Patent Publication Number: US-2005139579-A1

Title: Vacuum switchgear system

Description:
CLAIM OF PRIORITY  
      The present application claims priority from Japanese patent application serial No. 2003-433376, filed on Dec. 26, 2003, the content of which is hereby incorporated by reference into this application.  
     FIELD OF THE INVENTION  
      The present invention relates to a vacuum switchgear system, and more particularly to a vacuum switchgear system comprising a plurality of switches accommodated in vacuum containers and an operation unit for operating each of the switchgears, which are suitable for receiving-distributing electric power of an electric power transmission system.  
      There are disposed switchgears as one element for receiving-distribution facilities of an electric power transmission system. Heretofore, air insulated switchgears have been widely used; however, gas insulated switchgears using SF 6  gas as an insulating gas are used for aiming at small sized facilities. Since the gas insulated switchgears may give adverse affects on environment, vacuum insulated switchgears using vacuum as an insulating medium are proposed in recent years.  
      As switchgears of the vacuum insulation system, there has been proposed a vacuum switchgear comprising a plurality of switches for a main circuit accommodated in a vacuum container, a fixed electrode and a movable electrode disposed in opposite relation with each other. The movable electrode is connected with the bus side conductor, and the fixed electrode is connected with the load side conductor. Each of the electrodes of the main switches is covered with an arc shield. Each of the bus side conductors is connected with the movable electrode by means of a flexible conductor (Patent document No.1). According to the vacuum switchgear disclosed in the patent document No. 1, which employs vacuum insulation, the insulating distance can be shorter than that of the insulating gas switchgear. Therefore, compact vacuum switchgears can be obtained. 
      (Patent document 1); Japanese patent laid-open 2000-26868 (pages 3 to 6, FIGS. 1-3)    

     DESCRIPTION OF THE INVENTION  
     SUMMARY OF THE INVENTION  
      The prior art does not consider the simplification of the structure of an operation unit to be connected with the switch of the switchgear and the relationship between the operation unit and the switch for downsizing the switchgear.  
      An object of the present invention is to downsize the switchgear system.  
      The present invention provides a vacuum switchgear system for a three phase system, which comprises three switchgears each comprising a vacuum switch and an operation unit, wherein each of the switches is accommodated in a vacuum container and each of the operation units is coaxially connected with an operating rod of each of the switches. The operation units of the three switchgears are connected with the adjoining operation units of the switchgears by means of link mechanisms connected with respective driving rods of the operation units. Each of the link mechanisms transmits a force of the driving rod assisted by an electro-magnet to the adjoining driving rods through the link mechanisms so that the three switchgears are operated in synchronism in response to a switch-on signal or a switch-off signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a front view of an essential part of a vacuum switchgear of one embodiment of the present invention.  
       FIG. 2  is a plane view of the essential part of the vacuum switchgear shown in  FIG. 1 .  
       FIG. 3  is a cross sectional view of the essential part of the vacuum switchgear shown in  FIG. 1 .  
       FIG. 4  is a front view of an essential part for explanation of relationship between the operation unit and the link mechanism of the switchgear of the present invention in an opening state.  
       FIG. 5  is a front view of an essential part for explanation of relationship between the operation unit and the link mechanism. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      In the present specification, the vacuum switchgear system means a system for a three phase power system comprising three vacuum switchgears, wherein the switchgear comprises a vacuum switch accommodated in a vacuum container and an operation unit connected with the switchgear. The vacuum switchgear means a vacuum switch comprising a vacuum container and at least one of a main switch or a load break switch, a circuit breaker and an earth switch.  
      The switchgear system for a three phase electric power transmission system of the present invention is featured by: 
      (a) There are three switchgears each comprises a vacuum switch and an operation unit.     (b) Each of the vacuum switches comprises a vacuum container and at least a main switch and earth switch accommodated in the vacuum container.     (c) The operation unit is coaxially connected with an operating rod of each of the switches.     (d) The operation units of each of the switchgears are connected with the adjoining operation units of the switchgear in the same phase by means of a link mechanism connected with respect to driving rods of the operation units.     (e) The link mechanism transmits a force of the driving rod to the adjoining driving rods so that the switches in the same phase are operated in synchronism in response to a switch-on signal or a switch-off signal.     (f) Each of the vacuum switchgears is independently operated from other vacuum switchgears, while the switches in the vacuum container in the same phase are operated synchronously.    

      Technical features of the present invention may be exemplified as follows. The vacuum switchgear system of the present invention may contain one or more of the following features. 
