Technical Field
[0001]
The present invention relates to an electrical
10 contact for vacuum valves (interrupters) and a process for
producing the electrical contact.
Background Art
[0002]
15 A Cu-Cr base contact material has heretofore widely
been used in an electrical contact of electric power
switches such as vacuum circuit breakers and vacuum switch
gears. This material has a structure in which chromium
(Cr) grains which are arc-resistant components are
20 dispersed in a copper (Cu) matrix phase having superior
current-carrying performance. Chromium (Cr) emits
electrons adequately and has a high melting point and arc
resistance, thus giving voltage resistance performance.
Therefore, increasing the amount of Cr improves high
25 voltage resistance performance, but the amount of Cu
1
111301247IN01_PL8 033IN
decreases relatively and current-carrying/breaking
performance lowers. For Cu-Cr base electrical contacts,
hence, the current-carrying/breaking performance and the
voltage resistance performance are contradictory with each
5 other and it is difficult to make them compatible with each
other.
[0003]
As an electrical contact to cope with this problem, a
Mo-Cr-Cu base material is proposed in, e.g., Patent
10 Literature (PTL) 1. This contact material has a structure
in which Cu is evenly dispersed in a matrix phase of Mo-Cr
micro alloy which is used as arc-resistant components and
is described to improve arc resistance and be able to
suppress an increase in the resistance of the contact.
15
Citation List
Patent Literature
[0004]
PTL 1: Japanese Patent Application Laid-Open
20 Publication No. 2012-7203
Summary of Invention
Technical Problem
[0005]
25 In the Mo-Cr-Cu base contact proposed in the above-
2
111301247IN01_PL8033IN
mentioned PTL 1, grains of highly conductive Cu aggregate
into large ones, 20 to 150 urn in size, and these large
grains of Cu exist in patches. This results in shortage of
current-carrying paths in a matrix phase and decreases the
5 conductivity of the contact material as a whole, which in
turn poses a problem in which current-carrying performance
and current-breaking performance become insufficient.
[0006]
An object of the present invention is to improve
10 current-carrying/breaking performance and voltage
resistance performance.
Solution to Problem
[0007]
15 The above object is achieved by the invention
described in claims.
Advantageous Effects of Invention
[0008]
20 According to the present invention, it is possible to
improve current-carrying/breaking performance and voltage
resistance performance.
Brief Description of Drawings
25 [0009]
3
111301247IN01_PL8033IN
[Figure 1] Figure 1 is a cross-sectional view showing
a structure of an electrode of a first embodiment.
[Figure 2] Figure 2 is a schematic diagram showing a
cross-sectional view of structure morphology of an
5 electrical contact of the first embodiment.
[Figure 3] Figure 3 is a diagram showing a structure
of a vacuum interrupter of a second embodiment.
[Figure 4] Figure 4 is a diagram showing a structure
of a vacuum circuit breaker of a third embodiment.
10
Description of Embodiments
[0010]
In producing an electrical contact including Mo-Cr-Cu
matrix phases and Cu-aggregation phases, the present
15 inventors considered improving current-carrying performance
and current-breaking performance by micrifying Cuaggregation
phases dispersed in an Mo-Cr-Cu matrix phase
and increasing the amount of Cu contained in the matrix
phases, thus increasing the conductivity of the entire
20 electrical contact.
[0011]
First, the present inventors thought that the grain
size of Cu-aggregation phases and the Cu content in an Mo-
Cr-Cu matrix phase depend on molten infiltration paths of
25 Cu of an Mo-Cr powder-compression compact, that is, its
4
111301247IN01 PL8033IN
porosity, and measured the porosity of the Mo-Cr powdercompression
compact after being heated. We compacted mixed
powders with a composition of 77wt%Mo to 23wt% at pressure
of 2 94 MPa and produced a powder-compression compact.
After leaving this powder-compression compact in vacuum at
temperature ranging from 400 to 1100 °C for one hour, we
measured its porosity. The porosity of the body after
being heated at 400 °C was 42%, whereas the porosity of the
body after being heated at 1100 °C was 35%. At higher
heating temperature, the porosity decreased. This is
because, at higher heating temperature, diffusion between
Mo and Cr becomes significant and narrows the paths (pores)
that molten Cu enters. Observation of a cross-section
structure of the powder-compression compact after being
heated revealed that pores (Kirkendall voids) which are
several 10 jam in size resulting from diffusion exist in
patches.
