Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 20-2015-0004227, filed on Jun. 24, 2015, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a locking device for an operating mechanism of a gas insulated switchgear, and more particularly, a locking device for an operating mechanism of a gas insulated switchgear, capable of locking or unlocking operations of an operating mechanism of disconnecting switches and earthing switches of the gas insulated switchgear. 
     2. Description of the Related Art 
     In general, a gas insulated switchgear (GIS) is an electric device which is installed between a power source side and a load side of a circuit of an electric power system. The gas insulated switchgear switches a circuit on purpose in a normal usage state or safely interrupts current when a fault current such as a ground fault or a short-circuit occurs to thus protect such electric power system and a load device. The gas insulated switchgear is generally used for an ultra-high electric power system. 
     The gas insulated switchgear generally includes a bushing unit receiving electric energy (power) from a high voltage power source, a circuit breaker (CB), a disconnecting switch (DS), an earthing switch (ES), a moving unit, a controller and the like. 
       FIGS. 1 and 2  are planar and longitudinal sectional views illustrating a DS and ES unit and an operating mechanism  9  of a gas insulated switchgear according to the related art. The DS and ES unit includes a tank  1  and spacers  2 , disconnecting switches  3 , earthing switches  4  and three-position switches  5  all disposed in the tank  1 , a driving shaft  6  installed at the operating mechanism  9 , and a driven shaft  8  operating the 3-position switches  5 . A link assembly  7  is provided between the driving shaft  6  and the driven shaft  8 . 
       FIG. 3  is a perspective view of the link assembly  7  of  FIG. 1 . The link assembly  7  includes a driving shaft lever  7   a  receiving a driving force of the operating mechanism  9  through the driving shaft  6 , a driven shaft lever  7   d  disposed with being spaced apart from the driving shaft lever  7   a  and transferring a force to the driven shaft  8 , link rods  7   b  connecting the driving shaft lever  7   a  to the driven shaft lever  7   d  to transfer the force from the driving shaft lever  7   a  to the driven shaft lever  7   d , and connection pins  7   c  rotatably connecting the driving shaft lever  7   a  or the driven shaft lever  7   d  to the link rods  7   b.    
       FIG. 4  illustrates an operation of the link assembly  7 . The driving shaft  6  is connected to the driving shaft lever  7   a . Movable contacts  5   a  of the three-position switches  5  are coupled for each phase to the driven shaft  8  coupled to the driven shaft lever  7   d . Also, fixed contacts  3   a  of the disconnecting switches DS and fixed contacts  4   a  of the earthing switches ES are illustrated. Here, the driven shaft  6 , the movable contact  5   a , the fixed contact  3   a  of each disconnecting switch DS and the fixed contact  4   a  of each earthing switch ES are merely conceptually illustrated for the sake of explanation. When a driving force of the operating mechanism  9  is transferred to the driving shaft lever  7   a  through the driving shaft  6 , the link assembly  7  including the driving shaft lever  7   a , the link rods  7   b  and the driven shaft lever  7   d  rotates the driven shaft  8 . Accordingly, the movable contact  5   a  of each of the three-position switches  5  coupled to the driven shaft  6  is rotated or slid into one of a closed state of the disconnecting switch DS (DS closed state or position), a neutral (trip) state, and a closed state of the earthing switch ES (ES closed state or position). 
       FIGS. 5A and 5B, 6A and 6B, and 7A and 7B  are views illustrating a case where the driving shaft is in the neutral state, a case where the disconnecting switch is in the closed state, and a case where the earthing switch is in the closed state, respectively, in relation to  FIGS. 2 and 3 . 
     Here, the link assembly  7  connecting the driving shaft  6  and the driven shaft  8  to each other has a simple quadric link structure. Also, the link assembly  7  merely serves to transfer the driving force of the operating mechanism  9  to the driven shaft  8  and is not provided with a separate safety device or a locking device. This may be likely to bring about the following problems. 
     First, while operating (or switching on) the gas insulated switchgear, when a user operates it in an unexpected way carelessly or due to misjudgment, damages on facilities or casualties may be caused. 
