CN117936328A

CN117936328A - Miniature circuit breaker

Info

Publication number: CN117936328A
Application number: CN202211266655.4A
Authority: CN
Inventors: 周荣伟; 王晓
Original assignee: Delixi Electric Co Ltd
Current assignee: Delixi Electric Co Ltd
Priority date: 2022-10-17
Filing date: 2022-10-17
Publication date: 2024-04-26

Abstract

The invention discloses a miniature circuit breaker which comprises a movable contact, a fixed contact, a movable contact conducting rod and thermal bimetal, wherein the movable contact is arranged on the movable contact conducting rod, the miniature circuit breaker further comprises a coil excitation module, the coil excitation module comprises a coil, the coil is used for generating a driving magnetic field to elongate an electric arc generated between the movable contact and the fixed contact when current passes through, and the coil is arranged between the movable contact conducting rod and the thermal bimetal, and two ends of the coil are respectively and electrically connected with the movable contact conducting rod and the thermal bimetal. According to the invention, the coil excitation module is arranged between the movable contact conducting rod and the thermal bimetal, and when the miniature circuit breaker is opened, an arc generated between the movable contact and the fixed contact is prolonged by a driving magnetic field generated by a coil of the coil excitation module, so that arc extinction is realized by arc discharge of the driving magnetic field under the condition that the miniature circuit breaker is limited in size, and further smooth opening and closing of the miniature circuit breaker to critical small current are realized.

Description

Miniature circuit breaker

Technical Field

The invention relates to the technical field of electrical equipment, in particular to a miniature circuit breaker.

Background

The miniature circuit breaker, MCB (Micro Circuit Breaker/Miniature Circuit Breaker) is the most widely used terminal protection electrical appliance in the introduction of a building electrical terminal distribution device, and is commonly used for protecting single-phase and three-phase short circuits, overload, overvoltage and the like below 125A.

In the use process of the miniature circuit breaker, aiming at the small-current breaking process, because the current is smaller and the magnetic blowing force is smaller, an arc can be generated between a movable contact and a fixed contact in the miniature circuit breaker when the critical small current is broken, and because the driving force for the arc is smaller, the arc between the movable contact and the fixed contact is difficult to be driven to elongate, and then the arc between the movable contact and the fixed contact is difficult to extinguish, therefore, in the traditional miniature circuit breaker, the critical small-current breaking mainly depends on increasing the opening distance between the movable contact and the fixed contact to cut off, so that a larger opening distance is required to be designed between the movable contact and the fixed contact in product design, or the opening distance is increased in a multipole series connection mode to meet the cutting requirement of the current.

However, the miniature circuit breaker is difficult to design with larger opening distance due to smaller volume of the miniature circuit breaker, and meanwhile, the miniature circuit breaker cannot increase an arc-extinguishing magnetic field through a permanent magnet when being applied to alternating current and direct current nonpolar supply scenes, so that the cutting-off difficulty of critical small current is larger.

Therefore, how to realize smooth breaking of the miniature circuit breaker to the critical small current is a technical problem that needs to be solved by the person skilled in the art.

Disclosure of Invention

In view of the above, the present invention is directed to a miniature circuit breaker to realize smooth breaking of the miniature circuit breaker to a critical small current.

In order to achieve the above purpose, the present invention provides the following technical solutions:

The utility model provides a miniature circuit breaker, includes moving contact, stationary contact, moving contact conducting rod and hot bimetal, the moving contact set up in on the moving contact conducting rod, still include coil excitation module, coil excitation module includes the coil, the coil is used for producing driving magnetic field in order to lengthen when the electric current passes through the moving contact with the electric arc that produces between the stationary contact, the coil set up in between the moving contact conducting rod with the hot bimetal just the first end of coil with the moving contact conducting rod electricity is connected, the second end with the hot bimetal electricity is connected.

Preferably, in the miniature circuit breaker, the coil excitation module further comprises an iron core penetrating through the coil.

Preferably, in the miniature circuit breaker, the coil excitation module further includes a magnetic conductive plate, the magnetic conductive plate is fixedly connected to two sides of the axis of the iron core, and the magnetic conductive plate extends to two sides of the opening paths of the movable contact and the stationary contact.

