Patent Publication Number: US-7915985-B2

Title: Switching device for direct-current applications

Description:
CROSS REFERENCE TO PRIOR APPLICATIONS 
     Priority is claimed to German Patent Application No. 10 2007 054 958.1, filed Nov. 17, 2007, the entire disclosure of which is incorporated by reference herein. 
     FIELD 
     The present invention relates to a switching device for direct-current applications, which is built employing components of switching devices for alternating-current applications such as, for example, safety cutouts, circuit-breakers, load-break switches and residual-current protectors. 
     BACKGROUND 
     In order to switch off short-circuit currents in secondary distribution systems, for the most part switching devices are employed that have one or more current paths which, in turn, encompass stationary and movable switching contact elements. Here, the movable switching contact elements can be jointly moved between a closed position, in which the movable and stationary switching contact elements that are associated with each other make contact with each other, and an open position, in which an air break is formed between each of the movable and stationary switching contact elements that are associated with each other. As soon as the movable switching contact elements are moved under load—that is to say, are moved under a current flow—into the open position, (breaking) arcs are created along the air breaks. The duration of the arcs determines the switching time since the current flow between the switching contact elements is maintained. Moreover, the arcs release a large quantity of heat that leads to thermal destruction of the switching contact elements and thus to a shortening of the service life of the switching device. Consequently, there is a need to quench the arcs as quickly as possible, which can be done by arc-quenching devices such as, for example, arc splitters, arc-quenching plates or deion plates. These quenching devices split the arcs into individual partial arcs; the arcs are reliably quenched when the arc voltages are higher than the driving voltages. 
     For alternating-current applications, the quenching of the arcs is facilitated in that the current has a natural zero passage. When high (short-circuit) currents have to be switched off, however, an arc-back can occur after the zero passage; however, the arcs formed at high currents, in turn, create such a large self-magnetic field that they are automatically deflected towards the arc-quenching devices and are ultimately quenched. 
     When it comes to switching devices for direct-current applications, no automatic interruption of the arc occurs as is the case with the zero passage of alternating current. Consequently, for direct-current applications, so-called blow-out magnets are employed that generate a magnetic field whose strength and orientation exert a deflecting force (Lorentz force) on the arcs, thus deflecting the arcs towards the arc-quenching devices. The arcs are stretched, cooled and split into partial arcs in the arc-quenching devices, as a result of which they are quenched. 
     Switching devices of the above-mentioned type for alternating-current applications are described, for example, in DE 103 52 934 B4, DE 102 12 948 B4, DE 20 2005 007 878 U1, EP 1 594 148 A1, EP 0 980 085 B1 and EP 0 217 106 B1. 
     Typically, a distinction is made between alternating-current and direct-current switching devices. Whereas alternating-current switching devices of the one-pole or multi-pole type can be produced inexpensively in large quantities, direct-current switching devices in the form of one-pole or two-pole switching devices are manufactured in considerably smaller production runs. Consequently, direct-current switching devices, some with a prescribed direction of incoming supply, are special devices. The use of renewable sources of energy such as, for instance, solar energy, fuel cells, battery series and so forth calls for more switching devices that have a direct-current switching capability as well as an isolating function in the low and medium current ranges at voltages of up to about 1000 V. 
     SUMMARY 
     The present invention is directed to cost-effectively producing switching devices with a direct-current switching capability and a direct-current isolating function. 
