U.S. patent application number 10/914290 was filed with the patent office on 2005-05-19 for vacuum switchgear.
Invention is credited to Kobayashi, Masato, Satou, Kazuhiro, Shirone, Takashi, Tsuchiya, Kenji, Utsumi, Tomoaki.
Application Number | 20050103514 10/914290 |
Document ID | / |
Family ID | 34431518 |
Filed Date | 2005-05-19 |
United States Patent
Application |
20050103514 |
Kind Code |
A1 |
Utsumi, Tomoaki ; et
al. |
May 19, 2005 |
VACUUM SWITCHGEAR
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. This arrangement
instantly eliminates a dielectric breakdown phenomenon that occurs
at electric field concentrated regions by the shields to prevent a
dielectric breakdown caused by particulate foreign matters and
thereby improve an insulation reliability of the devices.
Inventors: |
Utsumi, Tomoaki; (Hitachi,
JP) ; Satou, Kazuhiro; (Hitachi, JP) ;
Shirone, Takashi; (Hitachi, JP) ; Tsuchiya,
Kenji; (Hitachi, JP) ; Kobayashi, Masato;
(Hitachi, JP) |
Correspondence
Address: |
CROWELL & MORING LLP
INTELLECTUAL PROPERTY GROUP
P.O. BOX 14300
WASHINGTON
DC
20044-4300
US
|
Family ID: |
34431518 |
Appl. No.: |
10/914290 |
Filed: |
August 10, 2004 |
Current U.S.
Class: |
174/350 |
Current CPC
Class: |
H01H 1/5822 20130101;
H01H 33/66261 20130101; H01H 31/003 20130101; H01H 33/6661
20130101; H01H 2033/66284 20130101; H01H 33/022 20130101; H01H
2033/6668 20130101 |
Class at
Publication: |
174/035.00R |
International
Class: |
H05K 009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 17, 2003 |
JP |
2003-386385 |
Claims
1. A vacuum switchgear comprising: a vacuum container required to
be earthed; a switching unit accommodated in said vacuum container
and having a stationary electrode and a movable electrode; a bus
side conductor and a load side conductor arranged to extend in and
out of said vacuum container; wiring conductors arranged in said
container, connecting said stationary electrode to one of said bus
side conductor and said load side conductor and connecting said
movable electrode to the other of said bus side conductor and said
load side conductor; and a shield arranged inside said vacuum
container to shield a part or all of an area where particulate
foreign matters are produced by an open-close operation of said
switching unit, said shield being insulated from and secured to
said vacuum container.
2. A vacuum switchgear according to claim 1, wherein said shield is
formed of a metal plate and secured to said vacuum container
through an insulating member.
3. A vacuum switchgear according to claim 1, wherein said shield is
formed of an insulating material containing ceramics and secured to
said vacuum container through an insulating member.
4. A vacuum switchgear according to claim 1, wherein said shield is
formed of a plate-shaped insulating material and secured to said
vacuum container through an insulating member.
5. A vacuum switchgear according to claim 1, wherein said shield is
formed of a metal plate and secured to said vacuum container
through an insulating member, and said metal plate is partly or
wholly covered with an insulating coating.
6. A vacuum switchgear according to claim 1, wherein a distance
between said shield and said vacuum container is set to be able to
withstand a service voltage of a power system connected to said bus
side conductor.
7. A vacuum switchgear according to claim 1, wherein said shield is
arranged to face electric field concentrated regions of said
switching unit, said bus-side conductor, said load side conductor
and said wiring conductors in said container.
8. A vacuum switchgear according to claim 1, wherein said shield is
arranged in a lower part of said vacuum container to face electric
field concentrated regions of said switching unit, said bus-side
conductor, said load side conductor and said wiring conductors in
said container.
9. A vacuum switchgear according to claim 1, wherein said shield is
formed of a metal plate and secured to said vacuum container
through an insulating member, and said insulating member has its
surface formed with a highly resistive conducting layer connecting
said metal plate and said vacuum container.
