Patent Publication Number: US-6211757-B1

Title: Fast acting high force trip actuator

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a circuit breaker trip actuator, and, more particularly, to a fast acting, high force trip actuator. 
     Modem circuit breakers rely on electronics for the detection of potentially damaging over-current conditions. These electronics, known as trip units, sense current in a protected portion of an electrical distribution circuit and initiate a trip signal if the sensed current indicates an over-current condition. In such circuit breakers, an electromechanical actuator, known as a trip actuator or trip mechanism, is used to unlatch a circuit breaker operating mechanism in response to the trip signal. The operating mechanism is a spring-operated linkage arrangement. When unlatched, the operating mechanism separates a pair of main contacts to stop the flow electrical current to the protected portion of the distribution circuit. The operation of such circuit breakers is well known. 
     During the operation of the circuit breaker, it is desirable to part the main contacts is fast is possible after a trip signal is given by the electronic trip unit. Opening the contacts faster minimizes the arcing energy seen by the main contact structure, prolonging contact life. 
     The trip actuator is responsible for a large part of the time required in releasing these contacts. Typically, a trip actuator includes a solenoid or flux shifter that pushes or releases an actuating arm in response to the trip signal. The trip actuator also typically includes a mechanical linkage arrangement that translates the action of the actuating arm into a force that will unlatch the operating mechanism. 
     Increases in the speed or power of trip actuators have been accomplished through the use of a larger solenoid or flux shifter. However, the use of a larger solenoid or flux shifter requires that the trip unit to provide a higher firing voltage (trip signal) to the solenoid or flux unit. In addition, the larger solenoid or flux unit requires a greater amount of space in a tight circuit breaker housing. 
     BRIEF SUMMARY OF THE INVENTION 
     In an exemplary embodiment of the invention, a trip actuator for actuating an operating mechanism in a circuit breaker includes a trip arm biased to pivot in a first direction about a first axis and a latch arranged to pivot about a second axis. The trip arm acts on the latch at a first distance from the second axis to create a moment in a second direction about the second axis. The trip actuator also includes an electromechanical device with a plunger. The plunger acts on the latch at a second distance from the second axis to create a moment in the first direction about the second axis. The second distance is greater than said first distance. When a trip actuation signal is provided to the electromechanical device, the electromechanical device releases the plunger to allow the trip arm to pivot in the first direction and actuate the operating mechanism. 
     This invention has many advantages over the prior art, one of which includes the ability to increase the speed and power of the trip actuator without increasing the size or firing voltage of the electromechanical device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a circuit breaker; 
     FIG. 2 is an exploded perspective view of a circuit breaker including a trip actuator of the present invention; 
     FIG. 3 is a perspective view of the trip actuator and operating mechanism of FIG. 2; 
     FIG. 4 is a side view depicting the general operation of the circuit breaker operating mechanism of FIG. 3; 
     FIG. 5 is a perspective view of the trip actuator of FIG. 3 in a reset state; 
     FIG. 6 is a side view of the trip actuator of FIG. 3 in a latched and ready to operate state; and 
     FIG. 7 is a side view of the trip actuator of FIG. 3 in a tripped released state. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A top perspective view of a molded case circuit breaker  2  is provided at FIG.  1 . Molded case circuit breaker  2  is generally interconnected within a protected circuit between multiple phases of a power source (not shown) at line end  4  and a load to be protected (not shown) at load end  6 . Molded case circuit breaker  2  includes a housing  5  with a base  8 , a mid cover  10  and a top cover  12 . An operating handle  18  passes through top cover  12  and interconnects with a circuit breaker operating mechanism  14 . A trip actuator  66  is generally positioned within mid cover  10 . 
     Referring now to FIG. 2, an exploded view of molded case circuit breaker  2  is provided. A series of circuit breaker cassettes  20  are generally well known and may be, for example, of the rotary type. Circuit breaker cassettes  20  are seated approximately upstanding within base  8 , and one of the cassettes  20  includes operating mechanism  14  positioned thereon. One cassette  20  is provided for each phase of the electrical distribution circuit. Each cassette  20  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. Each cassette  20  is commonly operated by a first bar  22  and a second bar  24  that interface with the internal mechanisms of cassettes  20  and with operating mechanism  14  such that operating mechanism  14  operates all cassettes  20 . 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  2 . 
     Referring to FIG. 3, circuit breaker operating mechanism  14  includes a frame  16  having spaced apart sidewalls. An operating handle-yoke  26  generally fits over frame  16 . Operating handle  18  is interconnected with operating handle-yoke  26 . Operating mechanism  14  includes an operating mechanism cover  28  with a handle opening  30  formed therein allowing operating handle  18  to pass therethrough. Handle-yoke  26  includes a reset tab  32  depending generally perpendicularly therefrom to allow interface with trip actuator  66 , and more specifically to interact with a reset tab  72  of trip actuator  66 . Frame  16  includes a secondary latch  52  pivotally secured thereto. Secondary latch  52  includes a secondary latch tab  50  depending generally perpendicularly therefrom. Secondary latch tab  50  interfaces with a trip paddle  96  extending from trip actuator  66 . 
