Patent Publication Number: US-2002011908-A1

Title: Circuit breaker with electro-magnetic trip apparatus

Description:
BACKGROUND OF THE INVENTION  
       [0001] The invention relates to a circuit breaker for interrupting an electric circuit in the detection of an overcurrent exceeding a rated value, and more particularly to a circuit breaker for interrupting an electric circuit in the detection of an overcurrent exceeding a rated value in which the detection of a predetermined overcurrent and following shut-off operation of an electric circuit may be carried out electro-magnetically.  
       [0002] In general, circuit breakers for electric lines in houses are used to prevent any electricity induced fires from taking place. The circuit breaker for an electric line is adapted to interrupt an electric circuit when electric currents in use exceed a rated value while a load is being applied, or when any instantaneous overcurrent takes place.  
       [0003] In the case of persistent low levels of overcurrent, the overcurrent heats a circuit breaker while passing through it, and thus a bimetal within the circuit breaker bends due to the heat. Bending of the bimetal also flexes an armature which is integrally attached to the bimetal. The flexed armature is separated from a latching means into which the armature is engaged and thus causes a trip mechanism to operate. Then, an electric circuit within the circuit breaker is interrupted, thereby interrupting the whole electric circuit. Such an interruption is referred to time-lag tripping. In time-lag tripping, an electric circuit is regulated to be shut off within 1 hour under the overcurrent of about 135% of a normal alternating current, and within 4 minutes under about 200%.  
       [0004] In the case of a phase-to-phase short caused by a motor tool or a metal object at the load side, a higher level of instantaneous overcurrent takes place. The overcurrent magnetizes a magnetic yoke within the circuit breaker to attract the armature thereby interrupting the electric circuit. The magnetic yoke, which is provided around the bimetal in the form of a stationary iron core, can be magnetized instantly on any overcurrent to interrupt an electric circuit within a very short time. Therefore, such an interruption is referred to as instantaneous tripping.  
       [0005] The foregoing two types of trippings, i.e., time-lag tripping and instantaneous tripping are widely adapted to conventional circuit breakers for electric lines. These types of trippings are disclosed in various documents including U.S. Pat. No. 4,080,582 entitled “Circuit Breaker with Improved Trip Mechanism.”  
       [0006] The foregoing time-lag tripping which uses a bimetal, however, may have the following problems:  
       [0007] First, it is required to arrange a bimetal and an armature within a circuit breaker as combined in a predetermined angle relative to each other, so that the armature may bend as the bimetal bends and thus being released from engagement with the latching means. However, there may be disadvantages that a very precise operation is required to form this arrangement, and that the bimetal and the armature also may not carry out the desired precise cooperation even though arranged as above.  
       [0008] Second, the bimetal is induced to bend by heat produced in the electric circuit or the electric line by an overcurrent. Therefore, the electric line is continuously exposed to heat until the electric circuit is interrupted by a time-lag tripping.  
       [0009] In particular, the time-lag tripping requires a high temperature state to be continued for more than a predetermined amount of time, thereby causing the electric line to be heated for a long time. Covering material of the electric line undergoes thermal degradation when the high temperature state takes place repeatedly. This thermal degradation is caused when the covering material is heated for a long time, and thus the covering material loses its own characteristics. The electric line then has a very weak physical state or fragility to any outer impact, and also tends to generate arc thereby causing fire. In short, the mechanical tripping method of the prior art based on the bending of the bimetal and the armature coupled thereto suffers from thermal degradation of the covering material and thus makes electric line structure frail.  
       [0010] To solve the foregoing problems, a circuit breaker which can perform tripping in a relatively lower overcurrent to interrupt an electric circuit is proposed in documents such as U.S. Pat. No. 4,933,653 entitled “Circuit breaker with low current magnetic trip”. In the foregoing document, it is disclosed, trip means which comprises a supplemental bimetal and armature so that tripping can be carried out in a lower overcurrent to improve workability. However, even in the foregoing arrangement, it is very difficult to precisely arrange the bimetal and the armature so that they can cooperate to perform tripping. Also, it is hardly expected that the bimetal and the armature can perform a precise operation as desired even when arranged as above. Furthermore, this tripping also requires a certain amount of lag time so that the problem of the electric line and the covering material thereof may be heated and thus degraded.  