10. A vacuum switchgear according to claim 1, wherein said shield
comprises a plurality of shield plates and an insulating member is
interposed between adjacent shield plates.
11. A vacuum switchgear comprising: a vacuum container required to
be earthed; switching units of the same number as that of phases to
be dealt with by the switchgear, said switching units being
accommodated in said vacuum container and each having a stationary
electrode and a movable electrode; bus side conductors and load
side conductors of the same number as that of the phases, said bus
side conductors and said load side conductors being arranged to
extend in and out of said vacuum container; wiring conductors for
each phase arranged in said container, connecting the stationary
electrode of each phase to one of the bus side conductor and the
load side conductor of the same phase and connecting the movable
electrode of the same phase to the other of the bus side conductor
and the load side conductor of the same phase; and shields arranged
inside said vacuum container to shield a part or all of areas where
particulate foreign matters are produced by an open-close operation
of said switching unit of each phase, said shields being insulated
from and secured to said vacuum container.
12. A vacuum switchgear comprising: a vacuum container required to
be earthed; one or more switching units accommodated in said vacuum
container and each having a stationary electrode and a movable
electrode; a bus side conductor and a load side conductor arranged
to extend in and out of said vacuum container; wiring conductors
arranged in said container, connecting the stationary electrode to
one of the bus side conductor and the load side conductor and
connecting the movable electrode to the other of the bus side
conductor and the load side conductor; an intermediate shield
arranged around said switching units to shield arcs produced by an
open-close operation of said switching units; and a shield arranged
inside said vacuum container to shield a part or all of areas where
particulate foreign matters are produced by an open-close operation
of said switching units, said shield being insulated from and
secured to said vacuum container.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a vacuum switchgear and
more particularly to a vacuum switchgear, in which a switch having
a stationary electrode and a movable electrode is enclosed in a
vacuum container that requires grounding.
[0002] As a conventional vacuum switchgear, for example, there is a
construction, in which a vacuum container accommodates a main
circuit switching unit for connecting and disconnecting a main
circuit conductor to and from a load side conductor or a bus side
conductor and a main circuit/earth selecting unit for connecting
the main circuit conductor to and from the bus side conductor or
the load side conductor and an earthing conductor and in which the
vacuum container is formed of a grounded metal or an insulating
material with a grounded layer on its surface. This vacuum
container accommodates the main circuit conductor and a part of
each of the bus side conductor, the earthing conductor and the load
side conductor. Further, the vacuum container also has an air
terminal unit that respectively connects in air those portions of
the bus side conductor, the earthing conductor and the load side
conductor projecting from the vacuum container to the bus side, the
earth side and the load side. On the outside of the vacuum
container, drive mechanisms are installed to operate the main
circuit switching unit and the main circuit/earthing selecting
unit. This construction is seen in JP-A-2001-346306, page 4-6 and
FIG. 4, for instance.
[0003] By integrating an interrupting function, a disconnecting
function and an earthing function in the single earthed vacuum
container, the interruption and insulation performance can be
enhanced, allowing the devices to be made compact. During assembly,
the vacuum container with the integrated functions serves as one
component. There is therefore an advantage that the number of
components can be reduced and the reliability improved. Further, by
earthing the vacuum container an inspection can be performed
online.
[0004] In the conventional vacuum switchgear, particulate foreign
matters of a few micron meters may be formed by the open-close
operation of the switching unit or during the manufacturing
process. If these particulates reach a high electric field area in
vacuum, a dielectric breakdown may occur even at service voltage.
