Abstract:
A secondary disconnect for a circuit breaker drawout system is provided. The secondary disconnect includes a plurality electrical connectors that are coupled to spacer frames. The spacer frames are movably mounted to guide pins that couple the secondary disconnect to the circuit breaker. A compression spring is disposed about the guide pin and bias&#39;s the secondary disconnect. A second spring positioned within the spacer frame applies a biasing force when the circuit breaker is in the racked-in position.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter disclosed herein relates to a secondary disconnect mechanism for a circuit breaker. In particular, the subject matter disclosed herein relates to a secondary disconnect that provides a secondary source of electrical power to accessories in the racked-in and test positions of a circuit breaker drawout system. 
         [0002]    Drawout circuit breakers often include a mechanism for moving the breaker in and connecting the breaker to corresponding electrical contacts, a location known as the “racked-in” position. When in the racked-in position, the circuit breaker is coupled to the main electrical circuit and provides the interruption functionality for which it is intended. If the drawout mechanism is reversed to the “racked-out” position, the circuit breaker is disconnected from the electrical contacts and the main electrical circuit. The circuit breaker may be moved to the racked-out position, for example, when maintenance is performed on the main electrical circuit. Typical racking mechanisms often include a third or test position. In the test position the circuit breaker can be closed, opened or tripped in order to check internal and external accessories such as auxiliary switches, shunt trip and under voltage and secondary circuits. 
         [0003]    To test the accessories, electrical power is provided to the accessories to enable proper functioning. The electrical power is typically provided from a secondary source, such as a disconnectable mechanism that includes slidable electrical contacts. However, these disconnectable mechanisms typically require a large amount of physical space in which to operate. As smaller circuit breakers, such as molded case circuit breakers for example, are used with drawout mechanisms, it is increasingly difficult to fit the slidable mechanism within the available space. 
         [0004]    While existing secondary disconnects for drawout mechanisms are suitable for their intended purposes, there still remains a need for improvements particularly regarding secondary disconnecting mechanisms that provide a reliable and cost effective means for providing electrical power to circuit breaker accessories when in the racked-in and test positions. 
       SUMMARY OF THE INVENTION 
       [0005]    A secondary disconnect mechanism for a circuit breaker drawout is provided having at least one electrical contact movable between a first position and a second position. A first spring is coupled to the at least one electrical contact where the first spring bias&#39; the at least one electrical contact in a first direction. A second spring is coupled to the at least one electrical contract. The second spring bias&#39; the at least on electrical contact when the at least one electrical contact is in the first position. 
         [0006]    A secondary disconnect mechanism for a circuit breaker drawout is also provided. The secondary disconnect mechanism includes a first electrical connector, a second electrical connector and a third electrical connector arranged in parallel, wherein the first electrical connector, the second electrical connector and the third electrical connector are movable between a first position and a second position. A base plate is coupled between the first electrical connector, the second electrical connector and the third electrical connector. A first frame is coupled to the base plate and between the first electrical connector and the second electrical connector. A second frame is coupled to the base plate and between the second electrical connector and the third electrical connector. A first spring is arranged to bias the first frame in a first direction. A second spring is arranged to bias the second frame in the first direction. A third spring is coupled to the first frame and arranged to bias the first frame when the first electrical connector, the second electrical connector and the third electrical connector are in the first position. A fourth spring coupled to the second frame and arranged to bias the second frame when the first electrical connector, the second electrical connector and the third electrical connector are in the first position. 
