Patent Publication Number: US-2023145798-A1

Title: Vacuum circuit breaker

Description:
TECHNICAL FIELD 
     The present disclosure relates to a vacuum circuit breaker. 
     BACKGROUND ART 
     Utility Model Laying-Open No. 53-39258 (PTL 1) is a prior document that discloses a configuration of the vacuum circuit breaker. The vacuum circuit breaker described in PTL 1 includes an insulating container, a movable shaft, a bellows, a disk member, a guide member, and a shrinkage preventing member. The disk member is provided at a joint between the two bellows. 
     CITATION LIST 
     Patent Literature 
     PTL 1: Utility Model Laying-Open No. 53-039258 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the vacuum circuit breaker described in PTL 1, when the movable shaft is braked during an interruption process, an amplitude of an axial vibration caused by resonance of the bellows increases from a start of the braking until a stop of the movable shaft, and a fatigue life of the bellows is shortened. 
     The present disclosure has been made in view of the above problems, and an object of the present disclosure is to provide a vacuum circuit breaker that can reduce the amplitude of the axial vibration of the bellows to prolong the fatigue life of the bellows. 
     Solution to Problem 
     A vacuum circuit breaker according to the present disclosure includes a fixed contactor, a movable contactor, a container, a movable shaft, a plate-shaped member, a coupling bellows, a coupling member, and a pressing member. The movable contactor can be contactable with and separable from the fixed contactor. The container accommodates each of the fixed contactor and the movable contactor and holds the inside in vacuum. The movable shaft extends in the axial direction from the outside of the container, is connected to the movable contactor, and moves in the axial direction to drive the movable contactor. The plate-shaped member is attached to the movable shaft inside the container and extends around the axis of the movable shaft. The coupling bellows includes a first bellows that is expandable and contractible in the axial direction and a second bellows, which is positioned side by side with the first bellows in the axial direction and is expandable and contractible in the axial direction and has a spring constant higher than that of the first bellows, and airtightly connects the plate-shaped member and the inner surface of the container outside the movable shaft. The coupling member includes a hole, which extends in the radial direction of the movable shaft so as to protrude to at least one of the inner peripheral side and the outer peripheral side of each of the first bellows and the second bellows, is joined to each of the first bellows and the second bellows adjacent to each other, and is inserted with the movable shaft so as to be movable in the axial direction. The pressing member is disposed on the inner peripheral side or the outer peripheral side of the first bellows, and moves in the axial direction toward the coupling member along with movement of the movable shaft in a direction in which the movable contactor is separated from the fixed contactor to press the coupling member, thereby contracting the second bellows. 
     Advantageous Effects of Invention 
     According to the present disclosure, because the second bellows has the spring constant higher than that of the first bellows, the natural frequencies of the first bellows and the second bellows can be made different from each other to prevent generation of resonance in the coupling bellows, so that the amplitude of the axial vibration of the coupling bellows can be decreased to lengthen the fatigue life of the coupling bellows. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a longitudinal sectional view illustrating a configuration of a vacuum circuit breaker according to a first embodiment. 
         FIG.  2    is an enlarged longitudinal sectional view illustrating a periphery of a coupling bellows when the vacuum circuit breaker of the first embodiment is closed. 
         FIG.  3    is an enlarged longitudinal sectional view illustrating the periphery of the coupling bellows before a pressing member presses a coupling member in a middle of opening of the vacuum circuit breaker according to the first embodiment. 
         FIG.  4    is an enlarged longitudinal sectional view illustrating the periphery of the coupling bellows while the opening of the vacuum circuit breaker of the first embodiment is completed. 
         FIG.  5    is a longitudinal sectional view illustrating a configuration of a vacuum circuit breaker according to a second embodiment. 
         FIG.  6    is a longitudinal sectional view illustrating a configuration of a vacuum circuit breaker according to a third embodiment. 
         FIG.  7    is a graph illustrating a relationship between time from a start of opening and axial displacement of a movable shaft of each of a plate-shaped member and the coupling member in a vacuum circuit breaker according to a fourth embodiment. 
         FIG.  8    is a longitudinal sectional view illustrating a distance between a first surface and a second surface during closing in a vacuum circuit breaker according to a fifth embodiment. 
         FIG.  9    is a longitudinal sectional view illustrating an opening stroke that is a distance between a fixed contactor and a movable contactor when opening is completed in the vacuum circuit breaker of the fifth embodiment. 
         FIG.  10    is an enlarged perspective view illustrating only a part of each of the pressing member and the coupling member in the vacuum circuit breaker according to a ninth embodiment. 
         FIG.  11    is a front view illustrating a positional relationship between the pressing member and the coupling member when the vacuum circuit breaker of the ninth embodiment is closed. 
         FIG.  12    is a front view illustrating the positional relationship between the pressing member and the coupling member when opening of the vacuum circuit breaker of the ninth embodiment is completed. 
         FIG.  13    is an enlarged perspective view illustrating only a part of each of the pressing member and the coupling member in the vacuum circuit breaker according to a tenth embodiment. 
         FIG.  14    is a longitudinal sectional view illustrating a configuration of a vacuum circuit breaker according to an eleventh embodiment. 
         FIG.  15    is a longitudinal sectional view illustrating a configuration of a vacuum circuit breaker according to a twelfth embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a vacuum circuit breaker according to each embodiment of the present invention will be described with reference to the drawings. In the following description of the embodiments, the same or corresponding portions in the drawings are denoted the same reference numeral, and the description will not be repeated. 
     First Embodiment 
       FIG.  1    is a longitudinal sectional view illustrating a configuration of a vacuum circuit breaker according to a first embodiment.  FIG.  2    is an enlarged longitudinal sectional view illustrating a periphery of a coupling bellows when the vacuum circuit breaker of the first embodiment is closed. 
     As illustrated in  FIGS.  1  and  2   , a vacuum circuit breaker  1  of the first embodiment includes a fixed contactor  110 , a movable contactor  120 , a container  100 , a movable shaft  130 , a plate-shaped member  140 , a coupling bellows  150 , a coupling member  160 , and a pressing member  180 . Vacuum circuit breaker  1  of the first embodiment further includes a fixed shaft  111  and a guide member  131 . 
