Abstract:
A release unit for a circuit breaker is equipped with a magnet yoke and an armature collaborating with it for actuating a release device, in which case a nonmagnetic weight element that increases the inertia of the armature is applied to the armature.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a selective release unit for a circuit breaker.  
         BACKGROUND OF THE INVENTION  
         [0002]    A release unit with an armature or gate and a yoke is known from the prior art. If the gate is applied, it has to shift the front gate further so that a brief high current does not result in release. The insertion of a magnet flap in a direction leading away from the magnet yoke in order to brake the magnet flap in its closing movement is also known from the prior art. It is thus possible to prevent a release in the case of brief overcurrents.  
           [0003]    One disadvantage of prior art solutions is that in circuit breakers switched in series with one large and several small parallel circuit breakers, the disengagement of one of the small circuit breakers could possibly lead to disengagement of the large circuit breakers, such that the entire operation no longer has any current. But only the subordinate breakers should release in the case of a strong overcurrent or short circuit. For example, selectivity should be achieved in circuit breakers up to 10 kA such that no disengagement occurs with a current of 3 kA at 5 msec in large circuit breakers.  
           [0004]    A release mechanism for a circuit breaker shown in FIG. 6 is known from the earlier German patent application No. 199 03 911.9. This breaker  1  has a moveable contact  2  that is rotatably supported on the shaft  3  of a selector shaft  4 . The selector shaft  4  is itself supported in a polhode housing (not shown) and has two diametrically opposed satellite shafts  5  and  6  that are entrained around the axis  3  with a rotation of the selector shaft  4 . The axis  5  is the point of application for an articulation mechanism  7  that is connected with a ratchet lever  8 . The ratchet lever is pivotably supported on a shaft  10  positioned on the breaker housing  9  and is released in the case of an overcurrent or short circuit by a breaker latch  11  to enable the separated state of the contact  2  shown in FIG. 6.  
           [0005]    The breaker latch  11  can be actuated by a release lever  13  pivotable around a rotation axis  12 . The release lever  13 , on the other hand, is in working connection with a release shaft  14  that is supported on a shaft  15  carried by the breaker housing  9 . A lifter  16  is formed on the release shaft  14 , which is pivotable against the force of a spring wound around the shaft  15  (not shown in detail here) in the clockwise direction in FIG. 6.  
           [0006]    A magnet yoke  17  is mounted on the breaker housing  9  in the lower section of the circuit breaker and encompasses an electric rail  19  connected with the contacts of the breaker  1 . An armature element  21  designed as a flap is located opposite the magnet yoke  17  and it is pivotably connected via a hinge connection  18  with a stationary section of the circuit breaker (not shown in detail). The flap  21  is also connected through a spring  20  with a stationary section of the rail  19 , said spring acting on the flap in the clockwise direction. In its upper region, as shown in Figure the flap  21  is equipped with a bracket  23  permanently attached to it which, by a pivoting movement of the flap  21 , can be brought into contact with the cam  16  to rotate the release shaft  14 , thereby actuating the breaker latch  11  via the release lever  13  and thus initiating the disengagement process in the circuit breaker  1 . Reference is made to the description of the above-mentioned German patent application for further details on this prior solution.  
         SUMMARY OF INVENTION  
         [0007]    The purpose of the invention is to make available a selective release unit, which, if incorporated in a large circuit breaker, does not cause release of the latter if release occurs in a subordinate smaller circuit breaker. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0008]    The invention is explained in the following on the basis of two embodiments, with reference to the drawings.  
         [0009]    [0009]FIG. 1 is a perspective view of a selective release unit.;  
         [0010]    [0010]FIG. 2 is a front view of a circuit breaker equipped with the release unit shown in FIG. 1;  
         [0011]    [0011]FIG. 3 is a perspective view of the circuit breaker shown in FIG. 2;  
         [0012]    [0012]FIG. 4 is a front view of a circuit breaker equipped with an alternate embodiment of the release unit;  
         [0013]    [0013]FIG. 5 is a perspective view of the circuit breaker shown in FIG. 4;  
         [0014]    [0014]FIG. 6 is a representation of the prior art mechanism of a circuit breaker with a relevant release unit. 
     
    
     DETAILED DESCRIPTION  
       [0015]    According to a first embodiment, the selective release unit has essentially the same construction as in FIG. 6, except that a weight  25  of 3-15 g, preferably 9-11 g, is applied to the flap  21  on the side of the flap facing away from the magnet yoke  17 . As a result of this measure, the inertia of the flap is increased sufficiently to prevent the flap from closing immediately after a short circuit. It is obvious here that the size of the weight is designed by taking into account the characteristics of the spring shown in FIG. 2 and the other characteristics of the breaker system so that no release is induced if a release occurs in a subordinate smaller circuit breaker. This embodiment involves a circuit breaker with a nominal current of 125 A, in which an overcurrent 50 times the nominal current develops within 1 msec.  
         [0016]    As shown in FIG. 2, bimetallic plate  27  (not shown in detail in FIG. 1) is applied in the U-shaped magnet yoke  17  and is located with its lower section  29  on the rail  19 . Along the remaining section, the bimetallic plate  27  is separated by an air gap from the rail  19  running upward in FIG. 2.  
         [0017]    The release unit described above functions as follows: If the current flowing through the rail  19  exceeds a nominal current by 5-30%, heating of the bimetallic plate  27  occurs such that the upper section of the bimetallic plate effects actuation of the breaker latch  11  and produces a release movement. In the case of a short circuit current exceeding an overcurrent, the flap  21  is drawn to the magnet yoke  17 , while a current strength sufficient to release a subordinate circuit breaker draws the flap  21  provided with the weight element  25  to the magnet yoke  17  only to a certain degree, under the additional braking action of the spring  22 . During this last process, release is not yet reached, which assures selectivity with regard to the subordinate breakers. The spatial arrangement of the above components of the release unit is evident from the representation in FIG. 3.  
         [0018]    The second embodiment of the release unit according to the invention, as shown in FIGS. 4 and 5, differs from the first one in that an external L-shaped part of the rail  19  is designed as a conductor element  31  separated from the rest of the rails, and is connected through a conducting arm  33  and a flexible lead connected to it with the upper section of the bimetallic plate  27 . This construction has essentially the same characteristics as the first embodiment, with the additional advantage that as a result of the current flowing through the bimetallic plate  27 , direct heating of the latter and thus a response of the release mechanism of the circuit breaker can also be guaranteed with lower overcurrents.  
         [0019]    Different variants of the above-mentioned embodiments of a release unit according to the invention are possible; they are defined to some extent in the subclaims. For example, the rails  19  and the conducting element  31  can advantageously be of copper in the second embodiment. It is also advantageous in this second embodiment if the rail  19  does not run simply as a broad strip through the U-shaped magnet yoke, as in the first embodiment, but also runs outside of the magnet yoke.  
         [0020]    Although the present invention has been described with reference to certain embodiments, it will be appreciated that these embodiments are not limitations and that the scope of the invention is defined by the following claims.