     In an embodiment, the present invention provides a switching device for direct-current applications. The switching device includes a housing having a first wall and a second wall disposed opposite each other and a plurality of receiving areas for respective mutually substantially parallel current paths, the receiving areas being disposed next to each other in the housing between the first and second walls. Each of the current paths has a respective stationary switching contact element and a respective movable switching contact element, the movable switching element being actuatable into a closed position so that the movable switching element is in contact with the respective stationary switching contact, and into an open position so as to form a respective air break so that an arc extending along the air break is formable, the respective movable switching contact elements being actuatable simultaneously between the open position and the closed position. The switching device includes a plurality of arc-quenching devices associated with the current paths and disposed next to each other between the first and the second walls, and at least one magnet disposed on an outside of at least one of the first and second walls. The at least one magnet is configured to generate a magnetic field having magnetic field lines in a direction crosswise to the respective air breaks so as to generate a deflection force on the arcs so as to deflect the respective arcs toward at least one of the respective arc-quenching devices. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is described in greater depth below on the basis of several embodiments and making reference to the drawings. In the figures: 
         FIG. 1  shows a side view of a three-pole alternating-current switching device housing with movable switching contact elements in their closed position in accordance with an aspect of the present invention; 
         FIG. 2  shows a side view similar to that of  FIG. 1 , but with the movable switching contact elements in their open position in accordance with an aspect of the present invention; 
         FIG. 3  shows a top view of the switching device housing shown in  FIGS. 1 and 2 , whereby an additional element is arranged to the side of each of the two opposite side walls of the housing, each of these elements having two permanent magnets in accordance with an aspect of the present invention; 
         FIG. 4  a perspective view of one of the side elements shown in  FIG. 3  in accordance with an aspect of the present invention; 
         FIG. 5  a perspective view of an alternatively configured switching device for direct-current applications in which the external magnets are magnetically coupled via magnetic return elements in accordance with an aspect of the present invention; 
         FIG. 6  a perspective view of the magnet arrangement with magnetic return elements, as employed in the embodiment of the switching device housing shown in  FIG. 5  in accordance with an aspect of the present invention; 
         FIG. 7  a top view of another embodiment of an alternating-current switching device housing that has been modified for use as a direct-current switching device housing in accordance with an aspect of the present invention; and 
         FIG. 8  a top view similar to that of  FIG. 7 , whereby an alternatively configured alternating-current switching device housing is shown that has been modified for use as a direct-current switching device in accordance with an aspect of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     An embodiment of the present invention provides a switching device for direct-current applications that is provided with
         a housing having two side walls situated opposite from each other,   at least three receiving areas for current paths that are essentially parallel to each other and that have air breaks, whereby the receiving areas are arranged next to each other in the housing between its side walls, and at least two of the receiving areas are each provided with a current path, and each current path has at least one stationary switching contact element and one movable switching contact element that can be moved into a closed position in order to contact the stationary switching contact element and into an open position in order to form the air break, and in said open position, an arc extending along the air break can be formed, whereby all of the movable switching contact elements can be moved together out of their open position into their closed position and vice versa,   arc-quenching devices that are associated with the current paths and that are likewise arranged next to each other in the housing between its two side walls, and   at least one magnet, preferably a permanent magnet, arranged on the outside of at least one of the side walls, having a magnetic field with field lines that extend essentially crosswise to the air breaks and with an orientation for generating deflection forces that act upon the arcs and that drive them into the arc-quenching devices.       

     According to another embodiment of the present invention, a switching device for direct-current applications is put forward that is provided with
         a housing having two side walls situated opposite from each other,   at least three receiving areas for current paths that are essentially parallel to each other and that have air breaks, whereby the receiving areas are arranged next to each other in the housing between its side walls, and at least two of the receiving areas are each provided with a current path, and each current path has at least one stationary switching contact element and one movable switching contact element that can be moved into a closed position in order to contact the stationary switching contact element and into an open position in order to form the air break and, in said open position, an arc extending along the air break can be formed, whereby all of the movable switching contact elements can be moved together out of their open position into their closed position and vice versa,   whereby at least one of the receiving areas is free of a current path and free of at least the movable switching contact element,   arc-quenching devices that are associated with the current paths and that are likewise arranged next to each other in the housing between its two side walls,   at least one magnet, preferably a permanent magnet, arranged in the at least one free receiving space, having a magnetic field with field lines that extend essentially crosswise to the air breaks and with an orientation for generating deflection forces that act upon the arcs and that drive them into the arc-quenching chambers.       

