Abstract:
The time period is shortened till a cutoff spring force is released when a switchgear is cut off. This switchgear comprises: a closing shaft; a main lever fixed turnably on the closing shaft and associated with a movable contact; a closing spring; a sub shaft; a sub lever and a latch lever fixed on the sub shaft; a roller mounted on the leading end of the latch lever; a turnable latch and a kick lever; a lock lever made turnable with respect to the latch; a latch returning spring for biasing the latch; a lock returning spring for biasing the kick lever and the lock lever; and a stopper for restricting the turns of the lock lever and the latch.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part (CIP) application of International Application PCT/JP2008/001994, the entire content of which is incorporated herein by reference. This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2007-195992, filed in the Japanese Patent Office on Jul. 27, 2007, the entire content of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a switchgear for opening/closing an electrical circuit and its operating mechanism and, more particularly, to a switchgear and its operating mechanism suitably configured for cutting off high-voltage current in short time periods. 
         [0003]    In general, there are available, as an operating mechanism of a switchgear, one using a hydraulic operating force for large power and one using a spring operating force for middle/small output power. The former is referred to as “hydraulic operating mechanism” and the latter as “spring operating mechanism”. In recent years, the advancement of size reduction of an arc-extinguishing chamber of a gas-insulated circuit breaker which is a type of a switchgear allows fault current to be cut off with a smaller operating force, so that application of the spring operating mechanism becomes popular. However, a gas-insulated circuit breaker of extra high-voltage class requires high-speed operating capability called “2-cycle operation” that is capability of achieving cutoff within a time length corresponding to two-cycle time periods of alternating current. A conventional spring operating mechanism typically has operating capability equivalent to about 3-cycle operation, and it is not easy to realize the two-cycle cutoff capability due to poor responsiveness of a retention mechanism or retention control mechanism of a spring force. 
         [0004]    A first type of conventional example of an operating mechanism of such a switchgear is disclosed in Japanese Patent Application Laid-Open Publications No. 11-213824 (FIGS. 1 and 7) and No. 2000-40445 (FIGS. 1 and 3), the entire contents of which are incorporated herein by reference. In operation mechanisms disclosed in these documents, a force of a cutoff spring is retained by a retention mechanism constituted by a latch, O-prop (opening-hook lever), and a catch through an output lever. In this configuration, when a trip current is applied to a solenoid serving as a retention control mechanism, a plunger of the solenoid activates the catch to allow the engagement between the catch and prop to be released, which releases the engagement between the output lever and the latch to rotate the output lever to release the cutoff spring force, thereby achieving cutoff operation. 
         [0005]    A second type of conventional example of the switchgear operating mechanism is disclosed in Japanese Patent No. 3497866 (FIGS. 1 to 4), the entire content of which is incorporated herein by reference. In a spring operating mechanism disclosed in this document, a pull-out lever and a retention lever are provided for retaining a cutoff spring force. In this configuration, the retention lever is activated not by the cutoff spring force but by a force of an acceleration spring at the cutoff operation time so as to release the cutoff spring force. 
         [0006]    In the first type of conventional example of the switchgear operating mechanism, operation for releasing the cutoff spring force (cutoff operation) is constituted by the following three steps: operation of the catch driven by excitation of the solenoid, operation of the O-prop, and operation of electrical contacts including the cutoff spring. The operational relationship between the above components is illustrated in  FIG. 16 . The horizontal axis denotes time, and vertical axis denotes a stroke of each components. In  FIG. 16 , the lowermost curve represents the waveform of a trip current and, above this, the stroke of the catch is depicted. Above this, the strokes of the O-prop and the cutoff spring are depicted. The uppermost curve represents an energizing signal of the contact in an arc-extinguishing chamber of a gas-insulated circuit breaker. 
         [0007]    Time length from the start of application of the trip current until the operation of the O-prop is started along with the operation of the catch is assumed to be T 1 . Time length from the start of operation of the O-prop to the start of operation of the cutoff spring is assumed to be T 2 . Time length from the start of operation of the cutoff spring until the cutoff spring reaches its contact opening point is assumed to be T 3 . Assuming that contact opening time is T 0 , 
         [0000]        T 0= T 1+ T 2+ T 3  (1) 
         [0000]    is satisfied. 
         [0008]    In order to realize 2-cycle operation, it is necessary to reduce contact opening time T 0  to a given value. Thus, in a typical spring operating mechanism, operations of the components from the catch to the cutoff spring, which occur after the trip current application, are not started simultaneously. That is, the catch operates to some degree to release the engagement between itself and the O-prop to thereby allow operation of the O-prop to be started, and the cutoff spring starts operating after the O-prop operates to some degree. Thus, a mechanism that-retains a cutoff spring force operates in a stepwise manner, so that it is necessary to reduce respective time lengths T 1 , T 2 , and T 3  in order to reduce T 0 . 
         [0009]    However, since the cutoff spring force is determined by the weight of a movable portion of the arc-extinguishing chamber, opening speed, and drive energy, there is a limit to a reduction of T 3 . With regard to T 2 , weight reduction of the O-prop and increase in a force (retention force) of retaining the cutoff spring force allow high-speed operation of the O-prop. However, when the retention force is increased, the size of the O-prop needs to be increased for strength, which limits the weight reduction of the O-prop. It follows that there occurs a limit in the improvement in operation speed relying on the increase in the retention force. Further, when the retention force is increased, a large force is applied to the engagement portion between the O-prop and the catch, so that there occurs a need to increase the size of the catch for strength and to provide a solenoid having a large electromagnetic power for activating the catch. 
         [0010]    At present, an excitation method using a large-sized condenser is adopted for obtaining a large power of the solenoid. However, the upper limit value for a current value flowing to the solenoid is specified in the standard, so that there is a limit in the improvement in the output power of the solenoid. As described above, it is difficult to reduce the contact opening time in the conventional spring operating mechanism. 
         [0011]    Also in the second type of conventional example, operation for releasing the cutoff spring force is constituted by the following three steps: operation of a pull-off hook driven by an electromagnet; simultaneous operation of a reset lever, acceleration spring, and a retention lever; and simultaneous operation of a pull-off lever and a cutoff spring. In this example, the direction of a retention force (pressuring force) of the cutoff spring is made substantially coincident with the rotation center of the retention lever, thereby reducing a force required for the operation of the retention lever. 
         [0012]    Further, the speed of movement of the retention lever, which is included in the above second step, is made higher by the accelerating spring to thereby reduce the operation time. However, it is physically difficult to reduce the operation time of the second step to zero and, therefore, it is difficult to significantly reduce the entire contact opening time, also in terms of the problems described in the first example. 
         [0013]    Further, the direction of a pressuring force to a portion at which the pull-off lever and the retention lever are engaged with each other is made substantially coincident with the rotation center of the retention lever, so that when an external vibration is applied to the retention lever to force the same to vibrate, the pull-off lever is rotated in the cutoff operation direction, and the cutoff operating mechanism may start operating without a cutoff command. 
