Abstract:
A circuit breaker for a transformer includes means for interrupting circuitry in the transformer upon a fault condition in the transformer (the “fault interruption means”). The circuit breaker also includes means for interrupting the circuitry when a level of dielectric fluid in a tank of the transformer is unacceptably low (the “low oil trip means”). The fault interruption means includes a magnet, metal element, and first actuator. Upon the fault condition, the magnet and metal element separate, moving the first actuator to cause the electrical circuitry to open. The low oil trip means includes a float, insulating rod, and second actuator. When the dielectric fluid level drops to an unacceptably low level, the float and insulating rod drop, moving the second actuator to cause the circuitry to open. The low oil trip means operates independently of the fault interruption means, opening the circuitry without separating the magnet and metal element.

Description:
RELATED PATENT APPLICATIONS 
       [0001]    This non-provisional patent application claims priority under 35 U.S.C. §119 to U.S. Provisional Patent Application No. 61/119,914, entitled “Low Force Trip Mechanism for Primary Circuit Breaker,” filed Dec. 4, 2008. This application is related to U.S. Pat. No. 4,435,690, entitled “Primary Circuit Breaker,” filed April 26, 1982, U.S. Pat. No. 4,611,189, entitled “Underoil Primary Circuit Breaker,” filed Feb. 7, 1985, and U.S. Pat. No. 4,550,298, entitled “Trip Assembly for a Circuit Breaker,” filed Jan. 23, 1984. The complete disclosure of each of the foregoing priority and related patent applications is hereby fully incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates generally to a circuit breaker, and more particularly, to a low force low oil trip mechanism for a circuit breaker. 
       BACKGROUND 
       [0003]    A transformer is a device that transfers electrical energy from a primary circuit to a secondary circuit by magnetic coupling. Typically, a transformer includes a primary winding coupled to the primary circuit and at least one secondary winding coupled to the secondary circuit. The windings are wrapped around a core of the transformer. An alternating voltage applied to the primary winding creates a time-varying magnetic flux in the core, which induces a voltage in the secondary windings. Varying the relative number of turns of the primary and secondary windings around the core determines the ratio of the input and output voltages of the transformer. For example, a transformer with a turn ratio of 2:1 (primary:secondary) has an input voltage (from the primary circuit) that is two times greater than its output voltage (to the secondary circuit). 
         [0004]    Over-current protection devices are widely used to prevent damage to the primary and secondary circuits of transformers. For example, distribution transformers have conventionally been protected from fault currents by circuit breakers. Circuit breakers interrupt continuity in the electrical circuitry of the transformer upon detecting a fault therein. Unlike a fuse, which operates once and then has to be replaced, a circuit breaker can be reset and reused multiple times. 
         [0005]    It is well known in the art to cool high-power transformers and over-current protection devices thereof using a dielectric fluid, such as a highly-refined mineral oil. The dielectric fluid is stable at high temperatures and has excellent insulating properties for suppressing corona discharge and electric arcing in the transformer. For example, the dielectric fluid can suppress corona discharge and electric arcing that occurs when a circuit breaker interrupts the electrical circuitry of the transformer. Typically, the transformer includes a tank that is at least partially filled with the dielectric fluid. The dielectric fluid surrounds the transformer core and windings and at least part of the circuit breaker. 
         [0006]    The dielectric fluid in the tank may recede for any of a variety of reasons. For example, the dielectric fluid may recede because of a leak in the transformer tank. It can be problematic and even dangerous if the dielectric fluid in the tank recedes below a particular level. For example, if the dielectric fluid recedes below one or more components of the circuit breaker, the dielectric fluid may not provide sufficient insulative protection during a fault condition. In addition, if the dielectric fluid has dropped below the level of an arc chamber in the circuit breaker, an arc produced on interruption will be in air medium and may not extinguish until major damage has been done to the transformer. 
         [0007]    Therefore, it is desired to provide a circuit breaker that includes functionality for interrupting the electrical circuitry of the transformer when the dielectric fluid level of the transformer tank recedes to an unacceptable level. 