      (1) A pair of an operation unit and a vacuum switch constitute a vacuum switchgear in the vacuum switchgear system of three phases. One pair of the vacuum switch and the operation unit constitutes a vacuum switchgear. The three switchgears constitute a vacuum switchgear system of the present invention.     (2) The three operation units are connected to constitute an operation unit system by means of a link mechanism. A reciprocal movement of a driving rod of an operation unit is converted swing force into a reciprocal movement.     (3) Each of the operation units and each of the switchgear are coaxially connected on the same axis. In the conventional vacuum switchgear, one large sized operation unit was employed. Such the operation unit has a large magnet and a large link mechanism to transmit a large power for operating three switchgears. The size of the switchgear system of the present invention becomes remarkably small because each of the operation units and link mechanisms can be downsized.     (4) The adjoining operation units are connected by a link mechanism comprising a pin for swing movement and a connecting rod, connected with the pin, for lateral movement or reciprocating movement.     (5) Each of the vacuum switches comprises a main switch or load break switch, an earth switch and a circuit breaker.     (6) A magneto-motive force generated by a combination of an electro-magnet and a permanent magnet is utilized. The permanent magnet is particularly useful as an initial force to start separation of the electrodes. The electro-magnet is utilized for switching on and off for the switches.     (7) The operation units are arranged zigzag in a plane of the switchgear system. Since each of the operation units has a small size, the operation units can be arranged zigzag so that the occupying area of the switchgear can be minimized.    

      According to the present invention, there is provided a vacuum switchgear system for a three phase electric power transmission system, which comprises three switchgears each comprising a vacuum switch and an operation unit, wherein each of the switches is accommodated in a vacuum container and each of the operation units is coaxially connected with an operating rod of each of the switches, wherein the operation units of the three switchgears are connected with the adjoining operation units of the switchgears by means of link mechanisms connected with respective driving rods of the operation units, and wherein each of the link mechanisms transmits a force of the driving rod to the adjoining driving rods through the link mechanisms so that the three switchgears are operated in synchronism in response to a switch-on signal or a switch-off signal.  
      In the above vacuum switchgear system, each of the link mechanism comprises a swing member one end of which is connected with one end of the driving rod of each of the operation units to convert a reciprocal movement of the driving rod into a swing movement and a connecting rod one end of which is connected with the swing member and the other end is connected with the adjoining swing member to convert the swing movement into a lateral movement.  
      Further, in the above vacuum switchgear system, the driving rod is assisted by an electromagnet in closing the switches and is assisted by the electromagnet and a permanent magnet in opening the switches.  
      Still further, in the above vacuum switchgear system, the link mechanisms are restrained in the system so as to synchronize the lateral movement of the connecting rods of the three switchgears. The base members  128 ,  134 ,  148 ,  158 , etc support the link mechanisms in the switchgear system and restrain the link systems in the system.  
      In the above vacuum switchgear system, the switchgear system comprises three switchgears for three phases each comprising a vacuum switch and an operation unit, wherein each of the switches comprises at least a main switch and an earth switch, and if necessary a circuit breaker, accommodated in a vacuum container, each of the operation units being coaxially connected with an operating rod of each of the switches. The operation units of the three switchgears are connected with the adjoining operation units of the switchgear by means of a link mechanism, which has a first member connected with one end of a driving rod of each of the operation units and is disposed to swing around its connecting point as a fulcrum and a second member which is connected with one end of the first member to convert a swing movement of the first member into a lateral movement and transmit the lateral force to the adjoining link mechanisms, whereby the switches in the same phase in the same vacuum container are operated synchronously in response to a switch on signal or a switch off signal.  
      In the above vacuum switchgear system, each of the operation units is connected with each of the switches by means of an operating rod, wherein each of the operation units imparts the operating force by magneto-motive force to the operating rod in closing the switches. In opening of the switches an operating force by elasticity in the reverse direction with respect to the electromotive force to the operating rod, each of the operation units of each of the phases being connected with two switches having relation with the operation unit. Each of the switches and each of the operation units having relation with the switch are arranged in the closest relation on a same axis with respect to the operating rod. Each of the operation units is disposed above each of the switches having relation with the operation unit on an axis of the operating rod. Each of the switches comprises three load break switches, a circuit breaker and earth switches. The operation units for each switchgear are arranged zigzag in a plane.  