         [0014]    Further, the direction of the pressuring force may fluctuate with respect to the rotation center of the retention lever due to deformation of the engagement surface between a roller provided on the pull-off lever and the retention lever, so that when the pressuring force acts in the cutoff operation direction of the retention lever, the pull-off lever may be released without a cutoff command. 
         [0015]    Further, although not described in Japanese Patent No. 3497866, it is just conceivable that the retention lever operates in the cutoff direction due to an impact force applied when the roller pushes aside the retention lever for reengagement in the closing operation to allow the cutoff operation to be started without a cutoff command. As described above, in the second example, it is difficult to significantly reduce the contact opening time and it is likely that a retention state of the cutoff spring becomes unstable. 
         [0016]    The present invention has been made to solve the above problems, and an object thereof is to provide a switchgear for opening/closing an electrical circuit and its operating mechanism in which retention/release of the cutoff spring force is performed by a combination of a latch and its lock mechanism to reduce a time period for the cutoff spring force to be released so as to significantly reduce the entire contact opening time and, at the same time, stability and reliability of a retention state of the cutoff spring force are improved. 
       BRIEF SUMMARY OF THE INVENTION 
       [0017]    In order to achieve the object, according to an aspect of the present invention there is provided a switchgear operating mechanism for reciprocatively driving a movable contact of a switchgear so as to shift the switchgear between a cutoff state and a closed state, the operating mechanism comprising: a frame; a closing shaft which is rotatably disposed relative to the frame; main lever which is rotatably fixed to the closing shaft and which can be swung in conjunction with the movable contact; a cutoff spring which is disposed such that it accumulates energy when the switchgear operating state is shifted from the cutoff state to the closed state in accordance with rotation of the closing shaft while it discharges its accumulated energy when the switchgear operating state is shifted from the closed state to the cutoff state; a sub-shaft which is rotatably disposed relative to the frame so as to be positioned around a rotation axis substantially parallel to a rotation axis of the closing shaft; a sub-lever which is swingably fixed to the sub-shaft; a main-sub connection link which rotatably connects a leading end of the sub-lever and the main lever; a cam mechanism which swings the sub-shaft in accordance with a rotation of the closing shaft; a latch lever which is swingably fixed to the sub-shaft; a roller which is rotatably fixed to a leading end of the latch lever; a latch which is disposed so as to be rotated relative to the frame around a rotation axis substantially parallel to the rotation axis of the closing shaft; a kick lever which is disposed so as to be rotated relative to the latch around a rotation axis substantially parallel to the rotation axis of the latch and has a through hole therein; a lock lever which is disposed so as to be rotated relative to the latch around a different rotation axis substantially parallel to the rotation axis of the latch; a latch return spring which biases the latch so as to rotate the latch in a predetermined direction; a lock return spring which biases the lock lever and the kick lever so as to rotate the lock lever and the kick lever in a predetermined direction; stopper which is fixed to the frame so as to restrict the rotation of the biasing direction of the lock lever and the latch; and a connection pin which is attached to the lock lever so as to be moved and rotated in the through hole formed in the lock lever relative to the through hole, wherein in the closed state, the roller pushes the leading end of the latch in an opposite direction to the biasing direction of the latch return spring and causes the leading end of the lock lever to be engaged with the stopper to stop the operation of the latch, and in a state where the switchgear operating state is shifted from the closed state to the cutoff state, the lock lever is pulled so as to be rotated in an opposite direction to the biasing direction of the lock return spring and the latch is pulled in an opposite direction to the biasing direction of the latch return spring to release an engagement between the roller and the leading end of the latch, which causes the cutoff spring to discharge its energy to rotate the sub-shaft and the main lever. 
         [0018]    According to another aspect of the present invention there is provided a switchgear operating mechanism for reciprocatively driving a movable contact of a switchgear so as to shift the switchgear between a cutoff state and a closed state, the operating mechanism comprising: a frame; a closing shaft which is rotatably disposed relative to the frame; a main lever which is rotatably fixed to the closing shaft and which can be swung in conjunction with the movable contact; a cutoff spring which is disposed such that it accumulates energy when the switchgear operating state is shifted from the cutoff state to the closed state in accordance with rotation of the closing shaft while it discharges its accumulated energy when the switchgear operating state is shifted from the closed state to the cutoff state; a sub-shaft which is rotatably disposed relative to the frame so as to be positioned around a rotation axis substantially parallel to a rotation axis of the closing shaft; a sub-lever which is swingably fixed to the sub-shaft; a main-sub connection link which rotatably connects a leading end of the sub-lever and the main lever; a cam mechanism which swings the sub-shaft in accordance with a rotation of the closing shaft; a latch lever which is swingably fixed to the sub-shaft; a roller which is rotatably fixed to a leading end of the latch lever; a latch which is disposed so as to be rotated relative to the frame around a rotation axis substantially parallel to the rotation axis of the closing shaft; a lock lever which is disposed so as to be rotated relative to the frame around a rotation axis substantially parallel to the rotation axis of the latch; a latch return spring which biases the latch so as to rotate the latch in a predetermined direction; a lock lever return spring which biases the lock lever in a direction opposite to the biasing direction of the latch return spring; and a stopper which is fixed to the frame so as to restrict the rotation of the biasing direction of the lock lever return spring of the lock lever, wherein in the closed state, the roller pushes the leading end of the latch in a direction opposite to the biasing force of the latch return spring, and in a state where the switchgear operating state is shifted from the closed state to the cutoff state, the lock lever is pulled so as to allow the latch to be rotated in an opposite direction to the biasing direction of the latch return spring to release an engagement between the roller and the leading end of the latch, which causes the cutoff spring to discharge its energy to rotate the sub-shaft. 
         [0019]    According to another aspect of the present invention there is provided a switchgear having a movable contact that can be moved in a reciprocating manner and an operating mechanism that reciprocatively drives the movable contact and configured to be shifted between a cutoff state and a closed state by the movement of the movable contact, the operating mechanism comprising: a frame; a closing shaft which is rotatably disposed relative to the frame; a main lever which is rotatably fixed to the closing shaft and which can be swung in conjunction with the movable contact; a cutoff spring which is disposed such that it accumulates energy when the switchgear operating state is shifted from the cutoff state to the closed state in accordance with rotation of the closing shaft while it discharges its accumulated energy when the switchgear operating state is shifted from the closed state to the cutoff state; a sub-shaft which is rotatably disposed relative to the frame so as to be positioned around a rotation axis substantially parallel to a rotation axis of the closing shaft; a sub-lever which is swingably fixed to the sub-shaft; a main-sub connection link which rotatably connects a leading end of the sub-lever and the main lever; a cam mechanism which swings the sub-shaft in accordance with a rotation of the closing shaft; a latch lever which swingably fixed to the sub-shaft; a roller which is rotatably fixed to a leading end of the latch lever; a latch which is disposed so as to be rotated relative to the frame around a rotation axis substantially parallel to the rotation axis of the closing shaft; a kick lever which is disposed so as to be rotated relative to the latch around a rotation axis substantially parallel to the rotation axis of the latch; a lock lever which is disposed so as to be rotated relative to the latch around a different rotation axis substantially parallel to the rotation axis of the latch; a latch return spring which biases the latch so as to rotate the latch in a predetermined direction; a lock return spring which biases the lock lever and the kick lever so as to rotate the lock lever and the kick lever in a predetermined direction; a stopper which is attached to the frame so as to restrict the rotation of the biasing direction of the lock lever and the latch; and a hole disposed in the kick lever so as to be engaged with a pin disposed on the lock lever, wherein in the closed state, the roller pushes the leading end of the latch in an opposite direction to the biasing direction of the latch return spring and causes the leading end of the lock lever to be engaged with the stopper to stop the operation of the latch, and in a state where the switchgear operating state is shifted from the closed state to the cutoff state, the lock lever is pulled so as to allow the lock lever to be rotated in an opposite direction to the biasing direction of the lock return spring and the latch is pulled in an opposite direction to the biasing direction of the latch return spring to release an engagement between the roller and the leading end of the latch, which causes the cutoff spring to discharge its energy to rotate the sub-shaft and the main lever. 
