Abstract:
The invention relates to a power circuit breaker that is suitable for switching electrical voltages. The power circuit breaker according to the invention comprises two main electrodes, to each of which a respective pole of the voltage to be switched can be connected. During the switching process, at least one of said main electrodes follows a switching path. The power circuit breaker is characterized in that secondary electrodes are additionally provided, which protrude into the vicinity of the switching path and are designed and arranged in such a way that arcs can be produced (a) between the main electrodes and the secondary electrodes and (b) between the individual secondary electrodes during the switching process. The power circuit breaker according to the invention can be advantageously used in vehicles and in ultra-high-voltage AC and HVDC (high-voltage direct current) transmission systems and causes arcs to be extinguished as early as possible during the switching process.

Description:
TECHNICAL FIELD 
     The present invention relates to a power circuit breaker that is suitable for switching electrical voltages or electrical currents and powers. 
     BACKGROUND OF THE INVENTION 
     Usually, a power circuit breaker contains two electrodes, to each of which, in operation, a respective pole of the voltage to be switched is applied. In particular when the electrodes are separated, there is a high likelihood that an undesired arc will occur. Even when this arc is extinguished in the meantime, there is the danger that it can reignite and indeed continue to do so until the separating gap is sufficiently large. 
     In order to ensure that such arcs are extinguished insofar as possible, the insulating gas SF 6  (sulfur hexafluoride) is utilized in many known high-voltage power circuit breakers. However, this is a very strong greenhouse gas, which can escape into the atmosphere, particularly in the event of leakage and after the end of the service life. 
     Therefore, in particular for reasons of environmental compatibility, vacuum circuit breakers were developed for switching high voltages. In order to prevent arcing in vacuum circuit breakers, they are generally employed in alternating current systems. For alternating current, there is a periodic zero-crossing of the current, which is favorable to extinguishing the arc. 
     However, there is an increased need for the transmission of high-voltage direct current. Such systems of high-voltage direct current transmission (HVDC) have been proposed in current discussions by various parties on the energy transition and the expansion of the electrical grid, in particular for the connection of off-shore wind parks or the installation of coupling points. This is because direct current technology appears to be advantageous for higher powers given identical line widths, longer distances, and, above all, longer cable connections. 
     The reliable switching of high direct-current voltages is often realized by connecting a plurality of high-voltage power circuit breakers in series. 
     The European Patent EP 0 556 616 B1—or its German translation DE 693 02 716 T2—describes a direct current breaker arrangement that closes a commutating switch after interruption of a vacuum circuit breaker and transforms arcing direct current into an alternating waveform by means of commutation so as to end the interruption. This is intended to interrupt a direct current reliably so as to prevent any escalation of an operational malfunction. 
     The object of the present invention is to be able to switch an alternating current or direct current (or a corresponding power) in a simple and reliable way. 
     SUMMARY OF THE INVENTION 
     This object is achieved by the power circuit according to claim  1 . Advantageous further developments are presented in the dependent claims. 
     The power circuit breaker according to the invention comprises two electrodes, to each of which can be connected a pole of an electrical voltage, which can be switched on or off. These electrodes also will be referred to as main electrodes in the following. The switch according to the invention is fundamentally suitable for switching voltages of any values. In doing so, arcing is to be prevented or the existence thereof during the switching operation is to be ended as soon as possible. For this reason, the switch according to the invention is especially suitable for all fields of application in which such arcs are particularly detrimental, such as, for example, in vehicles having an electric powertrain and/or internal-combustion engines, as well as during switching of high voltages. High voltage is understood here to mean a voltage that can have a value of approximately 50-500 kilovolts or even more. The power circuit breaker offers special advantages as part of a system for the transmission of ultrahigh-voltage alternating current (AC) or of high-voltage direct current (HVDC). 
