Patent Publication Number: US-7902479-B2

Title: Vacuum switchgear

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a vacuum switchgear used in a power receiving and distribution apparatus that receives power from a bus and distributes the received power to various types of electric devices, a cubicle-type insulated switching apparatus, or the like. 
     2. Prior Art 
     A power receiving and distribution apparatus that receives power from a bus and distributes the received power to various types of electric devices, for example, accommodates in a container bus-side conductors connected to the bus, load-side conductors connected to loads, a main circuit switch for connecting the bus-side conductors to the load-side conductors and disconnecting them from the load-side conductors, and ground switches for grounding the load side conductors. 
     In an exemplary power receiving and distribution apparatus of this type, the above devices etc. are disposed in a superiorly insulated container under vacuum in order to reduce the size of the apparatus and increase the stability of installation, as disclosed in Patent Document 1. 
     In another power receiving and distribution apparatus, its main circuit switch is configured as a vacuum valve, and the vacuum valve and devices connected to it are molded with epoxy resin or another insulating material in order to reduce the number of parts to be assembled and improve an installation thereof, as disclosed in Patent Document 2. 
     Patent Document 1: Japanese Application Patent Laid-open Publication No. 2000-268685 
     Patent Document 2: Japanese Application Patent Laid-open Publication No. 2003-333715 
     SUMMARY OF THE INVENTION 
     Vacuum switchgears as described above are required to be highly reliable, compact, and inexpensive. To meet these requirements, various switchgears as described in Patent Documents 1 and 2 above are proposed. 
     Reliability as well as compactness and inexpensiveness of the vacuum switchgear are mutually conflicting requirements. Specifically, if an attempt is made to further increase the reliability (safety), expensive material have to be used, resulting in a high cost. Consequently, the problem with the compactness and inexpensiveness is not solved. If an emphasis is placed on compactness and inexpensiveness, the quality is lowered and the reliability may be sacrificed. The vacuum switchgear described in Patent Document 1 is designed to meet the conflicting requirements for reliability as well as compactness and inexpensiveness. However, epoxy resin or another insulating material used for molding may be exposed to a severe environment, in which case deterioration by aging is unavoidable. 
     If the insulating material such as epoxy resin is deteriorated as described above, its insulating property is lowered, possibly causing a ground fault. To prevent the ground fault, the insulating material has to be thick enough to withstand years of service. This increases the amount of insulating material used, resulting in a high cost. Vacuum switchgears at present still need improvement in terms of reliability, compactness, and inexpensiveness. 
     The present invention addresses the problems described above with the object of providing a compact, inexpensive vacuum switchgear having a further improved reliability. 
     To achieve the above object, a vacuum switchgear according to an aspect of the present invention has a mold section to which conductors connected to fixed electrodes of switches are molded with resin and includes a vacuum container, disposed on the mold section, that accommodates the switches, each of which comprises the fixed electrode and a movable electrode connectable to and disconnectable from the fixed electrode. 
     A vacuum switchgear according to another aspect of the present invention has a mold section to which ground switches and conductors connected to fixed electrodes of switches are molded with resin and includes a vacuum container, disposed on the mold section, that accommodates the switches, each of which comprises the fixed electrode and a movable electrode connectable to and disconnectable from the fixed electrode. 
     A vacuum switchgear according to still another aspect of the present invention has a mold section to which ground switches and conductors connected to fixed electrodes of switches that function as a circuit breaker and load break switches are molded with resin and includes a vacuum container, disposed on the mold section, that accommodates the circuit breaker and load break switches, each of which comprises the fixed electrode and a movable electrode connectable to and disconnectable from the fixed electrode. 
     A vacuum switchgear according to yet another aspect of the present invention has a mold section to which ground switches and conductors connected to fixed electrodes of switches that function as a circuit breaker and disconnecting switches are molded with resin and includes a vacuum container, disposed on the mold section, that accommodates the circuit breaker and disconnecting switches, each of which comprises the fixed electrode and a movable electrode connectable to and disconnectable from the fixed electrode. 
     According to the present invention, the mold resin member used as the main insulator between the main circuit and ground can be localized near the conductors connected to the fixed electrodes, which significantly reduces the amount of resin used. Furthermore, the spacing between the main circuit section in the vacuum container and ground is isolated doubly by vacuum and the resin member or air, increasing the insulation reliability. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a longitudinal front view illustrating an embodiment of the inventive vacuum switchgear. 
