Patent Publication Number: US-7223932-B2

Title: Vacuum Switchgear

Description:
This is a continuation application of U.S. Ser. No. 10/845,110, filed May 14, 2004 now U.S. Pat. No. 7,135,652. 

   CLAIM OF PRIORITY 
   The present application claims priority from Japanese application serial No. 2003-140761, filed on May 19, 2003, the content of which is hereby incorporated by reference into this application. 
   DETAILED DESCRIPTION OF THE INVENTION 
   1. Technical Field of the Invention 
   The present invention relates to a vacuum switchgear, and more particularly to a vacuum switchgear provided with a plurality of switches in a vacuum container, which is suitable for a power distribution-transmission system. 
   2. Related Art 
   As one of components for a power distribution-transmission system, the distribution system has a switchgear. Air insulation type switchgears have been used for the distribution-switches; gas insulation type switchgears using SF 6  gas as an insulation medium have become used so as to downsize the system. However, the gas insulation type switchgears may give an adverse affect on environment; vacuum type switchgears have recently been proposed. 
   As switchgears of vacuum insulation type, a plurality of main circuit switches each comprising a movable electrode, a fixed electrode disposed to face the movable electrode is disposed in a vacuum container, wherein the movable electrode is connected to a conductor of a bus, and the fixed electrode is connected to a load conductor. Each of the electrodes of the main bus switches is covered with a shield, and each of the buses is connected by means of a flexible conductor as disclosed in Japanese Patent Laid-open 2000-268685. The content of the publication may be incorporated into the part of the present specification. 
   In the above mentioned art, since each of the main switches is covered with an arc shield, a trip action is performed at the time of a short-circuit accident, for example. Thus, when the movable electrode and the fixed electrode are separated, generated metallic vapor is shielded by the arc shield. However, since part of the metallic vapor may disperse or scatter through the gap between the arc shields to adhere or deposit on the vacuum container, it has been tried to form a dual vacuum container to prevent the scattering or dispersing of metallic vapor. 
   If the inner vacuum container is closed from or not communicated with the outer vacuum container, the vacuum degree or vacuum pressure of the inner vacuum container where the movable electrodes and fixed electrode are disposed may temporarily drop due to gases evolved from the melted electrodes. The gasses may be contained in the materials of the switchgear such as electrodes, shields, etc. Therefore, it is necessary to enlarge the volume of the inner vacuum container so as to maintain desired insulation resistance. As the number of switching operation time increases, the vacuum degree hardly recover to the predetermined value. As a result, the insulation resistance will decrease. If the volume of the inner vacuum container is enlarged, the size of the vacuum switchgear enlarges. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a vacuum switchgear, which can be downsized, keeping desired insulation resistance. One aspect of the vacuum switchgear according to the present invention comprises an outer vacuum container made of or having an electro-conductive material, a plurality of inner vacuum container insulated from the outer vacuum container, a plurality of switches each being disposed in each of the inner vacuum containers, wherein the outer vacuum containers and the inner vacuum containers are communicated with through-holes formed in the walls of the inner vacuum containers. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is an elevational cross sectional view of the vacuum switchgear of an embodiment according to the present invention. 
       FIG. 2  is a cross sectional view of a main part of the switch used in the embodiment shown in  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Before describing the embodiments in details, several aspect of the present invention will be explained. 
   At first, another aspect of the present invention provides a vacuum switchgear comprising an electro-conductive outer vacuum container, a plurality of inner containers disposed in the outer vacuum container, the inner containers and the outer container being electrically isolated from each other. The outer container is made of stainless steel plate, for example. 
   One of the inner vacuum containers accommodates a ground switch for keeping the circuit open while the switchgear is opened, having a movable electrode connected to an operating mechanism, and a fixed electrode connected to fixed electrode rod. Another inner vacuum container accommodates a function switch capable of having at least one of functions of a circuit breaker for breaking a circuit at the time of accident, a disconnector for disconnecting the circuit at the time of opening the circuit and a load switch for switching the circuit with a load. 
   A plurality of electrode shields each surrounds the movable electrodes and fixed electrodes of the ground switch and of the function switch. The ground switch and the function switch are disposed separately in separate vacuum inner containers. The outer vacuum container and the inner containers are communicated by means of through-holes formed in the walls of the inner vacuum containers. 
   The through-holes are formed in at least one of the top and bottom walls of the inner vacuum containers in such a manner that leaking out or scattering of metallic vapor generated at the time of separation of the electrodes into the outer container is prevented by the shields. 
   The outer vacuum container of the vacuum switchgear is earthed while it is in the circuit or in service. 