     Yet another embodiment of the present invention provides a switching device for direct-current applications that is provided with
         a housing having two side walls situated opposite from each other,   at least three receiving areas for current paths that are essentially parallel to each other and that have air breaks, whereby the receiving areas are arranged next to each other in the housing between its side walls and at least two of the receiving areas are each provided with a current path, and each current path has at least one stationary switching contact element and one movable switching contact element that can be moved into a closed position in order to contact the stationary switching contact element and into an open position in order to form the air break and, in said open position, an arc extending along the air break can be formed, whereby all of the movable switching contact elements can be moved together out of their open position into their closed position and vice versa,   arc-quenching devices that are associated with the current paths and that are likewise arranged next to each other in the housing between its two side walls, and   in the housing, receiving spaces for magnetic-field amplifying elements—formed on both sides of the pairs having a movable and a stationary switching contact element—for amplifying the self-magnetic field of an arc formed along the air break,   whereby a magnet, preferably a permanent magnet, having a magnetic field with field lines that extend essentially crosswise to the air breaks and with an orientation for generating deflection forces that act upon the arcs and that drive them into the arc-quenching devices is arranged in at least one of the receiving spaces.       

     The above-mentioned embodiments of the switching device according to the present invention for direct-current applications share the notion of utilizing the housing of a switching device for alternating-current applications for the production of the switching device in order to adapt this housing to the direct-current application in a manner that is simple and involves little effort. This means that the housing of the switching device for alternating-current applications has to be augmented by a magnet, preferably a permanent magnet. This magnet can be arranged either on the outside of the housing or else integrated into one of the at least three receiving areas for the current paths, whereby then, the appertaining receiving area is free of the movable switching contact element, or else it is integrated into a special receiving space of the housing of the switching device for alternating-current applications, in which normally a magnetic-field amplifying element is accommodated in order to amplify the self-magnetic field of the arc. 
     A feature of the switching device according to the present invention for direct-current applications lies in the fact that the introduction of internal or external magnets, preferably permanent magnets, considerably increases the direct-current switching capability of conventional alternating-current switching devices. In this context, each air break and each arc-quenching device does not necessarily have to be associated with an individual magnet, as is the case with the prior-art direct-current switching devices. 
     In an embodiment of the switching device according to the present invention, there is at least one (external) magnet on the outside of at least one of the two side walls of the housing. It is advantageous if at least one external magnet is arranged on both side walls. The field lines of the external magnet(s) “penetrate” the side-by-side air breaks of the individual current paths inside the housing. The magnetic flux or the magnetic field that traverses the air breaks can be amplified by means of a magnetic return element to which the two magnets are coupled. All of these components (one or more external magnets as well as one or more magnetic return elements) can be arranged in a simple manner on the outside of the housing of the alternating-current switching device in order to improve its direct-current switching capability. Furthermore, when a housing of an alternating-current switching device is employed as the switching device for direct-current applications, it is possible to dispense with at least one of the current paths (and here especially at least one of the movable switching contact elements), as is necessary for the alternating-current application. The reason for this is that, whereas alternating-current switching devices are usually configured as three-pole or four-pole devices, at best two-pole versions are needed in the case of direct-current switching devices. Therefore, it is possible to dispense with the third or fourth current path for the construction of a direct-current switching device on the basis of a housing for an alternating-current switching device. This likewise reduces the production costs of the direct-current switching device. At the same time, however, it is also possible to retain the current paths of an alternating-current switching device housing and to connect at least two of the current paths in series for purposes of utilizing such a switching device possibly for purposes of a one-pole switch-off for direct-current applications employing several air breaks. 
     If at least one current path and especially at least one movable switching contact element is not present in the case of a three-pole or four-pole alternating-current switching device housing, then the corresponding receiving area of the switching device housing can be employed to accommodate the (blow-out) magnet or an additional (blow-out) magnet. 
     The switching devices according to the present invention can be configured as ON-OFF switching devices (so-called load interrupter switches) or else as safety cutouts or circuit-breakers which, going beyond a load interruptor switch, are provided with an additional functionality, namely, automatic detection and switch-off in the eventuality of a short-circuit current or the like. 
