Patent Publication Number: US-7897890-B2

Title: Vacuum insulated switchgear

Description:
CLAIM OF PRIORITY 
     The present application claims priority from Japanese application Serial No. 2006-253895, filed on Sep. 20, 2006, the content of which is hereby incorporated by reference into this application. 
     FIELD OF THE INVENTION 
     The present invention relates to a vacuum insulated switchgear and in particular to a vacuum insulated switchgear suitably used in receiving and transforming equipment. 
     BACKGROUND OF THE INVENTION 
     In power receiving and transforming equipment, there is installed a closed switchboard (referred to as a switchgear). It is constructed by housing the following items in an enclosure; a vacuum circuit breaker for interrupting a load current or a fault current; a disconnector and an earthing switch for ensuring the safety of a worker who conducts maintenance work on a load; detectors for system voltage and current; a protective relay; and the like. 
     With respect to this type of switchgear, it is required to give consideration to the position and direction of power cables connecting the switchgear. Therefore, it has been desired that the switchgear can cope with the position and direction of the power cables. 
     In one of measures for the improvement of this regard, various positions and directions of power cables cope with each other as follows. Multiple switches are housed in respective vacuum cases and integrally molded; this molded portion is provided with terminals for power cable connection; and these terminals for power cable connection are protruded in various directions. (Refer to Patent Document 1, for example.) 
     [Patent Document 1] JP-A-2000-306474 (FIG. 16) 
     The above-mentioned switchgear is so constructed that the following can be implemented with respect to multiple switches, buses, terminals for power cable connection, and the like housed in an enclosure having a door: the disposition of them in the enclosure can be changed to cope with various positions and directions of power cables. 
     With respect to power receiving and transforming equipment having this type of switchgear, users&#39; demands have been diversified. An example will be taken. The type of load and operating conditions differ depending on the purpose of use on the customers&#39; sites. When a distribution system is planned, therefore, consideration is given to the requirements for safety, reliability, the maintenance of operation, and expected increase in load. In this planning for power distribution, it is also required to take the following into account: control of a circuit breaker, a disconnector, an earthing switch, and the like constructing the power receiving and transforming equipment and monitoring and measurement of their voltage, current, power, and the like. 
     In this case, important considerations are how the installation space for the above devices and monitoring and measuring instruments should be reduced for size and weight reduction and suppression of investment in installation. 
     Further, it is important to give sufficient consideration to safety as well as a wide variety of users&#39; other demands. For example, some of important considerations are to enhance the safety of installed switchgear against earthquakes and the like and to fulfill a failsafe function in a failure in an operating system for a circuit breaker. 
     SUMMARY OF THE INVENTION 
     The invention has been made based on the foregoing. An object of the invention is to provide vacuum insulated switchgear that makes it possible to enhance the safety and reliability of the switchgear against earthquakes and the like during transportation and setting and after installation, and to fulfill a failsafe function in a failure, such as breakage in an operating mechanical section of the switchgear. 
     To attain the above object, the present invention provides a vacuum insulated switchgear comprising an enclosure having a switch block defined by a grounded metal plate, a bus block positioned above the switch block, and a cable block positioned beside the switch block; a switch installed in the switch block; a bus electrically connected with the switch and installed in the bus block; and a cable electrically connected with the switch and installed in the cable block. 
     The present invention further provides a vacuum insulated switchgear comprising an enclosure having a switch block defined by a grounded metal plate, a bus block positioned above the switch block, and a cable block positioned beside the switch block; a switch and an operating device therefor installed in the switch block; a bus electrically connected with the switch and installed in the bus block; and a cable electrically connected with the switch and installed in the cable block. In this switchgear, the switch block is positioned at a lower level than the intermediate portion of the enclosure in the direction of height; and the switch and the operating device are disposed in the switch block. The switch can be provided with a movable contact positioned below its fixed contact. 
     In a vacuum insulated switchgear according to the invention, a switch and an operating mechanical section interlocking therewith are disposed in a switch block positioned at a lower level than the intermediate portion of an enclosure in the direction of height. The switch is the heaviest one among the devices housed in the enclosure. Therefore, the center of gravity of the entire switchgear can be set to a low position. As a result, the stability of the switchgear during transportation and setting is enhanced, and thus workability can be enhanced. Further, the installed switchgear is excellent in stability against earthquakes and the like, and its safety and reliability can be enhanced. 
