U.S. patent application number 09/909769 was filed with the patent office on 2002-03-07 for superconducting cable for alternating current.
Invention is credited to Miyoshi, Kazutomi, Mukoyama, Shinichi, Tsubouchi, Hirokazu.
Application Number | 20020027014 09/909769 |
Document ID | / |
Family ID | 26596460 |
Filed Date | 2002-03-07 |
United States Patent
Application |
20020027014 |
Kind Code |
A1 |
Mukoyama, Shinichi ; et
al. |
March 7, 2002 |
Superconducting cable for alternating current
Abstract
A superconducting cable for alternating current, comprising
conductor layers formed by a plurality of tape-shaped
superconducting wires wound around a center member, an electric
insulating layer formed outside the conductor layers, and a
plurality of shielding layers formed outside the insulating layer,
wherein (a) the conductor layers are formed, where N is a number of
layers in the conductor layers and expressed by an integer, by
gradually increasing a winding pitch of conductor layers in the
same direction from an inner first layer to an N/2 layer when the
number of layers is even, or from an inner first layer to a (N-1)/2
layer when the number of layers is odd, and then by gradually
decreasing a winding pitch of conductor layers in an opposite
direction to the inner layers from a N/2+1 layer to an N layer when
the number of layers is even, or from a (N+1)/2 layer to an N layer
when the number of layers is odd; and (b) the shielding layers are
formed, where n is the number of layers in the shielding layers and
expressed by an integer, by gradually increasing a winding pitch of
shielding layers in the same direction from an inner first layer to
an n/2 layer when the number of layers is even, or from an inner
first layer to a (n-1)/2 layer when the number of layers is odd,
and then by gradually decreasing the winding pitch of shielding
layers in an opposite direction to the inner layers from a n/2+1
layer to an n layer when the number of layers is even, or from a
(n+1)/2 layer to an n layer when the number of layers is odd.
Inventors: |
Mukoyama, Shinichi; (Tokyo,
JP) ; Tsubouchi, Hirokazu; (Tokyo, JP) ;
Miyoshi, Kazutomi; (Tokyo, JP) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
620 NEWPORT CENTER DRIVE
SIXTEENTH FLOOR
NEWPORT BEACH
CA
92660
US
|
Family ID: |
26596460 |
Appl. No.: |
09/909769 |
Filed: |
July 20, 2001 |
Current U.S.
Class: |
174/125.1 |
Current CPC
Class: |
H01B 12/02 20130101;
Y02E 40/60 20130101; Y10T 29/49014 20150115; Y02E 40/641
20130101 |
Class at
Publication: |
174/125.1 |
International
Class: |
H01B 012/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 21, 2000 |
JP |
JP2000-221140 |
Jun 27, 2001 |
JP |
JP2001-193921 |
Claims
What is claimed is:
1. A superconducting cable for alternating current, comprising a
conductor layers formed by a plurality of tape-shaped
superconducting wires wound around a center member, an electric
insulating layer formed outside the conductor layers, and a
plurality of shielding layers formed outside the insulating layers,
wherein (a) the conductor layers are formed, where N is a number of
layers in the conductor layers and expressed by an integer, by
gradually increasing a winding pitch of conductor layers in the
same direction from an inner first layer to an N/2 layer when the
number of layers is even, or from an inner first layer to a (N-1)/2
layer when the number of layers is odd, and then by gradually
decreasing a winding pitch of conductor layers in an opposite
direction to the inner layers from a N/2+1 layer to an N layer when
the number of layers is even, or from a (N+1)/2 layer to an N layer
when the number of layers is odd; and (b) the shielding layers are
formed, where n is the number of layers in the shielding layers and
expressed by an integer, by gradually increasing a winding pitch of
shielding layers in the same direction from an inner first layer to
an n/2 layer when the number of layers is even, or from an inner
first layer to a (n-1)/2 layer when the number of layers is odd,
and then by gradually decreasing the winding pitch of shielding
layers in an opposite direction to the inner layers from a n/2+1
layer to an n layer when the number of layers is even, or from a
(n+1)/2 layer to an n layer when the number of layers is odd.
2. The superconducting cable for alternating current as claimed in
claim 1, wherein the winding in the conductor layers is an opposite
in direction and the winding pitch are substantially the same
between first layer and N-th layer, between second layer and
(N-1)-th layer, in like manner, and, between N/2-th layer and
(N/2+1)-th layer when the number of conductors is even, or between
(N-1)/2-th layer and (N+3)/2-th layer when the number of conductor
layers is odd.
