Patent Publication Number: US-9842717-B2

Title: High speed closing switch

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     Pursuant to 35 U.S.C. §119(a), this application claims the benefit of earlier filing date and right of priority to Korean Application No. 10-2015-0076247, filed on May 29, 2015, the contents of which are hereby incorporated by reference herein in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a high speed closing switch, and particularly, to a high speed closing switch in which a returning rod coupled to a movable electrode protrudes to an outer side of a case such that the returning rod may interwork with the movable electrode. 
     2. Background of the Invention 
     In general, a switchgear panel receives electric power and supplies electric power required for a load facility installed in each power customer, and to this end, the switch gear panel converts extra-high voltage power into a low voltage power and distributes the same to each customer. In general, the switchgear panel includes a switch, an arrester, a circuit breaker, an arc protection system, various measurement equipment, and the like. 
     The arc protection system includes a high speed closing switch. When the switchgear panel is normal, a high voltage electrode and a ground electrode of the high speed closing switch are maintained in an open state (non-conducting state), and when an arc accident occurs in the switchgear panel, the movable electrode positioned adjacent to the ground electrode is moved toward the high voltage electrode at a high speed such that the high voltage electrode is grounded through the movable electrode, thus bypassing a fault current. 
     In order to maintain an internally insulating state, the high speed closing switch is filled with an inert insulating gas, SF6, having excellent insulating characteristics. 
     As known, the high speed closing switch includes a high voltage electrode, a ground electrode, a movable electrode having a flange portion, first and second Thomson coils for moving the movable electrode to opening and closed positions of the movable electrode via the flange portion, and sensors for sensing the opening and closed positions of the movable electrode within a case formed of an insulating material such as an epoxy, or the like. 
     The high voltage electrode is connected to a bus of the switchgear panel and high voltage power is constantly applied thereto, and the ground electrode is grounded through a separate ground bus bar or a ground cable. 
     A first embodiment of the high speed closing switch is disclosed in Korean Patent Laid-Open Publication No. 10-2010-0063556A. 
     In the document of KR 10-2010-0063556A according to the first embodiment, a movable electrode of a high speed closing switch is positioned on a ground electrode side and open in a standby state, and when a fault current such as an arc occurs, a current is applied to a first Thomson coil disposed toward one side of a flange portion. 
     When the first Thomson coil is magnetized as the current applied thereto, an eddy current is generated at the flange portion of the movable electrode disposed toward one side of the first Thomson coil, and repulsive force is generated between electromagnetic force generated by the eddy current and electromagnetic force of the first Thomson coil. 
     Accordingly, the movable electrode is moved toward the high voltage electrode, and the high voltage electrode and the ground electrode are electrically connected through the movable electrode, whereby the high speed closing switch is in a closed state in which the fault current is grounded. 
     Thereafter, in case the movable electrode is to be returned to an open state, a current is applied to the second Thomson coil disposed toward the other side of the flange portion. 
     When the second Thomson coil is magnetized upon receiving the current, the movable electrode is moved toward the ground electrode according to an action of electromagnetic force based on the same principle as that described above, and the movable electrode is positioned in the original position, that is, positioned on the ground electrode side, whereby the high speed closing switch is in the open state. 
     As explained above, the high speed closing switch is placed in the open state or the closed state according to position of the movable electrode. 
     However, if movement of the movable electrode is defective and thus, the movable electrode fails to sufficiently move toward the ground electrode in the open state, a sufficient insulating distance is not secured between the movable electrode and the high voltage electrode, and thus, the movable electrode and the high voltage electrode are damaged due to defective insulation. 
     In addition, when the movable electrode fails to sufficiently move toward the high voltage electrode in the closed state due to defective movement thereof, a sufficient electrical contact is not secured between the movable electrode and the high voltage electrode and the movable electrode and the high voltage electrode are damaged by heating due to contact resistance therebetween. 
     For these reasons, in the high speed closing switch according to the first embodiment, contact sensors are installed within the case to recognize whether a position of the movable electrode is normal. When it is recognized that the movable electrode is in an abnormal position, rather than in an open position or closed position, the arc protection system informs a worker that the movable electrode is in the abnormal position. 