     PREFERRED EMBODIMENTS OF THE INVENTION  
      In the following, one of embodiments of the present invention will be explained by reference to drawings. A typical example of the switchgear system of the present invention comprises a circuit breaker  18  of U phase in a vacuum container  10  is connected with an operation unit by means of an operating rod  24  and a driving rod  78 ; a circuit breaker  18  of V phase in a vacuum container  10  is connected with an operation unit by means of an operating rod  24  and a driving rod  78 ; and a circuit breaker  18  of W phase in a vacuum container  10  is connected with an operation unit by means of an operating rod  24  and a driving rod  78 .  
      In a switching on operation by an operation unit  22 , magneto-motive force generated from an electromagnet  76  is imparted to the driving rod  78  and the operating rod  24  to switch on the circuit breaker  18 . In a switching off operation by the operation unit  22 , elastic force accumulated in a trip spring  80  is impaired to the driving rod  78  and the operating rod  24  to switch off the circuit breaker  18 . Operation force generated in each of the operation units  22  is transmitted to the other two phases by means of a link mechanism  26  to switch on or off the operation units of three phases simultaneously.  
       FIG. 1  is a front view of an essential part of the vacuum switchgear system of an embodiment of the present invention, and  FIG. 2  is a plane view of the switchgear system shown in  FIG. 1 .  FIG. 3  is a cross sectional view of the essential part of the switchgear system shown in  FIG. 1 . In FIGS.  1  to  3 , a three-phase vacuum switchgear system comprises a U phase vacuum container  10 , a V phase vacuum container  12  and a W phase vacuum container  14 . Each of the vacuum containers  10 ,  12 ,  14  made of stainless steel accommodates as switches three earth switches  16  and three circuit breakers (or a load break switches)  18  in corresponding to a first line to third line. Three operation units  20  for operating the earth switches  16  and three operation units  22  for operating the circuit breakers  18  are disposed above the vacuum containers  10 ,  12 ,  14  of the respective phases in corresponding to the earth switches  16  and the circuit breakers  18  of the respective phases.  
      The operation units  20 ,  22  of the respective phases are arranged alternately, and they are arranged zigzag for each phase in a same plane as shown in  FIG. 2 . The operation units  20  are connected with earth switches  16  by means of operating rods  24 , and the operation units  22  of the respective phases are connected with the circuit breakers  18  by means of operating rods  24 . That is, the operation units  20 ,  22  of the respective phases are disposed above the vacuum containers  10 ,  12 ,  14  in opposite relation with the earth switches  10  and circuit breakers  18 , and arranged coaxially with the earth switches  16  and the circuit breakers  18  along the axis of the operating rod  24 .  
      The operation units  20 ,  22  of the first line to third line of the respective phases are separately constituted so as to operate independently from each other for the respective phases. On the other hand, the operation units  20 ,  22  of the first line, the operation units  20 ,  22  of the second line and the operation units  20 ,  22  of the third line are connected with related operation units by means of link mechanisms  26 . For example, the operation units  20 ,  22  of the U phase in the first line are connected with the operation units  20 ,  22  of the other two phases (V phase and W phase) by means of the link mechanisms. That is, the operation units in different phases are independently operated and synchronously operated in the same phase in the same vacuum container.  
      On the other hand, the vacuum containers  10 ,  12 ,  14  of the respective phases to be earthed are provided with cable heads  28  in corresponding to the respective circuit breakers  18 . Each of the cable heads  28  is fixed to the lower plate member  30  in such a state that a part thereof is projected from the bottom of the vacuum container  10 ,  12 ,  14  through the through-holes  32  formed in the lower plate member  30 . Each of the cable heads  28  comprises a conductor  34  of a columnar shape made of copper and an insulating bushing  36  made of ceramics that surrounds the conductor  34 . Screw portions  38  are formed at the axial ends of the conductor  34 . Cables to be connected with the distribution system are screwed to the screw portions, and one end of the conductor  34  is connected with the load conductor or the bus conductor of the three phases by means of cables. The other end of the conductor  34  is connected with the circuit breaker  18  and also connected with the earth switch  16  by means of the plate conductor  40 .  
      The circuit breakers  18  of the first line to third line are provided with movable electrodes  42  and fixed electrodes  44  as control switches for opening-closing the conducting circuits connecting between the load conductors and the bus conductors, and the movable electrodes  42  and the fixed electrodes  44  are arranged in opposite relation. The upper parts of the movable electrodes  42  connected with the operating rods  24 , and also connected with the conductor  48  by means of a flexible conductor  48 . The plate conductors  48  are arranged over the circuit breakers  18  for the first line to the third line.  