     Further, in the vacuum insulated switchgear according to the invention, the switch is disposed in the enclosure so that its movable contact is positioned below its fixed contact. If the operating mechanical section is broken, therefore, the movable contact is moved away from the fixed contact by its own weight. Therefore, a failsafe function is fulfilled, and the safety can be enhanced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partly cross sectional side view illustrating an embodiment in which vacuum insulated switchgear of the invention is applied to a feeder panel; 
         FIG. 2  is a partly cross sectional front view of the embodiment illustrated in  FIG. 1 ; 
         FIG. 3  is a partly cross sectional back view of the embodiment illustrated in  FIG. 1 ; 
         FIG. 4  is a partly cross sectional perspective view of the embodiment illustrated in  FIG. 1 ; 
         FIG. 5  is a drawing illustrating a front door illustrated in  FIG. 1 ; 
         FIG. 6  is a longitudinal cross sectional view of the vacuum insulated switchgear illustrated in  FIG. 1 ; 
         FIG. 7  is a partly cross sectional enlarged perspective view of an embodiment of an operating mechanism for the vacuum insulated switchgear illustrated in  FIG. 1 ; 
         FIG. 8  is a side view explaining the operation of an emergency manual handle operating section of the vacuum insulated switchgear of the invention, which is applied as a feeder panel; 
         FIG. 9  is a partly cross sectional side view of another embodiment of a vacuum insulated switchgear of the invention, which is applied as a feeder panel; 
         FIG. 10  is a partly cross sectional side view of still another embodiment of a vacuum insulated switchgear of the invention; and 
         FIG. 11  is a partly cross sectional side view of a still further embodiment of a vacuum insulated switchgear of the invention, which is applied as a feeder measuring board. 
     
    
    
     Reference numerals used in the drawings are: 
       1  denotes an enclosure,  1   a  a bus block,  1   b  a switch block,  1   c  a cable block,  1   d  a low voltage control block,  1   e  a front door at the front side, if a rear door at the rear side,  2   a - 2   d  a grounded metal plate,  3   a  cable,  4  a current transformer,  5  a bus,  5   a  a connecting bushing,  7  a fuse,  8  a vacuum double-break three-position switch,  9  a vacuum earthing switch,  10  a single-phase wound voltage transformer,  11  an operating device,  12  epoxy resin,  20  a T shaped cable head,  20   a  a cable connecting terminal,  80 ,  91  a vacuum case,  80   a ,  91   a  an insulating cylinder,  81   a ,  81   b ,  92 , a fixed contact,  82   a ,  82   b ,  93  a movable contact,  83 ,  84  a feeder,  85  a movable conductor,  86 ,  94  a vacuum insulated operating rod,  87 ,  95  a metal bellows,  88  an air insulated insulating operating rod,  113  a supporting plate,  200  a first operating mechanism,  300  a second operating mechanism, and  400  a third operating mechanism. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As mentioned before, The vacuum insulated switchgear of the invention that achieves the above mentioned objects is realized by a low-cost and simple construction. 
     First Embodiment 
     Hereafter, description will be given to an embodiment of a vacuum insulated switchgear of the invention with reference to drawings. 
       FIG. 1  to  FIG. 5  illustrate an embodiment in which vacuum insulated switchgear of the invention is applied to a feeder panel. 
     In the vacuum insulated switchgear in these drawings, its enclosure  1  is partitioned into the following by grounded metal plates  2   a ,  2   b ,  2   c ,  2   d  disposed therein: a bus block  1   a , a switch block  1   b , a cable block  1   c , and a low-voltage control block  1   d . The enclosure  1  is provided on its front side (right side of  FIG. 1 ) with a font door  1   e  and on its rear side (left side of  FIG. 1 ) with a rear door  1   f.    
     The bus block  1   a  is disposed in proximity to the center of the direction of the depth of the enclosure  1  (horizontal direction in  FIG. 1 ) on the upper side. The switch block  1   b  is disposed below the bus block  1   a , and the cable block  1   c  is disposed on the rear side of the enclosure  1  (left side of  FIG. 1 ). The low-voltage control block  1   d  is disposed on the upper side of the back face of the front door  1   e , and is positioned opposite to the bus block  1   a.    
     In the bus block  1   a , three-phase solid insulated buses (BS)  5  are disposed in parallel with the front face of the enclosure  1  through connecting bushings  5   a  (in the direction orthogonal to the plane of  FIG. 1 ). The buses  5  are insulated by a solid insulator and are made free from gas. Avoidance of use of gas makes gas management unnecessary and the switchgear easier to handle. In addition, even when dust or foreign mater enters the room of installation, insulation is maintained and the safety remains ensured because of solid insulation. 
     In the switch block  1   b , the following, described in detail later, are disposed: a vacuum double-break three-position switch (vacuum double-break three-position circuit breaker-disconnector CBDS)  8 ; a vacuum earthing switch (ES)  9 ; and an operating device  11 . 