     However, in the high speed closing switch, the worker cannot recognize a position state of the movable electrode by intuition with his naked eyes, and since the contact sensors are installed within the case, reliability in recognizing the position of the movable electrode is degraded in case an electric line or a related circuit connected to the sensors are disconnected. 
     A second embodiment of the high speed closing switch according to the related art is similar to the configuration of KR 10-2010-0063556A of the first embodiment as described above. The second embodiment of the high speed closing switch according to the related art discloses that the second Thomson coil is omitted, and that in order to return a movable electrode to an open state, a flange portion of the movable electrode in a closed state is held by using a pair of returning rods actuated through external power and the movable electrode is returned to its original position, that is, toward the ground electrode. 
     In the high speed closing switch according to the second embodiment, when the movable electrode is returned to its original position, the returning rods are positioned in an initial standby state. This is because, when the flange portion of the movable electrode is repulsed by the first Thomson coil and moves again toward the high voltage electrode, the flange portion of the movable electrode is not to interfere with the returning rods. 
     In the high speed closing switch according to the related art second embodiment having the foregoing configuration, the movable electrode is opened, that is, returned, by the separate returning rods, while the movable electrode is closed by the first Thomson coil, and thus, the returning rods are considered not to mechanically interwork with a movement of the movable electrode. 
     As such, since the returning rods and the movable electrode do not interwork with each other, the worker cannot recognize a position of the movable electrode through a position of the returning rods. 
     Thus, in the high speed closing switch according to the second embodiment, although the returning rods protrude to outside of the case, since the returning rods do not interwork with the movable electrode, in order to recognize a position state of the movable electrode, contact sensors need to be installed within the case as in the high speed closing switch according to the technique of KR 10-2010-0063556A of the first embodiment described above. Thus, the high speed closing switch according to the second embodiment has the same problem as that of the high speed closing switch according to the first embodiment. 
     In addition, in the high speed closing switches according to the first and second embodiments, a fault current such as an arc is applied and components thereof are moved at a high speed, applying a big load. Thus, in the high speed closing switches according to the first and second embodiments, in order to secure operation reliability, the number of closing operations is set by capacity and by model. 
     In order to recognize the number of closing operations of the high speed closing switch, the number of operations of the movable electrode needs to be counted. 
     In the high speed closing switches according to the first and second embodiments, in order to count the number of operations of the movable electrode, a separate counting-dedicated controller is required to receive signals generated form the sensors according to movement of the movable electrode and accumulate the signals to count the number of operations of the movable electrode. 
     However, counting the operations of the movable electrode in an electrical manner degrades reliability, compared with a mechanical counter, in case an electrical line or a related circuit of the sensors or the counting-dedicated controller is disconnected. 
     SUMMARY OF THE INVENTION 
     Therefore, an aspect of the detailed description is to provide a high speed closing switch including a returning rod changed in a degree of protruding from outside of a case according to a position of a movable electrode, allowing a worker may easily determine the position of the movable electrode upon seeing the degree of protruding of the returning rod. 
     Therefore, another aspect of the detailed description is to provide a high speed closing switch having a function to reliably check the number of times of closing of the high speed closing switch through a mechanical counter driven by a returning rod moved according to movement of a movable electrode. 
     Technical subjects of the present invention that may be obtained in the present invention are not limited to the foregoing technical subjects and any other technical subjects not mentioned herein may be easily understood by a person skilled in the art from the present invention and accompanying drawings. 
     To achieve these and other advantages and in accordance with the purpose of this specification, as embodied and broadly described herein, a high speed closing switch includes: a case having an interior which is hermetically closed; a ground electrode installed within the case; a high voltage electrode installed within the case and spaced apart from the ground electrode by a predetermined interval; a movable electrode installed within the case and configured to move from a first position in which the ground electrode and the high voltage electrode are not connected to a second position in which the ground electrode and the high voltage electrode are connected; a coil installed below the movable electrode and configured to generate electromagnetic force to cause the movable electrode to be moved from the first position to the second position; a returning rod having one end fixedly connected to the movable electrode and the other end protruding to outside of the case; and a driving device installed outside of the case, coupled to the returning rod protruding to outside of the case, and configured to drive the returning rod such that the movable electrode is moved from the second position to the first position. 
