Abstract:
A trip device is disclosed, the device comprising: a power source side heater connected to a power source side of a molded case circuit breaker (MCCB) to receive current; a load side heater connected to a load side of the MCCB to receive the current; and a bimetal including a direct heat unit contacting the power source side heater and an indirect heating unit facing the power source side heater, wherein the bimetal is partially fixed between the power source side heater and the load side heater and is curved when over-current or short-circuited current flows in the MCCB.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is based on, and claims priority from, Korean Application Number 10-2008-0138852, filed Dec. 31, 2008, the disclosure of which is incorporated by reference herein in its entirety. 
     FIELD OF THE INVENTION 
     The present disclosure relates to a trip device, and more particularly to a trip device applied to a molded case circuit breaker (MCCB) which provide protection of electrical circuitry from damage due to an over-current condition when an electrical failure such as overload or short-circuit occurs. 
     DESCRIPTION OF THE RELATED ART 
     The molded case circuit breaker (MCCB) integrally housing an open/close device and a trip device in a vessel of an electrically-insulated material can open/close an electrical conductive path in response to manual or electrical manipulation, and protect an electrical circuitry from damage due to an over-current condition such as overload or a relatively high level short-circuit or fault condition by interrupting current. 
     In general, the MCCB refers to a circuit breaker in a molded case used for protection of an electrical circuitry of less than AC 600 volts or DC 250 volts. The MCCB is widely used to replace the conventional knife switch and fuse due to small size, easiness in manipulation and less cumbersomeness of maintenance or repair that requires replacement of fuse. 
     The trip device may be categorized into three types, that is, a bimetal type which carries out a trip operation by being heated and bending in response to a persistent over-current condition, an electromagnetic field type which operates by sucking a core in response to an electromagnetic field formed on a coil when an over-current flows, and an electronic type which adopts a microprocessor. 
     The trip characteristic is that trip activation is not operated even if a 100% rated current continuously flows but is operated for a predetermined period of time in a case when a current exceeding 125% or 150% of the rated current flows. 
     SUMMARY OF THE INVENTION 
     The present disclosure is directed to solve drawbacks of low-voltage circuit breaker and high-voltage circuit breaker and provide a multi-purpose trip device capable of improving sensitivity during interruption of over-current and obtaining reliability during interruption of short-circuited current. 
     In describing the present disclosure, detailed descriptions of constructions or processes known in the art may be omitted to avoid obscuring appreciation of the invention by a person of ordinary skill in the art with unnecessary detail regarding such known constructions and functions. Accordingly, the meaning of specific terms or words used in the specification and claims should not be limited to the literal or commonly employed sense, but should be construed or may be different in accordance with the intention of a user or an operator and customary usages. Therefore, the definition of the specific terms or words should be based on the contents across the specification. 
     In accordance with one general aspect of the present disclosure, a trip device comprises: a power source side heater connected to a power source side of a molded case circuit breaker (MCCB) to receive current; a load side heater connected to a load side of the MCCB to receive the current; and a bimetal including a direct heat unit contacting the power source side heater and an indirect heating unit facing the power source side heater, wherein the bimetal is partially fixed between the power source side heater and the load side heater and is curved when over-current or short-circuited current flows in the MCCB. 
     The trip device according to the present disclosure takes up both advantages of the direct heating type trip device and an indirect heating type trip device to be used as a multi-purpose trip device for both the low voltage and high voltage MCCBs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a lateral view illustrating an indirect heating type trip device as an imaginary comparative embodiment. 
         FIGS. 2 to 4  are lateral views illustrating various drawbacks of a direct heating type trip device as an imaginary comparative embodiment. 
         FIG. 5  is a lateral view illustrating a schematic diagram of a MCCB provided with a trip device according to the present invention. 
         FIGS. 6 and 7  are a lateral view and a perspective view of a trip device according to an exemplary embodiment of the present disclosure. 
         FIG. 8  is a lateral view of a trip device according to another exemplary embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     First of all, an explanation is given to an imaginary exemplary embodiment as compared with the present invention. 
