Patent Publication Number: US-8975550-B2

Title: Switch unit and switchgear

Description:
CLAIM OF PRIORITY 
     The present application claims priority from Japanese Patent application serial No. 2011-895, filed on Jan. 6, 2011, the content of which is hereby incorporated by reference into this application. 
     TECHNICAL FIELD 
     The present invention relates to a switch unit and switchgear. 
     BACKGROUND ART 
     A power receiving facility has an enclosed switchboard (called switchgear) that houses a circuit breaker for interrupting a load current or fault current, a disconnector and an earth switch that assure safety for a worker during maintenance of a load, a detector for detecting a system voltage and current, and all or part of other devices such as a protective relay. 
     Switchgear is often installed in a limited space and is thereby required to be compact. Since a switch unit including switches such as breakers occupies a large volume in the switchgear, it is desirable to make the switch unit compact when the size of the switchgear is determined. 
     A conventional switch is described in, for example, Patent Literature 1. In FIG. 2 of Patent Literature 1, two contact portions are linearly provided in the vertical direction; two moving contact rods are also provided in the vertical direction; and contact disks are provided between the upper and lower moving contact rods. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: Patent Application Publication No. 2009-508294 (Corresponding Publications: US2008/0245772A1) 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     In the structure described in FIG. 2 of Patent Literature 1, however, the contact disks provided on the fixed contact piece are electrically connected to each other, so buses and cables are decentralized and the high-voltage part becomes large, making it difficult to reduce the size of the switch unit. In view of this situation, an object of the present invention is to provide a switch unit or switchgear that can be made to be compact. 
     Solution to Problem 
     To solve the above problem, the switch unit according to the present invention has a plurality of linearly arranged switches, in which a movable electrode in a switch and a fixed electrode in another switch are electrically connected to each other. 
     The switchgear according to the present invention has the above switch unit, a bus connected to the switch unit, a cable connected to the switch unit, and a cabinet in which at least part of these components are accommodated. 
     Advantageous Effects of Invention 
     The present invention can provide a switch unit or switchgear that can be made to be compact. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a side view that partially illustrates a cross section in an embodiment of the present invention. 
         FIG. 2  is a rear view in the embodiment of the present invention. 
         FIG. 3  is a cross sectional view of a mold switch in the embodiment of the present invention in  FIG. 1 . 
         FIG. 4  is a side view that partially illustrates a cross section in another embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Preferable embodiments in the present invention will be described below with reference to the drawings. The embodiments described below are just examples that embody the present invention, and do not limit the present invention to specific aspects of the following embodiments. 
     First Embodiment 
     A first embodiment will be described with reference to  FIGS. 1 to 3 . 
     As shown in  FIG. 1 , the switchgear  1  is substantially structured with a mold switch  2  equivalent to a switch unit, a bus  80  through which electric power is supplied from a power system to the mold switch  2 , a cable  90  through which electric power is supplied from the mold switch  2  to a load, manipulation units  5  and  6  that operate switches in the mold switch  2 , linkage units  51  and  61  that link the switches in mold switch  2  to the manipulation units  5  and  6 , and a cabinet  21  that encloses these components. Note that  FIG. 1  shows the components only for 1 phase, however, as shown in  FIG. 2 , the components having the same structure are arrayed for 3 phases while changing the height of the buses in the switchgear  1 . 
     As shown in  FIG. 3 , the mold switch  2  is formed by integrally molding, with an epoxy resin  10 , a vacuum insulated switch  3  having a function of closing and interrupting a current, an air insulated switch  4  that is switchable among three positions, which are a closed position, a disconnected position, and a grounded position, a voltage detector  7  for measuring a voltage to be applied to a load side, a bus connecting bushing  8  connected to the bus  80 , and a cable connecting bushing  9  connected to the cable  90 , through which a current is supplied to the load. The vacuum insulated switch  3  and air insulated switch  4  are linearly disposed. 