     A sensor configured to sense an operation of the returning rod may be installed in a movement path of the returning rod protruding to outside of the case. 
     The high speed closing switch may further include: a counting-dedicated controller configured to accumulate a signal applied from the sensor and count the number of operations of the movable electrode. 
     The high speed closing switch may further include: a mechanical counter brought into contact with the returning rod in the movement path of the returning rod protruding to outside of the case and configured to count an operation of the movable electrode interworking with the returning rod. 
     The sensor may be a contact sensor which is not in contact with the returning rod when the movable electrode is placed in the first position, and which is brought into contact with the returning rod to sense a movement of the returning rod when the movable electrode is moved to the second position. 
     The case may include: a body part having top and bottoms portions which are open; an upper case configured to hermetically close the open top portion of the body part, to which the high voltage electrode is coupled; and a lower case configured to hermetically close the open bottom portion of the body part, to which the ground electrode is coupled, wherein the returning rod protrudes to outside of the lower case, and a sealing member is installed between the lower case and the returning rod in order to maintain airtightness therebetween. 
     The sealing member may be at least one of an O-ring and a guide wear ring. 
     Further scope of applicability of the present application will become more apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the scope of the invention will become apparent to those skilled in the art from the detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments and together with the description serve to explain the principles of the invention. 
       In the drawings: 
         FIG. 1  is an overall schematic view of a switchgear panel in which a high speed closing switch according to an embodiment of the present invention is installed. 
         FIG. 2  is a partial cross-sectional perspective view of a high speed closing switch according to an embodiment of the present invention. 
         FIG. 3  is a cross-sectional view illustrating an open state of a high speed closing switch according to an embodiment of the present invention. 
         FIG. 4  is a cross-sectional view illustrating a closed state of a high speed closing switch according to an embodiment of the present invention. 
         FIGS. 5A and 5B  are schematic views according to first and second embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, embodiments will be described in detail with reference to the accompanying tables and drawings such that they can be easily practiced by those skilled in the art to which the present invention pertains. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. 
     In the accompanying drawings, a portion irrelevant to description of the present invention will be omitted for clarity. Like reference numerals refer to like elements throughout. 
       FIG. 1  is an overall schematic view of a switchgear panel  1  in which a high speed closing switch according to an embodiment of the present invention is installed. 
     Referring to  FIG. 1 , a switchgear panel  1  includes an arc protection system  2 , a transformer  3 , a main circuit breaker  4 , a current sensor  5 , a first circuit breaker  6 , and a second circuit breaker  7 , and further includes a high speed closing switch  100 . 
     In order to determine whether a fault current is an arc accident, a light receiving sensor (not shown) receiving light emitted from an arc generated within the switchgear panel  1  is installed. When an arc accident occurs, the arc protection system  2  may determine whether an arc accident has occurred upon receiving a light signal sensed by the light receiving sensor or an overcurrent signal provided from the current sensor  5  provided within the switchgear panel  1 . 
     Or, the arc protection system  2  may determine whether an arc accident has occurred upon simultaneously receiving the two signals, that is, the overcurrent signal and the light signal. 
     When the arc protection system  2  determines that an arc has occurred in the switchgear panel  1 , the arc protection system  2  issues a closing command to the dedicated high speed closing switch  100  and simultaneously issues a trip command to the main circuit breaker  4 . 
     According to the closing command from the arc protection system  2 , the high speed closing switch  100  performs a closing operation before the circuit breaker  4  performs its own closing operation, so the arc fault current is bypassed toward a ground, and accordingly, damage that may be done due to the arc within the switchgear panel  1  may be minimized. 
     Thereafter, according to the closing command from the arc protection system  2 , the circuit breaker  4  also breaks the fault current to protect the switchgear panel  1  from the fault current. 
       FIG. 2  is a partial cross-sectional perspective view of a high speed closing switch according to an embodiment of the present invention.  FIG. 3  is a cross-sectional view illustrating an open state of a high speed closing switch according to an embodiment of the present invention.  FIG. 4  is a cross-sectional view illustrating a closed state of a high speed closing switch according to an embodiment of the present invention. 