     In a case when sensitivity is compensated for an over-current interruption to have a distinct difference for each section of a low voltage current in a low-voltage (40 A) MCCB, a trade-off may be generated that is weak in interruption of short-circuited current having an instantaneous peak value. Meanwhile, there is a drawback in a high voltage MCCB in that the over-current interruption characteristic is not distinct for each section of current size. 
     The bimetal may be classified into two types based on heating method, that is, an indirect heating type and a direct heating type.  FIG. 1  represents a lateral view illustrating a trip device of an indirect heating type as an imaginary comparative embodiment. 
       FIG. 1  depicts a trip device in which a current flows from a power source side to a load side in the order of stator  11 , a rotor  12  and a load terminal  15 . The stator  11  is connected to a power source side, while the rotor  12  is operated by an open/close device (not shown) to be switched where contact of the rotor  12  is switched to an ON/OFF position relative to the stator  11 . 
     The current bypasses a bimetal  13  to directly flow to a load side terminal  15 . The heating of the rotor  12  by the current applied to the power source side serves to heat the bimetal  13 , and the heated bimetal  13  is thermally deformed to activate the open/close device, whereby the stator  11  and the rotor  12  are disconnected to interrupt the over-current or the short-circuited current. 
     The trip device of  FIG. 1  is an indirect heating type trip device that heats the bimetal  13  by transmitting the heat of the rotor  12  using a heat transmission unit  14 , unlike the direct heating type trip device of  FIG. 2 . 
     The indirect heating type trip device may be adequate to a high voltage MCCB, because the bimetal  13  is not over-deformed over an entire area but is heated later by heat transmission to adjacent elements, compared to the direct heating type trip device that directly applies the current to the bimetal  13 . However, there is a limit in applying to a low voltage MCCB requiring sensitivity to over-current interruption, due to the fact that the bimetal  13  is not sensitively thermally-deformed to a narrow variation width of rated current. 
       FIGS. 2 to 4  are lateral views illustrating various drawbacks of a direct heating type trip device as an imaginary comparative embodiment, where a direct heating type trip device is depicted in which a current flows to a load side terminal  15  directly through the stator  11  and the bimetal  13 . 
     An armature  17  is instantly activated when a failure such as short-circuit is generated in a circuit to interrupt the current, where the armature  17  is therefore activated separately from the bimetal  13 . 
       FIG. 2  illustrates a portion (a) in which the bimetal  12  which is a combination of two different materials is melted and separated when a large current is interrupted, because the bimetal  13  is directly heated by a current at the power source side.  FIG. 3  illustrates a drawback in which a portion (b) welded by a wire between the load side terminal  15  and the bimetal  13  is separated due to weakness to heat, and  FIG. 4  illustrates a portion (c) in which the bimetal  13  is bent reversely due to over thermal deformation over an entire area. 
     The present disclosure provides a multi-purpose trip device that is incorporated with advantages and that compensates disadvantages of the indirect and direct heating type trip devices, and the multi-purpose trip device proposed in the present disclosure takes up only the advantages of the indirect and direct heating type trip devices to thereby be applied to low-voltage MCCB and high-voltage MCCB at the same time. 
       FIG. 5  is a lateral view illustrating a schematic diagram of an MCCB provided with a trip device according to the present invention,  FIGS. 6 and 7  are a lateral view and a perspective view of a trip device according to an exemplary embodiment of the present disclosure, and  FIG. 8  is a lateral view of a trip device according to another exemplary embodiment of the present disclosure. 
     The present disclosure now will be described more fully hereinafter with reference to  FIGS. 5 to 8 , in which exemplary embodiments of the present disclosure are shown. First of all, it will be understood that sizes or shapes of constituent elements may have been exaggerated for clarity and explanation of the description. Furthermore, terms and phrases used in the specification and claims may be interpreted or vary in consideration of construction and use of the present invention according to intentions of an operator or customary usages. The terms and phrases therefore should be defined based on the contents across an entire specification. 