     Each component will be described in detail. The vacuum insulated switch  3  has a vacuum case  30  formed by mutually connecting a fixed-side ceramics insulative tube  30   b , a movable-side ceramics insulative tube  30   a , a fixed-side end plate, and a movable-side end plate; the vacuum case  30  includes a fixed-side electrode  31 , a movable-side electrode  32 , a fixed-side conductor  22  connected to the fixed-side electrode  31 , a movable-side conductor  34  connected to the movable-side electrode  32 , and an arc shield  36  that protects the ceramics insulative tubes  30   a  and  30   b  from arcs generated when the electrodes are opened and closed. The movable-side conductor  34  extends outwardly of the vacuum case  30  through a metal bellows  35  and is connected to a central bushing conductor  33  for cable connection through a flexible conductor  11  to supply electric power from a bus side to the load side. The movable-side electrode  32  is also connected to an insulative manipulation rod  52 , so a manipulation force generated at the manipulation unit  5  is transmitted through the linkage unit  51  to the insulative manipulation rod  52 . 
     The air insulated switch  4 , which is connected to a central bushing conductor  23  for bus connection, includes a fixed electrode  40  connected to the bus side through the central bushing conductor  23 , a ground-side fixed electrode  42  connected to ground, and an intermediate fixed electrode  41  disposed at an intermediate position between the fixed electrode  40  and the ground-side fixed electrode  42  in their axial direction, which functions as a guide for a movable electrode  43  and is electrically connected to the fixed-side conductor  22  in the vacuum insulated switch  3  through a connection conductor  44 . The interior of the air insulated switch  4  is air-insulated. All these fixed electrodes have the same inner diameter and are linearly disposed. When the movable electrode  43  linearly moves among these fixed electrodes in the air insulated switch  4 , a switchover among the three positions, which are the closed position, disconnected position, and grounded position, becomes possible. The movable electrode  43  is linked to an air-insulated manipulating rod  62 . The air-insulated manipulating rod  62  is connected to the manipulation unit  6  through a linking device  61 . Accordingly, the air-insulated manipulating rod  62  can be operated by the manipulation unit  6 . Since spring contacts  24  are provided at portions with which the fixed electrodes come into contact, contacts are reliably formed due to elastic forces without impeding the movement of the movable electrode  43 . 
     As described above, the vacuum insulated switch  3  is a switch disposed on the load side, and the air insulated switch  4  is a switch disposed on the bus side. 
     Electric connection between the vacuum insulated switch  3  and the air insulated switch  4  will be described. The intermediate fixed electrode  41  is always in contact with the movable electrode  43 , regardless of the position of the movable electrode  43 , so the intermediate fixed electrode  41  and movable electrode  43  always have the same potential. Since the intermediate fixed electrode  41  is electrically connected to the fixed-side conductor  22  in the vacuum insulated switch  3 , the movable electrode  43 , which is always at the same potential as the intermediate fixed electrode  41 , is also electrically connected to the fixed-side conductor  22  in the vacuum insulated switch  3 . However, the fixed-side conductor  22  and fixed electrode  40 , which are placed close to each other, are insulated from each other due to solid insulation provided by the epoxy resin  10 . 
     The bus connecting bushing  8  is formed by covering the circumference of the central bushing conductor  23  for bus connection with the epoxy resin  10 , and the cable connecting bushing  9  is formed by covering the circumference of the central bushing conductor  33  for cable connection with the epoxy resin  10 . The voltage detector  7  for measuring the potential of the load side is provided in the cable connecting bushing  9  in such a way that the voltage detector  7  is electrically connected to the central bushing conductor  33  for cable connection that passes through the interior of the cable connecting bushing  9 . These two types of bushings are disposed on the same plane at the same side. The cable connecting bushing  9  is longer than the bus connecting bushing  8 . 
       FIG. 2  is a rear view of the two-panel switchgear  1  structured by placing two panels side by side; the bus connecting bushings  8  disposed on each panel are mutually connected with the bus  80 . Although, in this embodiment, each cable  90  is drawn through the relevant cable connecting bushing  9  downwardly on the drawing sheet to supply electric power to the unit used as the load, the cable  90  can also be drawn upwardly on the drawing sheet by making the cable connecting bushing  9  longer than the bus connecting bushing  8 . 