     Referring to  FIGS. 2 through 4 , the high speed closing switch  100  includes a case  110 , forming an outer appearance, a ground electrode  130  installed within the case  110 , a high voltage electrode  140  installed within the case  110  and spaced apart from the ground electrode  130 , a movable electrode  150  movably installed within the case  110 , a closing coil  160  installed within the case  110  and moving the movable electrode  150  to a closed position, and a returning rod  170  having one end coupled to the movable electrode  150  installed within the case  110  and the other end protruding to outside of the case  110 . 
     The case  110  may include a body part  111  formed of an insulating material such as epoxy and having open top and bottom portions, an upper case  112  coupled to the top portion of the body portion  111  to cover the open top portion of the body part  111  and formed of a conductive material, and a lower case  113  coupled to the bottom portion of the body part  111  to cover the open bottom portion of the body part  111  and formed of a conductive material. 
     Here, the upper case  112  may be integrally formed with the high voltage electrode  140 . 
     Alternatively, the upper case  112  may be configured as a member separated from the high voltage electrode  140  and coupled to the high voltage electrode  140 , and in this case, the high voltage electrode  140  is installed in an upper portion within the case  110 . 
     The upper case  112  and the lower case  113  may be installed in the body part  111  to hermetically close the interior of the case  110 , and after the interior of the case  110  is hermetically closed by the upper and lower cases  112  and  113 , the interior of the case  110  may be filled with an insulating gas through a separate passage (not shown). 
     However, a configuration in which the interior of the case  110  is filled with the insulating gas is not limited to the aforementioned example and any known configuration may be used. 
     Also, the insulating gas filling the interior of the case  110  is not particularly limited and any known gas may be used as long as it is an inert gas. 
     For example, the inert gas may be, preferably SF6, N2 or air without moisture. 
     The ground electrode  130  is supported by a pipe  120  supported on the lower case  113 . 
     In detail, the ground electrode  130  is coupled to and supported by an upper inner surface of the pipe  120 , and a lower end of the pipe  120  is supported by the lower case  113 . 
     Here, the pipe  120  is formed of a conductive material, and the lower case  113  and the ground electrode  130  are conducted. 
     The ground electrode  130  may be installed in a middle portion of the case  110 . 
     The ground electrode  130  has an insertion hole  131  formed in an axial direction thereof. 
     The movable electrode  150  is inserted into the insertion hole  131 . 
     When a closing operation is performed, the insertion hole  131  allows the movable electrode  150  is moved toward the high voltage electrode  140  in a sate in which an outer circumferential surface of the movable electrode  150  is in contact with an inner circumferential surface of the ground electrode  130 . 
     The high voltage electrode  140  has a connection hole  141  formed in an axial direction thereof. 
     The connection hole  141  is formed to allow an outer circumferential surface of the movable electrode  150  is in contact with an inner circumferential surface of the high voltage electrode  140  formed by the connection hole  141 , when the movable electrode  150  is inserted into the connection hole  141 . 
     On a bottom surface of the upper case  112  positioned within the high voltage electrode  140 , an arc electrode  190  is installed to minimize an arc that may occur between the high voltage electrode  140  and the movable electrode  150  when a closing operation or an opening operation is performed. 
     Meanwhile, as mentioned above and as illustrated, the high voltage electrode  140  and the ground electrode  140  are configured to be spaced apart from one another within the case  110 , but the present disclosure is not limited thereto and any known configuration may be used. 
     The high voltage electrode  140  may be electrically connected to an electric circuit of at least one among an incoming panel, a distribution board, and the switchgear panel  1  described above through the upper case  112 , and the ground electrode  130  may be electrically connected to a ground side through the pipe  120  and the lower case  113 . 
     Within the case  110 , the movable electrode  150  is installed to move between a first position, that is, an open position, in which the ground electrode and the high voltage electrode  140  are not electrically connected, and a second position, that is, a close position, in which the ground electrode  130  and the high voltage electrode  140  are electrically connected. 
     The movable electrode  150  includes a moving portion  152  and a flange portion  153 . 
     The moving portion  152  of the movable electrode  150  is formed to be hollow. 
     The moving portion  152  of the movable electrode  150  may also be formed to be solid, but in order to facilitate the understanding of the present disclosure, the hollow moving portion  152  is provided. 
