Abstract:
Systems and methods provide a magnetic actuator having more than one air gap. After the trip unit is triggered, a first armature is accelerated to quickly close a first air gap and then mate with a second armature. The first and second armature then move toward a core to close a second air gap and reach the final combined armature position, causing a contact to open. A faster reaction time is provided, yet without increasing the number of turns of the trip coil winding, and provides a more efficient actuator.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates generally to magnetic actuators, and, more particularly, to magnetic actuator configurations including more than one air gap. 
     Devices such as circuit breakers, accessories for circuit breakers, and relays, for example, include a trip unit that, when a predetermined level of current is sensed, opens the current path to stop the flow of the current through an electrical circuit. Circuit breakers are well-known and commonly used to provide this automatic circuit interruption when undesired overcurrent conditions occur. Overcurrent conditions can include, but are not limited to, overload conditions, ground faults, and short-circuit conditions. The ability to break the flow of current is usually achieved by having a movable contact(s), which is attached to a movable arm or blade, that separates from a stationary contact(s), which is attached to a stationary arm or blade. The trip unit includes a magnetic actuator, which is the component that drives the tripping action using, in general, a spring-biased mechanism to force the movable blade, and therefore the movable contact, away from the stationary contact. 
     In general, the magnetic actuator component of the trip unit is designed to react as quick as possible, yet magnetic actuators with one air gap, however, start slowly due to their initial mass and large initial airgap and therefore generate low forces during the initial portion of the travel. Attempts have been made to improve the reaction time, but these improvements have come with unwanted costs. For example, a higher number of turns of a trip coil winding would increase the force acting on the magnetic actuator allowing for a faster reaction time, but with the higher number of turns of the coil winding comes an unwanted and unacceptable increase of power loss from the circuit breaker, thereby causing inefficiency and an increase in overall size. 
     It would, therefore, be desirable to have magnetic actuators that provide improved reaction times, but without the drawbacks that comes along with known magnetic actuators. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The present embodiments overcome the aforementioned problems with providing a faster reaction time of the magnetic actuator by providing systems and methods including a magnetic actuator having more than one air gap. After the trip unit is triggered, a first armature is accelerated to quickly close a first air gap and then mate with a second armature. The first and second armature then move toward a core to close a second air gap and reach the final combined armature position, causing the contact to open. This novel solution provides a faster reaction time, yet without increasing the number of turns of the trip coil winding, and provides a more efficient solution. 
     Accordingly, embodiments of the present invention include a magnetic actuator for opening a contact to interrupt the flow of current. The actuator comprises a first armature and a second armature, the first armature and the second armature spaced apart by a first qap while in a reset position. The second armature and a core are spaced apart by a second gap while in the reset position. 
     To the accomplishment of the foregoing and related ends, the embodiments, then, comprise the features hereinafter fully described. The following description and the annexed drawings set forth in detail certain illustrative aspects of the invention. However, these aspects are indicative of but a few of the various ways in which the principles of the invention can be employed. Other aspects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: 
         FIG. 1  is a perspective view in section of an exemplary circuit breaker including a single gap magnetic actuator; 
         FIG. 2  is a side view in section of the single gap magnetic actuator shown in  FIG. 1 ; 
         FIG. 3  is a side view in section of a magnetic actuator according to embodiments of the invention, and including more than one actuator gap; 
         FIG. 4  is a side view in section of an alternative magnetic actuator according to embodiments of the invention, and including more than one actuator gap; 
         FIG. 5  is a side view in section of another alternative magnetic actuator according to embodiments of the invention, and including more than one actuator gap; 
         FIG. 6  is a side view in section of yet another alternative magnetic actuator according to embodiments of the invention, and including more than one actuator gap; 
         FIGS. 7 through 10  show the magnetic actuator of  FIG. 5 , showing actuator positions from reset to contacts open; 
         FIGS. 11 and 12  show graphical comparisons of a single gap actuator compared to a two gap actuator, and indicate an efficiency improvement with the two gap actuator; 
         FIG. 13  is a graphical comparison of the magnetic force F for a given current between a single gap actuator and a two gap actuator; and 
         FIG. 14  shows the gain of activation current (n times rated current) for a two gap actuator compared to one gap actuators. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning now to the drawings, and referring initially to  FIG. 1 , an exemplary circuit breaker  10  containing a magnetic actuator  12  with a single gap  14  positioned within a housing  15  is shown. The circuit breaker  10  includes a line wire input  16  for electrically connecting a current carrying input wire (not shown) to the input of the circuit breaker, and a line wire output  18  for electrically connecting a current carrying output wire (not shown) to the output of the circuit breaker. The current carrying wires and the circuit breaker  10  comprise a portion of an electrical circuit. Once the input and output wires are electrically connected to the circuit breaker  10 , and the trip mechanism  20  is reset, current is able to flow through the circuit breaker  10 . The current flows from the line wire input  16  to the trip coil  22 . The trip coil  22  includes n number of turns around a coil former  24 , where n is a predetermined number depending on the circuit breaker configuration. The single gap magnetic actuator  12  is shown generally within the coil former  24 . Current flows through the trip coil and to a contact  26 . In one embodiment, the circuit breaker includes a first contact  27  and second contact  28 . A movable contact arm  30  electrically couples the first contact  27  to the second contact  28 . When the first and second contacts are closed, current is able to flow through the movable contact arm  30  and to the line wire output  18 . 