       SUMMARY OF THE INVENTION  
       [0011] Considering the foregoing problems, it is an objective of the invention to provide a circuit breaker which has a bimetal and an armature arranged as separated, and electro-magnetically performs overcurrent detection, tripping control and tripping operation.  
       [0012] It is another object of the invention to provide a circuit breaker which can be electro-magnetically operated, thereby preventing degradation of the covering material of the electric line due to any mechanical time-lag tripping.  
       [0013] According to an embodiment of the invention to obtain the foregoing objects, it is provided a circuit breaker for interrupting an electric circuit in detection of an overcurrent exceeding a rated value, the circuit breaker comprising: detection means for detecting the flow of overcurrent exceeding a predetermined rated value in the electric circuit from the bending of a bimetal, and creating a detection signal; control means for sending an tripping signal in response to the detection signal from the detection means; and trip means being electro-magnetically operated in response to the tripping signal from the control means to interrupt the electric circuit.  
       [0014] The trip means may comprise a stationary contact; rotation means provided with a movable contact which can be butted with the stationary contact; latch means engaged into the rotation means for rotating the rotation means; an armature for gripping the latch means; a solenoid being operated in response to the tripping signal from the control means; and trigger means detachably engaged into the armature for drawing the armature in response to the operation of the solenoid. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0015] The foregoing objects and other advantages of the invention will be more apparent by describing in detail the preferred embodiments thereof with reference to the accompanying drawings, in which;  
     [0016]FIG. 1 to FIG. 4 are plane views of a circuit breaker of the invention with the cover thereof being removed for illustrating steps of electromagnetic tripping;  
     [0017]FIG. 5 is a perspective view of an armature and a latching mechanism in use for the circuit breaker of the invention;  
     [0018]FIG. 6 is an exploded perspective view for illustrating relations among a solenoid, a trigger mechanism and an armature in use for the circuit breaker of the invention;  
     [0019]FIG. 7 is a block diagram for illustrating a concept of the circuit breaker of the invention;  
     [0020]FIG. 8 is a circuit diagram of the circuit breaker of the invention;  
     [0021]FIG. 9 is an exploded perspective view of a part of the circuit breaker shown in FIG. 1;  
     [0022]FIG. 10A is a plane view for illustrating an arc quencher of the invention;  
     [0023]FIG. 10B is a perspective view of a grid in use for the arc quencher of the invention;  
     [0024] To FIG. 11A is a bottom view of a bimetal-magnetic yoke assembly of the invention;  
     [0025]FIG. 11B is a vertical sectional view taken in I-I line of FIG. 11 a;    
     [0026]FIG. 11C is a vertical sectional view similar to FIG. 11 b,  which is taken from another example of a bimetal-magnetic yoke assembly of the invention; and  
     [0027]FIG. 12 is a vertical sectional view of a bimetal-magnetic yoke assembly of the prior art. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0028]FIG. 1 to FIG. 4 are plane views of a circuit breaker of the invention with the cover thereof being removed for illustrating steps of electromagnetic tripping. Basic arrangement of the circuit breaker of the invention will be understood with reference to FIG. 1 to FIG. 4.  
     [0029] The reference numeral  100  indicates a circuit breaker of the invention. The circuit breaker  100  has a housing  101 , which is made with an insulating material with resistance to impact and heat such as high strength plastic. A plurality of screw holes  102  are provided in the section of the housing  101  for fixing a cover(not shown) to be coupled to the same. At the upper right side of the housing  101 , a rotating mechanism  110  with a handle  111  is arranged. At the left side of the rotating mechanism  110 , a movable member  112  which has one end engaged into a recess of the rotating mechanism  110  is arranged. Also, at the left side of the rotating mechanism  110 , a latching mechanism  115  is arranged with a recess in the middle thereof. A coil spring  114  is provided with one end secured to the movable member  112  and the other end to the rotating mechanism  110  to restrain the movable member  112  to the recess of the rotating mechanism  110 . The latching mechanism  115  is pivotally coupled into a keeper pin  103  integrally formed with the housing  101  at the upper end thereof, and defines a catch  116  at the lower end thereof. The catch  116  is inserted into a slot of an armature  140  shown in more detail in FIG. 5, which is placed under the catch  116  and latches onto the inserted catch  116 .  