     The main electrodes have to be brought together or separated for the switching operation. This generally occurs by a mechanical movement of one of the two main electrodes. The other main electrode is then stationary, that is, fixed in position inside of the power circuit breaker. However, it is also conceivable that the two main electrodes are moved simultaneously or successively. 
     This switching movement takes place along a switching path. This path usually is rectilinear and, namely, perpendicular with respect to the switching surface of the stationary main electrode. However, any other form that is advantageous for mechanical and/or electrical reasons, is also conceivable. 
     The present invention is characterized in that there is at least one secondary electrode. This secondary electrode (or a plurality thereof) protrudes into the region in the vicinity of the switching path. As a result of this, a main arc forms between the two main electrodes during the separation process and as the distance of the main electrodes from each other progresses, additional arcs are formed and in fact, between the main electrodes and the secondary electrode. These additional arcs are thus switched parallel to the original main arc and cause the latter to be extinguished substantially earlier than in the case of hitherto known power circuit breakers. In order to optimize the creation of additional arcs, it is advantageous when the minimum distance between the switching path and the secondary electrode is less than 10 mm, with values between about 0.5 to 1 mm having especially proven useful. 
     The invention is based on the realization that the existence of arcs is unstable and obeys statistical laws. When a plurality of individual arcs then arise instead of a main arc and are connected virtually in series, there is a markedly greater probability that one of these individual arcs is extinguished. When this happens, the other individual arcs will also be extinguished quickly, as a result of which the entire chain of arcs is ultimately extinguished. Through the creation of such a chain of arcs instead of a single main arc, the presence of arcs during the switching process is ended more quickly and the operational reliability of the power circuit breaker is thus increased. 
     The presence of the secondary electrodes according to the invention is fundamentally possible for a power circuit breaker that contains a gas such as the insulating gas SF 6 , for example. However, the arrangement of the secondary electrodes is especially advantageous in vacuum power circuit breakers in which a gas pressure in the range of 10 −4  to 10 −8  mbar prevails, with values in the range of 10 −5  to 10 −7  mbar usually being especially preferred. 
     The secondary electrode (or a plurality thereof) can be designed in various ways. In order to be able to ensure the greatest possible operational reliability, it has proven useful to design the secondary electrode in the shape of a ring or a flat area, with an opening being provided through which the switching path passes. 
     It has proven further useful when the secondary electrode (or a plurality thereof) has a contour, as a result of which it is thinner in the region of the switching path than on the side facing away from the switching path. Such a contour can be realized, for example, by a triangular course (see also  FIG. 5 ). It is also conceivable that the respective secondary electrode has a curved profile (see also  FIG. 4 ), which can be described on the basis of a small radius (r) and a large radius (R), with r&lt;R. 
     For further increase in the operational reliability, it has proven useful when a plurality of secondary electrodes are present, at least individual ones of which are connected together electrically by an electronic grid, which includes at least one varistor and/or at least one ohmic resistor. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       In the following, further details and advantages of the present invention are described on the basis of preferred exemplary embodiments. Shown are: 
         FIG. 1  a symbolic illustration of a power circuit breaker 
         FIG. 2  a cross-sectional illustration of the power circuit breaker 
         FIG. 3 a    schematically illustrates a first position of the main electrodes and the secondary electrodes 
         FIG. 3 b    schematically illustrates a second position of the main electrodes and the secondary electrodes 
         FIG. 3 c    schematically illustrates a third position of the main electrodes and the secondary electrodes 
         FIG. 3 d    schematically illustrates a fourth position of the main electrodes and the secondary electrodes 
         FIG. 3 e    schematically illustrates a fifth position of the main electrodes and the secondary electrodes 
         FIG. 3 f    schematically illustrates a sixth position of the main electrodes and the secondary electrodes 
         FIG. 3 g    schematically illustrates a seventh position of the main electrodes and the secondary electrodes 
         FIG. 3 h    schematically illustrates an eighth position of the main electrodes and the secondary electrodes 
         FIG. 4  an enlarged illustration of the secondary electrode  30   a  from  FIG. 2   
         FIG. 5  secondary electrodes having a triangular contour 
         FIG. 6  another embodiment of the power circuit breaker with circuitry. 