[0012]
In this way, when a powder-compression compact is
infiltrated with Cu after being sintered, it becomes hard
to make a matrix phase to be infiltrated with Cu (it
becomes hard to trap Cu in a matrix phase) and, moreover,
Cu with which a matrix phase has not been infiltrated
enters a large pore and forms a large aggregation phase.
[0013]
5
111301247IN01_PL8033IN
Based on this knowledge, in an embodiment disclosed
herein, an Mo-Cr-Cu matrix phase including Cu is formed by
making an Mo-Cr powder-compression compact infiltrated with
molten Cu after ensuring plenty of Cu infiltration paths in
5 the Mo-Cr powder-compression compact and the grain size of
Cu-aggregation phases dispersed in a matrix phase was
controlled to be smaller than ever before.
[0014]
An electrical contact of the present embodiment can
10 be obtained by a process described below. First, Cr and Mo
powders are mixed and the mixed powders are compacted to
produce a powder-compression compact. Then, the powdercompression
compact is infiltrated with molten Cu. In this
infiltration process, atmosphere should preferably be inert
15 gas (such as Ar) atmosphere or depressurized environment
(high vacuum) below atmospheric pressure, because Cu is
hard to oxidize in such atmosphere. The powder-compression
compact is sintered by heat of the molten Cu with which the
powder-compression compact is infiltrated. Cu infiltration
20 and sintering that go on simultaneously bring about
suppression of diffusion between Mo and Cr, ensuring plenty
of Cu infiltration paths, and making a larger amount of Cu
than ever before contained in a Mo-Cr-Cu matrix phase.
Besides, the size of pores resulting from Mo-Cr diffusion
25 can be reduced and the size of Cu-aggregation phases which
6
111301247IN01 PL8033IN
arc formed by Cu entering the pores can be controlled to be
4 to 20 ^m.
[0015]
An electrical contact of the present embodiment has a
5 structure in which Cu-aggregation phases whose grain size
is 4 to 20 (Jim are dispersed in a matrix phase including Mo-
Cr-Cu. When the total Cu content in the electrical contact
is denoted by Wt, the Cu content (Wm) in a matrix phase is
expressed by C x Wt, where C ranges from 0.54 to 0.81. A
10 matrix phase is comprised of ternary system of Mo-Cr-Cu and
a large amount of Cu which is a good electrical conductor
is contained in a matrix phase as well; this brings a
marked improvement in the conductivity of the electrical
contact. Nevertheless, a matrix phase also includes traces
15 of inevitable elements other than the three components of
Mo-Cr-Cu. Moreover, the grain size of Cu-aggregation
phases existing in patches can be reduced to a relatively
small size. This enables dispersion of the Cu-aggregation
phases more evenly in the electrical contact and
20 contributes to an improvement in the conductivity. Since
the Cu content in a matrix phase is proportional to the
total Cu content in the electrical contact, it would become
easy to design a material composition to obtain desired
electrical characteristics and, besides, three-dimensional
25 coupling of Cu in the matrix phase forms conduction paths
7
111301247IN01 PL8033IN
including Cu aggregation phases. Improvement in the
conductivity as described above leads to improvement in
current-carrying performance and current-breaking
performance.
5 [0016]
Composition of the entire electrical contact is as
follows: Mo is 40 to 60 wt%, Cr is 10 to 20 wt%, and the
remainder is Cu and inevitable impurities. Having this
composition including large amounts of Mo and Cr, the
10 electrical contact can develop sufficiently high voltage
resistance. An Mo-Cr-Cu matrix phase in which Cu minutely
penetrates a skeletal structure formed with adequately
dispersed Mo-Cr is formed and the size of Cu-aggregation
phases can be reduced. Thus, superior conductivity as
15 described above can be provided and current-carrying
performance and current-breaking performance can be
improved without need to add Cu excessively.