         [0020]    According to another aspect of the present invention there is provided a switchgear having a movable contact that can be moved in a reciprocating manner and an operating mechanism that reciprocatively drives the movable contact and configured to be shifted between a cutoff state and a closed state by the movement of the movable contact, the operating mechanism comprising: a frame; a closing shaft which is rotatably disposed relative to the frame; a main lever which is rotatably fixed to the closing shaft and which can be swung in conjunction with the movable contact; a cutoff spring which is disposed such that it accumulates energy when the switchgear operating state is shifted from the cutoff state to the closed state in accordance with rotation of the closing shaft while it discharges its accumulated energy when the switchgear operating state is shifted from the closed state to the cutoff state; a sub-shaft which is rotatably disposed relative to the frame so as to be positioned around a rotation axis substantially parallel to a rotation axis of the closing shaft; a sub-lever which is swingably fixed to the sub-shaft; a main-sub connection link which rotatably connects a leading end of the sub-lever and the main lever; a cam mechanism which swings the sub-shaft in accordance with a rotation of the closing shaft; a latch lever which swingably fixed to the sub-shaft; a roller which is rotatably fixed to a leading end of the latch lever; a latch which is disposed so as to be rotated relative to the frame around a rotation axis substantially parallel to the rotation axis of the closing shaft; a lock lever which is disposed so as to be rotated relative to the frame around a rotation axis substantially parallel to the rotation axis of the latch; a latch return spring which biases the latch so as to rotate the latch in a predetermined direction; a lock lever return spring which biases the lock lever in a direction opposite to the biasing direction of the latch return spring; and a stopper which is fixed to the frame so as to restrict the rotation of the biasing direction of the lock lever return spring of the lock lever, wherein in the closed state, the roller pushes the leading end of the latch in a direction opposite to the biasing force of the latch return spring, and in a state where the switchgear operating state is shifted from the closed state to the cutoff state, the lock lever is pulled so as to allow the latch to be rotated in an opposite direction to the biasing direction of the latch return spring to release an engagement between the roller and the leading end of the latch, which causes the cutoff spring to discharge its energy to rotate the sub-shaft. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The above and other features and advantages of the present invention will become apparent from the discussion hereinbelow of specific, illustrative embodiments thereof presented in conjunction with the accompanying drawings, in which: 
           [0022]      FIG. 1  is a front view illustrating a closed state of a retention unit and a retention control unit of a switchgear operating mechanism according to a first embodiment of the present invention; 
           [0023]      FIG. 2  is a developed front view illustrating a cutoff state of the spring operating mechanism of the switchgear illustrated in  FIG. 1 ; 
           [0024]      FIG. 3  is a developed front view illustrating a closed state of the spring operating mechanism of the switchgear illustrated in  FIG. 1 ; 
           [0025]      FIG. 4  is a front view of the main part of the switchgear of  FIG. 1 , which illustrates a cutoff operation process from the closed state to the cutoff state; 
           [0026]      FIG. 5  is a front view of the main part of the switchgear of  FIG. 1 , which illustrates a cutoff operation process continued from  FIG. 4 ; 
           [0027]      FIG. 6  is a front view of the main part of the switchgear of  FIG. 1 , which illustrates a closing operation process from the cutoff state to the closed state; 
           [0028]      FIG. 7  is a front view of the main part of the switchgear of  FIG. 1 , which illustrates a closing operation process continued from  FIG. 6 ; 
           [0029]      FIG. 8  is a front view illustrating a closed state of a retention unit and a retention control unit of a switchgear operating mechanism according to a second embodiment of the present invention; 
           [0030]      FIG. 9  is a developed front view illustrating a cutoff state of the spring operating mechanism of the switchgear illustrated in  FIG. 8 ; 
           [0031]      FIG. 10  is a developed front view illustrating a closed state of the spring operating mechanism of the switchgear illustrated in  FIG. 8 ; 
           [0032]      FIG. 11  is a front view of the main part of the switchgear of  FIG. 8 , which illustrates a cutoff operation process from the closed state to the cutoff state; 
           [0033]      FIG. 12  is a front view of the main part of the switchgear of  FIG. 8 , which illustrates a cutoff operation process continued from  FIG. 11 ; 
           [0034]      FIG. 13  is a front view of the main part of the switchgear of  FIG. 8 , which illustrates a closing operation process from the cutoff state to the closed state; 
           [0035]      FIG. 14  is a front view of the main part of the switchgear of  FIG. 8 , which illustrates a closing operation process continued from  FIG. 13 ; 
           [0036]      FIG. 15  is a front view illustrating a closed state of a retention unit and a retention control unit of a switchgear operating mechanism according to a third embodiment of the present invention; and 
           [0037]      FIG. 16  is a time chart for explaining the cutoff operation of a conventional switchgear. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0038]    Embodiments of an operating mechanism of a switchgear according to the present invention will be described below with reference to the accompanying drawings. 
       First Embodiment 
       [0039]    First, with reference to  FIGS. 1 to 7 , a first embodiment of a switchgear operating mechanism according to the present invention will be described.  FIG. 1  is a front view illustrating a closed state of a retention unit and a retention control unit of a switchgear operating mechanism.  FIG. 2  is a view illustrating a cutoff state of a spring operating mechanism including the units illustrated in  FIG. 1 .  FIG. 3  is a view illustrating a closed state of a spring operating mechanism including the units illustrated in  FIG. 1 .  FIGS. 4 and 5  are views illustrating a cutoff operation process from the closed state to the cutoff state.  FIGS. 6 and 7  are views illustrating a closing operation process from the cutoff state to the closed state. 
         [0040]    In  FIGS. 2 and 3 , a movable contact  200  is connected to the left side of a link mechanism  6 . When the link mechanism  6  is moved in the right direction as illustrated in  FIG. 2 , the movable contact  200  becomes “open” to achieve a cutoff state. On the other hand, when the link mechanism  6  is moved in the left direction as illustrated in  FIG. 3 , the movable contact  200  becomes “closed” to achieve a closed state. One end of the link mechanism  6  is rotatably engaged with the leading end of a main lever  11 , and the main lever  11  is rotatably fixed to a closing shaft  81 . The closing shaft  81  is rotatably supported by a bearing (not illustrated) fixed to a frame (support structure)  14 . 