       SUMMARY 
       [0008]    A circuit breaker for a transformer is described herein. The circuit breaker includes a stationary contact configured to be electrically coupled to a circuit of a transformer. A movable contact is movable relative to the stationary contact and can open and close the circuit. A trip mechanism coupled to the movable contact is actuated when a fault condition exists in the transformer or when a level of dielectric fluid in a tank of the transformer is unacceptably low. 
         [0009]    A curie metal element is electrically coupled to the circuit. A magnet is coupled to the curie metal element when the circuit is closed. A temperature of the curie metal element increases in response to temperature increases in the dielectric fluid and/or fault conditions in the circuitry. As the temperature of the curie metal element increases, the magnetic coupling between the magnet and the curie metal element releases, causing movement of a first actuator coupled to the magnet. The first actuator causes the trip mechanism to open the circuit. 
         [0010]    A float member of the circuit breaker includes material that is responsive to changes in the dielectric fluid level in the transformer. The float member material has slightly less than neutral buoyancy, which allows the float member to float when dielectric fluid is present and to weigh a significant amount when the dielectric fluid is removed. As the dielectric fluid level drops, the float member drops and moves a second actuator, which causes the trip mechanism to open the circuit. The float member and second actuator operate independently of the magnet, curie metal element, and first actuator such that the float member and second actuator can cause the circuit to open without releasing the magnetic coupling between the magnet and metal element. 
         [0011]    In one embodiment, a circuit breaker for a transformer includes (a) fault interrupting means for causing circuitry in the transformer to open upon a fault condition in the transformer, and (b) low oil trip means for causing the circuitry to open when a level of dielectric fluid in a tank of the transformer is below a threshold level. The low oil trip means operates independently of the fault interrupting means to open the circuitry without actuating any components of the fault interrupting means. 
         [0012]    In another embodiment, a circuit breaker for a transformer includes a stationary contact configured to be electrically coupled to a circuit of a transformer. The circuit breaker includes a movable contact, a member coupled to the movable contact, and a tripping apparatus that moves the member to move the movable contact relative to the stationary contact to open and close the circuit. The circuit breaker also includes a fault interrupting apparatus that causes the tripping apparatus to open the circuit upon a fault condition in the transformer, and a low oil trip apparatus that causes the tripping apparatus to open the circuit when a level of dielectric fluid in a tank of the transformer is below a threshold level. The low oil trip apparatus operates independently of the fault interrupting apparatus to open the circuitry without actuating any components of the fault interrupting apparatus. As used herein, the term “apparatus” can include only one component or multiple components that may or may not be coupled to one another. 
         [0013]    In yet another embodiment, a circuit breaker assembly for a transformer includes a plurality of circuit breakers. Each circuit breaker includes a fault interrupting means for causing transformer circuitry associated with the circuit breaker to open upon a fault condition in the transformer, and low oil trip means for causing the circuitry to open when a level of dielectric fluid in a tank of the transformer is below a threshold level. The low oil trip means operates independently of the fault interrupting means to open the circuitry without actuating any components of the fault interrupting means. A linkage bar is coupled to each of the circuit breakers and rotates in response to the fault interrupting means of one of the circuit breakers causing the transformer circuitry associated with the one of the circuit breakers to open. The rotating of the linkage bar causes the fault interrupting means of each other circuit breaker to open the transformer circuitry associated with the other circuit breaker. 
         [0014]    In another embodiment, a method for protecting circuitry of a transformer, includes the steps of (a) determining whether a fault condition exists in a transformer; (b) in response to determining that a fault condition exists in the transformer, releasing a magnetic coupling to cause circuitry in the transformer to open; (c) determining whether a level of dielectric fluid in a tank of the transformer is below a threshold level; and (d) in response to determining that the level of dielectric fluid is below the threshold level, causing the circuitry in the transformer to open without releasing the magnetic coupling. 
         [0015]    These and other aspects, objects, features, and embodiments will become apparent to a person of ordinary skill in the art upon consideration of the following detailed description of illustrative embodiments exemplifying the best mode for carrying out the invention as presently perceived. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    For a more complete understanding of the invention and the advantages thereof, reference is now made to the following description, in conjunction with the accompanying figures briefly described as follows. 
