arc-starting foot 113 towards the arc-extinguishing chamber. As the arc moves a certain distance towards the arc-extinguishing chamber, it continues to move under the force of magnetic field line A. (See also...) Figure 6A and 6B Each dot indicates the force acting on the electric arc. It can be seen that the arc is subjected to a downward force until it reaches the centerline of the permanent magnet. In other words, the guiding effect of the permanent magnet and the magnetizing block on the arc continues until the arc reaches the centerline of the permanent magnet.
[0060] It is evident that the arrangement scheme disclosed herein cleverly transforms the magnetic leakage phenomenon, which is usually considered a disadvantage, into an advantage, effectively guiding the electric arc through a special magnetic field line layout.
[0061] To better guide the electric arc, such as Figures 3-4As shown, preferably, the permanent magnet 30 and the magnetizing block 40 are located on one side of the two arc-starting feet 113, specifically on the right side of the two arc-starting feet 113, as illustrated. Furthermore, the upper edge of the magnetizing block 40 is higher than the height of the ends of the arc-starting feet 113. This arrangement allows for effective utilization of the magnetic field above and to the left of the permanent magnet 30 and the magnetizing block 40.
[0062] Preferably, the height of the magnetizing block 40 decreases in the direction away from the stationary contact 10. This saves material without reducing the magnetic guiding force and allows space for the movement of the moving contact 20.
[0063] Preferably, the stacking direction and height direction of the permanent magnet 30 and the magnetizing block 40 are parallel to the extension direction of the two arc-starting feet 113. Specifically, the stacking direction and height direction of the permanent magnet 30 and the magnetizing block 40, as well as the extension direction of the two arc-starting feet 113, are approximately along the y-direction, i.e., from the arc-generating region towards the location of the arc-extinguishing chamber.
[0064] Preferably, both the permanent magnet 30 and the magnetizing block 40 are sheet-like structures, with a thickness significantly smaller than their dimensions in the other two directions. In the thickness directions of the permanent magnet 30 and the magnetizing block 40, such as... Figure 5 As shown, the permanent magnet 30 and the magnetizing block 40 are preferably located between the two arc-starting feet 113.
[0065] Figures 7A to 7D Several exemplary structures of the permanent magnet 30 and the magnetizing block 40 are shown. Figure 7A In the preferred embodiment shown, the permanent magnet 30 and the magnetizing block 40 have uniform thicknesses, and the thickness of the permanent magnet 30 is greater than the thickness of the magnetizing block 40. Figure 7B In the preferred embodiment shown, the permanent magnet 30 and the magnetizing block 40 have uniform thickness, and the thickness of the permanent magnet 30 is equal to the thickness of the magnetizing block 40. Figure 7C In the preferred embodiment shown, the thickness of the magnetizing block 40 decreases uniformly in the direction away from the permanent magnet 30. Figure 7C and 7D In the preferred embodiment shown, the thickness of the portion of the magnetizing block 40 near the permanent magnet 30 gradually decreases in the direction away from the permanent magnet 30, while the thickness of the portion away from the permanent magnet 30 remains constant. Figure 7C and 7D The 40 magnetic blocks in the middle are all of uniform thickness. These preferred designs can all utilize the principle of magnetic leakage to achieve good arc guidance. Meanwhile, Figures 7A to 7D Only a partial exemplary structure of the permanent magnet 30 and the magnetizing block 40 is shown; other structural forms are also conceivable.
[0066] According to a preferred embodiment of this disclosure, the permanent magnet 30 and the magnetizing block 40 are enclosed by an insulating shell 50. Figure 8 A schematic diagram of the plastic housing 50 of the permanent magnet 30 and the magnetizing block 40 is shown. The insulating housing 50 protects the permanent magnet 30 and the magnetizing block 40 from ablation and damage.
[0067] The high-speed airflow generated during the arc generation and guidance process can travel along the channel between the insulating housing 50 and the switching device housing. Under certain conditions, the airflow may form a shock wave. The end of the insulating housing 50 near the arc generation region preferably has a tapered shape, which reduces flow resistance and facilitates gas flow towards the arc-extinguishing chamber.
