Note: Descriptions are shown in the official language in which they were submitted.
~;~8~72
The present invention generally relates to a
vacuum interrupter, and more particularly to an axial
magnetic field applied type vacuum interrupter which applies
an axial magnetic field in parallel to an arc current path
produced between separated electrodes within the vacuum
envelope of the interrupter.
Description of the Prior Art
U.S. Patent No. 4,661,666 issued on April 28, 1987
discloses a prior-art vacuum interrupter. Such an
interrupter has a vacuum envelope and a disc-shaped
stationary electrode and a movable electrode disposed within
the vacuum envelope and operable for forming or interrupting
electrical contact therebetween. The vacuum envelope
comprises an insulating cylinder, a disc-shaped metal end
plate hermetically secured to one edge of the insulating
cylinder via a metal seal ring, a bottomed metal cylinder
the open end of which is hermetically secured to the other
edge of the insulating cylinder via a metal seal ring. The
stationary and movable electrodes are located wi-thin the
metal cylinder.
A stationary lead rod passes hermetically through
and is ~ixed to a flat bottom of the metal cylinder. An
inner end of the stationary lead rod carries the stationary
electrode within the metal cylinder. On the other hand, a
movable lead rod passes loosely through the metal end plate
and is hermetically secured to the metal end plate via a
metal bellows. An inner end of the movable 'ead rod carries
the movable electrode within the metal cylinder. Thus, the
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, , .
movable lead rod is considerably longer than the stationary
lead rod. The bellows is located within the insulating
cylinder with its inner surface exposed to the atmosphere.
The bellows is as remote from the electrodes within the
vacuum envelope as possible in orcler to protect the bellows
from the deposi-tion of the metal vapor generated by the
electrodes during opening and closing operations. A cup-
shaped bellows shield is fixed to an intermediate portion of
the movable lead rod. The bellows shield also protects an
inner end area of the bellows from deposition of the metal
vapor.
A coil of substantially one turn surrounds the
stationary and movable electrodes ou-tside the cylindrical
portion of the metal cylinder. The coil produces an axial
magnetic field running parallel to the arc current path
between the separated stationary and movable electrodes for
dispersing the arc evenly across the opposing faces of the
electrodes thereby increasing the current interruption
performance of the interrupter. One end of the coil is
electrically connected to an outer end of the stationary
lead rod. The other end of the coil is electrically
connected to one end of a first outer lead rod which is
located outside the vacuum envelope. The first outer lead
rod extends perpendicularly to the stationary lead rod.
A second outer lead rod which is located outside
the vacuum envelope extends parallel to the first outer lead
rod. One end of the second outer lead rod has a slide
contact which mechanically and electrically engages an outer
end of the movable lead rod. A main shield is fixed to an
inner cylindrical surface of the metal cylinder. The
electrical potential of the main shield is equal to that of
the stationary lead rod but different from that of the
movable lead rod. An auxiliary shield is fixed to the end
plate.
-- 2 --
172
In -the operation of the above-described
interrupter, a current (e.g., a fault current) passes
through a sequencee comprising the first outer lead rod, the
coil, the stationary lead rod, the stationary electrode, the
arc current path between the stationary electrode and the
movable electrode, the movable electrode, the movable lead
rod, the slide contact and the second outer lead rod and
vice versa. Therefore, the stationary and movable lead rods
are subjected to a resulting electro-magnetic force with a
radial vector in accordance with the left-hand rule when a
current passes through the above-described sequence. The
electro-magnetic force radially inclines the movable lead
rod when the stationary and movable electrodes are out of
contact. This inclination displacement reduces the
clearance between the movable lead rod and the main shield
which have different potentials, which in turn reduces the
dielectric strength of the vacuum interrupter. An
inclination displacement of the movable lead rod due to the
electro-magnetic force of the coil causes the stationary and
movable electrodes to be in point-to-point contact at outer
peripheries of the stationary and movable electrodes. Thus,
a mechanical impact force occurring during closing operation
of the stationary and movable electrodes concentrates at the
point of contact between the stationary and movable
electrodes. This concentration of the mechanical impact
force can possibly split or break the stationary and movable
electrodes during many opening and closing operations. Thus
the radial displacement of the movable electrode 2 causes
premature wear and reduced dielectric strength in the vacuum
interrupter. Furthermore, the lengthiness of the movable
lead rod increases the total weight of the movable assembly
associated with the movable lead rod, and the load of weight
on the associated operating mechanism for the movable lead
rod.