     In the cable block  1   c , the following are provided: a cable connecting terminal  20   a  connected to the fixed contact  81   a  of the vacuum double-break three-position switch  8  and the fixed contact of the vacuum earthing switch  9  and led into the cable block  1   c ; a T-shaped cable head  20  rotatably provided on the cable connecting terminal  20   a ; two pairs of cables  3  (6 cables for three phases) disposed at the upper part or the lower part by rotating the T-shaped cable head  20  and connected to the terminal  20   a ; and a system protecting current transformer (CT)  4  provided on the circumferential surface of the cable connecting terminal  20   a . In this example, the cables  3  are led into the cable block  1   c  from the lower part of the enclosure  1 . The cable connecting terminal  20   a  is connected by means of a member with a fuse  7  and a single-phase wound voltage transformer (VT)  10 . The fuse  7  and the single-phase wound voltage transformer  10  are disposed on the upper side in the cable block  1   c.    
     In the low-voltage control block  1   d , the following is disposed on the back face of the front door  1   e : a low-voltage control section composed of capacitors  1   da  and a protective relay  1   dab . On the front face of the front door  1   e , as illustrated in  FIG. 4  and  FIG. 5 , the following are disposed from top down: an alarm display section lea for displaying alarms about grounding and short-circuiting faults, capacitor anomaly, vacuum pressure anomaly, and the like; an operating switch section  1   eb  including various operating switches; and the emergency manual handle operating section  1   ec.    
     In the alarm display section  1   ea , for example, the following are disposed: two display sections  500  for displaying grounding and short-circuiting faults; a display section  501  for enable or disable of interlock; an anomaly display section  502  for capacitor; an anomaly display section  503  for vacuum pressure; and a display section  504  for displaying the completion of capacitor charge. 
     In the operating switch section  1   eb , for example, the following are installed: an operation selector switch  505  for the vacuum double-break three-position switch  8  and the vacuum earthing switch  9 ; a remote-local selector switch  506 ; an operating switch  507  for turning on/off or disconnecting the vacuum double-break three-position switch  8 ; position indicator lamps  508  for the vacuum double-break three-position switch  8 ; a mechanical position display section  509  for the vacuum double-break three-position switch  8 ; an operating switch  510  for grounding or turning off the vacuum earthing switch  9 ; a mechanical position display section  511  for the vacuum earthing switch  9 ; voltage detecting and phase indicating terminals  512 ; and the like. 
     Further, the emergency manual handle operating section  1   ec  is installed below them. The configuration of the emergency manual handle operating section  1   ec  will be described later. 
     The vacuum double-break three-position switch  8  and the vacuum earthing switch  9  disposed in the above-mentioned switch block  1   b  are integrally molded with epoxy resin  12  as illustrated in  FIG. 1  and  FIG. 6 . This unitizes the switch portion for size and weight reduction. The unitized switch portion is of phase separation structure, and is installed orthogonal to the front face of the enclosure  1 . Further, a shielding panel is disposed between united switch portions to suppress the occurrence of a short-circuiting fault between phases. The outer surface of the above-mentioned molded epoxy resin  12  is grounded by conductive coating material applied thereto to ensure the safety in case of contact. 
     Detailed description will be given to the configuration of the above-mentioned unitized switch portion with reference to  FIG. 1  and  FIG. 6 . 
     As illustrated in these drawings, the vacuum double-break three-position switch  8  includes: a vacuum case  80  having insulating cylinders  80   a ; two fixed contacts  81   a  and  81   b  housed in the vacuum case  80 ; two movable contacts  82   a  and  82   b  that can be respectively brought into and out of contact with the fixed contacts  81   a  and  81   b ; and arc shields  90  that are supported in the respective insulating cylinders  80   a  and cover the areas surrounding the left and right fixed contact  81   b ,  81   b  and movable contacts  82   a ,  82   b  including these contacts. Double break is achieved by the two fixed contacts  81   a  and  81   b  and two movable contacts  82   a  and  82   b.    
     The right fixed contact  81   a  in  FIG. 6  is connected to a bus  5  through a feeder  83 , and the left fixed contact  81   b  is connected to a terminal  2   a  through a feeder  84 . The movable contact  82   a  and the movable contact  82   b  are coupled with each other through a movable conductor  85  reinforced by metal, such as stainless steel, that is not annealed at high temperature. The movable conductor  85  is coupled with a vacuum insulated operating rod  86 , and the vacuum insulated operating rod  86  is coupled with a coupling rod  86   a . The coupling rod  86   a  is vacuum sealed with a metal bellows  87 , and is led out to the exterior of the vacuum case  80  and coupled with an air insulated operating rod  88 . The area around the joint between the air insulated operating rod  88  and the coupling rod is enveloped with a rubber or metal bellows  89 . As illustrated in  FIG. 1 , the air insulated operating rod  88  is coupled with an operating rod  111  operated through the operating device  11 . 