   Each of the movable electrodes of the ground switch and the function switch is connected to a respective operation mechanism (electro-magnetic operator) outside of the outer vacuum container, and wherein each of the fixed electrodes is connected to a cable outside of the outer vacuum container. Since the movable electrode is connected to the operation mechanism which is disposed outside of the vacuum container is well known in the art, the explanation of the operation mechanism is omitted in order to avoid redundancy of the specification. This is the same as cables to which the fixed electrodes are capable of being connected. 
   Each of the inner vacuum containers is constituted by an insulating hollow body surrounding the movable electrode and the fixed electrode, a top member connected in movement relation to the movable electrode, and a bottom member connected in fixed relation to the fixed electrode. 
   Still another aspect of the present invention relates to a vacuum switchgear comprising an outer vacuum container being electrically conductive to be earthed, a plurality of inner containers disposed in the outer container, the inner containers and outer container being electrically isolated from each other, and a plurality of switches disposed in the inner container each having a movable electrode with an electrode and a fixed electrode, wherein each of the movable electrodes is connected to an operation mechanism outside of the outer vacuum container, the fixed electrode is connected to a cable outside of the outer vacuum container, and each of the inner containers is communicated with the outer vacuum container by a through-hole disposed in the wall of the inner vacuum container. 
   Part of the electrode shield is located within an area confined by a straight line connecting the outermost edge of the movable electrode and the through-hole and a straight line connecting the outermost edge of the fixed electrode and the through-hole. According to this structure, the scattering of metal vapor into the outer vacuum container is effectively prevented. 
   The outer vacuum container is provided with an opening to be connected to a vacuum pressure monitor so that the vacuum degree of the inner vacuum container can rapidly recover to a predetermined value. 
   The switches are a ground switch for grounding the vacuum switchgear while in opening and at least two function switches selected from a circuit breaker for breaking a circuit at an accident or the like, and a disconnector switch for disconnecting the circuit for a certain period of time. 
   The function switches are the circuit breaker, the disconnector and a load switch for switching the vacuum switchgear from the load conductor. 
   In the following, the embodiments of the present invention will be explained in detail by reference to the drawings. 
   In  FIG. 1 , the vacuum switchgear comprises an outer vacuum container  10  as one element for a power distribution-transmission system. The container may be made of an electro-conductive material such as stainless steel plate. The outer vacuum container  10  is constituted by an upper plate member  12 , a lower plate member  14  and a side plate member  16 . The peripheries of these members are united by a suitable manner such as welding. 
   The outer casing can be earthed when the switchgear is in service. Thus, the maintenance or inspection of the switchgear can be conducted with safety and ease, because operators or inspection staffs can work near the switchgear or they can even touch it. 
   The upper plate member  12  has through-holes  18 ,  20 ,  22 . Each of the through-holes  18 ,  20 ,  22  is provided with an annular base  24 ,  26 ,  28 , which is fixed to each of the inner peripheries of the through-holes. There are spaces within the annular bases, where columnar movable electrode rods  30 ,  32 ,  34  are fitted in such a manner that the electrode rods are reciprocally moved up and down by means of bellows  36 ,  38 ,  40 . One end of each of the bellows is fixed to the upper plate member. The other end of the bellows is fixed to the movable electrode rod. One end of each of the electrode rods is capable of being connected to an operation mechanism (not shown), which drives the rods in response to signals given by a control apparatus (not shown) Thus, the outer vacuum container is air-tightly sealed. 
   A vacuum evacuator (not shown) can be connectable to the upper plate member of the outer vacuum container  10 , for example. 
   There may also be formed through-holes  42 ,  44 ,  46  in the lower plate member  14  to which insulating bushings  48 ,  50 ,  52  are fixed. Insulating bushings  48 ,  50 ,  52  are fixed to the peripheries of the through-holes  42 ,  44 ,  46 . Insulating bushings  48 ,  50 ,  52  air-tightly seal the through-holes  42 ,  44 ,  46  and fixed electrode rods  60 ,  62 ,  64  with insulating bases  54 ,  56 ,  58 . One end of each of the fixed electrode rods  60 ,  62 ,  64  is connected to a cable or distribution line (not shown). 
   The side plate member  16  is provided with an aperture  66 , which is communicated with a vacuum pressure monitor  68  by which the vacuum pressure or the degree of vacuum in the outer vacuum container  10  is always monitored. 
   There are inner vacuum containers  70 ,  72 ,  74  in which switches  88 ,  90 ,  92  are disposed in the respective inner vacuum containers. In this embodiment, the three switches  88 ,  90 ,  92  constitute a desired function of the vacuum switchgear. That is, there are a ground switch or earthing switch, a circuit breaker and a load switch. If necessary, an additional switch such as a disconnector switch is added. The circuit breaker interrupts circuit at an accident to protect the circuit. The load switch switches the power line and a load. The disconnector switch switches off the circuit from the power line, while the circuit is open. 