           [0017]      FIG. 1  is a side elevational view of a circuit breaker in a normal operating position, with certain elements removed for clarity. 
           [0018]      FIG. 2  is a side elevational view of the circuit breaker depicted in  FIG. 1 , in a normal operating position. 
           [0019]      FIG. 3  is a side elevational view of the circuit breaker depicted in  FIG. 1 , in a normal operating position. 
           [0020]      FIG. 4  is a side elevational view of the circuit breaker depicted in  FIG. 1 , in a tripped position. 
           [0021]      FIG. 5  is a side elevational view of a circuit breaker in a normal operating position, in accordance with certain exemplary embodiments. 
           [0022]      FIG. 6  is a side cross-sectional view of the circuit breaker depicted in  FIG. 5 , in a normal operation position. 
           [0023]      FIG. 7  is an exploded perspective side view of the circuit breaker depicted in  FIG. 5 , with certain elements removed for clarity. 
           [0024]      FIG. 8  is a side cross-sectional view of the circuit breaker depicted in  FIG. 5 , in a normal operation position, with certain elements removed for clarity. 
           [0025]      FIG. 9  is a side perspective view of a circuit breaker mechanism, in accordance with certain alternative exemplary embodiments. 
           [0026]      FIG. 10  is a side perspective view of a trip collar of the circuit breaker mechanism depicted in  FIG. 9 , in accordance with certain exemplary embodiments. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0027]    Turning now to the drawings, in which like numerals indicate like elements throughout the figures, exemplary embodiments are described in detail.  FIGS. 1-4  illustrate a circuit breaker  100  for a transformer  300  ( FIG. 3 ). With reference to  FIGS. 1-4 , the circuit breaker  100  is immersed in dielectric fluid  305  in a tank  310  of the transformer  300  and connected in series with a primary circuit  200  of the transformer  300 . The circuit breaker  100  is operable to open the primary circuit  200  in response to detected fault currents and temperature levels of the dielectric fluid  305 , as described below. 
         [0028]    The circuit breaker  100  includes a frame or base  102  to which an arc extinguishing assembly  204  is coupled. The arc extinguishing assembly  204  includes a central core formed of an arc extinguishing material, such as a polyester, which is enclosed within a housing  204   d.  The core includes a bore with a base  204   a  at the bottom and a cap  204   b  at the top. The base  204   a  and cap  204   b  may be formed as integral parts of the core. 
         [0029]    The space between the base  204   a  and the cap  204   b  defines an arc chamber  204   c  which is open to the bore through openings in the core. The openings allow gases created by arcing during interruption or opening of the circuit breaker  100  to expand into the arc chamber  204   c.  The expanding gases are confined in the arc chamber  204   c  by the housing  204   d.  A relief port may be provided on the periphery of the cap  204   b  to allow for the restricted discharge of oil and/or gases from the arc chamber  204   c  on interruption and to allow for the ingress of dielectric fluid into the arc chamber  204   c  when the circuit breaker  100  is immersed in the dielectric fluid  305 . All of the axial forces of the expanding gases are confined to the space between the base  204   a  and the cap  204   b.    
         [0030]    The upper end of the bore is closed by means of a conductive contact  615  ( FIG. 6 ) provided in the arc extinguishing assembly  204 . The contact  615  is electrically coupled to the primary circuit  200  via a high voltage input line  223 . A conductive rod  101  is movable within the bore of the arc extinguishing assembly  204  to open and close the primary circuit  200 . When the conductive rod  101  engages the conductive contact  615 , the primary circuit  200  is closed; when the conductive rod  101  is separated from the conductive contact  615 , the primary circuit  200  is opened. 
