Abstract: A vacuum insulated switchgear comprising a vacuum container accommodating at least a pair of movable contacts and a pair of fixed contacts, wherein the movable contacts are capable of taking three positions, the switchgear being a double-break three-position type switch having breaking and disconnecting functions.

Abstract: An electrode assembly for use in a vacuum interrupter is made by joining a first side of a substantially disk-shaped structure to an end of a substantially cylindrical coil segment, and joining an electrical contact to a second side of the disk-shaped structure. The disk-shaped structure has a higher resistivity than a resistivity of the coil segment.

Abstract: A power switch, especially a high-current switch, has at least one pole unit with a pole head and a pole base and a vacuum switching tube interposed therebetween. The vacuum switching tube has a stationary contact and a movable contact. The stationary contact is connected to a first conductor rail of the pole unit via a first connecting element. The moving contact is connected to a second conductor rail of the pole unit via a second connecting element. The power switch has a higher current carrying capacity because the first connecting element is welded to the first conductor rail and the stationary contact and the second connecting element is welded to the second conductor rail and the moving contact.

Abstract: Magnetically latching and releasing a voice coil actuator for controlling electrical switchgear. The voice coil actuator includes a voice coil magnet disposed on a common longitudinal axis with respect to a voice coil assembly. A coil of the voice coil assembly exerts a magnetic force on the voice coil assembly, thrusting the voice coil assembly towards the voice coil magnet. At least one pair of latching members mounted to the voice coil assembly creates a permanent magnet circuit between the latching members and the voice coil magnet. The permanent magnet circuit maintains the position of the voice coil assembly relative to the voice coil magnet, even when power to the coil is removed. This latch can be released by applying a current in the coil or by applying an external, physical force to a member coupled to the voice coil assembly.

Abstract: The vacuum insulated switch-gear is configured to be capable of being lifted up with a jack-up bolt to adjust a seated height of the vacuum insulated switch-gear. The switch-gear comprises a nut fixed on a base plate forming a bottom of the vacuum insulated switch-gear. The nut is used as a mating component with the jack-up bolt.

Abstract: The invention relates to a vacuum switch, especially a vacuum circuit breaker, for medium and high voltages, comprising a mobile switch unit arranged inside a vacuum switch compartment (1) and provided with mutually mobile elements including a contact tappet (17), an insulator (18), and a driving or switching rod (11) introduced into the vacuum switch compartment (1) by means of metal bellows. Said vacuum switch also comprises a fixed contact inserted into the housing of the vacuum switch compartment (1). The upper end of the insulator (18) is fixed to the contact tappet (17), and the lower end of the insulator (18) is fixed to the driving or switching rod (11). The contact tappet (17) is connected to a conductor (8) by a flexible, electroconductive connection (20), said conductor being electroconductively connected to at least one laterally arranged output contact (6). The aim of the invention is to enable an improved embodiment of the switching and contact surfaces.

Abstract: To structure a large-capacity vacuum circuit breaker that can increase a current shutdown capacity and enables its rated current to be increased, at least two vacuum circuit breaker units 1A, 1B are placed side by side and connected in parallel. These at least two vacuum circuit breaker units 1A, 1B are operated by a single common operating unit 10 to concurrently perform current shutdown operations. Each vacuum circuit breaker unit 1A, 1B has a vertical magnetic field generating means for generating a vertical magnetic field when an operation to shut down current is performed. The vertical magnetic field generating means is formed by vertical magnetic field electrodes 3, 4 provided in the vacuum container 2 of the vacuum circuit breaker unit 1A, 1B or an external coil 11 provided on the outer circumference of the vacuum container 2.

Abstract: A manual opening device is for an electrical switching apparatus, such as a synchronous circuit breaker, including a housing having an opening, a plurality of pole mechanisms each comprising separable contacts, and at least one operating mechanism including a number of actuators adapted to open and close the separable contacts. The operating mechanism is supported by the housing and includes a corresponding pole shaft. The manual opening device comprises an operating handle, a cam assembly, and a drive assembly. A first end of the operating handle protrudes through the opening of the housing and the second end is coupled to the cam assembly. The drive assembly couples the cam assembly to the corresponding pole shaft of the operating mechanism and cooperates with the corresponding pole shaft and actuators to simultaneously open the separable contacts when the operating handle is moved from a first position to a second position.