         [0007]    A drawout mechanism is also provided having a housing. A mechanism within the housing and movable between a first position, a second position and a third position. Electrical contacts are positioned within the housing and operably coupled to the mechanism. A plug-in base is adjacent to the electrical contacts. A circuit breaker is coupled to the mechanism, wherein the circuit breaker is electrically connected to the electrical contacts in the first position, and disconnected from the electrical contacts when in the second and third positions. A secondary disconnect is coupled to the circuit breaker and electrically coupled to the plug-in base when said the circuit breaker is in the first position and the second position, the secondary disconnect including an electrical connector. A first spring is coupled between the circuit breaker and the electrical connector, the first spring arranged to bias the electrical connector towards the first position. A second spring is provided that is coupled to the electrical connector, the second spring being arranged to bias the electrical connector when the circuit breaker is in the first position. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Referring now to the drawings, which are meant to be exemplary and not limiting, and wherein like elements are numbered alike: 
           [0009]      FIG. 1  is a schematic perspective view illustration of a drawout circuit breaker system in accordance with the exemplary embodiment; 
           [0010]      FIG. 2  is a schematic plan side view illustration of the drawout circuit breaker system of  FIG. 1  in the racked-in position; 
           [0011]      FIG. 3  is a schematic plan side view illustration of the drawout circuit breaker system of  FIG. 1  in the test position; 
           [0012]      FIG. 4  is a schematic plan side view illustration of the drawout circuit breaker system of  FIG. 1  in the withdrawn or racked-out position; 
           [0013]      FIG. 5  is a side plan view illustration of the secondary disconnect mechanism of  FIG. 2  in the racked-in position; 
           [0014]      FIG. 6  is a side plan view illustration of the secondary disconnect mechanism of  FIG. 3  in the test position; 
           [0015]      FIG. 7  is a side plan view illustration of the secondary disconnect mechanism of  FIG. 4  in the racked-out position; and, 
           [0016]      FIG. 8  is a partial perspective view illustration of the secondary disconnect mechanism in accordance with the exemplary embodiment; and, 
           [0017]      FIG. 9  is a partial side plan sectional view illustration of the secondary disconnect mechanism of  FIG. 8 . 
       
    
    
     DETAILED DESCRIPTION 
       [0018]      FIGS. 1-4  illustrate a drawout circuit breaker system  20 . The drawout circuit breaker  20  is coupled between a main electrical circuit  22  having a protected load  24  and a power source  26  such as an electrical utility network. The drawout circuit breaker  20  includes a housing  28 . A door  30  is coupled to the housing  28  by hinges  32 . The door  30  includes an opening  34  that allows the operator access to a circuit breaker  36  located within the housing  28 . Another opening  38  allows the operator to activate a drawout mechanism  40 . The circuit breaker  36  is electrically coupled between the power source  26  and the protected load  24 . 
         [0019]    It should be appreciated that the circuit breaker  36  is illustrated in the exemplary embodiment having a single connection to the power source  26  and the protected load  24 . However, the circuit breaker  36  may comprise of multiple electrical phases or connections. Further, the circuit breaker  36  may be known as a multi-pole circuit breaker having multiple contact arms that connect and disconnected the main electrical circuit  22  from the power source  26 . A “multi-pole” circuit breaker the circuit breaker will typically have three or four poles, each carrying a different phase of electricity through the circuit breaker  36 . Further, in the exemplary embodiment, the circuit breaker  36  is a molded case circuit breaker (MCCB) where the circuit breaker components are housed within an insulated polymer housing. However, but other types of circuit breakers, such as open frame air circuit breakers may also be used. 
         [0020]    The circuit breaker  36  may further include one or more accessories, including but not limited to a shunt trip  46  and an under-voltage accessory  48  for example. The shunt trip  46  is a device mounted within the circuit breaker that allows an operator to remotely switch the circuit breaker from the on to the off position. Typically, the shunt trip  46  is connected to an external switch (not shown). When the switch is closed, an electromagnetic coil inside the shunt trip energizes and applies a force to the circuit breaker handle. An under-voltage accessory used with circuit protective apparatus to interrupt the circuit current when the systems voltage falls below a predetermined value. Similar to the shunt trip  46 , the under-voltage accessory  48  acts upon the circuit breaker mechanism causing the circuit breaker to switch from the on to the off positions when the undesired condition occurs. 