     An MCCB according to  FIG. 5  may include a trip device  200  mounted inside a body  110  for tripping an over-current or a short-circuited current, an open/close device  130  comprised of a plurality of links for connecting or disconnecting a rotor  150  to and from a stator (not shown) at the power source side, and a warning device  140  for indicating the presence or absence of failure such as over-current or short-circuited current in association with the open/close device  130 . 
     The open/close device  130  may include a handle  131  rotatably supported by the body  110 , a latch  132  connected to the handle  131  to be changed in response to the rotation of the handle  131  and to move the rotor  150 , a latch holder  133  connected to the latch  132  to restrict the operation of the latch  132 , a driving pin  134  connected to the latch holder  133  to move in response to the movement of the latch holder  133 , and a cross bar  135  restricting the latch holder  133 . 
     The warning device  140  may include a micro switch  141  mounted inside the body  110  and having a contact point  144  thereunder, a switching lever  142  rotatably mounted at the body  110  to be restricted by the driving pin  134  of the open/close device  130 , and a spring  143  connected to the switching lever  142  to provide a restoring force. 
     The open/close device  130  is released by two operations, that is, a mechanical operation and an electrical operation. 
     First, in case of release of the open/close device  130  by the mechanical operation, a user depresses a trip button to release the open/close device  130 , or the trip device  200  is activated to release the open/close device  130 , the operations of which are explained below. 
     In a case a restricted condition of the latch holder  133  is released by the operation of the cross bar  135  to rotate the latch holder  133 , the restricted condition of the latch  132  restricted by the latch holder  133  is removed, and as a result thereof, the restriction of the rotor  150  is removed to interrupt a circuit between the power source side and the load side. 
     At the same time, in a case the driving pin  134  is moved by the movement of the latch holder  133 , the restriction of the switching lever  142  is released. As a result, the switching lever  142  is rotated clockwise by the resilient restoring force of the spring  143  to allow a distal end of the switching lever  142  to depress the contact point of the micro switch  141 , whereby the micro switch  141  sends a warning signal to the outside to indicate an interrupted condition of the circuit breaker. 
     The release operation of the open/close device  130  by the electrical failure such as over-current or short-circuited current is explained under. 
     First, the cross bar  135  is pushed and moved by a curved bimetal  230  in a case an over-current flows. The latch holder  133  supported by the cross bar  135  in response to the movement of the cross bar  135  is moved to release the restriction of the latch  132  restricted by the latch holder  133 , whereby the rotor  150  is released of its restriction to interrupt the circuit between the power source side and the load side. 
     At the same time, the driving pin  134  is moved in response to the movement of the latch holder  133  to release the restriction of the switching lever  142 , and as a result thereof, the switching lever  142  is rotated clockwise by the resilient restoring force of the spring  143  to allow a distal end of the switching lever  142  to depress the contact point of the micro switch  141 , whereby the micro switch  141  sends a warning signal to the outside to indicate a tripped condition of the circuit breaker. 
     Meanwhile, the trip device  200  according to the present disclosure may include a power source side heater  210  connected to a power source side of the MCCB {e.g., a stator (not shown)} or to the rotor  150  to receive the electric power or a current, a load side heater  220  connected to a load side of the MCCB to transmit a current of the power source, and a bimetal  230 . 
     The bimetal  230  is partially contacted and fixed between the power source side heater  210  and the load side heater  220  to be curved when an over-current or a short-circuited current flows in the MCCB. In a case the bimetal  230  is curved, a contact piece  232  at a distal end of the bimetal  230  pushes out the cross bar  135  to release the open/close device  130 . 
     The bimetal  230  may include a direct heating unit (L 2 ) that is directly contacted to the power source side heater  210  to get conducted, and an indirect heating unit (L 1 ) disposed in opposition to the power source side heater  210 . The bimetal  230  is heated at the direct heating unit (L 2 ) by heat conduction and an ohmic resistance of the direct heating unit (L 2 ). 