Abstract: A control system for controlling and synchronizing a plurality of medium-voltage vacuum contactors comprises a two-level network structure. A dedicated network includes a plurality of servant control units operably coupled to the vacuum contactors and configured to ascertain a plurality of different data and conditions thereof. In addition, the dedicated network includes a master control unit in serial communication with the servant control units and configured to send and receive communications therewith. The master control unit is operably coupled to a control network including a plurality of various control devices. The master control unit is configured to send predetermined data received from the servant control units to the control network. The two-level network structure enables relatively jitter free communication on the dedicated network while not overwhelming the control network with unnecessary data.

Abstract: A vacuum insulated switchgear comprising a vacuum container accommodating at least a pair of movable contacts and a pair of fixed contacts, wherein the movable contacts are capable of taking three positions, the switchgear being a double-break three-position type switch having breaking and disconnecting functions.

Abstract: A vacuum insulated switchgear comprising a vacuum container accommodating at least a pair of movable contacts and a pair of fixed contacts, wherein the movable contacts are capable of taking three positions, the switchgear being a double-break three-position type switch having breaking and disconnecting functions.

Abstract: A vacuum switchgear system, which comprises a plurality of vacuum switchgears each comprising a vacuum container for accommodating the desired number of vacuum switches selected from a disconnecting switch or load break switch, an earth switch and an vacuum circuit breaker. Each of the vacuum switches has connecting terminals. The switchgears constitute different types of switchgears, the switchgears being classified into the power receiving side and power distribution side. The switchgears are connected with the adjoining switchgear or an element selected from an arrester and a PCT by means of an insulated connecting conductor having terminals around both ends thereof. The terminals are electrically connectable with and detachable from the connecting terminals of the switchgears.

Abstract: An electrical switchgear has a first switching point and a second switching point The first switching point is arranged inside an evacuated region. The second switching point is arranged outside the evacuated region. The first switching point is surrounded by the second switching point. For the connection process of the electrical switchgear, the first switching point is switched on before the second switching point, and for the disconnection process, the first switching point is switched off after the second switching point.

Abstract: The disclosure relates to a method for producing circuit-breaker parts and plastic components for low, medium and high-voltage switching stations and to a corresponding circuit-breaker part. To obtain a simpler method of production with a higher variance of material characteristics, the outer insulation sleeve is produced in a plastic injection molding method, in which a vacuum interrupter chamber is sheathed in plastic.

Abstract: The aim of the invention is to improve the breaking ability of vacuum interrupter in the medium- and high-voltage range. Said aim is achieved whereby the contact pieces which may be displaced relative to each other are moved with a relatively high speed during a first phase (S1) of the separation process until about ¼ to ½ of the ultimate separation (extinction stroke Eh) and are brought to the given ultimate separation (isolating stroke Eh) during a second phase (S2) with relatively low speed.

Abstract: A switching installation (5) having a circuit breaker (12), which is connected to a cable connection (33), and optionally a disconnector (14) for making or breaking a conductive connection between the cable connection (33) and a rail system (15), and an electrically insulating barrier (10). The electrically insulating barrier (10) surrounds at least the parts which are under electric voltage in operation from the circuit breaker (12) to the rail system (15), including a branch (18) leading to a rail (15) of the rail system, separately for each phase of the switching installation (5). Furthermore, inside the electrically insulating barrier (10) the switching installation may be provided with field-control means and/or voltage-sealing means (22, 25, 37).

Abstract: A visible open indicator for high voltage vacuum interrupters and switches, which use a vacuum bottle having a high voltage contact and an actuating element that opens and closes the contact, is provided. The visible open indicator includes: an actuating mechanism that operates the actuating element; a housing that contains the actuating mechanism; an indicator attached to the actuating mechanism, wherein the indicator shows that the contact is in an open position or closed position; a viewing window extending through the housing, wherein the viewing window is aligned with the indicator so that the indicator can be viewed through the viewing window. The indicator includes a first indicating portion and a second indicating portion. The first indicating portion is visible through the viewing window when the contact is open and the second indicating portion is visible through the viewing window when the contact is closed.

