Patent Publication Number: US-6985059-B2

Title: Circuit breaker handle block

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates generally to circuit breakers and more particularly to circuit breaker operating mechanisms having a handle blocking means for restricting movement of the handle when the current carrying contacts are welded. 
   Molded case current limiting circuit breakers are well known in the art. Circuit breakers of this type have a manual operating handle for the purpose of switching the circuit breaker between on and off states. The on-off operation is accomplished through a mechanism spring that connects the operating handle with a toggle linkage. The toggle linkage in turn is connected to a contact carrier assembly that performs the operation of connecting and interrupting current flow to a protected circuit. 
   When the operating handle is moved from the on to the off position, the direction of the force applied by the mechanism spring changes as the spring rotates with the handle. At some point during the motion, the direction of the force changes from one side of a toggle linkage pivot to the other. This results in the toggle linkage collapsing and rotation of the contact carrier assembly. 
   The circuit breaker generally provides some visual indication as to the position of the contact carrier assembly. However, on extreme and rare occasions the contacts of the circuit breaker can become welded. In this case if the operating handle were allowed to be returned to the off position, it would give the operator the false indication that the protected circuit has been disconnected from the power source. Some regulatory agencies such as the International Electrotechnical Commission (IEC) require that the operating handle be blocked from moving to the off position when the contacts are welded. It is also required by such regulatory agencies that the circuit breaker indicate the position of the contacts. In many circuit breakers when the contacts are welded, the handle automatically returns to the on position. This not only provides correct visual indication of the state of the contacts, but also provides the operator with an indication that there is some malfunction. 
   A circuit breaker of the type mentioned herein having a mechanism with the toggle type linkage that is described in U.S. Pat. No. 5,200,724. In this circuit breaker the handle movement is blocked by projections extending from both the upper link and the lower link of the toggle linkage. The upper link projection interacts with the handle to block handle rotation while the lower link projection interacts with a crossbar assembly to prevent rotation of the toggle linkage. 
   Further, U.S. Pat. No. 5,543,595 describes a circuit breaker, which utilizes reversing levers that are attached to a cradle. The reversing levers interact with an upper link and the handle to prevent rotation of the handle to a position where the toggle linkage can rotate if the contacts are welded. 
   If the weld is of sufficient strength, the contact arm cannot be rotated and the contacts remain closed. Still, it may be possible to rotate the handle to the off position. Furthermore, in some installations, the circuit breaker is operated by a motor operator or other external mechanical means which can force the operating handle to the off position even though the contacts are welded closed. Obviously, this is a very unsatisfactory situation. 
   Typically a maintenance operator will place the handle of a circuit breaker in the “OFF” position to remove electrical power from the system before doing corrective maintenance. The maintenance operator may also padlock the handle in this position as an added measure to prevent others from placing the breaker in the “ON position while this maintenance is being done. 
   Thus, a mechanical means is desired to prevent the maintenance operator from placing the handle in the “OFF” or “RESET” position and possibly padlocking the handle in this position, in the event that contacts should become welded and power cannot be interrupted by handle movement. Further, there is a need for an improved positive off mechanism for a circuit breaker which is rigid enough to block movement of the operating handle to the off position despite the application of a force to the operating handle to the “OFF” position when the contacts are welded closed. 
   BRIEF DESCRIPTION OF THE INVENTION 
   The above discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by a circuit breaker having a crank for coupling a rotary arm breaker mechanism to the cradle. The crank has a protrusion which cooperates with a handle yoke to restrict movement of the operating handle when the contacts of the circuit breaker are welded. The crank protrusion is arranged such that it does not interfere with the handle under normal operating conditions. 