.. ..
L'7~2
Most of the metal vapor produced during the
opening operation of the stationary and movable electrodes
disperses to a space behind the movable electrode in the
insulating cylinder rather than the space behind the
stationary electrode because the space behind the movable
electrode is greater than the space behind the stationary
electrode. Therefore, some of the dispersing metal vapor
deposits on the surface of the be]Llows during many (no less
than 10,000 times) opening and closing operations in spite
of the presence of the bellows shield. The metal vapor
deposited on the bellows melts a little bit of the surface
of the bellows and causes the adjacent annular portions o
the bellows to s-tick each other because the bellows
contracts during the opening operation of the stationary and
movable electrodes when the vapor is formed. The sticking
together of the adjacent annular portions of the bellows
causes them to tear and leak thus compromizing the vacuum
within the vacuum envelope.
In the prior-art vacuum interrupter, the short
s-tationary lead rod connects the stationary and movable
electrodes to -the coil, so that Joule heat due to contact
resistance between the stationary and movable electrodes
cannot be dissipated sufficiently through the stationary
lead rod. Moreover, Joule heat produced by the coil is
added to that produced by contact resistance. Thus, the
temperature of the vacuum interrupter may be caused to
exceed the maximum temperature (e.g., a temperature of a
silver-plating-free lead rod being 90C under an ambient
temperature of 40 C) permissible for the vacuum interrupter.
In addition, the vacuum interrupter usually
constitutes part of a circuit breaker installed in a metal-
clad switchgear, the s-tationary lead rod being located in an
upper portion of the vacuum interrupter. Thus, the coil as
a heat transmi-tter surrounds the upper portion of the vacuum
, . . , , ~ .
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interrupter. This arrangement blocks the natural convection
along the outer length of the vacuum envelope within the
surrounding atmosphere, thus blocking heat dissipation from
the vacuum interrupter.
SUMMARY OF TH~ IN~ENTION
. . _ . .
An object of this invention is to provide a vacuum
interrupter with an improved dielectric strength.
Another object of this invention is to provide a
vacuum interrupter in which point-to-point contac-t between
the electrodes does not occur.
A further object of this invention is to provide a
vacuum interrupter with improved heat dissipation
capability.
In order to achieve these and other objects,
an inventive vacuum interrupter comprises :
a vacuum envelope including an insulating cylinder, a
metal end plate hermetically sealed to one edge of the
insulating cylinder and a bottomed metal cylinder having an
open end hermetically sealed to the other edge of the
insulating cylinder;
a pair of disc-shaped electrodes comprising a
stationary electrode and a movable electrode disposed facing
each other within the metal cylinder, the movable electrode
being movable for establishing or interrupting contact with
the stationary electrode;
a stationary lead rod passing hermetically through the
metal end plate and the insulating cylinder and fixed to the
metal end plate, the stationary lead rod having an inner end
fixed to the stationary electrode;
a movable lead rod passing through the bottom of the
metal cylinder and being movable coaxially with the
stationary lead rod, the movable lead rod having an inner
~'2~
end fixed to the movable electrode and having an outer end
located outside the vacuum envelope, the movable lead rod
being shorter than the stationary lead rod;
a metal bellows surrounding part of the movable lead
rod and hermetically and electrically connecting the movable
lead rod to the bottom of the metal cylinder, the metal
bellows being located outside the metal cylinder and having
an exterior exposed to the air and an interior exposed to a
vacuum of the vacuum envelope; and
a substantially cylindrical coil located outside the
metal cylinder and surrounding the stationary and movable
electrodes, the coil having one end electrically connected
to the movable lead rod via a slide contact engaging the
surface of the movable lead rod and having the other end
electrically connected to an outer lead means, the coil
producing an axial magnetic field in parallel to an arc
current path formed between the stationary and movable
electrodes when the movable electrode is separated from the
stationary electrode.