     Fixed contactor  110  is joined to a tip of fixed shaft  111  in the axial direction. Movable contactor  120  is disposed opposite to fixed contactor  110  so as to be contactable with and separable from fixed contactor  110 . When vacuum circuit breaker  1  is closed, movable contactor  120  comes into contact with fixed contactor  110  to be in an energized state. 
     Container  100  accommodates each of fixed contactor  110  and movable contactor  120  and holds the inside of container  100  in a vacuum. Container  100  has a top surface  101  at an upper portion and a bottom surface  102  at a lower portion. Fixed shaft  111  is fixed to top surface  101 . 
     Movable shaft  130  extends in the axial direction of movable shaft  130  from the outside of container  100  and is connected to movable contactor  120 . Movable shaft  130  is inserted into a cylindrical guide member  131  penetrating bottom surface  102 . An outer peripheral surface of movable shaft  130  is in sliding contact with an inner peripheral surface of guide member  131 . Movable shaft  130  passes through the inside of guide member  131  and is connected to a spring type or electromagnetic type drive mechanism (not illustrated) outside container  100 . 
     Movable shaft  130  moves in the axial direction of movable shaft  130  to drive movable contactor  120 . When the drive mechanism operates, movable shaft  130  moves toward a side opposite to a side of fixed contactor  110  in the axial direction of movable shaft  130  while being in sliding contact with guide member  131 . Thus, when movable contactor  120  is separated from fixed contactor  110 , vacuum circuit breaker  1  is opened, and energization is cut off between fixed contactor  110  and movable contactor  120 . 
     Plate-shaped member  140  is attached to movable shaft  130  in container  100 . Plate-shaped member  140  extends around the axis of movable shaft  130 . Desirably plate-shaped member  140  is attached to movable shaft  130  so as to extend in a direction orthogonal to the axial direction of movable shaft  130 . In the first embodiment, plate-shaped member  140  has a disk-shaped outer shape. 
     Coupling bellows  150  airtightly connects plate-shaped member  140  and an inner surface of container  100  outside movable shaft  130 . Thus, an internal space of container  100  outside coupling bellows  150  is airtightly held. Coupling bellows  150  includes a first bellows  151  and a second bellows  152 . 
     First bellows  151  can expand and contract in the axial direction of movable shaft  130 . An upper end  151   t  of first bellows  151  is connected to plate-shaped member  140 . Upper end  151   t  of first bellows  151  and plate-shaped member  140  are joined to each other by, for example, welding or brazing. 
     Second bellows  152  is positioned side by side with first bellows  151  in the axial direction of movable shaft  130 , and can expand and contract in the axial direction of movable shaft  130  while having a spring constant higher than that of first bellows  151 . A lower end  152   b  of second bellows  152  is connected to bottom surface  102  of container  100 . Lower end  152   b  of second bellows  152  and bottom surface  102  of container  100  are joined to each other by, for example, welding or brazing. 
     Each of first bellows  151  and second bellows  152  has a crest and a valley alternately arranged in the axial direction of movable shaft  130 . Each of first bellows  151  and second bellows  152  contracts when adjacent crests and valleys approach each other with axial movement of movable shaft  130 , and extends when the adjacent crests and valleys are separated from each other. The numbers of crests and valleys of each of first bellows  151  and second bellows  152  may be provided in the number of range that can withstand the expansion and contraction due to the axial movement of movable shaft  130 . 
     The difference between a spring constant of first bellows  151  and a spring constant of second bellows  152  can be caused by a difference in at least one of a film thickness, a difference between an inner diameter and an outer diameter, the number of crests, and a material of each of first bellows  151  and second bellows  152 . 
     When vacuum circuit breaker  1  is for a high voltage, in order to ensure required withstand voltage performance, the distance between contacts between fixed contactor  110  and movable contactor  120  when vacuum circuit breaker  1  is opened is, for example, greater than or equal to 50 mm and less than or equal to 100 mm. A length of coupling bellows  150  in the axial direction of movable shaft  130  is determined corresponding to displacement of an inter-contact distance between fixed contactor  110  and movable contactor  120  when vacuum circuit breaker  1  is opened. 
     When a general vacuum circuit breaker is opened and closed at a high speed, an impact displacement load close to an impulse input acts on the bellows at the moment when the movable shaft starts to move, and axial vibration is generated. The axial vibration is generated by resonance of the bellows, and is vibration having the same frequency as the natural frequency of the bellows. Due to the axial vibration, a larger load is repeatedly generated than when static displacement load acts on the bellows, so that the fatigue life of the bellows is reduced. Because the fatigue life of the bellows becomes the life of the vacuum circuit breaker, the extension of the fatigue life of the bellows is an important issue. Therefore, vacuum circuit breaker  1  of the first embodiment includes coupling bellows  150  having the above configuration. 
     As illustrated in  FIGS.  1  and  2   , coupling member  160  includes a coupling unit  161  extending in a radial direction of movable shaft  130  so as to project to at least one of an inner peripheral side and an outer peripheral side of each of first bellows  151  and second bellows  152 . Coupling unit  161  is joined to each of first bellows  151  and second bellows  152  adjacent to each other. In the first embodiment, coupling unit  161  extends in the radial direction of movable shaft  130  so as to project to both the inner peripheral side and the outer peripheral side of each of first bellows  151  and second bellows  152 . Coupling unit  161  has an annular shape. 
     As illustrated in  FIG.  1   , first bellows  151  is located above coupling unit  161 , and second bellows  152  is located below coupling unit  161 . Coupling unit  161  is joined to each of a lower end  151   b  of first bellows  151  and an upper end  152   t  of second bellows  152 . Coupling unit  161  is joined to each of lower end  151   b  and upper end  152   t  by, for example, welding or brazing. 
     As illustrated in  FIG.  2   , coupling member  160  includes a first surface  160   c  that comes into contact with pressing member  180 . In the first embodiment, first surface  160   c  is an upper surface of coupling unit  161 . Lower end  151   b  of first bellows  151  is connected to first surface  160   c.    