         [0041]    A cutoff spring  12  has one end fixed to an attachment surface  10   d  of the frame  14  and the other end fitted to a cutoff spring receiver  16 . A damper  17  is fixed to the cutoff spring receiver  16 . In the damper  17 , a fluid is encapsulated and a piston  17   a  is provided so as to translationally slide. One end of the damper  17  is fixed to a cutoff spring link  15 , which is rotatably attached to a pin  11   a  of the main lever  11 . 
         [0042]    A sub-shaft  70  is rotatably disposed relative to the frame  14 , and a sub-lever  71  is fixed to the sub-shaft  70 . A pin  71   a  is disposed at the leading end of the sub-lever  71 . A pin  11   d  disposed on the main lever  11  and the pin  71   a  are connected by a main-sub connection link  80 . A latch lever  72  is fixed to the sub-shaft  70 , and a roller  72   a  is rotatably fitted to the leading end of the latch lever  72 . Further, a cam lever  73  is fixed to the sub-shaft  70 , and a roller  73   a  is rotatably fitted to the leading end of the cam lever  73 . 
         [0043]    A closing spring  13  has one end fixed to an attachment surface  10   d  of the frame  14  and the other end fixed to a closing spring receiver  18 . A pin  18   a  is disposed on the closing spring receiver  18 . The pin  18   a  is connected to a pin  82   a  of a closing lever  82  which is fixed to the end portion of the closing shaft  81  through a closing link  83 . A closing cam  84  is fixed to the closing shaft  81  and releasably engaged with the roller  73   a  in accordance with the rotation of the closing shaft  81 . 
         [0044]    A tab  82   b  is disposed at one end of the closing lever  82  and is releasably engaged with a half-column portion  62   a  provided in an anchoring lever  62  for closing which is rotatably disposed relative to the frame  14 . Further, a return spring  62   b  is disposed at one end of the anchoring lever  62  for closing. The other end of the return spring  62   b  is fixed to the frame  14 . The return spring  62   b  is a compression spring and the spring force thereof always acts on the anchoring lever  62  for closing as a clockwise torque. However, the rotation of the anchoring lever  62  is restricted by an engagement between a plunger  22   a  of an electromagnetic solenoid  22  for closing which is fixed to the frame  14  and the anchoring lever  62  for closing. 
         [0045]    In the cutoff state illustrated in  FIG. 2 , a center  101  of the closing shaft  81  is displaced to the left relative to the center axis (or the axis connecting the centers of the pin  18   a  and the pin  82   a ) of the closing link  83 , so that a counterclockwise torque is applied to the closing lever  82  by the closing spring  13 . However, the rotation of the closing lever  82  is retained by an engagement between the tab  82   b  and the half-column portion  62   a.    
         [0046]    A two-forked support portion  90   b  is formed at the leading end of an anchoring lever  90 . The support portion  90   b  is engaged with a stopper  14   b  which is fixed to the frame  14 , which fixes the position of the anchoring lever  90  relative to the frame  14 . 
         [0047]    A latch  91  is rotatably disposed around a latch axis pin  100  which is fixed to the end portion of the anchoring lever  90 . A latch return spring  91   a  is disposed between the anchoring lever  90  and the latch  91 . The latch return spring  91   a  always generates a clockwise torque for the latch  91 . The clockwise rotation of the latch  91  is restricted by an abutment between a stopper pin (stopper)  90   a  disposed on the anchoring lever  90  and the latch  91 . A leading end  102  of the latch  91  is formed by a substantially cylindrical surface, and the center axis position of the cylindrical surface falls within a range between the rotation center of the latch  91 , (i.e., center axis of the latch axis pin  100 ) and position spaced from the center axis of the latch axis pin  100  on the stopper  90   a  side by a distance corresponding to the radius of the latch axis pin  100 . 
         [0048]    A kick lever  51  is rotatably disposed around a rotary shaft  51   a  which is fixed to the latch  91 . A protrusion portion  51   c  to be described later is formed in the kick lever  51 . Further, a substantially rectangular through hole  51   d  is formed in the kick lever  51 . 
         [0049]    A lock lever  52  is rotatably disposed around a rotary shaft  52   a  which is fixed to the latch  91 . A connection pin  52   d  is disposed on the lock lever  52 , and the kick lever  51  and the lock lever  52  are connected to each other through an engagement between the connection pin  52   d  and a through hole  51   d . The through hole  51   d  has a size allowing the connection pin  52   d  to move and rotate to some degree in the through hole  51   d  relative to the same. 
         [0050]    A lock return spring  52   c  is disposed around the connection pin  52   d . The lock return spring  52   c  has one end anchored to the rotary shaft  52   a  and the other end anchored to a pin  51   b  disposed on the kick lever  51  and always generates a clockwise torque for the lock lever  52 . For the kick lever  51 , the lock return spring  52   c  always generates a counterclockwise torque. 
         [0051]    A torque generated by the lock return spring  52   c  is restricted by an abutment between a cut portion  52   b  formed at one end of the lock lever  52  and the stopper  90   a . The rotation of the kick lever  51  is restricted by an abutment between the through hole  51   d  and the connection pin  52   d . In the closed state illustrated in  FIG. 1 , the connection pin  52   d  abuts the side surface of the through hole  51   d  at the rotary shaft  51   a  side. This causes the direction of a contact force between the connection pin  52   d  and the through hole  51   d  to be directed toward the rotary shaft  52   a.    
         [0052]    Since the cut portion  52   b  is engaged with the stopper pin  90   a  in the closed state illustrated in  FIGS. 1 and 3 , the counterclockwise rotation of the latch  91  is restricted. A protrusion portion  51   c  is formed in the kick lever  51 , and it is releasably engaged with the roller  72   a.    
         [0053]    A pull-off link mechanism has a pull-off link  53  and a pull-off lever  54  rotatably and translationally engaged with one end of the pull-off link  53 . A pin  52   e  disposed on the lock lever  52  and the end portion of the pull-off link  53  is connected in a rotatable manner. The pull-off link  53  has an elongated hole  53   a  at the engagement portion with the pull-off lever  54 . A pin  54   b  is disposed on the pull-off lever  54 . The pin  54   b  is engaged with the elongated hole  53   a , allowing the pin  54   b  and the elongated hole  53   a  to be moved and rotated relative to each other within the range of the elongated hole  53   a . The pull-off lever  54  is rotatably disposed relative to the frame  14  and always receives a clockwise torque by a pull-off return spring  54   a.    
         [0054]    The leading end of a plunger  21   a  of an electromagnetic solenoid  21  for cutoff which is fixed to the frame  14  is releasably engaged with the pull-off lever  54 , which restricts the torque of the pull-off return spring  54   a  and causes the pull-off lever  54  to be rotated in the counterclockwise direction upon input of a cutoff command. 
