High-voltage switches with arc preventing or extinguishing devic – Arc preventing or extinguishing devices – Vacuum
Reexamination Certificate
2001-06-14
2002-07-30
Donovan, Lincoln (Department: 2832)
High-voltage switches with arc preventing or extinguishing devic
Arc preventing or extinguishing devices
Vacuum
C218S123000, C218S128000
Reexamination Certificate
active
06426475
ABSTRACT:
TECHNICAL FIELD
This invention relates to a vacuum valve.
BACKGROUND ART
Generally, in order to improve a breaking efficiency of a vacuum valve, an arc control method of applying a magnetic field parallel to a vacuum arc generated between electrodes has been used to suppress the arc. A typical vacuum valve using the method is a longitudinal-flux-type vacuum valve. One of electrode structures of the longitudinal-flux-type vacuum valve is shown in FIG.
11
.
FIG.11
shows a structure of a movable electrode. A structure of a stationary electrode is the same with the structure of the movable electrode and the stationary electrode is arranged to face the movable electrode for contacting thereto.
In
FIG. 11
, a round concave
6
a
is dug at a top of a movable conduction element
6
B of copper. A ring-shaped reinforcing element
18
of stainless steel has a collar
18
a
of its lower portion and the collar
18
a
is engaged in the round concave
6
a
and brazed to it. A bush
14
a
of copper projecting from a center of a coil electrode
14
is inserted around the collar
18
a
and brazed with the collar
18
a
and the movable conduction column
6
B.
Four arms
14
b
projects from the bush
14
a
in a radial pattern as to space 90° each other around the bush
14
a
and in the direction perpendicular to the axial direction of the bush
14
a
. A base portion of an arc coil element
14
c
is brazed to each end of the arms
14
b
. A through hole
14
d
is bored at a top of the coil element
14
c
along the axial direction. A disk-shaped contact element
13
made of copper and having a center column is provided to the top of the coil element
14
c
and the center column of which is inserted into the top of the coil element
14
c
and is brazed thereto.
A disc-shaped electrode plate
2
B made of copper with grooves cut in a radial pattern from the center to the circumference thereof is provided on the end of the reinforcing element
18
and that is brazed to the surfaces of the reinforcing element
18
and the contact element
13
. A disc-shaped contact element
1
A made of tungsten alloy with grooves cut in a radial pattern from the center to the circumference thereof and with a roundly chamfered outer edge is brazed to the electrode plate
2
B.
In this vacuum valve having the electrode of the structure set forth above, a breaking current from the movable conduction column
6
B to the contact element
1
A mainly flows from the bush
14
a
through the arms
14
b
to the end of the coil element
14
c
of the coil electrode
14
and the small part of the current flows through the reinforcing element
18
to the electrode plate
2
B.
The current flowing into the coil element
14
c
runs there half round so as to produce a longitudinal magnetic field and flows into the electrode plate
2
B via the contact element
13
at the end of the coil element
14
c
and the lower surface of the electrode plate
2
B. The current further runs through the upper surface of the electrode plate
2
B and comes out from the contact element
1
A. This current coming out from the contact element
1
A flows into a contact element of the stationary electrode (not shown in
FIG. 11
) contacting to the surface of the contact element
1
A and it runs through an electrode plate, a contact element and coil element of the stationary electrode and flows out into a stationary conduction column.
FIG. 12
shows a distribution of magnetic flux density between the electrodes produced by the coil electrode
14
(given at an area halfway between the movable and stationary electrodes when they are pulled apart). The longitudinal flux density between the electrodes is greatest at the center area of the electrode and it gradually lowers toward the circumference thereof. Here, in order to effectively suppress an eddy current to be generated by the coil electrode
14
, slits are made in the electrode plate
2
B and the contact element
1
A. The coil electrode
14
is designed as the flux density to be larger even at the circumference of the electrode than a flux density Bcr which causes the lowest arc voltage to respective breaking currents.
By controlling the vacuum arc generated between the electrodes through this distribution of flux density, the breaking current that causes an arc concentration is greatly improved comparing to that to be caused under the condition without the magnetic field, and the breaking efficiency is also greatly improved. However, it does not mean that the arc concentration can be prevented to the indefinitely great current under the condition that the diameter of the electrode is defined. The arc concentration tends to occur in the center area of the electrode (in the neighborhood of an anode) in a strong magnetic field that is produced by a greater current than a critical value.
Additionally, as shown in
FIG. 12
of the distribution of the magnetic flux density, the current density in the center area of the electrode has been detected very great even in the lower current region than the critical current. This tends to cause the current density in the center area to reach to the critical current density so that the arc shifts from its dispersed state to concentrated state and finally falls into non-breakable state.
In order to raise the critical current, it seems to be effective to unify the distribution of current density by changing the magnitude and the distribution of flux density to be adjusted. However, as to the intensity of the magnetic field, the inventors carried out current-breaking tests by using trial electrodes enabling to produce intensified magnetic fields but the result did not show the effectiveness.
Accordingly, the distribution improvement of flux density has been expected to be a solution for raising the critical current and there has been proposed several methods in line with this approach in the past. Here, one typical method for improving the distribution of flux density will be explained.
FIG. 13
shows curves of radial-direction distribution of flux density between the electrodes, which is cited from the paper (IEEE Transs. on Power Delivery, Vol. PWTD-
1
, No. 4, Oct. 1986) presented by the inventors. These curves show that, although the distribution of flux density differs according to the gap distance between the electrodes, the maximum value of flux density always appears at the circumferential side of the electrode. However, the maximum density in the radial direction appears at around 55% point of the radius 28.5 mm of the electrode and it is out of the scope of the distribution characteristic of flux density proposed by this invention. Further, the conventional distribution characteristic of flux density can not effectively disperse the arc generated between the electrodes to their circumferential areas.
There are three kinds of method known which can lower the flux density in the center area of the electrode.
(1) One of which is a method of producing a reverse magnetic field by an eddy current flowing the electrode plate and contact element by not cutting the slits in the electrode plate
2
B and the contact element
1
A.
(2) Other method is that provides an other coil electrode for producing the reverse magnetic field in the center area of the electrode.
(3) The third method is that brings the coil electrodes
14
of the movable side and the stationary side closer as possible.
Japanese Laid Open Application PS57-212719 discloses an electrode structure using the method (1). FIG.
14
(
a
) shows a distribution of flux density of this electrode and FIG.
14
(
b
) shows the structure of the electrode. A coil electrode
11
is joined to an end of a movable conduction column
6
C and a join port
15
is made therein and a spacer
18
is joined in the center area thereof. An electrode plate
12
is joined to the coil electrode
11
via the join port
15
and the spacer
18
. A field adjust plate
36
of pure copper is buried in a surface
35
of the electrode plate
12
so as the reverse magnetic field to be produced by the eddy current generated by this field adjust plate
36
Honma Mitsutaka
Kagenaga Kiyoshi
Kaneko Eiji
Sato Jun-ichi
Somei Hiromichi
Donovan Lincoln
Foley & Lardner
Kabushiki Kaisha Toshiba
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