     The moving portion  152  has an outer circumferential surface inserted into the insertion hole  131  of the ground electrode  130  and the connection hole  141  of the high voltage electrode  140  so as to be in contact with an inner circumferential surface of the ground electrode  130  and an inner circumferential surface of the high voltage electrode  140 , when a closing operation is performed. 
     Also, the moving portion  152  has an inner circumferential surface which is moved in contact with an outer circumferential surface of the arc electrode  190 , when a closing operation is performed. 
     The flange portion  153  of the movable electrode  150  is formed at a lower end of the moving portion  152 . 
     The flange portion  153  is disposed between the closing coil  160  and the high voltage electrode  140  and acts as a repulsive plate repulsive to electromagnetic force of the closing coil  160 . 
     The closing coil  160  is provided above the lower case  113 , and the closing coil  160  may be a Thomson coil  160 . 
     The Thomson coil  160  may be wound in an annular shape and installed on a support member  180  formed of an insulating material disposed on an upper surface of the lower case  113  of the case  110 . 
     When the Thomson coil  160  is magnetized upon receiving power applied thereto, an eddy current is generated in the flange portion  153  of the movable electrode  150  installed to face the Thomson coil  160 , and repulsive force is generated between electromagnetic force generated by the eddy current and electromagnetic force of the Thomson coil  160 , and thus, the movable electrode  150  is moved toward the high voltage electrode  140 , that is, the movable electrode  150  is moved from an open position to a close position. 
     When the movable electrode  150  is moved to the high voltage electrode  140  in a closing operation, while the moving portion  152  of the movable electrode  150  is maintained in a state of being in contact with an inner circumferential surface of the ground electrode  130 , a front inner circumferential surface of the moving portion  152  is first brought into contact with an outer circumferential surface of the arc electrode  190 , and a front outer circumferential surface of the moving portion  152  is then inserted into the connection hole  141  of the high voltage electrode  140  and is brought into contact with the inner circumferential surface of the high voltage electrode  140  formed by the connection hole  141  of the high voltage electrode  140 . 
     Thus, in the closed position, the high voltage electrode  140  is electrically connected to the ground electrode  139  through the movable electrode  150 . 
     Accordingly, a fault current such as an arc generated in an electric circuit does not flow to the electric circuit but flow to the high voltage electrode  140 , the movable electrode  150 , and the ground electrode  130 , whereby the electric circuit such as the incoming panel, a distribution board, and the switchgear panel  1  can be protected from the fault current. 
     The returning rod  170  is configured such as one end thereof is coupled to the movable electrode  150  and the other end thereof protrudes to outside of the case  110 . 
     To this end, through holes  114  and  181  through which one end of the returning rod  170  penetrates are formed in the lower case  113  and the support member  180 , respectively. 
     One end of the returning rod  170  is inserted through the through hole  114  of the lower case  113  and the through hole  181  of the support member  180  and subsequently coupled by a known coupling unit such as a bolt  200  so as to be supported by the bottom surface of the movable electrode  150 . 
     Meanwhile, since the returning rod  170  is moved with respect to the lower case  113 , an insulation gas hermetically sealed in the case  110  may be leaked between the lower case  113  and the returning rod  170 . 
     Thus, as illustrated in  FIGS. 2 through 4 , in order to prevent leakage of the insulation gas between the lower case  113  and the returning rod  170 , a sealing member  210 , for example, at least one of an O-ring  211  and a guide wear ring  212 , covering an outer circumferential surface of the returning rod  170 , may be installed in the lower case  113 . 
     In the high speed closing switch according to the present invention, since the movable electrode  150  and the returning rod  170  are coupled together, when the movable electrode  150  is moved to the closed position of the upper portion of the case  110 , the returning rod  170  is also moved to the upper portion of the case  110  cooperatively according to the movement of the movable electrode  150 . 
     Here, a length of the returning rod  170  protruding outside of the case  110  is greater than a distance by which the movable electrode  150  is moved from the open position to the closed position within the case  110 . 
     In other words, as illustrated in  FIG. 3 , when the movable electrode  150  is placed in the open position, the returning rod  170  may protrude by a first length H 1  to outside of the case  110 . 