         [0055]    In the closed state, the main lever  11  always receives a clockwise torque by an expanding spring force of the cutoff spring  12 . The force transmitted to the main lever  11  is then transmitted to the sub-lever  71  through the main-sub connection link  80 . The transmitted force becomes a torque for always rotating the sub-lever  71  in the counterclockwise direction. This counterclockwise torque is supplied also to the latch lever  72 . However, in the closed state, the leading end  102  of the latch  91  and the roller  72   a  are engaged with each other to restrict the counterclockwise rotation of the latch lever  72 . Accordingly, the subsequent members from the sub-lever  71  to the cutoff spring  12  maintain their static state. 
         [0056]    In the present embodiment, the rotation shafts, such as the closing shaft  81  and the sub-shaft  70 , and axes of the respective pins are parallel to each other. 
         [0057]    (Cutoff Operation) 
         [0058]    In the present embodiment having the configuration described above, a cutoff operation from the closed state illustrated in  FIGS. 1 and 3 , through states illustrated in  FIGS. 4 and 5 , to the cutoff state illustrated in  FIG. 2  will be described below. First, in the closed state illustrated in  FIGS. 1 and 3 , upon input of an external command, the electromagnetic solenoid  21  for cutoff is excited to move the plunger  21   a  in the direction of an arrow B. Since the pull-off lever  54  is engaged with the plunger  21   a , it is rotated in the counterclockwise direction. In conjunction with the rotation, the elongated hole  53   a  is moved to the right while being engaged with the pin  54   b  to rotate the lock lever  52  in the counterclockwise direction. This state is illustrated in  FIG. 4 . 
         [0059]    The pull-off link  53  rotates the latch  91  in the counterclockwise direction through the lock lever  52 , which releases an engagement between the roller  72   a  and the leading end  102  of the latch  91 . The latch lever  72  receives a counterclockwise torque from the cutoff spring  12 , so that it is rotated in the counterclockwise direction while pushing the latch  91 . At this time, the elongated hole  53   a  moves along the pin  54   b , so that the pull-off link  53  and the pull-off lever  54  operate independently of each other. In this state, the protrusion portion  51   c  of the kick lever  51  has been moved to the pull-off lever  54  side by the rotation of the lock lever  52 , so that it is not engaged with the roller  72   a . This state is illustrated in  FIG. 5 . 
         [0060]      FIG. 2  illustrates the end state of the cutoff operation. In this state, the kick lever  51  and the lock lever  52  have been returned to substantially the same position as those in the closed state ( FIGS. 1 and 3 ) by the lock return spring  52   c  ( FIG. 1 ). Further, the pull-off link  53  and the pull-off lever  54  have been returned to substantially the same position as those in the closed state by the pull-off return spring  54   a . Furthermore, the latch  91  has been returned to substantially the same position as that in the closed state by the latch return spring  91   a.    
         [0061]    When an engagement between the latch  91  and the roller  72   a  is released in  FIG. 3 , the cam lever  73  and the sub-lever  71 , which are fixed to the latch lever  72  and the sub-shaft  70 , are rotated in the counterclockwise direction (denoted by arrows C and D). Then, the main lever  11  is rotated in the clockwise direction (denoted by an arrow E) to cause the cutoff spring  12  and damper  17  to be moved in the direction of an arrow F. Then, the link mechanism  6  and the movable contact  200  connected to the link mechanism  6  are moved to the right to start the cutoff operation. 
         [0062]    When the cutoff spring  12  is displaced by a given distance, the piston  17   a  abuts the stopper  14   a  fixed to the frame  14  to generate a braking power of the damper  17  to thereby stop the movement of the cutoff spring  12 . The movements of the link levers connected to the cutoff spring  12  are accordingly stopped, thereby completing the cutoff operation. This state is illustrated in  FIG. 2 . 
         [0063]    (Closing Operation) 
         [0064]    Next, a closing operation from the cutoff state illustrated in  FIG. 2 , through states illustrated in  FIGS. 6 and 7 , to the closed state illustrated in  FIGS. 1 and 3  will be described. 
         [0065]      FIG. 2  illustrates the cutoff state where the closing spring  13  has accumulated energy. Upon input of an external command, the electromagnetic solenoid  22  for closing is excited to move the plunger  22   a  in the direction of an arrow H. The anchoring lever  62  for closing is engaged with the plunger  22   a , so that it is rotated in the counterclockwise direction. Then, the engagement between the half-column portion  62   a  and the tab  82   b  is released. Accordingly, the closing lever  82  and the closing shaft  81  are rotated in the counterclockwise direction (denoted by an arrow I) by a spring force of the closing spring  13 . The closing spring  13  is stretched in the direction of an arrow J and discharges its accumulated energy. The closing cam  84  fixed to the closing shaft  81  is rotated in the direction of an arrow K to be engaged with the roller  73   a . When the roller  73   a  is pushed by the closing cam  84 , the cam lever  73  is rotated in the clockwise direction (denoted by an arrow L) and, at the same time, the sub-lever  71  is rotated in the direction of an arrow M. 
         [0066]    When the rotation of the sub-lever  71  is transmitted to the main lever  11 , the main lever  11  is rotated in the counterclockwise direction (denoted by an arrow N). Then, the link mechanism  6  and the movable contact  200  connected to the link mechanism  6  are moved to the left to start the closing operation. The cutoff spring  12  is compressed in association with the rotation of the main lever  11  to accumulate energy to establish an engagement between the roller  72   a  and the latch  91  once again, thereby completing the closing operation. 
         [0067]    When the latch lever  72  is rotated in the clockwise direction in a state where the operation is shifted from the cutoff state illustrated in  FIG. 2  to the closing operation, the roller  72   a  is engaged with the protrusion portion  51   c  of the kick lever  51  in the first place. This engagement causes the kick lever  51  to be rotated in the clockwise direction and, accordingly, the side surface of the through hole  51   a  on the latch  91  side is engaged with the connection pin  52   d  to thereby cause the lock lever  52  to be rotated in the counterclockwise direction. This releases an engagement between the lock lever  52  and the stopper  90   a , allowing the counterclockwise rotation of the latch  91 . This state is illustrated in  FIG. 6 . 
         [0068]      FIG. 7  illustrates a state where the latch  91  is rotated further in the counterclockwise direction by the roller  72   a .  FIGS. 1 and 3  illustrate a state where the closing operation has been completed. 
         [0069]    When an engagement between the closing cam  84  and the roller  73   a  is released, the latch  91  is returned to substantially the same position as that in the closed state by the torque of the latch return spring  91   a . At this time, the lock lever  52  and the kick lever  51  are also returned to substantially the same position as those in the closed state by the torque clue to the lock return spring  52   c . Further, the roller  72   a  is engaged with the leading end  102  of the latch  91  once again by the expanding force of the cutoff spring  12 . At this reengagement operation, a force acting from the roller  72   a  to the latch  91  is directed to a range between substantially the rotation center of the latch  91  and position spaced from the rotation center of the latch  91  on the stopper  90   a  side by a distance corresponding to the radius of the latch axis pin  100 . This is because that the leading end  102  of the latch  91  is formed by a substantially cylindrical surface, and the center position of the cylindrical surface falls within a range between substantially the rotation center of the latch  91 , (i.e., center of the latch axis pin  100 ) and position spaced from the rotation center of the latch axis pin  100  on the stopper  90   a  side. Therefore, the latch  91  is pressed to rotate in the counterclockwise direction. However, the counterclockwise rotation of the latch  91  is restricted because the cut portion  52   b  of the lock lever  52  is engaged with the stopper  90   a . Thus, a mechanism for locking the latch  91  is achieved. 