     Coupling member  160  includes a hole  163  inserted with movable shaft  130  so as to be movable in the axial direction of movable shaft  130 . In the first embodiment, coupling member  160  includes an annular sliding contact unit  162  that comes into sliding contact with the outer peripheral surface of guide member  131  in order to prevent coupling bellows  150  from buckling due to pressure inside coupling bellows  150 . A hole  163  is located inside sliding contact unit  162 . Coupling unit  161  is connected to the outer peripheral surface of sliding contact unit  162 . 
     Pressing member  180  is disposed on the inner peripheral side or the outer peripheral side of first bellows  151 . In the first embodiment, pressing member  180  is disposed on the outer peripheral side of first bellows  151 . Pressing member  180  extends downward from the lower surface of plate-shaped member  140 . An upper end of pressing member  180  is connected to plate-shaped member  140 . Pressing member  180  is located above coupling unit  161 . 
     Pressing member  180  includes a second surface  180   c  that comes into contact with coupling member  160 . In the first embodiment, second surface  180   c  is a lower surface of pressing member  180 . Second surface  180   c  of pressing member  180  comes into contact coupling unit  161 . 
     Pressing member  180  has a cylindrical shape, but the shape of pressing member  180  is not limited to the cylindrical shape, and may be any shape as long as the pressing member  180  comes into contact with coupling unit  161  and can move coupling member  160  in the axial direction of movable shaft  130 . For example, second surface  180   c  of pressing member  180  may be discontinuous in a circumferential direction of movable shaft  130 . 
     Vacuum circuit breaker  1  of the first embodiment brakes movable shaft  130  during an interruption process in order to secure the time to extend and extinguish an arc generated during the opening. Movable shaft  130  starts the braking after movable contactor  120  is separated from fixed contactor  110  by the start of the movement of movable shaft  130 , and a moving speed in the axial direction of movable shaft  130  decreases. Specifically, movable shaft  130  is braked by a braking mechanism (not illustrated) after movable contactor  120  is separated from fixed contactor  110  until the opening of vacuum circuit breaker  1  is completed. At the start of the braking, the input load having a phase opposite to the input load at the moment when movable shaft  130  starts to move acts on coupling bellows  150 . 
       FIG.  3    is an enlarged longitudinal sectional view illustrating the periphery of the coupling bellows before the pressing member presses the coupling member in a middle of the opening of the vacuum circuit breaker according to the first embodiment.  FIG.  4    is an enlarged longitudinal sectional view illustrating the periphery of the coupling bellows while the opening of the vacuum circuit breaker of the first embodiment is completed. 
     As illustrated in  FIGS.  3  and  4   , pressing member  180  moves in the axial direction of movable shaft  130  toward coupling member  160  along with the movement of movable shaft  130  in the direction in which movable contactor  120  is separated from fixed contactor  110  to press coupling member  160 , thereby contracting second bellows  152 . 
     Because second bellows  152  has the spring constant larger than that of first bellows  151 , first bellows  151  more easily expands and contracts in the axial direction of movable shaft  130  than second bellows  152 . Accordingly, first bellows  151  preferentially contracts from the start of the opening of vacuum circuit breaker  1  until pressing member  180  and coupling member  160  come into contact with each other. When first bellows  151  contracts and second surface  180   c  of pressing member  180  comes into contact with first surface  160   c  of coupling member  160 , the contraction of first bellows  151  stops. After pressing member  180  and coupling member  160  come into contact with each other, only second bellows  152  contracts until the opening of vacuum circuit breaker  1  is completed. 
     In vacuum circuit breaker  1  of the first embodiment, because second bellows  152  has the spring constant higher than that of first bellows  151 , the natural frequencies of first bellows  151  and second bellows  152  can be made different from each other to prevent the generation of the resonance in coupling bellows  150 . For this reason, even when movable shaft  130  is braked during the interruption process, the amplitude of the axial vibration of coupling bellows  150  can be decreased to prolong the fatigue life of coupling bellows  150 . 
     In addition, in vacuum circuit breaker  1  of the first embodiment, first bellows  151  preferentially contracts from the start of the opening of vacuum circuit breaker  1  until pressing member  180  and coupling member  160  come into contact with each other, and only second bellows  152  contracts until the opening of vacuum circuit breaker  1  is completed after pressing member  180  and coupling member  160  come into contact with each other, so that the load generated in each of first bellows  151  and second bellows  152  can be made uniform. 
     As described above, when the load distribution in coupling bellows  150  is uniformized while the amplitude of the axial vibration of coupling bellows  150  is decreased, the maximum load of coupling bellows  150  can be decreased to lengthen the fatigue life of coupling bellows  150 . 
     Second Embodiment 
     A vacuum circuit breaker according to a second embodiment will be described below. The vacuum circuit breaker of the second embodiment is different from vacuum circuit breaker  1  of the first embodiment only in the configurations of the coupling member and the pressing member, and thus the description of other configurations will not be repeated. 
       FIG.  5    is a longitudinal sectional view illustrating the configuration of the vacuum circuit breaker of the second embodiment. As illustrated in  FIG.  5   , in the vacuum circuit breaker of the second embodiment, coupling unit  161  extends in the radial direction of movable shaft  130  so as to protrude only to the inner peripheral side of each of first bellows  151  and second bellows  152 . In the second embodiment, first surface  160   c  is an upper surface of sliding contact unit  162 . 
     Pressing member  180  is disposed on the inner peripheral side of first bellows  151 . The inner diameter of the pressing member  180  is larger than the outer diameter of guide member  131 . In the second embodiment, second surface  180   c  of pressing member  180  comes into contact with sliding contact unit  162 . 
     In the vacuum circuit breaker of the second embodiment, coupling member  160  extends in the radial direction of movable shaft  130  so as to protrude only to the inner peripheral side of each of first bellows  151  and second bellows  152 , so that volume of coupling member  160  can be decreased as compared with vacuum circuit breaker  1  of the first embodiment. Thus, mass of coupling member  160  is decreased, so that the natural frequency of coupling bellows  150  connected to coupling member  160  can be increased. By increasing the natural frequency of coupling bellows  150 , the amplitude of the axial vibration of coupling bellows  150  can be decreased to lengthen the fatigue life of coupling bellows  150 . 