Abstract: A connector system for a high voltage vacuum switch which includes: a voltage source connector; a load connector; a first contact in a vacuum bottle; and a second contact connected in series with the first contact, wherein the second contact is external to the vacuum bottle. The voltage source is connected to the load through the first and second contacts and the second contact includes a first separable interface, a second separable interface and a conducting pin. When the conducting pin is removed, an insulating pin can be inserted in its place. In preferred embodiments, the connector system includes a housing and a sight glass which extends through the housing for viewing the conducting pin. The connector system can also include a first and second connectors for the first and second separable interfaces, which are used for test connections and/or grounding connections.

Abstract: A switchgear having interrupters wherein at least two moving contacts are capable of being open and close with respect to respective fixed contacts. The switchgear comprises a non-earthed metal vacuum chamber enclosing the interrupters therein, a connection conductor for connecting the moving contacts, an operating rod connected to the connecting conductor by means of an insulator and protruding from the non-earthed metal vacuum chamber, a sealing means for sealing the protrusion of the operating rod at the non-earthed metal vacuum chamber, circuit terminals protruding from the non-earthed vacuum chamber, an earth layer surrounding an outer periphery of the insulating mold, and a potential control means. The control means for controlling the potential of the non-earthed metal vacuum chamber is connected between the circuit terminals and is connected to the non-earthed metal vacuum chamber at the intermediate point of the potential control means.

Abstract: An encapsulated medium voltage vacuum circuit interrupter includes a line terminal, a load terminal, a vacuum interrupter, an operating mechanism and an elongated, insulated, generally cylindrical encapsulating housing. The vacuum interrupter includes a vacuum envelope containing a fixed contact assembly and a movable contact assembly movable between a closed circuit position in electrical communication with the fixed contact assembly and an open circuit position spaced apart from the fixed contact assembly. The fixed contact assembly is electrically interconnected with the line terminal. A flexible conductor electrically connects the movable contact assembly with the load terminal. The operating mechanism moves the movable contact assembly between the closed circuit position and the open circuit position. The housing includes a first end supporting the line terminal and an opposite second end supporting the load terminal.

Abstract: A vacuum interrupter for reducing contact resistance and thereby reducing electromagnetic repulsive force between electrodes, is obtained. The vacuum interrupter includes a stationary electrode rod fixedly placed on one closed end of a cylindrical evacuated envelope closed at both ends thereof; a movable electrode rod movably placed on the other closed end; disc shaped contacts placed on opposing ends of the electrode rods; and reinforcement members for reinforcing the contact placed between each electrode rod and the associated contact. In such a configuration, a coefficient of linear expansion of the reinforcement member differs from that of the contact, and the reinforcement member and the associated contact are jointed by soldering at a plurality of opposing parts thereof.

Abstract: Disclosed is a vacuum switchgear comprising an electro-conductive outer vacuum container, a plurality of inner container disposed in the outer vacuum container. The inner containers and the outer container are 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, a disconnector and a load switch. A plurality of electrode shields each surrounds the electrodes of the ground switch and of the function switch. The ground switch and the function switch are disposed in separate vacuum inner containers, respectively.

Abstract: A vacuum switch comprises a vacuum container, a grounding switch and a load switch disposed in the container, and an external connection conductor disposed in the vacuum container and to be connected electrically inside and outside the vacuum container, and it is characterized in that the grounding switch and the external connection conductor are electrically connected to each other in the vacuum container.

Abstract: On both sides of a metal switching chamber, the novel vacuum switch tubes are respectively provided with two ceramic insulators which have the same diameter. Axially interspaced cylindrical vapor shields are fixed to the wing parts of said components. The easy to produce low-volume structure means that is possible to control operating voltages of more than 60 kV.

Abstract: A main circuit switching unit and an isolator are accommodated in a vacuum container. A first conductor and a main circuit conductor are arranged to extend in and out of the vacuum container. A movable electrode of the main circuit switching unit is connected to the first conductor through a first flexible conductor, and a movable electrode of the isolator is connected to the main circuit conductor through a second flexible conductor. A shield is arranged around the first conductor and the main circuit conductor. Another shield is arranged around a connecting portion between the first flexible conductor and the movable electrode of the main circuit switching unit. A still another shield is arranged around the isolator. A further another shield is arranged around the second flexible conductor. These shields are secured to the vacuum container through insulating spacers.