         [0070]    According to the present embodiment, after the electromagnetic solenoid  21  for cutoff is excited upon input of a cutoff command, the cutoff operation is completed by two operation steps: a first operation step in which the latch  91  is directly driven through the pull-off lever  54 , the pull-off link  53  and the lock lever  52  to release an engagement between the latch  91  and the roller  72   a ; and a second operation step in which the cutoff spring  12  operates. As described above, the number of operation steps for completing the cutoff operation is reduced from three (in the case of conventional spring operating mechanism) to two, thereby significantly reducing the cutoff operation time. This means that T 2  is removed from the expression (1) representing the contact opening time, so that it is possible to reduce the contact opening time. 
         [0071]    Further, the engagement surface of the leading end  102  of the latch  91  is formed by a substantially cylindrical surface, and the center position of the cylindrical surface falls within a range between substantially the rotation center of the latch, (i.e., center of the latch axis pin  100 ) and position spaced from the rotation center of the latch axis pin  100  on the stopper  90   a  side by a distance corresponding to the radius of the latch axis pin  100 , so that a torque of the roller  72   a  acting on the latch  91  in the closed state becomes small. This allows a reduction of the size and the weight of the latch  91  and the lock lever  52  to thereby minimize a force required for releasing its engagement, which can minimize the size of the electromagnetic solenoid. 
         [0072]    Further, by forming the protrusion portion  51   c  in the kick lever  51  and engaging the protrusion portion  51   c  with the roller  72   a  at the time of the closing, it is possible to realize an action for easily releasing an engagement between the lock lever  52  and the stopper  90   a  with a simple structure, contributing to size reduction of the latch  91 . 
         [0073]    The elongated hole  53   a  is disposed at one end of the pull-off link  53 , and the pin  54   b  disposed on the pull-off lever  54  and the elongated hole  53   a  are engaged with each other. This configuration allows an engagement between the pull-off link  53  and the pull-off lever  54  to be released at the time when the latch  91  is returned to the closing state. As a result, it is possible to minimize the weight of the movable portion of the latch  91  to thereby reduce the time required for the latch  91  to return to the position of the closed state, enabling high speed operation. 
         [0074]    There is a possibility that the connection pin  52   d  may abut the though hole  51   d  at the time when the kick lever  51  returns to the position of the closed state to apply an abutment force on the lock lever  52  to generate a torque in the lock lever  52 . However, the connection pin  52   d  abuts the side surface of the through hole  51   d  at its rotary shaft  51   a  side, so that the abutment force is directed to the center of the rotary shaft  52   a , preventing a torque from being generated. 
       Second Embodiment 
       [0075]    First, with reference to  FIGS. 8 to 14 , a second embodiment of the switchgear operating mechanism according to the present invention will be described.  FIG. 8  is a front view illustrating a closed state of a retention unit and a retention control unit of a switchgear operating mechanism.  FIG. 9  is a view illustrating a cutoff state of a spring operating mechanism including the units illustrated in  FIG. 8 .  FIG. 10  is a view illustrating a closed state of a spring operating mechanism including the units illustrated in  FIG. 8 .  FIGS. 11 and 12  are views illustrating a cutoff operation process from the closed state to the cutoff state.  FIGS. 13 and 14  are views illustrating a closing operation process from the cutoff state to the closed state. 
         [0076]    In  FIGS. 9 and 10 , a movable contact  200  is connected to the left side of a link mechanism  6 . When the link mechanism  6  is moved in the right direction as illustrated in  FIG. 9 , the movable contact  200  becomes “open” to achieve a cutoff state. On the other hand, when the link mechanism  6  is moved in the left direction as illustrated in  FIG. 10 , the movable contact becomes “closed” to achieve a closed state. One end of the link mechanism  6  is rotatably engaged with the leading end of a main lever  11 , and the main lever  11  is rotatably fixed to a closing shaft  81 . The closing shaft  81  is rotatably supported by a bearing (not illustrated) fixed to a frame (support structure)  14 . 
         [0077]    A cutoff spring  12  has one end fixed to an attachment surface  10   d  of the frame  14  and the other end fitted to a cutoff spring receiver  16 . A damper  17  is fixed to the cutoff spring receiver  16 . In the damper  17 , a fluid is encapsulated and a piston  17   a  is provided so as to translationally slide. One end of the damper  17  is fixed to a cutoff spring link  15 , which is rotatably attached to a pin  11   a  of the main lever  11 . 
         [0078]    A sub-shaft  70  is rotatably disposed relative to the frame  14 , and a sub-lever  71  is fixed to the sub-shaft  70 . A pin  71   a  is disposed at the leading end of the sub-lever  71 . A pin  11   d  disposed on the main lever  11  and the pin  71   a  are connected by a main-sub connection link  80 . A latch lever  72  is fixed to the sub-shaft  70 , and a roller  72   a  is rotatably fitted to the leading end of the latch lever  72 . Further, a cam lever  73  is fixed to the sub-shaft  70 , and a roller  73   a  is rotatably fitted to the leading end of the cam lever  73 . 
         [0079]    A closing spring  13  has one end fixed to the attachment surface  10   d  of the frame  14  and the other end fixed to a closing spring receiver  18 . A pin  18   a  is disposed on the closing spring receiver  18 . The pin  18   a  is connected to a pin  82   a  of a closing lever  82  which is fixed to the end portion of the closing shaft  81  through a closing link  83 . A closing cam  84  is fixed to the closing shaft  81  and releasably engaged with the roller  73   a  in accordance with the rotation of the closing shaft  81 . 
         [0080]    A tab  82   b  is disposed at one end of the closing lever  82  and is releasably engaged with a half-column portion  62   a  provided in an anchoring lever  62  for closing which is rotatably disposed on the frame  14 . Further, a return spring  62   b  is disposed at one end of the anchoring lever  62  for closing. The other end of the return spring  62   b  is fixed to the frame  14 . The return spring  62   b  is a compression spring and the spring force thereof always acts on the anchoring lever  62  for closing as a clockwise torque. However, the rotation of the anchoring lever  62  is restricted by an engagement between a plunger  22   a  of an electromagnetic solenoid  22  for closing, which is fixed to the frame  14 , and the anchoring lever  62  for closing. 
         [0081]    In the cutoff state illustrated in  FIG. 9 , the center  101  of the closing shaft  81  is displaced to the left relative to the center axis (or the axis connecting the centers of the pin  18   a  and the pin  82   a ) of the closing link  83 , so that a counterclockwise torque is applied to the closing lever  82  by the closing spring  13 . However, the rotation of the closing lever  82  is restricted by an engagement between the tab  82   b  and the half-column portion  62   a.    
         [0082]    A projecting support portion  390   b  is formed in an anchoring lever  390 . The support portion  390   b  is engaged with a stopper  14   b  which is fixed to the frame  14 , which fixes the position of the anchoring lever  390  relative to the frame  14 . 