     
    
    
     DETAILED DESCRIPTION 
     Identical and similar means are provided in the figures with identical reference numbers. A repeated description occurs only insofar as it seems necessary for understanding the invention or exemplary embodiments. Although the exemplary embodiments describe the switching of high voltage, it is pointed out once again that the power circuit breaker according to the invention is suitable for the switching of electrical voltages of any value. 
       FIG. 1  shows a symbolic illustration of a preferred power circuit breaker  10 , which is suitable for switching direct voltages of up to 100 kV and more. It is preferably designed as a vacuum circuit breaker in which a pressure of approximately 10 −6  mbar usually prevails. The preferred embodiment is essentially circularly symmetrical or cylindrically symmetrical in design. This means that the housing of the power circuit breaker  10  comprises an essentially cylindrically shaped insulator  12  as well as a top end plate  14  and a bottom end plate  16 , each of which is nearly disc-shaped. The power circuit breaker  10  further contains a top main electrode  18  having a top shaft  20  and a bottom main electrode  22  having a bottom shaft  24 . A high voltage can be switched on or interrupted via the main electrodes  18 ,  22 . The two shafts  20 ,  24  are electrically conductive and each of them is in both mechanical and electrically conductive connection with its respective main electrode  18  and  22 . 
     The top shaft  20  is fastened to the top end plate  14 , so that the top main electrode  18  is nearly fixed in position inside of the power circuit breaker  10 . A top junction port A, to which the first pole of the high voltage to be switched can be applied, is connected to the top main electrode  18  via the electrically conductive top shaft  20 . The bottom shaft  24  can be moved perpendicularly back and forth along the arrow  26  through an opening, which is not depicted here, inside of the bottom end plate  16 . In this way, it is thus possible to move the bottom main electrode  22 , that is, up and down, along a switching path, which is indicated here by the dashed lines sl and sr. The second pole of the high voltage to be switched can be applied via a bottom junction port B. This port B is in electrically conductive connection with a sliding contact  28 , which, in turn, makes possible a contact between the electrically conductive bottom shaft  24  and thus also to the bottom main electrode  22 . 
     The power circuit breaker  10  further comprises five secondary electrodes  30   a , . . . ,  30   e , each of which is designed nearly disc-shaped and each of which is retained by the respective retainer  31   a , . . . ,  31   e . The retainers  31  are preferably formed as metal plates, which are fastened to the insulator  12  or to one of the end plates  14 ,  16  (see also  FIG. 2 ) and thus retain the secondary electrodes in a stable position. Alternatively, it is also possible for the retainers  31  to be designed as crosspieces or the like. 
     The secondary electrodes  30  each have an opening  32   a , . . .  32   e  in the center portion, said openings being designed and arranged in such a way that the movable bottom main electrode  22  can be moved through it there. Preferably, the openings  32  are symmetrical to the positions of the bottom main electrode  22  along the perpendicular switching path thereof. When these positions are in the center of the openings  32 , there is a minimum distance d between the exterior of the main electrode  22  and the interior of such an opening  32 , as shown in  FIG. 1 . This distance d between the switching path sr and the secondary electrode  30  is less than 10 mm, with values of between 0.5 and 1 mm having especially proven useful. It is also possible that the topmost secondary electrode  30   a  is arranged in such a way that the top main electrode  18  is situated in the region of the opening  32   a . Such designs are illustrated in  FIGS. 3 a -3 h    and  4 , for example. 
