Abstract:
A tripping unit is configured to send an electrical tripping-signal to a switching unit of a circuit breaker so as to trip main contacts of main circuits of the circuit breaker in response to a detection of a current being above a predetermined level in at least one of the main circuits. The tripping unit includes a fuse configured to be connected in series to a main circuit of the circuit breaker and a detection unit connected in parallel with the fuse and configured to generate the tripping signal for the switching unit in response to the fuse being blown.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to European Patent Application No. EP 10 165 233.7, filed Jun. 8, 2010, which is hereby incorporated by reference herein in its entirety. 
       FIELD 
       [0002]    The invention relates to a tripping unit for tripping the main contacts of main circuits of a circuit breaker by sending an electrical tripping-signal to a switching unit of the circuit breaker when a current above a certain level is detected in at least one of the main circuits. 
       BACKGROUND 
       [0003]    Circuit breakers can be configured as motorcircuit breakers or as automatic circuit breakers that are employed to switch a load on and off and that have a protective function by separating or interrupting the load in case of an electrical fault. Electrical faults can be e.g. short circuits or overcurrents. Such circuit breakers comprise essentially a base module, a manual actuating device, an electronic control unit, an actor unit and a tripping element. Through the use of the manual actuating device, at least a switching mechanism is activated by means of a rotary knob and of an actuating shaft, whereby the actuating device is accommodated in a housing part that protrudes from the operating front of the circuit breaker. 
         [0004]    As a motor circuit breaker, circuit breakers can have a tripping behavior that is adapted to the electric motor to be protected, or which serve as line circuit breakers to protect electric lines or systems against thermal overload or short-circuit damage. The tripping behavior and thus the use of such circuit breakers are determined by the thermal and short-circuit tripping values. To implement different tripping behavior in a circuit breaker, it is well known in the state of the art to build up a modular circuit breaker which includes a replaceable tripping module. 
         [0005]    The German patent application DE 36 42 719 A1 describes a manually operated protective circuit breaker which comprises a plug-in exchangeable overcurrent tripping unit. 
         [0006]    These tripping units can comprise very complex mechanical and/or electrical parts and the production of these kind of tripping units can be very expensive. 
         [0007]    Another drawback of such similar circuit breakers is that the thermal elongation, which activates the tripping unit, must be very high. 
       SUMMARY 
       [0008]    In an embodiment, the present invention provides a tripping unit configured to send an electrical tripping-signal to a switching unit of a circuit breaker so as to trip main contacts of main circuits of the circuit breaker in response to a detection of a current being above a predetermined level in at least one of the main circuits. The tripping unit includes a fuse configured to be connected in series to a main circuit of the circuit breaker and a detection unit connected in parallel with the fuse and configured to generate the tripping signal for the switching unit in response to the fuse being blown. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Exemplary embodiments of the invention are described in more detail below, with reference to the drawings, in which: 
           [0010]      FIG. 1   a  is a schematic depiction of a front view of a tripping unit; 
           [0011]      FIG. 1   b  is a schematic depiction of a side view of a tripping unit; 
           [0012]      FIG. 2  is a schematic depiction of the internal assembly of a tripping unit; 
           [0013]      FIG. 3  is a schematic depiction of the circuit breaker and a tripping unit drawn in form of a block diagram. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    An aspect of the present invention is to provide at tripping unit that overcomes the above drawbacks. In an embodiment of the present invention a tripping unit for tripping the main contacts of main circuits of a circuit breaker by sending an electrical tripping-signal to a switching unit of the circuit breaker when a current above a certain level is detected in at least one of the main circuits is characterized in that the tripping unit comprises at least one fuse which is connected in series to a main circuit of the circuit breaker and wherein a detection unit which is connected in parallel to the at least one fuse is adapted to generate the tripping-signal for the switching unit after at least one of the fuses is blown. A fuse, especially a micro-fuse, reacts very fast in case of an over-current. A fast reaction time of the fuse results in a high protection of connected devices such as drives and motors. It is also cost effective to just replace a blown fuse instead of replacing the whole tripping unit. 
         [0015]    In an embodiment of the invention, each main circuit of the circuit breaker is connected in series with a fuse of the tripping unit. In this embodiment, all main circuits can be controlled by the tripping unit of the circuit breaker. 
         [0016]    In a further embodiment of the invention, the detection unit comprises a rectifier package which rectifies the electrical tripping-signal for the switching unit after the fuse is blown. A rectified tripping-signal can be easier to handle in the electronic part of the switching unit. 
         [0017]    In a further embodiment of the invention, a resistor is connected in series with the rectifier package to reduce the voltage of the rectified electrical tripping-signal for the switching unit after the fuse is blown. A low current value means that smaller electrical components can be used which is cost effective. 
         [0018]    In a further embodiment of the invention, the tripping unit is plugged into the circuit breaker. It is easy to replace the tripping unit with other tripping units comprising different parameters. 