         [0021]    Circuit breaker accessories, such as shut trip  46  and under-voltage accessory  48  for example, require a power source to operate. Further, the power source must be available when the circuit breaker is in certain positions, but disconnected in others. Referring now to  FIGS. 2-4 , the positions of the drawout system  20  will be described. The drawout system  20  is used to allow an operator to physically connect and remove the circuit breaker  36  into and out of connection with the electrical circuit  22  without having to manually remove the cabling or other electrical connections. An operator may need to disconnect the circuit breaker  36  so that downstream maintenance tasks may be performed for example. To accomplish this, the circuit breaker  36  is mounted to a drawout mechanism  40  as is known in the art. The drawout mechanism  40  includes means for moving the circuit breaker  36  into and out of contact with electrical contacts  42 ,  44 . The inlet contacts  42  connect the circuit breaker  36  to the power source  26  while the outlet contacts  44  provide a connection to the load  24 . When the drawout mechanism  40  moves the circuit breaker  36  away from the contacts  42 ,  44  ( FIG. 3 ,  FIG. 4 ), the electrical connection is broken and no electrical power can flow from the power source  26  to the load  24 . 
         [0022]    A secondary disconnect  50  is also coupled to the circuit breaker  36 . The secondary disconnect  50  includes a movable portion  52  and a stationary portion  54 . As will be discussed in more detail below, the movable portion  52  and the stationary portion  54  cooperate to provide electrical power to secondary accessories, such as shunt trip  46  for example, when the circuit breaker  36  is in the racked-in and test positions, but is disconnected when the circuit breaker is in the racked-out position. It should be appreciated that while the stationary portion  54  and the electrical contacts  42 ,  44  are shown as being discrete components, these components may be integrated into a single assembly known as a plug-in base as is known in the art. 
         [0023]    In general, drawout systems have three positions in which the circuit breaker  36  may be positioned. In the racked-in position illustrated in  FIG. 2 , the circuit breaker  36  is coupled to the contacts  42 ,  44  and electrical power will flow if the circuit breaker  36  is closed. The contacts  42 ,  44  may be in the form of a movable terminal connector and a stationary stab, or other such similar structure as is known in the art. At the opposite end of the range of travel is the withdrawn or “racked-out” position illustrated in  FIG. 4 . In the racked-out position, the circuit breaker is disconnected from the contacts  42 ,  44  and the secondary disconnect movable portion  52  is disconnected from the stationary portion  54 . Further, when in the racked-out position, the drawout system  20  will typically have an interlock arrangement that prevents the circuit breaker  36  from being operated. Finally, as illustrated in  FIG. 3 , intermediate to the racked-in and racked-out positions is what is commonly referred to as the test position. When in the test position, the circuit breaker  36  is not interlocked and may be operated so that the functions of the circuit breaker may be tested. As will be discussed below, the movable portion  52  and the stationary portion  54  of the secondary disconnect  50  remain electrically coupled when in the test position and allow the secondary accessories, such as shunt trip  46  to be operated in the test position. 
         [0024]    Referring now to  FIGS. 5-9 , the operations of the secondary disconnect  50  will be described. The secondary disconnect movable portion  52  is coupled to the circuit breaker  36  and moves with the circuit breaker as the circuit breaker  36  is moved between the positions described above. The movable portion includes male electrical connectors  56 ,  58  and  60 . The electrical connectors  56 ,  58  and  60  contain a plurality of male electrical contacts  62 . The electrical contacts  62  are connected to wires (not shown) that electrically connect the electrical contacts  62  to secondary accessories, such as shunt trip  46  for example. 
         [0025]    Spacer frames  64  are positioned between each of the electrical connectors  56 ,  58  and  60 . A base plate  66  couples the electrical connectors  56 ,  58 ,  60  and the spacer frames  64 . The electrical connectors  56 ,  58 ,  60  and the spacer frames  64  are coupled to the circuit breaker  36  by guide pins  68 . In the exemplary embodiment, the guide pins  68  are u-shaped pins that are coupled to the spacer frames  64  to allow the spacer frames  68  to move in the direction of arrow  70 . Alternatively, the guide pins  68  may be comprised individual pins rather than a single u-shaped member. An optional intermediate plate  82  may be coupled to the guide pins  68  and used to mount the movable portion  52  to the circuit breaker  36 . 