[0017]
The Mo-Cr-Cu matrix phase has a crystal grain size of
20 less than 4 urn and includes Cu as much as the above Cu
content (Wm) . This produces three-dimensional coupling of
Cu in the matrix phase, so that the electrical contact
develops high conductivity. Besides, by reducing the
percentage of the Cu contents in the Cu-aggregation phases
25 in the entire electrical contact to 20 wt% or less, the
8
111301247IN01_PL8033IN
total amount of Mo and Cr can be increased to 80 wt%; thus
high voltage resistance can be obtained.
[0018]
An electrical contact of the present embodiment has a
5 disc shape and the outer periphery of its one side surface
is bonded onto a current-carrying member. When separating
two electrical contacts facing each other, each having the
above shape, to break current, an arc produced between the
contacts can be trapped by generating a vertical magnetic
10 field between the contacts and extinguishing the arc in the
magnetic field. By means of this, an electrode having
superior current-breaking performance can be obtained.
[0019]
A disc-shape electrical contact has a shape in which
15 it has a center hole formed in the disc center and a
plurality of perforated slit grooves formed from the disc
center toward the outer periphery, but not communicating
with the center hole. With this windmill-like shape, it is
possible to drive out an arc produced between the
20 electrical contacts toward the outer periphery of the
contacts by electromagnetic force and break current quickly
and the contacts develop superior current-breaking
performance.
[0020]
25 A vacuum interrupter of an embodiment disclosed
9
111301247IN01 PL8033IN
herein is equipped with a pair of a stationary electrode
and a movable electrode in a vacuum case. At least one of
the stationary and movable electrodes is configured as an
electrode of the present embodiment. An electric power
5 switch such as a vacuum circuit breaker and a vacuum switch
gear is equipped with an electrical opening/closing means
in which a plurality of vacuum interrupters of the present
embodiment are connected in series by conductors and a
movable electrode is driven. By means of this, it is
10 possible to realize a vacuum load-break switch with a
relatively large capacity, satisfying both of high voltage
resistance and large current breaking.
[0021]
In the following, embodiments will be described in
15 detail, but the present invention is not limited to these
embodiments.
Embodiment 1
[0022]
20 Electrical contacts having a composition which is
specified in Table 1 were produced and an electrode 100 was
produced using these contacts. In Table 1, contact
composition is specified with the exclusion of purities for
convenience. Figure 1 is a cross-sectional view showing a
25 structure of an electrode 100 produced. In Figure 1,
10
111301247IN01 PL8033IN
reference numeral 1 denotes an electrical contact; 2
denotes a curved slot for giving a driving force to an arc;
3 denotes a reinforcing plate made of stainless steel; 4
denotes an electrode rod; 5 denotes brazing filler metal;
5 and 44 denotes a center hole for preventing an arc produced
in the center of the electrical contact 1 from staying
there.
[0023]
A process of producing an electrical contact 1 of an
10 example specified in Table 1 is as follows. First, an Mo
powder (an average grain size of 3 fim) and a Cr powder
(gain size is less than 60 jam) in predetermined quantities
were mixed, these mixed powders were put in a mold with a
diameter of 70 mm, and the mixed powders were compacted at
15 a pressure of 157 to 294 MPa, and a powder-compression
compact was obtained. In this process, a mix ratio of Mo
and Cr powders and the compaction pressure were adjusted so
that contact composition values after molten Cu
infiltration will be obtained approximately as specified in
20 Table 1. If the compaction pressure is less than 157 MPa,
a compacted body loosens when infiltrated with Cu and its
structure and composition become inhomogeneous; therefore,
the compaction pressure should preferably be equal to or
more than 157 MPa. Then, a predetermined quantity of an
25 oxygen-free cupper ingot was put on the powder-compression
11
111301247IN01 PL0033IN
compact, it was heated at 1160 °C for 2 hours in vacuum on
the order of 10~2 Pa, the powder-compression compact was
infiltrated with molten Cu, and the material of the
electrical contact 1 was produced.
5 [0024]
An arbitrary cross section of the material of the
electrical contact 1 obtained was observed with an optical
microscope and an area ratio of an Mo-Cr-Cu matrix phase
and Cu-aggregation phases was measured using an image
10 processing device. A maximum grain size of Cu-aggregation
phases is a value representing the greatest one of the
maximum diameters of all grains in an image. Thus obtained
area ratios of each phase are converted to the weight
percentages of the components which are also presented in
15 Table 1. As examples of structure morphology, a crosssection
structure of embodiment example No. 3 is shown in
Figure 2(a) and a cross-section structure of comparative
example No. 8 is shown in Figure 2(b) in schematic diagrams.