         FIG. 2  is a longitudinal side view of the embodiment of the inventive vacuum switchgear shown in  FIG. 1 . 
         FIG. 3  is a plan view of the embodiment of the inventive vacuum switchgear shown in  FIG. 1 . 
         FIG. 4  is an electric schematic circuit diagram of a ring main unit configured in the embodiment of the inventive vacuum switchgear. 
         FIG. 5  is a longitudinal front view illustrating another embodiment of the inventive vacuum switchgear. 
         FIG. 6  is a side view in which part of the other embodiment of the inventive vacuum switchgear shown in  FIG. 1  is omitted. 
         FIG. 7  is an electric schematic circuit diagram of a cubicle-type switching apparatus configured in the other embodiment of the inventive vacuum switchgear. 
         FIG. 8  is a front view of an exemplary switching apparatus having the other embodiment of the inventive vacuum switchgear shown in  FIG. 5 . 
         FIG. 9  is a cross-sectional view showing section IX-IX of the switching apparatus in  FIG. 8 . 
         FIG. 10  is a longitudinal front view illustrating still another embodiment of the inventive vacuum switchgear. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of a vacuum switchgear according to the present invention will be described with reference to the drawings. 
       FIGS. 1 to 4  illustrate an embodiment of a vacuum switchgear according to the present invention.  FIG. 1  is a longitudinal front view illustrating the embodiment of the inventive vacuum switchgear.  FIG. 2  is a longitudinal side view of the embodiment of the inventive vacuum switchgear shown in  FIG. 1 .  FIG. 3  is a plan view of the embodiment of the inventive vacuum switchgear shown in  FIG. 1 .  FIG. 4  is an electric schematic circuit diagram of a ring main unit configured in the embodiment of the inventive vacuum switchgear. 
     First, the ring main unit in  FIG. 4  generally comprises a vacuum switch which is constituted a circuit breaker (CB), two load break switches (LBSs), earth switches (ESS), and feeder conductors (Fs) connected to each of the fixed electrodes of the circuit breaker (CB) and the two load break switches (LBSs). The feeder conductors (Fs) and earth switches (ESs) are molded with resin. A vacuum container  8  is placed on the mold section  7 . The vacuum container  8  includes the circuit breaker (CB) and the two load break switches (LBSs). The outer periphery or surface of the vacuum container  8  is covered by a insulating mold case  10  with resin. 
     An embodiment of the inventive vacuum switchgear that constitutes the above ring main unit will be described in detail with reference to  FIGS. 1 to 3 . 
     The vacuum switch is constituted a circuit breaker (CB)  1 , two load break switches (LBSs)  2 , feeder conductors (Fs)  3  connected to each of the fixed electrodes  22  of the circuit breaker (CB)  1  and the two load break switches (LBSs)  2 , and earth switches (ESs)  4  connected to the feeder conductors  3 . Current transformers  5  and voltage dividers  6  which are being provided on the feeder conductors  3 , are molded with resin and constitute the mold section  7 , as shown in  FIGS. 1 and 2 . The earth switch  4  has a solid insulating tube  41  made of, for example, ceramic and kept under vacuum, a fixed electrode  42  fixed at the upper part of the solid insulating tube  41  and connected to the feeder conductor  3 , and a movable electrode  44  disconnectably connected to the fixed electrode  42  at the lower part of the solid insulating tube  41  through a bellows  43 . The movable electrode  44  of the earth switch  4  is made movable by an earth switch opening/closing mechanism  45  that comprises a rod, a link, and the like. The movable electrode  44  of the earth switch  4  is connected to an earth bus  46 . 
     A vacuum container  8  made of stainless or another material is fixed on the mold section  7  by bolts  9  shown in  FIG. 3 . The outer periphery or surface of the vacuum container  8  is molded by the insulating mold case  10  with a thermosetting molding material  10   a  such as unsaturated polyester resin. 
     The circuit breaker  1  disposed in the vacuum container  8  has an insulating tube  11 , a fixed electrode  12 , a movable electrode  13 , an insulating rod  15  and an arc shield  16  disposed on the inner surface of the insulating tube  11 ; the fixed electrode  12  is fixed in the insulating tube  11  and connected to the feeder conductor  3  brought into the vacuum container  8 ; the movable electrode  13  is brought into the insulating tube  11  and can be connected to and disconnected from the fixed electrode  12 ; the insulating rod  15  is connected to the movable electrode  13  through a bellows  14 . The insulating rod  15  for the circuit breaker is connected to a circuit breaker opening/closing mechanism  17  that comprises a rod, a link, and the like. The bellows  14  has a bag shape and has less sealing portions, increasing the reliability for vacuum hermeticity. 