3. The superconducting cable for alternating current as claimed in
claim 1 or 2, wherein the winding in the shielding layers is an
opposite in direction and the winding pitch are substantially the
same between first layer and n-th layer, between second layer and
(n-1)-th layer, in like manner, and, between n/2-th layer and
(n/2+1)-th layer when the number of conductors is even, or between
(n-1)/2-th layer and (n+3)/2-th layer when the number of conductor
layers is odd.
4. The superconducting cable for alternating current as claimed in
claim 1 or 2, wherein the N/2-th and (N/2+1)-th layers in the
conductor layers when the number of conductor layers is even, or,
the conductor layers from the (N-1)/2-th to (N+3)/2-th layers when
the number of conductor layers is odd, are formed by the
tape-shaped superconducting wires of which filaments are untwisted,
and the N-th conductor layer and the first shielding layer are
formed by the tape-shaped superconducting wires of which filaments
are twisted.
5. The superconducting cable for alternating current as claimed in
claim 3, wherein the N/2-th and (N/2+1)-th layers in the conductor
layers when the number of conductor layers is even, or, the
conductor layers from the (N-1)/2-th to (N+3)/2-th layers when the
number of conductor layers is odd, are formed by the tape-shaped
superconducting wires of which filaments are untwisted, and the
N-th conductor layer and the first shielding layer are formed by
the tape-shaped superconducting wires of which filaments are
twisted.
6. The superconducting cable for alternating current as claimed in
claim 1 or 2, wherein the n/2-th and (n/2+1)-th layers in the
shielding layers when the number of shielding layers is even, or,
the shielding layers from the (n-1)/2-th to (n+3)/2-th layers when
the number of shielding layers is odd, are formed by the
tape-shaped superconducting wires of which filaments are
untwisted.
7. The superconducting cable for alternating current as claimed in
claim 2, wherein the winding pitch is selected within a range from
50 to 1000 mm, a tolerance for the substantially same winding pitch
in the conductor layers and shielding layers is within a double of
the winding pitch.
8. The superconducting cable for alternating current as claimed in
claim 3, wherein the winding pitch is selected within a range from
50 to 1000 mm, a tolerance for the substantially same winding pitch
in the conductor layers and shielding layers is within a double of
the winding pitch.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a superconducting
power-transmission cable using superconductive materials, and in
particular, to a superconducting power-transmission cable of which
conductor layers and shielding layers are adjusted in both winding
pitchs and winding directions.
RELATED ART
[0002] In superconducting cables for transmitting power with less
loss, a conductor is formed by winding tape-shaped superconducting
wires around a core or the like in spiral forms, so that
flexibility is given to the cable itself. When the cable is
required to transmit a large amount of current, the number of
layers in the conductor is increased so as to form multi-layered
conductor, thus increasing current capacity. Furthermore, in order
that an electromagnetic field generated by current flowing through
the conductor is avoided from leaking out of the cable, an
insulator is formed on and around the outer surface of the
conductor, and then tape-shaped superconducting wires are wound on
and around the insulator in a spiral form to form shielding layers.
The number of those wound wires in the shielding layers is almost
the same as that of the conductors, thus containing the
electromagnetic field within the cable.
[0003] Japanese Patent Provisional Publication No. 62-180910
publication discloses a superconducting cable, which is formed by
winding a complex multi-filamentary superconducting member in
spiral forms around the outer surface of a normal conducting member
so that right-handed wound layers and left-handed wound layers are
formed alternately thereon.
[0004] Moreover, Japanese Patent Provisional Publication No.
8-287746 publication discloses a superconducting cable for
alternating current, in which a plurality of layers of tape-shaped
superconducting wires are wound around a center member. In the
superconducting cable, the winding pitch of the wires becomes
larger as the windings proceed to outer layers, in order to make
all the layers equal in inductance to each other.
[0005] Moreover, Japanese Patent Provisional Publication No.
9-45150 publication discloses a multi-layer superconductor, in
which a superconducting wires are wound in spiral forms around a
core to form a plurality of layers. In the multi-layer
superconductor, a maximum of the winding pitch is specified, and
the winding pitch becomes shorter as the winding proceeds from an
inner layer to an outer layer.