       FIGS. 1 to 4  show a first embodiment of a switching device  10  according to the present invention for direct-current applications that is constructed on the basis of a switching device for alternating-current applications. The switching device  10  has a switching device housing  12  in which three receiving areas  16 ,  18 ,  20  are arranged next to each other between two opposite (external) side walls  14 , whereby a current path  22  is situated in each receiving space. Here, each current path  22  includes a movable switching contact element  24  as well as two stationary switching contact elements  26 ,  28  situated opposite from each other, which are each provided with terminals  30 . The three movable switching contact elements  24  can be jointly moved between a closed position (see  FIG. 1 ) and an open position (see  FIG. 2 ), namely, by means of an actuator  32  configured in this embodiment as a knob switch  31  that interacts in a familiar manner with a breaker latching mechanism  34  for purposes of locking the movable switching contact elements  24  in their closed position and for jointly releasing the movable switching contact elements  24 . In a familiar manner, two arc-quenching devices  36 ,  38 —which are each configured in the form of individual quenching plates  40  arranged one above the other—are associated with the individual current paths  22 . Moreover, each current path  22  has two air breaks  42 ,  43  that, when the movable switching contact elements  24  are opened, are formed between their ends and the first and second stationary switching contact elements  26 ,  28  associated with these ends (see  FIG. 2 ). When the three-pole switching device  10  is opened under load, arcs are formed along these air breaks  42 ,  43 , and these arcs have to be quenched by means of the arc-quenching devices  36 ,  38 . Since, in the case of direct-current applications, the extinction of the arcs cannot be facilitated or achieved on the basis of the zero passage of the current, in order for the switching device  10  to be used for direct-current applications, first and second permanent magnets  44 ,  46  have to be provided which, in the embodiment shown in  FIGS. 1 to 4 , are arranged on the outside of the side walls  14  and held in place by disk-shaped holding elements  48 ,  50 . Here, the first magnets  44  have a magnetic field with field lines that are oriented crosswise to the air breaks  42 ,  43  and that generate a Lorentz force onto arcs formed along these air breaks  42 ,  43 , said force driving the arcs towards the first arc-quenching devices  36 . The second external magnets  46 , in turn, generate a magnetic field with field lines that are oriented crosswise to the second air breaks  43  and that generate a Lorentz force onto arcs formed along these air breaks  43 , said force deflecting the arcs towards the second arc-quenching devices  38 . In this context, the first magnets  44  are oriented towards the first air breaks  42 , while the second magnets  46  are arranged as an extension of the second air breaks  43  that lie side by side. In this manner, the three-pole switching device  10  that was originally conceived for alternating-current applications can also be employed for direct-current applications, whereby its direct-current switch-off capability is markedly improved in comparison to the direct-current switching capability of an alternating-current switching device, without a need for any major design changes. Rather, all that is necessary is to arrange the above-mentioned magnets  44 ,  46  on the outside of the opposite external sides  14  of the housing  12  of the switching device  10 , whereby it should be mentioned that, in each case, a single first or a second magnet is fundamentally needed for all of the first air breaks  42  and for all of the second air breaks  43 . By the same token, it should also be mentioned at this juncture that, in order to realize the present invention, it is not absolutely necessary to provide a switching device  10  that has two air breaks per current path. The adaptation of an alternating-current switching device that is to be used for direct-current applications is also possible with alternating-current switching device housings that have only one single air break per current path  22 , in other words, one movable switching contact element and one single stationary switching contact element per current path  22 , so that then just one single magnet is needed for all of the air breaks. 