     The load break switch  2  disposed in the vacuum container  8  has an insulating tube  21 , a fixed electrode  22 , a movable electrode  23 , an insulating rod  25  and an arc shield  26  disposed on the inner surface of the insulating tube  21 ; the fixed electrode  22  is fixed in the insulating tube  21  and connected to the feeder conductor  3  brought into the vacuum container  8 ; the movable electrode  23  is brought into the insulating tube  21  and can be connected to and disconnected from the fixed electrode  22 ; the insulating rod  25  is connected to the movable electrode  23  through a bellows  24 . 
     As with the above bellows  14 , the bellows  24  has a bag shape and has less sealing portions, increasing the reliability for vacuum hermeticity. The insulating rod  25  for the load break switch is connected to a load break switch opening/closing mechanism  27  that comprises a rod, a link, and the like. 
     The movable electrode  13  for the circuit breaker  1  and one of the movable electrodes  23  for the load break switch  2  are interconnected by a flexible conductor  28 , and that movable electrode  23  for the load break switch  2  and the other movable electrode  23  for the load break switch  2  are also interconnected by another flexible conductor  28 . The flexible conductor  28  is provided with a flexible conductor shield  29 . The flexible conductor  28  is fixed to the movable electrodes  13 ,  23  by screwing and brazing. When the moving electrode  13 ,  23  moves, the flexible conductor  28  generates a return force in the lateral direction in  FIG. 1 , since the flexible conductor  28  is fixed by screws to resist to the return force, so that work involved in the brazing is simplified. 
     Each feeder conductor  3  brought into the vacuum container  8  is supported by the vacuum container  8  through a solid insulator  30  made of, for example, ceramic. A side of each of the feeder conductors  3  opposite to its fixed electrode is a cable connection terminal  31 . 
     Next, the operation of an embodiment of the inventive vacuum switchgear will be described in detail with reference to  FIGS. 1 to 3 . 
     In the circuit breaker  1 , the circuit breaker opening/closing mechanism  17  is operated according to a detection signal for an overcurrent, shortcircuit, ground fault, or other failure that is detected on the load side by a detecting means. The movable electrode  13  is then disconnected from the fixed electrode  12  to open the connection circuit. 
     Each of the load break switches  2  is operated by the load break switch opening/closing mechanism  27 . The movable electrode  23  is then disconnected from the fixed electrode  22  to disconnect the connection circuit. This embodiment uses a phase separation construction. For three phases, another unit construction described above may be provided. 
     Since the vacuum container  8  is disposed on the mold section  7 , the vacuum container is maintained in a floating voltage state, increasing the insulation performance of the vacuum container  8  with respect to the ground. This reduces the probability of ground faults and improves reliability. 
     In parts at which vacuum sealing is not necessary, such as the solid insulating tube  41  of the earth switch  4 , swaging or ceramic metallization by use of an active brazing material is eliminated, which enables the use of inexpensive ceramic and reduces the manufacturing cost. In the mold section  7 , the feeder conductors  3 , earth switches  4 , current transformers  5 , and voltage dividers  6  are molded, so the mold section  7  is compact as compared with the entire vacuum switchgear, which also contributes to the reduction in the manufacturing cost. 
     The earth switches  4  are disposed in the mold section  7 , which is outside the vacuum container  8 , so the weight and capacity of the vacuum container  8  can be reduced, which significantly reduces the size of the vacuum container  8  having the circuit breaker  1  and load break switches  2  and greatly cuts down the cost. Even if a ground fault occurs in the earth switch  4 , the ground fault current is automatically shut down within one cycle by highly vacuum tight arc-suppressing performance, suppressing the ground fault from spreading. 
     According to the above embodiment of the present invention, the vacuum container  8  including the circuit breaker  1  and load break switches  2  is disposed on the mold section  7 , so the electric potential of the vacuum container  8  is a floating voltage that is approximately equal to the ground potential, thereby increasing the safety and reliability of the vacuum container  8  against ground faults. 
     The earth switches  4  disposed outside the vacuum container  8 , that is, in the mold section  7 , so the structures of the circuit breaker  1 , the load break switches  2  and the like in the vacuum container  8  can be simplified, and the vacuum container can be made compact. 