     Upon assembly, trip actuator  66  is positioned such that the trip paddle  96  is adjacent to latch tab  50 , and a reset tab  72  is adjacent to reset tab  32 . This is generally accomplished by seating trip actuator  66  alongside operating mechanism  14  within mid cover  10  (FIGS.  1  and  2 ). 
     Referring to FIGS. 3 and 4, the operation of the circuit breaker operating mechanism  14  will be generally described. FIG. 4 shows the operating mechanism  14  in three discrete positions: the “ON” position, the “OFF” position and the “RESET” position. Upon activation of trip actuator  66 , trip paddle  96  will be displaced generally in a forward direction (toward reset tab  72 ) and will contact latch trip tab  50 , displacing tab  50  from the “Latched” position to the “Unlatched” position as shown in FIG.  3 . This will release latch  52  allowing operating mechanism  14  to move from the “ON” position to a “TRIPPED” position (not shown), opening the set of circuit breaker contacts (not shown). In the “TRIPPED” position, handle  18  is located between the “ON” and “OFF” positions shown. Before operating handle  18  may be returned to the quiescent operation position (i.e., “ON”), circuit breaker operating mechanism  14  and trip actuator  66  must be reset. This is accomplished by manually rotating operating handle  18  in the counter-clockwise direction against the forces of one or more springs (not shown) to the “RESET” position, thereby moving the secondary latch  52  of operating mechanism  14  from the “Unlatched” position to the “Latched” position. The motion of operating handle  18  rotates reset tab  32 , thereby driving reset tab  72  towards trip paddle  96  to reset trip actuator  66 , as will be described in further detail hereinafter. 
     Referring to FIG. 5, a perspective view of trip actuator  66  is shown. Trip actuator  66  includes a frame  100 , an electromechanical device such as a flux shifter  102 , a trip arm  104 , a trip spring  106 , a reset lever  108 , and a latch  110 . Frame  100  includes a back wall  112  with two sidewalls  114 ,  116  depending substantially perpendicular therefrom. The sidewalls  114 ,  116  extend substantially parallel to each other, and are joined by a frame pins  118  that extend from side wall  114  to side wall  116 . Frame  100  is preferably formed from a single plate of metal. 
     Trip arm  104  is hingedly secured to sidewalls  114 ,  116  by a trip arm pivot  120 , which extends from side wall  114  to side wall  116 . Trip arm  104  includes two hinge portions  122  which accept trip arm pivot  120 , and a hinge support portion  124  that extends between hinge portions  122 . Trip arm  104  also includes a latch portion  125  that extends downwardly from support portion  124  and along the outside of side wall  116 . Trip paddle  96  depends substantially perpendicularly latch portion  125 . A latch surface  126  is formed on an edge of latch portion  125  opposite the trip paddle  96 . Trip arm  104  is preferably formed from a single plate of metal. 
     Trip spring  106  is shown as a torsion spring disposed around trip arm pivot  120 . One end of trip spring  106  is secured to the circuit breaker mid cover  10  (FIG.  2 ), while the other end is positioned beneath the hinge support portion  124  of the trip arm  104 . When installed in mid cover  10 , trip spring  106  acts to bias trip arm  104  in the clockwise direction, as shown in FIG.  5 . 
     Latch  110  is formed as a substantially rectangular shaft having a boss  126  disposed on a central portion thereof. A slot  128  formed in boss  126  accepts the head of a plunger  130 , which extends from flux shifter  102 . The ends of latch  110  are pivotally secured to frame sidewalls  114  and  116  by a latch pivot  132 . A latch pin  134  is secured to an end of latch  110 , and extends from latch  110  through an arcuate slot  136  disposed in side wall  116 . Latch pin  134  is arranged to interact with the latch surface  126  of trip arm  104  in a manner described hereinbelow. 
     Reset lever  108  includes side arms  138  that extend from a central support  140 . Side arms  138  extend along side walls  114 ,  116  and are pivotally secured to side walls  114 ,  116  by latch pivot  132 . Reset tab  72  and a reset pin  142  depend substantially perpendicularly from the side arm  138  proximate side wall  116 . Reset tab  72  and reset pin  142  extend through an arcuate slot  144  formed in sidewall  116 . 
     Flux shifter  102  is an electromechanical device mounted to rear wall  112  of the frame  100 . The construction and operation of flux shifter  102  is known in the art and is similar in operation to that described in U.S. Patent No.  5 , 453 , 724 . Flux shifter  102  includes the plunger  130 , which slidably extends from a body  146 . Plunger  130  is releasably secured by a magnet (not shown) within body  146 . Flux shifter  102  is arranged to receive a triggering signal (e.g., a trip signal) from an electrical device (e.g., a trip unit). Upon receipt of the triggering signal, a coil (not shown) in the flux shifter  102  shunts out the magnet, and the plunger  130  is released from the magnet. Once released by the magnet, the plunger  130  is free to extend outward from the body  146 . 