         [0083]    A latch  391  is rotatably disposed around a latch axis pin  100  which is fixed to the end portion of the anchoring lever  390 . A latch return spring  391   a  is disposed between the anchoring lever  390  and the latch  391 . The latch return spring  391   a  always generates a clockwise torque for the latch  391 . The clockwise rotation of the latch  391  is restricted by an abutment between a stopper pin (stopper)  390   a  disposed on the anchoring lever  390  and the latch  391 . A leading end  102  of the latch  391  is formed by a substantially cylindrical surface, center position of the cylindrical surface substantially coincides with the rotation center of the latch  391 , i.e., center axis of the latch axis pin  100  or falls within the radius of the latch axis pin  100 . 
         [0084]    A lock lever  352  is a V-shape plate and has, at its bent portion of the V-shape, a pin  352   a , through which the lock lever  352  and the latch  391  are rotatably engaged with each other. An engagement portion  352   b  which is releasably engaged with the stopper pin  390   a  is formed at one end of the V-shape lock lever  352 . A protrusion portion  352   c  to be described later is formed at the other end of the V-shape lock lever  352 . 
         [0085]    A counterclockwise torque is always applied to the lock lever  352  by a lock lever return spring  352   e , and the lock lever  352  receives the torque when the engagement portion  352   b  abuts the stopper pin  390   a.    
         [0086]    In the closed state illustrated in  FIGS. 8 and 10 , the engagement portion  352   b  engages with the stopper pin  390   a  and the engagement state is retained by the lock lever return spring  352   e . Therefore, counterclockwise rotation of the latch  391  is prevented by the presence of the lock lever  352  and the stopper pin  390   a . A protrusion portion  352   c  is formed in the lock lever  352  and is releasably engaged with the roller  72   a.    
         [0087]    A pull-off link mechanism has a pull-off link  353  and a pull-off lever  354  movably and rotatably engaged with one end of the pull-off link  353 . The pull-off link  353  has an elongated hole  353   a  which penetrates the engagement portion between itself and a pull-off lever pin  354   b  disposed on the pull-off lever  354 . The pull-off lever pin  354   b  can be moved and rotated relative to the elongated hole  353   a  within the range of the elongated hole  353   a . A lock lever pin  352   d  is disposed on the lock lever  352  and is rotatably engaged with the end portion of the pull-off link  353  at the opposite side to the elongated hole  353   a . The pull-off lever  354  is rotatably disposed relative to the frame  14  and always receives a clockwise torque by a pull-off return spring  354   a.    
         [0088]    The leading end of a plunger  21   a  of an electromagnetic solenoid  21  for cutoff which is fixed to the frame  14  is releasably engaged with the pull-off lever  354 , which causes the pull-off lever  354  to be rotated in the counterclockwise direction upon input of a cutoff command. 
         [0089]    In the closed state, the main lever  11  always receives a clockwise torque by an expanding spring force of the cutoff spring  12 . The force transmitted to the main lever  11  is then transmitted to the sub-lever  71  through the main-sub connection link  80 . The transmitted force becomes a torque for always rotating the sub-lever  71  in the counterclockwise direction. This counterclockwise torque is supplied also to the latch lever  72 . However, in the closed state, the leading end  102  of the latch  391  and the roller  72   a  are engaged with each other to restrict the counterclockwise rotation of the latch lever  72 . Accordingly, the subsequent members from the sub-lever  71  to the cutoff spring  12  maintain their static state. 
         [0090]    In the present embodiment, the rotation shafts, such as the closing shaft  81  and the sub-shaft  70 , and the axes of the pins are parallel to each other. 
         [0091]    (Cutoff Operation) 
         [0092]    In the present embodiment having the configuration described above, a cutoff operation from the closed state illustrated in  FIGS. 8 and 10 , through states illustrated in FIGS.  11  and  12 , to the cutoff state illustrated in  FIG. 9  will be described. First, in the closed state illustrated in  FIGS. 8 and 10 , upon input of an external command, the electromagnetic solenoid  21  for cutoff is excited to move the plunger  21   a  in the direction of an arrow B. Since the pull-off lever  354  is engaged with the plunger  21   a , it is rotated in the counterclockwise direction. In conjunction with the rotation, the pull-off link  353  is moved to the right while being engaged with the lock lever pin  352   d  to rotate the lock lever  352  in the clockwise direction. As a result, an engagement between the engagement portion  352   b  and the stopper pin  390   a  is released. This state is illustrated in  FIG. 11 . 
         [0093]    The pull-off link  353  rotates the latch  391  in the counterclockwise direction through the lock lever  352 , which releases an engagement between the roller  72   a  and the leading end  102  of the latch  391 . The latch lever  72  receives a counterclockwise torque from the cutoff spring  12 , so that it is rotated in the counterclockwise direction while pushing the latch  391 . At this time, the pull-off link  353  moves while the elongated hole  353   a  and the pull-off lever pin  354   b  are engaged with each other, so that it operates independently of the pull-off lever  354 . In this state, the protrusion portion  352   c  of the lock lever  352  has been shifted to the pull-off lever  354  side from the latch  391 , so that it is not engaged with the roller  72   a . This state is illustrated in  FIG. 12 . 
         [0094]      FIG. 9  illustrates the end state of the cutoff operation. In this state, the lock lever  352  has been returned to substantially the same position as those in the closed state ( FIGS. 8 and 10 ) by the lock lever return spring  352   e  ( FIG. 1 ). Further, the pull-off link  353  and pull-off lever  354  have been returned to substantially the same position as those in the closed state by the pull-off return spring  354   a  ( FIG. 8 ). Furthermore, the latch  391  has been returned to substantially the same position as that in the closed state by the latch return spring  391   a.    
         [0095]    When an engagement between the latch  391  and the roller  72   a  is released in  FIG. 10 , the cam lever  73  and the sub-lever  71 , which are fixed to the latch lever  72  and the sub-shaft  70 , are rotated in the counterclockwise direction (denoted by arrows C and D). Then, the main lever  11  is rotated in the clockwise direction (denoted by an arrow E) to cause the cutoff spring  12  and the damper  17  to be moved in the direction of an arrow F. Then, the link mechanism  6  and the movable contact  200  connected to the link mechanism  6  are moved to the right to start the cutoff operation. 
         [0096]    When the cutoff spring  12  is displaced by a given distance, the piston  17   a  abuts the stopper  14   a  fixed to the frame  14  to generate a braking power of the damper  17  to thereby stop the movement of the cutoff spring  12 . The movements of the link levers connected to the cutoff spring  12  are accordingly stopped, thereby completing the cutoff operation. This state is illustrated in  FIG. 9 . 
         [0097]    (Closing Operation) 
         [0098]    Next, a closing operation from the cutoff state illustrated in  FIG. 9 , through states illustrated in  FIGS. 13 and 14 , to the closed state illustrated in  FIGS. 8 and 10  will be described. 
