Patent Publication Number: US-10770255-B2

Title: Self-resetting current limiter

Description:
CROSS-REFERENCE TO PRIOR APPLICATIONS 
     Priority is claimed to German Patent Application No. DE 10 2016 124 639.5, filed on Dec. 16, 2016. 
     FIELD 
     The invention relates to a self-resetting current limiter for interrupting a current path when a short-circuit current occurs in the current path. 
     BACKGROUND 
     A current limiter is usually used together with a switching or basic device, for example a circuit breaker or a protective motor switch, in order to increase the short-circuit breaking capacity of the switching or basic device. The switching device and the current limiter effectively share the switching work for switching off the short-circuit current. In so doing, the current limiter assists the switching device by relieving the switching device of some of the required breaking capacity. The breaking capacity can thus be increased overall. High short-circuit currents, for example currents of up to 150 kA, can be safely switched off by means of an arrangement of this kind consisting of a switching device and a current limiter. 
     SUMMARY 
     In an embodiment, the present invention provides a self-resetting current limiter, comprising: a first connecting contact configured to bring the current limiter into contact with a first electrical conductor; a second connecting contact configured to bring the current limiter into contact with a second electrical conductor; a first movable contact member; and a second movable contact member, wherein the first and the second movable contact members are electrically interconnected in a first position of the first and the second movable contact member, such that a current path between the first and the second connecting contact is closed, and wherein the first and the second movable contact members are separated from one another in a second position of the first and the second movable contact member, such that the current path between the first and the second connecting contact is interrupted. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be described in even greater detail below based on the exemplary figures. The invention is not limited to the exemplary embodiments. Other features and advantages of various embodiments of the present invention will become apparent by reading the following detailed description with reference to the attached drawings which illustrate the following: 
         FIG. 1A  is a sectional view of a first embodiment of a self-resetting current limiter, 
         FIG. 1B  is an enlarged view of a contact region between movable contact members of the self-resetting current limiter, 
         FIG. 2  shows components of the self-resetting current limiter for producing a current path in a closed state, 
         FIG. 3A  is a self-resetting current limiter comprising a slot motor made of two U-shaped parts, 
         FIG. 3B  is a self-resetting current limiter comprising an insulation cover for insulating the movable contact members with respect to the slot motor, 
         FIG. 4  is a first perspective view of a second embodiment of a self-resetting current limiter, 
         FIG. 5A  is a self-resetting current limiter having movable contact members in a first position, 
         FIG. 5B  is a self-resetting current limiter having movable contact members in a second position, 
         FIG. 6  shows a contact force-distance characteristic curve of the self-resetting current limiter, 
         FIG. 7A  is a first arrangement of a self-resetting current limiter and a switching device, 
         FIG. 7B  is a second arrangement of a self-resetting current limiter and a switching device. 
     
    
    
     DETAILED DESCRIPTION 
     An aspect of the present invention provides a self-resetting current limiter which makes it possible to safely interrupt a current path when a very high short-circuit current occurs in combination with a switching or basic device, the current limiter being immediately ready for operation again after the breaking operation. 
     In an embodiment, the present invention provides a self-resetting current limiter for interrupting a current path when a very high short-circuit current occurs in the current path, and for independently resetting the current limiter into the closed state after the short-circuit current has been switched off. 
     The self-resetting current limiter comprises a first connecting contact for bringing the current limiter into contact with a first electrical conductor, and a second connecting contact for bringing the current limiter into contact with a second electrical conductor. The self-resetting current limiter further comprises a first movable contact member and a second movable contact member. 
     The first and the second movable contact member are electrically interconnected in a particular first position, as a result of which a current path between the first and the second connecting contact is closed. The first and the second movable contact member are separated from one another in a particular second position of the first and the second movable contact member, as a result of which the current path between the first and the second connecting contact is interrupted. 
     As well as the first and the second movable contact member, the self-resetting current limiter has a contact system that can be opened by dynamic current forces. The movable part of the contact system is formed of two parts which consist of the first and the second movable contact member. Contacts, referred to as loose contacts, are arranged on the respective ends of the movable contact members, which contacts form the actual contact point via which the current flows between the two movable contact members in the closed state of the current path. Owing to the antiparallel current conduction, greater acceleration is generated at the loose contacts of the opening contact system, by means of which acceleration the two loose contacts are moved or spun away from one another. 
     In order to further increase the acceleration, a slot motor can be fitted in the housing of the current limiter. 