     The two movable contacts  82   a  and  82   b  are operated through the operating device  11  coupled with the operating rod  111  so that they are stopped in the three positions illustrated in  FIG. 6 : closed position Y 1  for energization; open position Y 2  for interrupting a load current or a fault current; and disconnected position Y 3  for ensuring the safety of inspecting personnel against surge voltage of lightening and the like. 
     As illustrated in  FIG. 6 , the above-mentioned two movable contacts  82   a  and  82   b  respectively ensure an interrupting gap g 2  in the open position Y 2 . This gap is equivalent to the distance between the closed position Y 1  and the open position Y 2 . The two movable contacts  82   a  and  82   b  respectively ensure an isolating gap g 2 +g 3  in the disconnected position Y 3 . The isolating gap g 2 +g 3  is so set that a pole-to-pole distance equivalent to substantially twice the interrupting gap g 2  is ensured. As mentioned above, the isolating gap g 2 +g 3  in isolation is set to substantially twice the interrupting gap g 2 . These multiplied-long gaps contribute to improvement of the insulation performance. 
     The following relation can be established by providing mold insulation between phases and vacuum insulation between the poles of contacts and varying the above-mentioned pole-to-pole distance and a number of poles: relation expressed as “phase-to-phase insulation&gt;pole-to-pole insulation in isolation&gt;pole-to-pole insulation in interruption&gt; the pole-to-pole insulation of earthing switch.” This facilitates insulation coordination between phases. As a result, the severity of grounding faults is lightened to one-line ground at the worst, and it is possible to suppress spreading of faults as much as possible. Since the above-mentioned air insulated operating rod  88  is enveloped with the rubber or metal bellows  89  and is shielded from the outside air, the reliability of insulation is ensured for long-term use. 
     Detailed description will be given to the configuration of the above-mentioned vacuum earthing switch  9  with reference to  FIG. 1  and  FIG. 6 . 
     As illustrated in these drawings, the vacuum earthing switch  9  includes: a vacuum case  91  having an insulating cylinder  91   a ; a fixed contact  92  housed in the vacuum case  91  and connected to the feeder  84 ; a movable contact  93  that can be brought into and out of contact with the fixed contact  92 ; and an arc shield  97  that is supported in the insulating cylinder  91   a  and covers the area around the fixed contact  92  and the movable contact  93 . The movable contact  93  is coupled with a movable conductor  94 . The movable conductor  94  is led out of the vacuum case  91  through a metal bellows  95 , and is coupled with an insulated operating rod  112  for the vacuum earthing switch  9 . Stainless steel is used for the material of the vacuum case  80  and this enhances their environment resistance. As illustrated in  FIG. 1 , the movable contact  93  is connected to ground by a conductor  96  through the movable conductor  94 . 
     Detailed description will be given to the configuration of the operating device  11  with reference to  FIG. 1  and  FIG. 7 . The operating device  11  is for changing the position of the vacuum double-break three-position switch  8  among the three positions: the closed position Y 1  for energization; the open position Y 2  for interrupting a load current or a fault current; and the disconnected position Y 3  for ensuring the safety of inspecting personnel against surge voltage of lightening and the like. The operating device  11  is also for turning on and off the vacuum earthing switch  9 . 
     As illustrated in these drawings, the components of the operating device  11  are fixed on a supporting plate  113  provided in the switch block  1   b . The operating device  11  is substantially constructed of: a first operating mechanism  200  for shifting the movable contacts  82   a ,  82   b  of the vacuum double-break three-position switch  8  between the closed position Y 1  and the open position Y 2 ; a second operating mechanism  300  for shifting the movable contacts  82   a ,  82   b  of the vacuum double-break three-position switch  8  between the open position Y 2  and the disconnected position Y 3 ; and a third operating mechanism  400  for operating the movable contact  93  of the vacuum earthing switch  9 . 
     Description will be given to the configuration of the first operating mechanism  200  with reference to  FIG. 7  and  FIG. 1 . As illustrated in these drawings, a first shaft  201  is rotatably supported by the supporting plate  113 , and three levers  202  are fixed on the first shaft  201  on one side in the direction of the axis of the first shaft  201 . The tips of the levers  202  are respectively coupled with the operating rods  111 . On the opposite side of the first shaft  201 , a lever  203  is fixed in the opposite side to the direction of the levers  202 . 
     As illustrated in  FIG. 7 , the lever  203  is coupled with the driving shaft  206  of an electromagnet  205  through a coupling member  204 . On the driving shaft  206 , there is fixed a moving core  207  having T-shaped sections. Around the moving core  207 , there is provided a fixed core  208  fixed on the supporting plate  113 , and in the fixed core  208 , there are disposed a coil  209  and an annular permanent magnet  210 . On the opposite side to the lever  203  with respect to the driving shaft  206 , there is provided a trip spring bearing  211 , and a trip spring  212  is provided between the trip spring bearing  211  and the fixed core  208 . 