     [0030] The movable member  112  has a movable contact  113  at the free end, which is butted into a stationary contact  156 . The stationary contact  156  is provided to the second power terminal  155  which is arranged in the upper left side of the housing  101 . These contacts  113 ,  156  are made with a material which has good electric conductivity together with sufficient strength to withstand frequent contact and separation therebetween. Examples of the material include silver, tungsten, silver-tungsten alloy, silver-cadmium alloy, sintered alloy thereof, carbon sintered alloy thereof, and etc. The contacts made of these materials are fixed to the movable member  112  and the second power terminal  155  by way of a suitable operation such as spotting or riveting.  
     [0031] Under the second power terminal  155 , three grids are arranged which will be described in detail later with reference to FIG. 10A and FIG. 10B.  
     [0032] Under the armature  140  in the lower part of the housing  101 , a bimetal  120  is arranged which is surrounded in part with a magnetic yoke  121 . The bimetal  120  has a free end  120   a  attached with a wire  105   a  which electrically connects the bimetal  120  to the foregoing movable member  112 . The bimetal  120  has a stationary end  120   b  opposed to the free end  120   a,  which is fixed to a connecting member  123  via riveting or spotting. The connecting member  123  has the shape of r and fixed to the housing via a screw  124 . The connecting member  123  is attached with a wire  105   b  which is connected to another contact  106  in the side of the first power terminal  150 . Therefore, the bimetal  120  is electrically connected to the second power terminal  155  via the wire  105   a,  the movable member  112  and the contacts  113 ,  156  in the free end  120   a  side, and to the first power terminal  150  via the connecting member  123 , the wire  105   b  and the contact  106  in the side of the stationary end  120   b.    
     [0033] A calibration plate  130  is arranged under the free end  120   a  of the bimetal  120  with a predetermined distance. The calibration plate  130  is supported by a sensitive screw  131  which is shown only in part since covered with a screw cover  132 . Also, the calibration plate  130  is electrically connected to a SCR, i.e. semiconductor controlled rectifier, which is arranged on a circuit board  107  and shown in FIG. 8.  
     [0034] The SCR is connected to a solenoid  133  and a ground terminal via the circuit board  107 . The solenoid  133  is arranged in the lower central part of the drawing and the ground terminal is not shown since it is arranged under the first power terminal  150 . Solenoid  133  is connected to the first power terminal  150  and the SCR via the circuit board  107 . Therefore, it can be understood that the first power terminal  150 , the solenoid  133 , the SCR and the ground terminal are connected via the circuit board  107 . The electrically connected relation of these elements arranged in the circuit board  107  will be described in detail later with reference to FIG. 7 and FIG. 8.  
     [0035] In general, the SCR controls input and output of load according to a signal voltage applied to a gate terminal. Herein, the signal voltage means a voltage applied to the calibration plate  130 . Therefore, when the bimetal  120  bends by the heat generated from any overcurrent flowing through the circuit breaker  100  which exceeds a rated value thereby causing the free end  120   a  of the bimetal  120  to come in contact with the calibration plate  130 , the SCR is applied with a signal voltage from the calibration plate  130  side and thus electrically connect the solenoid  133  and the ground terminal in response to the signal voltage. In this case, the solenoid  133  is connected to the SCR in one end and to the first power terminal  150  in the other terminal via the circuit board  107  so that electricity can be supplied to the solenoid  133 . Therefore, the solenoid is in a parking position in the natural state, and in operating position when the SCR is operated and thus generates a magnetic force.  
     [0036] Time-lag tripping of the circuit breaker of the invention according to the operation of the solenoid  133  will be described hereinafter in the reference to FIG. 2 and FIG. 3.  