     When the operating mechanism is rotated excessively more or less than a normal rotation angle due to being defectively assembled or other causes, a poor contact (contact trouble) between the movable contact  5   a  and the fixed contacts  3   a  and  4   a  may be brought about, thereby lowering a product performance. In this instance, components may be damaged due to collision between the components. 
     In addition, when the driving shaft is disassembled or removed to repair or replace the operating mechanism which currently operates, the movable contact  5   a  may be freely rotated without a restriction due to a non-presence of a supporting structure, and abnormally comes in contact with the fixed contacts  3   a  and  4   a  on which current flows, which may be likely to cause an unexpected accident. 
     SUMMARY 
     Therefore, to obviate those drawbacks of the related art, an aspect of some embodiments of the present disclosure is to provide a locking device for an operating mechanism of a gas insulated switchgear, capable of preventing an accident, ensuring an assembly property and operation reliability of the device, and improving safety of maintenance, by restricting operations of a disconnecting switch and an earthing switch due to a user&#39;s carelessness. 
     To achieve these and other advantages and in accordance with the purpose of this disclosure, as embodied and broadly described herein, there is provided a locking device for an operating mechanism of a gas insulated switchgear, the locking device including a driving shaft lever connected to the operating mechanism to perform a rotation motion, first and second link rods coupled to upper and lower ends of the driving shaft lever, respectively, to transfer the motion, a driven shaft lever including upper and lower ends connected to the first and second link rods, respectively, to perform a rotation motion, and provided with a stopping groove on a part thereof, a supporter installed at a tank, a locking lever coupled to the supporter to perform a rotation motion or a parallel motion, the locking lever locking the motion of the driven shaft lever when being inserted into the stopping groove, and a driven shaft rotated by a force transferred by the driven shaft lever. 
     Here, the stopping groove may be provided in plurality, which are formed at positions corresponding to a closed state of a disconnecting switch, a neutral state and a closed state of an earthing switch, respectively. 
     Also, the supporter may include a base plate coupled to the tank, and a pair of side walls coupled with the locking lever. 
     The locking device may further include a lever pin inserted through the locking lever and serving as a rotation shaft of the locking lever. 
     A fixing plate restricting the motion of the locking lever may be coupled to an upper surface of one of the side walls. 
     A lock hole may be formed through a part of the fixing plate, and a lock that is latched through the lock hole may be provided. 
     A ring through which the lock is latched may be provided on an upper portion of another of the side walls. 
     A fixing pin may be provided to fix the fixing plate to the one side wall. 
     A screw hole may be formed through a part of at least one of the side walls, and a wing bolt may be inserted into the screw hole to lock the locking lever. 
     The locking lever may be configured as a rod movable in parallel between the side walls. 
     In a locking device for an operating mechanism of a gas insulated switchgear according to one exemplary embodiment of the present disclosure, a state of a link assembly can be locked by a locking unit provided at one side of the link assembly, and thus a change in a contact state may not occur even by a user&#39;s operation made randomly or by mistake, thereby ensuring stability of device and power system. 
     A normal operating state of a disconnecting switch/earthing switch can be determined on the basis of a coupled state between the link assembly and the locking unit. 
     A current state of the operating mechanism can be recognized on the basis of the coupled state between the link assembly and the locking unit, thereby preventing an operation made by mistake. 
     The locking unit may be provided with locking devices, such as a lock, a wing bolt and the like to fix a specific state, thereby preventing a random operation. 
     In addition, for repairing or replacing the operating mechanism which is currently operating, a situation that a movable contact is freely moved due to a detachment or removal of a driving shaft can be prevented, so as to prevent an abnormal contact between the movable contact and fixed contacts along which current flows, resulting in prevention of casualty or facility damage. 
     Further scope of applicability of the present disclosure 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 disclosure, are given by way of illustration only, since various changes and modifications within the spirit and scope of the disclosure 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 disclosure and are incorporated in and constitute a part of this disclosure, illustrate exemplary embodiments and together with the description serve to explain the principles of the disclosure. 