     The bimetal  230  and the power source side heater  210  face each other to transmit the heat by way of radiation. In this case, the bimetal  230  and the power source side heater  210  may face each other as shown in  FIGS. 6 and 7 , or the bimetal  230  and the power source side heater  210  may be contacted as illustrated in  FIG. 8 . 
     That is to say, as shown in the exemplary embodiments of  FIGS. 6 and 7 , an air gap may be formed at the indirect heating unit (L 1 ) between the bimetal  230  and the power source side heater  210 , where the bimetal  230  is heated and curved by the indirect heating unit (L 1 ) in the form of convective heat transmission. 
     Meanwhile, as illustrated in the exemplary embodiment of  FIG. 8 , the bimetal  230  and the power source side heater  210  are mutually contacted, where the bimetal  230  is heated and curved by the heat conduction of the indirect heating unit (L 1 ). 
     To wrap up, the bimetal  230  and the power source side heater  210  may be mutually contacted and fixed at the direct heating unit (L 2 ) and directly heated by the direct heating unit (L 2 ) in the form of ohmic resistance to thereby obtain a heating effect by heat conduction. This corresponds to the function of the direct heating type device. In the meantime, an indirect heating effect may be obtained by using the indirect heating unit (L 1 ) in the form of convection or conductive heat transmission. This corresponds to the function of the indirect heating type device. 
     Therefore, the trip device according to the present disclosure can take up both the advantages of the direct heating type trip device and the indirect heating type trip device, such that the trip device according to the present disclosure can be used as a multi-purpose trip device that can be used for both the low-voltage MCCB and the high voltage MCCB. 
     Meanwhile, the bimetal  230  of the direct heating unit (L 2 ) is configured in such a manner that a first surface  230   a  is contacted and fixed by the power source side heater  210 , and a second surface  230   b  (which is a rear surface of the first surface  230   a ) is contacted and fixed by the load side heater  220 . Material of the first surface  230   a  is different from that of the second surface  230   b  in the bimetal  230  which is a combination of different materials. 
     In a case the first surface  230   a  is fixed by the power source side heater  210  and the load side heater  220 , only one material may be heated as shown in  FIG. 2  to generate a fusion, and in order to prevent the fusion, it is therefore preferable that the first surface  230   a  be fixed by the power source side heater  210  while the second surface  230   b  of the bimetal  230  be fixed by the load side heater  220 . Therefore, the fusion of  FIG. 2  and the reverse curving of  FIG. 4  that might be generated when heating is concentratively applied to a single material can be restricted. 
     It is also preferable that the power source side heater  210  and the load side heater  220  be fixed to the bimetal  230  by a rivet  250 . The reason of fixing by rivet  250  is to reduce or restrict the occurrence of defect of  FIG. 3 , in which case the fixation by welding or bonding method is destructed by thermal energy. 
     Meanwhile, a fixed contact position of the power source side heater  210  and a fixed contact position of the load side heater  220  relative to the bimetal  230  are preferably placed at the same height when viewed in a direction the bimetal  230  is extended. Therefore, the entire area of the bimetal  230  is not affected by the occurrence of over-current which only affects the direct heating unit (L 2 ), such that the over-current affects part of the bimetal  230  to prevent the possible defect as exemplified in  FIG. 4 . 
     Meanwhile, a fixed contact position of the power source side heater  210  and a fixed contact position of the load side heater  220  relative to the bimetal  230  are preferably placed at different places when vertically viewed in a direction the bimetal  230  is extended, which enables formation of the riveted positions at the same height as noted above, and obtainment of heating effect by the ohmic resistance of the direct heating unit (L 2 ) at each riveted position. 
     It will be appreciated that the examples disclosed herein are not to be construed as limiting of the disclosure as they are intended merely as illustrative of particular embodiments of the disclosure as enabled herein. Indeed, various modifications of the disclosure in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description and fall within the scope of the appended claims. It is therefore evident that the particular embodiments disclosed above may be all or partially altered or modified, and such features or aspects may be combined with one or more other features and/or aspects of other implementations as may be desired.