   In an exemplary embodiment of the present invention, a molded case circuit breaker includes a mechanism having a handle, movable between an on and off position, with the handle being configured to restrict movement thereof when the contacts of the circuit breaker are welded or otherwise fixed in the ON position and prevented from opening. The handle includes a handle yoke having a projection extending therefrom and being movable between an on position and an off position with the handle. A contact arm supports at least one contact and is movable between a closed position and an open position. A crank is operably coupled to the handle yoke and the contact arm to move the contact arm from the closed position to the open position when the handle yoke is moved from the on position to the off position. The crank has a blocking lever or protrusion extending therefrom interacting with the projection of the handle yoke to prevent the handle yoke from being moved to the off position when the contact arm is fixed in the closed position. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring now to the drawings wherein like elements are numbered alike in the several FIGURES: 
       FIG. 1  is a top perspective view of a molded case circuit breaker; 
       FIG. 2  is an exploded perspective view of a molded case circuit breaker; 
       FIG. 3  a partial sectional view of the rotary contact structure and operating mechanism of  FIG. 3  in the “on” position; 
       FIG. 4  is a partial sectional view of a rotary contact structure and operating mechanism embodied by the present invention in a “off” position; 
       FIG. 5  is a partial sectional view of a rotary contact structure and operating mechanism embodied by the present invention in an “on” position having the contacts in a welded position as the operating handle is attempted to be moved toward an “off” position; and 
       FIG. 6  is a partial sectional view of a rotary contact structure and operating mechanism embodied by the present invention in a “tripped” position. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Ueferring to  FIG. 1 , a top perspective view of a molded case circuit breaker  10  is generally shown. Molded case circuit breaker  10  is generally interconnected within a protected circuit between multiple phases of a power source (not shown) at line end  14  and a load to be protected (not shown) at load end  12 . Molded case circuit breaker  10  includes a base  18 , a mid cover  20  and a top cover  22  having a toggle handle  44  (operating handle) extending through an opening  24 . Toggle handle  44  is interconnected with a circuit breaker operating mechanism  38  ( FIG. 2 ) and allows for external operation of cassettes  32 ,  34  and  36 . A switch (e.g., a bell alarm switch and or auxiliary switch)  26  may be positioned within the mid cover  20  as shown in phantom, and interfaces with circuit breaker operating mechanism  38 . The circuit breaker in  FIG. 1  shows a typical three phase configuration, however, the present invention is not limited to this configuration but may be applied to other configurations, such as the typical one, two or four phase circuit breakers. 
   Referring now to  FIG. 2 , an exploded view of molded case circuit breaker  10  is provided. A series of circuit breaker cassettes  32 ,  34 ,  36  are generally well known and may be, for example, of the rotary type. Examples of rotary contact structures that may be operated by operating mechanism  38  are described in more detail in U.S. Pat. Nos. 6,114,641 and 6,396,369, both entitled “Rotary Contact Assembly For High-Ampere Rated Circuit Breakers”, and U.S. Pat. No. 6,175,288, entitled “Supplemental Trip Unit For Rotary Circuit Interrupters”. 
   Circuit breaker cassettes  32 ,  34 ,  36  are seated approximately upstanding within base  18 , and the cassette  34  includes operating mechanism  38  positioned thereon. The individual phases of current are divided into three phases, wherein each phase passes through one of the circuit breaker cassettes  32 ,  34 ,  36 . Each of cassettes  32 ,  34 ,  36  includes one or more contact pairs therein for passage of current when the contacts are closed and for preventing passage of current when the contact pairs are opened. It is contemplated that the number of phases, or specific type of cassette utilized, can vary according to factors including, but not limited to, the type of load circuit being protected and the type of line input being provided to the circuit breaker  10 . 
   Still referring to  FIG. 2 , each cassette  32 ,  34 ,  36  is commonly operated by a first cross bar (cross pin)  40  that interfaces with the internal mechanisms of cassettes  32 ,  34 ,  36  such that when one of cassettes  32 ,  34 ,  36  are opened or closed, the other cassettes  32 ,  34 ,  36  will operate cooperatively. It will be recognized by one skilled in the pertinent art that only one cross bar may be used to interface with the internal mechanisms of cassettes  32 ,  34 ,  36  such that when one of cassettes  32 ,  34 ,  36  are opened or closed, the other cassettes  32 ,  34 ,  36  will operate cooperatively. Positioning rods  33  and protrusions  35  in cassettes  32 ,  36  are also employed to position the cassettes  32 ,  34 ,  36  adjacent to each other. Positioning rods  31  are also used to position mechanism  38  to locate cross bar  40  to align with rotary contact assembly  56  within cassettes  32 ,  34 ,  36 . Operating mechanism  38  is positioned and configured atop cassette  34 , which is generally disposed intermediate to cassettes  32  and  36 . Operating mechanism  38  operates substantially as described herein and as described in U.S. Pat. No. 6,218,919, entitled “Circuit Breaker Latch Mechanism with Decreased Trip Time”. It should also be noted that employment of other operating mechanisms is contemplated, as well. The cassettes  32 ,  34 ,  36  are typically formed of high strength plastic material and each include opposing sidewalls. 