Conductivity also specified in Table 1 is conductivity
20 measurements taken in an arbitrary cross section with an
eddy current conductivity meter and is represented as
values (IACS) relative to the conductivity of annealed pure
cupper assumed as 100%.
[0025]
25 The ranges of the compositions of embodiment examples
12
1113012 47IN01_PL0033IN
No. 1 to No. 7 are as follows: Mo is 40 to 60 wt%, Cr is 10
to 20 wt%, and Cu occupies the remainder. Assuming that
the total Cu content in the electrical contact is denoted
by Wt, when the Cu content (Wm) in an Mo-Cr-Cu matrix phase
5 is expressed C x Wt, C falls in a range of 0.54 to 0.81.
Moreover, the maximum grain size of Cu-aggregation phases
is 4 to 20 |am and the percentage of these phases in the
entire contact is less than 20 wt%.
[0026]
10 In contrast to these examples, comparative example No.
8 was obtained by heating the powder-compression compact at
1100 °C before Cu infiltration. Since Mo-Cr diffusion in
the powder-compression compact progresses to narrow Cu
infiltration paths, the Cu content in the Mo-Cr-Cu matrix
15 phase decreases and the value of C in the equation Wm = C x
Wt decreases. On the other hand, since the entire contact
composition of the example No. 8 falls within the range of
embodiment examples, surplus Cu that failed to enter the
matrix phase forms Cu-aggregation phases as shown in Figure
20 2(b) and both the size (grain size) and amount of these
phases have values out of the range of embodiment examples.
[0027]
For comparative examples No. 9 and No. 10, their
entire contact compositions are out of the range of
25 embodiment examples. Example No. 9 has a smaller amount of
13
111301247IN01 PL8033IN
Cr and most of Cr dissolves in Mo when the powdercompression
compact is heated, which narrows Cu
infiltration paths, with the result that the value of C in
the equation Wm = C x Wt decreases. On the other hand, an
5 absolute amount of Cu is larger in the example No. 9; this
makes a structure in which large Cu-aggregation phases
exist unevenly in patches. Example No. 10 has a smaller
amount of Cu in total; this makes a structure only with a
Mo-Cr-Cu matrix phase without the formation of Cu-
10 aggregation phases.
[0028]
The obtained material was machined and an electrical
contact 1 with a diameter of 65 mm, which is shown in
Figure 1, was produced. A process of producing an
15 electrode 100 is as follows. An electrode rod 4 made of
oxygen-free copper and a reinforcing plate 3 made of SUS304
were produced in advance by machining. The electrical
contact 1 obtained as described previously, the reinforcing
plate 3, and the electrode rod 4 with the intermediate
20 positioning of brazing filler metal 5 between the
electrical contact and each of the plate and rod were
assembled and this assembly was heated at 970 °C for 10
minutes in vacuum at 8.2 x 10~4 Pa or below. The electrode
100 was thus produced which is shown in Figure 1. If the
25 electrical contact 1 has sufficient strength, the
14
111301247IN01_PL0033IN
reinforcing plate 3 may be omitted.
Embodiment 2
[0029]
5 A vacuum interrupter 200 was produced by using the
electrode 100 produced in Embodiment 1. Figure 3 is a
diagram showing the structure of the vacuum interrupter of
the present embodiment. Rated specifications of this
vacuum interrupter 200 are as follows: voltage is 24 kV,
10 current is 1250 A, and breaking current is 25 kA. In
Figure 3, reference numeral la denotes a stationary
electrical contact; lb denotes a movable electrical
contact; 3a and 3b denote reinforcing plates; 4a denotes a
stationary electrode rod; and 4b denotes a movable
15 electrode rod. Using these members, a stationary electrode
6a (100) and a movable electrode 6b (100) are configured.
In the present embodiment, the stationary and movable
electrical contacts are placed so that their curved grooves
will be aligned on the contact surface.