     [0037] When the solenoid  133  generates a magnetic force, a plunger  135  is attracted and moved toward the solenoid  133  along a guide passage  134   a  which is shown in more detail in FIG. 6 as defined within a guide member  134 . Then, the plunger  135  draws a trigger  136  engaged thereinto toward the solenoid  133 . In this case, the trigger  136  which is also engaged into the armature  140  draws the armature  140  downward. Then, the armature  140  pivots clockwise thereby releasing the catch  116  of the latching mechanism  115  which is latched thereto. When the catch  116  is released from the armature  140 , the latching mechanism  115  pivots clockwise about the upper end thereof which is coupled with the keeper pin  103 , and thus the rotating mechanism  110  which is coupled with the latching mechanism  115  also pivots clockwise. Then, the coil spring  114  attached to the movable member  112  is applied with tension, and thus the movable member  112  is drawn downward. As a result, the movable member  112  rotates counter clockwise abruptly due to the elasticity of the coil spring  114  and thus the movable contact  113  is separated from the stationary contact  156 . The time-lag tripping is carried out like this. Again, the latching mechanism  115  and the rotating mechanism  110  connected to the movable member  112  moves up to the position where the handle  111  is in a substantially horizontal position as shown in FIG. 2.  
     [0038] Then, as shown in FIG. 3, the movable member  112  further rotates counter clockwise due to the elasticity of the coil spring  114 , the latching mechanism  115  rotates the reverse way instead to return to the original position, and the rotating mechanism  110  further rotates clockwise so that the handle  111  is oriented in the right downward direction.  
     [0039] Again, as shown in FIG. 2 and FIG. 3, when the movable contact  113  is separated from the stationary contact  156  and thus the electric circuit is interrupted, the solenoid  133  does not operate. Then, the magnetic force is not generated any longer and thus the attraction to the plunger  135  disappears. As a result, the drawing force of the plunger  135  to the armature  140  via the trigger  136  disappears also.  
     [0040] When the drawing force disappears, the armature is returned into the initial position by the return means.  
     [0041] The return means comprises a flange  142  formed at first end of the armature  140 , a spring  143  pressing a first face of the flange  142 , a first supporting member  104   a  provided adjacent to a second face of the flange  142  for supporting the flange  142  and a second supporting member provided beyond the spring  143  from the first face of the flange  142  to support the spring  143 .  
     [0042] The armature  140  is provided with a flange  142  in the end remote from the slot  141 . The flange  142  is supported in one face which is remote from the slot  141  by the first supporting member  104   a.  The flange  142  is supported in the other face adjacent to the slot  141  by a spring  143  which is supported by a second supporting member  104   b.  Then, the armature  140  is forced to pivot counter clockwise from the position parallel with the bimetal  120 . As a result, when the solenoid  133  does not operate, the armature  140  pivots counter clockwise to return to its initial position as shown in FIG. 4, thereby gripping the catch  116  of the latching mechanism  115  again.  
     [0043]FIG. 5 is a perspective view of an armature and a latching mechanism in use for the circuit breaker of the invention.  
     [0044] The armature  140  has a slot  141  adjacent to one end, and a flange  142  at the other end. In the latching mechanism, only the catch  116  is shown. The catch  116  is gripped when inserted and engaged into the slot  141 , thereby fixing the latching mechanism  115 .  
     [0045]FIG. 6 is an exploded perspective view for illustrating relations among a solenoid, a trigger mechanism and an armature in use for the circuit breaker of the invention.  
     [0046] The solenoid  133  has a recess  133 a which is adapted to receive the tubular body of the guide member  134  and surround the same. The guide member  134  has a guide passage  134   a  and 2 stop members  134   b.  The guide passage  134   a  is defined within the tubular body of guide member  134  and adapted for the plunger  135  to move through the same. The stoppers  134   b  are defined in the front part of the guide member  134  to be butted against a front flange  136 a of the trigger  136  which is drawn by the plunger  135 . When the plunger  135  is moved to a predetermined distance, the front flange  136   a  of the trigger  136  is blocked by the stoppers  134   b  and thus the trigger  136  is stopped from moving.  
     [0047] The plunger  135  has a head  135   a  and a neck  135   b  which has a smaller diameter than the head  135   a.  The trigger  136  has a first opening  136   b  defined in the front part of the base of the trigger  136  and in the lower part of the front flange  136   a,  and a second opening  136   c  continued from the first opening  136   b  and having a width which is narrower than the first opening  136   b.  Therefore, when the plunger  135  is moved with the head  135   a  beyond the flange  136   a  through the first opening  136   b  in the left direction and then upward, the neck  135   b  is fit in the second opening  136   c.  Then the plunger  135  and the trigger  136  engage to move together. Again, the trigger  136  has a rear flange  136   d  opposed to the front flange  136   a.  The trigger  136  can draw the armature  140  with the rear flange  136   d.    
