Patent Description:
The electrical performance index Icm/Icw of an automatic transfer switch (ATS) is an index that considers the ability of the product to withstand high currents in the circuit. At present, there are two main types of failures for this index: fusion welding and contact burnout.

The automatic transfer switch with a clamping contact system usually has excellent performance in short-term current withstand index because of an electric clamping force formed between clamping contacts. However, there is still room for further improvement in the short-term current withstand index of the clamping contact system.

There are also some automatic transfer switches may fail in the short-term current withstand test and thus results in a greatly reduced short-term current withstand index of the automatic transfer switches due to the form of its contact structure.

Therefore, there is a need for a contact system for automatic transfer switch, such as a clamping contact system, which has improved short-term current withstand index, can reduce the failure under short-term current withstand working condition, and improve the stability and reliability of the contact system.

The present disclosure aims to overcome at least some of the abovementioned problems in the prior art.

According to one or more embodiments of the present disclosure, a dimension of the chamfered corner in the horizontal direction is <NUM>%-<NUM>% of a dimension of the first part in the horizontal direction.

According to one or more embodiments of the present disclosure, a dimension of the chamfered corner in the vertical direction is <NUM>%-<NUM>% of a dimension of the second part in the vertical direction.

According to the invention, the at least one stationary contact further includes a magnetically conductive block connected to the chamfered corner, and the magnetically conductive block is formed of a magnetically conductive material.

According to one or more embodiments of the present disclosure, a thickness of the magnetically conductive block is greater than a thickness of the at least one stationary contact.

According to one or more embodiments of the present disclosure, the at least one stationary contact further includes an arc striking corner extending in the horizontal direction from the second vertical end of the first part, and an extending direction of the arc striking corner is the same as an extending direction of the second part.

According to one or more embodiments of the present disclosure, the movable contact includes a pair of movable contact pieces which are parallel to each other and spaced apart from each other, in the first contact position of the movable contact, the movable contact pieces clamp the stationary contact engagement part of the first stationary contact therebetween, and, in the second contact position of the movable contact, the movable contact pieces clamp the stationary contact engagement part of the second stationary contact therebetween.

According to one or more embodiments of the present disclosure, each of the pair of movable contact pieces includes a front surface facing the other one of the movable contact pieces and a back surface opposite to the front surface, and at least one of the movable contact pieces includes a magnet enhancement piece, and the magnet enhancement piece is formed of a magnetically conductive material.

According to one or more embodiments of the present disclosure, the magnet enhancement piece is a flat plate structure and is arranged on the back surface of at least one of the movable contact pieces.

According to one or more embodiments of the present disclosure, the magnet enhancement piece includes a U-shaped structure, a bottom of the U-shaped structure of the magnet enhancement piece is arranged on the back surface of at least one of the movable contact pieces, and two arms of the U-shaped structure of the magnet enhancement piece are arranged on respective lateral surface of the at least one of the movable contact pieces.

According to one or more embodiments of the present disclosure, the at least one stationary contact includes the first stationary contact and the second stationary contact.

According to an aspect of the present disclosure, an automatic transfer switch is provided. The automatic transfer switch includes one or more contact systems for the automatic transfer switch as claimed.

Embodiments of the present disclosure are described in detail below, examples of which are shown in the accompanying drawings, wherein same or similar reference numerals indicate same or similar elements or elements with the same or similar functions. The embodiments described below by reference to the accompanying drawings are exemplary and are intended only to explain the present disclosure, and cannot be understood as limitations of the present disclosure.

Unless otherwise defined, technical terms or scientific terms used here shall have their ordinary meanings as understood by skilled person in the field to which the present disclosure belongs. In the description of the present disclosure, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" is based on the orientation or positional relationship shown in the accompanying drawings, which is only for the convenience of describing the present disclosure and simplifying the description, and does not indicate or imply that the referred device or element must have the specific orientation, and be constructed and operated in the specific orientation, so it cannot be understood as a limitation to the present disclosure. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

The present disclosure provides a contact system for automatic transfer switch, which includes a first stationary contact, a second stationary contact and a movable contact. The first stationary contact and/or the second stationary contact includes a first part extending in a vertical direction and a second part extending in a horizontal direction, and the first part and the second part meet each other end to end. A chamfered corner is formed at a joint position of the first part and the second part. The inventor(s) of the present disclosure found that the current in the first part of the stationary contact extending in the vertical direction generates an electromagnetic field, which applies an electromagnetic force (Lorentz force) on the current in the movable contact assembly. This electromagnetic force tends to separate the movable contact assembly from the stationary contact. In the present disclosure, by forming the chamfered corner at the joint position of the first part and the second part, the length of the current section in the first part of the stationary contact is significantly reduced, thereby significantly reducing the electromagnetic force (Lorentz force) that tends to separate the movable contact assembly from the stationary contact. Therefore, the short-term current withstand index of the contact system is improved.