       FIG. 2  shows a cross-sectional illustration of the preferred power circuit breaker  10 , which—as already mentioned above—is designed in an essentially circularly symmetrical or cylindrically symmetrical shape. For reasons of clarity, only three of the secondary electrodes  30   a , . . . ,  30   e  were illustrated.  FIG. 2  shows, in addition, further possible modifications. Thus, in this case, the insulator  12  has first sections  12   a , which are electrically conductive, as well as second sections  12   b , which are electrically insulating. The first sections  12   a  are preferably made of metal. The second sections  12   b  are made of conventional material, such as ceramic or the like. Moreover, the top main electrode  18  is designed to be quite large in  FIG. 2 , so that the lateral dimension thereof is greater than that of the bottom main electrode  22 . 
     Furthermore, the power circuit breaker  10  has a shielding metal plate  33  in this case. Together with the retainers  31   a  and  31   e , which are preferably designed likewise as metal plates and thus also function as shielding metal plates, the dielectric face of the insulators  12  is thus shielded against flows of metal particles that ensue during creation and presence of an arc. 
     Illustrated in  FIG. 2  are also an electromagnet  34 , a permanent magnet  36 , and a spring  38 , which, when there is appropriate switching and actuation by suitable means (not shown here), make possible a vertical actuation of the bottom shaft  24 —and thus also of the bottom main electrode  22 —and hence are able to bring about a desired switching process by interconnecting or separating the two main electrodes  18 ,  22 . 
     The arrangement of the magnets  34 ,  36  as well as the springs  38  shown in  FIG. 2  is merely symbolic and indicates a power circuit breaker  10 , which is realized as a gas-filled circuit breaker. For a vacuum circuit breaker, by contrast, the electromagnet  34  and the spring  38  are preferably mounted below the bottom end plate  16  and outside of the vacuum chamber. 
     What is unique in the present invention are the secondary electrodes  30  shown in the exemplary embodiments. These enable the arcs that usually form during the switching process to be extinguished in a simple way. This will be explained in detail by means of the following  FIGS. 3 a   - 3   h.    
       FIGS. 3 a  to 3 h    schematically represent a sequence in the switching process regarding the main electrodes  18 ,  22  and the secondary electrodes  30   a  . . .  30   e . During a switching process, in which the two main electrodes  18 ,  22  are separated from each other, various respective positions of the bottom main electrode  22  are shown in  FIGS. 3 a  to 3 h   , one after the other. In addition, the secondary electrodes  30   a , . . . ,  30   e  are depicted as well as various arcs that can form during such a switching process. In the illustrated exemplary embodiment, the topmost secondary electrode  30   a  is situated essentially at the same height as the first main electrode  18 , which is nearly fixed in position. It is assumed (not depicted here) that the bottom main electrode  22  was initially actuated in such a way that the two main electrodes  18 ,  22  came into contact and thereby a direct voltage of approximately 50 kV or more was switched. When the two main electrodes  18 ,  22  are separated, various arcs arise, which will be addressed in detail below. They are formed inside of a vacuum power circuit breaker in that metal particles are released from the material of the electrodes. Such arcs are unstable, however, and the occurrence or extinguishing thereof obeys statistical laws. 
       FIG. 3 a    shows the two main electrodes  18 ,  22  shortly after the separation thereof; here, the bottom main electrode  22  has assumed a position in which it is situated at about the same height as the secondary electrode  30   b . Initially, in the separation process, an arc  110  is formed between the two main electrodes  18 ,  22 . An arc  112  (between the top main electrode  18  and the secondary electrode  30   a ), an arc  114  (between the secondary electrodes  30   a ,  30   b ), and an arc  116  (between the secondary electrode  30   b  and the bottom secondary electrode  22 ) also arise nearly simultaneously. 
       FIG. 3 b    shows a situation in which the bottom main electrode  22  has moved further downward during the switching process. As a result, the distance between the main electrodes  18 ,  22  has become larger and the arc  110  that was originally present is extinguished. By contrast, the arcs  112 ,  114 , and  116  are still present. For reasons of clarity, arcs that have already been described once are not provided separately with reference numbers again in the subsequent figures, as in the case here for the arcs  112 ,  114 , and  116 . Only in  FIG. 3 h    are all arcs present there provided once again with reference numbers for completeness. 