SUMMARY OF THE INVENTION
[0006] One embodiment of the superconducting cable for alternating
current according to the present invention is a superconducting
cable for alternating current comprising conductor layers formed by
a plurality of tape-shaped superconducting wires wound around a
center member, an electric insulating layer formed outside the
conductor layers, and a plurality of shielding layers formed
outside the insulating layers, wherein the cable comprises:
[0007] (a) the conductor layers being formed, where N is the number
of layers in the conductor layers and expressed by an integer, by
gradually increasing a winding pitch of conductor layers in the
same direction from an inner first layer to an N/2 layer when the
number of layers is even, or from an inner first layer to a (N-1)/2
layer when the number of layers is odd, and then by gradually
decreasing the winding pitch of conductor layers, in an opposite
direction to the inner layers, from a N/2+1 layer to an N layer
when the number of layers is even, or from a (N+1)/2 layer to an N
layer when the number of layers is odd; and
[0008] (b) the shielding layers being formed, where n is the number
of layers in the shielding layers and expressed by an integer, by
gradually increasing a winding pitch of shielding layers in the
same direction from an inner first layer to an n/2 layer when the
number of layers is even, or from an inner first layer to a (n-1)/2
layer when the number of layers is odd, and then by gradually
decreasing the winding pitch of shielding layers, in an opposite
direction to the inner layers, from a n/2+1 layer to an n layer
when the number of layers is even, or from a (n+1)/2 layer to an n
layer when the number of layers is odd.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a schematic side view showing a multi-layer
superconducting cable according to an embodiment 1 of the present
invention.
[0010] FIG. 2 is a schematic side view showing a multi-layer
superconducting cable according to an embodiment 2 of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0011] Embodiments of the superconducting cable according to the
present invention will now be described.
[0012] A practical superconducting cable is generally manufactured
by the following procedures. For example, a first layer in the
conductor layers is formed by winding, in a spiral form and without
gap therebetween, tape-shaped superconducting wires made of oxide
superconducting material around a pipe-like flexible core made of
stainless steel. After completion of winding the first layer, the
tape-shaped superconducting wires are further wound on and around
the first layer in a spiral form without gap therebetween, in the
same manner as in the first layer, thus forming the second layer.
In a similar way to that, the wires are wound in consecutive order
in the spiral form and without gap therebetween on the outer
circumference of the second layer, thus forming the third, the
fourth, . . . layers. This way of winding brings about a plurality
of conductor layers.
[0013] Because high voltage is applied to the conductor layers, an
insulting layer is to be formed outside the conductor layers. The
insulating layer, which uses such materials effecting electric
insulation as polymer material or paper, are formed so as to be
wound around the conductor layers. Like the conductor layers,
multi-layer shielding layers are formed on (the outer surface of)
the insulating layer by winding in spiral form tape-shaped
superconducting wires. Current is also applied to the shielding
layers, but its flowing direction is opposite to that to the
conductor layers, so that the shielding layers can have a function
of preventing a magnetic field from leaking out of the cable.
[0014] An object of the present invention is to reduce an
alternating current loss of the superconducting cable.
[0015] In order to solve conventional problems, the present
inventors have studied intensively. As a result it is found that by
means of adjusting winding directions and winding pitches of
conductor layers and shielding layers, current flowing through all
the layers is made uniform to lower alternating current loss, and
concurrently, generation of the longitudinal magnetization is
suppressed to lower alternating current loss caused by the
longitudinal magnetic field. Furthermore, a recent study conducted
by the present inventors has revealed that a circumferential
magnetic field was considered a primary cause for magnetization
loss, however, the longitudinal magnetization that remains within
the tape increases alternating current loss (magnetization loss due
to the longitudinal magnetization), which prevents the
superconducting cable from having decreased alternating current
loss.
[0016] One embodiment of the superconducting cable for alternating
current according to the present invention is a superconducting
cable for alternating current, comprising conductor layers formed
by a plurality of tape-shaped superconducting wires wound around a
center member, an electric insulating layer formed outside the
conductor layers, and a plurality of shielding layers formed
outside the insulating layer, wherein
[0017] (a) the conductor layers are formed, where N is a number of
layers in the conductor layer and expressed by an integer, by
gradually increasing a winding pitch of conductor layers in the
same direction from an inner first layer to an N/2 layer when the
number of layers is even, or from an inner first layer to a (N-1)/2
layer when the number of layers is odd, and then by gradually
decreasing a winding pitch of conductor layers in an opposite
direction to the inner layers from a N/2+1 layer to an N layer when
the number of layers is even, or from a (N+1)/2 layer to an N layer
when the number of layers is odd; and
[0018] (b) the shielding layers are formed, where n is the number
of layers in the shielding layers and expressed by an integer, by
gradually increasing a winding pitch of shielding layers in the
same direction from an inner first layer to an n/2 layer when the
number of layers is even, or from an inner first layer to a (n-1)/2
layer when the number of layers is odd, and then by gradually
decreasing the winding pitch of shielding layers in an opposite
direction to the inner layers from a n/2+1 layer to an n layer when
the number of layers is even, or from a (n+1)/2 layer to an n layer
when the number of layers is odd.