20 [0030]
The movable electrode 6b is brazed onto a movable
electrode holder 12 with the intermediate positioning of a
movable-side shield 8 which prevents scattering of metal
vapor or the like at current breaking. These members are
25 held in high vacuum in a brazed and sealed case formed of a
15
111301247IN01__PL8033IN
stationary-side end plate 9a, a movable-side end plate 9b,
and an insulated barrel 13. This vacuum interrupter is
connected to external conductors at threaded portion on the
stationary electrode 6a and the movable electrode holder 12.
5 At the inner side of the insulated barrel 13, a shield 7 is
provided to prevent scattering of metal vapor or the like
at current breaking. Also, a guide 11 for supporting a
sliding portion is provided between the movable-side end
plate 9b and the movable electrode holder 12. Bellows 10
10 are provided between the movable-side shield 8 and the
movable-side end plate 9b to enable the movable electrode
holder 12 to go up and down, making the stationary
electrode 6a and the movable electrode 6b open and close,
while keeping vacuum inside the vacuum interrupter.
15
Embodiment 3
[0031]
A vacuum circuit breaker 300 equipped with the vacuum
interrupter 200 produced in Embodiment 2 was produced.
20 Figure 4 is a structure diagram of the vacuum circuit
breaker 300, showing the vacuum interrupter 14 (200) in the
present embodiment and its operating mechanism.
[0032]
The vacuum circuit breaker 300 has a structure in
25 which the operating mechanism is located in its front side
16
111301247IN01 PL8033IN
and three cpoxy barrels 15 which arc of a three phase
integration type and support the vacuum interrupter 14
(200) are located in its back side. The vacuum interrupter
14 (200) is opened and closed by the operating mechanism
via an insulated operating rod 16.
[0033]
When the vacuum circuit breaker 300 is placed in a
closed state, current flows through an upper terminal 17,
the electrical contact 1, a current collector 18, and a
lower terminal 19. Contact force between the electrodes is
maintained by a contact spring 20 attached to the insulated
operating rod 16. The contact force between the electrodes
and electromagnetic force due to a short-circuit current
are held by a holding lever 21 and a prop 22. When a
closing coil 30 is excited, a plunger 23 pushes a roller 25
up via a knocking rod 24 from an open state, thereby
turning a main lever 26 to close the electrodes. After
that, the closed state is held by the holding lever 21.
[0034]
When the vacuum circuit breaker 300 is placed in a
trippable state, a tripping coil 27 is excited, and a
tripping lever 28 disengages the prop 22, thereby turning
the main lever 26 to open the electrodes.
[0035]
When the vacuum circuit breaker 300 is. placed in an
17
111301247IN01 PL8033IN
open state, after the electrodes have been opened, the link
recovers by the action of a reset spring 29 and, at the
same time, the prop 22 engages. In this state, exciting
the closing coil 30 puts the circuit breaker into the
5 closed state. Reference numeral 31 denotes an exhaust
stack.
Embodiment 4
[0036]
10 A performance test was conducted in which the
electrical contacts 1 produced in Embodiment 1 were
employed in the vacuum interrupter 200 described in
Embodiment 2, installed in the vacuum circuit breaker 300
described in Embodiment 3. For each electrical contact, a
15 maximum breaking current value and judgment of whether the
contact can keep voltage resistance performance after
breaking are also specified in Table 1. Rated
specifications of this vacuum interrupter 200 are as
follows: voltage is 24 kV, current is 1250 A, and breaking
20 current is 25 kA. A maximum breaking current value that is
required in practical use is 35 kA. Voltage resistance
performance is 50 kV in commercial frequency. Therefore, a
contact whose maximum breaking current value is above 35 kA
was judged as "good (O)" and a contact that can keep
25 resistant to a voltage of 50 kV was judged as "good (O)".
1 8
111301247IN01_PL8033IN
[0037]
Electrical contacts of embodiment examples No. 1 to
No. 7 each show values in a proper range in terms of
composition, Cu content in an Mo-Cr-Cu matrix phase, grain
5 size of Cu-aggregation phases, etc. and were capable of
satisfactorily keeping a voltage resistance state along
with good conductivity and a breaking current value above
35 kA.
[0038]
10 An electrical contact of example No. 8 has sufficient
conductivity of the entire contact and was capable of
keeping voltage resistance performance after breaking.