         [0031]    A latch mechanism  218  is operable to move the conductive rod  101  to open and close the primary circuit  200 . As best seen in  FIG. 4 , the latch mechanism  218  includes a first lever arm  401 , a second lever arm  402 , and a trip assembly  251 . The first lever arm  401  is normally latched or locked to the second lever arm  402  and is released from the lever arm  402  by the trip assembly  251  to open the circuit breaker  100  under a fault condition. More particularly, the first lever arm  401  is pivotally mounted at one end on a pivot pin  252  provided in the frame  102 . The conductive rod  101  is coupled to the other end of the lever arm  401 . Pivotal movement of the lever arm  401  moves the conductive rod  101  axially in the bore of the arc extinguishing assembly  204 , into and out of engagement with the conductive contact  615 . 
         [0032]    The second lever arm  402  is pivotally mounted on the pin  252  and is bent in the form of a “U” (as best seen in  FIG. 7 ) to provide a slot to straddle the first lever arm  401 . The lever arm  401  is held in the slot by a rod  264 , which is movable into engagement with a flange  466  provided on the lever arm  401 . With reference to  FIGS. 1-4  and  7 , the end of lever arm  402  proximate the conductive rod  101  is bent at a substantially right angle to form an extension  705  ( FIG. 7 ), which is bent at a second substantially right angle to form a stop arm  710  ( FIG. 7 ). An end  715  ( FIG. 7 ) of the stop arm  710  is bent at a substantially right angle to form a limit stop to downward motion of the lever arm  402 . The extension  705  includes a guide slot  720  for the rod  264  and a main spring opening  735 . 
         [0033]    The trip assembly  251  includes a trip lever  263  mounted for pivotal motion on the pin  252  and the rod  264 . The trip lever  263  includes an opening  465  at one end and a first cam  467  and second cam  469  at the other end. The rod  264  has one end bent to enter the opening  465  in the trip lever  263 . The other end of the rod  264  extends through the guide slot  720  in the lever arm  402 , to position the rod  264  to engage the flange  466  on the lever arm  401 . An o-ring  786  disposed around the extension  705  biases the rod  264  against the flange  466 . The rod  264  is pulled out from the flange  466  on rotation of the trip lever  263  clockwise and pushed toward the flange  466  on rotation of the trip lever  263  counter-clockwise. 
         [0034]    The lever arms  401  and  402  are normally biased in opposite directions by a spring  456 . The spring  456  is anchored in openings  449  and  458  in the lever arms  401  and  402 , respectively. A slot  453  in the lever arm  401  provides clearance for the end of the spring  456  anchored in the opening  458 . When the rod  264  engages the flange  466 , the lever arms  401  and  402  will move together, as a unit. On disengagement of the rod  264  from the flange  466 , the lever arm  401  will rotate away from the lever arm  402 , pulling the conductive rod  101  away from the conductive contact  615 , thereby opening the primary circuit  200 . 
         [0035]    Once the circuit breaker  100  has been tripped to the open position, the trip mechanism may be reset by: (a) rotating the lever arm  402  clockwise into alignment with the lever arm  401 , (b) re-coupling the lever arms  401  and  402  together by repositioning the rod  264  within the flange  466 , and (c) rotating the lever arms  401  and  402 , as a unit, counter-clockwise so that the conductive rod  101  electrically engages the conductive contact  615 . This is accomplished, in part, using an overcenter spring  261 , which is moved between an upper position and a lower position by means of a crank shaft  220 . In the upper position, an end  261   a  of the spring  261  is disposed at point  203 ; in the lower position, the end  261   a  is disposed at point  209 . The end  261   a  of the spring  261  is connected to an opening  296  in a yoke  298  that is mounted on the crank shaft  220 . The other end of the spring  261  is connected to the spring opening  735  on the extension  705  of the lever arm  402 . The crank shaft  220  is operable to be rotated manually by means of an external handle  320 . The yoke  298  is rotated counterclockwise from the circuit breaker open position shown in  FIG. 4  to the circuit breaker closed position shown in  FIG. 2 . As the spring  261  is rotated past the pivot axis of the pin  252 , the bias force of the spring  261  on the lever arm  402  is reversed. As the spring  261  moves overcenter, the lever arm  402  will snap either upward or downward. 