Abstract: A vacuum interrupter includes end covers having a curved or looped portion, which serves to connect a coil segment of the vacuum interrupter to a ceramic envelope of the vacuum interrupter, and thereby help maintain a vacuum seal for the interrupter. The curved portion acts as a spring when the vacuum interrupter is exposed to heat, thereby absorbing any expansion or contraction in the length of the vacuum interrupter due to the heating or cooling. The curved portion also protects an end of the ceramic envelope from any build-up of metallic arcing products and eliminates the need for elaborate fixturing during assembly. Additionally, a guide may be affixed to the end cover, the guide having ears which ride in a slot in a moving rod of the vacuum interrupter, to thereby prevent a twisting of a bellows of the interrupter during a brazing process. Thus, no elaborate fixturing is necessary to prevent this twisting.

Abstract: A new vacuum switching chamber is intended for power breakers in the low-voltage range and is distinguished by a compact form with a small physical height and a high switching capacity. Its enclosure includes a plate-like power current connection, a cylindrical wall part which surrounds flat spiral contacts, an annular insulator and a membrane disk with a centrally arranged power current supply bolt.

Abstract: A vacuum switch comprises a vacuum container, a grounding switch and a load switch disposed in the container, and an external connection conductor disposed in the vacuum container and to be connected electrically inside and outside the vacuum container, and it is characterized in that the grounding switch and the external connection conductor are electrically connected to each other in the vacuum container.

Abstract: Disclosed is a vacuum switchgear wherein a ground switch, a load switch, and an external connecting conductor to be electrically connected with the inside and outside of the vacuum container are provided in a vacuum container; the ground switch and the external connecting conductor are electrically connected in the vacuum container; and the vacuum container has a joint construction of a body portion having openings on both ends thereof, and a lid joined to the opening of the body.

Abstract: A vacuum switch comprises a vacuum container, a grounding switch and a load switch disposed in the container, and an external connection conductor disposed in the vacuum container and to be connected electrically inside and outside the vacuum container, and it is characterized in that the grounding switch and the external connection conductor are electrically connected to each other in the vacuum container.

Abstract: A switchgear assembly includes a vacuum interrupter assembly having an internal switching contact. A conductive current exchange is in electrical contact with the switching contact, and the current exchange defines an internal chamber within the current exchange. A plug of non-conductive, compliant material has a first portion that extends into the internal chamber in contact with the current exchange. An insulative encapsulation surrounds the vacuum interrupter assembly, the current exchange, and the plug.

Abstract: An improved vacuum interrupter is disclosed. The vacuum interrupter includes a ring-shaped structure placed between a contact support structure and an electrical contact associated with the contact support structure. A resistivity of the ring-shaped structure is higher than that of the contact support structure, so that current traversing the ring-shaped structure on its way from the contact support structure to the electrical contact is evenly distributed. The ring-shaped structure may be fit into an end portion of the contact support structure, the end portion having an diameter less than an outer diameter of the support structure, but greater than an inner diameter of the support structure. Alternatively, the end portion may be used without the ring-shaped portion, in which case the electrical contact may be shaped to fit into the end portion.

Abstract: An improved vacuum interrupter is disclosed. The vacuum interrupter includes end covers having a curved or looped portion, which serves to connect a coil segment of the vacuum interrupter to a ceramic envelope of the vacuum interrupter, and thereby help maintain a vacuum seal for the interrupter. The curved portion acts as a spring when the vacuum interrupter is exposed to heat, thereby absorbing any expansion or contraction in the length of the vacuum interrupter due to the heating or cooling. The curved portion also protects an end of the ceramic envelope from any build-up of metallic arcing products and eliminates the need for elaborate fixturing during assembly. Additionally, a guide may be affixed to the end cover, the guide having ears which ride in a slot in a moving rod of the vacuum interrupter, to thereby prevent a twisting of a bellows of the interrupter during a brazing process. Thus, no elaborate fixturing is necessary to prevent this twisting.

Abstract: An electrode of a vacuum circuit breaker has a cup member and a contact. The cup member has an opening and a periphery which is formed with a slit so as to form a coil section. An electric current flows in the coil section so as to generate a longitudinal magnetic field in a direction along an axis of the cup member. The slit is bent and continuously extends on the periphery from a first end of the cup member to a second end of the cup member opposite to the first end of the cup member. The contact is shaped into a plate, and seals the opening of the cup member.