However, because of its inhomogeneous structure in which
Cu-aggregation phases with a relatively large grain size
15 exist in patches, Cu sublimation spots are generated
unevenly by arc heating. Its current breaking behavior is
unstable and its maximum breaking current value is below 35
kA. Its current breaking performance was regarded as
insufficient.
20 [0039]
For an electrical contact of example No. 9, the
absolute amount of Cu included in it is large and it has
high conductivity. Thus, it shows a relative high value as
the maximum breaking current value, but its voltage
25 resistance performance was regarded as insufficient because
19
111301247IN01_PL8 033IN
Mo-Cr amounts are small.
[0040]
For an electrical contact of example No. 10, its
conductivity is significantly low because the absolute
5 amount of Cu is small and its current breaking performance
is regarded as insufficient. Besides, the contact surface
after current breaking becomes considerably rough and this
induces discharge between the contacts. Therefore, its
voltage resistance performance was not kept.
10 [0041]
In this way, it was verified that the electrical
contacts of embodiment examples satisfy both of high
voltage resistance and large current breaking and can be
applied to an electric power switch with a relatively large
15 capacity.
20
111301247IN01_PL8033IN
Reference Signs List
[0043]
1: Electrical contact,
la: Stationary electrical contact,
5 lb: Movable electrical contact,
2: Curved slit groove,
3, 3a, 3b: Reinforcing plate,
4, 4a, 4b: Electrode rod,
5: Brazing filler metal,
10 6a: Stationary electrode,
6b: Movable electrode,
7: Shield,
8: Movable-side shield,
9a: Stationary-side end plate,
15 9b: Movable-side end plate,
10: Bellows,
11: Guide,
12: Movable electrode holder,
13: Insulated barrel,
20 14: Vacuum interrupter,
15: Epoxy barrel,
16: Insulated operating rod,
17: Upper terminal,
10: Current collector,
25 19: Lower terminal,
22
20: Contact spring,
21: Holding lever,
22: Prop,
23: Plunger,
24: Knocking rod,
25: Roller,
26: Main lever,
27: Tripping coil,
28: Tripping lever,
29: Reset spring,
30: Closing coil,
31: Exhaust stack,
44: Center hole,
100: Electrode,
200: Vacuum interrupte
300: Vacuum circuit br
111301247IN01__PL8033IN

CLAIMS
1. An electrical contact in which aggregation phases
including Cu are dispersed in a matrix phase including Mo,
5 Cr, and Cu, wherein:
a maximum grain size of the aggregation phases falls
in a range of 4 to 20 |J.m, and
when the total Cu content in the electrical contact
is denoted by Wt, the Cu content in the matrix phase is
10 expressed by C x Wt, where C ranges from 0.54 to 0.81.
2. The electrical contact according to claim 1, wherein
composition of the entire electrical contact comprises Mo
of 40 to 60 wt%, Cr of 10 to 20 wt%, and the remainder
15 consisting of Cu and inevitable impurities.
3. The electrical contact according to claim 1 or 2,
wherein the matrix phase has a crystal grain size of less
than 4 pm.
20
4. The electrical contact according to any one of claims
1 to 3, wherein the Cu contents in the aggregation phases
are 20 wt % or less in the entire electrical contact.
25 5. An electrode comprising an electrical contact
24
111301247IN01_PL8033IN
according to any one of claims 1 to 4 having a disc shape
and an electrode rod attached to one-side surface of the
electrical contact.
5 6. A vacuum interrupter comprising a pair of a
stationary electrode and a movable electrode in a vacuum
case, wherein at least one of the stationary electrode and
the movable electrode is an electrode as set forth in claim
5.
10
7. An electric power switch comprising an electrical
opening/closing means in which a plurality of vacuum
interrupters as set forth in claim 6 are connected in
series by conductors and the movable electrode is driven.
15
8. A process for producing an electrical contact
including Mo, Cr, and Cu, comprising:
a step of compacting mixed Mo and Cr powders, thus
forming a powder-compression compact; and
20 a step of making the powder-compression compact
infiltrated with molten Cu.
9. The process for producing an electrical contact
according to claim 8, wherein the step of making the
powder-compression compact infiltrated with molten Cu is
performed in inert gas atmosphere or depressurized
atmosphere.