         [0026]    The spacer frames  64  include a pair of compression springs  72  that are arranged within a generally hollow portion  74 . The springs  72  are disposed about pins  76  that are coupled between a plate  78  and the spacer frame  64 . The plate  78  is also coupled to guide pin  68  to allow the plate to move with the spacer frame  64 . As will be discussed below, the compression springs  72  provide a biasing force to create a positive contact when the circuit breaker is in the racked-in position of  FIG. 2 . In one embodiment, the compression springs  72  are sized to provide a small gap between the plate  78  and the surface  94  of the spacer frame  64 . 
         [0027]    A compression spring  80  is disposed about the guide pin  68  between the plate  78  and the bottom of the circuit breaker  36 . The compression spring  80  biases the spacer frame  64  away from the circuit breaker  36 . In the exemplary embodiment, the compression spring  80  is a conical compression spring. The spring  80  is arranged such that the angle of the spring allows the wire diameter for each turn of the spring to telescope or overlap with the adjacent “row” of the spring as the spring  80  is compressed. As will be discussed below, this provides an advantage in that the spring  80  may be fully compressed to a solid height that is equal to one to two thickness of the wire diameter. In the exemplary embodiment, there are four conical compression springs  80 . Each of the conical compression springs  80  is disposed about the legs  92  of the guide pins  68   
         [0028]    During operation, the circuit breaker is in the racked-in position ( FIG. 5 ). When in this position, the electrical contacts  62  on the electrical connectors  56 ,  58  and  60  mate with corresponding female electrical connectors  84 ,  86 , and  88  on the stationary portion  54 . When in this position, the compression spring  80  is fully compressed to approximately its solid height. The compression spring  72  is sized to allow compression of the spring  72  once the compression spring  80  has reached its solid height. This allows the spring  72  to maintain a positive force on the electrical connectors  56 ,  58  and  60  while the circuit breaker  36  is in the racked-in position while also minimizing the space needed to fit the secondary disconnect  50  in the space provided within the housing  28 . The combination of the springs  72 ,  80  also provides other advantages. The interior of the housing  28  often operates at elevated temperatures due to the heat generated by the flow of electrical current. Due to these elevated temperatures along with high stresses, the conical spring may experience thermal aging or creep issues causing the spring  80  to lose force over time. Thus the combination of the springs  72 ,  80  further compensates for any potential degradation in performance over time. 
         [0029]    If the operator desires to disconnect the main electrical circuit  22  and perform testing on the circuit breaker  36  accessories, the drawout mechanism  40  is activated and the circuit breaker  36  is moved to the test position ( FIG. 6 ). In this position, the circuit breaker  36  is disconnected from the inlet contact  42  and the outlet contact  44  and no electrical power flows from the power source  26  to the load  24 . However, as the circuit breaker  36  moves, the compression springs  80  expand and applies a force on the spacer frames  64  keeping the male electrical connectors  56 ,  58  and  60  in contact with the female electrical connectors  84 ,  86  and  88 . The compression spring  80  is sized to maintain an adequate force on the electrical connectors to maintain the electrical connection when the circuit breaker  36  is in the test position. 
         [0030]    There are times, such as when maintenance is required on the drawout system  20  for example, when it is desirable to completely disconnect all electrical power from the circuit breaker  36  including the secondary accessories. To achieve this, the operator further activates the drawout mechanism  40  and moves the circuit breaker  36  to the racked-out position ( FIG. 7 ). As the circuit breaker continues to move away from the electrical connectors  56 ,  58  and  60  stay in contact with the connectors  84 ,  86 , and  88  until the space frames  64  contact the bottom portion  90  of the guide pins  68 . At this point, the travel of the electrical connectors  56 ,  58  and  60  relative to the guide pins  68  ends and the female electrical connectors  56 ,  58  and  60  separate from the female connectors  84 ,  86  and  88 . The gap between the electrical connectors increases until the circuit breaker  36  reaches the racked-out position. 
         [0031]    It should be appreciated that the secondary disconnect  50  arrangement provides a number of advantages to service personnel and in the manufacture of the drawout system  20 . The secondary disconnect  50  allows the manufacturer to reduce the size and space requirements of the drawout system  20 . The secondary disconnect  50  also provides a reliable and positive contact between the movable portions and stationary portions. The secondary disconnect further compensates for harsh environmental conditions that would degrade spring performance over time. 
         [0032]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.