BRIEF DES~IPTION OF T~IE DRA~INGS
. .
FIG. 1 is a longitudinal section through a prior-
art vacuum interrupter;
FIG. 2 is a longitudinal section through a vacuum
interrupter according to a first embodiment of this
invention;
FIG. 3 is a longitudinal section through a vacuum
interrupter according to a second embodiment of this
invention;
FIG. 4 is an enscaled view of an encircled part IV
of FIG. 3;
FIG. 5 illustra-tes an installation of a vacuum
interrupter according to a third embodiment of this
-- 6
7~
invention in a drawn-out type circui-t breaker;
FIG. 6 is a longitudinal section -through a vacuum
interrupter according to a third embodiment of this
invention.
DESCRIPTION OF THE PREFERRED EMBODIM~NTS
Referring to the figures, FIG. 1 shows an
interrupter which has a vacuum envelope 1 and a disc-shaped
stationary electrode 2 and a mova~le electrode 3 disposed
within the vacuum envelope 1 and operable for forming or
interrupting alectrical contact therebetween. The vacuum
envelope 1 comprises an insulating cylinder 4, a disc-shaped
metal end plate 5 hermetically secured to one edge of the
insulating cylinder 4 via a metal seal ring 6, a bottomed
metal cylinder 7 the open end of which is hermetically
secured to the other edge of the insulating cylinder 4 via a
metal seal ring 6. The stationary and movable electrodes 2
and 3 are located within the metal cylinder 7.
A stationary lead rod 9 passes hermetically
through and is fixed to a flat bottom 7a of the metal
cylinder 7. An inner end of the stationary lead rod 9
carries the stationary electrode 2 within the metal cylinder
7. on the other hand, a movable lead rod 10 passes loosely
through the metal end plate 5 and is hermetically secured to
the metal end plate 5 via a metal bellows 11. An inner end
of the movable lead rod 10 carries the movable electrode 3
within the metal cylinder 7. Thus, the movable lead rod 10
is considerably longer than the stationary lead rod 9. The
bellows 11 is located within the insulating cylinder 4 with
its inner surface exposed to the atmosphere. The bellows 11
is as remote from the electrodes 2 and 3 within the vacuum
envelope 1 as possible in order to protect the bellows 11
from the deposition of the metal vapor generated by the
~2~L72
electrodes 2 and 3 during opening and closing operations. A
cup-shaped bellows shield 12 is fixed to an intermediate
portion of the movable lead rod 10. The bellows shield 12
also protects an inner end area of the bellows 11 from
deposition of the metal vapor.
A coil 13 of substantially one turn surrounds the
stationary and movable electrodes 2 and 3 outside the
cylindrical portion of the metal cylinder 7. The coil 13
produces an axial magnetic field running parallel to the arc
current path between the separated stationary and movable
electrodes 2 and 3 for dispersing -the arc evenly across the
opposing faces of the electrodes thereby increasing the
current interruption performance of the interrupter. One
end 13a of the coil 13 is electrically connected to an outer
end of the stationary lead rod 9. The other end 13b of the
coil 13 is electrically connected to one end of an outer
lead rod 14 which is located outside the vacuum envelope 1.
The outer lead rod 14 extends perpendicularly to the
stationary lead rod 9.
An outer lead rod 15 which is located outside the
vacuum envelope 1 extends parallel to the ou-ter lead rod 14.
One end of the outer lead rod 15 has a slide contact 16
which mechanically and electrically engages an outer end of
the movable lead rod 10. A main shield 17 is fixed to an
inner cylindrical surface of the metal cylinder 7. The
electrical potential of the main shield 17 is equal -to -that
of the stationary lead rod 9 but differen-t from that of the
movable lead rod 10. An auxiliary shield 13 is fixed to the
end plate 5.