   The inner vacuum containers  70 ,  72 ,  74  are constituted by cylindrical insulators  76 ,  78 ,  80 ,  82 ,  84 ,  86  surrounding the movable electrodes and fixed electrodes, top plate members  88 ,  90 ,  92 , and bottom plate members  94 ,  96 ,  98 . Top plate members  88 ,  90 ,  92  are connected to the movable electrodes  30 ,  32 ,  34  by means of bellows  106 ,  108 ,  110 . One end of the bellows  106 ,  108 ,  110  is connected to the top plate member  88 ,  90 ,  92  and the other end is connected to the movable electrode rod  30 ,  32 ,  34 . The top plate members have through-holes  100 ,  102 ,  104  through which the inner vacuum containers communicate with the outer vacuum container. The bottom plate members may also have through-holes. The top plate members and the bottomplate members are made of an electro-conductive material such as stainless steel plate. 
   Cylindrical electrode shields  112 ,  114 ,  116  made of stainless steel, for example, surround the movable electrodes  118 ,  120 ,  122  and the fixed electrodes  124 ,  126 ,  128 . The middle portions of the shields are supported by the insulating shields  76 ,  78 ,  80 ,  82 ,  84 ,  86 . That is, the electrode shields  112 ,  114 ,  116  are so disposed as to prevent metal vapor from scattering or dispersing to outside of the cylindrical shields  112 ,  114 ,  116 . Further, the movable electrodes  118 ,  120 ,  122  are fixed to the movable electrode rods  30 ,  32 ,  34  at the ends thereof in the axial direction. 
   The through-holes  100 ,  102 ,  104  formed in the metal plates  88 ,  90 ,  92  have such a size that metal vapor generated in the movable electrodes  118 ,  120 ,  124  and the fixed electrodes  124 ,  126 ,  128  in interrupting or switching off the current does not scatter from the inner vacuum container into the outer vacuum container  10 . In interrupting current, if the vacuum degree of the inner vacuum containers decreases temporarily, the size of the through-holes formed in the top or bottom plates  88 ,  90 ,  92 ,  94 ,  96 ,  98  have such s size that the vacuum degree of the inner vacuum container immediately recovers. 
   In forming the through-holes  100 ,  102 ,  104  in the metal plates  88 ,  90 ,  92 , the size and shape of the through-holes are determined by the electrode shields  112 ,  114 ,  116 , as shown in  FIG. 2 . In  FIG. 2(   a ), the inner vacuum container is constituted by a cylindrical insulation shield  78 , a movable electrode side metal plate  88  and a fixed electrode side metal plate  94 . The inner container covers the movable electrode  118 , fixed electrode  124 , and the bellows  106  as well. The electrodes  118 ,  124  are covered with an electrode shield  112 . The movable electrode side metal plate has a through-hole that communicates with the outer vacuum container. In  FIG. 2(   b ), the structure of the inner vacuum container is the same as that in  FIG. 2(   a ), except that a bellows  106  is outside of the inner vacuum container. That is, the electrode shields are preferably disposed within an area defined by a line connecting the outer peripheries of the movable electrodes and the through-holes  100 ,  102 ,  104  and broken-lines connecting the outer peripheries of the fixed electrodes  124 ,  126 ,  128  and the through-holes  100 ,  102 ,  104 . By this arrangement, the metal vapor and/or electrons do not scatter from the inner vacuum containers  70 ,  72 ,  74  into the outer vacuum container  10  through the through-holes in interrupting current. Since the metal vapor and electrons travel in a straight direction, the above-mentioned structure can prevent scattering and/or leaking of the metal vapor and/or electrons. 
   Since the vacuum degree in the inner vacuum containers can recover immediately after interruption of current, the reduction in insulation resistance or interruption performance can be avoided. Accordingly, if interrupting current becomes large, it is possible to improve interruption performance without enlarging the volume of the inner vacuum containers  70 ,  72 ,  74 . The vacuum degree of the outer vacuum container  10  and the inner vacuum containers can be kept equal; the vacuum degree of the outer and inner containers is monitored by the vacuum degree monitor  68 . 
   In the above mentioned embodiment, bellows  106 ,  108 ,  110  are disposed in the inner vacuum containers  70 ,  72 ,  74 .  FIG. 3  shows another embodiment wherein bellows are disposed outside of the inner vacuum containers, keeping air-tightness of the inner vacuum containers. According this structure, the volume of the inner vacuum containers can be made minimum. 
   The through-holes  88 ,  90 ,  92  can be formed in the lower plate members  94 ,  96 ,  98 . The through-holes  100 ,  102 ,  104  can be shaded by a suitable plates or members so as to surely prevent scattering of metal vapor and/or electrons.