Abstract: An electric contact member has a texture wherein fire proof metal powder having the form of a flat plate is diffused in a matrix of a highly conductive metal. The flat surface is oriented in one direction and the surface in parallel with the flat surface of the fire proof metal powder is used as a contact point face.

Abstract: Vacuum circuit breaker, provided with a casing, in which a fixed and movable contact member are each attached to a supporting contact rod and supported therein in a mutually electrically isolated manner, and a coil coaxial to the casing and surrounding the contact members and having end connections. A first end connection of the coil is connected to one of the contact members. The contact member to which the first end connection of the coil is connected is coupled via a first coupling element to a feeder or outgoer connection of the vacuum circuit breaker. The second end connection of the coil is coupled via a second coupling element to the feeder or outgoer connection.

Abstract: The aim of the invention is to improve the breaking ability of vacuum interrupter in the medium- and high-voltage range. Said aim is achieved whereby the contact pieces which may be displaced relative to each other are moved with a relatively high speed during a first phase (S1) of the separation process until about ¼ to ½ of the ultimate separation (extinction stroke Eh) and are brought to the given ultimate separation (isolating stroke Eh during a second phase (S2) with relatively low speed.

Abstract: An improved electrical interrupter apparatus includes a stationary contact and a movable contact within an enclosed region, with the movable contact being operatively connected with a drive unit that employs a pull-to-close mechanism to engage the movable contact with the stationary contact. When the contacts are desired to be closed, the drive unit applies a tensile force to an elongated rod that extends between the drive unit and a crank mechanism, which converts the tensile force in the rod into a compressive force applied to the movable contact.

Abstract: A tank filled with an insulating gas accommodates insulator tubes incorporating vacuum-valve breakers for individual phases. One end of each insulator tube is fixed to the inside of the tank. Each vacuum-valve breaker is installed generally on a common longitudinal axis with the relevant insulator tube in such a manner that its movable electrode rod is directed toward the fixed end of the insulator tube. The insulator tube has as its integral part a bus line fixing portion projecting in a direction intersecting the longitudinal axis of the insulator tube from the proximity of its end opposite to the fixed end to support a bus-side conductor in an insulated fashion.

Abstract: The invention concerns a switching device system including at least one switching device, signal means and control means. Each switching device includes at least one mobile contact part, an electric motor and, coupling means. The coupling means is arranged to transfer motion from the electric motor to the mobile contact part. The control means is arranged to control the switching device. According to the invention the control means is at least partly remotely located from the switching device. The signal means transmit signals from the switching device to the remotely located control means and vice/versa. The signals represent real-time data and/or off-line data The invention concerns also a switching device, control means and methods related to the invented system as well as computer program products for such system and electric power system being provided with such system.

Abstract: A contact and a vacuum interrupter using the contact. The contact includes a hollow cylindrical contact carrier and a contact plate disposed on one of the axial end faces of the contact carrier. First slits and second slits extend from the one of the axial end faces of the contact carrier and the other thereof, respectively. The first slits and the second slits are inclined with respect to the center axis of the contact carrier and have a first height x and a second height y extending in the axial direction of the contact carrier, respectively. Assuming that the axial length of the contact carrier is 1, the first height x and the second height y satisfies a relationship given by the following expressions (1)-(3): (1) 0.9≧x, (2) x≧y≧0.2x, (3) 1.4≧x+y≧0.8.

Abstract: The aim of the invention is to optimize, in vacuum interrupters, the connection area (12, 13, 14) between housing parts (2, 3, 4, 5), which are coaxially assigned to one another, with regard to the complexity of production for centering measures and with regard to the execution of the soldering process. To this end, a ring-like discoidal centering means (15) is used, which is made of a silver-coated copper and which comprises centering lugs (18) located on a tubular flange (17) that is arranged on the inner periphery of the centering means. Said centering lugs extend in an axial direction of the coaxial assignment and are provided in the form of tabs that point toward the ring-like discoidal area (24) of the centering means. The centering means is thereby overlapped by a tubular copper part, which is joined to the centering means and which serves as a shielding (10) inside the vacuum interrupter.