         [0036]    Means are provided to assure the engagement of the rod  264  with the flange  466  when the lever arm  402  is snapped to the down position, in realigning the lever arm  402  with the lever arm  401 . Such means is in the form of a crank shaft section  292  of the crank shaft  220 . The crank shaft section  292  is rotated manually toward the first cam  467  of the trip lever  263  and engages the first cam  467  to rotate the trip lever  263  counterclockwise on the pin  252 . The motion of the trip lever  263  pushes the rod  264  toward the flange  466 . 
         [0037]    Continued rotation of the section  292  will move the end of the rod  264  to a position below the flange  466 . To ensure that the rod  264  moves under the flange  466  when the lever arm  402  is snapped down by the spring  261 , the crank shaft  220  is rotated far enough to move the section  292  against the lever arm  402 . The o-ring  786  biases the rod  264  laterally toward the flange  466 . When the section  292  is rotated against the lever arm  402 , the rod  264  will be moved below the flange  466 , allowing the o-ring  786  to bias the rod  264  against the side of the lever arm  402 . 
         [0038]    Once the rod  264  is positioned in the flange  466  and the lever arms  401  and  402  are thereby secured together, the circuit breaker  100  may be reset by rotating the crank shaft  220  clockwise. On rotation of the crank shaft  220  clockwise, the yoke  298  will be returned to the position shown in  FIG. 2 , reversing the bias of the spring  261  on the lever arm  402 , causing it to rotate counterclockwise. Because the rod  264  is now engaged with the flange  466 , the lever arm  401  will follow the upward motion of the lever arm  402 . The motion of the lever arm  401  will move the conductive rod  101  upward in the bore of the arc extinguishing assembly  204 , into engagement with the contact  615 , to close the primary circuit  200 . 
         [0039]    Tripping of the circuit breaker  100  is controlled by a temperature sensing assembly  219 , which includes a magnet  208 . As a material approaches the curie temperature, the magnetic properties of the material will be reduced, resulting in a loss of attraction to a corresponding magnet. A metal element  205  of the circuit breaker  100  is immersed in the dielectric fluid of the transformer and operatively positioned to sense the heat of a fault current on the primary circuit  200  thereof. The metal element  205  will respond to both the temperature of the dielectric fluid and the temperature of any fault current. 
         [0040]    The trip assembly  219  includes a bell crank  210  pivotally mounted on a pin  212  in the frame  102 . The magnet  208  is mounted on one end of the bell crank  210 , in a position to engage the metal element  205 . The metal element  205  includes a folded coil with electrical insulation between the folds. The metal element  205  is connected in series with lines  224  and  226 . Line  224  is electrically coupled to the conductive rod  101 . Line  226  is electrically coupled to the primary circuit  200  and is an output line of the circuit breaker  100 . 
         [0041]    Under normal load, the resistance of the folded coil will increase the temperature of the metal element  205  slightly. Under fault conditions, an immediate temperature rise will occur in the folded coil. The bell crank  210  includes an actuating end  216  and a latch member  217 . A spring  214  biases the bell crank  210  in a counterclockwise direction. 
         [0042]    The rotary motion of the bell crank  210  will move the latch member  217  away from the cam  469  of the trip lever  263  and will move the end  216  of the bell crank  210  into engagement with the cam  469 . As best seen in  FIG. 7 , a spring  284  coupled to the frame  102  and the cam  469  of the trip lever  263  biases the cam  469  in the clockwise direction. When the latch member  217  is moved away from the cam  469 , the spring  284  actuates the cam  469  in the clockwise direction, pulling the rod  264  away from the lever arm  401 . Rotation of the bell crank  210  also may cause the actuating end  216  to assist with rotation of the trip lever  263  clockwise. 
         [0043]    The magnet  208  prevents the bell crank  210  from rotating due to the bias of the spring  214 . The magnetic force of the magnet will hold the magnet  208  against the element  205 . In the event of a fault in the primary circuit  200  of the transformer  300 , the temperature of the folded coil will increase the temperature of the element  205  in relation to the fault current. The resistance of the folded coil will produce an immediate rise in the temperature of the metal element  205 . As the element temperature approaches the curie temperature, the magnetic holding force of the magnet  208  will be reduced, thereby reducing the magnetic attraction of the magnet  208  to the metal element  205  and allowing the bell crank  210  to rotate due to the bias of the spring  214 . The same condition will occur if the dielectric fluid temperature increases the temperature of the metal element  205 . 