     The electromagnet  205  is so constructed that the following is implemented when the movable contacts  82   a ,  82   b  are held in the closed position Y 1 : holding force countervailing the accumulate energy of the trip spring  212  and a pressure contact spring (not shown) provided on the air insulated operating rod  88  can be obtained by the attractive force of the coil  209  and the permanent magnet  210 . 
     Description will be given to the configuration of the second operating mechanism  300  with reference to  FIG. 7 . The second operating mechanism  300  is for shifting the movable contacts  82   a ,  82   b  of the vacuum double-break three-position switch  8  between the open position Y 2  and the disconnected position Y 3 . As illustrated in the drawing, a lever  301  is fixed on the intermediate portion of the first shaft  201  in the direction of length on the supporting plate  113 . The lever  301  is provided at its tip with an interlock pin  302 . The pin  302  has a roller  303  abutted against it, and the roller  303  is rotatably provided at the end of a crank lever  304  on one side. The crank lever  304  is supported so that it can be rotated to the underside of the supporting plate  113 . 
     The end of the crank lever  304  on the other side is coupled with the driving shaft  306  of an electromagnet  305 , and on the driving shaft  306 , there is fixed a moving core  307 . Around the moving core  307 , there is provided a fixed core  308  fixed on the supporting plate  113 , and in the fixed core  308 , there are disposed two coils  309 ,  310  in the vertical direction. A return spring  311  is disposed between the moving core  307  and the upper part of the fixed core  308 . 
     The electromagnet  305  excites the individual coils  309 ,  310  to move the moving core  307  in the vertical direction, and the crank lever  304  is rotated by this operation. The position of abutment between the interlock pin  302  and the roller  303  is changed by this rotation of the crank lever  304 . As a result, the lever  203  is prevented from rotating around the first shaft  201  or permitted to rotate. 
     Thus, the movable contacts  82   a ,  82   b  of the vacuum double-break three-position switch  8  are prevented from moving from the open position Y 2  to the disconnected position Y 3  illustrated in  FIG. 6  and held in the open position Y 2 . Or, they are permitted to move from the open position Y 2  to the disconnected position Y 3 . That is, this construction makes a first interlock mechanism of the movable contacts  82  of the vacuum double-break three-position switch  8  between the open position Y 2  and the disconnected position Y 3 . 
     Description will be given to the configuration of the third operating mechanism  400  for operating the movable contact  93  of the vacuum earthing switch  9  with reference to  FIG. 7 . As illustrated in the drawing, a second shaft  401  is rotatably supported on the supporting plate  113 , and on one side of the second shaft  401 , there are fixed three levers  402  in the direction of the axis of the second shaft  401 . The tips of the levers  402  are respectively coupled with the operating rods  112 , and on the other side of the second shaft  401 , there is fixed a lever  403  in the opposite direction to the levers  402 . 
     The lever  403  is coupled with the driving shaft  406  of an electromagnet  405  through a coupling member  404 . The electromagnet  405  is constructed similarly with the above-mentioned electromagnet  205  of the first operating mechanism  200 . On the driving shaft  406 , there is fixed a moving core  407  having T-shaped sections. Around the moving core  407 , there is provided a fixed core  408  fixed on the supporting plate  113 , and in the fixed core  408 , there are disposed a coil  409  and an annular permanent magnet  410 . Between the fixed core  408  and the lower face of the supporting plate  113 , there is provided a trip spring  411 . 
     Between the third operating mechanism  400  of the vacuum earthing switch  9  and the second operating mechanism  300 , there is provided a second interlock mechanism. The second operating mechanism  300  is for shifting the movable contacts  82   a ,  82   b  of the vacuum double-break three-position switch  8  between the open position Y 2  and the disconnected position Y 3 . The second interlock mechanism is related to various elements so that the operation described below is carried out. When the movable contacts  82   a ,  82   b  of the vacuum double-break three-position switch  8  are in a third position, or the disconnected position Y 3  for ensuring the safety of inspecting personnel against surge voltage of lightening and the like, the second interlock mechanism performs the following operation: it enables the movable contact  93  of the vacuum earthing switch  9  to be brought into contact with the fixed contact by the electromagnet  405 . When the movable contacts  82   a ,  82   b  of the vacuum double-break three-position switch  8  are in a second position, or the open position Y 2  for interrupting a current, it disables the movable contact  93  of the vacuum earthing switch  9  to be brought into contact with the fixed contact by the electromagnet  405 . When the movable contact  93  is in contact with the fixed contact  92  of the vacuum earthing switch  9 , it disables the operation of the electromagnet  205  of the second operating mechanism  300 . 