[0019] In addition, in the superconducting cable for alternating
current according to the present invention, the winding in the
conductor layers is an opposite in direction and the winding pitch
are substantially the same between first layer and N-th layer,
between second layer and (N-1)-th layer, in like manner, and,
between N/2-th layer and (N/2+1)-th layer when the number of
conductors is even, or between (N-1)/2-th layer and (N+3)/2-th
layer when the number of conductor layers is odd.
[0020] Moreover, in the superconducting cable for alternating
current according to the present invention, the winding in the
shielding layers is an opposite in direction and the winding pitch
are substantially the same between first layer and n-th layer,
between second layer and (n-1)-th layer, in like manner, and,
between n/2-th layer and (n/2+1)-th layer when the number of
conductors is even, or between (n-1)/2-th layer and (n+3)/2-th
layer when the number of conductor layers is odd.
[0021] Moreover, the N/2-th and (N/2+1)-th layers in the conductor
layers when the number of conductor layers is even, or, the
conductor layers from the (N-1)/2-th to (N+3)/2-th layers when the
number of conductor layers is odd, are formed by the tape-shaped
superconducting wires of which filaments are untwisted, and the
N-th layer in the conductor layers and the first layer in the
shielding layers are formed by the tape-shaped superconducting
wires of which filaments are twisted.
[0022] Moreover, the n/2-th and (n/2+1)-th layers in the shielding
layers when the number of shielding layers is even, or, the
shielding layers from the (n-1)/2-th to (n+3)/2-th layers when the
number of shielding layers is odd, are formed by the tape-shaped
superconducting wires of which filaments are untwisted.
[0023] Moreover, the winding pitch is selected within a range from
50 to 1000 mm, a tolerance for the substantially same winding pitch
in the conductor layers and shielding layers is within a double of
the winding pitch.
[0024] The superconducting cable for alternating current according
to the present invention is based on the following concept. More
specifically, in order to uniformly provide current into each of
the multi-layer conductors, it is necessary that the value of
impedance in each layer is the same. When current flows uniformly
into each layer, the impedance Z.sub.i of the i-th layer can be
expressed by the following equation (1): 1 Z i = A ( L i + i j M ij
) , ( 1 )
[0025] wherein L.sub.i is the self-inductance of each layer,
M.sub.ij is the mutual inductance between the i-th layer and
another j-th layer, and A is a constant. In addition, the
self-inductance L.sub.i and mutual inductance M.sub.ij can be
expressed by the following equations (2) and (3), respectively: 2 L
i = 0 r i 2 lp i 2 + 0 2 ln ( D r i ) , ( 2 ) M ij = a i a j 0 lp i
lp j r i 2 + 0 2 ln ( D r j ) , ( 3 )
[0026] Wherein .mu..sub.0 is the vacuum permeability, r.sub.i and
r.sub.j are the radii of the i-th and j-th layers, respectively,
lp.sub.i an lp.sub.j are the winding pitch in the i-th and j-th
layers, respectively, D is the outermost radius of the shielding
layers, and a.sub.i and a.sub.j are constants indicative of the
winding directions (the right-handed screw direction is +1 and the
left-handed screw direction is -1).
[0027] An object of the present invention is to make the impedance
Zi of each layer equal to each other by changing the winding pitch,
winding direction, and winding radius of each layer on the basis of
the foregoing equation (1). In the present invention, the winding
pitchs becomes gradually larger in the same direction as to the
inner first layer to the N/2-th layer (when the number of conductor
layers is odd, to the (N-1)/2-th layer), then becomes gradually
smaller in the opposite direction to the inner one as to the
(N/2+1)-th layer (when the number of conductor layers is odd, the
(N+1)/2-th layer) to the N-th layer, thus forming the conductor
layer.
[0028] In FIG. 1, the first layer of conductor layers is formed by
winding, in a spiral form without gap therebetween, a tape-shaped
superconducting wire 5 around a cylindrical hollow center member 1
made of a flexible material, such as copper, aluminum, and
stainless steel or the like. After completing the winding of the
first layer 2a, the tape-shaped superconducting wire 5 is wound on
and around the first layer 2a in a spiral form without gap
therebetween, like the first layer 2a, thus forming the second
layer 2b. In the same manner, the wires are wound in a spiral form
without gap therebetween so as to form a plurality of layers 2c to
2f, thereby forming conductor layers 6 made up of a plurality of
layers 2a to 2f. An electric insulating layer 3 is further formed
on the conductor layers 6, and then shielding layers 8 are formed
on the insulating layer 3 by winding, four layers in spiral forms,
a tape-shaped superconducting wires 7 around the insulating layer
3. The tape-shaped superconducting wires 7 are shaped in a similar
manner to that used in the conductor layers 6.