     In addition, a counter force can act on the first and the second movable contact member when they are spun on, which counter force is produced by a compression spring in each case. The compression spring assigned to the first and the second movable contact member acts on a lever arm of the first and the second movable contact member in each case. The arrangement consisting of movable contact members and the compression spring assigned to the particular contact member is designed such that the lever arm shortens as the spin-on path increases, such that a torque acting on the lever arm remains almost constant despite the increasing compression of the compression spring. 
     Greater acceleration of the movable contact members can be achieved by means of the compression spring which acts on each of the movable contact members, which spring does not allow its compression spring force to increase linearly when the movable contact members are spun on, but rather it shortens its lever arm as the spin-on path increases. The contact members therefore reach their end position quicker when they are moving apart from one another, as a result of which a high arc voltage can be generated more rapidly. As a result, even better short-circuit current limitation can be achieved. However, there is less torque acting in the compressed state of the compression spring owing to the shortened lever arm, meaning that the acceleration at which the movable contact members fall back into their starting position is reduced. As a result, the loose contacts can be prevented from being welded together after they have fallen back. 
     A first embodiment 1 of a self-resetting current limiter is described in more detail in the following with reference to  FIGS. 1A, 1B and 2 . The self-resetting current limiter  1  comprises a first connecting contact  100  for bringing the current limiter into contact with a first electrical conductor, for example the electrical conductor of a cable. In order to attach the electrical conductor to the connecting contact  100 , the connecting contact  100  has a terminal screw  101 . In addition, the current limiter  1  has a second connecting contact  200  for bringing the current limiter into contact with a second electrical conductor. The second electrical conductor can be, for example, a busbar of a switching device to which the current limiter is connected. The second connecting contact  200  can be designed in particular as a connecting bar, which is electrically connected to the busbar of the subsequent switching device. The switching device can be a circuit breaker, an automatic circuit breaker or a protective motor switch. 
     The self-resetting current limiter  1  further comprises a first movable contact member  110  and a second movable contact member  210 . The first and the second movable contact member  110 ,  210  are arranged so as to be able to rotate about a particular rotary shaft  130 ,  230 . The rotary shaft  130 ,  230  can be formed by a current bar  120 ,  220 . 
     The self-resetting current limiter  1  further comprises a first stationary connector  170 , which is electrically connected to the first connecting contact  100 . A first flexible connecting member  180  of the self-resetting current limiter is arranged between the first stationary connector  170  and the first movable contact member  110 . The first stationary connector  170  is electrically connected to the first movable contact member  110  by means of the first flexible connecting member  180 . 
     The self-resetting current limiter  1  comprises a second stationary connector  270 , which is electrically connected to the second connecting contact  200 . In addition, the self-resetting current limiter  1  has a second flexible connecting member  280 , which is arranged between the second stationary connector  270  and the second movable contact member  210 . The second flexible connecting member  280  electrically connects the second stationary connector  270  to the second movable contact member  210 . The first and the second flexible connecting member  180 ,  280  can have a solder cup  181 ,  281 , which is arranged on one of the movable contact members  110 ,  210  in each case. The stationary connectors  170 ,  270  are each electrically connected to the movable contact members  110 ,  210  by means of an electrical stranded wire  182 ,  282  of the first and the second flexible connecting member  180 ,  280 . 
     The self-resetting current limiter further comprises an electrically non-conductive housing  10 , in which the first and the second connecting contact  100 ,  200 , the first and the second movable contact member  110 ,  210 , the connector  170 ,  270  and the connecting member  180 ,  280  are housed. The housing  10  is closed by a cover part  40 . The housing  10  has an electrically non-conductive channel  41 , which extends from outside the housing  10  to the first connecting contact  100 . The channel  41  is formed as a bulge that projects from the side of the housing. The channel  41  is dimensioned such that or protrudes so far out of the housing  10  that the mode of connection of the current limiter meets the requirement of an increased air gap and leakage path according to the UL 489 Standard. 
     In order to produce a restoring force which acts on the first and the second movable contact member  110 ,  210  when said contact members are spun on, a first compression spring  140  and a second compression spring  240  are provided. The two compression springs are arranged in the cover part  40 . The first compression spring  140  produces a restoring force on the first movable contact member when the first movable contact member  110  is spun on. The second compression spring  240  produces a restoring force on the second movable contact member when the second movable contact member  210  is spun on. 
     As can be seen in  FIG. 2 , the first movable contact member  110  has a first arm  111  comprising a support element  150  on which the first compression spring  140  rests in order to exert a force on the first arm  111  of the first movable contact member  110 . The first arm  111  of the first movable contact member  110  extends from the support element  150  to the rotary shaft  130 . The second movable contact member  210  has a first arm  211  comprising a support element  250  on which the second compression spring  240  rests in order to exert a force on the first arm  211  of the second movable contact member  210 . The first arm  211  of the second movable contact member  210  extends from the support element  250  to the rotary shaft  230 . 