     Specifically, the above-mentioned second interlock mechanism is constructed of: a pin  412  provided at the lower end of the driving shaft  406  of the electromagnet  405  of the third operating mechanism  400 ; a shaft  413  provided in parallel with the second shaft  401  below the electromagnet  305  of the operating mechanism  300 ; a lever (not shown) provided on the shaft  413  and coupled with the lower end of the driving shaft  306  of the electromagnet  305  of the second operating mechanism  300 ; and a lever  414  provided on the shaft  413  and engaged with the pin  412 . 
     Description will be given to the operation of an embodiment in which vacuum insulated switchgear of the invention is applied to a feeder panel with reference to  FIG. 1  to  FIG. 7 . 
     When the movable contacts  82   a ,  82   b  of the vacuum double-break three-position switch  8  are set in the open position Y 2  for interrupting a load current or a fault current, the following takes place: the lever  203  of the first operating mechanism  200  is supplied with counterclockwise torque in  FIG. 7  with the first shaft  201  taken as the fulcrum by return force of the trip spring  212  of the first operating mechanism  200 . 
     Thus, the interlock pin  302  provided at the tip of the lever  301  constructing the second operating mechanism  300  is abutted against the outer circumferential surface of the roller  303 . Further counterclockwise rotation is prevented by return force of the trip spring  212 . That is, transition from the open position Y 2  for interrupting a load current or a fault current to the disconnected position Y 3  for ensuring the safety of inspecting personnel against surge voltage of lightening and the like is arrested. 
     Description will be given to the operation for transition from the open position Y 2  to the closed position Y 1  by the first operating mechanism  200  (making operation). 
     When the coil  209  of the electromagnet  205  of the first operating mechanism  200 , the driving shaft  206  is moved downward in  FIG. 7 . By this downward movement of the driving shaft  206 , the levers  202  are rotated clockwise in  FIG. 7  with the first shaft  201  taken as the fulcrum, and the movable contacts  82   a ,  82   b  are moved toward the closed position Y 1 . In this closed state, energy is accumulated in the trip spring  212  and the pressure contact spring, and these springs are ready for contact parting operation. 
     As the result of this making operation, the interlock pin  302  is parted from the outer circumferential surface of the roller  303 . The roller  303  does not change its position because of the return spring  311  of the second operating mechanism and is held in its initial position. 
     As mentioned above, the second operating mechanism  300  constructs a mechanical interlock mechanism so that the following is implemented to satisfy needs for enhanced safety: when the vacuum double-break three-position switch  8  is closed, isolating operation by the first operating mechanism  200  is disabled. That is, the following operation as one of mechanical interlocks between interruption and isolation is accomplished: “when a movable contact is in a closed position, isolating operation is disabled.” 
     Description will be given to the operation for transition from the closed position Y 1  to the open position Y 2  by the first operating mechanism  200  (contact parting operation). 
     When the coil  209  of the electromagnet  205  of the first operating mechanism  200  is excited in the opposite direction to the direction in making operation to cancel the magnetic flux of the permanent magnet  210 , the following takes place: the driving shaft  206  is moved upward in  FIG. 7  by the accumulated energy of the trip spring  212  and the pressure contact spring. By this upward movement of the driving shaft  206 , the lever  301  is rotated counterclockwise in  FIG. 7  through the lever  203  and the first shaft  201 . However, the counterclockwise rotation of the lever  301  is suppressed by the abutment between the interlock pin  302  of the second operating mechanism and the outer circumferential surface of the roller  303 . As a result, the movable contacts  82   a ,  82   b  of the vacuum double-break three-position switch  8  can be held in the open position Y 2 . 
     Description will be given to the operation for transition from the open position Y 2  to the disconnected position Y 3  by the second operating mechanism  300  (isolating operation). 
     When the upper coil  309  of the electromagnet  305  of the second operating mechanism  300  is excited with the vacuum double-break three-position switch  8  in the closed state, mentioned above, the driving shaft  306  is moved downward against the return spring  311 . The downward movement of the driving shaft  306  rotates the roller  303  clockwise in  FIG. 7  through the crank lever  304 . By the clockwise rotation of the roller  303 , the position of abutment between the roller  303  and the interlock pin  302  is shifted upward by the force of trip spring  212 . As a result, the operating rods  111  are moved downward through the lever  301 , first shaft  201 , and levers  202 , and the movable contacts  82   a ,  82   b  of the vacuum double-break three-position switch  8  are moved to the disconnected position Y 3 . 
     In this isolated state, the moving core  207  of the electromagnet  205  of the first operating mechanism  200  is positioned outside the coil  209 . For this reason, even if the coil  209  of the electromagnet  205  of the first operating mechanism  200  is excited in the isolated state, substantially no magnetic flux passes through the moving core  207  and attractive force is not produced. That is, the following operation as a mechanical interlock between a circuit breaker and a disconnector is accomplished: when a movable contact is in a disconnected position, making operation is disabled.” 