     In addition, the feeder conductors  3  are part of the integrated mold section  7 , so its molding cost can be reduced and thereby the entire manufacturing cost can also be reduced. 
     Although the earth switches  4  are disposed outside the vacuum container  8  in the above embodiment, it is also possible to dispose them in the vacuum container  8 . Even in this case, the electric potential of the vacuum container  8  can be reduced nearly to the ground potential as in the above embodiment, and the safety and reliability of the vacuum container  8  against ground faults can be increased. 
     In the above embodiment, the thermosetting molding material  10   a  provided on the outer periphery or surface of the vacuum container  8  such as unsaturated polyester resin is further used to prevent ground faults. Owing to the use of the thermosetting molding material  10   a , withstanding the operation voltage for a half cycle is sufficiently in the unlikely event of a discharge between a conductor and the vacuum container  8 . It is also possible to coat conductive paint to the inner surface of the thermosetting molding material  10   a  to prevent corona discharges generated due to small gaps between the vacuum container  8  and thermosetting molding material  10   a . Instead of using the thermosetting molding material  10   a , a metallic cover may be provided with a spacing from the vacuum container  8  that is just enough to withstand the operation voltage. 
       FIGS. 5 to 7  illustrate another embodiment of a vacuum switchgear according to the present invention.  FIG. 5  is a longitudinal front view illustrating the other embodiment of the inventive vacuum switchgear.  FIG. 6  is a side view in which part of the other embodiment of the inventive vacuum switchgear shown in  FIG. 1  is omitted.  FIG. 7  is an electric schematic circuit diagram of a cubicle-type switching apparatus configured in the other embodiment of the inventive vacuum switchgear. The parts in these drawings are assigned the same reference numerals as the identical or equivalent parts in  FIGS. 1 to 4 . 
     First, the cubicle-type switching apparatus in  FIG. 7  generally comprises a vacuum switch which is constituted a circuit breaker (CB), a disconnecting switch (DS), an earth switch (ES), a feeder conductor (F) connected to a fixed electrode of the circuit breaker (CB), and a branching bus (F 1 ) connected to a fixed electrode of the disconnecting switch (DS). The feeder conductor (F), branching bus (F 1 ), and earth switch (ES) are molded with resin. A vacuum container  8  is placed on the mold section  7 . The vacuum container  8  includes the circuit breaker (CB) and the disconnecting switch (DS). The outer periphery or surface of the vacuum container  8  is covered by an insulating mold case  10  with resin. 
     The other embodiment of the inventive vacuum switchgear that constitutes the cubicle-type switching apparatus described above will be described in detail with reference to  FIGS. 5 and 6 . 
     The feeder conductor (F)  3  connected to the fixed electrode  12  of the circuit breaker (CB)  1 , the branching bus (F 1 )  3 A connected to the fixed electrode  22  of the disconnecting switch (DS)  2 , the earth switch (ES)  4  connected to the feeder conductor  3 , and the voltage dividers  6  provided on the feeder conductor  3  are molded with resin and constitute a mold section  7 , as shown in  FIG. 5 . The earth switch  4  has a solid insulating tube  41  made of, for example, ceramic and kept under vacuum, a fixed electrode  42  fixed at the lower part of the fixed insulating tube  41  and connected to the feeder conductor  3 , and a movable electrode  44  disconnectably connected to the fixed electrode  42  at the upper part of the solid insulating tube  41  through a bellows  43 . The movable electrode  44  of the earth switch  4  is made movable by an earth switch opening/closing mechanism  45  that comprises a rod, a link, and the like. The movable electrode  44  of the earth switch  4  is connected to an earth bus  46 . 
     A vacuum container  8  made of stainless or another material is disposed on the mold section  7 . The vacuum container  8  has a two-part structure that comprises a lower part  8 A and an upper part  8 B. The lower part  8 A of the vacuum container  8  is disposed on the mold section  7  through a solid insulator  30  made of, for example, ceramic. The outer periphery or surface of the lower part  8 A and upper part  8 B of the vacuum container  8  are covered by an insulating mold case  10  with resin that is formed integrally with the mold section  7 . 
     After the conductor, bellows, contacts, and other constituting parts are brazed in the lower part  8 A of the vacuum container  8 , the upper part  8 B is fitted onto the lower part  8 A and then the joint part is brazed. Finally, the vacuum container is vacuum sealed. 