   Referring now to  FIGS. 3 ,  4 , and  5 , the operating mechanism  38  will now be detailed. An exemplary rotary contact assembly  56  is shown disposed within each cassette  32 ,  34 ,  36  and shown in the “on”, “off” and “welded” conditions, respectively. Also depicted are partial side views of operating mechanism  38 , the components of which are described in greater detail further herein. Rotary contact assembly  56  includes a load side contact strap  58  and line side contact strap  62  for connection with a power source and a protected circuit (not shown), respectively. Load side contact strap  58  includes a stationary contact  64  and line side contact strap  62  includes a stationary contact  66 . Rotary contact assembly  56  further includes a movable contact arm  68  having a set of contacts  72  and  74  that mate with stationary contacts  64  and  66 , respectively. In the “off” position ( FIG. 4 ) of operating mechanism  38 , wherein toggle handle  44  is oriented slightly off center to the right (e.g., via a manual or mechanical force), contacts  72  and  74  are separated from stationary contacts  64  and  66 , thereby preventing current from flowing through contact arm  68 . 
   In the “on” position ( FIG. 3 ) of operating mechanism  38 , wherein toggle handle  44  is oriented to the left as depicted in  FIG. 4  (e.g., via a manual or mechanical force), contacts  72  and  74  are mated with stationary contacts  64  and  66 , thereby allowing current to flow through contact arm  68 . In the “welded” position ( FIG. 5 ) of operating mechanism  38 , toggle handle  44  is attempted to be oriented between the “on” position and the “off” position (typically by either the release of mechanism springs within operating mechanism  38  or manipulation of handle  44  to the “off” position, described in greater detail herein). In this “welded” position, contacts  72  and  74  are welded to stationary contacts  64  and  66  and power cannot be interrupted by handle  44  movement or by the action of operating mechanism  38 , thereby maintaining current flowing through contact arm  68 . Once the welded contacts are separated or after the operating mechanism  38  is in the “tripped” position (See  FIG. 6 ), it must ultimately be returned to the “on” position for operation. This is effectuated by applying a reset force to move toggle handle  44  to a “reset” condition, which is beyond the “off” position (i.e., further to the left of the “off” position in  FIG. 4 ), and then back to the “on” position. This reset force must be high enough to overcome the mechanism springs, described herein. 
   Contact arm  68  is mounted on a rotor structure  76  that houses one or more sets of contact springs (not shown). Contact arm  68  and rotor structure  76  pivot about a common center  78 . Cross pin  40  interfaces through an opening  82  within rotor structure  76  generally to cause contact arm  68  to be moved from the “on”, “off” and “tripped” position. 
   Referring now to  FIGS. 3 ,  4 ,  5 , and  6 , the components of operating mechanism  38  will now be described in further detail in relation to interfacing between the operating mechanism  38  and the rotor contact assembly  56 . As viewed in  FIG. 3 , operating mechanism  38  is in the closed or “on” position after being reset. Operating mechanism  38  has operating mechanism side frames  86  configured and positioned to straddle sidewalls  46 ,  48  of cassette  34  ( FIG. 2 ). 
   Toggle handle  44  is rigidly interconnected with a drive member or handle yoke  88 . Handle yoke  88  includes opposing side portions (only one shown)  89 . Each side portion  89  includes a U-shaped portion  92  at the bottom portion of each side portion  89 . U-shaped portions  92  are rotatably positioned on a pair of bearing portions  94  protruding outwardly from side frames  86 . 