     Description will be given to the operation for transition from the disconnected position Y 3  to the open position Y 2  by the second operating mechanism  300 . When the upper coil  309  of the electromagnet  205  of the second operating mechanism  300  is excited in the isolated state, the following takes place: the roller  303  pushes downward the interlock pin  302  abutted against it by the downward movement of the driving shaft  206  and the counterclockwise rotation of the crank lever  304 . As a result, the movable contacts  82   a ,  82   b  of the vacuum double-break three-position switch  8  are moved to the open position Y 2 . 
     When the movable contacts  82   a ,  82   b  of the vacuum double-break three-position switch  8  are in the open position Y 2  for interrupting a current, the following takes place: the lever  414  of the second interlock mechanism is engaged with the pin  412  provided at the lower end of the driving shaft  406  of the electromagnet  405  of the third operating mechanism  400 . Therefore, it is disabled by the electromagnet  405  to close the movable contact  93  of the vacuum earthing switch  9 . 
     When the movable contact  93  is in contact with the fixed contact  92  of the vacuum earthing switch  9 , the lever  414  of the second interlock mechanism is engaged with the pin  412  provided at the upper end of the driving shaft  406  of the electromagnet  405 . Therefore, operation by the second operating mechanism  300  is disabled. Further, when the movable contacts  82   a ,  82   b  of the vacuum double-break three-position switch  8  are in the disconnected position Y 3  for ensuring the safety of inspecting personnel against surge voltage of lightening and the like, the following takes place: the lever  414  of the second interlock mechanism enables the movement of the pin  412  provided at the upper end of the driving shaft  406  of the electromagnet  405 . Therefore, the vacuum earthing switch  9  can be turned on by the third operating mechanism  400 . 
     In the above-mentioned embodiment, the rotatable roller  303  is used for the second operating mechanism  300 . A partly arc-shaped cam may be substituted for the roller  303 . The disposition of the first operating mechanism  200  and the third operating mechanism  400  may be changed as appropriate. In the above-mentioned embodiment, an electromagnetic operating system is applied to the first operating mechanism  200 . Instead, any other operating system, such as electric spring system, may be adopted. 
     In the above-mentioned embodiment of the invention, the vacuum double-break three-position switch  8 , which is the heaviest one of the devices housed in the enclosure  1 , and the operating device  11  are disposed as illustrated in  FIG. 1 . That is, they are disposed in the space lower than the intermediate portion of the enclosure  1  in the direction of height. Therefore, the center of gravity of the entire switchgear can be set low. As a result, the safety of transportation and installation work for the switchgear is enhanced, and if an earthquake happens, the installed switchgear is prevented from being toppled and the safety can be ensured. 
     In the above-mentioned embodiment of the invention, the vacuum double-break three-position switch  8  is disposed in the enclosure  1  so that its movable contacts  82   a ,  82   b  are positioned below its fixed contacts  81   a ,  81   b . In addition, the operating device  11  for operating the movable contacts  82   a ,  82   b  is also disposed at a lower level in the enclosure  1  in the direction of height in a lump. If the operating device  11  becomes faulty for some reason, therefore, the movable contacts  82   a ,  82   b  of the vacuum double-break three-position switch  8  are moved downward by their own weight and parted from the fixed contacts  81   a ,  81   b . Thus, a fail safe function is fulfilled, and the safety can be enhanced. 
     In the above-mentioned embodiment of the invention, the following measures are taken in addition to the above construction: the buses  5  are disposed above the vacuum double-break three-position switch  8 , and the vacuum double-break three-position switch  8  and the operating device  11  are disposed at a lower level. Therefore, no operating device is positioned near the joints of the buses  5 . This makes it possible to enhance the safety of work of connecting the buses  5 . 
     In the above-mentioned embodiment of the invention, the work of connecting a bus  5  to a bus joint is conducted as follows: the bus  5  is guided from a side of the enclosure  1  into the enclosure  1  and this bus  5  is pulled down from above the bus joint toward the bus joint. As illustrated in  FIG. 1 , the buses  5  and the bus joints are disposed above the vacuum double-break three-position switch  8 . Therefore, the buses  5  and the bus joints are positioned at the level of the worker&#39;s breast, and the worker can stably conduct bus connecting work without being required to be in stressful posture. When the front door  1   e  is opened, the low-voltage control section positioned on the back face of the front door  1   e  is moved together out of the enclosure  1 . Therefore, the working space for the above-mentioned bus connecting work can be ensured by an amount equivalent to the movement of the low-voltage control section. 
     A required number of pieces of switchgear are disposed in line before the above-mentioned bus connecting work is conducted. In the above-mentioned embodiment, since a bus connecting work can be conducted after the required switchgears being arranged in a state that each of the switchgears is provided with necessary components that have been subjected to routine tests, the reliability can be enhanced. 