More specifically, an intermediate shield is provided around the
main circuit switching unit among the switching units in the vacuum
switchgear to shield an arc produced during the open-close
operation, and a dielectric breakdown is prevented from being
triggered by an arc. However, the other conductors than the main
circuit switching unit also provide electric field concentrated
regions but are not shielded. If foreign particles enter the
electric field concentrated regions, therefore, they can conduct
electricity between the conductors in the field concentrated
regions and the grounded vacuum container, resulting in a
dielectric breakdown. This dielectric breakdown may occur even when
the dielectric strength of devices is verified in a withstand
voltage test to be several times the service voltage. When this
dielectric breakdown is detected as a ground fault by a protective
control system in the power system, a circuit breaker may be
tripped, resulting in a power system failure. To prevent the
dielectric breakdown the field intensity of the electric field
concentrated regions has to be reduced, and therefore the sizes of
the devices require increasing to lengthen the insulation
distances.
SUMMARY OF THE INVENTION
[0005] An object of this invention is to prevent a dielectric
breakdown due to foreign particulates and improve the insulation
reliability of devices.
[0006] To achieve the above object, the present invention is
contrived that a switching unit having a stationary electrode and a
movable electrode is accommodated in a vacuum container required to
be earthed, the stationary electrode and the movable electrode are
connected to a bus side conductor and a load side conductor or vice
versa through wiring conductors in the container, a shield is
arranged inside the vacuum container to shield a part or all of an
area where particulate foreign matters are produced by open-close
operation of the switching unit, and the shield is secured to the
vacuum container in a insulated condition therefrom.
[0007] In this construction, for instance, when particulate foreign
matters reach a high electric field area near the conductors, a
dielectric breakdown phenomenon occurs only between the conductors
and the shield but not between the shield and the vacuum container.
Thus, this dielectric breakdown does not result in a ground fault,
nor does it lead to a power system failure. More specifically, in
the event that a dielectric breakdown phenomenon is caused by
particulate foreign matters, the shield and the conductors are
instantly brought to the same potential. However, since the shield
is insulated from the vacuum container, an electric field between
the conductors and the shield disappears, no longer accelerating
charged particles generated by the dielectric breakdown. The
dielectric breakdown therefore can no longer persist, and the
dielectric strength can recover instantly, preventing damages to
the devices. This in turn can prevent a ground fault and also
prevent the dielectric breakdown phenomenon from providing a cause
for a possible power system failure.
[0008] According to the invention it is possible to prevent damages
to the devices and a ground fault and to prevent a cause for a
possible power system failure.
[0009] Other objects, features and advantages of the invention will
become apparent from the following description of the embodiments
of the invention taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a vertical sectional view of a vacuum switchgear
showing an embodiment of the invention.
[0011] FIG. 2 is a vertical sectional view of a vacuum switchgear
showing the second embodiment of the invention.
[0012] FIG. 3 is a plan view of the vacuum switchgear shown in FIG.
2.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0013] An embodiment of the invention will be now described with
reference to the accompanying drawings. FIG. 1 is a vertical
sectional view of a vacuum switchgear showing the embodiment of the
invention. In FIG. 1, the vacuum switchgear is represented by one
phase of one unit in a power receiving and distribution board
comprised of a plurality of units. In this embodiment, a main
circuit switching unit 10, an isolator 20, flexible conductors 63,
64, an earthing device 30 and so on are accommodated in vacuum
containers 1, 2 that need to be grounded, i.e., in the vacuum
containers which are grounded and formed of a metal (stainless
steel). A conductor 61 and a main circuit conductor 62 are arranged
to extend inside and outside the vacuum containers 1, 2.
[0014] The main circuit switching unit 10 has a movable electrode
11 and a stationary electrode 12 and is installed in the vacuum
container 1, separated by a spacer 15 from the isolator 20. An
intermediate shield 13 is arranged around the movable electrode 11
and the stationary electrode 12 to shield an arc generated when the
circuit is opened and closed. The stationary electrode 12 is
inserted through a through-hole in a central part of the spacer 15
to be supported by the spacer 15 and is connected to a stationary
electrode 22 of the isolator 20. Around the movable electrode 11 is
arranged an insulator 14 to prevent charged particulates produced
during opening and closing of the movable electrode 11 and the
stationary electrode 12 from diffusing outward. The insulator 14 is
connected to an end of the intermediate shield 13. The movable
electrode 11 is connected to the conductor 61 through the flexible
conductor 63 which serves as a wiring conductor in the container.