   Operating mechanism  38  has a pair of cranks  208  operably connected to a cradle  210 . Examples of rotary contact structures having such a cradle that may be operated by operating mechanism  38  are described in more detail in U.S. patent application Ser. No. 09/795,017 filed 27 Feb. 2001. Each crank  208  pivots about a center  78 . Crank  208  has an opening corresponding with opening  82  within rotor structure  76  where a cross pin  40  ( FIG. 2 ) passes through into arcuate passage  52  of cassettes  32 ,  34  and  36  ( FIG. 2 ). 
   Still referring to  FIG. 3 , cradle  210  is disposed adjacent to corresponding side frames  86  and pivots with respect to a cradle pivot pin  201  disposed through a corresponding opening (not shown) disposed in cradle  210 . Cradle  210  includes a top edge surface including a cradle latch surface  164  disposed at one end thereof. Upper link pivot pin  200  is pivotally connected to the cradle  210  and to an upper link  211  that is pivotally connected to a lower link  212  at an opposite end via a rivet or toggle pin  214 . An opposite end of lower link  212  in turn is pivotally coupled to crank  208  via a pin  218 . 
   A primary latch  126  is positioned within side frame  86 . A secondary latch  138  is pivotally positioned within side frames  86 . Secondary latch  138  extends from operating mechanism  38  as to allow an interface with, for example, a shunt trip (not shown), or a thermal magnetic trip unit (not shown) to release the engagement between primary latch  126  and secondary latch  138  thereby causing operating mechanism  38  to move to the “tripped” position (in  FIG. 6 ), described below. Secondary latch  138  includes a latch surface generally shown at  139  that aligns with a corresponding primary latch surface to release primary latch  126 . The interface between primary latch  126  and secondary latch  138  (i.e., between primary latch surface and secondary latch surface), and between cradle  210  and primary latch  126  is not affected when a force is applied to toggle handle  44  to change from the “off” position to the “on” position. 
   Referring now to  FIG. 6 , in the “tripped” condition, secondary latch  138  has been displaced (e.g., by a thermal magnetic trip unit not shown) when secondary latch  138  pivots clockwise about a trip lever pin  140 , and the interface between primary latch  126  and secondary latch  138  is released. The primary latch  126  is disengaged from cradle latch surface  164  (e.g., by rotating clockwise), and cradle  210  is rotated counter-clockwise about the cradle pivot pin  201  (shown in  FIG. 6 ). The movement of cradle  210  transmits a force to crank  208  via pin  200  corresponding to upper link  211  connected to lower link  212  with corresponding rivet  214  (as best seen with reference to  FIG. 5  and shown with phantom lines in  FIGS. 3 ,  4 , and  6 ), the lower link  212  causing crank  208  to rotate counter clockwise about center  78  and drive cross pin  40  to an upper portion of the arcuate passage  52  configured in the cassette. The forces transmitted through cross pin  40  to rotary contact assembly  56  via opening  52  cause movable contacts  72 ,  74  to separate from stationary contacts  64 ,  66  (see  FIGS. 4 and 6 ), unless the movable contacts  72 ,  74  become welded to stationary contacts  64 ,  66  (see  FIG. 5 ). 
   The remaining internal components of the circuit breaker are described with reference to the Figures where handle  44  is attached to a mechanism spring  216  within an arcuate cavity configured therein which attaches at its opposite end to toggle pin  214 . The toggle pin  214  connects the toggle linkage  211 ,  212  with the mechanism spring  216 . As will be described herein, the force generated by the movement of the handle  44  will cause the toggle linkage  211 ,  212  to extend or collapse, which in turn results in the circuit breaker turning ON or OFF depending on the movement of the handle  44 . The upper link  211  of the toggle linkage attaches to cradle  210  at pin  200 . The lower link  212  attaches to crank  208  via pin  218 . 
   The crank  208  pivots on pin  78  attached to the side frames  86  and connects with a multi-pole rotary contact system  56  via pin  40 . The rotary contact system operates in substantially the same manner as that described in U.S. patent application titled “Circuit Breaker Mechanism for a Rotary Contact Assembly” Ser. No. 09/196,706 filed on Nov. 20, 1998 which is incorporated herein by reference. Opposite pin  40 , the crank  208  includes a blocking lever  220  extending therefrom. Under certain operations, the blocking lever  220  interacts with a handle yoke projection  222  (as best seen with reference to  FIG. 5 ). The importance of the interaction between the lever projection  220  and the handle yoke projection  222  will be made clearer herein. 