      Each of the conductors  48  has a through-hole  50  at a position corresponding to an axis of the circuit breaker  18 . Each of the operating rods  24  is inserted into the through-hole  50  in reciprocal relation (up and down movement). The operating rod  24  is inserted into the through-hole  54  formed in the upper plate member  52  in reciprocal relation (up and down movement). The upper part of the operating rod  24  is covered with a cylindrical bellows  56  and a disc base  58 ; the bellows  58  is fixed to the surface of the upper plate  52 .  
      Each of the earth switches  16  for earthing each of the circuit breakers comprises a movable electrode  60  and a fixed electrode  62 ; the electrodes are arranged to oppose to each other. The fixed electrode  62  is connected with a conductor  40 ; a ceramic supporting member  64 , which is fixed to the lower plate member  30  supports the fixed electrode side of the conductor  40 .  
      The movable electrode  60  is connected with the operating rod  24  of the operation unit  20  for the earth switch and connected with the conductor  48  by means of a flexible conductor  68 . The conductor  68  which is shaped into a plate as same as the plate conductor  48  is arranged over the switches  16  of the first line to the third line. The end of the plate conductor is connected with a connecting terminal  70 . That is, the earth switches  16  ground the circuit breakers  18  with the conductor  40 , the earth switches  16 , the flexible conductor  66 , the conductor  68  and the earthing terminal  70  upon contacting the movable electrode  60  with the fixed electrode  62 . The conductor  68  is provided with a through-hole (not shown) for reciprocating the operating rod  24  (up and down movement). The bellows  56  and the base surround the operating rod  24 .  
      On the other hand, each of the operation units  20 ,  22  of each of the phases is fixed to the fixing plates  72  as shown in  FIG. 4 . A switchboard (not shown) supports the fixing plates  72 . Each of the operation units  20 ,  22  of each phase is arranged in a line for each of the first line to the third line. In order to impart operation force of magneto-motive force to the operating rods  24  upon closing of each of the earth switches  16  and each of the circuit breakers  18 , each of the operation units  20 ,  22  comprises an electro-magnet  74 , a permanent magnet  76 , a driving rod  78 , etc. Each of the operation units  20 ,  22  is provided with a trip spring  80  so that operation force of the elastic force in the reverse direction of that of the magneto-motive force is imparted to each of the operating rods  24  upon opening of each of the earth switches  16  and each of the circuit breakers  18 . Further, each of the driving rods  78  is connected with the link mechanism  26  for each of the first line, the second line and the third line, thereby to perform three phase operation.  
      The electro-magnet  74  is provided with a driving rod  78  as one element, and also provided with a movable iron core (plunger)  82 , a fixed iron core  84 , a coil bobbin  86 , a coil  88 , movable disc plates  90 ,  92 , iron supporters  94 ,  96 ,  98  of disc form, iron covers  100 ,  102  of a cylindrical form, a fixed rod  104 , etc. The lower part of the fixed rod  104  is fixed to the fixing base plate  72  by means of a bolt and a nut. The driving rod  78  having a columnar shape is arranged on a coaxial line of the operating rod  24  so that the driving rod  78  is capable of reciprocating up and down in the through-hole or a hollow formed in the center of the iron supporters  94 ,  96 ,  98 . The movable iron core  82  and the movable plates  90 ,  92  are fixed around the driving rod  78 , and a fixed iron core  84  is disposed opposite to the diving rod  78 .  
      The fixed iron core  78  of an annular shape is fixed to the surface of the iron supporter  98 . The coil bobbin  86  of an annular shape is disposed to surround the driving rod  78  and the fixed iron core  84 . The coil bobbin  86  of an annular shape is arranged to surround the driving rod  78  and the fixed iron core  84 . The supporters  96 ,  98  support the top end and the bottom end of the coil bobbin. An annular coil  88  is disposed in the coil bobbin  86 . An annular permanent magnet  76  is disposed adjoining the coil  88  and is supported by the supporting plate  96 .  