     Referring to FIGS. 5,  6 , and  7 , operation of the trip actuator  66  will now be described. FIG. 6 shows the trip actuator  66  in a latched and ready to operate state. In this state, the trip spring  106  is loaded to bias the trip arm  104  in a clockwise direction about the longitudinal axis of trip arm pivot  120 . The latch surface  126  of the trip arm  104  acts with a force “f” against the latch pin  134 . Latch surface  126  is configured such that the force “f” is directed at an angle “θ” past a line formed between the longitudinal axis of latch pivot  132  and the point of contact between the latch surface  126  and latch pin  134 . The directional component “f x ” of force “f” creates a counterclockwise moment about the axis of latch pivot  132 , with a moment arm of length “l”. The directional component “f y ” of force “f” acts through the longitudinal axis of latch pivot  132  and, therefore, does not add to the counterclockwise moment. 
     The latch  110  is held in an upright position by the plunger  130 , and the plunger  130  is held in tension by a magnet  150  disposed in the body  146  of the flux shifter  102 . The force “F” of the plunger  130  on the link  110  creates a clockwise moment about the axis of latch pivot  132 , with a moment arm of length “L”. In the latched and ready to operate state shown, the clockwise moment created by force “F” opposes the counterclockwise moment created by force “f”, to hold the latch  110  in the upright position against the force of the trip arm  104 . Because the moment arm “L” is much longer than moment arm “ 1 ”, and because only the horizontal component “f x ” must be overcome, the force “F” needed to maintain the latch  110  in the upright position is much less than the force “f” applied by the trip arm  104 . As a result, the magnet  150  need only provide a magnetic force sufficient to oppose force “F” and not the entire force “f” of the trip arm  104 . Thus, by adjusting lengths “l” and “L” and the angle “θ”, the force “f” provided by the trip arm  104  can be increased (e.g., by increasing the strength of spring  106 ) or decreased without having to increase or decrease the size of the flux shifter  102 . 
     When a trip (triggering) signal is provided to the flux shifter  102 , the coil (not shown) in the flux shifter  102  shunts out the magnetic circuit, releasing the plunger  130 . With the force “F” removed, the trip arm  104  will drive the latch pin  134 , causing the latch  110  to rotate counterclockwise about the latch pivot  132 . As the latch  110  and trip arm  104  rotate about their respective pivots  132 ,  120 , the latch pin  134  slides off the latch surface  126 , fully releasing the trip arm  104  and allowing the trip paddle  96  to move towards and into contact with the secondary latch tab  50 . The trip arm  104  may also contact one or more levers (not shown) to actuate other mechanisms, such as a bell alarm (not shown). Movement of secondary latch tab  50  trips the operating mechanism  14 , as described with reference to FIG. 4 hereinabove. The trip actuator  66  comes to rest in the tripped released state shown in FIG. 7, where the latch  110  is prevented from rotating further in the counterclockwise direction by contact with the frame pin  118  and the trip arm  104  is prevented from rotating further in the clockwise direction by contact with the reset tab  72 . 
     The trip actuator  66  is reset (i.e. placed in the latched and ready to operate state of FIG. 6) by the reset motion of the operating handle  18 . As the operating handle  18  is rotated to the “RESET” position, as described with reference to FIG. 4, the reset tab  32  of the operating handle  18  pushes the reset tab  72  of the trip actuator  66 . This action causes the reset lever  108  to pivot in a clockwise direction about latch pivot  132  and causes reset pin  142  to contact the reset surface  127  of the trip arm  104 . Trip arm  104  is thus rotated in the counterclockwise direction. As the trip arm  104  is driven counterclockwise, the latch pin  134  is released from beneath the latch surface  126  allowing the plunger  130  to be drawn back into the body  146  of the flux shifter  102  by the magnet  150  (which is no longer being shunted by the triggering signal). As the plunger  130  is drawn back into the body  146 , the plunger  130  causes the latch  110  to rotate to its upright position. With the latch  110  in its upright position, the trip arm  104  becomes latched, and the trip actuator  66  is in the latched and ready to operate state of FIG.  6 . 
     The high force, fast acting trip actuator described herein allows the speed or power of the trip actuator to be increased without the need for a larger flux shifter or higher firing voltages, as was required in trip actuators of the prior art. Speed and power can be increased, for example, by increasing the strength of spring  106 , and lengths “l” and “L” and the angle “θ” can be adjusted to allow the use of the same flux shifter or similar electromechanical device. 
     While the invention has been described with reference to a preferred 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 the 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.