Preferably, in the miniature circuit breaker, the miniature circuit breaker further comprises a magnetic increasing sheet surrounding the opening paths of the movable contact and the fixed contact, wherein the magnetic increasing sheet is used for enhancing the magnetic field intensity in the surrounding area.

Preferably, in the miniature circuit breaker, the miniature circuit breaker further comprises a magnetic increasing sheet surrounding the opening paths of the movable contact and the stationary contact, wherein the magnetic increasing sheet is used for enhancing the magnetic field intensity in the surrounding area, and the magnetic increasing sheet and the magnetic conduction plate are of an integrated structure.

Preferably, in the miniature circuit breaker, the magnetic conductive plates are arranged in parallel.

Preferably, in the miniature circuit breaker described above, the iron core is made of ferromagnetic material.

Preferably, in the miniature circuit breaker, the coil is wound from a hard copper wire or a soft copper wire, or

The coil is wound by a hard copper wire and a soft copper wire which are connected by welding.

Preferably, in the miniature circuit breaker, the miniature circuit breaker further comprises an arc extinguishing chamber, a fixed contact arc striking plate and a moving contact arc striking plate, wherein when the moving contact is disconnected with the fixed contact, the driving magnetic field drives two ends of an arc generated between the moving contact and the fixed contact to respectively jump to the moving contact arc striking plate and the fixed contact arc striking plate, and an arc path between the moving contact arc striking plate and the fixed contact arc striking plate passes through the arc extinguishing chamber.

Preferably, in the miniature circuit breaker, an arc extinguishing gate is arranged in the arc extinguishing chamber.

From the above technical solution, it can be seen that the miniature circuit breaker provided by the invention comprises a moving contact, a fixed contact, a moving contact conducting rod and a thermal bimetal, wherein the moving contact and the fixed contact are used for controlling the closing and opening of the miniature circuit breaker through contact and separation, the moving contact is arranged on the moving contact conducting rod so as to realize the contact and separation action with the fixed contact through the movement of the moving contact conducting rod, the moving contact conducting rod is a component for an operator to operate to switch on and switch off the miniature circuit breaker, in particular, the miniature circuit breaker provided by the invention further comprises a coil excitation module, the coil excitation module comprises a coil, and the coil is arranged between the moving contact conducting rod and the thermal bimetal in consideration of the space condition in the miniature circuit breaker, meanwhile, the first end of the coil is electrically connected with the moving contact conducting rod, the second end of the coil is electrically connected with the thermal bimetal, when the circuit in the miniature circuit breaker is switched on, the wire path comprises a fixed contact, a movable contact conducting rod, a coil exciting module and hot bimetal, current can pass through the coil of the coil exciting module and generate a driving magnetic field, the coil is arranged in a form that the magnetic induction wire of the driving magnetic field passes through the opening path of the movable contact and the fixed contact and can generate driving force for driving the electric arc between the movable contact and the fixed contact, so that when the miniature circuit breaker is switched on and off with small current, the electric arc is generated between the movable contact and the fixed contact, and when the opening distance between the movable contact and the fixed contact can not meet the arc extinguishing distance of the electric arc, the electric arc between the movable contact and the fixed contact is driven to move away from the opening position of the movable contact and the fixed contact, namely the driving magnetic field stretches the electric arc between the movable contact and the fixed contact, so that the voltage required by maintaining the electric arc at two ends of the electric arc is increased, the arc current is reduced, thereby achieving arc extinction.

The miniature circuit breaker is provided with the coil excitation module, the coil of the coil excitation module is arranged between the movable contact conducting rod and the thermal bimetal, two ends of the coil are respectively electrically connected with the movable contact conducting rod and the thermal bimetal, so that when the miniature circuit breaker is switched on, a current path passes through the coil of the coil excitation module, the coil can generate a driving magnetic field, the coil is arranged to enable a magnetic induction wire of the driving magnetic field to pass through an opening path of the movable contact and the stationary contact, when the miniature circuit breaker is used for cutting off critical small current, the driving magnetic field drives an arc between the movable contact and the stationary contact to move away from the opening positions of the movable contact and the stationary contact, namely, the arc between the movable contact and the stationary contact is elongated through the driving magnetic field generated by the coil passing through current, so that when the miniature circuit breaker is limited in size, the opening of the movable contact and the stationary contact cannot meet the current cutting-off requirement, the voltage at two ends of the arc is elongated through the driving magnetic field, the arc current is reduced, and the cut-off of the miniature circuit breaker is smoothly carried out.