     Third Embodiment 
     A vacuum circuit breaker according to a third embodiment will be described below. The vacuum circuit breaker of the third embodiment is different from vacuum circuit breaker  1  of the first embodiment only in the configurations of the coupling bellows and the pressing member, and thus the description of other configurations will not be repeated. 
       FIG.  6    is a longitudinal sectional view illustrating the configuration of the vacuum circuit breaker of the third embodiment. As illustrated in  FIG.  6   , in the vacuum circuit breaker of the third embodiment, second bellows  152  is located above coupling unit  161 , and first bellows  151  is located below coupling unit  161 . Coupling unit  161  is joined to each of upper end  151   t  of first bellows  151  and lower end  152   b  of second bellows  152 . In the third embodiment, first surface  160   c  is a lower surface of coupling unit  161 . Upper end  151   t  of first bellows  151  is connected to first surface  160   c.  Upper end  152   t  of second bellows  152  is connected to plate-shaped member  140 , and lower end  151   b  of first bellows  151  is connected to bottom surface  102  of container  100 . 
     Pressing member  180  is disposed on the outer diameter side of coupling bellows  150 . Pressing member  180  extends upward from the upper surface of bottom surface  102 . A lower end of pressing member  180  is connected to bottom surface  102 . Pressing member  180  is located below coupling unit  161 . 
     First bellows  151  preferentially contracts from the start of the opening of the vacuum circuit breaker of the third embodiment to the contact between pressing member  180  and coupling member  160 . When first bellows  151  contracts and second surface  180   c  of pressing member  180  comes into contact with first surface  160   c  of coupling member  160 , the contraction of first bellows  151  stops. After pressing member  180  and coupling member  160  come into contact with each other, only second bellows  152  contracts until the opening of vacuum circuit breaker  1  is completed. 
     Also in the vacuum circuit breaker of the third embodiment, by making the load distribution in coupling bellows  150  uniform while the amplitude of the axial vibration of coupling bellows  150  is decreased, the maximum load of coupling bellows  150  can be decreased to lengthen the fatigue life of coupling bellows  150 . 
     Fourth Embodiment 
     A vacuum circuit breaker according to a fourth embodiment will be described below. The vacuum circuit breaker of the fourth embodiment is different from the vacuum circuit breaker of the second embodiment only in the timing when the plate-shaped member and the coupling member come into contact with each other, and thus the description of other configurations will not be repeated. 
       FIG.  7    is a graph illustrating a relationship between time from the start of the opening and axial displacement of the movable shaft of each of the plate-shaped member and the coupling member in the vacuum circuit breaker of the fourth embodiment. In  FIG.  7   , a vertical axis represents the displacement, and a horizontal axis represents the time. 
     The time from the start of the movement of movable shaft  130  to the start of pressing force of pressing member  180  against coupling member  160  is defined as a first elapsed time t i . The time from the start of the movement of movable shaft  130  to the start of the braking is defined as a second elapsed time t b . 
     As illustrated in  FIG.  7   , movable shaft  130  starts the braking to decrease the moving speed in the axial direction of movable shaft  130  after movable contactor  120  is separated from fixed contactor  110  by the start of the movement of movable shaft  130 . That is, the inclination indicating the change in displacement per unit time of plate-shaped member  140  fluctuates before and after second elapsed time t b  elapses, and after the start of braking, the inclination is gentler than before the start of braking. 
     When first elapsed time t i  is shorter than second elapsed time t b , due to the large impact due to the collision between pressing member  180  and coupling member  160 , coupling member  160  may vibrate greatly in the vertical direction, and the maximum displacement of coupling bellows  150  may increase. 
     In the vacuum circuit breaker of the fourth embodiment, because first elapsed time t i  is longer than second elapsed time t b , braked and decelerated pressing member  180  collides with coupling member  160 , so that the impact caused by the collision between pressing member  180  and coupling member  160  can be reduced. As a result, the maximum load of coupling bellows  150  can be decreased to lengthen the fatigue life of coupling bellows  150 . 
     Fifth Embodiment 
     A vacuum circuit breaker according to a fifth embodiment will be described below. The vacuum circuit breaker of the fifth embodiment is mainly different from the vacuum circuit breaker of the second embodiment in the positional relationship between the pressing member and the coupling member, and thus the description of other configurations will not be repeated. 
       FIG.  8    is a longitudinal sectional view illustrating the distance between the first surface and the second surface during the closing in the vacuum circuit breaker of the fifth embodiment.  FIG.  9    is a longitudinal sectional view illustrating an opening stroke that is the distance between the fixed contactor and the movable contactor when the opening is completed in the vacuum circuit breaker of the fifth embodiment. 
     As illustrated in  FIGS.  8  and  9   , in the vacuum circuit breaker of the fifth embodiment, when a distance d 1  between pressing member  180  and coupling member  160  during the closing of the vacuum circuit breaker and an opening stroke d during the completion of the opening of the vacuum circuit breaker are used, the displacement amount of first bellows  151  in the axial direction of movable shaft  130  is d 1 , and the displacement amount of second bellows  152  is (d−d 1 ). 
     When the number of crests of first bellows  151  is set to n 1  and the number of crests of second bellows  152  is set to n 2 , a deformation amount per pitch between the crest of first bellows  151  in the axial direction of movable shaft  130  during the opening and the closing of the vacuum circuit breaker is d 1 /n 1 , and a deformation amount per pitch between the crests of second bellows  152  is (d−d 1 )/n 2 . 
     In the fifth embodiment, because the spring constant of second bellows  152  is larger than the spring constant of first bellows  151 , the load acting on second bellows  152  is larger than the load acting on first bellows  151  when the deformation amount per pitch is equal between the crests of first bellows  151  and second bellows  152 . In order to decrease the difference in the load acting on each of first bellows  151  and second bellows  152 , the deformation amount per pitch between the crests of second bellows  152  needs to be smaller than that of first bellows  151 . 
     Accordingly, in the vacuum circuit breaker of the fifth embodiment, the deformation amount in the axial direction per pitch between the crests adjacent to each other in the axial direction of movable shaft  130  is smaller in second bellows  152  than in first bellows  151 . Specifically, opening stroke d, distance d 1 , the number n 1  of the crests of the first bellows  151 , and the number n 2  of the crests of the second bellows  152  are set so as to satisfy a relationship of d 1 &gt;n 1 d/(n 1 +n 2 ) as a condition that the deformation amount per pitch between the crests in the axial direction of movable shaft  130  is smaller in second bellows  152  than in first bellows  151 . 