         [0044]    The temperature sensing assembly  219  is reset on the counterclockwise rotation of the crank shaft  220 . The crank shaft section  292  of the crank shaft  220  will engage the cam  467  to rotate the trip lever  263  counterclockwise. The cam  469  will engage the end  216  of the bell crank  210 , rotating the bell crank  210  clockwise. As the magnet  208  is moved into close proximity to the metal element  205 , the magnetic force of the magnet  208  will provide the final movement in resetting the temperature responsive assembly. 
         [0045]    The circuit breaker  100  includes a low oil lockout functionality that causes the circuit breaker  100  to become unusable in the event that a level of the dielectric fluid in the transformer tank  310  drops unacceptably low. The circuit breaker  100  includes a float member  297  that includes material that is responsive to changes in the dielectric fluid level in the transformer. In particular, the float member  297  material has slightly less than neutral buoyancy, which allows the float member  297  to float when dielectric fluid is present and to weigh a significant amount when the dielectric fluid is removed. 
         [0046]    As the dielectric fluid level drops, the float member  297  and an insulating rod  298  connected thereto move axially downward. The insulating rod  298  is supported in an opening (not shown) in the frame  102  and an opening  249  in a guide plate  250  coupled to the arc extinguishing assembly  204 . When the float member  297  and insulating rod  298  are in a normal operating position in which the dielectric fluid level is satisfactory, a bottom end of the insulating rod is disposed above the crank shaft section  292  and is prevented from further upward movement by a pin  253  which engages the guide plate  250 . When the float member  297  and insulating rod  298  move downward in response to a drop in the dielectric fluid level, the bottom end of the insulating rod  298  is disposed in the path of motion of the crank shaft section  292 , preventing manual opening of the circuit breaker  100 . 
         [0047]      FIGS. 5-8  illustrate a circuit breaker  500  in accordance with certain exemplary embodiments. The circuit breaker  500  is similar to the circuit breaker  100  described above in connection with  FIGS. 1-4  except that the circuit breaker  500  includes a modified trip mechanism with a low oil trip functionality. With reference to  FIGS. 5-8 , the modified trip mechanism includes a modified bell crank  504 , a lever  501 , and a float lever mechanism  740 , which enable the circuit breaker  500  to open in response to an unacceptably low level of dielectric fluid  305 . 
         [0048]    The modified bell crank  504  includes a first end  504   a  and a second end  504   b.  The magnet  208  is coupled to the first end  504   a.  The ends  504   a  and  504   b  are disposed substantially perpendicular to one another, with a member  504   c  being disposed between the ends  504   a  and  504   b.    
         [0049]    The lever  501  is coupled to the end  504   b  and is disposed substantially between the cam  469  and the member  504   c.  As best seen in  FIG. 8 , a spring  601  is coupled to the lever  501  and the end  504   b  and biases the lever  501  in a clockwise direction. The end  501   a  of the lever  501  engages the cam  469  and prevents the cam  469  from rotating clockwise to trip the circuit breaker  500  absent a force from the bell crank  504  or a force from the float lever mechanism  740 , as described below. 
         [0050]    The bell crank  504  rotates counterclockwise in response to a fault condition, substantially as described above in connection with the bell crank  210  of the circuit breaker  100 . When the bell crank  504  rotates counterclockwise, a protrusion  604  on a side of the bell crank  504  actuates an end  501   b  of the lever  501  in the counterclockwise direction, releasing the cam  469  from the lever  501  and allowing the spring  284  to cause the cam  469  to rotate clockwise to trip the circuit breaker  500 . 