     As mentioned above, the low-voltage control section positioned on the back face side of the front door  1   e  is unitized, and the low-voltage control section detachably attached to the back face of the front door  1   e . This makes it possible to easily check the low-voltage control section with ease during maintenance inspection. In addition, a protective relay and the like housed in the low-voltage control section can be easily replaced. 
     On the front face of the above-mentioned front door  1   e , as illustrated in  FIG. 4  and  FIG. 5 , the alarm display section lea is disposed at the level of workers&#39; eyes and the operating switch section  1   eb  including various operating switches is disposed at the level of workers&#39; hands. Therefore, workers can easily and efficiently conduct inspecting work. Further, the emergency manual handle operating section  1   ec  is disposed in a lower stage different from the stage of the operating switch section  1   eb  for normal operation. Therefore, the possibility that a worker manually operates it without careful consideration is minimized. 
     The above-mentioned emergency manual handle operating section  1   ec  is operated as illustrated in  FIG. 8 , for example. That is, the tip of a manual handle  900  is inserted into a hole  901  in the front door  1   e , and is screwed into a threaded portion  902  fixed on a side panel of the enclosure  1 . Thus, the conical tip of the manual handle  900  is abutted against the lower end of the coupling member  204  of the first operating mechanism  200  in the operating device  11 , and pushes the coupling member  204  upward. This makes the accumulated energy of the trip spring  212  and the pressure contact spring larger than the magnetic force of the permanent magnet  207  of the first operating mechanism  200 . As a result, the movable contacts  82   a ,  82   b  of the vacuum double-break three-position switch  8  are moved downward, and an open-circuit condition can be established. When the manual handle  900  is thereafter pulled out of the hole  901  in the front door  1   e , the operation can be completed. 
     In addition, as illustrated in  FIG. 1 , the voltage transformer  10  and the protection fuse  7  are disposed in the cable block  1   c  on the rear face side of the enclosure  1 . When the rear door if of the enclosure  1  is opened, therefore, the voltage transformer  10  and the protection fuse  7  can be easily inspected, and this enhances the working efficiency. 
       FIG. 9  illustrates another embodiment in which vacuum insulated switchgear of the invention is applied to a feeder panel. In  FIG. 9 , the members marked with the same reference numerals as in  FIG. 1  are those identical with or equivalent to those in  FIG. 1 , and the detailed description of them will be omitted. 
     This embodiment is so constructed that two cables  3  in the cable block  1   c  are pulled out to above the enclosure  1  and the voltage transformer  10  and the protection fuse  7  are disposed at the lower part in the cable block  1   c . The other constructions are the same as illustrated in  FIG. 1 . 
     According to this embodiment, the same effect as the above-mentioned embodiment can be obtained, and further the switchgear can be flexibly connected and installed in correspondence with a wiring pattern of a power cable on the installation site. 
       FIG. 10  illustrates a further embodiment in which vacuum insulated switchgear of the invention is applied to a feeder panel. In  FIG. 10 , the members marked with the same reference numerals as in  FIG. 1  are those identical with or equivalent to those in  FIG. 1 , and the detailed description of them will be omitted. 
     In this embodiment, one cable  3  is provided in the cable block  1   c  to cope with cases where an amount of power supply can be reduced. This cable  3  is pulled out to below the enclosure  1 , and the voltage transformer  10  and the protection fuse  7  are disposed at the lower part in the cable block  1   c . The other constructions are the same as illustrated in  FIG. 1 . 
     According to this embodiment, the same effect as the above-mentioned embodiments can be obtained, and further the switchgear can be flexibly connected and installed in correspondence with a wiring pattern of a power cable on the installation site, needless to add. Various amounts of power supply can be flexibly coped with. 
       FIG. 11  illustrates a further embodiment in which vacuum insulated switchgear of the invention is applied to a feeder panel. In  FIG. 11 , the members marked with the same reference numerals as in  FIG. 1  are those identical with or equivalent to those in  FIG. 1 , and the detailed description of them will be omitted. 
     In this embodiment, one cable  3  is provided in the cable block  1   c  to cope with cases where an amount of power supply can be reduced as in the embodiment illustrated in  FIG. 10 . This cables  3  is pulled out to above the enclosure  1 , and the voltage transformer  10  and the protection fuse  7  are disposed at the lower part in the cable block  1   c . The other constructions are the same as illustrated in  FIG. 1 . 
     According to this embodiment, the same effect as the embodiment illustrated in  FIG. 10  can be obtained. 
     In the above-mentioned embodiments, the voltage transformer  10  and the protection fuse  7  are provided in the cable block  1   c . However, they may be omitted as required.