Furthermore, the stationary contact assembly includes a magnetically conductive block connected to the chamfered corner of the stationary contact. The magnetically conductive block can guide the electromagnetic field or magnetic flux, so that the magnetic flux is better concentrated in the magnetically conductive block, thereby reducing the magnetic flux in the movable contact assembly, thus reducing the electromagnetic force (Lorentz force) that tends to separate the movable contact assembly from the stationary contact. Therefore, the magnetically conductive block can further improve the short-term current withstand index of the contact system.

In addition, in some embodiments, a magnet enhancement piece formed of a magnetically conductive material is provided on the movable contact. Due to the presence of the magnet enhancement piece, the electromagnetic field generated by the movable contact pieces is guided to be better concentrated, so that a pair of movable contact pieces of the clamping contact system form a greater clamping force on the stationary contact assembly between the pair of movable contact pieces when there is current on the clamping contact system. Therefore, the magnet enhancement piece can further improve the short-term current withstand index of the contact system.

<FIG> shows a perspective view of an automatic transfer switch <NUM> according to one or more embodiments of the present disclosure. The automatic transfer switch <NUM> includes a plurality of first power input terminals 12a, a plurality of second power input terminals 12b and a plurality of output terminals <NUM>. The automatic transfer switch <NUM> also includes a plurality of contact systems <NUM> (only one contact system is shown in the figure). The contact system <NUM> includes a movable contact assembly <NUM>, a first stationary contact assembly <NUM> and a second stationary contact assembly <NUM>. The first stationary contact assembly <NUM> is electrically connected to a corresponding one of the first power input terminals 12a, the second stationary contact assembly <NUM> is electrically connected to a corresponding one of the second power input terminals 12b, and the movable contact assembly <NUM> is electrically connected to a corresponding one of the output terminals <NUM>. The movable contact assembly <NUM> is movable between a first contact position in contact with the first stationary contact assembly <NUM> and a second contact position in contact with the second stationary contact assembly <NUM>, so that the automatic transfer switch <NUM> switches between a first power supply (not shown) electrically connected to the first power input terminal 12a and a second power supply (not shown) electrically connected to the second power input terminal 12b. In the embodiment shown in <FIG>, the automatic transfer switch <NUM> has four first power input terminals, four second power input terminals and four output terminals, and four contact systems (only one contact system is shown in the figure). In other embodiments according to the present disclosure, the automatic transfer switch can have any suitable numbers of first power input terminals, second power input terminals, output terminals and contact systems. In still other embodiments according to the present disclosure, the automatic transfer switch can have any suitable form and number of terminals, and is not limited to the form and number of terminals shown in <FIG> (the first power input terminals, the second power input terminal and the output terminal), as long as these terminals of the automatic transfer switch can be properly connected to the stationary contacts and the movable contact of the contact system.

<FIG> shows a perspective view of the contact system <NUM>. The movable contact assembly <NUM> of the contact system <NUM> includes a pair of movable contact pieces <NUM>, a movable contact actuating device <NUM> and a movable contact conductive member <NUM>. The movable contact actuating device <NUM> drives the pair of movable contact pieces <NUM> to move. The movable contact conductive member <NUM> is electrically connected to the pair of movable contact pieces <NUM> of the movable contact assembly <NUM>, for electrically connecting the pair of movable contact pieces <NUM> to the output terminals of the automatic transfer switch <NUM>. The pair of movable contact pieces <NUM> are parallel to each other and spaced apart from each other, and define a receiving space therebetween. Upon the movable contact assembly being in contact with the first stationary contact assembly or the second stationary contact assembly, the pair of movable contact pieces <NUM> of the movable contact assembly clamp the corresponding stationary contact therebetween. The first stationary contact assembly <NUM> includes a first stationary contact <NUM> and a first stationary contact conductive member <NUM>. The first stationary contact conductive member <NUM> is electrically connected to the first stationary contact <NUM>, for electrically connecting the first stationary contact <NUM> to the corresponding power input terminal. The second stationary contact assembly <NUM> includes a second stationary contact <NUM> and a second stationary contact conductive member <NUM>. The second stationary contact conductive member <NUM> is electrically connected with the second stationary contact <NUM>, for electrically connecting the second stationary contact <NUM> to the corresponding power input terminal.