     The circuit breaker  1  disposed in the vacuum container  8  has a fixed electrode  12  connected to the feeder conductor  3 , a movable electrode  13  can be connected to and disconnected from the fixed electrode  12 , and an insulating rod  15  connected to the movable electrode  13  through a bellows  14 . The insulating rod  15  is connected to a circuit breaker opening/closing mechanism  17  for the circuit breaker that comprises a rod, a link, and the like. The bellows  14  has a bag shape and has less sealing portions, increasing the reliability for vacuum. 
     The disconnecting switch  2  disposed in the vacuum container  8  has a fixed electrode  22  connected to the branching bus  3 A brought into the vacuum container  8 , a movable electrode  23  connectable to and disconnectable from the fixed electrode  22 , an insulating rod  25  connected to the movable electrode  23  through a bellows  24 , and an arc shield  26  disposed on the inner surface of the vacuum container  8 . The insulating rod  25  is connected to a load break switch opening/closing mechanism  27  for the disconnecting switch that comprises a rod, a link, and the like. As with the above bellows  14 , the bellows  24  has a bag shape and has less sealing portions, increasing the reliability for vacuum hermeticity. 
     The arc shield  26  has the same electric potential as the vacuum container  8 . Therefore, the arc shield  26  prevents metallic particles released from the electrode of the disconnecting switch  2  at the time of current shutdown from adhering to the electrode and thereby prevents the withstand voltage from being reduced. Furthermore, when the electrodes of the disconnecting switch  2  and circuit breaker  1  are both turned off, the insulation reliability at the time of disconnection of the disconnecting switch  2  is increased. 
     The movable electrode  13  for the circuit breaker  1  and the movable electrode  23  for the disconnecting switch  2  are interconnected by a flexible conductor  28 . The flexible conductor  28  is fixed to the movable electrodes  13 ,  23  by screwing and brazing. When the moving electrode  13 ,  23  moves, the flexible conductor  28  generates a return force in the lateral direction in  FIG. 1 . Since the flexible conductor  28  is fixed by screws to resist to the return force, so that work involved in the brazing is simplified. 
     A side of the feeder conductor  3  opposite to its fixed electrode is a cable connection terminal brought to the lower part of the vacuum container  8 . A side of the branching bus  3 A opposite to its fixed electrode is a bus connection terminal horizontally brought to the lower part of the vacuum container  8 . Bushings of these terminals are provided at the lower part of the vacuum container  8 . 
     Next, the operation of another embodiment of the inventive vacuum switchgear will be described in detail with reference to  FIGS. 5 and 6 . 
     In the circuit breaker  1 , the circuit breaker opening/closing mechanism  27  is operated according to a detection signal for an overcurrent, shortcircuit, ground fault, or other failure that is detected on the load side by a detecting means. The movable electrode  13  is then disconnected from the fixed electrode  12  to open the connection circuit. 
     The disconnecting switch  2  is operated by its opening/closing mechanism  27 , and disconnects the movable electrode  23  from the fixed electrode  22  to disconnect the connection circuit. This embodiment uses a phase separation construction. For three phases, another unit construction described above may be provided. 
     Even if a ground fault occurs in the earth switch  4 , the ground fault current is automatically shut down within one cycle, suppressing the ground fault from spreading. 
     Since the vacuum container  8  is constructed as two parts, sealing can be done easily by brazing the joint portion of the lower part  8 A and upper part  8 B of the vacuum container  8 . 
     According to the above embodiment of the present invention, the vacuum container  8  including the circuit breaker  1  and disconnecting switch  2  is disposed on the mold section  7 , so the electric potential of the vacuum container  8  is a floating voltage, thereby increasing the safety and reliability of the vacuum container  8  against ground faults. 
     The earth switch  4  is disposed outside the vacuum container  8 , that is, in the mold section  7 , so the structures of the circuit breaker  1 , the disconnecting switch  2 , and the like in the vacuum container  8  can be simplified, and the vacuum container can be made compact. 
     Since the main elements of the mold section  7  are the feeder conductors  3  and the branching buses (F 1 s)  3 A, the molding cost can be reduced and thereby the entire manufacturing cost can also be reduced. 
     In the above embodiment, the insulating mold case  10  provided on the outer periphery or surface of the vacuum container  8  is used to prevent ground faults. The insulating mold case is preset so that it can withstand an increase in electric potential that is caused by arc generation at the time of current shutdown by the circuit breaker  1 . When the outer surface of the insulating mold case  10  is coated with paint having conductive material, so the electric potential of the vacuum container  8  is fixed to the ground potential, even if a person touches directly the insulating mold case  10 , the person can be kept safety. 