[0029] In the present invention, the conductor layers 6 and
shielding layers 8 of the superconducting cable are formed into
N-pieces of layers and n-pieces of layers, respectively. Suppose
that the layers of each of the conductor and shielding layers 6 and
8 are counted in turn from the inside as being the first layer, the
second layer, and so forth. In the conductor layers 6, when the
number of layers is even, the winding pitch in each layer becomes
larger and larger in order as being "the first layer<the second
layer<. . .<the N/2-th layer, then becomes smaller and
smaller in order as being "the (N/2+1)-th layer>the (N/2+2)-th
layer>. . .>the (N-1)-th layer>the N-th layer. In
contrast, when the number of layers is odd, the winding pitch in
each layer becomes larger and larger in order as being "the first
layer<the second layer<. . .<the (N-1)/2-th layer, then
becomes smaller and smaller in order as being "the (N+1)/2-th
layer>the (N+1)/2+1-th layer>. . .>the (N-1)-th
layer>the N-th layer.
[0030] In the shielding layers 8, when the number of layers is
even, the winding pitch in each layer becomes larger and larger in
order as being "the first layer<the second layer<. . .<the
n/2-th layer, then becomes smaller and smaller in order as being
"the (n/2+1)-th layer>the (n/2+2)-th layer>. . .>the
(n-1)-th layer>the n-th layer. In contrast, when the number of
layers is odd, the winding pitch in each layer becomes larger and
larger in order as being "the first layer<the second layer<.
. .<the (n-1)/2-th layer, then becomes smaller and smaller in
order as being "the (n+1)/2-th layer>the (n+1)/2+1-th layer>.
. .>the (n-1)-th layer>the n-th layer.
[0031] As to the winding directions, the same winding direction is
applied to inner layers including the first layer to N/2-th layer
in the conductor layers 6 and the first layer to the n/2-th layer
(to the (n-1)/2-th layer when the number of layers is odd) in the
shielding layers 8. The opposite winding direction to that applied
to the inner layers is applied to the remaining outer layers
including from the (N/2+1)-th layer (the (N+1)/2-th layer when the
number of conductor layers is odd) to the N-th layer in the
conductor layers and the (n/2+1)-th layer (the (n+1)/2-th layer
when the number of conductor layers is odd) to the n-th layer in
the shielding layers. Additionally, it is preferable that the
initial winding directions for the first layers in both conductor
and shielding layers 6 and 8 are the same.
[0032] As to the winding pitch, the winding pitch for inner
conductor layers and inner shielding layers are assigned as
follows. For inner layers including the first layer to the N/2-th
layer (to the (N-1)/2-th layer when the number of conductor layers
is odd) in the conducting layers and the first layer to the n/2-th
layer (to the (n-1)/2-th layer when the number of shielding layers
is odd) in the shielding layers, the winding pitch is set so as to
be larger as the layer advances outward, with the same winding
direction kept. Likewise, for outer layers including the (N/2+1)-th
layer (the (N+1)/2-th layer when the number of conductor layers is
odd) to the N-th layer in the conductor layers and the (n/2+1)-th
layer (the (n+1)/2-th layer when the number of shielding layers is
odd) to the n-th layer in the shielding layers, the winding pitch
is set so as to be smaller as the layer advances outward, with
keeping the same winding direction which is opposite to that of the
inner layers. The above-mentioned way of setting of the winding
pitch allows the impedance of each layer to be equal to each other,
thus current flowing each layer being uniform. Therefore, current
distributions become uniform over the layers, thus reducing an
alternating current loss.
[0033] Furthermore, the winding pitchs of both conductor layers and
insulating layers have the following relationships:
[0034] the first layer.apprxeq.the N-th layer; the second
layer.apprxeq.the (N-1)-th layer; the third layer.apprxeq.the
(N-2)-th layer, . . . ; and
[0035] the first layer.apprxeq.the n-th layer; the second
layer.apprxeq.the (n-1)-th layer; the third layer.apprxeq.the
(n-2)-th layer, . . . , where the sign ".apprxeq." means that both
winding pitchs are substantially the same.