     Also, as illustrated in  FIG. 4 , when the movable electrode  150  is moved to the closed position, the returning rod  170  is moved together with the movable electrode  150  to the interior of the case  110 , and here, the returning rod  170  protrudes to outside of the case by a second length H 2  as a length corresponding to a distance by which the movable electrode  150  has moved is reduced from the first length H 1 . 
     In the high speed closing switch according to the present invention configured as described above, the closing of the movable electrode  150 , that is, movement of the movable electrode from the first position to the second position, is performed by the closing coil  160 , that is, the Thomson coil  160 . 
     Meanwhile, the opening of the movable electrode, that is, movement of the movable electrode  150  from the second position to the first position, is performed by a returning device  300  as illustrated in  FIGS. 5A and 5B . 
     In detail, the returning device  300  is coupled to the returning rod  170  protruding to outside of the case  110 , and drives the returning rod  170  in a downward direction to move the movable electrode  150  from the second position to the first position. Accordingly, the movable electrode  150  fixedly connected to one end of the returning rod  170  is moved to the open position. 
     Here, the returning device  300  may be operated by various driving units such as a motor, a Thomson coil, or the like. 
     Meanwhile, in the high speed closing switch  100  according to a first embodiment of the present invention, as illustrated in  FIG. 5A , a sensor  400  for sensing an operation of the returning rod  170  may be installed in a movement path of the returning rod  170  protruding to outside of the case  110 . 
     As the sensor  400 , any one of a contact sensor or a non-contact sensor may be installed, and for example, the sensor  400  may be a limit switch directly in contact with the returning rod  170  protruding to outside of the case  110 . 
     A signal generated by the sensor  400  is applied to the arc protection system  2  to determine whether a position of the movable electrode  150  is normal. 
     When the sensor  400  for recognizing a position of the movable electrode  150  is installed outside of the case  110 , the sensor  400  and a line related to the sensor as well may be easily checked. 
     Also, in the high speed closing switch  100  according to the first embodiment of the present invention, since the returning rod  170  moved by interworking with the movable electrode  150  is provided on an outer side of the case  110 , a worker may check a position of the returning rod  170  through his naked eyes, as well as recognizing position state information of the returning rod  170  through the arc protection system  2  according to information applied from the sensor  400 , whereby a position of the movable electrode  150  may be indirectly recognized. 
     In the high speed closing switch  100  according to the first embodiment of the present invention, as illustrated in  FIG. 5A , the number of times that the returning rod  170  is sensed by the sensor  400  is counted by using a counting-dedicated controller  410 , whereby the number of closing of the high speed closing switch  100  may be counted. 
     Meanwhile, in the first embodiment of the present invention, the sensor  400  may be configured as a contact sensor which is not in contact with the returning rod  170  when the movable electrode  150  is placed in the first position, that is, in the open position, and which is brought into contact with the returning rod  170  to sense movement of the returning rod  170  when the movable electrode  150  is moved to the second position, that is, to the closed position. 
     Meanwhile, in the high speed closing switch  100  according to the present invention, in order to obtain more reliable count information of the movable electrode  150 , as illustrated in a second embodiment illustrated in  FIG. 5B , a mechanical counter  500  may be installed in a movement path of the returning rod  170  protruding to outside of the case  110  and brought into contact with the returning rod  170  to count operations of the movable electrode  150 . 
     Here, in the second embodiment, the counting-dedicated controller  410  as in the first embodiment of  FIG. 5A  to accumulate signals from the sensor  400  to count the number of closing of the movable electrode  150  is not required to be used. 
     The mechanical counter  500  according to  FIG. 5B  has high durability, and thus, usage reliability thereof in the high speed closing switch  100  requiring an accurate number of closing is guaranteed. 
     The foregoing embodiments and advantages are merely exemplary and are not to be considered as limiting the present invention. The present teachings can be readily applied to other types of apparatuses. This description is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art. The features, structures, methods, and other characteristics of the exemplary embodiments described herein may be combined in various ways to obtain additional and/or alternative exemplary embodiments. 
     As the present features may be embodied in several forms without departing from the characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be considered broadly within its scope as defined in the appended claims, and therefore all changes and modifications that fall within the metes and bounds of the claims, or equivalents of such metes and bounds are therefore intended to be embraced by the appended claims.