     As seen in  FIGS. 1 and 2 , the magnetic actuator  12  is shown with a single gap  14  between the pole faces of an armature  40  and a core  52 . Referring particularly to  FIG. 2 , the armature  40  includes a first end  42  and a second end  44 , the second end being a generally flat pole face. The first end  42  releasably couples to the trip mechanism  46 . The armature  40  is partially housed within an upper portion  48  of the coil former  24 . As previously discussed, the trip coil  22  winds around the coil former  24 . The traditional magnetic actuator  12  includes only this one gap  14  between the second end  44  of the armature  40  and the first end  50  of the core  52 . The first end  50  being a mating generally flat pole face. 
     The core  52  includes the first end  50  and a second end  54 , and is positioned near a lower portion  56  of the coil former  24 , and may be retained in the coil former  24  with a termination cover  58  at or near the lower portion  56  of the coil former. A spring  60  provides an expansion force between the armature  40  and the core  52 . A non-magnetic push rod  62  slidably extends through the core  52 . 
     In use, the armature  40  is the component of the magnetic actuator  12  that moves when a magnetic field generated by current flow through the trip coil  22  exceeds the expansive force of the spring  60 . The magnetic field causes the armature  40  to move in the direction of the core  52 . During the movement of the armature  40  toward the core  52 , the second end  44  of the armature  40  contacts the first end  64  of the push rod  62 . The second end  66  of the push rod  62  is mechanically coupled to the movable contact arm  30 . 
     The gap  14  is sized to allow a predetermined amount of downward travel of the armature  40  before the second end  44  of the armature  40  contacts the first end  64  of the push rod  62  before the pole faces mate. The size of gap  14  determines the extent of travel of the armature  40 . As the armature  40  overcomes the initial force of the spring  60  and travels towards the core  52  due to the magnetic force, the second end  44  of the armature  40  contacts the first end  64  of the push rod  62 . The armature  40  continues to travel toward the core  52 , thereby pushing the push rod  62  downward, which in turn causes the movable contact arm  30  to separate from the fixed portions  70  and  72  of contacts  27  and  28  respectively, and open the contacts  27  and  28 , thereby breaking the flow of current through the circuit breaker  10 . The gap  14  is closed when the second end  44  of the armature  40  contacts the first end  50  of the core  52 . 
     Referring now to  FIGS. 3 ,  4 ,  5 , and  6 , trip units according to embodiments of the invention are shown. As can be seen in each of the embodiments, the armature may be separated into at least two individual armature components, although it is to be appreciated that more than two armature components are contemplated as part of the invention. A first actuator gap  102  is provided between a first armature  104  and a second armature  106 , and a second actuator gap  108  is provided between the second armature  106  and the stationary core  110 . Each of the embodiments shown in  FIGS. 3 ,  4 ,  5 , and  6  will now be described in greater detail. Where applicable, like elements will bear like reference numerals. 
     Referring to  FIG. 3 , a novel magnetic actuator  100  is shown including a first actuator gap  102  and a second actuator gap  108 . The magnetic actuator  100  includes a first armature  104  a second armature  106 , both with generally flat pole faces. The first armature  104  includes a first end  112  and a second end  114 , and the second armature  106  includes a first end  116  and a second end  118 . The first end  112  of the first armature  104  releasably couples to the trip mechanism  46 . The first armature  104  may be partially housed within the upper portion  48  of the coil former  24 , and in one embodiment is retained from sliding upward from within the coil former by a lip or rim  120  on the inner wall  122  of the coil former. As with the traditional magnetic actuator  12 , the trip coil  22  winds around the coil former  24 . The novel magnetic actuator  100  includes the first actuator gap  102  between the second end  114  of the first armature  104  and the first end  116  of the second armature  106 . 