[0068] Preferably, the insulating shell 50 has a first inclined wall 51 and a second inclined wall 52 with a defined tapering shape, which can be connected by an arc. The included angle between the two inclined walls is an acute angle. More preferably, the included angle is in the range of 0° to 20°, for example, in the range of 3° to 15°, 5° to 12°, or 7° to 9°. This angle range ensures that the insulating shell 50 has good structural strength while also enabling good gas flow. When a strong compression wave is generated, the shock wave can be kept attached to the boundary layer of the shell surface, minimizing the impact of shock wave drag.
[0069] Preferably, the insulating housing 50 further has a first body wall 53 and a second body wall 54 extending parallel to each other from the first inclined wall 51 and the second inclined wall 52, respectively, wherein the first inclined wall 51 and the first body wall 53, and the second inclined wall 52 and the second body wall 54, all form obtuse angles. This design facilitates the formation of an expansion flow, accelerating the arc in the direction of travel.
[0070] The exemplary implementation of the solution proposed in this disclosure has been described in detail above with reference to preferred embodiments. However, those skilled in the art will understand that various modifications and alterations can be made to the above specific embodiments without departing from the spirit of this disclosure, and various combinations can be made to the various technical features and structures proposed in this disclosure without exceeding the protection scope of this disclosure, which is determined by the appended claims.
Claims
1. A switching device, characterized in that, include: A stationary contact (10) and a moving contact (20) that cooperates with the stationary contact (10); Arc-extinguishing chamber; An arc-inducing structure (11) is provided on the stationary contact (10). The arc-inducing structure (11) includes two arc-inducing feet (113) located on both sides of the stationary contact point of the stationary contact (10). The two arc-inducing feet (113) extend toward the arc-extinguishing chamber. A permanent magnet (30) and a magnetizing block (40) connected to the permanent magnet (30) are located between the arc-generating region at the stationary contact (10) and the moving contact (20) and the arc-extinguishing chamber, wherein the permanent magnet (30) and the magnetizing block (40) are arranged such that the magnetizing block (40) is closer to the arc-generating region than the permanent magnet (30).
2. The switching device as described in claim 1, characterized in that, The permanent magnet (30) and the magnetizing block (40) are located on one side of the two arc-starting feet (113), and the height of the upper edge of the magnetizing block (40) is higher than the height of the end of the arc-starting foot (113).
3. The switching device as described in claim 1, characterized in that, The stacking direction and height direction of the permanent magnet (30) and the magnetizing block (40) are parallel to the extension direction of the two arc-leading feet (113).
4. The switching device as described in claim 1, characterized in that, Both the permanent magnet (30) and the magnetizing block (40) are sheet-like structures. In the thickness direction of the permanent magnet (30) and the magnetizing block (40), the permanent magnet (30) and the magnetizing block (40) are located between the two arc-starting feet (113).
5. The switching device as described in claim 1, characterized in that, The arc-initiating structure (11) includes a first arc-initiating segment (111) extending toward the arc-extinguishing chamber and a second arc-initiating segment (112) extending from the first arc-initiating segment (111) toward the direction away from the permanent magnet (30) and the magnetizing block (40), and the two arc-initiating feet (113) extend from the second arc-initiating segment (112).
6. The switching device as claimed in claim 1, characterized in that, The arc-inducing structure (11) is integrally formed with the stationary contact (10).
7. The switching device as claimed in claim 1, characterized in that, The permanent magnet (30) and the magnetizing block (40) have uniform thickness, and the thickness of the permanent magnet (30) is greater than or equal to the thickness of the magnetizing block (40).
8. The switching device as claimed in claim 1, characterized in that, The thickness of the magnetizing block (40) decreases in the direction away from the permanent magnet (30).
9. The switching device as claimed in claim 1, characterized in that, The height of the magnetizing block (40) decreases in the direction away from the stationary contact (10).
10. The switching device as claimed in claim 1, characterized in that, The permanent magnet (30) and the magnetizing block (40) are enclosed by an insulating shell (50), the end of which near the arc generation region has a tapered shape.
11. The switching device as claimed in claim 10, characterized in that, The insulating housing (50) has a first inclined wall (51) and a second inclined wall (52) defining a tapered shape, the included angle between the two inclined walls being an acute angle.
12. The switching device as claimed in claim 11, characterized in that, The insulating housing (50) also has a first body wall (53) and a second body wall (54) extending from the first inclined wall (51) and the second inclined wall (52) and parallel to each other, wherein the first inclined wall (51) and the first body wall (53) and the second inclined wall (52) and the second body wall (54) form obtuse angles.