[0036] The winding pitch should be adjusted within the range from
50 to 1000 mm. With the winding pitch being below 50 mm, the bend
radius of the tape wire to be wound becomes too small for bending.
As a result, bending distortion becomes large, thus deteriorating
the critical current characteristic of a superconducting wire. On
the other hand, with the winding pitch being over 1000 mm, a
winding force required to wind the tape around the center member is
lowered, thus causing disturbances in winding. A further preferable
winding pitch is within the range from 80 to 600 mm.
[0037] Since irregularities in current distributions are reduced as
low as being no obstacles for practical applications, as far as the
range of pitch lengths is within the length ranging from the
winding pitch to two times of the same winding pitch, a winding
pitch selected up to the range whose maximum is equal to the double
of a certain winding pitch may be tolerated as being substantially
the same winding pitch. For example, if the winding pitch at a
certain layer is 100 mm, the winding pitch ranging from 100 to 200
mm is tolerated as being substantially the same in length.
[0038] In the conductor layers, the first layer to the N/2-th layer
(the (N-1)/2-th layer when the number of conducting layers is odd)
(i.e., inner layers) are opposite in the winding directions to the
(N/2+1)-th layer (the (N+1)/2-th layer when the number of conductor
layers is odd) to the N-th layer (i.e., outer layers). In addition,
the winding pitch of the corresponding layers (counted from the
boundary therebetween, i.e., N/2-1 and N/2+2, N/2-2 and N/2+3 for
example) in the inner layers and outer layers are substantially the
same. Therefore, longitudinal magnetic field generated from the
corresponding layers are cancelled out, so that an eddy current
loss and alternating current loss in the tape-shaped
superconducting wire due to the longitudinal magnetic field are
reduced. The same function and effect are shown in the shielding
layers. As a result, compared to the conventional superconducting
cable, the alternating current loss can be remarkably lowered in
the present invention.
[0039] The winding directions of the first layer of the conductor
layers and the first layer of the shielding layers are set in such
a manner that both longitudinal magnetic field each remaining in
the shielding layers and the conductor layers due to incomplete
cancellation are directed to mutually opposite directions. This
allows the residual longitudinal magnetic field to be cancelled
out. Thus, the eddy current loss and the alternating current loss
of the tape-shaped superconducting wire are lowered.
[0040] The tape-shaped superconducting wire has the following
property: when the filaments of the wire are twisted, the wire
exhibits a smaller amount of alternating current loss under the
transverse magnetic field, while it exhibits a larger amount of
alternating current loss under the longitudinal magnetic field. On
the contrary, when the filaments of the wire are untwisted, the
wire exhibits a larger amount of alternating current loss under the
transverse magnetic field, while it exhibits a smaller amount of
alternating current loss under the longitudinal magnetic field.
[0041] The tape-shaped superconducting wire with its filament
untwisted is used for layers each of which longitudinal magnetic
field (i.e., a magnetic field generated in the axial direction of a
conductor) is relatively higher in strength, more specifically, the
layer in which the longitudinal magnetic field is at least
one-third of the transverse magnetic field. Such layers are the
N/2-th and (N/2+1)-th layers (from (N-1)/2-th to (N+3)/2-th layers
when the number of conductor layers is odd) in the conductor
layers, and the n/2-th and (n/2+1)-th layers (the (n-1)/2-th to
(n+3)/2-th layers when the number of shielding layers is odd) in
the shielding layers. On the other hand, the tape-shaped
superconducting wires with filaments twisted are used for layers
each of which transverse magnetic field (i.e., a magnetic field
generated in the circumferential direction of a conductor) is
relatively higher in strength, more specifically, the layer in
which the transverse magnetic field is at least 200 gauss and at
least five times the longitudinal magnetic field. Such layers
include the N-th layer of the conductor layers and the first layer
of the shielding layers.
[0042] Intermediate layers of the conductor and shielding layers,
which are relatively higher strength for the longitudinal magnetic
field and lower strength for the transverse magnetic field, are
formed by winding in spiral form the tape-shaped superconducting
wires with filaments untwisted. The outermost layer of the
conductor layers and the innermost layer of the shielding layers,
which are smaller in the strength of the longitudinal magnetic
field and larger in the strength of the transverse magnetic field,
are formed by winding in spiral form the tape-shaped
superconducting wire with filaments twisted. Thus winding the
tape-shaped superconducting wires in the above manner provides a
superconducting cable of which alternating current loss is further
decreased.