The conductor 61 is inserted into a through-hole in a ceramic
connecting portion 81 arranged in and out of the vacuum container
1. The conductor 61 is integrally formed at its end with a
disk-shaped portion 61a for reducing an electric field
concentration. This conductor 61 serves as a bus side conductor
when it is connected to a bus disposed outside the vacuum container
1 and as a load side conductor when it is connected to a power line
connected to a load.
[0015] The movable electrode 11 is connected through an insulating
rod 17 to a bellows 18 and an operation rod 19. The movable
electrode 11 is thus operated for engagement with or disengagement
from the stationary electrode 12 by switching operation of the
operation rod 19 coupled to an outside driving mechanism. That is,
the main circuit switching unit 10 is adapted to connect or
disconnect the conductor 61 and the main circuit conductor 62 by
open and close operation of the movable electrode 11 and the
stationary electrode 12. The movable electrode 11 and the
stationary electrode 12 are formed by mixing a slight amount of
such substances as chromium and cobalt to copper to improve an arc
resistance and thereby have an excellent current interrupting
capability. The flexible conductor 63 is made by laminating a
plurality of thin copper plates.
[0016] The isolator 20 is received in the vacuum container 2 as an
auxiliary switch with a stationary electrode 22 and a movable
electrode 21 and is so constructed as to connect or disconnect the
main circuit conductor 62 and the main circuit switching unit 10.
The movable electrode 21 is connected to the main circuit conductor
62 through the flexible conductor 64 serving as a wiring conductor
in the container. The main circuit conductor 62 is inserted into a
through-hole in a ceramic connecting portion 82 arranged in and out
of the vacuum container 2 and is integrally formed at its almost
central part with a disk-shaped portion 62a for reducing an
electric field intensity. The main circuit conductor 62 serves as a
bus side conductor when it is connected to the bus situated outside
the vacuum container 2 and as a load side conductor when it is
connected to the power line connected with the load. The movable
electrode 21 is connected through an insulating rod 27 to a bellows
28 and an operation rod 29. The isolator 20 is opened or closed as
the operation rod 29 is operated by an outside driving mechanism.
An end of the flexible conductor 64 and an end of the main circuit
conductor 62 are each connected to an earthing device 30 having a
bellows 38 and an earthing conductor 39. The earthing conductor 39
is opened and closed by an outside driving mechanism. The main
circuit conductor 62 is earthed through the earthing conductor 39.
The flexible conductor 64 is made by laminating a plurality of thin
copper plates.
[0017] Ceramic materials used for the connecting portions 81, 82
include alumina, silica, magnesium oxide, titanium oxide, mica,
boron nitride, aluminum fluoride and the like.
[0018] In the vacuum switchgear of the above construction, when a
high electric field is applied, the electric field tends to
concentrates on corners, bent portions, protruding portions and
ends of the disk-shaped portion 61a of the conductor 61, the
disk-shaped portion 62a of the main circuit conductor 62, the
flexible conductors 63, 64, the main circuit switching unit 10 and
the isolator 20. Particulate foreign matters of a few micron meters
may be produced in the manufacturing process or during open-close
operations. These particulate foreign matters, if left as are, may
lead to a dielectric breakdown. Equipment is basically designed and
manufactured in a manner that prevents formation of such
particulate foreign matters. However, if the particulate foreign
matters formed nevertheless can be made harmless, the manufacturing
process can be simplified and the equipment reliability
improved.