In the operation of the above-described
interrupter, a current (e.g., a fault current) passes
through a sequence comprising the outer lead rod 14, the
coil 13, the stationary lead rod 9, the stationary electrode
2, the arc current path between the stationary electrode 2
,, :.
~2~
and the movable electrode 3, the movable electrode 3, the
movable lead rod lO, the slide contact 16 and the outer lead
rod 15 and vice versa. Therefore, the stationary and
movahle lead rods 9 and 10 are subjected to a resulting
electro-magnetic force with a radial vector in accordance
with the left-hand rule when a curren-t passes through the
above-described sequence. The electro-magnetic force
radially inclines the movable lead rod 10 when the
stationary and movable electrodes 2 and 3 are out of
contact. ~his inclination displacement reduces the
clearance between the movable :Lead rod lO and the main
shield 17 which have different potentials, which in turn
reduces the dielectric strength of the vacuum interrupter.
An inclination displacement of the movable lead rod lO due
to the electro-magnetic force of the coil 13 causes the
stationary and movable electrodes 2 and 3 to be in point-to-
point contact at outer peripheries of the stationary and
movable electrodes 2 and 3. Thus, a mechanical impact force
occurring during closing operation of the stationary and
movable electrodes 2 and 3 concentrates at the point of
contact between the stationary and movable electrodes 2 and
3. This concentration of the mechanical impact force can
possibly split or break the stationary and movable
electrodes 2 and 3 during many opening and closing
operations. Thus the radial displacement of the movable
electrode 2 causes premature wear and reduced dielectric
strength in the vacuum interrupter. Furthermore, the
lengthiness of the movable lead rod 10 increases the total
weight of the movable assembly associated with -the movable
lead rod lO, and the load of weight on the associated
operating mechanism for the movable lead rod lO.
Most of the metal vapor produced during -the
opening operation of the stationary and movable electrodes 2
and 3 disperses to a space behind the movable electrode 3 in
- 8a -
.. . .
~2~
the insulating cylinder 4 rather than the space behind the
stationary electrode 2 because the space behind the movable
electrode 3 is greater than the space behind the stationary
electrode 2. Therefore, some of the dispersing metal vapor
deposits on the surface of the bellows 11 during many (no
less than 10,000 times) opening and closing operations in
spite of the presence of the bellows shield 12. The metal
vapor deposited on the bellows 11 melts a little bit of the
surface of the bellows 11 and causes the adjacent annular
portions of the bellows 11 to stick each other because the
bellows 11 contracts during the opening operation of the
stationary and movable electrodes 2 and 3 when the vapor is
formed. The sticking together of the ad]acent annular
portions of -the bellows causes them to tear and leak thus
compromi2ing the vacuum within the vacuum envelope 1.
In this prior-art vacuum interrupter, the short
stationary lead rod 9 connects the stationary and movable
electrodes 2 and 3 to the coil 13, so that Joule heat due to
contact resistance between the stationary and movable
electrodes 2 and 3 cannot be dissipated sufficiently through
the stationary lead rod 9. Moreover, Joule heat pr~duced by
the coil 13 is added to that produced by contact resistance.
Thus, the temperature of the vacuum interrupter may be
caused to exceed the maximum temperature (e.g., a
temperature of a silver-plating-free lead rod being 90 C
under an ambient temperature of 40C) permisible for the
vacuum interrupter.
In addition, the vacuum interrupter usually
constitutes part of a circuit breaker installed in a metal-
clad switchgear, the stationary lead rod 9 being located inan upper portion of the vacuum interrupter. Thus, the coil
13 as a heat transmitter surrounds the upper portion of the
vacuum interrupter. This arrangement blocks the natural
convection along the outer length of the vacuum envelope
- 8b -
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within the surrounding atmosphere, thus blocking heat
dissipation from the vacuum interrupter.
The preferred embodiments of this invention will
be described with reference to FIGS. 2 to 6.