Drawings

In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

Fig. 1 is a schematic structural diagram of a miniature circuit breaker according to an embodiment of the present invention;

fig. 2 is a schematic diagram of arc stress when the miniature circuit breaker provided in the embodiment of the invention is opened;

Fig. 3 is a schematic structural diagram of a miniature circuit breaker according to another embodiment of the present invention;

Wherein, 1 is a movable contact conducting rod, 2 is a thermal bimetal, 10 is a movable contact, 20 is a static contact, 30 is a coil excitation module, 310 is a coil, 320 is an iron core, 330 is a magnetic conduction plate, 40 is a magnetic increasing plate, 50 is an arc extinguishing chamber, 60 is a movable contact arc striking plate, and 70 is a static contact arc striking plate.

Detailed Description

The core of the invention is to disclose a miniature circuit breaker so as to realize smooth breaking of the miniature circuit breaker on critical small current.

In order to better understand the solution of the present invention, the following description of the embodiments of the present invention refers to the accompanying drawings. Furthermore, the embodiments shown below do not limit the summary of the invention described in the claims. The whole contents of the constitution shown in the following examples are not limited to the solution of the invention described in the claims.

As shown in fig. 1-3, the miniature circuit breaker provided by the embodiment of the invention comprises a common moving contact 10, a fixed contact 20, a moving contact conducting rod 1, a thermal bimetal 2 and other components in the miniature circuit breaker, wherein the moving contact 10 and the fixed contact 20 are used for controlling the closing and opening of the miniature circuit breaker through contact and separation, the moving contact 10 is arranged on the moving contact conducting rod 1 so as to realize the contact and separation action with the fixed contact 20 through the movement of the moving contact conducting rod 1, the moving contact conducting rod 1 is a component for an operator to operate so as to conduct the micro circuit breaker to be connected and disconnected, in particular, the miniature circuit breaker provided by the invention further comprises a coil exciting module 30, the coil exciting module 30 comprises a coil 310, the coil 310 is used for generating a driving magnetic field when current passes through so as to lengthen the electric arc of a magnetic induction line coverage area of the driving magnetic field, the embodiment of the invention sets the coil 310 at a space position between the moving contact conducting rod 1 and the thermal bimetal 2 so as to set the coil 310 under the condition that the volume of the miniature circuit breaker is not increased, meanwhile, a first end of the coil 310 is connected with the moving contact conducting rod 1, and a second end of the moving contact conducting rod 1 is used for conducting the coil to be connected with the coil 2 through the thermal bimetal 2, and the coil exciting module 30 is connected with the coil exciting module 30, and the coil exciting module 30 is used for generating a magnetic field when the coil exciting module is connected with the coil 2 and the thermal bimetal 2 and the coil exciting module.

It should be noted that, the first end and the second end of the coil 310 are two ends extending from the wire wound around the coil 310, and the electrical connection refers to a conductive connection in the embodiment of the present invention, that is, when one of the two components is energized, the other component also passes a current.

It should be further noted that, the coil 310 is connected to a circuit to achieve the purpose of generating a driving magnetic field by the coil 310, and the two ends of the coil 310 are electrically connected to the moving contact conducting rod 1 and the thermal bimetal 2 respectively, so that the length of the wires extending from the two ends of the coil 310 can be reduced, thereby reducing the heat generation of the coil 310 and avoiding the excessive temperature rise of the coil 310.