[0043] Materials used as the insulating layer 3 include insulating
tapes, such as kraft paper, polyethylene films, polyethylene paper,
and polypropylene laminated paper. The insulating tapes are wound
in a spiral form around the conductor layers to form laminated
insulating layers. It is enough for the insulating layer that there
is caused no cracks or crashes in the insulating layer at the
temperature of liquid nitrogen. Thus, for example, the insulating
layer may be formed by polyethylene resin.
[0044] The superconducting cable for alternating current according
to the present invention is available for superconducting
power-transmission cables used as underground cables, which
transmit high voltages of 6 to 100 kV or ultra-high voltages of at
least 100 kV. In this case, when the present invention is applied
to such cables, current flowing through each layer can be uniform
and its alternating current loss can be lowered. Concurrently, the
longitudinal magnetic field to be generated can be suppressed down
to a small amount, thus reducing its alternating current loss
caused by the longitudinal magnetic field.
[0045] According to the superconducting cable for alternating
current according to the present invention, the following
conventional problems can be overcome:
[0046] More specifically, (1) when each layer of the conductor
layers is wound in the same direction, the longitudinal magnetic
field is large, so that eddy current is caused in the center member
due to the longitudinal magnetic field, thus increasing the
alternating current loss. (2) When conductor layers and the
shielding layers are wound, layers by layers, in alternate
direction, with the same winding pitchs in order to decrease the
alternating current loss of the superconducting cable due to its
longitudinal magnetic field, current that should flow into each
layer shifts to outer layers, resulting in that a current
distribution over the layers becomes unbalanced, thereby leading to
a large amount of altering current loss. On the other hand, when
wires are wound in the same direction in spiral forms and the
winding pitch becomes shorter as the winding advances to an outer
one in order to obtain a uniform current distribution over the
layers, alternating current loss occurs due to the longitudinal
magnetic field, resulting in that expected alternating current loss
cannot be attained. (3) If the wires are wound in the same
direction, magnetic field (longitudinal magnetic field) is
generated along the axial direction of the cable. This longitudinal
magnetic field causes eddy current in the center member or the
like, which leads to a large amount of alternating current loss.
(4) When right-handed and left-handed layers are formed alternately
with their winding pitchs maintained at the same value, current
that should flow into the layers concentrates to outer layers,
because impedance becomes smaller as the winding proceeds up to an
outer layer. As a result, the alternating current loss
increases.
EXAMPLE
[0047] The superconducting cable for alternating current according
to the present invention will now be explained in more detail by
examples
Example 1
[0048] FIG. 1 shows a schematic side view for explaining a
multi-layer superconducting cable in this example. A center member
1 is 18 mm in outer diameter and shaped into a flexible hollow pipe
made of copper. On and around the center member 1, tape-shaped
superconducting wires 5, which is 3 mm in width and 0.2 mm in
thickness, were wound in spiral form to provide six layers from a
layer 2a to a layer 2f, thereby forming conductor layers 6. On and
around the conductor layers (superconducting layer) 6, a
polypropylene laminated paper tape, which is 30 mm in width and 0.1
mm in thickness) was wound in a spiral form to have a plurality of
layers laminated one after another. The tapes were laminated up to
a thickness of 6 mm, thus forming an electrically insulating layer
3. On and around the electrically insulating layer 3, a tape-shaped
superconducting wire 7 of which width is 3 mm (the same in width as
the conductor layers) and of which thickness is 0.2 mm was wound in
spiral form to form four layers, thereby providing shielding layers
8. The manufactured superconducting cable had an outer diameter of
39 mm.
[0049] The winding directions and winding pitchs in the spiral form
are shown in Table 1. Also, in this example, peak values (when
current of 3000 A is supplied) of the vertical and transverse
magnetic fields at the center of each layer of the superconducting
cable are shown in Table 2. As clearly shown in Table 2, layers
that exhibits relatively stronger longitudinal magnetic field (each
of which is, in strength, at least one-third of the transverse
magnetic layer) are the third and fourth conductor layers, as well
as the second and third shielding layers. Additionally, layers that
exhibits stronger transverse magnetic fields (each of which is, in
strength, at least 200 gauss and at least five times the
longitudinal magnetic field) are the fifth and sixth conductor
layers, as well as the first shielding layer.
[0050] When alternating current of 3000 A was supplied through the
conductors, alternating current loss per 1 meter was 1 W/m. It is
found that the amount of the loss is reduced to one-hundredth of
that of the cable in which the wires are wound in alternately
changed winding directions but with the same winding pitch. It is
also found that the loss is reduced to one-thousandth of that of
the cable in which the wires are wound with adjusted winding pitch
but with the same winding direction.