FIG. 2 illustrates a vacuum interrupter according
to a first embodiment of this invention. This vacuum
interrupter has a vacuum envelope 20 with a stationary disc-
shaped electrode 21 and a movable
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/
- 8c -
.
disc-shaped electrode 22 disposed within it. The vacuum
envelope 1 comprises an insulating cylinder 23 made of
glass or insulating ceramics, a disc-shaped metal end
plate 24 hermetically secured to one end 23a of the
insulating cylinder 23 via an annular metal seal ring 25
made of Koval* (i.e. a Fe~Ni-Co alloy), and a metal
cylinder 26 made of non-magnetic stainless steel, e.g., an
austenitic stainless steel, the open end of the metal
cylinder 26 being hermetically secured to the other edge
23b of the insulating cylinder 23 via an annular metal
seal ring 25. The interior of the vacuum envelope 20 is
evacuated to a pressure equal to or below 6.67 mPa. The
stationary and movable electrodes 21 and 22 are located
within the metal cylinder 26. The stationary electrode 21
and the movable electrode 22 can be moved into or out of
contact with each other within the metal cylinder 26.
A stationary lead rod 27 which is located within
the vacuum envelope 20 passes hermetically through and is
fixed to the metal end plate 24. An inner end of the
stationary lead rod 27 carries the stationary electrode 21
within the metal cylinder 26. On the other hand, a
movable lead rod 28 passes loosely through the flat bottom
26a of the metal cylinder 26. The movable lead rod 28 is
hermetically secured to the bottom 26a of the metal
cylinder 26 via a metal bellows 29. The inner end of the
movable lead rod 28 carries the movable electrode 22
within the metal cylinder 26. Thus, the stationary lead
* Koval is a trade mark.
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rod 27 is considerably longer than the movable lead rod
28. The bellows 2g is located adjacent to the outside of
the flat bottom 26a of the metal cylinder 26 so that the
inner surface of the bellows 29 is exposed to the vacuum
inside the vacuum envelope 200
A cylindrical coil 30 of substantially one turn
surrounds the stationary and movable electrodes 21 and 22
outside the cylindrical portion of the metal cylinder 26.
The coil 30 produces an axia] magnetic field parallel to
~O an arc current path produced between the separated
stationary and movable electrodes 21 and 22. One end 30a
of the coil 30 has a slide contact 31 which mechanicall~
and electrically engages an outer end of the movable lead
rod 28. The other end 30b of the coil 30 is electrically
connected to one end of an outer lead rod 32 which is
located outside the vacuum envelope 20. The outer lead
rod 32 extends perpendicularly to the movable lead rod 28.
An outer lead rod 33 which is located outside the vacuum
envelope 20 extends in parallel to the outer lead rod 32.
One end of the outer lead rod 33 is electrically connected
to an outer end of the stationary lead rod 27.
A main shield 34 made of non-magnetic stainless
steel, e.g., an austenitic stainless steel is fixed to an
inner cylindrical surface of the cylinder 26 behind the
stationary electrode 21. The electrical potential of the
main shield 3~ is different from that of the stationary
lead rod 27 and the stationary electrode 21. The
-- 10 --
electrical potential of the main shield 34 and the metal
cylinder 2~ is equal to that of the movable lead rod 28
and the movable electrode 22.
In the operation of the above-described vacuum
interrupter according to a first embodiment of this
invention, a current (e.g., a fault current) passes
through a sequence of the outer lead rod 33, the
stationary lead rod 27, the stationary electrode 21, the
arc current path between the stationary electrode 21 and
the movable electrode 22, the movable electrode 22, the
movable lead rod 2~, the slide contact 31~ the coil 30 and
the outer lead rod 32 and vice versa. Therefore, the
stationary and movable lead rods 27 and 28 are subjected
to a resulting electro-magnetic force with a radial vector
in accordance with the left-hand rule when a current
passes through the above-described sequence.