     The second armature  106  is housed within the mid section  124  of the coil former  24 , and, in one embodiment may also be restrained from sliding upward from within the coil former by a second lip or rim  126  on the inner wall  122  of the coil former. A non-magnetic transmission plunger  130  having a first end  132  and a second end  134  slidably extends through the second armature  106 , with the second end  134  contacting a spring  60 . The spring  60  provides an expansion force between the second end  134  of the transmission plunger  130  and the core  110 . The core  110  includes a first end  136  and a second end  138  and is positioned near the lower portion  56  of the coil former  24  and may be retained in the coil former  24 , such as with a termination cover  58  at or near the lower portion  56  of the coil former. A non-magnetic push rod  140  having a first end  142  and a second end  144  extends through the core  110 , with the second end  144  of the push rod  140  being mechanically coupled to the movable contact arm  30  (see  FIG. 7 ). A plunger gap  148  may be positioned between the second end  134  of the transmission plunger  130  and the first end  142  of the push rod  140 . 
     The first actuator gap  102  and the second actuator gap  108  may be equal in spacing, or one gap may be larger than the other. In a preferred embodiment, the first actuator gap  102  spacing is smaller than the second actuator gap  108  spacing, such that the first actuator gap  102  closes before the second actuator gap  108  closes. The first actuator gap  102  may be sized to allow a predetermined amount of travel of the first armature  104  and the transmission plunger  130  toward the core  110  before the second end  134  of the transmission plunger  130  contacts the first end  142  of the push rod  140 . After the second end  134  of the transmission plunger  130  contacts the first end  142  of the push rod  140 , the first armature  104  continues to travel until the first actuator gap  102  closes, such that the second end  114  of the first armature  104  contacts the first end  116  of the second armature  106 . 
     The first armature  104  and the second armature  106 , along with the transmission plunger  130 , continue to travel toward the core  110  until the second armature gap  108  closes, whereby the second end  118  of the second armature  106  contacts the first end  136  of the core  110 . 
     As seen in  FIG. 3 , in some embodiments, the second end  114  of the first armature  104  comprises a generally flat surface or pole face  150 . The first end  116  of the second armature  106  may also comprise a generally flat mating surface or pole face  152 , such that when the first gap  102  closes, surface  150  mates with surface  152  for maximum surface contact. 
     Similarly, in some embodiments, the second end  118  of the second armature  106  comprises a generally flat surface or pole face  154 . The first end  136  of the core may also comprise a generally flat mating surface or pole face  156 , such that when the second actuator gap  108  closes, surface  154  mates with surface  156  for maximum surface contact. 
     In some embodiments, the first end  132  of the transmission plunger  130  comprises a generally flat surface  158 , and in other embodiments, the first end may comprise a more rounded surface  160  (see  FIG. 4 ), and in yet other embodiments, the first end may comprise a generally flat surface with a chamfered edge  162  (see  FIG. 5 ). It is to be appreciated that the both the first end  132  and the second end  134  of the transmission plunger  130  may comprise a variety of other shapes and/or other configurations, and are contemplated as part of the invention. 
     Referring to  FIG. 4 , an alternative embodiment of the novel magnetic actuator  170  is shown. In this embodiment, the second end  114  of the first armature  104  comprises a generally flat surface  172  with a chamfered edge  174 , generally appearing as an inverted frustoconical shaped pole face. The first end  116  of the second armature  106  comprises a generally mating inverted frustoconical shaped surface or pole face  176 , such that when the first actuator gap  102  closes, the second end surface  174  mates with surface  176  for maximum surface contact. 
     Referring to  FIG. 5 , an additional alternative embodiment of the novel magnetic actuator  180  is shown. In this embodiment, the second end  114  of the first armature  104  comprises a generally frustoconical surface or pole face  172 , and may include a generally flat surface  174  at the edges of the frustoconical surface. The first end  116  of the second armature  106  comprises a generally mating frustoconical surface or pole face  176 , and may include a mating generally flat surface  178  at the edges, such that when the first actuator gap  102  closes, surfaces  172  and  174  mate with surfaces  176  and  178  for maximum surface contact. 
     Referring to  FIG. 6 , yet an additional alternative embodiment of the novel magnetic actuator  190  is shown. In this embodiment, the second end  118  of the second armature  106  comprises a generally inverted frustoconical surface or pole face  182 . The first end  136  of the core  110  comprises a generally mating frustoconical surface or pole face  184 , such that when the second actuator gap  108  closes, surface  182  mates with surface  184  for maximum surface contact. The pole faces of the first actuator gap  102  are shown to be similar or the same as the pole faces of gap  102  in  FIG. 5 . It is to be appreciated that a variety of other pole face shaped and combinations of shapes for the first actuator gap  102  and the second actuator gap  108  are contemplated as part of the invention. 