      The coil  88  is provided with current in response to a closing signal or an opening signal. When electric current is supplied to the coil  88 , a magnetic field is generated around the coil  88  a path consisting of movable iron core  82 —fixed iron core  84 —supporting plate  98 —cover  102 —supporting plate  96 —movable iron core  82 . The magnetic field causes the bottom portion of the movable iron core  82  in the axial direction thereof generate an attractive force in the downward direction so that the movable iron core  82  and the driving rod  78  move toward the fixed iron core  84 . Thus, the movable iron core  82  is adsorbed to the fixed iron core  84  to make contact between the movable iron core  82  and the fixed iron core  84 . In this case, since the direction of the magnetic field generated by the permanent magnet  76  is same as that of the magnetic field generated by the coil  88 , the movable iron core  82  moves toward the fixed iron core  84  in such state that the magneto-motive force generated by the electro-magnets  74  is enhanced, i.e. the adsorption force is enhanced. The magneto-motive force generated by the electro-magnets  74  and the permanent magnets  76  is imparted to the driving rod  78  as an operating force for pressing down the driving rod  78  (toward the operating rod  24 ).  
      The lower part of the driving rod  78  is connected with the upper part of the operating rod  24  by means of the connecting rods  106 ,  108 . Therefore, the operating rod  24  moves downward as the driving rod moves downward so that the earth switch  16  or the circuit breaker  18  is switched on. The connecting rod  106  is inserted together with the connecting rod  108  into the through-hole  110  formed in the fixing plate  72 , thereby to reciprocate (up and down movement). The supporting plate  112  is fixed to the upper side of the connecting rod  106 . A trip spring  80  is disposed between the supporting plate  112  and the fixing plate  72 . An elastic force (spring force) is accumulated in the trip spring  80  when the driving rod  78  moves down.  
      On the other hand, the trip spring  80  imparts accumulated elastic force (spring force) to the driving rod  18  and the operating rod  24  when the coil  88  becomes non-conduction in response to opening signal or opening operation. The operating force of the elastic force is set to be larger than the magneto-motive force of the permanent magnet  76 ; when the elastic force accumulated in the trip spring is imparted to the driving rod  78  and the operating rod  24  as the operating force, the driving rod  78  and the operating rod  24  moves upward against the magneto-motive force of the permanent magnet  76  to open the earth switch  16  or circuit breaker  18 .  
      The link mechanism  26  converts operating force along the vertical direction with respect to the operating rod  24  to an operating force in the direction intersecting the driving rod  78  and the operating rod  24 , that is, the direction along the horizontal direction so that the operation units of the respective three phases are operated.  
      More concretely, the link mechanism  26  comprises links  114 ,  116 ,  118 ,  120  and connecting rods  122 ,  124 ; one end of the link  114  is connected swingingly with the base  128  by means of a pin  126 . The base  128  is fixed to the supporting plate  94  by means of a bolt and a nut. The other end of the link  114  is connected swingingly with one end of the link  116 .  
      The link  116  is connected swingingly as a link for W phase with the base  134  by means of the pin  132 , and the base  134  is fixed to the supporting plate  94  by means of a bolt and a nut. The link  116  is disposed swingingly with respect to the pin  132  as a fulcrum. Pins  136 ,  138  are fixed to the link  116  on the line connecting the center of the pin  130  and pin  132 , wherein the pin  132  is located between the pins  136  and  138 . A pin  140  is fixed at a position that intersects the line connecting the center of the pin  130  and the center of the pin  138 . The driving rod  78  is connected with the pin  136  to swing, and one end of the connecting rod  122  is connected with the pin  140  to swing. A stopper  142  is disposed below the pin  138 , which is fixed to the supporting plate  94 . The pin  138  prevents the link  116  from downward swinging by contacting with the stopper  142 , when the operation units  20 ,  22  of the W phase are operated to open.  
      The connecting rod  122  is disposed reciprocally along the horizontal direction that intersects the driving rod  78 , and the one end of the axis of the connecting rod  122  is connected swingingly with the link  118  by means of the pin  144 . The link  118  as a link for V phase is swingingly connected with the base  148  by means of the pin  146 . The base  148  is fixed to the supporting plate  94  by means of a bolt and a nut. The link  118  is disposed swingingly with respect to the pin  146  as a fulcrum. The pin  150  is fixed on the line connecting the center of the pin  146  and the center of the pin  144 . The pin  152  is fixed in the direction interesting the line connecting the center of the pin  146  and the center of the pin  150 .  