       In the drawings: 
         FIG. 1  is a planar view of a disconnecting switch and earthing switch unit of a gas insulated switchgear according to the prior art; 
         FIG. 2  is a longitudinal sectional view of  FIG. 1  according to the prior art; 
         FIG. 3  is a perspective view of a link assembly in  FIG. 1  according to the prior art; 
         FIG. 4  is an operation view of  FIG. 3  according to the prior art; 
         FIGS. 5A and 5B  are views illustrating a case where a driving shaft is placed in a neutral state according to the prior art, in relation to  FIGS. 2 and 3 ; 
         FIGS. 6A and 6B  are views illustrating a case where a disconnecting switch is placed in a closed state according to the prior art, in relation to  FIGS. 2 and 3 ; 
         FIGS. 7A and 7B  are views illustrating a case where an earthing switch is placed in a closed state according to the prior art, in relation to  FIGS. 2 and 3 ; 
         FIG. 8  is a perspective view illustrating a locking device for an operating mechanism of a gas insulated switchgear in accordance with some embodiments of the present disclosure; 
         FIG. 9  is a disassembled perspective view of a locking unit in  FIG. 8 ; 
         FIG. 10  is a view illustrating a locked state of a link assembly; 
         FIG. 11  is an operation view of the locking device for the operating mechanism of the gas insulated switchgear in accordance with the some embodiments of the present disclosure; 
         FIG. 12  is a view illustrating a normal operating state of the locking device for the operating mechanism of the gas insulated switchgear in accordance with the some embodiments of the present disclosure; 
         FIG. 13  is a view illustrating an incomplete operating state of the locking device for the operating mechanism of the gas insulated switchgear in accordance with the some embodiments of the present disclosure; 
         FIG. 14  is a view illustrating an unlocked state of the locking device for the operating mechanism of the gas insulated switchgear in accordance with the some embodiments of the present disclosure; and 
         FIG. 15  is a planar view illustrating a locking device for an operating mechanism of a gas insulated switchgear in accordance with some embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Description will now be given of preferred configurations, with reference to the accompanying drawings, which is to explain in detail enough that those skilled in the art to which the present disclosure belongs can easily practice the disclosure. It should not be construed to limit the technical scope and spirits of the present disclosure. 
       FIG. 8  is a perspective view illustrating a locking device for an operating mechanism of a gas insulated switchgear in accordance with some embodiments of the present disclosure,  FIG. 9  is a disassembled perspective view of a locking unit in  FIG. 8 ,  FIG. 10  is a view illustrating a locked state of a link assembly, and  FIG. 11  is an operation view of the locking device for the operating mechanism of the gas insulated switchgear in accordance with the some embodiments of the present disclosure. 
     Hereinafter, description will be given in detail of a locking device for an operating mechanism of a gas insulated switchgear in accordance with some embodiments of the present disclosure, with reference to the accompanying drawings. (Here, a disconnecting switch and earthing switch unit and an operating mechanism, except for a link assembly and a locking unit, have the same configuration to those according to the related art, so description thereof will be omitted. Also, the same reference numerals are used for the similar or same components to those in the related art, so they can be understood with reference to those drawings of the related art.) 
     The locking device for the operating mechanism of the gas insulated switchgear according to the some embodiments of the present disclosure may include a driving shaft lever  11  connected to the operating mechanism to perform a rotation motion, first and second link rods  20  and  25  coupled to upper and lower ends of the driving shaft lever  11 , respectively, to perform a rotation motion and a parallel motion, a driven shaft lever  30  including upper and lower ends connected to the first and second link rod  20  and  25 , respectively, to perform rotation motion, and provided with stopping grooves  31 ,  32  and  33  formed at a part thereof, a supporter  41  installed at a tank (enclosure), a locking lever  50  coupled to the supporter  41  to perform a rotation motion or a parallel motion and restricting a motion of the driven shaft lever  30  when being inserted into the stopping grooves  31 ,  32  and  33 , and a driven shaft  8  rotated by a force transferred by the driven shaft lever  30 . 
     The locking device for the operating mechanism of the gas insulated switchgear according to the some embodiments of the present disclosure may include a link assembly  10  and a locking unit  40  restricting a motion of the link assembly  10 . 
     The link assembly  10  may be configured as a quadric link. The link assembly  10  may include a driving shaft lever  11  and a driven shaft lever  30  provided on left and right ends, respectively, and first and second link rods  20  and  25  provided on upper and lower ends thereof. 