The coil 310 is arranged in such a manner that a magnetic induction line of the driving magnetic field passes through an opening path of the movable contact 10 and the stationary contact 20 and can drive the arc to elongate after the movable contact 10 and the stationary contact 20 are opened, so that when the miniature circuit breaker is opened by small current, an arc is generated between the movable contact 10 and the stationary contact 20, and when the opening distance between the movable contact 10 and the stationary contact 20 cannot meet the arc extinguishing distance of the arc, the driving magnetic field drives two ends of the arc between the movable contact 10 and the stationary contact 20 to move away from the opening positions of the movable contact 10 and the stationary contact 20, namely, the driving magnetic field lengthens the arc between the movable contact 10 and the stationary contact 20, thereby increasing the required voltage for maintaining the existence of the arc at the two ends of the arc, and reducing the arc current, thereby realizing arc extinguishing.

When the miniature circuit breaker is turned on, the coil 310 generates a corresponding driving magnetic field due to an arc between the movable contact 10 and the stationary contact 20, and during the arc extinction between the movable contact 10 and the stationary contact 20, the driving magnetic field generated by the coil 310 is continuously present due to the continuous presence of the arc, and the movement of the arc is driven to be elongated, that is, the coil 310 continuously maintains the presence of the driving magnetic field by current during the arc presence, and at the same time, after the arc is elongated and extinguished, the driving magnetic field disappears, and the coil 310 completes the arc extinction and simultaneously avoids the generation of more heat.

According to the miniature circuit breaker provided by the invention, the coil excitation module 30 is arranged, the two ends of the coil 310 of the coil excitation module 30 are respectively and electrically connected with the movable contact conducting rod 1 and the thermal bimetal 2, so that when the miniature circuit breaker is switched on, a current path passes through the coil 310 of the coil excitation module 30, so that the coil 310 can generate a driving magnetic field, the magnetic induction wire of the driving magnetic field passes through the opening paths of the movable contact 10 and the fixed contact 20, when the miniature circuit breaker is used for cutting off a critical small current, the driving magnetic field drives an arc between the movable contact 10 and the fixed contact 20 to move away from the opening positions of the movable contact 10 and the fixed contact 20, namely the arc between the movable contact 10 and the fixed contact 20 is elongated through the driving magnetic field generated by the coil 310 passing through the current, when the opening of the miniature circuit breaker is limited in size, and when the opening of the movable contact 10 and the fixed contact 20 cannot meet the current cutting-off requirement, the voltage at the two ends rises, the current is reduced, and the arc between the movable contact 10 and the fixed contact 20 is cut off.

Further, as shown in fig. 2, in order to enhance the magnetic field strength of the driving magnetic field generated by the coil 310 when the current passes through to enhance the driving force of the driving magnetic field to the arc, in an embodiment of the present invention, the coil excitation module 30 further includes an iron core 320, and the iron core 320 is disposed through the coil 310 to concentrate the magnetic induction lines passing through the coil 310, thereby enhancing the magnetic induction strength to enhance the driving force of the magnetic field to the arc.

In order to further optimize the above technical solution, in another embodiment of the present invention, the coil excitation module 30 further includes a magnetic conductive plate 330, where the magnetic conductive plate 330 is made of a conductive material and is fixedly connected to two sides of the opening path of the iron core 320, the magnetic conductive plate 330 extends to two sides of the opening path of the moving contact 10 and the stationary contact 20, the magnetic conductive wire in the iron core 320 is transferred along the magnetic conductive plate 330, and when the magnetic conductive plate 330 extends to two sides of the opening path of the moving contact 10 and the stationary contact 20, the magnetic conductive wire of the driving magnetic field generated by the coil 310 can extend to two sides of the opening path of the moving contact 10 and the stationary contact 20, so that when the driving magnetic field starts to drive the arc, the magnetic conductive wires of the magnetic field generated by the coil 310 are distributed along the two sides of the iron core 320 until the space on the two sides of the opening path of the moving contact 10 and the stationary contact 20, so as to ensure that the driving force of the magnetic field is continuously received in the arc from the generation to the arc extinction process, thereby improving the arc extinction speed of the arc.

Specifically, as shown in fig. 2, in an embodiment of the present invention, the flowing direction of the current in the coil 310 is shown by an arrow, at this time, the driving magnetic field generated by the coil 310 is enhanced by the iron core 320, and is guided by the magnetic conductive plate 330 to two sides of the opening path of the moving contact 10 and the stationary contact 20, and is shown as a point a to a point B on two sides of the opening path of the moving contact 10 and the stationary contact 20, at this time, the arc area formed between the moving contact 10 and the stationary contact 20, i.e., the C area moves in a direction away from the moving contact conductive rod 1 under the action of the lorentz force of the magnetic field, i.e., the C area arc is elongated, so that the arc extinguishing effect is achieved by elongating the arc.