Abstract: An arc generating switching unit 2 which adds an electrical resistance in a circuit during current interruption to attenuate a current to be interrupted, a vacuum bulb 1 which is electrically connected in series with the arc generating switching unit 2 and interrupts the attenuated current and a current conducting switching unit 3 connected in parallel with the series circuit of the vacuum bulb 1 and the arc generating switching unit 2 are provided, and for current conduction the current conducting switching unit 3 is closed after the vacuum bulb 1 and the arc generating switching unit 2 are closed, and for current interruption after opening the current conducting switching unit 3, the vacuum bulb 1 and the arc generating switching unit 2 are opened. Thereby, a small sized power use circuit breaker which performs current conduction and interruption of a large current containing a DC component is obtained.

Abstract: This invention relates to a novel vacuum interrupter. The aim of the invention is for said is for said interrupter to perform the functions switching, disconnection and earthing and to be economically producible. Said aim is achieved by means of a first contact system produced with radial- or axial-magnetic filed contacts, the movable contact of which is connected to the movable contact of a second contact system, comprising annular discs. The stationary contact of the second contact system forms an annular part of the housing to which two tubular insulators are connected. One of the insulators encloses both contact systems and is protected by a screen fixed to the movable contact piece, which separates the plasma physics of the both contact systems.

Abstract: The invention relates to a contact arrangement for a vacuum switch tube for low-voltage power switches. The aim of the invention is to reduce the contact force required to control short circuit currents. To this end, a twin-contact contact arrangement is used wherein every contact comprises a plurality of separate individual contacts having a defined spring rate. At least one of the contact bodies (4) is configured as a two-layer spiral contact with a lower layer consisting of a highly elastic material and an upper layer (7) consisting of a highly electroconductive material. A contact coat (9) consisting of a contact material is provided on the upper layer in the outer zone of every contact arm (10).

Abstract: A circuit interrupter including a housing having an internal cavity. The internal cavity includes a space at a first end thereof, and includes an internal wall extending from the space to a second end of the housing. A vacuum interrupter is disposed in the space. The vacuum interrupter has at least one movable contact for contacting at least one stationary contact. An operating rod extends through the cavity, and is operable to move the moveable contact At least one baffle is fixed to the operating rod, and disposed in the cavity. In a preferred embodiment, at least one step is formed in the wall. The step separates a first internal wall section from a second internal wall section, and the first internal wall section is closer to the space than the second internal wall section.

Abstract: A vacuum switch comprises a vacuum container, a grounding switch and a load switch disposed in the container, and an external connection conductor disposed in the vacuum container and to be connected electrically inside and outside the vacuum container, and it is characterized in that the grounding switch and the external connection conductor are electrically connected to each other in the vacuum container.

Abstract: A glazed ceramic article is provided which comprises a glaze layer formed on an outer surface of a ceramic main body. The glaze layer is made of a glaze comprising 60 to 74% by weight of Si when calculated in terms of SiO2 and 16 to 30% by weight of Al when calculated in terms of Al2O3. Such a composition can raise the softening temperature and can prevent deterioration of the appearance due to the surface roughening caused at the time of soldering of a metallic member to the ceramic main body after glost firing and deterioration of the insulation ability due to adherence of dirt to the surface of the glaze layer. A metal and ceramic assembly having such a glazed ceramic article, and a vacuum switch having such a metal and ceramic assembly are also provided.

Abstract: To reduce the size of a gas-insulated switch for the purpose of utilizing the space of a power station or substation effectively and improving the economy thereof. A gas-insulated switch equipped with a fixed contact and a moving contact that can contact with and separate from the fixed contact, wherein the breakage of the moving contact is operated with a single shock absorber in both the breaking action and the closing action of the moving contact. As a result that use of the gas-insulated switch according to the present invention improves the overall energy efficiency of components, a device with further reduced driving energy can be realized for a gas-insulated switch of the same specification.

Abstract: An object of this invention is to provide a vacuum switch in which the assembling property of the parts to be accommodated in the interior of the vacuum container is improved, the configuration of the vacuum container is simplified, and the parts to be accommodated in the interior of the container can be assembled easily. This invention is a vacuum switch wherein a ground switch, a load switch, and an external connecting conductor to be electrically connected with the inside and outside of the vacuum container are provided in a vacuum container; the ground switch and the external connecting conductor are electrically connected in the vacuum container; and the vacuum container has a joint construction of a body portion having openings on both ends thereof, and a lid joined to the opening of the body.