     The driving shaft lever  11  may be formed in the shape of a flat plate. The driving shaft lever  11  may be rotatably coupled to one ends of the first and second link rods  20  and  25 , respectively. The driving shaft lever  11  may be connected to the driving shaft  6  of the operating mechanism  9  and rotated by the driving force of the operating mechanism  9 . 
     The first and second link rods  20  and  25  may be coupled to the upper and lower ends of the driving shaft levers  11 , respectively. The one ends of the first and second link rods  20  and  25  may be coupled to the driving shaft lever  11  by coupling members  12 , such as pins, rivets, bolts and the like, in a rotatable manner, not in a fixed manner. Split slits  21  and  26  in which the driving shaft lever  11  or the driven shaft lever  30  is inserted may be formed at both end portions of the first and second link rods  20  and  26 , respectively. The split slits  21  and  26  may be formed at the both end portions of the first and second link rods  20  and  25 , respectively, in a lengthwise direction. When viewing the first and second link rods  20  and  25  from a top, the first and second link rods  20  and  25  may be symmetrically formed, respectively, on the basis of the split slits  21  and  26 . As the driving shaft lever  11  is inserted into the split slits  21  and  26 , the coupled state between the first and second link rods  20  and  25  and the driving shaft lever  11  can be stably maintained, and a loss of the driving force transferred from the driving shaft lever  11  can be minimized. The first link rod  20  and the second link rod  26  may be arranged in parallel to each other. 
     The driven shaft lever  30  may be rotatably coupled to another ends of the first and second link rods  20  and  25 , respectively. The first link rod  20  may be coupled to an upper end of the driven shaft lever  30 , and the second link rod  25  may be coupled to a lower end of the driven shaft lever  30 . The coupling characteristic between the driving shaft lever  11  and the first and second link rods  20  and  25  can be similarly or equally applied to the coupling between the driven shaft lever  30  and the first and second link rods  20  and  25 . 
     The driven shaft lever  30  may be formed in the shape of a flat plate. A shaft hole  35  to which the driven shaft can be coupled may be formed through the driven shaft lever  30 . The driven shaft lever  30  may have an outer surface that protrudes into a semicircular shape. A plurality of stopping grooves  31 ,  32  and  33  may be formed on the outer surface of the driven shaft lever  30 . The plurality of stopping grooves  31 ,  32  and  33  may separately be referred to as a first stopping groove  31 , a second stopping groove  32 , and a third stopping groove  33 , from top to bottom. Here, the stopping grooves  31 ,  32  and  33  may be formed to correspond to three positions (a DS-closed position, a neutral or trip position and an ES-closed position) of the three-position switch. 
     The stopping grooves  31 ,  32  and  33  may be located at positions spaced apart from one another by a uniform angle (e.g., 60°). That is, at a neutral position as illustrated in  FIG. 8 , the driven shaft lever  30  may be in a state without being brought into contact with both of the disconnecting switch and the earthing switch (i.e., the neutral or trip state), and the locking unit  140  may be inserted into the second stopping groove  32 . If the driving shaft  6  is rotated by 60° in a counterclockwise direction, the first link rod  20  may be moved to left and the second link rod  25  may be moved to right such that the driven shaft lever  30  can be rotated by 60° in the counterclockwise direction. In this instance, the locking unit  40  can be inserted into the first stopping groove  31 . If the driving shaft  6  is rotated by 60° in a clockwise direction, the first link  20  may be moved to right and the second link rod  25  may be moved to left such that the driven shaft lever  30  can be rotated by 60° in the clockwise direction. In this instance, the locking unit  40  can be inserted into the third stopping groove  33 . 
     The locking unit  40  may be disposed to lock or unlock the movement of the link assembly  10 . In detail, the locking unit  40  may be inserted into one of the stopping grooves  31 ,  32  and  33  of the driven shaft lever  30  to lock the movement of the link assembly  10  in a specific state, and unlock the link assembly  10  when it is not inserted into any of the stopping grooves  31 ,  32  and  33 . 
     As one embodiment of the locking unit  40 , the locking unit  40  may include as core components a supporter  41  and a locking lever  50 . Also, the locking unit  40  may further include components, such as a lever pin  55  for coupling the locking lever  50  to the supporter  41 , a fixing plate  60  for restricting a motion of the locking lever  50 , a lock  70 , a wing bolt  66 , and the like. 