In a specific embodiment of the present invention, as shown in fig. 1, in order to enhance the magnetic field intensity around the opening paths of the movable contact 10 and the stationary contact 20, magnetic increasing sheets 40 are disposed around the opening paths of the movable contact 10 and the stationary contact 20, and the magnetic increasing sheets 40 are disposed around both sides of the opening paths, so as to gather the magnetic induction lines at the opening paths of the movable contact 10 and the stationary contact 20, and accelerate the elongation process of the electric arc between the movable contact 10 and the stationary contact 20.

In a preferred embodiment of the present invention, as shown in fig. 3, the miniature circuit breaker is provided with a magnetic increasing plate 330 in the coil excitation module 30 while surrounding the opening paths of the movable contact 10 and the stationary contact 20, and the magnetic conducting plate 330 and the magnetic increasing plate 40 are integrally constructed to simplify the installation structure inside the miniature circuit breaker and enhance the arc extinguishing effect.

Further, in an embodiment of the present invention, the magnetic induction plates 330 are arranged in parallel to ensure uniformity of magnetic induction intensity around the magnetic induction plates 330.

Further, the iron core 320 penetrating the coil 310 is made of ferromagnetic materials such as iron-chromium-cobalt, alnico, or neodymium-iron-boron.

In addition, the first end of the coil 310 is electrically connected to the moving contact conductive rod 1, and the second end of the coil 310 is electrically connected to the thermal bimetal 2, and the connection mode of the coil 310 may be a rigid connection or a flexible connection, so long as the requirement that a driving magnetic field can be generated to drive an arc generated between the moving contact 10 and the fixed contact 20 when a current flows through the coil 310 is met, and similarly, the electrical connection mode of the two ends of the coil 310 may be a rigid connection or a flexible connection, so in the miniature circuit breaker provided by the embodiment of the invention, the coil 310 in the coil excitation module 30 may be made of a hard copper wire, a soft copper wire or a hard copper wire and a soft copper wire which are connected by welding.

Further, as can be seen from the above embodiments, the miniature circuit breaker provided by the embodiment of the present invention can realize smooth opening when opening with critical small current, but the miniature circuit breaker still passes through large current when opening with short circuit or when current suddenly changes, and when large current is generated in the path of the miniature circuit breaker and the miniature circuit breaker is opened, arc between the movable contact 10 and the stationary contact 20 is difficult to realize arc extinction by elongation, and the jumps at two ends of the arc are difficult to control, so that a certain difficulty of opening is provided, and in order to enable the miniature circuit breaker provided by the embodiment of the present invention to meet smooth opening under corresponding working conditions, as shown in fig. 1 and 3, in a specific embodiment of the present invention, the miniature circuit breaker further comprises an arc extinguishing chamber 50, a stationary contact arc striking plate 70 and a movable contact arc striking plate 60, wherein, the arc extinguishing chamber 50 is used for extinguishing an arc entering the arc extinguishing chamber, the fixed contact arc striking plate 70 is electrically connected with the fixed contact 20, the moving contact arc striking plate 60 is electrically connected with the moving contact 10, so that when the miniature circuit breaker breaks a large current, the arc generated between the moving contact 10 and the fixed contact 20 can jump to the fixed contact arc striking plate 70 and the moving contact arc striking plate 60 due to the arc striking effect of the arc striking plate, and the process of jumping to the fixed contact arc striking plate 70 and the moving contact arc striking plate 60 at the two ends of the arc is smoother due to the arrangement of the coil exciting module 30, meanwhile, the fixed contact arc striking plate 70 and the moving contact arc striking plate 60 are arranged at two sides of the arc extinguishing chamber 50, so that the two ends of the arc pass through the arc extinguishing chamber 50 when jumping to the fixed contact arc striking plate 70 and the moving contact arc striking plate 60, and the miniature circuit breaker breaks a large current working condition.