Example 2
[0051] FIG. 2 shows another superconducting cable for alternating
current according to the present invention. In the similar manners
to those in Example 1, the conductor layers, insulating layers, and
shielding layers were formed. In fabricating this superconducting
cable, an intermediate conductor layer (the (N/2+1)-th layer) 9 is
wound using a tape-shaped superconducting wire 10 with untwisted
filaments. In addition, an intermediate shielding layer (the
(n/2+1)-th layer) 11 is wound using a tape-shaped superconducting
wire 13 with untwisted filaments. The outermost conductor layer
(the N-th layer) 13 is formed using a tape-shaped superconducting
wire 14 with twisted filaments 17. Furthermore, the innermost
shielding layer (the first layer) 15 is formed using a tape-shaped
superconducting wire 16 with twisted filaments.
[0052] Alternating current of 3000 A was supplied through the
conductors. As a result, it is found that the alternating current
loss further reduces by 1/2, compared to a cable in which, like
Example 1, all the layers are formed with tape-shaped
superconducting wires of twisted filaments with winding pitch
adjusted.
Example 3
[0053] As an example 3, there will be explained a cable having
conductor layers and shielding layers, in which the number of
conductor layers and the number of shielding layers are odd,
respectively. In the similar manners to those in Example 1, a
center member is 18 mm in outer diameter and shaped into a flexible
hollow pipe made of copper. On and around the center member,
tape-shaped superconducting wires were wound in spiral form to
provide seven layers, thereby forming conductor layers. On and
around the conductor layers (superconducting layer), a
polypropylene laminated paper tapes were wound in a spiral form to
have a plurality of layers laminated one after another. The tapes
were laminated up to a thickness of 6 mm, thus forming an
electrically insulating layer. On and around the electrically
insulating layer, like the conductor layers, a tape-shaped
superconducting wires were wound in spiral form to form five
layers, thereby providing shielding layers. The winding directions
and winding pitchs are shown in Table 3.
1TABLE 1 Direction and Pitch of Spiral Winding Conductor Layer
Winding Pitch Shielding Layer Winding Pitch 1 (Innermost 80 mm
Left- 1 (Innermost 125 mm Right- Layer) Handed Winding Layer)
Handed Winding 2 115 mm Left- 2 305 mm Right- Handed Winding Handed
Winding 3 300 mm Left- 3 580 mm Left- Handed Winding Handed Winding
4 580 mm Right- 4 (Outermost 100 mm Left- Handed Winding Layer)
Handed Winding 5 150 mm Right- Handed Winding 6 (Outermost 80 mm
Right- Layer) Handed Winding
[0054]
2TABLE 2 Winding Pitch Longitudinal Transverse Longitudinal
Transverse Magnetic Magnetic Magnetic Magnetic Conductor Field
Field Shielding Field Field Layer (Gauss) (Gauss) Layer (Gauss)
(Gauss) 1(Innermost 19 105 1(Innermost 4 333 Layer) Layer) 2 60 204
2 82 245 3 115 297 3 110 161 4 135 384 4(Outermost 94 79 Layer) 5
124 467 6(Outermost 82 545 Layer)
[0055]
3TABLE 3 Direction and Pitch of Spiral Winding Conductor Layer
Winding Pitch Shielding Layer Winding Pitch 1 (Innermost 80 mm
Left- 1 (Innermost 100 mm Left- Layer) Handed Winding Layer) Handed
Winding 2 120 mm Left- 2 230 mm Left- Handed Winding Handed Winding
3 320 mm Left- 3 640 mm Right- Handed Winding Handed Winding 4 600
mm Right- 4 120 mm Right- Handed Winding Handed Winding 5 171 mm
Right- 5 (Outermost 85 mm Right- Handed Winding Layer) Handed
Winding 6 103 mm Right- Handed Winding 7 (Outermost 70 mm Right
Layer) Handed Winding
[0056] In the superconducting cable for alternating current
according to the present invention, optimizing combinations of the
winding directions and winding pitchs of the conductor and
shielding layers makes it possible to uniform currents each flowing
through each layer. Moreover, reducing the longitudinal magnetic
field permits the alternating current loss caused in the cable to
be reduced remarkably. Hence, loss of power caused when transmitted
through this superconducting cable can be lowered, and cooling
power required to cool the superconducting cable can thus be
lowered. An energy saving effect is excellent. For such global
objects as saving energy resources which are limited and
suppressing the generation of CO2, the superconducting cable of the
present invention is remarkably effective.
* * * * *