       FIGS. 5 and 6  show a switching device  10 ′ that has been modified in comparison to the embodiment shown in  FIGS. 1 to 4 ; its housing  12  is constructed and configured as depicted in  FIGS. 1 to 3  and has alternatively configured external first and second magnets  44 ,  46 . To the extent that the individual components of the housing  12  shown in  FIGS. 5 and 6  are the same or have the same function as the individual components of the switching device  10  shown in  FIGS. 1 to 4 , they have been given in  FIGS. 5 and 6  the same reference numerals as in  FIGS. 1 to 4 . Thus,  FIGS. 5 and 6  show that the two first magnets  44  and the two second magnets  46  are magnetically coupled to each other via magnetic return elements  52 ,  54 , which translates into an amplification of the magnetic field between the first and second magnets  44 ,  46  that are opposite from each other. Therefore, this results in an amplified magnetic field that runs crosswise to the first or second air breaks  42 ,  43 , which accounts for an improved or enhanced arc-quenching function or which makes it possible to employ smaller magnets  44 ,  46  to achieve the same arc-quenching function as in the embodiment shown in  FIGS. 1 to 4 . 
       FIG. 7  shows a top view of the housing  12  of a modified switching device  10 ″, with the upper part removed and with a modification for direct-current applications. To the extent that the individual components of the housing  12  shown in  FIG. 7  are the same or have the same function as the individual components of the switching device  10  shown in  FIGS. 1 to 4 , they have been given in  FIG. 7  the same reference numerals as in  FIGS. 1 to 4 . 
     Fundamentally, the housing  12  shown in  FIG. 7  is structured in a similar way as depicted in  FIGS. 1 to 3 . In addition, the housing  12  as shown in  FIG. 7  has receiving spaces  56  that are associated with the air breaks  42 ,  43  and are arranged on both sides of these air breaks. In an alternating-current switching device, these receiving spaces  56  serve to receive self-magnetic field amplifying elements of the type needed for smaller short-circuit currents in alternating-current switching devices in order to deflect the arcs into the arc-quenching device, where the arc is then quenched. For purposes of using or adapting the alternating-current device housing  12  for direct-current applications, the magnetic-field amplifying elements are removed so that the receiving spaces  56  are then free to receive the magnets  44 ,  46 . In this context, diverging from what is shown in  FIG. 7 , it is possible that, for instance, the center current path  22  is removed, so that the switching device  10 ″ can be employed as a two-pole direct-current switching device. 
     At this juncture, it should be pointed out that the three current paths of the switching devices  10 ,  10 ′ and 10″ can be connected in series (by means of external electric conductors, not shown in the figures) in order to function as a one-pole switching device with a total of six air breaks. By the same token, however, it is also conceivable to make use of only two of the three potentially possible current paths in order to implement a two-pole direct-current switching device. In the case of a four-pole alternating-current switching device that is to be modified for direct-current applications, all four current paths can be connected in series or else only two of the current paths can be employed as a two-pole direct-current switching device. 
       FIG. 8  shows another embodiment of a direct-current switching device  10 ′″ that is constructed on the basis of an alternating-current switching device housing  12 . Regarding  FIG. 8 , it also applies that those individual components of the switching device housing  12  that have the same function or are constructed in the same manner as the elements of the switching device housing  12  shown in  FIGS. 1 to 3  have been given the same reference numerals. 
     Diverging from the embodiment shown in  FIGS. 1 to 3 , the embodiment in  FIG. 8  does not have the center current path  22 , that is to say, the center receiving area  18  is free of a current path  22  and especially free of the movable switching contact element  24 .  FIG. 8  also shows that the center receiving area  18  does not have any arc-quenching devices. Consequently, the center receiving area  18  can now be employed to receive the first and second magnets  44 ,  46  that are arranged in the center receiving area  18  at the height of the air breaks  42  or  43  of the current paths  22  of the adjacent receiving areas  16  and  20 . 
     The advantages of the use according to the present invention of conventional alternating-current switching devices for direct-current applications can be seen in the minor modification of the conventional alternating-current switching devices that can be manufactured in large production runs and thus cost-effectively, as well as in the associated inexpensive manufacture of direct-current switching devices (low investment in terms of time and development work for the modification as well as no need to conduct one&#39;s own development work for a purely direct-current switching device). 
     The present invention is not limited to the embodiments described herein, and reference should be had to the appended claims.