     In  FIG. 3 c   , the arc  116  is extinguished. Instead of it, an arc  130  (between the secondary electrodes  30   b ,  30   c ) and an arc  132  (between the secondary electrode  30   c  and the bottom electrode  22 ) have newly arisen. In  FIG. 3 d   , the bottom main electrode  22  is situated below the secondary electrode  30   c . However, the same arcs are present as in  FIG. 3   c.    
     In  FIGS. 3 e  and 3 f   , the bottom main electrode  22  is situated at the same height as the secondary electrode  30   d  or just below it. As a result, the arc  132  is extinguished. However, an arc  150  (between the secondary electrodes  30   c  and  30   d ) and an arc  152  (between the secondary electrode  30   d  and the bottom main electrode  22 ) are formed. 
     In  FIGS. 3 g  and 3 h   , the bottom main electrode  22  is situated at the height of the secondary electrode  30   e  or just below it. As a result, the arc  152  is extinguished. However, an arc  170  (between the secondary electrodes  30   d  and  30   e ) and an arc  172  (between the secondary electrode  30   e  and the bottom main electrode  22 ) are formed. 
     The arcs  112 ,  114 ,  130 ,  150 ,  170 , and  172  that are present during the switching process as well as in the position according to  FIG. 3 h   , in particular, have formed owing to the special design and positioning of the secondary electrodes  30  with respect to one another as well as with respect to the position of the top main electrode  18  and the switching path of the bottom main electrode  22 . These arcs are connected virtually in series. This means that, when one of these arcs is extinguished owing to statistical laws, the entire spark gap is interrupted. As a result, arcs in the high-voltage power circuit breaker according to the invention are extinguished substantially earlier than in hitherto known power circuit breakers. 
       FIG. 4  is a cutout of  FIG. 2  and shows, in enlargement, particularly the first secondary electrode  30   a . It is clearly shown here that this secondary electrode  30   a  has a contour for which, toward the switching path—indicated here by its left boundary sl—a smaller radius r is realized than on the opposite-lying side, where a larger radius R exists. This means, therefore, that it has proven useful in the preferred embodiments for at least individual secondary electrodes  30  to be designed to be thinner or more pointed in the direction of the switching path sl, sr than on the other side. In this way, on the one hand, the secondary electrodes  30  have a quite small distance of a few millimeters in the outer region, that is, on the side facing away from the switching path sl, sr, as a result of which the arcs  114 ,  130 ,  150 , and  170  (see  FIGS. 3 a -3 h   ) can form; on the other hand, the secondary electrodes  30  have a markedly greater distance from one another in the region of the switching path sl, sr than toward the switching path sl, sr itself, as a result of which the arcs  112 ,  116 ,  132 ,  152 , and  172  (see  FIGS. 3 a -3 h   ) can form. 
       FIG. 5  shows two secondary electrodes  30 ′ a  and  30 ′ b  with an alternative contour, which—in perspective view—runs in each case from the switching path sl, sr outward in a triangular shape. In this way, it is possible for the distance between the secondary electrodes  30 ′ to be greater in the region of the switching path sl or sr than on the outer side of the secondary electrode  30 ′. 
       FIG. 6  shows, in a symbolic manner, another exemplary embodiment of the power circuit breaker  10  according to the invention. What is unique in it is the electronic circuit  50 , which is composed of a plurality of ohmic resistors  52  as well as a plurality of voltage-dependent resistors  54 , which will be referred to as varistors below. The resistors  52  and the varistors  54  are each connected in series. It has proven useful for a high-voltage power circuit breaker for each of the resistors  52  to have a value greater than 100 kΩ, with a range between 100 kΩ and 1 MΩ being especially advantageous. In the preferred exemplary embodiment, the varistors are designed in such a way that they have a limit voltage (threshold voltage) of approximately 1 kV. 