     The first movable contact member  110  has a second arm  112 , which extends from the rotary shaft  130  to an end portion E 112  of the second arm  112  of the movable contact member  110 . The first movable contact member  110  is bent along its longitudinal axis at the rotary shaft  130 . The second arm  112  of the first movable contact member  110  is thus not arranged in the extension of the direction of the first arm  111  of the first movable contact member  110 . 
     The second movable contact member  210  has a second arm  212 , which extends from the rotary shaft  230  to an end portion E 212  of the second arm  212  of the second movable contact member  210 . The second movable contact member  210  is formed and arranged mirror-symmetrically with respect to the first movable contact member  110 . In particular, the second arm  212  of the second movable contact member  210  is not arranged in the extension of the direction of the first arm  211  of the second movable contact member  210 . The second movable contact member  210  is, rather, bent along its longitudinal axis in the region of the rotary shaft  230 . 
     The self-resetting current limiter further comprises a first loose contact  160 , which is arranged on the end portion E 112  of the second arm  112  of the first movable contact member  110 . A second loose contact  260  is likewise arranged on the end portion E 212  of the second arm  212  of the second movable contact member  210 . 
     According to the embodiment of the self-resetting current limiter  1  shown in  FIGS. 1A, 1B and 2 , an adapter  20  is arranged between the end portion E 112  of the second arm  112  of the first movable contact member  110  and the end portion E 212  of the second arm  212  of the second movable contact member  210 . The adapter  20  has a first fixed contact  21  and a second fixed contact  22 . The first and the second fixed contact  21 ,  22  are arranged on an upper portion of the adapter. When the current path is closed during normal operation, the loose contact  160  is in contact with the fixed contact  21  and the loose contact  260  is in contact with the fixed contact  22 . A lower portion of the adapter  20  is arranged between a first arc chute  190  and a second arc chute  290 . Alternatively, instead of the separate arc chutes, only one arc chute can also be used, which extends along the length of the arc chutes  190  and  290 . 
       FIG. 1B  shows the adapter  20  having the fixed contacts  21  and  22  applied on either side and the lower portion of the adapter  20  arranged between the two arc chutes  190 ,  290 . The arc chutes  190 ,  290  have a plurality of deion plates  191 ,  291 , which are surrounded by a chute wall  192 ,  292 . Blow-out openings  193 ,  293  are provided in the lower region of the chute wall  192 ,  292 , through which openings breaking gases occurring during current flow are blown out into a blow-out channel  80  when the movable contact members  110 ,  210  are separated. 
     As is shown in the embodiment of the self-resetting current limiter in  FIG. 1A , the current limiter can have a slot motor  30 , which is arranged around the first and the second movable contact member  110 ,  210 . According to the embodiment shown in  FIG. 1A , the slot motor  30  can be designed as an annular or loop-shaped closed frame. In contrast to the slot motor shown in  FIG. 1A  as an integral, single part, the slot motor can comprise two U-shaped parts which are separated from one another by a gap, according to another embodiment shown in  FIG. 3A . A material having good magnetic conductivity, for example iron, in particular a soft-iron material, can be used as the material for the slot motor. 
     The slot motor made of an electrically conductive material can be insulated from the other conductive parts, in particular from the movable contact members  110 ,  210 . The insulation cover  50  shown in  FIG. 1A  and  FIG. 3B  is provided for the purpose of said insulation. As can be seen in  FIG. 3B , the insulation cover  50  can additionally be designed to guide the movable contact members  110 ,  210  and to mount said members over the current bars  120 ,  220 . 
       FIG. 4  shows a second embodiment 2 of a self-resetting current limiter. In the following, only the differences from the first embodiment 1 will be described. In contrast to the first embodiment 1 of the self-resetting current limiter, in the second embodiment 2, an additional deion plate  60  is provided between the first arc chute  190  and the second arc chute  290 , rather than the adapter  20 . According to an alternative embodiment, the arc chutes  190 ,  290  and the deion plate  60  can be consolidated to form a single or common arc chute. The deion plate  60  does not extend between the two movable contact members  110 ,  210  as the adapter  20  does. Instead, the loose contacts  160 ,  260  of the movable contact members  110 ,  210  are in direct contact with one another when the current limiter is operated in normal operation, i.e. not in the event of a short circuit, and the current path is closed. 