[0019] In this embodiment, therefore, shields 101, 103, 105, 107
and 109 that shield a part or all of areas where particulate
foreign matters are produced during the operation of the main
circuit switching unit 10 and the isolator 20, such as electric
field concentrated regions, are arranged inside the vacuum
containers 1, 2. The respective shields 101, 103, 105, 107 and 109
are insulated from the vacuum containers 1, 2. That is, the shields
101, 103, 105, 107 and 109 are secured to the vacuum containers 1,
2 through spacers 100, 102, 104, 106, 108 made of insulating
material. The shields 101, 107 are formed cylindrical and the
shields 103, 105, 109 are formed like a plate. The shields 101,
103, 105, 107, 109 have their ends bent inward to reduce electric
field concentration. The shield 101 is constructed to shield
particulate foreign matters produced by the conductor 61, the
disk-shaped portion 61a and the flexible conductor 63. The shield
107 is constructed to shield particulate foreign matters coming
from the main circuit conductor 62 and the disk-shaped portion 62a.
The shield 103 is designed to shield particulate foreign matters
coming from a connecting portion between the flexible conductor 63
and the movable electrode 11. The shield 105 is designed to shield
particulate foreign matters coming from the isolator 20. The shield
109 is designed to shield particulate foreign matters coming from
the flexible conductor 64 and the main circuit conductor 62.
[0020] With the above construction, if a dielectric breakdown
phenomenon occurs in the electric field concentrated regions due to
the formation of particulate foreign matters, in that instant, an
electricity flows between the field concentrated regions and the
shields 101, 103, 105, 107, 109 through the particulate foreign
matters, and they have the same potential, for example, an
operational voltage of 2 kV. However, since the shields 101, 103,
105, 107, 109 are insulated from the vacuum containers 1, 2, at the
moment when the shields 101, 103, 105, 107, 109 and the electric
field concentrated regions are brought to the same potential, an
electric field between the conductors of the field concentrated
regions and the shields 101, 103, 105, 107, 109 disappears and
charged particles produced by the dielectric breakdown phenomenon
are no longer accelerated by the field, making it impossible for
the dielectric breakdown phenomenon to persist. Then, once the
dielectric breakdown phenomenon disappears, the particulate foreign
matters which triggered the dielectric breakdown phenomenon
disappear with it. Further, since the dielectric strength of the
devices when there are no particulate foreign matter is more than
several times the service voltage, the dielectric strength is
instantly restored, protecting the devices against damages. By
setting the dielectric strength between the shields 101, 103, 105,
107, 109 and the vacuum containers 1, 2 strong enough to withstand
the service voltage, it is also possible to avoid a ground fault
and prevent a dielectric breakdown phenomenon from causing a
possible failure of the power system.
[0021] Next, a second embodiment of the invention will be described
with reference to FIG. 2 and FIG. 3. In this embodiment two
isolators 20 are received in the vacuum container 1 in addition to
the main circuit switching unit 10, with each isolator 20
electrically connected to the main circuit switching unit 10. The
main circuit switching unit 10 and the isolators 20 are each
provided with an earthing device 30 so that they can be earthed
independently of each other. The movable electrode 21 of each
isolator 20 is connected through the flexible conductor 64 to the
conductor 65, which in turn is connected to the conductor 66. The
movable electrode 11 of the main circuit switching unit 10 is
connected through the flexible conductor 63 to the conductor 65.
The conductor 65 of the main circuit switching unit 10 is connected
through a conductor 67 to the conductor 65 of the adjoining
isolator 20.
[0022] In this embodiment, shields 111, 113, 115, 117, 121 made of
a metal plate are arranged inside the vacuum container 1 to enclose
the main circuit switching unit 10, the isolators 20 and the
earthing devices 30 by taking areas surrounding the main circuit
switching unit 10 and the isolators 20 as particulate foreign
matter generation areas. The respective shields 111, 113, 115, 117
are secured to the vacuum container 1 through spacers 110, 112,
114, 118 as insulating members, and the insulating plates 121 are
secured to the vacuum container 1 through insulating rods 17, 27.
The shields 111, 113, 115, 117, 121 each shaped like a plate have
their opposite ends bent inward in a large radius to allow
reduction of electric field concentration. Covering the ends of the
shields with an insulating material can further enhance the
dielectric strength. Covering of the ends with the insulating
material may be carried out by covering them with a ceramic sheet
or by forming a diamond-shaped carbon thin film.