     Referring now to  FIGS. 7 through 10  and  FIG. 13 , a magnetic actuator according to an embodiment of the invention will be described in use.  FIGS. 7 and 13  show position one where the magnetic actuator  180  is in a reset position. In the reset position, current is allowed to flow through the closed contacts  27  and  28  and through the circuit breaker  10 . In the reset position, the spacing of the first actuator gap  102  is greater than zero, and the spacing of the second actuator gap is also greater than zero. The plunger gap  148  between the second end  134  of the plunger  130  and the first end  142  of the push rod  140  is also greater than zero. The spring  60  is under compression and is applying an expansion force against the transmission plunger  130  and the core  110 . 
     Referring to  FIGS. 8 and 13  showing position two, when an undesired overcurrent condition occurs, the trip mechanism  46  is triggered. The first armature  104  travels toward the core  110 , and in turn pushes the transmission plunger  130  toward the push rod  140 . In one embodiment, the second end  134  of the plunger contacts the first end  142  of the push rod  140  causing the plunger gap  148  to become zero before the first actuator gap  102  reaches zero. Contacts  27  and  28  may still be closed but with the continued pressure applied by the first armature  104 , the contacts  27  and  28  may start to open. 
     Referring to  FIGS. 9 and 13  showing position three, the first armature  104  continues to travel, causing the first actuator gap  102  to reduce to zero, where the second end  114  of the first armature  104  mates with the first end  116  of the second armature  106 . At this stage, in one embodiment, the first actuator gap  102  equals zero, the plunger gap  148  equals zero, and the second actuator gap  108  is greater than zero. Contacts  27  and  28  start to open. 
     Referring to  FIGS. 10 and 13 , in position four, the first armature  104  and the second armature  106  together travel toward the core  110  until the second actuator gap  108  is reduced to zero, where the second end  118  of the second armature  106  mates with the first end  136  of the core  110 . The force applied by the first armature  104  and the second armature  106 , via the plunger  130  on the push rod  140 , causes contacts  27  and  28  to open. Current is no longer able to flow through the contacts  27  and  28  and through the circuit breaker  10 . It is to be appreciated that the descriptions of positions one, two, three, and four are for explanation purposes only. 
       FIGS. 11 and 12  show graphical comparisons of a single gap actuator  12  compared to a two gap actuator  100  and  180 . The graphs indicate an efficiency improvement with the two gap actuator. As can be seen, with all other parameters being equal, the activation current required for the single gap actuator  12  is equal to 100 percent, which has been set as the reference. In comparison, in  FIG. 11 , the two gap actuator  100  with generally flat pole faces requires only 87 percent of the activation current, and in  FIG. 12 , the two gap actuator  180  with the first actuator gap  102  having generally frustoconical pole faces requires only 79 percent of the activation current. Each two gap actuator  100  and  180  shows a significant efficiency improvement. 
       FIG. 13  shows a graphical comparison of the magnetic force F for a given current between a single gap actuator and a two gap actuator. The graph shows the qualitative traces of the magnetic force over armature travel. Notably, the starting point (position one) of the two gap actuator  100  is a magnitude higher shown as ΔF init  than the starting point of the one gap actuator  12 . This improved increase on the magnetic force on the armatures  104  and  106  results from the shorter first actuator gap  102  and enables a desirable early release of the trip mechanism. 
       FIG. 14  graphically shows the gain of activation current (n times rated current). Standard one gap actuators for motor protection circuit breakers are typically designed to trip at approximately 12 times rated current. Some line protection circuit breaker standards require so called trip characteristics “C” or “D” for example, which operate within a range where “C” is 5 to 10 times rated current, and “D” is 10 to 20 times rated current. These operational limits are indicated in  FIG. 14 . In one example, to meet the “C” characteristics, standard one gap actuators must increase the volume of the trip unit considerably, which creates inefficiencies, and increases cost and size. 
     In comparison, for example, using a two gap actuator with frustoconical pole faces in the first armature gap  102  (see  FIG. 5 ) enables the unit to trip at approximately 6.7 times rated current instead of approximately 12 times rated current for the one gap actuator. In this novel configuration, the trip time is shortened by approximately 30 percent. 
     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. 
     Finally, it is expressly contemplated that any of the processes or steps described herein may be combined, eliminated, or reordered. Accordingly, this description is meant to be taken only by way of example, and not to otherwise limit the scope of this invention.