      The pin  152  is connected swingingly with the driving rod  78 , and the pin  150  is connected swingingly with the connecting rod  124 . The connecting rod  124  is disposed swingingly in the direction that intersects the driving rod  78  and the operating rod  24 , i.e. the horizontal direction. One end of the oprtating rod  24  in the axial direction is swingingly connected with the pin  154  of the link  120 . The link  120  as a link for U phase is provided with the pin  156 ; the pin  156  is connected swingingly with the base  158 . The base  156  is fixed to the supporting plate  94  by means of a bolt and a nut. The link  120  is disposed swingingly with respect to the pin  156  as a fulcrum. The pin  160  is fixed in the direction perpendicular to the line connecting the center of the pin  154  and the pin  156 . The pin  160  is connecting swingingly with the end portion of the driving rod  78 .  
      In the above construction, when an operation signal is given the operation unit  20  or  22  of the first line and when the coil  88  of the electromagnet is turned on, the movable iron core  82  moves toward the fixed iron core  84  and the driving rod  78  and the operating rod  74  move downward. The operating force is transmitted to the links  116 ,  118 ,  120 , and each of the links  116 ,  118 ,  120  is swung in the direction of the arrow X around the pins  132 ,  146 ,  156  as a fulcrum as shown in  FIG. 4 . As a result, the operating force of each of the phases is transmitted to the operation units of the other two phases to simultaneously switch on each of the earth switches  16  or each of the circuit breakers. That is, each of the earth switches  16  and each of the circuit breakers  18  are switched on simultaneously without displacement.  
      On the other hand, when an opening instruction is issued to the operation unit  20  or  22  of the first line to switch off each of the coils  88  (non-excited state), the movable iron core  82  separates from the fixed iron core  84  to move the driving rod  78   24  upward. At the same time, each of the links  116 ,  118 ,  120  of the respective phases swing in the direction of the arrow Y as shown in  FIG. 5  around the pins  132 ,  146 ,  156  as a fulcrum to transmit the operating force generated from each of the operation units to the other two operation units. As a result, each of the earth switches  16  or each of the circuit breakers  18  of the respective phases is switched off simultaneously with other switches.  
      According to this embodiment, if the operation units  20 ,  22  of each of the phases are switched on, the magneto-motive force generated from the electro-magnets  74  and the permanent magnets  76  is given the driving rod  78  and the operating rod  24 , and if the operation units  20 ,  22  of each of the phases are switched off, the elastic force accumulated in the trip spring is given the driving rod  78  and the operating rod  24 . Accordingly, the operation units  20 ,  22  can be made smaller than the operation units using only elastic force of springs.  
      Since the three phase switching on or off operation by transmitting the operating force generated from the operation units  20 ,  22  to the other two operation units, there is no displacement among the phases and the earth switches  16  or the circuit breakers  18  are switched on or off simultaneously or in synchronism.  
      Further, since the operation units of the respective phases are constituted by the same elements, the elements can be shared and assembly work is simplified.  
      Since the operation units  20 ,  22 , the earth switches  16  and the circuit breakers  18  are arranged on the same axis, the distance between the operation units  20 ,  22  and the vacuum containers  10 ,  12 ,  14  can be made small so that the switchgears and the installation area can be made small.  
      Since the operation units  20 ,  22  of the respective phases are arranged zigzag, the distance between the operation units  20 ,  22  can be made small so that the installation area can be made further small.  
      Since the operation units  20 ,  22  of the respective phases are disposed above the vacuum containers  10 ,  12 ,  14  and since the part of the cable heads  28  is projected from the lower part of the vacuum containers  10 ,  12 ,  14 , the height of the switchgear becomes smaller.  
      In the above-described embodiment, the earth switches  16  and the circuit breakers  18  of the respective phases are accommodated in separate vacuum containers; the earth switches  16  and the circuit breakers  18  of the respective phases can be accommodated in a single vacuum container.  
      Although the above description has been made on the switchgear comprising operation units  20 ,  22  which have the electro-magnets  74  and the permanent magnets  76 , the permanent magnets  76  can be omitted if the electro magnets generate the magneto-motive force of a sufficient strength.  
      In the above described embodiment, although the coils of the electromagnets  20 ,  22  are made switched off (non-conductive) when the operation units  20 ,  22  are switched off, current is supplied to the coils  88  of the operation units  20 ,  22  in the direction opposite to that of switching on, the magneto-motive force whose direction is opposite to that of switching on is generated from the electromagnet  74  and the magneto-motive force is given the driving rod  78 . As a result, the operating force in switching off can be further enhanced. In this case, the trip spring having a smaller elastic force (spring force) than the spring in the former embodiment can be employed.  
      In the embodiment, if the circuit breakers  18  are covered with arc shields, the arc shields shield metal vapor generated at the time of contacting and separating of the electrodes.