         [0099]      FIG. 9  illustrates a state where the closing spring  13  accumulates energy in the cutoff state. Upon input of an external command, the electromagnetic solenoid  22  for closing is excited to move the plunger  22   a  in the direction of an arrow H. The anchoring lever  62  for closing is engaged with the plunger  22   a , so that it is rotated in the counterclockwise direction. Then, the engagement between the half-column portion  62   a  and the tab  82   b  is released. Accordingly, the closing lever  82  and the closing shaft  81  are rotated in the counterclockwise direction (denoted by an arrow I) by a spring force of the closing spring  13 . The closing spring  13  is stretched in the direction of an arrow J and discharges its accumulated energy. The closing cam  84  fixed to the closing shaft  81  is rotated in the direction of an arrow K to be engaged with the roller  73   a . When the roller  73   a  is pushed by the closing cam  84 , the cam lever  73  is rotated in the clockwise direction (denoted by an arrow L) and, at the same time, the sub-lever  71  is rotated in the direction of an arrow M. 
         [0100]    When the rotation of the sub-lever  71  is transmitted to the main lever  11 , the main lever  11  is rotated in the counterclockwise direction (denoted by an arrow N). Then, the link mechanism  6  and the movable contact  200  connected thereto are moved to the left to start the closing operation. The cutoff spring  12  is compressed in association with the rotation of the main lever  11  to accumulate energy to establish an engagement between the roller  72   a  and the latch  391  once again, thereby completing the closing operation. 
         [0101]    When the latch lever  72  is rotated in the clockwise direction in a state where the operation is shifted from the cutoff state illustrated in  FIG. 9  to the closing operation, the roller  72   a  is engaged with the protrusion portion  352   c  of the lock lever  352  in the first place. This engagement causes the lock lever  352  to be rotated in the clockwise direction. This releases an engagement between the engagement portion  352   b  of the lock lever  352  and the stopper pin  390   a , allowing the counterclockwise rotation of the latch  391 . This state is illustrated in  FIG. 13 . 
         [0102]      FIG. 14  illustrates a state where the latch  391  is rotated further in the counterclockwise direction by the roller  72   a .  FIGS. 8 and 10  illustrate a state where the closing operation has been completed. 
         [0103]    When an engagement between the closing cam  84  and the roller  73   a  is released, the roller  72   a  is engaged with the leading end  102  of the latch  391  once again by the expanding force of the cutoff spring  12 . At this reengagement operation, a force acting from the roller  72   a  to the latch  391  is directed to substantially the rotation center of the latch  391 . This is because that the leading end  102  of the latch  391  is formed by a substantially cylindrical surface, and the center position of the cylindrical surface substantially coincides with the rotation center of the latch  391  (i.e., center axis of the latch axis pin  100 ). However, there is a possibility that the latch  391  is rotated in the counterclockwise direction due to lack of accuracy in the engagement surface, deformation of the engagement surface, or impact force at the time of engagement, to release the roller  72   a  from the latch  391 . At this time, however, an engagement between the engagement portion  352   b  of the lock lever  352  and the stopper pin  390   a  have already been established by the lock lever return spring  352   e , the lock lever  352  functions as a malfunction preventing mechanism to prevent the counterclockwise rotation of the latch  391 . 
         [0104]    According to the present embodiment, after the electromagnetic solenoid  21  for cutoff is excited upon input of a cutoff command, the cutoff operation is completed by two operation steps: a first operation step in which the latch  391  is directly driven through the pull-off lever  354  and pull-off link  353  to release an engagement between the latch  391  and the roller  72   a ; and a second operation step in which the cutoff spring  12  operates. As described above, the number of operation steps for completing the cutoff operation is reduced from three (in the case of conventional spring operating mechanism) to two, thereby significantly reducing the cutoff operation time. This means that T 2  is removed from the expression (1) representing the contact opening time, so that it is possible to reduce the contact opening time. 
         [0105]    Further, the lock lever  352  can prevent a disengagement of the latch  391  due to an external vibration or a change in the retention direction resulting from deformation of the leading end  102  of the latch  391 , thereby increasing operational reliability of the spring operating mechanism. 
         [0106]    Furthermore, the engagement surface of the leading end  102  of the latch  391  is formed by a substantially cylindrical surface, and the center position of the cylindrical surface substantially coincides with the rotation center of the latch (i.e., center axis of the latch axis pin  100 ), so that a torque of the roller  72   a  does not act on the latch  391  in the closed state. This allows size reduction of the latch  391  to thereby minimize a force required for releasing the engagement between the latch  391  and the roller  72   a , which can minimize the size of the electromagnetic solenoid. 
         [0107]    Further, by forming the protrusion portion  352   c  in the lock lever  352  and engaging the protrusion portion  352   c  with the roller  72   a  at the time of the closing, it is possible to realize an action for easily releasing an engagement between the engagement portion  352   b  of the lock lever  352  and the stopper pin  390   a  with a simple structure, contributing to size reduction of the latch  391 . 
       Third Embodiment 
       [0108]    Next, with reference to  FIG. 15 , a third embodiment of the switchgear operating mechanism according to the present invention will be described. The third embodiment is a modification of the second embodiment, and the same reference numerals as those in the second embodiment denote the same or corresponding parts as those in the second embodiment, and the repetitive description is omitted. 
         [0109]    The present embodiment is obtained by omitting the lock lever return spring  352   e  of  FIG. 8  and partly modifying the lock lever  352 . More specifically, as illustrated in  FIG. 15 , a return spring pin  352   f  is disposed in the lock lever  352 , and one end of a latch return spring  391   a  is engaged with the return spring pin  352   f . As a result, the latch  391  is biased in the clockwise direction through the lock lever  352 , and the lock lever  352  is biased in the counterclockwise direction. 
         [0110]    With the above configuration, it is possible to obtain the same effect as that in the second embodiment. 
       Other Embodiments 
       [0111]    The embodiments described above are merely given as examples, and it should be understood that the present invention is not limited thereto. For example, although compression coil springs are used as the cutoff spring  12  and the closing spring  13  in the above embodiments, other elastic bodies, such as torsion coil springs, disc springs, spiral springs, plate springs, air springs, and the expanding springs may be used alternatively. Further, although coil springs or torsion coil springs are used as the return springs  91   a ,  52   c ,  54   a ,  391   a ,  352   e , and  354   a  provided in the latches  91 ,  391 , lock levers  52 ,  352  and the pull-off levers  54 ,  354 , other elastic bodies such as disc springs, spiral springs, or plate springs may be used alternatively. 
         [0112]    The present invention can also be applied to an apparatus having a plurality of cutoff springs or plurality of the closing springs. 
         [0113]    Further, although the stopper pin ( 90   a ,  390   a ) for restricting the rotation of the lock lever ( 52 ,  352 ) also serves as a stopper for restricting the rotation of the latch ( 91 ,  391 ), in the above embodiments, the above functions may be provided separately. 
         [0114]    Further, since the anchoring levers  90 ,  390  are fixed to the frame  14 , they may be omitted. In this case, the stoppers  90   a ,  390   a  or the like are directly fixed to the frame  14 . Further, the stoppers  90   a ,  390   a  may be integrated with the anchoring levers  90 ,  390  or the frame  14 .