<FIG> and <FIG> show front views of the contact system <NUM>, wherein <FIG> shows a double separation position where the movable contact assembly <NUM> is not in contact with both the first stationary contact assembly <NUM> and the second stationary contact assembly <NUM>, and <FIG> shows a first contact position where the movable contact assembly <NUM> is in contact with the first stationary contact assembly <NUM>. The contact assembly system <NUM> also includes a second contact position (not shown) where the movable contact assembly <NUM> is in contact with the second stationary contact assembly <NUM>.

<FIG> show front views of the first stationary contact assembly <NUM> according to one or more embodiments of the present disclosure. As shown in the figures, the first stationary contact <NUM> includes a first part (vertical extension part) <NUM> extending in a vertical direction and a second part (horizontal extension part) <NUM> extending in a horizontal direction. A lower end (a first vertical end) of the first part <NUM> meets a right end (a first horizontal end) of the second part <NUM> to form a generally L-shape. The second part <NUM> includes a conductive connection part <NUM> arranged at or close to a left end (a second horizontal end) of the second part <NUM>. The conductive connection part <NUM> is connected with the first stationary contact conductive member <NUM> for electrically connecting the first stationary contact <NUM> to the corresponding power input terminal of the automatic transfer switch <NUM>.

At the first contact position where the movable contact assembly <NUM> is in contact with the first stationary contact assembly <NUM>, a first stationary contact engagement part <NUM> of the first stationary contact <NUM> is in contact with and electrically connected with the pair of movable contact pieces <NUM> of the movable contact assembly <NUM>. The first stationary contact engagement part <NUM> is at or close to an upper end (a second vertical end) of the first part <NUM> of the first stationary contact <NUM>. At the first contact position, the current flows from the corresponding power input terminal of the automatic transfer switch <NUM> to the first stationary contact conductive member <NUM>, through the conductive connection part <NUM> of the first stationary contact <NUM> and the body of the first stationary contact <NUM> to the first stationary contact engagement part <NUM>, and then to the output terminal of the automatic transfer switch <NUM> through the movable contact assembly <NUM>.

As shown in the figure, a chamfered corner <NUM> is formed at a joint position of the first part <NUM> and the second part <NUM> of the first stationary contact <NUM>. The chamfered corner <NUM> has a horizontal dimension D1 and a vertical dimension D2. The first part <NUM> has a horizontal dimension D3 and the second part <NUM> has a vertical dimension D4. In the illustrated embodiment, D1>D3 and D2>D4. In some other embodiments according to the present disclosure, D1 is <NUM>%-<NUM>% of D3, and D2 is <NUM>%-<NUM>% of D4.

As shown, the first stationary contact <NUM> further includes an arc striking corner <NUM> extending in a substantially horizontal direction from the upper end (second vertical end) of the first part <NUM>. An extending direction of the arc striking corner <NUM> is the same as an extending direction of the second part <NUM>, so that the first part <NUM>, the second part <NUM> and the arc striking comer <NUM> of the first stationary contact <NUM> together form a substantially U-shape. The arc striking corner <NUM> has a generally conical shape, and the vertical dimension of the arc striking corner <NUM> gradually decreases with the distance from the first part <NUM>.