It should be noted that, because the current is larger when the heavy current is turned on and off, the heating value of the moving contact is larger when the heavy current is turned on and off, the moving contact is easy to burn, and the coil excitation module 30 can drive the electric arc to quickly jump through the driving magnetic field, and the moving contact and the fixed contact are separated from each other, so that the burning loss of the electric arc to the moving contact is reduced.

It should be further noted that, when the miniature circuit breaker is turned on or off with a large current, the copper wire cross-sectional area of the coil 310 is significantly smaller than the cross-sectional areas of other components in the conducting circuit, so that the current flux is limited, and a certain current limiting effect can be achieved on the turning on or off of the large current, so that the arc extinguishing difficulty in the turning on or off process of the large current is reduced.

Further, in an embodiment of the present invention, an arc extinguishing gate is disposed in the arc extinguishing chamber 50, and the arc extinguishing gate is made by parallel fixing multiple layers of steel sheets, so that when the electric arc between the fixed contact arc striking plate 70 and the moving contact arc striking plate 60 enters the arc extinguishing chamber 50 under the driving force of the driving magnetic field of the coil 310, the electric arc is divided into multiple sections of short electric arcs and is extinguished.

The terms first, second, left and right in the description and the claims of the present invention and in the above-described drawings, etc. are used for distinguishing between different objects and not for describing a particular sequential order. Furthermore, the terms "comprise" and "have," as well as any variations thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to the listed steps or elements but may include steps or elements not expressly listed.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. The utility model provides a miniature circuit breaker, includes moving contact (10), stationary contact (20), moving contact conducting rod (1) and hot bimetal (2), moving contact (10) set up in on moving contact conducting rod (1), its characterized in that still includes coil excitation module (30), coil excitation module (30) include coil (310), coil (310) are used for producing the drive magnetic field in order to lengthen when the electric current passes through moving contact (10) with the electric arc that produces between stationary contact (20), coil (310) set up in between moving contact conducting rod (1) and hot bimetal (2) just the first end of coil (310) with moving contact conducting rod (1) electricity is connected, the second end with hot bimetal (2) electricity is connected.

2. The miniature circuit breaker of claim 1, wherein said coil excitation module (30) further comprises an iron core (320) disposed through said coil (310).

3. The miniature circuit breaker of claim 2, wherein said coil excitation module (30) further comprises a magnetically permeable plate (330), said magnetically permeable plate (330) being fixedly connected to both sides of said core (320) in an axial direction, said magnetically permeable plate (330) extending to both sides of an opening path of said movable contact (10) and said stationary contact (20).

4. The miniature circuit breaker of claim 1, further comprising a magnetic increasing sheet (40) for surrounding an opening path of said movable contact (10) and said stationary contact (20), said magnetic increasing sheet (40) for increasing a magnetic field strength in a surrounding area.

5. A miniature circuit breaker according to claim 3, further comprising a magnetic increasing sheet (40) surrounding the opening path of the movable contact (10) and the stationary contact (20), the magnetic increasing sheet (40) being for increasing the magnetic field strength in the surrounding area, the magnetic increasing sheet (40) being of integral construction with the magnetic conducting plate (330).

6. A miniature circuit breaker according to claim 3, characterized in that the magnetic plates (330) are arranged in parallel.

7. The miniature circuit breaker of claim 2, wherein said core (320) is made of ferromagnetic material.

8. The miniature circuit breaker of claim 1, characterized in that the coil (310) is made of hard or soft copper wire wound, or

The coil (310) is wound from welded hard and soft copper wires.

9. The miniature circuit breaker of claim 1, further comprising an arc extinguishing chamber (50), a stationary contact arc striking plate (70) and a moving contact arc striking plate (60), wherein when the moving contact (10) is disconnected from the stationary contact (20), the driving magnetic field drives both ends of an arc generated between the moving contact (10) and the stationary contact (20) to jump to the moving contact arc striking plate (60) and the stationary contact arc striking plate (70), respectively, and an arc path between the moving contact arc striking plate (60) and the stationary contact arc striking plate (70) passes through the arc extinguishing chamber (50).

10. Miniature circuit breaker according to claim 9, characterized in that the arc extinguishing chamber (50) is provided with arc extinguishing bars.