     The vacuum insulated switch  3  is operated by the electromagnetically operated manipulation unit  5 , which is a first manipulation unit, through the linkage unit  51 . A switchover among the three positions in the three-position air insulated switch  4  is carried out by the motor-driven manipulation unit, which is a second manipulation unit  6 , through the linkage unit  61 , the three positions being a closed position for supplying electric power, a disconnected position for protecting a maintenance worker from a surge voltage due to, for example, lightning and assuring safety for the worker, and a ground preparation position for grounding. 
     Although the first manipulation unit  5  is electromagnetically operated and the second manipulation unit  6  is driven by a motor, it is also possible to operate these manipulation units by other operating systems, for example, the motor charged spring stored energy system. 
     The closing, interrupting, disconnecting, and grounding operations of the mold switch  2  will be described. 
     The state in  FIG. 1  is a closing state. 
     To shift from the closing state to an interrupting state, the manipulation unit  5  is manipulated so that the insulative manipulation rod  52  is moved away from the fixed-side electrode  31  through the linkage unit  51 . The movable-side electrode  32  disposed at the end of the insulative manipulation rod  52  so as to face the fixed-side electrode  31  is then separated from the fixed-side electrode  31 , causing the interrupting operation in the vacuum insulated switch  3 . 
     A disconnecting operation is carried out next. A shift from the closing state to the disconnecting state is carried out after the interrupting operation has been completed. In this case, the manipulation unit  6  is manipulated so that the air-insulated manipulating rod  62  in the air insulated switch  4  is moved away from the fixed electrode  40  through the linkage unit  61 . An inter-electrode distance between the movable electrode  43  and the fixed electrode  40  and another inter-electrode distance between the spring contact  24  attached to the movable electrode  43  and the fixed electrode  40  are then prolonged, shifting to the disconnecting state, in which the spring contact  24  is moved to a position at which the spring contact  24  is not placed in contact with the ground-side fixed electrode  42  or the fixed electrode  40 . The switch unit in this embodiment has a double disconnection structure in which the state between the electrodes in the vacuum insulated switch  3  is the interrupting state and the air-insulated manipulating rod  62  is placed in the disconnecting state. The inter-electrode distances between the movable electrode  43  and the fixed electrode  40  and between the spring contact  24  attached to the movable electrode  43  and the fixed electrode  40  are preferably longer than the inter-electrode distance in the vacuum insulated switch  3  at the interrupting position so that even if, for example, the vacuum insulated switch  3  causes a vacuum leak, the reliability of the disconnecting state is not lowered. 
     The disconnecting state is then shifted to a grounding state. In the shift to the grounding state, the manipulation unit  6  is first manipulated after the above disconnecting operation has been completed so that the air-insulated manipulating rod  62  in the air insulated switch  4  is further moved away from the fixed electrode  40  through the linkage unit  61  until the spring contact  24  on the same side as the air-insulated manipulating rod  62  comes into contact with the ground-side fixed electrode  42 . Accordingly, the ground-side fixed electrode  42  is electrically connected to the spring contact  24 , movable electrode  43 , intermediate fixed electrode  41 , connection conductor  44 , fixed-side conductor  22 , and fixed-side electrode  31  in that order, causing these components to have the ground potential. That is, the inter-electrode potential in the vacuum insulated switch  3  is a difference between the ground potential applied to the fixed-side electrode  31  and the load-side potential applied to the movable-side electrode  32 , so the load side is not grounded at that time. 
     The manipulation unit  5  is manipulated in this state so that the insulative manipulation rod  52  is moved toward the fixed-side electrode  31  through the linkage unit  51  until the movable-side electrode  32  disposed at the end of the insulative manipulation rod  52  facing the fixed-side electrode  31  comes into contact with the fixed-side electrode  31 . Accordingly, the fixed-side electrode  31  and movable-side electrode  32  are electrically connected to each other and thereby the load side is grounded, completing the grounding operation. 
     The operations from the closing state to the grounding state do not always need to be performed. To shift from the closing state to the interrupting state or to the disconnecting state, for example, it suffices to stop at the time when the interrupting state or disconnecting state is entered. In addition, to shift from the grounding state to the closing state through the disconnecting state and interrupting state (including partial shifts such as a shift from the disconnecting state to the closing state, besides the complete shift from the grounding state to the closing state), the above procedure may be reversed. 