<FIG> shows a front view of the first stationary contact assembly <NUM> of the automatic transfer switch according to a comparative embodiment, and <FIG> is a front view of the first stationary contact <NUM>, showing the current in the first stationary contact <NUM> when the movable contact assembly of the automatic transfer switch is in contact with the first stationary contact assembly <NUM>. As shown, the first stationary contact assembly <NUM> includes a first stationary contact <NUM> and a first stationary contact conductive member <NUM>. The first stationary contact <NUM> includes a first part <NUM> extending in the vertical direction and a second part <NUM> extending in the horizontal direction. The second part <NUM> has a conductive connection part <NUM> at or close to the left end of the second part <NUM>, and the conductive connection part <NUM> is connected with the first stationary contact conductive member <NUM>. The first stationary contact <NUM> also includes an arc striking corner <NUM>. The main difference between the first stationary contact assembly <NUM> and the first stationary contact assembly <NUM> is that the first stationary contact <NUM> does not include the chamfered corner. Other aspects of the first stationary contact assembly <NUM> are similar to those of the first stationary contact assembly <NUM>, and detailed description thereof is omitted herein.

As shown in <FIG>, the current in the first stationary contact <NUM> includes a current section p24 in the first part <NUM> and a current section p28 in the second part <NUM>. The inventor(s) of the present disclosure found that the electromagnetic field generated by the current section in the first part <NUM> of the first stationary contact <NUM> generates an electromagnetic force on the movable contact in contact with the first stationary contact <NUM>, which tend to make the movable contact to be separated from the first stationary contact <NUM>. when the current in the contact system is large, the movable contact may be separated from the first stationary contact <NUM>, which results in a reduced short-term current withstand index of the contact system.

<FIG> is a front view of a part of the contact system <NUM> according to the invention, showing the current in the contact system <NUM> at the first contact position of the movable contact assembly <NUM>. As shown in <FIG>, the current in the contact system <NUM> includes a current section p12 in the movable contact assembly <NUM>, a current section p14 in the first part <NUM> of the first stationary contact <NUM>, a current section p16 in a transition part between the first part <NUM> and the second part <NUM> of the first stationary contact <NUM>, and a current section p18 in the second part <NUM> of the first stationary contact <NUM>. Compared with the case shown in <FIG>, because the first stationary contact <NUM> includes the chamfered corner <NUM> at the joint position of the first part <NUM> and the second part <NUM>, the length of the current section p14 in the first part <NUM> of the first stationary contact <NUM> is shortened (compared with the current section p24 in <FIG>), and the current section p16 in the transition part is added between the current section p14 in the first part <NUM> and the current section p18 in the second part <NUM>, the current section p16 is inclined to the current section p14.

In <FIG>, black line segments p24, p28, p12, p14, p16 and p18 are used to represent the current passing through the first stationary contact <NUM> and the first stationary contact <NUM>. This representation is schematic, and the actual current is not limited to the position shown by the black line segments. For example, the current sections p14 and p16 in <FIG> roughly correspond to the currents in the regions indicated by dotted lines p14 and p16 in <FIG>, respectively.

<FIG> shows a schematic diagram of the electromagnetic force (Lorentz force) applied upon the current section p12 (movable contact assembly <NUM>) in <FIG>. As shown, the current section p14 in the first part <NUM> of the first stationary contact <NUM> generates an electromagnetic field M14, which generates a clockwise electromagnetic force (Lorentz force) F upon the current section p12 in the movable contact assembly <NUM>. This clockwise electromagnetic force F tends to separate the movable contact assembly <NUM> from the first stationary contact <NUM>. Because the first stationary contact <NUM> includes the chamfered corner <NUM>, the length of the current section p14 in the first part <NUM> of the first stationary contact <NUM> is significantly shortened compared with the current section p24 shown in <FIG>. Therefore, compared with the comparative embodiment of <FIG>, under the same current, the electromagnetic force of the current section p14 in the first part <NUM> of the first stationary contact <NUM> upon the movable contact assembly is significantly reduced. This improves the short-term current withstand index of the contact system <NUM>.

In addition, the current section p16 of the first stationary contact <NUM> also generates an electromagnetic field (not shown). The electromagnetic field generated by the current section p16 generates a counterclockwise electromagnetic force (Lorentz force, not shown) upon the current section p12 in the movable contact assembly <NUM>. Therefore, the current section p16 can partially counteract or cancel the clockwise electromagnetic force F generated by the current section p14. This further improves the short-term current withstand index of the contact system <NUM>. Those skilled in the art can understand that the electromagnetic force of p16 to the movable contact assembly <NUM> is much smaller than the electromagnetic force of p14 to the movable contact assembly <NUM> due to the relatively large distance between p16 and the movable contact assembly <NUM>.