     [0048]FIG. 7 is a block diagram for illustrating a concept of the circuit breaker of the invention, and FIG. 8 is a circuit diagram of the circuit breaker of the invention.  
     [0049] Referring to FIG. 7, reference numeral  500  means an overcurrent detector which delects any overcurrent flow exceeding a predetermined rated value,  600  means a tripping controller responsive to a detecting signal from the overcurrent detector  500 , and  700  means a tripping part for carrying out a tripping operation in response to a signal from the tripping controller  600 .  
     [0050] The overcurrent detector  500  includes various electric components such as the foregoing bimetal  120  and calibration plate  130 , the tripping controller  600  also includes various electric devices such as the foregoing SCR. The tripping part  700  includes the foregoing devices which actually perform tripping operation such as a solenoid  133 , guide member  134 , plunger  135 , trigger  136 , armature  140 , latching mechanism  115 , rotating mechanism  110 , movable member  112  and etc.  
     [0051] Hereinafter, the tripping operation of the circuit breaker  100  of the invention will be described with reference to FIG. 7 and FIG. 8.  
     [0052] In FIG. 8, SW 1  means a combination of devices such as the bimetal  120 , the calibration plate  130  and a diode D 19  of the overcurrent detector  500 , and SW 2  means a combination of the devices of the tripping part  700  with an exception to the solenoid S or  133 .  
     [0053] In the case of rated current, the current flows between 2 power terminals HOT 1 , HOT 2  via the SW 2  and the bimetal of the SW 1 . But, when the overcurrent exceeding the rated value flows through the circuit, a portion of the current proceeds to the SCR of the tripping controller  600  via the foregoing devices in the SW 1  such as the diode D 19 , a resistance R 36 , a diode D 17  and a resistance R 34  due to bending of the bimetal, thereby applying a signal voltage to the SCR. Then, the SCR electrically connects the solenoid S and a ground terminal NEU, and thus the solenoid S is magnetized. When the solenoid S is magnetized, the SW 2  is tripped to interrupt any current between the 2 power terminals HOT 1 , HOT 2 .  
     [0054] In FIG. 8, the diode D 19  is for rectifying any half wave from the SCR to the SW 1 , and the resistance R 13  and a capacitor C 9  are for preventing any erroneous operation of the SCR. At the right side of the SCR, 4 diodes D 3 , D 4 , D 5  and D 6  are arranged to rectify current flow.  
     [0055] When the overcurrent detector  500  detects any overcurrent, the signal or a portion of the current is also sent to an light emitting diode (LED) via D 19 , R 36  and R 35  to light the LED. Then, the user of the circuit breaker  100  of the invention can acknowledge that an overcurrent took place and thus the circuit breaker  100  carried out a time-lag tripping.  
     [0056]FIG. 9 is an exploded perspective view of a part of the circuit breaker shown in FIG. 1.  
     [0057] The first power terminal has a screw hole  150   a  which is screwed with a bolt  151 . The contact  106  is inserted into an opening  150   b  of the first power terminal  150 . The bolt  151  is inserted into the recess  106   a  of the contact  106  thus pressing the contact  106  against the inner wall of the first power terminal  150  to fix the same. Then, the outer power supply which is connected with the first power terminal  150  will be stably connected with the inner circuit of the circuit breaker  100  of the invention via the contact  106  and the wire  105   b.    
     [0058] The bolt  151  is generally made with metal. But, in the invention, the bolt  151  can be made with an insulating polymer. It is preferred that the insulating polymer used for the bolt  151  of the invention has a melting point of about 200 to 400° C. and a Rockwell hardness of about 100 to 200. In this case, examples of the insulating polymer may include polyvinylchloride, polypropylene, polystyrene, polyvinylalcohol, polymethylmetaacrylrate, polyvinylidenechloride(PVC), celluloseacetate, cellulose-3-acetate acetylbutylcellulose, poly-4-methylphentene, polytrifluoroethylene, polytetrafluoroethylene copolymer, polychloroethylene, tetrachloroethylene-hexafluoropropylene copolymer, tetrafluoroethylene copolymer, polychloroethylene, tetrachloroethylenehexafluoropropylene, nylon  6 , polyphenylideneoxide, polybutyleneterephtarate, polyethyleneterephtarate and polyolefin; compounds thereof; composites made with these resins; and etc.  