     In this embodiment, since the vacuum insulated switch  3  and air insulated switch  4  are structured so that a movable electrode in one switch and a fixed electrode in the other switch are electrically connected to each other, the bus and cable, which have a high voltage, are centralized rather than being distributed to the ends of the mold switch  2 , enabling the mold switch  2  to be made to be compact. Since the switches are centralized in the axial direction, it is of course possible to make the mold switch  2  substantially compact in directions other than the axial direction. Furthermore, since the mold switch  2  occupies a large volume in the entire switchgear, the entire switchgear can also be made to be compact. 
     In addition to the electrical connection between a movable electrode in one switch and a fixed electrode in the other switch, a fixed electrode in the one switch and the fixed electrode in the other switch are isolated from each other. Therefore, even in a case in which the movable electrode in the one switch and the fixed electrode in the other switch are electrically connected to each other, a dielectric breakdown can be prevented. In a specific aspect of insulation in this embodiment, the epoxy resin  10  is used for solid insulation. Since resin molds such as the epoxy resin  10  are highly insulative and the insulation distance can thereby be shortened, the two switches can be brought close to each other in the axial direction. In an aspect in which a plurality of switches that tend to become large in the axial direction are placed in the axial direction, therefore, this embodiment can prevent the entire switchgear from becoming large and is thus advantageous. 
     In this embodiment, four circuit conditions for closing (current supply), interrupting (shutdown), disconnecting, and grounding are created according to the combination of the vacuum insulated switch  3  and three-position air insulated switch  4 . Performance for closing, interrupting, and grounding is centrally achieved by the vacuum insulated switch  3 , and performance for energization and isolation is achieved by the two switches, vacuum insulated switch  3  and three-position air insulated switch  4 , simplifying the structure, providing insulation at a plurality of stages, and assuring safety and reliability. Even if a two-position air insulated switch is used instead of the three-position air insulated switch  4 , insulation to ground at the disconnected position is provided at only one stage but the same advantage as with the three-position air insulated switch  4  can be obtained. 
     Since, in this embodiment, a plurality of switches is axially placed, the mold switch  2  can be formed in a substantially cylindrical shape (the bushings connected to the bus  80  and cable  90  are excluded). When the plurality of switches are placed in the switchgear  1 , therefore, the size of the switchgear  1  can be reduced in directions other than the axial direction of the mold switch  2 , making the switchgear  1  compact and lightweight. In addition, the structure of the mold switch  2  itself is rotationally symmetrical, enabling productivity to be improved. 
     Conductors are placed parallel to, for example, the vacuum insulated switch  3 . When a current is passed in the conductors in the same direction as in the vacuum insulated switch  3  or in the reverse direction, an electromagnetic force is generated between the vacuum insulated switch  3  and the conductors in the suction direction or repulsion direction. To interrupt the current passing through the vacuum insulated switch  3 , a method is used by which arcs generated between the electrodes at the time of interrupting the current are extinguished by generating a vertical magnetic field between the electrodes. Another interrupting method is to move the arcs on the circumferences of the electrodes so that the arcs are distributed and extinguished. Since the electromagnetic force generated between the vacuum insulated switch  3  and the conductors is horizontally exerted on the arcs, however, the magnetic field between the electrodes may be changed and the interrupting performance may be lowered. When conductors are placed parallel to a vacuum insulated switch, the conventional practice is to leave a distance therebetween so that the magnetic field between the electrodes is not affected when the current is interrupted. In this embodiment, however, insulation of the vacuum insulated switch  3  and insulation of the air insulated switch  4  are independent, and a horizontal electromagnetic force is not exerted on arcs generated when a current is interrupted by the vacuum insulated switch  3 , thereby improving reliability. 
     Since a plurality of switches to be integrally molded are coaxially placed, the insulation structure of the plurality of switches becomes simple, so the spacing between the plurality of switches is not increased unnecessarily, enabling the thickness of the epoxy resin to be reduced. As a result, heat can be efficiently dissipated and the amount of resin to be used can be reduced. 