         [0019]    In a further embodiment of the invention, the at least one fuse is removable arranged in the tripping unit. Advantageously the at least one fuse is screwable arranged in the tripping unit. It is easy to replace a blown fuse and reactivate the tripping unit. 
         [0020]    In a further embodiment of the invention, the at least one fuse is a micro-fuse. 
         [0021]    The invention further relates to a circuit breaker with a tripping unit which comprises the features described above. 
         [0022]      FIG. 1   a  and  1   b  depict a tripping unit  1  comprising a body which contains three fuses  11   a ,  11   b ,  11   c . The fuses  11   a ,  11   b ,  11   c  are reachable from outside the body of the tripping unit  1 . It is easy to replace a fuse  11   a,    11   b ,  11   c,  when it is blown. The fuses  11   a ,  11   b ,  11   c  are preferably screwed in a fuse fitting. The fuses  11   a,    11   b ,  11   c  can also be plugged against a spring force into a fuse fitting. Also other kinds of fittings are conceivable. 
         [0023]      FIG. 2  depicts the internal assembly of an embodiment of a tripping unit  1 . This embodiment comprises a tripping unit  1  including three fuses  11   a,    11   b ,  11   c.  It is also possible to build up a tripping unit including more or less fuses  11   a,    11   b ,  11   c.  The number of fuses  11   a,    11   b ,  11   c  depends on the number of main circuits  3   a,    3   b,    3   c  which should be controlled.  FIG. 3  is a schematic depiction of a circuit breaker  2  and a tripping unit  1 . For a clear view, only one fuse  11   c  is shown which is connected in series with one main circuit  3   c.    FIG. 2  and  FIG. 3  will be described in combination further on. 
         [0024]    The tripping unit  1  is plugged onto the circuit breaker  2  such that the connectors  12   a,    13   a,    12   b,    13   b,    12   c,    13   c  connect the fuses  11   a,    11   b ,  11   c  in series to the main circuits  3   a,    3   b,    3   c.  The connectors  16   a,    16   b  connect the switching unit  22  of the circuit breaker  2  to the tripping-signal line of the tripping unit  1 . The switching unit  22  is adapted to switch off the main contacts  23   a,    23   b,    23   c  when a tripping-signal from the tripping unit  1  is detected. It is also possible to switch the main contacts  23   a,    23   b,    23   c  by manually turning the main switch  21  of the circuit breaker  2 . When the switching unit  22  detects a tripping-signal and switches off the main contacts  23   a,    23   b,    23   c,  the main switch  21  of the circuit breaker  2  will also turn in an OFF-position. 
         [0025]    When a current above a specified value flows through one of the main circuits  3   a,    3   b,    3   c  and also through one of the fuses  11   a,    11   b ,  11   c  which is connected in series with the main circuits  3   a,    3   b,    3   c,  this fuse  11   a,    11   b ,  11   c  blows. The specified value of the current is the minimum current at which each of the fuses  11   a ,  11   b ,  11   c  blows. By inserting different kind of fuses  11   a ,  11   b ,  11   c  into the tripping unit  1 , different values could be selected at which the circuit breaker  2  switches off the main contacts  23   a,    23   b ,  23   c.  When one of the fuses  11   a,    11   b ,  11   c  is blown, a voltage applies to one of the detection unit  14   a,    14   b,    14   c  which is connected in parallel to the blown fuse  11   a ,  11   b ,  11   c.  The tripping signals of all detection units  14   a,    14   b,    14   c  are connected such that a single tripping-signal line and a single ground line are connected via the connector  16   a,    16   b  with the switching unit  22 . 
         [0026]    The detection unit  14   a,    14   b,    14   c  can be every kind of resistor or preferably a rectifier package which is adapted to rectify the alternating voltage on the main circuits  3   a ,  3   b,    3   c.  The tripping-signal which is generated by the rectifier package  14   a,    14   b,    14   c  can be detected by the switching unit  22  of the circuit breaker  2 . The current-value of the tripping-signal can be reduced by a resistor  15  which is connected in series to the tripping-signal line. After a tripping-signal is present at one of the rectifier packages  14   a,    14   b,    14   c,  the switching unit disconnects the main contacts  23   a,    23   b,    23   c  of the main circuits  3   a,    3   b,    3   c . Preferably an indicator light at the tripping unit  1  can indicate a blown fuse  11   a ,  11   b ,  11   c . Therefore the indicating light can be connected in series to the generated tripping-signal. Preferably every fuse  11   a ,  11   b ,  11   c  comprises an indicator light such that an operator can detect which fuse  11   a,    11   b ,  11   c  is blown. Therefore indicator lights must be inserted in parallel to each fuse  11   a,    11   b ,  11   c.    
         [0027]    After the problem in the main circuit  3   a,    3   b,    3   c,  which causes the over-current, is solved, the blown fuse  11   a ,  11   b ,  11   c  can be replaced by an operator. After the fuse  11   a ,  11   b ,  11   c  is replaced the main circuits can be switched on by turning the main switch  21  of the circuit breaker  2 . 
         [0028]    While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.