The first stationary contact assembly <NUM> includes a magnetically conductive block <NUM> connected to the chamfered corner <NUM>. The magnetically conductive block <NUM> is made of a magnetically conductive material, which may be, for example, low carbon steel, silicon steel sheet, etc. Due to the existence of the magnetically conductive block <NUM>, the electromagnetic field or magnetic flux generated by the first stationary contact <NUM>, for example, the current section p14 therein, is guided, so as to be more intensively distributed in the magnetically conductive block <NUM>. Therefore, the electromagnetic field intensity of the electromagnetic field M14 generated by the current section p14 at the movable contact assembly <NUM> decreases, and the electromagnetic force F of the current section p14 to the movable contact assembly <NUM> decreases. Because the electromagnetic force F tends to separate the movable contact assembly <NUM> from the first stationary contact <NUM>, the contact system <NUM> can withstand greater current due to the reduction of the electromagnetic force F, which further improves the short-term current withstand index of the contact system <NUM>. As shown in the figure, the shape of the magnetically conductive block <NUM> basically corresponds to the shape of the chamfered corner <NUM>, so the magnetically conductive block <NUM> does not occupy extra space. In one or more embodiments according to the present disclosure, the magnetically conductive block <NUM> has an increased thickness, that is, the thickness of the magnetically conductive block <NUM> is greater than the thickness of the first stationary contact <NUM>, so that the electromagnetic field or magnetic flux generated by the current section p14 is more guided and concentrated in the magnetically conductive block <NUM>. This can further improve the short-term current withstand index of the contact system <NUM>. As used herein, the thickness direction of the magnetically conductive block and the stationary contact refers to the direction of into and out of the paper of <FIG>, <FIG> and <FIG>.

The above describes the contact system <NUM> of the present disclosure in connection to the first stationary contact assembly <NUM> and the movable contact assembly <NUM>. As shown, the second stationary contact assembly <NUM> has a structure and operation similar to that of the first stationary contact assembly <NUM>, and detailed description thereof is omitted herein.

In the embodiment shown, the first stationary contact <NUM> and the second stationary contact <NUM> have similar structures, that is, both the first stationary contact <NUM> and the second stationary contact <NUM> have chamfered corners and magnetically conductive blocks connected to the chamfered corners. In other embodiments according to the present disclosure, only one stationary contact of a pair of stationary contacts of the contact system may include a chamfered corner and a magnetically conductive block connected to the chamfered corner. In other embodiments according to the present disclosure, one or both of the pair of stationary contacts of the contact system may only include the chamfered corner and not include the magnetically conductive block connected to the chamfered corner.

In the illustrated embodiment, the first stationary contact <NUM> includes a recess 162a in the first part <NUM>. In other embodiments according to the present disclosure, the recess 162a of the first stationary contact <NUM> may be omitted, that is, the first stationary contact <NUM> may not include a recess 162a.

The contact system of the embodiment shown in the accompanying drawings is a clamping contact system, and its movable contact assembly includes a pair of movable contact pieces. The pair of movable contact pieces are parallel to each other and spaced apart from each other, and define a receiving space therebetween. When the movable contact assembly is in contact with the first stationary contact assembly or the second stationary contact assembly, the pair of movable contact pieces <NUM> of the movable contact assembly clamp the corresponding stationary contact therebetween. When there is current in the clamping contact system, the current flows in the same direction along the pair of movable contact pieces that are parallel to each other. The current on each movable contact piece in the pair of movable contact pieces generates an electromagnetic field, which acts upon the current of the other one of the movable contact pieces, and generates an electromagnetic force (Lorentz force) that pulls the movable contact pieces toward each other, so that the movable contact pieces form a greater clamping force on the stationary contact assembly therebetween. This improves the short-term current withstand index of the clamping contact system.