     Since the cable connecting bushing  9  and the bus connecting bushing  8  are placed on the same plane and on the same side, work operations can be performed for the switchgear  1  in one direction, improving workability during installation and maintenance. 
     Since the cable connecting bushing  9  is longer than the bus connecting bushing  8 , it is possible to flexibly meet various specifications according to the installation environment of the user, such as a direction in which the cable  90  connected to the load are drawn and a two-stage structure of the buses  80 . 
     As described above,  FIG. 2  illustrates a rear view of the switchgear structured by placing two panels side by side; the bus connecting bushings  8  disposed on each panel of the two-panel switchgear are mutually connected with the bus  80 , as an example; each cable  90  is drawn through the relevant cable connecting bushing  9  downwardly on the drawing sheet to supply electric power to the unit used as the load. However, the cable  90  can also be drawn upwardly on the drawing sheet by making the cable connecting bushing  9  longer than the bus connecting bushing  8 . 
     Although the bus connecting bushing  8  may of course be longer than the cable connecting bushing  9 , it is advantageous to freely wire the cables to be connected to the load to meet user requirements according to the installation environment of the user, so the cable connecting bushing  9  is made to be longer than the bus connecting bushing  8  to prevent the bus from interfering with the cable. If the cable connecting bushing  9  and the bus connecting bushing  8  are rotatably connected by, for example, using a T-shaped cable head, a direction in which the cables are drawn can be more advantageously adjusted at a site at which the switchgear is installed. 
     Second Embodiment 
     A second embodiment will be described with reference to  FIG. 4 . In this embodiment, a mold switch  102  is used, which is identical to the mold switch  2  used in the first embodiment, but is vertically reversed. To conform to this arrangement, the positions of manipulation units  105  and  106 , corresponding to the manipulation units  5  and  6 , are also vertically reversed as compared with the first embodiment, and the positions of linkage units  151  and  161 , corresponding to linkage units  51  and  61 , are also vertically reversed as compared with the first embodiment. The other components are the same as in the first embodiment, so duplicate descriptions will be omitted. 
     Even if the mold switch  102 , which is vertically reversed, is used as in this embodiment, the same effect as in the first embodiment described above can be obtained. 
     In the above embodiments, the fixed-side electrode in the vacuum insulated switch  3  and the movable electrode in the air insulated switch  4  connected to the bus side are electrically connected to each other, the vacuum insulated switch  3  and air insulated switch  4  being linearly disposed, and the bus  80  are placed near the center of the panel. Even if a need to vertically reverse the mold switch arises to meet user requirements or for some other reason, since the bus  80  remain near the center of the panel, workability is not largely changed. If the cable can be drawn upwardly and downwardly, the wiring of the cable is not impeded regardless of the positions of the cable connecting bushing  9 . 
     Since, in the above embodiments, the movable electrode in the air insulated switch  4 , which is connected to the bus side and has closing and grounding functions, and the fixed-side electrode in the vacuum insulated switch  3  are electrically connected to each other, even if a plurality of switches are coaxially and linearly disposed, a circuit can be formed in which a switch on the bus side has a grounding function and only a switch on the load side has an interrupting function. When a plurality of switches are linearly arranged, they are usually placed, due to a limitation on space, so that movable electrodes in the plurality of switches move away from each other. In this case as well, to have the switch on the bus side have a grounding function, it is necessary to connect the movable electrode in the switch on the bus side, rather than the fixed-side electrode, to the switch on the load side. This structure not only provides the above effect obtained from the linear arrangement but also eliminates the need for the switch on the bus side to have interrupting characteristics, simplifying the structure. 
     Furthermore, since the air insulated switch  4  has a disconnecting function as well, there is no need to provide a disconnector separately, further simplifying the structure and contributing to compactness. 
     When the present invention is implemented, each switch is not limited to a particular insulation method such as air insulation, vacuum insulation, or gas insulation. If an insulation method providing good insulation performance, such as vacuum insulation, is used, a further effect of contributing to compactness can be obtained.