   Under normal operating conditions when the circuit breaker is in the ON position, the mechanism  38  and rotary contact system  56  will be oriented as shown in  FIG. 3 . In this orientation, the movable contacts  72 ,  74  mate with the stationary contacts  64 ,  66  to allow current to flow through the circuit breaker. In this position, there is a small angle A between the mating surfaces of blocking lever  220  and the handle yoke projection  222  corresponding to a small gap therebetween. 
   When the user rotates the handle  44  to the OFF position (clockwise as oriented in  FIGS. 3–6 ), the line of force generated by the mechanism spring  216  on the toggle pin  214  rotates with the handle. At the point where the line of force generated by the mechanism spring  216  crosses the upper link pin or cradle pivot pin  200 , the toggle linkage  211 ,  212  will collapse as shown in  FIG. 4 . This collapsing of the toggle linkage  211 ,  212  rotates crank  208  in the clockwise direction separating the moveable contacts  72 ,  74  from the stationary contacts  64 ,  66 . When the contacts  64 ,  66 ,  72 ,  74  separate, electrical current flow through the circuit breaker is interrupted and the protected circuit is disconnected from the power source. 
   As the crank  208  continues to rotate to an angle B, the mating surfaces of blocking lever  220  and the handle yoke projection  222  correspond to a large gap therebetween. Since at this point the mating surface of the blocking lever  220  has rotated clockwise as illustrated in  FIG. 4 , the handle yoke projection  222  is not in contact with the crank  208  via lever  220  extending therefrom. The handle yoke projection  222  is free to rotate thereby not interfering with the blocking lever  220  and the user can rotate the handle  44  to the full OFF position shown in  FIG. 4 . 
   Under certain conditions, the contacts  64 ,  66 ,  72 , or  74  may become welded together. This welded condition prevents the mechanism  38  from separating the contacts  64 ,  66 ,  72 ,  74  as described above to disconnect the protected circuit. Certain quasi-regulatory agencies such as the International Electrotechnical Commission (IEC) require that the mechanism handle  44  be prevented from moving to the OFF position while the contacts  64 ,  66 ,  72 ,  74  are welded. To accomplish this, the present invention configures blocking lever  220  extending from crank  208  to interfere with the handle yoke projection  222  extending from handle yoke  88  to prevent the handle  44  from being placed in the OFF position and if the handle  44  is moved, it will automatically return to the ON position when the handle  44  is released. 
   When the contacts  64 ,  66 ,  72 ,  74  are welded, the crank  208  will stay in the closed position shown in  FIG. 5 . If the user attempts to reset the breaker, the handle yoke  88  rotates until the yoke projection  222  contacts the mating surface of the blocking lever  220 . Unlike the above situation, where the bias on the blocking lever  220  allowed the blocking lever  220  to rotate out of the path of the handle yoke projection  222 , the blocking lever is motionless as it is extends from crank  208  which in turn is operably connected to the rotor arm assembly  56  having welded contacts  64 ,  66 ,  72 ,  74 . Thus, the blocking lever  220  is prevented from rotating clockwise. Once the handle yoke projection  222  is interfered with by the mating surface of blocking lever  220 , further clockwise rotation of the handle  44  is prevented. It should be appreciated that once the handle  44  is released by the user, the line of force  230  on the handle  44  from the mechanism spring  216  will cause the handle yoke  88  and the handle  44  to rotate in the counter-clockwise direction about the handle yoke pivot or bearing portions  94  until it reaches the ON position. 
   Thus, a method and mechanical means is provided to prevent a user from moving the handle to the OFF or RESET position and possibly padlocking the handle in this position in the event that a contact becomes welded. The above-described method and mechanical means provides a cost effective means to employ handle blocking in a circuit breaker. More specifically, the above-described method and mechanical means for handle blocking is accomplished by modifying one component of the operating mechanism and one of the components of the rotary arm assembly for engagement therebetween in the event of welded contacts, thereby preventing movement of the handle to the OFF or RESET positions. 
   While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.