         [0051]    The float lever mechanism  740  includes a float lever  702 , a float lever bias spring  701 , a catch spring  703 , and a base member  704 . The base member  704  is coupled to the frame  102  via a screw  790  or other fastener. The float lever  702  is disposed substantially within a cavity  704   a  of the base member  704 , with a bottom portion  702   b  of the float lever  702  being disposed beneath the base member  704  and edges  702   c  and  702   d  of the float lever  702  engaging corresponding edges  704   b  and  704   c,  respectively, of the base member  704 . The float lever  702  is pivotable within the cavity  704   a,  substantially on a pivot point  702   e.    
         [0052]    The float lever bias spring  701  includes ends  701   a  that are coupled to the base member  704 . For example, each end  701   a  can be coupled to the base member  704  by engaging a corresponding notch  704   a  in a side edge of the base member  704 . A middle portion  701   b  of the float lever bias spring  701   b  rests on a top portion  702   a  of the float lever  702 . The float lever bias spring  701  biases the float lever  702  in a clockwise direction. The edge  702   c  of the float lever  702  rests on the catch spring  703 . 
         [0053]    As the level of dielectric fluid  305  in the transformer  300  drops, the float member  505  and an insulating rod  510  coupled thereto begin to drop, substantially as described above in connection with the float member  297  and insulating rod  298  of the circuit breaker  100 . As best seen in  FIG. 8 , the bottom end of the insulating rod  510  includes an angled surface  810 , which pushes the catch spring  703  laterally within the frame  102 . In certain exemplary embodiments, the frame  102  constrains the catch spring  703  and rod  805  so that the catch spring  703  only can rotate within the horizontal plane, and the rod  805  only can move axially. 
         [0054]    The weight of the float member  505  is such that it will push the catch spring  703  out of the way of the lever  702 , allowing the float lever bias spring  701  to move the lever  702  in a clockwise direction. When the lever  702  moves clockwise, an end  702   f  of the lever  702  actuates an end  501   a  of the lever  501  in a counterclockwise direction, overcoming the bias force of the spring  601 . This movement of the lever  501  releases the cam  469  so that the spring  284  can move the cam  469  clockwise, thereby causing the circuit breaker  500  to open. 
         [0055]    The circuit breaker  500  can be manually reset from the open position to the closed position substantially as described above in connection with the circuit breaker  100 . With reference to  FIGS. 1-8 , the circuit breaker  500  may be reset by: (a) rotating the lever arm  402  clockwise into alignment with the lever arm  401 , (b) re-coupling the lever arms  401  and  402  together by repositioning the rod  264  within the flange  466 , and (c) rotating the lever arms  401  and  402 , as a unit, counter-clockwise so that the conductive rod  101  electrically engages the conductive contact  615 . 
         [0056]    Depending on the level of dielectric fluid  305  in the transformer  300  during the reset operation, the float  505  may be in the up position (corresponding to an adequate level of dielectric fluid) or in the down position (corresponding to an inadequate level of dielectric fluid). If the float  505  is in the up position, the insulating rod  510  is disposed above the crank shaft section  292 . The crank shaft section  292  moves past the underside of the float lever  702 , pushing it up and charging the float lever bias spring  701 . The catch spring  703  moves out of the way during the reset operation and snaps back under the float lever  702  when fully reset. If the float  505  is in the down position during the reset operation, the insulating rod  510  is disposed in the path of motion of the crank shaft section  292 , restricting movement of the crank shaft section  292  and preventing the operator from re-energizing the circuit breaker  500 . 
         [0057]    Thus, the circuit breaker  500  includes: (a) a “fault trip” functionality for causing the circuit breaker  500  to open in response to a fault current or other temperature increase, (b) a “low oil trip” functionality for causing the circuit breaker  500  to open when the dielectric fluid  305  drops to an unacceptable level, and (c) a “low oil lock-out” functionality for disallowing the circuit breaker  500  to be reset when there is an unacceptable level of dielectric fluid  305  in the transformer tank  300 . The fault trip functionality operates substantially independent of the low oil trip and low oil lock-out functionality. In particular, the circuit breaker  500  may experience a low oil trip without releasing the magnet  208  or rotating the bell crank  504 . Instead, the low oil trip merely requires the insulating rod  510  to actuate the lever  702 . 