       FIGS. 8 and 9  show an exemplary switching apparatus having another embodiment of the vacuum switchgear shown in  FIGS. 5 and 6 .  FIG. 8  is a front view of the switching apparatus, and  FIG. 9  is a cross-sectional view showing section IX-IX in  FIG. 8 . The parts in these drawings are assigned the same reference numerals as the identical parts in  FIGS. 5 to 7 . A protective relay device  80  is provided above an opening/closing mechanism  17  for the circuit breaker and another opening/closing mechanism  27  for the disconnecting switch  2 . 
     Buses  3 A extending downward from the mold section  7  are each provided with a bus-side bushing  3 B. These bus-side bushings  3 B are mutually displaced as shown in  FIGS. 5 and 9  and interconnected by a horizontal bus-side bushing  3 C for each phase. 
     Feeder conductors  3  extend horizontally from the mold section  7  as shown in  FIGS. 5 and 8 . A T-shaped cable head  3 D is attached to each feeder conductor  3  as shown in  FIG. 8 , and a conductor  3 E extends downward from the T-shaped cable head. The conductor  3 E is provided with a current transformer  81 . 
     According to this embodiment, as in the above embodiments, the electric potential of the vacuum container  8  is a floating voltage, thereby increasing the safety and reliability of the vacuum container  8  against ground faults. The earth switch  4  is disposed outside the vacuum container  8 , that is, in the mold section  7 , so the structures of the circuit breaker  1 , the disconnecting switch  2 , and the like in the vacuum container  8  are simplified, and the vacuum container can be made compact. Since the main elements of the mold section  7  are the feeder conductors  3  and the branching buses (F 1 )  3 A, the molding cost can be reduced and thereby the entire manufacturing cost can also be reduced. 
     Since the bus-side bushings and feeder-side bushings are disposed at the bottom of the mold section  7 , devices for taking countermeasures against internal arc accompanying short-circuits may be disposed there, which simplifies maintenance of these devices. 
     Furthermore, in this embodiment, a voltage monitor to be connected to the current transformer  81  can be provided on the feeder side, and an interlock can also be provided so as not to permit the ground switch  4  to be turned on when the voltage monitor detects that a voltage is present. If a vacuum leakage occurs in the circuit breaker  1  or disconnecting switch  2 , for example, a voltage develops on the feeder side even when the circuit breaker  1  and disconnecting switch  2  are both shut off. If the disconnecting switch  2  is turned on in this state, a ground fault will occur. The interlock suppresses such ground faults. 
     In the embodiment described above, an electrode which can shut off a short-circuit current such as, for example, a spiral electrode or vertical electric field-type electrode, may be used to the electrode of the ground switch  4 . 
       FIG. 10  is a longitudinal front view illustrating another embodiment of the inventive vacuum switchgear. The parts in this drawing are assigned the same reference numerals as the identical or equivalent parts in  FIG. 5 . The vacuum switchgear has a plurality of circuit breakers  1  in the vacuum container  8 . The electrodes  13  of the plurality of circuit breakers  1  are operated concurrently to enable the use of turned-on, turned-off, and disconnected positions. 
     In this embodiment, as in the embodiments described above, the conductor  3  connected to the fixed electrode  12  of the circuit breaker  1 , the earth switch  4  connected to the conductor  3 , and the like are resin molded to the mold section  7 . A vacuum container  8  is provided on the mold section  7 . By this structure, the electric potential of the vacuum container  8  is a floating voltage, thereby increasing the safety and reliability of the vacuum container  8  against ground faults. The earth switch  4  is disposed outside the vacuum container  8 , that is, in the mold section  7 , so the vacuum switch structure of the circuit breaker  1  can be simplified, and the vacuum container  8  can be made compact. Since the main elements of the mold section  7  are the conductors  3 , the molding cost can be reduced and thereby the entire manufacturing cost can also be reduced. 
     In this embodiment, the movable electrodes  13  of the each circuit breakers  1  are operated concurrently. This eliminates the need to use a flexible conductor as the conductor for connecting the movable electrodes  13 . A copper sheet  28 A is sufficient. In addition, the conductors are derived at a small pitch, contributing to making the vacuum switch compact.