<FIG> show a movable contact piece <NUM> according to one or more embodiments of the present disclosure. The movable contact piece <NUM> includes a movable contact piece body <NUM> and a magnet enhancement piece <NUM> disposed on the movable contact piece body <NUM>. The magnet enhancement piece <NUM> is made of a magnetically conductive material, which may be, for example, low carbon steel, silicon steel sheet, etc. Due to the presence of the magnet enhancement piece <NUM>, when there is current in the clamping contact system, the electromagnetic field generated by the movable contact piece <NUM> is guided to be more concentrated. Therefore, the pair of movable contact pieces forms a greater clamping force on the stationary contact assembly between the pair of movable contact pieces. The clamping contact system with the magnet enhancement piece can increase the contact pressure or force at the moment of closing, avoiding contact bouncing and pulling arcs that may cause product fusion welding, and further improve the short-term current withstand index of the clamping contact system. As shown, the magnet enhancement piece <NUM> is a flat plate structure, which is arranged on the back surface of the movable contact piece body <NUM>, that is, the magnet enhancement piece <NUM> is on a surface of the movable contact piece <NUM> facing away from the other movable contact piece.

<FIG> show a movable contact piece <NUM>' according to another embodiment or embodiments of the present disclosure. The movable contact piece <NUM>' includes a movable contact piece body <NUM>' and a magnet enhancement piece <NUM>' arranged on the movable contact piece body <NUM>'. The difference between the movable contact piece <NUM>' and the movable contact piece <NUM> is that the magnet enhancement piece <NUM> has a flat structure, while the magnet enhancement piece <NUM>' has a U-shaped structure. The bottom of the U-shaped structure of the magnet enhancement piece <NUM>' is arranged on the back surface of the movable contact piece body <NUM>', and the two arms of the U-shaped structure of the magnet enhancement piece <NUM>' are arranged on the two lateral surfaces of the movable contact piece body <NUM>'. The U-shaped magnetized plate <NUM>' can better guide and concentrate the electromagnetic field, so the U-shaped magnetized plate <NUM>' can effectively improve the short-term current withstand index of the clamping contact system.

The inventor(s) of the present disclosure performed a short-term current withstand index experiment for the contact system of the Comparative embodiment and the contact system of the Experimental embodiment. The contact system of the Comparative embodiment in this experiment includes the stationary contact assembly as shown in <FIG>, while the contact system of the Experimental embodiment includes the stationary contact assembly as shown in <FIG>. The experimental results are provided as follows.

As seen from the above experimental results, the 20kA short-term current withstand experiment of the Comparative embodiment (the contact system with the stationary contact assembly shown in <FIG>) failed twice, so its short-term current withstand index was below 20kA, while the 30kA short-term current withstand experiment of the Experimental embodiment (the contact system with the stationary contact assembly shown in <FIG>) succeeded three times, so its short-term current withstand index was above <NUM> kA. Therefore, compared with the Comparative embodiment, the short-term current withstand index of the Experimental embodiment is improved by more than <NUM>%.

Claim 1:
A contact system (<NUM>) for automatic transfer switch, the contact system comprising a first stationary contact (<NUM>), a second stationary contact (<NUM>) and a movable contact (<NUM>), wherein
the first stationary contact and the second stationary contact each comprise a stationary contact engagement part (<NUM>) and a conductive connection part (<NUM>) suitable to be electrically connected to a wire connection terminal of the automatic transfer switch,
wherein the movable contact (<NUM>) is movable between a first contact position and a second contact position, the movable contact (<NUM>) being in contact with the stationary contact engagement part (<NUM>) of the first stationary contact (<NUM>) in the first contact position of the movable contact (<NUM>), and the movable contact being in contact with the stationary contact engagement part (<NUM>) of the second stationary contact (<NUM>) in the second contact position of the movable contact (<NUM>),
wherein at least one stationary contact of the first stationary contact (<NUM>) and the second stationary contact (<NUM>) comprises:
a first part (<NUM>) extending in a vertical direction and comprising a first vertical end and a second vertical end; and
a second part (<NUM>) extending in a horizontal direction and comprising a first horizontal end and a second horizontal end,
wherein the first vertical end of the first part (<NUM>) meets the first horizontal end of the second part (<NUM>), the stationary contact engagement part (<NUM>) of the at least one stationary contact is at or close to the second vertical end of the first part, the conductive connection part (<NUM>) of the at least one stationary contact is at or close to the second horizontal end of the second part (<NUM>), and a chamfered corner (<NUM>) is formed at a joint position of the first part (<NUM>) and the second part (<NUM>) of the at least one stationary contact (<NUM>),
characterized in that
the at least one stationary contact (<NUM>) further comprises a magnetically conductive block (<NUM>) connected to the chamfered corner (<NUM>), and the magnetically conductive block (<NUM>) is formed of a magnetically conductive material.