         [0058]    The amount of force required to actuate the lever  702  is minimal. Generally, the amount of force required is about 0.05 pounds. In contrast, the amount of force required to release the magnet  208  is about two pounds. By actuating the lever  702  without releasing the magnet  208 , the required force is reduced by about 97.5%. Less required force is advantageous because it allows the float to weigh less and displace less dielectric fluid  305  in the transformer tank  310 . For example, the float may weigh only about 40 grams. In certain exemplary embodiments, the float includes a buoyant foam material, such as Nitrile Butadiene Rubber (NBR) or another high temperature closed cell foam. The foam material also may include a dense material, such as steel, to provide necessary weight for operating the float. For example, the float may include foam that has been injected with steel members. 
         [0059]      FIG. 9  is a side perspective view of a circuit breaker mechanism  900 , in accordance with certain alternative exemplary embodiments. With reference to  FIG. 9 , the circuit breaker mechanism  900  includes three circuit breakers  905  that are mounted such that operating shafts of the circuit breakers  905  are linked together. For example, each circuit breaker  905  may be substantially similar to the circuit breaker  100  depicted in  FIGS. 1-4  or the circuit breaker  500  depicted in  FIGS. 5-8 . Each circuit breaker  905  is associated with and electrically coupled to a different circuit or portion of the same circuit. For example, each circuit breaker  905  may be electrically coupled to a different phase of a three-phase power system. Although depicted in  FIG. 9  as including three circuit breakers  905 , a person of ordinary skill in the art having the benefit of the present disclosure will recognize that the circuit breaker mechanism  900  can have any number of circuit breakers  905  in alternative exemplary embodiments. 
         [0060]    The bell crank (not shown) of each circuit breaker  905  is coupled to a trip collar  901  of the circuit breaker  905 .  FIG. 10  is a side perspective view of the trip collar  901 , in accordance with certain exemplary embodiments. With reference to  FIGS. 9 and 10 , the trip collars  901  of all the circuit breakers  905  are coupled to one another via at least one linkage bar  902 . Rotation of the bell crank on one circuit breaker  905  causes the trip collar  901  on that circuit breaker  905  to rotate, thereby causing the linkage bar  902  to rotate. That rotation of the linkage bar  902  causes the trip collars  901  and bell cranks on the other circuit breakers  905  to rotate, tripping all of the linked circuit breakers  905 . 
         [0061]    In certain exemplary embodiments, a common solenoid (not shown) may be mounted to electronically trip one or more of the circuit breakers  905 . For example, the solenoid may rotate the lever  501  on a circuit breaker  905  of the type depicted in  FIGS. 5-8 . In addition, or in the alternative, the solenoid may rotate the trip collar  901  and linkage bar  902  on a three phase circuit breaker mechanism  900  of the type depicted in  FIG. 9 . This may be accomplished with a rotary solenoid or a linear solenoid on a simple linkage bar  902 . 
         [0062]    To provide a thermal trip, a common bimetallic snap action structure or device such as a wax motor, that uses change of state or internal crystalline or mechanical structures to provided needed force over a distance, may be used to rotate the lever  501  on a circuit breaker  905  of the type depicted in  FIGS. 5-8  and/or the trip collar  901  and linkage bar  902  on a three phase circuit breaker mechanism  900  of the type depicted in  FIG. 9 . The device may be used to automatically trip and reset each circuit breaker  905 . Alternatively, each circuit breaker  905  may be manually reset as described above in connection with the circuit breakers  100  and  500 . 
         [0063]    Although specific embodiments have been described above in detail, the description is merely for purposes of illustration. It should be appreciated, therefore, that many aspects of the invention were described above by way of example only and are not intended as required or essential elements of the invention unless explicitly stated otherwise. Various modifications of, and equivalent steps corresponding to, the disclosed aspects of the exemplary embodiments, in addition to those described above, can be made by a person of ordinary skill in the art, having the benefit of this disclosure, without departing from the spirit and scope of the invention defined in the following claims, the scope of which is to be accorded the broadest interpretation so as to encompass such modifications and equivalent structures.