[0023] In this embodiment, since the shields 111, 113, 115, 117,
121 insulated from the vacuum container 1 are arranged inside the
vacuum container 1, if a dielectric breakdown phenomenon due to
particulate foreign matters occurs at electric field concentrated
regions on the main circuit switching unit 10, the isolators 20 and
the earthing devices 30, it is possible to prevent the dielectric
breakdown phenomenon from damaging the devices and to avoid a
ground fault. This in turn prevents the dielectric breakdown
phenomenon from causing a possible failure of the power system.
[0024] Further, in this embodiment, the connecting portions 81, 82,
the conductor 61 and the main circuit conductor 62 are arranged in
the same direction, and the operation rods 19, 29, 39 are also
arranged in the same direction as those of the conductor 61 and the
main circuit conductor 62. The switchgear therefore can be
constructed in a simple configuration with its sides almost planar,
and the shields 111, 113, 115 and 117 can also be in simple shapes.
This makes the installation easy.
[0025] Further, the disk-shaped shields 121 are arranged around the
insulating rods 17, 27. Therefore, if a dielectric breakdown
phenomenon occurs in an upper space of the vacuum container 1 due
to particulate foreign matters coming from an upper side of the
main circuit switching unit 10 and the isolators 20, this
dielectric breakdown phenomenon can be instantly eliminated by the
shields 121.
[0026] Further, also installing shields below the main circuit
switching unit 10 and the isolators 20 through insulating spacers
can prevent particulate foreign matters lying on the bottom of the
container from floating up.
[0027] Although in each of the above embodiments, the shields have
been described as being formed of metal plates, they may be formed
of an insulating material such as ceramics. If the shields are made
of ceramics, when a dielectric breakdown phenomenon occurs, the
surfaces of the shields become the same electrical potential with
that of the conductors. The ceramics material may be alumina,
silica, magnesium oxide, titanium oxide, mica, boron nitride and
aluminum fluoride.
[0028] Following a dielectric breakdown phenomenon occurring
between the shields and the conductors, there is a case where a
peak potential of AC service voltage remains on the shields. In
this case, a dielectric strength for withstanding the DC voltage is
required. If insulation distances corresponding to the required
dielectric strength are provided, there is no problem.
Alternatively, the DC voltage can be prevented from acting on the
shields by providing the surface of the insulating material with a
highly resistive conductive layer that does not affect the
insulation against an AC voltage and by dissipating charges
accumulated on the shields. This can reduce the insulation
distances and allows the devices to be made compact. For example, a
highly resistive conductive layer may be formed over the surfaces
of the shields made of a metal plate to connect the metal plate and
the vacuum container. Here, the resistance of the conductive layer
has to be more than 10.sup.10 .OMEGA..
[0029] Although the shields have been described as each being
arranged between the conductor and the vacuum container, a
plurality of shields may be stacked together and installed to
reduce a voltage applied to each of the shields, thus enhancing the
insulation reliability. In this case, a spacer as an insulating
material is inserted between the shields.
[0030] In installing the switching units such as the main circuit
switching unit 10 and the isolator 20 in the vacuum containers 1,
2, the same number of switching units, each having a stationary
electrode and a movable electrode, as that of phases, e.g. three
units for three phases, may be installed. In that case, used is
such a construction that the stationary electrode and the movable
electrode of each phase are connected to a bus side conductor and a
load side conductor of the corresponding phase or vice versa
through wiring conductors of the associated phase in the
containers, e.g. flexible conductors. Shields are installed inside,
and insulated from, the vacuum containers to shield a part or all
of areas where particulate foreign matters are produced by the
open-close operation of the switching unit of each phase.
[0031] It should be further understood that although the foregoing
description has been made on the embodiments of the invention, the
invention is not limited solely to the specific forms and various
changes and modifications may be made without departing from the
spirit of the invention and the scope of the appended claims.
* * * * *