The stationary lead rod 27 is subjected to a
large bending moment produced due to the electro-magnetic
force produced by a circuit current passing through the
interrupter because the length of the portion extendin~
from the metal end plate 24 to the stationary electrode 21
is greater than that of a corresponding portion of a
conventional stationary lead rod. However~ spatial
relationships between the stationary lead rod 27 (and
therefore the stationary electrode 21) and other
surrounding members (e~g., the main shield 34) of the
vacuum interrupter cannot be changed within the vacuum
-- 11 --
~28~
envelope 20 because the stationary lead rod 27 is firmly
secured to the metal end plate 24. Thus, the spatial
relationship between the stationary lead rod 27 and the
main shield 34 which have different potentials from each
other, is stable, so that the dielectric strength of gaps
between the stationary lead rod 27 (and therefore the
stationary electrode 21) and other surrounding members of
the vacuum interrupter remain unchanged.
On the other hand, the movable lead rod 28 is
subjected to a very small bending moment produced due to
the electro-magnetic force produced by the circuit current
because the length of the portion extending from the slide
contact 31 to the movable electrode 22 is smaller than
that of A corresponding portion of a conventional movable
lead rod. Therefore, the tendency of electro-magnetic
force produced by the circuit current to incline the
movable lead rod 28 is greatly reduced, thereby greatly
reducing the chance of a point-to-point contact occurring
at the outer peripheries of the electrodes 21 and 22.
Furthermore, while the electro-magnetic force produced by
the circuit current may cause a slight inclination
displacement of the movable lead rod 28, this inclination
displacement cannot deteriorate the dielectric strength of
the vaccum interrupter because of equipotentialities
between the movable lead rod 28 (also therefore the
movable electrode 22) and the surroundin~ members of the
vacuum interrupter (e.g., the metal cylinder 26).
- 12 -
~Z8~
In addition, the shortness of the movable lead
rod 28 greatly reduces the total weight of the movable
assembly associated with the movable lead rod 28 and the
weight load on the associated operating mechanism for the
movable lead rod 28.
Most o~ the metal vapor produced by the opening
operation of the stationary and movable electrodes 21 and
22 disperses to a space behind the stationary electrode 21
on the side of the insulating cylinder 23 rather than in
the space behind the movable electrode 22. Therefore very
little of dispersing metal vapor can deposit on the inner
surface of the bellows 29 and although some of the
dispersing metal vapor may deposit on the inner surface of
the bellows 29, adjacent annular portions of the bellows
29 cannot stick each other because the bellows 29 expands
in the opening operation of the electrodes 21 and 22.
Therefore, a damage to the bellows 29 due to sticking
together of the adjacent annular portions of a large
diameter of the bellows 29 does not occur.
Fig. 3 illustrates a vacuum interrupter
according to a second embodiment of this invention. The
same reference numerals will be applied to the parts
shared in common with the first embodiment of this
invention and the descriptions of those parts will not be
repeated. The parts of the vacuum interrupter according
to the second embodiment of this invention will be
described in detail when they are different from the parts
- 13 -
of the ~irst embodiment of this invention. This vacuum
interrupter has a vacuum envelope 40 and a pair of
disc-shaped electrodes 21 and 22. The vacuum envelope 40
comprises an insulating cylinder 41 made of glass or
insulating ceramics, the edges forming the opposite ends
41a and 41b of the insulating cylinder 41 having
metallized layers 42a and 42b, a metal end plate 24
hermetically brazed to one metallized layer 42a of the
insulating cylinder 41 via an annular seal ring 43 made of
copper or Koval, and a metal cylinder 26 the open end of
which being hermetically brazed to the other metallized
layer 42b of the insulating cylinder 41 via an annular
metal seal ring 44 made of copper or Koval The interior
of the vacuum envelope 40 is evacuated to a pressure equal
to or below 6.67 mPa.