     The supporter  41  may be installed at the tank  1  and support the locking lever  50  such that the locking lever  50  can perform a parallel motion or a rotation motion. The supporter  41  may include a base plate  42  coupled to the tank  1 , and a pair of side walls  43  coupled with the locking lever  50 . The base plate  42  may be provided with a plurality of fixing holes  42   a  for coupling the base plate  42  to the tank  1 . Each of the side walls  43  may be provided with a pin hole  43   a  through which the lever pin  55  is inserted. A ring  44  through which the lock  70  is latched may be provided at an upper portion of one of the side walls  43 . 
     The locking lever  50  may be installed at the supporter  41  and inserted into the stopping grooves  31 ,  32  and  33 . The locking lever  50  is a component which directly locks the driven shaft lever  30 . The locking lever  50  may be formed in the shape of a plate. The locking lever  50  may be provided with a pin hole  51  formed therethrough such that the lever pin  55  can be inserted therethrough. A protrusion  52  which is insertable into the stopping grooves  31 ,  32  and  33  may protrude from a part of the locking lever  50 . The protrusion  52  may be formed in various shapes, taking into account of an operation characteristic of the locking lever  50 , shapes of the stopping grooves  31 ,  32  and  33 , and the like. 
     The lever pin  55  may be provided to rotatably install the locking lever  50  at the supporter  41 . The lever pin  55  may be inserted sequentially through one of the pin holes  43   a  of the side walls  43 , the pin hole  51  of the locking lever  50  and the other of the pin holes  43   a . The locking lever  50  may be rotatable centering on the lever pin  55  as a shaft. When the locking lever  50  is rotated in a counterclockwise direction centering on the lever pin  55  as the shaft, the protrusion  52  which has been inserted in one of the stopping groove  31 ,  32 ,  33  may be separated from the one stopping groove (see  FIG. 8 ). On the other hand, when the locking lever  50  is rotated in a clockwise direction, the protrusion  52  may be inserted into one of the stopping groove  31 ,  32 ,  33  (see  FIG. 10 ). 
     Meanwhile, the fixing plate  60  which restricts the motion of the locking lever  50  may be disposed on an upper surface of another of the side walls  43 . A pin hole  61  may be formed through a part of the fixing plate  60  such that the fixing plate  60  can be fixed to the another side wall  43  by a fixing pin  65 . 
     A lock hole  62  may be formed through a part of the fixing plate  60  such that the lock  70  can be latched therethrough. 
     In the meantime, a screw hole  43   b  may be formed through a part of at least one of the side walls  43 . The wing bolt  66  may be inserted through the screw hole  43   b  and lock the locking lever  50 . 
     Although not illustrated separately, another embodiment may be implemented in a manner that the locking lever  50  is formed in a shape of a rod to be movable in parallel between the side walls  43 . In this instance, the locking lever  50  may be inserted into or separated from the stopping groove  31 ,  32 ,  33  of the driven shaft lever  30  by the parallel motion. 
     Hereinafter, description will be given of an operation of the locking device for the operating mechanism of the gas insulated switchgear according to some embodiments, with reference to  FIGS. 11 to 14 . 
     When the driving shaft lever  11  is rotated clockwise or counterclockwise by the driving force transferred from the driving shaft  6 , the first and second link rods  20  and  25  coupled to the upper and lower end portions of the driving shaft lever  11  are responsively moved. The first link rod  20  and the second link rod  25  are moved in opposite directions to each other to allow the driven shaft lever  30  to be moved clockwise or counterclockwise. In response to the movement of the driven shaft lever  30 , the driven shaft  8  is rotated and accordingly the movable contact  5   a  is moved. 