     However, when the spring constant of second bellows  152  is made larger than the spring constant of first bellows  151  by decreasing the number of crests of second bellows  152 , a relationship of d 1 =n 1 d/(n 1 +n 2 ) may be satisfied. Thus, the spring constant of second bellows  152  can be made larger than the spring constant of first bellows  151  while the loads acting on first bellows  151  and second bellows  152  are equal to each other. 
     In the vacuum circuit breaker of the fifth embodiment, because the axial amount deformation per pitch between the peak portions adjacent to each other in the axial direction of movable shaft  130  is smaller in second bellows  152  than in first bellows  151 , the maximum load acting on second bellows  152  can be prevented from becoming excessively large as compared with the maximum load acting on first bellows  151 , so that second bellows  152  can be prevented from being subjected to fatigue fracture at an early stage to prolong the fatigue life of coupling bellows  150 . 
     Sixth Embodiment 
     A vacuum circuit breaker according to a sixth embodiment will be described below. The vacuum circuit breaker of the sixth embodiment differs from the vacuum circuit breaker of the fourth embodiment only in the relationship between second elapsed time t b  and the natural frequency of the first bellows to be described later, and thus the description of other configurations will not be repeated. 
     In the vacuum circuit breaker of the sixth embodiment, first bellows  151  has a natural frequency f 1  proportional to the spring constant. The relationship between natural frequency f 1  of first bellows  151  and second elapsed time t b  satisfies t b ≥1/f 1 . 
     The relationship between natural frequency f 1  and second elapsed time t b  will be described more specifically. When the axial vibration is generated in first bellows  151  due to the start of the movement of movable shaft  130 , first bellows  151  resonates at natural frequency f 1 , and the vibration reciprocates in first bellows  151  at a period of 1/f 1 . At the start of the braking, the input load having a phase opposite to the input load at the moment when movable shaft  130  starts to move acts on first bellows  151 . 
     Accordingly, when second elapsed time t b  from the start of the movement of movable shaft  130  to the start of the braking coincides with an integer multiple of the period of the axial vibration of first bellows  151 , the input load at the start of the braking acts on first bellows  151  so as to cancel the input load at the moment when movable shaft  130  starts to move, and thus the axial vibration of first bellows  151  is prevented. That is, by satisfying a relationship of t b =N/f 1  (N=1, 2, 3, . . . ), the amplitude of the axial vibration of first bellows  151  can be reduced. Distance d 1  between pressing member  180  and coupling member  160  is preferably set so as to satisfy the relationship. 
     In addition, because the amplitude of the axial vibration of first bellows  151  decreases as natural frequency f 1  of first bellows  151  increases, when considering that period 1/f 1  of the axial vibration should be smaller, it can be considered that the amplitude of the axial vibration of first bellows  151  can be prevented by satisfying t i &gt;t b ≥1/f 1  for each of first elapsed time t i  and second elapsed time t b . 
     In the vacuum circuit breaker of the sixth embodiment, because the relationship between natural frequency f 1  of first bellows  151  and second elapsed time t b  satisfies t b ≥1/f 1 , the amplitude of the axial vibration of first bellows  151  can be reduced, so that the fatigue life of first bellows  151  can be lengthened. 
     Seventh Embodiment 
     A vacuum circuit breaker according to a seventh embodiment will be described below. The vacuum circuit breaker of the seventh embodiment differs from the vacuum circuit breaker of the fourth embodiment only in the relationship between second elapsed time t b  and the natural frequency of the second bellows to be described later, and thus the description of other configurations will not be repeated. 
     In the vacuum circuit breaker of the seventh embodiment, second bellows  152  has a natural frequency f 2  proportional to the spring constant. The relationship between natural frequency f 2  of second bellows  152  and second elapsed time t b  satisfies t b ≥1/f 2 . 
     The relationship between natural frequency f 2  and second elapsed time t b  will be described more specifically. When the axial vibration is generated in second bellows  152  due to the start of the movement of movable shaft  130 , second bellows  152  resonates at natural frequency f 2 , and the vibration reciprocates in second bellows  152  at a period of 1/f 2 . At the start of the braking, the input load having a phase opposite to the input load at the moment when movable shaft  130  starts to move acts on second bellows  152  through first bellows  151 . 
     Accordingly, when second elapsed time t b  from the start of the movement of movable shaft  130  to the start of the braking coincides with an integer multiple of the period of the axial vibration of second bellows  152 , the input load at the start of the braking acts on second bellows  152  so as to cancel the input load at the moment when movable shaft  130  starts to move, and thus the axial vibration of second bellows  152  is prevented. That is, by satisfying a relationship of t b =N/f 2  (N=1, 2, 3, . . . ), the amplitude of the axial vibration of second bellows  152  can be reduced. Distance d 1  between pressing member  180  and coupling member  160  is preferably set so as to satisfy the relationship. 
     In addition, because the amplitude of the axial vibration of second bellows  152  decreases as natural frequency f 2  of second bellows  152  increases, when considering that period 1/f 2  of the axial vibration should be smaller, it can be considered that the amplitude of the axial vibration of second bellows  152  can be prevented by satisfying t i &gt;t b ≥1/f 2  for each of first elapsed time t i  and second elapsed time t b . 
     In the vacuum circuit breaker of the seventh embodiment, because the relationship between natural frequency f 2  of second bellows  152  and second elapsed time t b  satisfies t b ≥1/f 2 , the amplitude of the axial vibration of second bellows  152  can be reduced, so that the fatigue life of second bellows  152  can be lengthened. 
     Eighth Embodiment 
     A vacuum circuit breaker according to an eighth embodiment will be described below. The vacuum circuit breaker of the eighth embodiment is different from the vacuum circuit breaker of the fourth embodiment only in the relationship between second elapsed time t b  and the natural frequency of the coupling bellows to be described later, and thus the description of other configurations will not be repeated. 
     In the vacuum circuit breaker of the eighth embodiment, coupling bellows  150  has a natural frequency f t  proportional to the spring constant. The relationship between natural frequency f t  of coupling bellows  150  and second elapsed time t b  satisfies t b ≥1/f t . 