     [0059]FIG. 10A is a plane view for illustrating an arc quencher of the invention, and FIG. 10B is a perspective view of a grid in use for the arc quencher of the invention. Hereinafter, it will be described with reference to FIG. 10A together with FIG. 10B for the sake of brevity.  
     [0060] In FIG. 10A, a plurality of dotted lines around the contacts  112 ,  156  mean arc, which is generated when the contacts  112 ,  156  are separated, and arrows mean flow of the arc. The majority of the arc is absorbed by 3 metal grids  160 . Then, the rest of the arc proceeds along an arc passage  161  defined between the housing  101  and a middle plate  108  and reaches a damping space  162 , where the remaining arc is damped and extinguished. Therefore, a minute amount of the arc can be discharged from the circuit breaker  100  through an arc outlet  163 . In this way, the arc is discharged only in a minute amount thereby preventing any probability of the arc induced fires.  
     [0061] The grids  160  are configured as a thin plate with a thickness of about 1 to 3 mm. Each of the grids  160  has a U-shaped indent  160   a  for providing a space adapted for the rotating member  112  to pivot, and a slit  160   b  for enlarging an absorbing area of arc. Each of the grids  160  is preferably distanced at about 2 to 4 mm from the next so that the arc can be properly absorbed and any arc induced deposition can be prevented from taking place at the same time.  
     [0062]FIG. 11A is a bottom view of a bimetal-magnetic yoke assembly of the invention, FIG. 11B is a vertical sectional view taken in I-I line of FIG. 11A, FIG. 11C is a vertical sectional view similar to FIG. 11B, which is taken from another example of a bimetalmagnetic yoke assembly of the invention, and FIG. 12 is a vertical sectional view of a bimetal-magnetic yoke assembly of the prior art. Hereinafter, it will be described with reference to FIG. 11A to FIG. 12 together for the sake of brevity.  
     [0063] First, referring to FIG. 1 to FIG. 4 again, the magnetic yoke  121  is arranged around the bimetal  120  under the armature  140 . As soon as an instantaneous overcurrent is induced by a phase-to-phase short in a current circuit, the magnetic yoke  121  is magnetized and thus draws the armature  140  from above. Then the latching mechanism  115 , the rotating member  112  and etc. cooperate to carry out tripping operation, thereby interrupting the current circuit. In this way, when an instantaneous overcurrent takes place, an instantaneous tripping is carried out without passing any time-lag tripping which requires a long time for interruption of the circuit.  
     [0064] Referring to FIG. 12, a magnetic yoke  21  of the prior art is perforated in the upper plane, and then a rivet  22  is inserted into the perforated part of the magnetic yoke  21  so that the magnetic yoke  21  can be attached around a bimetal  20 .  
     [0065] However, in the invention, the upper plane of the magnetic yoke  121  is impressed onto the bimetal  120  via pressing or punching in order to form a projection  121   a  which contacts the bimetal as shown in FIG. 11B. Then, the projection  121   a  is spotted and fixed to the bimetal  120  so that the magnetic yoke  121  can be fixedly attached around the bimetal  120 .  
     [0066] Again, in FIG. 11C, the upper plane of the magnetic yoke  221  can be provided with a projection  221   a  in the lower part by spotting without any punching or pressing. Then, the magnetic yoke  221  can be supported on the upper face of the bimetal  120  with the projection  221   a.    
     [0067] According to the invention, the circuit breaker of the invention has a bimetal and an armature, which are provided separately so that the detection of any overcurrent, tripping control and tripping operation can be carried out electro-magnetically in a tripping of a circuit.  
     [0068] Therefore, fabrication of the bimetal and the armature is easy and productivity in fabrication of the circuit breaker is increased. Also, a precise and rapid tripping can be carried out when overcurrents take place. Furthermore, time required for the time-lag tripping is reduced due to the rapid tripping and thus the degradation of a covering material can be reduced.  
     [0069] Hereinabove the invention has been described in reference to the preferred embodiment, but various other modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the present invention as defined in the appended claims.