     In order to position the two movable contact members  110  and  210 , when they fall back in a non-uniform manner after the opening process, a contact member stop  70  is provided. The two movable contact members  110  and  210  are not normally in contact with the contact member stop  70 . However, one of the movable contact members can hit the contact member stop  70  when it falls back into the starting position if, for example, the contact member falls back into the starting position more rapidly than the opposite contact member, or the material of the loose contact is burnt off for one of the contact members. The contact member stop  70  is thus to be understood as an auxiliary stop which limits the maximum movement of the contact member  110  or  210  when it falls back into the starting position, resulting in ideal contact covering. In addition, the contact member stop  70  prevents the movable contact members  110  and  210  from welding together when the loose contacts  160  and  260  are burnt off. In addition, the contact member stop  70  functions such that the breaking gases do not spread towards the flexible connecting members  180  or  280 , meaning that flashbacks in this region can be effectively prevented. 
       FIG. 5A  shows the self-resetting current limiter according to the first embodiment 1 in a normal state of operation, when no short-circuit current is flowing. The movable contact members  110 ,  210  are electrically interconnected in a particular first position of the two contact members, as a result of which a current path between the first connecting contact  100  and the second connecting contact  200  is closed. The loose contact  160 , in the first position of the movable contact member  110 , is in contact with the first fixed contact  21 . The loose contact  260 , in the first position of the movable contact member  210 , is in contact with the second fixed contact  22 . In normal operation, a current can thus flow from the connecting contact  100  via the stationary connector  170  and the flexible connecting member  180  to the movable contact member  110  and also via the adapter  20 , the movable contact member  210 , the flexible connecting member  280  and the stationary connector  270  to the connecting contact  200 . 
     When a short-circuit current occurs between the connecting contact  100  and the connecting contact  200 , a force caused by the short-circuit current acts on the first movable contact member  110 . A force caused by the short-circuit current likewise acts on the second movable contact member  210 . Owing to the action of force, the movable contact members  110  and  210  are rotated or spun on into the second position. In the second position, the ends of the contact members  110  and  210  hit the inner wall of the housing body  10 . The compression spring  140  exerts, on the first movable contact member  110 , a counter force with respect to the force caused by the short-circuit current when the first movable contact member  110  is spun on. The compression spring  240  likewise exerts, on the second movable contact member  210 , a counter force with respect to the force caused by the short-circuit current when the second movable contact member  210  is spun on. 
     The counter forces exerted by the two compression springs  140 ,  240  on the respective movable contact members  110 ,  210  cause the acceleration at the movable contact members  110  and  210  to reduce. Therefore, the increase in counter force is as small as possible, and it is thus ensured that the loose contacts  160  and  260  can be very quickly spun away from one another. In order to exert the counter force on the movable contact member  110 , the compression spring  140  is supported on the support element  150 , which can be formed as a straight pin  151 . The compression spring  240  is supported on the support element  250 , which can also be formed as a straight pin  251 . 
       FIG. 5B  shows the self-resetting current limiter when a short-circuit current occurs in the current path. The two movable contact members  110 ,  210  are spun on due to the high current and are temporarily located in a second position in which they are insulated from one another. The current path is thus interrupted between the connecting contacts  100  and  200 . The forces exerted on the support elements  150  and  250  by the compression springs  140  and  240  cause the movable contact members  110  and  210  to fall back into their starting position (shown in  FIG. 5A ) after having been spun on and after the short-circuit current has been switched off by the switching or basic device. The circuit can thus be switched on again (“self-resetting current limiter”) by actuating the switching or basic device, without additionally actuating the current limiter. 
     When a short-circuit current occurs, forces are generated in the region of the connection points of the two movable contact members  110  and  210 , which forces push the two movable contact members away from one another or away from the adapter  20 . Forces of this kind are known as current density forces or Holm forces and occur at constrictions of current paths. Current density forces are Lorentz forces which are formed on either side of a constriction of a current path owing to currents running in opposing directions. 
     The contact system is constructed such that the short-circuit currents flowing in the two movable contact members  110  and  210  are in opposite directions and thus also move or spin the moving contact members  110 ,  210  away from one another. As can be seen in  FIG. 5B , the two movable contact members  110 ,  210  are rotated or spun about their particular rotary shaft  130 ,  230  when a short-circuit current occurs in the current path between the connecting contacts  100  and  200 . The flexible connecting members  180 ,  280  and in particular the electrical stranded wires  182 ,  282  make it possible for the two rotatably mounted and movable contact members  110 ,  210  to be able to twist against the stationary connectors  170 ,  270 . 