     The relationship between natural frequency f t  and second elapsed time t b  will be described more specifically. When the axial vibration is generated in coupling bellows  150  due to the start of the movement of movable shaft  130 , coupling bellows  150  resonates at natural frequency f t , and the vibration reciprocates in coupling bellows  150  at a period of 1/f t . At the start of the braking, the input load having a phase opposite to the input load at the moment when movable shaft  130  starts to move acts on coupling bellows  150 . 
     Accordingly, when second elapsed time t b  from the start of the movement of movable shaft  130  to the start of the braking coincides with an integer multiple of the period of the axial vibration of coupling bellows  150 , the input load at the start of the braking acts on coupling bellows  150  so as to cancel the input load at the moment when movable shaft  130  starts to move, and thus the axial vibration of coupling bellows  150  is prevented. That is, by satisfying the relationship of t b =N/f t  (N=1, 2, 3, . . . ), the amplitude of the axial vibration of coupling bellows  150  can be reduced. Distance d 1  between pressing member  180  and coupling member  160  is preferably set so as to satisfy the relationship. 
     In addition, because the amplitude of the axial vibration of coupling bellows  150  decreases as natural frequency f t  of coupling bellows  150  increases, when considering that period 1/f t  of the axial vibration should be smaller, it can be considered that the amplitude of the axial vibration of coupling bellows  150  can be prevented by satisfying t i &gt;t b ≥1/f t  for each of first elapsed time t i  and second elapsed time t b . 
     In the vacuum circuit breaker of the eighth embodiment, because the relationship between natural frequency f t  of coupling bellows  150  and second elapsed time t b  satisfies t b ≥1/f t , the amplitude of the axial vibration of coupling bellows  150  can be reduced, so that the fatigue life of coupling bellows  150  can be lengthened. 
     Ninth Embodiment 
     A vacuum circuit breaker according to a ninth embodiment will be described below. The vacuum circuit breaker of the ninth embodiment is different from the vacuum circuit breaker of the second embodiment only in the configurations of the coupling member and the pressing member, and thus the description of other configurations will not be repeated. 
       FIG.  10    is an enlarged perspective view illustrating only a part of each of the pressing member and the coupling member in the vacuum circuit breaker of the ninth embodiment. As illustrated in  FIG.  10   , in the vacuum circuit breaker of the ninth embodiment, first surface  160   c  of coupling member  160  includes two first flat surfaces  160   f  perpendicular to the axial direction of movable shaft  130  and two first inclined surfaces  160   s  inclined with respect to two first flat surfaces  160   f.    
     Two first inclined surfaces  160   s  are located in parallel on opposite sides in the radial direction of movable shaft  130 . Two first flat surfaces  160   f  are located on opposite sides in the radial direction of movable shaft  130 . Two first flat surfaces  160   f  are located at different positions in the axial direction of movable shaft  130 . Two first flat surfaces  160   f  are connected to each other by two first inclined surfaces  160   s.    
     Second surface  180   c  of pressing member  180  includes two second flat surfaces  180   f  perpendicular to the axial direction of movable shaft  130  and two second inclined surfaces  180   s  inclined with respect to two second flat surfaces  180   f.  Two second inclined surfaces  180   s  are formed corresponding to two first inclined surfaces  160   s.  Two second flat surfaces  180   f  are formed corresponding to two first flat surfaces  160   f.    
     Specifically, second inclined surface  180   s  is provided at a position in contact with corresponding first inclined surface  160   s  when pressing member  180  moves in the axial direction of movable shaft  130  toward coupling member  160 . Second inclined surface  180   s  has a shape capable of sliding contact with first inclined surface  160   s.  An inclination angle of each of first inclined surface  160   s  and second inclined surface  180   s  is not limited to an inclination angle in  FIG.  10   , but may be any angle as long as the load in the axial direction of movable shaft  130  is dispersed in the direction orthogonal to the axial direction of movable shaft  130 . 
       FIG.  11    is a front view illustrating a positional relationship between the pressing member and the coupling member when the vacuum circuit breaker of the ninth embodiment is closed.  FIG.  12    is a front view illustrating the positional relationship between the pressing member and the coupling member when opening of the vacuum circuit breaker of the ninth embodiment is completed. 
     As illustrated in  FIG.  11   , when the vacuum circuit breaker is closed, the positions of first inclined surface  160   s  and second inclined surface  180   s  in the direction orthogonal to the axial direction of movable shaft  130  are shifted from each other, and the positions in the direction orthogonal to the axial direction of movable shaft  130  partially overlap each other. Coupling member  160  is movable in the direction orthogonal to the axial direction of movable shaft  130  by a gap between the inner peripheral surface of hole  163  and the outer peripheral surface of movable shaft  130 . 
     When pressing member  180  moves in the axial direction of movable shaft  130  toward coupling member  160  to presses coupling member  160 , second inclined surface  180   s  of pressing member  180  comes into sliding contact with first inclined surface  160   s  of coupling member  160  while abutting on first inclined surface  160   s.    
     When first inclined surface  160   s  and second inclined surface  180   s  come into sliding contact with each other, coupling member  160  moves in the direction orthogonal to the axial direction of movable shaft  130  as indicated by an arrow in  FIG.  12    while moving in the axial direction of movable shaft  130 . After first flat surface  160   f  comes into contact with second flat surface  180   f,  coupling member  160  moves only in the axial direction of movable shaft  130 . Coupling bellows  150  is deflected along with the movement of coupling member  160 , but this deflection amount is small, so that the deflection hardly affects the fatigue life of the coupling member  160 . When pressing member  180  is separated from coupling member  160  along with the axial movement of movable shaft  130 , the deflection of coupling bellows  150  is eliminated by the elasticity of coupling bellows  150 . 
     In the vacuum circuit breaker of the ninth embodiment, when pressing member  180  presses coupling member  160 , second inclined surface  180   s  of pressing member  180  comes into sliding contact with first inclined surface  160   s  of coupling member  160  while abutting on first inclined surface  160   s.  Therefore, a part of the load during the contact between pressing member  180  and coupling member  160  can be dispersed in the direction orthogonal to the axial direction of movable shaft  130  to reduce the amplitude of the axial vibration of coupling bellows  150 , so that the fatigue life of coupling bellows  150  can be lengthened. 