A stationary lead rod 45a which is aligned
coaxially with the vacuum envelope 40 passes through and
is hermetically fixed to the metal end plate 24. The
inner end of the stationary lead rod 45 carries the
stationary electrode 21 within the metal cylinder 26~ The
stationary lead rod 45 comprises a small diameter stem
portion 45a near its inner end, a large diameter stem
portion 45b adjacent to the small diameter stem portion
45a and an intermediate diameter stem portion 45c adjacent
to the large diameter stem portion 45b. Assuming that a
phantom line 46 commonly intersects the outer periphery of
a shoulder 45d formed between the small diameter stem
7~
portion 45a and the large diameter stem portion 45b and
past an outer periphery of the above-described one
metallized layer 42a equipotential to the stationary lead
rod 45 and the curled surface 47b of the main shield 47,
the line 46 forms an angle equal to or above 60 with the
one metallized layer 42a, thus forming a boundary
preventing the concentration of electric field at the
metallized layer 42a. The forward end of the small
diameter stem portion 45a has the stationary electrode ~1.
The rear end of the small diameter stem portion 45a
terminates in an intermediate area within the insulating
cylinder 41. The intermediate diameter stem portion 45c
passes through the metal end plate 24. A shoulder formed
between the intermediate diameter stem portion 45c and the
large diameter stem portion 45b contacts the inner surface
of the metal end plate 24. The intermediate diameter stem
portion 45c is electrically connected to one end of an
outer lead rod 33.
The pres~nce of the large diameter stem portion
45b prevents the concentration of electric field at the
metallized layer 42a and improves the mechanical strength
and ~he thermal dissipation property of the stationary
lead rod 45. The presence of the large diameter stem
portion 45b also improves the mechanical strengths of the
connections between the stationary lead rod 45 and the
metal end plate 24 and between ~he stationary lead rod 45
and the outer lead rod 33.
- 15 -
7;~
A cylindrical main shield 47 made of
non-magnetic stainless steel, e.g., an austenitic
stainless steel is located opposite the inner sur~aces of
the metal seal ring 44 and thle end 41b of the insulating
cylinder 41. One end of the main shield 47 has an
outwardly extending flange 47a which is fixed to a lower
edge of the metal seal ring 44,. The other end of the main
shield 47 has an outwardly cur:Led edge 47b. Assuming that
a phantom tangential line 48 commonly passes past an outer
periphery of one edge (an upper edge in Fig. 3) of the
coil 30 and past an outer surface of the curled edge 47b
of the main shield 47, the metallized layer 42b is located
on the side of the phantom line 48 as the coil 30 and the
main shield 47.
Fig. 4 illustrates the detail of the encircled
portion IV of Fig. 3. The metal seal ring 44 is in
abutment with the metallized layer 42b on the edge 41b of
the insulating cylinder 41. The metal seal ring 44 is
brazed to the metallized layer 42b by means of interior
and exterior brazing materials 49a and 49b. The
metallized layer 42b and the interior and exterior brazing
materials 49a and 49b are on the side o the main shield
47 and the coil 30 relative to the phantom line 48~ As
shown in Fig. 3, the potential of the main shield 47 is
equal to that of the coil 30 when the stationary and
movable electrcdes 21 and 22 are electrically separated.
Therefore, equipotential lines SO are so delineated near
- 16 -
the main shield 47 and the coil 30 as shown in Fig. 4, so
that a concentration of electric field does not occur at
the metallized layer 42b. The arrangement between the
main shield 47, the existing coil 30 and the other
metallized layer 42b degrades the concentration of
electric field at the metallized layer 42b and the
presence of the large diametler stem portion 45b of the
stationary lead rod 45 pre~ents the concentration of
electric field at the metallized layer 42a, thus improving
the dielectric strength of the outer surface of the vacuum
envelope 40.
In the second embodiment of this invention, the
metal seal ring 43 is secured in a knife edge seal to the
insulating cylinder 41. However, the connection between
the metal seal ring 43 and the insulating cylinder 41 is
not limited to such knife edge seal. Alternatively, one
end of the metal seal ring 43 may be embedded in one edge
41a of the insulating cylinder 41. In this case, a
phantom line commonly passing past the outer periphery of
the shoulder 45d of the stationary lead rod 45, past the
curled edge 47b of the main shield 47 and past the
embedded edge of the metal seal ring 43 should subtend an
angle equal to or above e.g., 60 with the plane including
the embedded annular edge of the metal seal ring 43 so
that the electric field does not become concentrated at
the embedded edge of the metal seal ring 43.