     The slot motor  30  causes the magnetic field to extend to the contact members  110  and  210 , which, on account of the Lorentz force, leads to an increase in the force acting on the movable contact members  110 ,  210  and thus accelerates the movable contact members  110 ,  210  even more in their spin-on movement. The arc between the loose contacts  160 ,  260 , which is produced when the two movable contact members  110 ,  210  move away from one another, damps the short circuit. 
     The mode of operation of the second embodiment 2 of the self-resetting current limiter according to  FIG. 4  corresponds to the mode of operation shown in  FIGS. 5A and 5B  for the first embodiment 1 of the self-resetting current limiter, in this case, however, the loose contact  160  and the loose contact  260  being in direct contact with one another in the first position of the movable contact members  110 ,  210 . 
       FIG. 6  shows a contact force-distance characteristic curve for the self-resetting current limiter. The arm  111  of the movable contact member  110  is oriented with respect to the arm  112  of the movable contact member  110  such that a contact force F acting perpendicularly on the surface of the loose contact  160  increases linearly from a strength F k  initially up to a strength F auf  when the first movable contact member  110  is moved from the first position s K  into the second position S auf . The arm  211  of the second movable contact member  210  is likewise oriented with respect to the arm  212  of the second movable contact member  210  such that a contact force F acting perpendicularly on the surface of the loose contact  260  increases linearly starting from a strength F k  up to a strength F auf  when the second movable contact member  210  is moved from the first position S K  into the second position S auf . 
     In addition, the arm  111  is oriented with respect to the arm  112  of the first movable contact member  110  such that a contact force F acting perpendicularly on the surface of the loose contact  160  decreases non-linearly from the strength F auf  down to the strength F k  when the first movable contact member  110  is moved from the second position S auf  into the first position S k . The arm  211  is likewise oriented with respect to the arm  212  of the second movable contact member  210  such that the contact force F acting perpendicularly on the surface of the loose contact  260  decreases non-linearly from the strength F auf  down to the strength F k  when the second movable contact member  210  is moved from the second position S auf  into the first position s k . The contact force decreases first quicker then slower per length of path. The speed when the two movable contact members  110  and  210  fall back can thus be reduced, as a result of which the loose contacts  160  and  260  are prevented from welding together when the current path closes, i.e. when the current limiter is reset. 
       FIGS. 7A and 7B  show different arrangements of the self-resetting current limiter in the first or second embodiment 1, 2 and a switching device  3 . The self-resetting current limiter can be arranged on the top of the switching device  3 , as shown in  FIG. 7A , or on the bottom of the switching device  3 , as shown in  FIG. 7B . 
     The self-resetting current limiter  1 ,  2  assists the switching device  3 , which is designed for example as a circuit breaker, an automatic circuit breaker or a protective motor switch, in switching off a short-circuit current. The magnetic quick-release and the mechanical latch of a switching device cause the contact apparatus to open permanently, while the movable contact members or repulsion contacts of the self-resetting current limiter  1 ,  2  fall back into their closed rest position independently. The self-resetting current limiter is thus ready for operation again without additional manual actuation or remote control. 
     The current limiter can be designed for one, two or even three poles. Depending on the number of poles, a plurality of the described components of the current limiter is arranged in the housing  10 . The number of channels or feeders  41  leading to the connecting contact  100  likewise increases. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. It will be understood that changes and modifications may be made by those of ordinary skill within the scope of the following claims. In particular, the present invention covers further embodiments with any combination of features from different embodiments described above and below. Additionally, statements made herein characterizing the invention refer to an embodiment of the invention and not necessarily all embodiments. 
     The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B and C” should be interpreted as one or more of a group of elements consisting of A, B and C, and should not be interpreted as requiring at least one of each of the listed elements A, B and C, regardless of whether A, B and C are related as categories or otherwise. Moreover, the recitation of “A, B and/or C” or “at least one of A, B or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B and C. 
     LIST OF REFERENCE SIGNS 
     
         
           1 ,  2  self-resetting current limiter 
           10  housing 
           20  adapter 
           21 ,  22  fixed contact 
           30  slot motor 
           40  cover part 
           41  channel/bulge 
           50  insulation cover 
           60  deion plate 
           70  contact member stop 
           80  blow-out channel 
           100 ,  200  connecting contact 
           110 ,  210  movable contact member 
           120 ,  220  current bar 
           130 ,  230  rotary shaft 
           140 ,  240  compression spring 
           150 ,  250  support element 
           151 ,  251  straight pin 
           160 ,  260  loose contact 
           170 ,  270  stationary connector 
           180 ,  280  flexible connecting member 
           190 ,  290  arc chute