     Operation positions of the movable contact  5   a  may be three positions of a DS-closed position, a neutral or trip position, and an ES-closed position. That is, the movable contact  5   a  may be located at a position contactable with the fixed contact  3   a  of the disconnecting switch DS, a position without being contactable with the fixed contacts  3   a  and  4   a , and a position contactable with the fixed contact  4   a  of the earthing switch ES. Accordingly, a primary circuit may be switched into a conductive state, a short-circuit state, and an earthed state. Here, the closed position of the disconnecting switch DS, the neutral or trip position and the closed position of the earthing switch ES may be positions at which the locking lever  50  of the locking unit  40  is insertable into the first stopping groove  31 , the second stopping groove  32  and the third stopping groove  33 , respectively. Accordingly, the locking lever  50  of the locking unit  40  can be inserted into one of the stopping grooves  31 ,  32  and  33  at each position to fix the link assembly  10  and lock the locking unit  40  using the lock  70  or the wing bolt  66 . This may allow for locking the link assembly  10  and also determining whether or not the operating mechanism properly operates by being placed correctly at each contact state. 
     Although not illustrated separately, a controller (not shown) may be provided to control an operating position of the movable contact  5   a . The controller may control a driving force of the driving shaft  6  of the operating mechanism such that each of the stopping grooves  31 ,  32  and  33  of the driven shaft lever  30  can be accurately aligned with the position of the locking lever  50  of the locking unit  40 . For example, the controller may control the locking lever  50  to be moved exactly by 60° each so as to be located at the DS-closed position, the neutral or trip position or the ES-closed position. 
       FIG. 12  illustrates a normal operating state among the operating states of the locking device for the operating mechanism of the gas insulated switchgear in accordance with some embodiments of the present disclosure.  FIG. 12  illustrates a state that the driven shaft lever  30  is rotated exactly by 60° in the clockwise direction such that the movable contact  5   a  is brought into contact correctly with the fixed contact  4   a  of the earthing switch and the locking lever  50  is insertable into the third stopping groove  33 . That is, the third stopping groove  33  of the driven shaft lever  30  is aligned with the locking lever  50  in a straight line. 
       FIG. 13  illustrates an incomplete operating state among the operating states of the locking device for the operating mechanism of the gas insulated switchgear in accordance with the some embodiments of the present disclosure.  FIG. 13  illustrates that the third stopping groove  33  of the driven shaft lever  30  is not aligned with the locking lever  50  of the locking unit  40  in the straight line. In this manner, when a rotation angle of the driven shaft lever  30  does not match (correspond to) a predetermined angle, the locking lever  50  may not be inserted into the stopping groove  31 ,  32 ,  33  and also the lock  70  cannot be latched. In addition, this may facilitate a user or operator to check with eyes that the movable contact  5   a  may not be in contact accurately with the fixed contact  4   a  of the earthing switch due to an inaccurate operation of the operating mechanism  8 . 
       FIG. 14  illustrates a state that the locking lever  50  of the locking unit  40  is released from the link assembly  10 , among the operating states of the locking device for the operating mechanism of the gas insulated switchgear in accordance with some embodiments of the present disclosure. Even in the released state, the lock  70  can be latched and thus the released state can be maintained and a loss of the lock can be prevented. 
       FIG. 15  is a planar view illustrating a locking device for an operating mechanism of a gas insulated switchgear in accordance with some embodiments of the present disclosure. 
     This embodiment illustrates that the locking unit  40  has the same configuration as that illustrated in the foregoing embodiment, excluding that the fixed plate  60  and the lock  70  are not employed and a wing bolt  67  is further provided to secure an inserted state of the locking lever  50 . 
     In a locking device for an operating mechanism of a gas insulated switchgear according to some embodiments of the present disclosure, a locking unit provided at one side of a link assembly can lock a state of the link assembly, which may prevent a change in a contact state even by a user&#39;s operation made randomly or by mistake, resulting in ensuring stability of an electric power system. 
     A normal operating state of a disconnecting switch/earthing switch can be determined on the basis of a coupled state between the link assembly and the locking unit. 
     A current state of the operating mechanism can be recognized on the basis of the coupled state between the link assembly and the locking unit, thereby preventing an operation made by mistake. 
     The locking unit may be provided with locking devices, such as a lock, a wing bolt and the like to fix a specific state, thereby preventing a random operation. 
     In addition, for repairing or replacing the operating mechanism which is currently operating, a situation that a movable contact is freely moved due to a detachment or removal of a driving shaft can be prevented, so as to prevent an abnormal contact between the movable contact and fixed contacts along which current flows, resulting in prevention of casualty or facility damage. 
     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 construed 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.

Technology Category: 5