     Tenth Embodiment 
     A vacuum circuit breaker according to a tenth embodiment will be described below. The vacuum circuit breaker of the tenth embodiment is different from the vacuum circuit breaker of the ninth embodiment only in the configurations of the coupling member and the pressing member, and thus the description of other configurations will not be repeated. 
       FIG.  13    is an enlarged perspective view illustrating only a part of each of the pressing member and the coupling member in the vacuum circuit breaker of the tenth embodiment. As illustrated in  FIG.  13   , in the vacuum circuit breaker of the tenth embodiment, first surface  160   c  includes four first flat surfaces  160   f  perpendicular to the axial direction of movable shaft  130  and four first inclined surfaces  160   s  inclined with respect to four first flat surfaces  160   f.    
     In the circumferential direction of movable shaft  130 , first inclined surface  160   s  and first flat surface  160   f  are alternately located. First surface  160   c  is four-time rotationally symmetric about the axis of movable shaft  130 . 
     Second surface  180   c  of pressing member  180  includes four second flat surfaces  180   f  perpendicular to the axial direction of movable shaft  130  and four second inclined surfaces  180   s  inclined with respect to four second flat surfaces  180   f.  Four second inclined surfaces  180   s  are formed corresponding to four first inclined surfaces  160   s.  Four second flat surfaces  180   f  are formed corresponding to four first flat surfaces  160   f.    
     Specifically, second inclined surface  180   s  is provided at a position in contact with corresponding first inclined surface  160   s  when pressing member  180  moves in the axial direction of movable shaft  130  toward coupling member  160 . Second inclined surface  180   s  has a shape capable of sliding contact with first inclined surface  160   s.  The inclination angle of each of first inclined surface  160   s  and second inclined surface  180   s  is not limited to the inclination angle in  FIG.  13   , but may be any angle as long as the load in the axial direction of movable shaft  130  is dispersed in the circumferential direction of movable shaft  130 . 
     When the vacuum circuit breaker is closed, the phases of first inclined surface  160   s  and second inclined surface  180   s  in the circumferential direction of movable shaft  130  are shifted from each other, and the positions in the circumferential direction of movable shaft  130  partially overlap each other. Coupling member  160  is movable in the circumferential direction of movable shaft  130 . 
     When pressing member  180  moves in the axial direction of movable shaft  130  toward coupling member  160  to presses coupling member  160 , second inclined surface  180   s  of pressing member  180  comes into sliding contact with first inclined surface  160   s  of coupling member  160  while abutting on first inclined surface  160   s.    
     When first inclined surface  160   s  and second inclined surface  180   s  come into sliding contact with each other, coupling member  160  moves in the circumferential direction of movable shaft  130  as indicated by an arrow in  FIG.  13    while moving in the axial direction of movable shaft  130 . After first flat surface  160   f  comes into contact with second flat surface  180   f,  coupling member  160  moves only in the axial direction of movable shaft  130 . Coupling bellows  150  is twisted along with the movement of coupling member  160 , but this twist amount is small, so that the twist hardly affects the fatigue life of the coupling member  160 . When pressing member  180  is separated from coupling member  160  along with the axial movement of movable shaft  130 , the twist of coupling bellows  150  is eliminated by the elasticity of coupling bellows  150 . 
     In the vacuum circuit breaker of the tenth embodiment, when pressing member  180  presses coupling member  160 , second inclined surface  180   s  of pressing member  180  comes into sliding contact with first inclined surface  160   s  of coupling member  160  while abutting on first inclined surface  160   s.  Therefore, a part of the load during the contact between pressing member  180  and coupling member  160  can be dispersed in the circumferential direction of movable shaft  130  to reduce the amplitude of the axial vibration of coupling bellows  150 , so that the fatigue life of coupling bellows  150  can be lengthened. 
     Eleventh Embodiment 
     A vacuum circuit breaker according to an eleventh embodiment will be described below. The vacuum circuit breaker of the eleventh embodiment is different from vacuum circuit breaker of the second embodiment only in the configurations of the coupling bellows, the coupling member, and the pressing member, and thus the description of other configurations will not be repeated. 
       FIG.  14    is a longitudinal sectional view illustrating the configuration of the vacuum circuit breaker of the eleventh embodiment. As illustrated in  FIG.  14   , in the vacuum circuit breaker of the eleventh embodiment, coupling bellows  150  includes two or more of at least one of first bellows  151  and second bellows  152 . 
     Specifically, in the eleventh embodiment, coupling bellows  150  includes one first bellows  151  and two second bellows  152 . Second bellows  152  is connected to both ends of first bellows  151 . At least one of both the ends of first bellows  151  may be connected to second bellows  152 . 
     In the eleventh embodiment, an upper coupling member  165  and a lower coupling member  170  are arranged side by side in the axial direction of movable shaft  130  as the coupling member. Upper coupling member  165  is located above lower coupling member  170 . 
     Upper coupling member  165  includes a coupling unit  166  and a sliding contact unit  167 . Sliding contact unit  167  is in sliding contact with the outer peripheral surface of movable shaft  130 . Upper coupling member  165  includes a hole  168  inserted with movable shaft  130  so as to be movable in the axial direction of movable shaft  130 . 
     Lower coupling member  170  includes a coupling unit  171  and a sliding contact unit  172 . Sliding contact unit  172  is in sliding contact with the outer peripheral surface of guide member  131 . Lower coupling member  170  includes a hole  173  inserted with the movable shaft  130  so as to be movable in the axial direction of movable shaft  130 . In the eleventh embodiment, first surface  160   c  is an upper surface of sliding contact unit  172 . 
     Pressing member  180  extends downward from the lower surface of coupling unit  166 . An upper end of pressing member  180  is connected to coupling unit  166 . Pressing member  180  is located above sliding contact unit  172 . In the eleventh embodiment, second surface  180   c  of pressing member  180  comes into contact with sliding contact unit  172 . 