     The preferred embodiment of the power circuit breaker  10  is designed in such a way that voltages in the range of approximately 200 kV can be switched. When five secondary electrodes  30   a , . . . ,  30   e  are present in this case (as also depicted), four gaps result between these secondary electrodes  30   a , . . . ,  30   e . In order to make possible an optimal spark gap with the sparks  114 ,  130 ,  150 ,  170  (see  FIGS. 3 a -3 h   ), a sufficient number of the resistors  54  are arranged between each of the two secondary electrodes ( 30   a - 30   b ,  30   b - 30   c ,  30   c - 30   d ,  30   d - 30   e ) such that, in each case, a limit voltage of 50 kV results. If, then, as assumed above, each of the varistors  54  has a limit voltage of 1 kV, then 50 varistors  54  are arranged between each of the secondary electrode pairs  30   a - 30   b ,  30   b - 30   c ,  30   c - 30   d ,  30   d - 30   e , so as to make possible the desired limit voltages. A good voltage distribution between the secondary electrodes  30  is ensured by the resistors  52 . 
     In this embodiment, the electronic circuit  50  is connected as follows. The retainers  31  are each made of plate metal in this case, so that each of these retainer metal plates also functions as a shielding metal plate. The first metal retaining plate  31   a  is connected via a first electrical conductor  56  to the top main electrode  18  via the top shaft  20 . Connected between the first metal retaining plate  31   a  and the second metal retaining plate  31   b  are a series of varistors  54 , to which a series of resistors  52  are connected in parallel. In  FIG. 6 , six resistors  52  as well as six varistors  54  are shown between the first metal retaining plate  31   a  and the second metal retaining plate  31   b . Six resistors  52  and six varistors  54  are also shown between each of the other adjacent metal retaining plates  31   b - 31   c ,  31   c - 31   d , and  31   d - 31   e . It is noted that this number is given only by way of example and can differ between adjacent metal retaining plates  31 . This also means, furthermore, that the number of resistors  52  can be different from the number of varistors  54 . Moreover, the last metal retaining plate  31   e  is electrically connected via a second electrical conductor  58  to the bottom main electrode  22  via the bottom shaft  24 . 
     The exemplary embodiments presented in the figures and hitherto described are preferred embodiments of the present invention, for which various further developments and modifications are possible. 
     LIST OF REFERENCE NUMBERS 
     
         
           10  power circuit breaker 
           12  insulator 
           12   a  first section of  12  (electrically conductive) 
           12   b  second section of  12  (electrically insulating) 
           14  top end plate 
           16  bottom end plate 
           18  top main electrode 
           20  top shaft 
           22  bottom main electrode 
           24  bottom shaft 
           26  arrow 
           28  sliding contact 
           30   a , . . . ,  30   e  secondary electrodes 
           31   a , . . . ,  31   e  retainers of secondary electrodes 
           32   a , . . . ,  32   e  openings in the secondary electrodes 
           33  shielding metal plate 
           34  electromagnet 
           36  permanent magnet 
           38  spring 
           50  electronic circuit 
           52  resistors 
           54  varistors 
           56  first electrical conductor 
           58  second electrical conductor 
           110 ,  112 ,  114 ,  116  arc in  FIG. 3 a , 3 b    (first time) 
           130 ,  132  arc in  FIG. 3 c , 3 d    (first time) 
           150 ,  152  arc in  FIG. 3 e , 3 f    (first time) 
           170 ,  172  arc in  FIG. 3 g , 3 h    (first time) 
         A, B junction ports for high voltage 
         d distance between boundary of the switching path and edge of  32   
         r radius of the secondary electrode in the region of the switching path 
         R radius of the secondary electrode opposite the switching path 
         sl, sr left and right boundary, respectively, of the switching path