Fig. 5 illustrates an installation of a vacuum
- 17 -
~2~
interrupter according to a third embodiment of thisinvention in a drawn-out type circuit breaker. The same
reference numerals will be applied to the parts shared in
common with first and second embodiments of this invention
and the descriptions of the those parts will not be
repeated. The parts of the vacuum interrupter according
to the third embodiment of this invention will be
described in detail when they are different from the parts
of the first and second embodiments o~ this invention.
As shown in Fig. 5, a drawn-out type circuit
breaker 60 which can move into and out of a metal-clad
switchgear (not shown) has an insulating frame 61 with a
U-shaped cross-section. The insulating frame 61 has no
top or bottom and extends vertically and is fixed to a
main frame of the circuit breaker by means of upper and
lower bolts 62. The insulating frame 61 has upper and
lower mounting brackets 63 and 64 projecting rearwardly
from a front wall 65 of the insulating frame 61.
A vacuum interrupter 66 according to a third
embodiment of this invention is installed between the
upper and lower mount brackets 63 and 64 in the insulating
frame 61. The intermediate diameter portion 45c of the
stationary lead rod 45 and a flat end 33a of the outer
lead rod 33 are secured to the upper mount bracket 63 by
bolts 67 and 68 and a pin 69 via a washer 70. The bolt 67
extends coaxially with the stationary lead rod 45 and
passes through the washer 70 and the Elat end 33a o~ the
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outer lead rod 33 and terminates in the intermediate
diameter portion 45c of the stationary lead rod 45. The
pin 69 is installed eccentrically of the stationary lead
rod 45 and passes through the washer 70 and the flat end
33a of the outer lead rod 33,. The pin 69 terminates in
the intermediate diameter portion 45c of the stationary
lead rod 45. The combination of the bolt 67 and the pin
69 positively fixes the positional relationship between
the washer 70, the outer lead rod 33 and the stationary
lead rod 45. The bolt 68 secures the washer 70 to the
upper mount bracket 63.
On the other hand, a metal arm 71 having an
annular slide contact 31 is secured by a bolt 72 to the
lower bracket ~4. The movable lead rod 29 passes through
the arm 71, the slide contact 31 and the lower mount
bracket 64. The arm 71 extends perpendicularly to the
movable lead rod 29 and constitutes an integral part o~ an
electrical connector 73 which is disposed between the
slide contact 31 and the inner end of the coil 30. An
outer end of the coil 30 is electrically connected to the
outer lead rod 32 via an electrical connector 740 The
electrical connector 74 and the outer lead rod 32 are
fixed by a combination o~ a bolt 75 and an eccentrically
located pin 7~ to the electrical connector 73 which is in
turn fixed to the lower mount bracket 64. The electrical
connectors 73 and 74 are insulated from each other by an
insulating bushing 77 inserted between the electrical
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1;~ !39~L7~
connectors 73 and 74. The inner and outer ends of khe
coil 30 are fixed to each other by bolt 78 and insulated
from each other by an insulating spacer 79.
Fig. 6 illustrates a longitudinal section
through the vacuum interrupter according to the third
embodiment of this invention which is similar to the
second embodiment of this invention. The vacuum
interrupter of the third embocliment has a bellows cover 80
surrounding the bellows 29.
0 Heated air ascends from the coil 30 as a heat
transmitter within the insulating frame 61 via natural
convection, so that heat dissipation for the vacuum
interrupter can be effected.
In addition, the stationary and movable
electrodes 21 and 22 are separated from the slide contact
31 and arm 71 by a distance corresponding to the length of
the bellows 29 which is greater than the distance
separating the stationary and movable electrodes 2 and 3
from the outer lead rod 14 in the prior-art vacuu~
interrupter of Fig. 1, so that the magnetic field produced
by the slide contact 31 and the arm 71 cannot adversely
affect the axial ~agnetic field produced by a turning
portion of the coil 30. This improves the interruption
performance of the vacuum interrupter of this inventionO
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