     Pressing member  180  moves in the axial direction of movable shaft  130  toward lower coupling member  170  along with the movement of movable shaft  130  in the direction in which movable contactor  120  is separated from fixed contactor  110 , and first bellows  151  preferentially contracts from the start of the opening of the vacuum circuit breaker until pressing member  180  and lower coupling member  170  come into contact with each other. When first bellows  151  contracts and when second surface  180   c  of pressing member  180  comes into contact with first surface  160   c  of lower coupling member  170 , the contraction of first bellows  151  stops. After pressing member  180  and lower coupling member  170  come into contact with each other, only two second bellows  152  contract until the opening of the vacuum circuit breaker is completed. 
     Pressing member  180  may be provided on the upper surface of coupling unit  171  of lower coupling member  170 , and the vacuum circuit breaker may be configured such that coupling unit  166  of upper coupling member  165  and pressing member  180  come into contact with each other. In addition, each of coupling unit  166  and coupling unit  171  may also protrude to the outer peripheral side of each of first bellows  151  and second bellows  152 , and pressing member  180  may be disposed on the outer peripheral side of first bellows  151 . 
     When the vacuum circuit breaker of the eleventh embodiment includes two or more of at least one of first bellows  151  and second bellows  152 , even in the case where opening stroke d is long, the maximum load of coupling bellows  150  can be decreased to lengthen the fatigue life of coupling bellows  150  by making the load distribution in coupling bellows  150  uniform while the amplitude of the axial vibration of coupling bellows  150  is decreased. 
     Twelfth Embodiment 
     A vacuum circuit breaker according to a twelfth embodiment will be described below. The vacuum circuit breaker of the twelfth embodiment is different from vacuum circuit breaker of the eleventh embodiment only in the configurations of the coupling bellows, the coupling member, and the pressing member, and thus the description of other configurations will not be repeated. 
       FIG.  15    is a longitudinal sectional view illustrating the configuration of the vacuum circuit breaker of the twelfth embodiment. As illustrated in  FIG.  15   , in the vacuum circuit breaker of the twelfth embodiment, coupling bellows  150  includes two or more of at least one of first bellows  151  and second bellows  152 . 
     Specifically, in the twelfth embodiment, coupling bellows  150  includes two first bellows  151  and two second bellows  152 . Two first bellows  151  are connected to each other. Two second bellows  152  are disposed so as to sandwich two first bellows  151  therebetween. It is sufficient that at least one of both ends of first bellows  151  is connected to second bellows  152 , and the number of combinations of first bellows  151  and second bellows  152  is not limited to two each. 
     In the twelfth embodiment, an extension coupling member  190  is disposed between upper coupling member  165  and lower coupling member  170 . Two first bellows  151  are connected to each other by extension coupling member  190 . 
     Extension coupling member  190  includes a coupling unit  191  extending in the radial direction of movable shaft  130  so as to protrude to at least one of the inner peripheral side and the outer peripheral side of each of two first bellows  151 . Coupling unit  191  is joined to each of two first bellows  151  adjacent to each other. In the twelfth embodiment, coupling unit  191  extends in the radial direction of movable shaft  130  so as to protrude to both the inner peripheral side and the outer peripheral side of each of two first bellows  151 . Coupling unit  191  has an annular shape. 
     Extension coupling member  190  includes a hole  193  inserted with movable shaft  130  so as to be movable in the axial direction of movable shaft  130 . In the twelfth embodiment, extension coupling member  190  includes an annular sliding contact unit  192  in sliding contact with the outer peripheral surface of guide member  131  in order to prevent coupling bellows  150  from buckling due to the pressure inside coupling bellows  150 . Hole  193  is located inside sliding contact unit  192 . Coupling unit  191  is connected to the outer peripheral surface of sliding contact unit  192 . 
     Pressing member  180  moves in the axial direction of movable shaft  130  toward lower coupling member  170  along with the movement of movable shaft  130  in the direction in which movable contactor  120  is separated from fixed contactor  110 , and first bellows  151  preferentially contracts from the start of the opening of the vacuum circuit breaker until pressing member  180  and lower coupling member  170  come into contact with each other through extension coupling member  190 . When first bellows  151  contracts and when second surface  180   c  of pressing member  180  comes into contact with first surface  160   c  of lower coupling member  170  through sliding contact unit  192  of extension coupling member  190 , the contraction of first bellows  151  stops. After pressing member  180  and lower coupling member  170  come into contact with each other through extension coupling member  190 , only two second bellows  152  contract until the opening of the vacuum circuit breaker is completed. 
     When the vacuum circuit breaker of the twelfth embodiment includes two or more of at least one of first bellows  151  and second bellows  152 , even when opening stroke d is long, the maximum load of coupling bellows  150  can be decreased to lengthen the fatigue life of coupling bellows  150  by making the load distribution in coupling bellows  150  uniform while the amplitude of the axial vibration of coupling bellows  150  is decreased. 
     It should be noted that the above embodiments disclosed herein is merely an example in all respects, and are not a basis for restrictive interpretation. Accordingly, the technical scope of the present disclosure is not to be construed only by the above-described embodiments. Furthermore, the meaning equivalent to the claims and all changes within the claims are included. In the description of the above-described embodiments, configurations that can be combined may be combined with each other. 
     REFERENCE SIGNS LIST 
       1 : vacuum circuit breaker,  100 : container,  101 : top surface,  102 : bottom surface,  110 : fixed contactor,  111 : fixed shaft,  120 : movable contactor,  130 : movable shaft,  131 : guide member,  140 : plate-shaped member,  150 : coupling bellows,  151 : first bellows,  151   b,    152   b:  lower end,  151   t,    152   t:  upper end,  152 : second bellows,  160 : coupling member,  160   c:  first surface,  160   f:  first flat surface,  160   s:  first inclined surface,  161 ,  166 ,  171 ,  191 : coupling unit,  162 ,  167 ,  172 ,  192 : sliding contact unit,  163 ,  168 ,  173 ,  193 : hole,  165 : upper coupling member,  170 : lower coupling member,  180 : pressing member,  180   c:  second surface,  180   f:  second flat surface,  180   s:  second inclined surface,  190 : extension coupling member, d: opening stroke, d 1 : distance between pressing member and coupling member during closing, f 1 , f 2 , f t : natural frequency, t b : second elapsed time, t i : first elapsed time