TRIAXIAL SUPERCONDUCTING CABLE
(Detailed Description of the Invention]
(Technical Field]
The present disclosure relates to a triaxial superconducting cable, and more
particularly a triaxial superconducting cable in which superconducting conductors
with each phase are coaxially disposed trebly to configure a core, and an outer
cryostat is configured with an aluminum tube having high conductivity to be used as
a neutral line.
(Background Art]
A superconducting cable may transmit a large amount of power in
comparison to a general normal conduction cable by using a superconducting wire
as a conductor.
The superconducting cable may be a one phase superconducting cable
having a single core, a multi-phase superconducting cable in which several cores
with each different electric phases are tied into a single one, or the like, and the
multi-phase superconducting cable particularly includes a three phase (A-B-C phase
or R-S-T phase) superconducting cable having three cores.
FIG. 1 is a schematic cross-sectional view showing a general three phase
superconducting cable.
Referring to FIG. 1, three cores 20 configuring phases (namely, A phase, B
phase and C phase) in a cryostat 10 are disposed·at three phase superconducting
cable 2. In addition, a fluid for maintaining a superconductor in an extremely low
•
'" temperature state flows in a space 20a between the cryostat 10 and the three cores
20. The three cores 20 are twisted to form a single integrated axis or common axis.
The core 20 having such an integrated or common axis shape is commonly called
'Co-axial' cable (in this specification, it is called 'three-core integrated cable' (three
co-axial cable cores in one cryostat)).
In the three-core integrated superconducting cable 2, the cryostat 10
includes an inner cryostat 11 made of a metallic tube, an adiabatic layer 12 made of
multi-layered adiabatic materials, and an outer cryostat 13 keeping a vacuum space
10a by a spacer 15, in order from the inner side to the outer side in a radial direction.
In addition, the superconducting cable core 20 of each phase includes a
former 21 having a solid shape or a hollow shape forming a coolant channel therein,
a superconducting conductor layer 22, an insulating layer 23 and a superconducting
shielding layer 24, in order from the center to the outer side in the radial direction.
As described above, the three-core integrated superconducting cable 2
should have the superconducting conductor layer 22 and the superconducting
shielding layer 24 for each of three cores 20 with each phase. Since the
superconducting wire occupies 90% of the production cost of a superconducting
cable, if the superconducting conductor layer 22 and the superconducting shielding
layer 24 of the three-core integrated superconducting cable 2 are made of
superconducting wires, a large amount of superconducting wires is required, which
deteriorates the competitiveness of the product. In addition, since three cores 20
with each phase are arranged in a triangular pattern in a sectional view, the diameter
of the entire cable is great, which increases the construction costs for installing the
superconducting cable.
In addition, the three-core integrated superconducting cable is short-circuited
'- from the superconducting shielding layer 24 in a terminal connection box and thus
plays a role of a neutral line at ordinary time. Moreover, the three-core integrated
superconducting cable should be configured to flow a fault current to the
superconducting shielding layer 24 during a short time before a circuit breaker or the
like operates when a fault such as earth or phase short occurs in a power system.
However, the superconducting shielding layer 24 may not bear an abrupt current
increase when a fault current is generated since it is made of a thin-film wire with a
small sectional area. Therefore, a copper conductor layer is further provided to be
used as a neutral line together with the superconducting shielding layer. As
described above, since a copper conductor neutral line should be stranded around
each of the cores 20 with three phases, the three-core integrated superconducting
cable has a complex structure, a complicated manufacturing process and a high
production cost.
Meanwhile, Patent Literature 1 discloses a cable (AC cable), which is also
called 'triaxial cable', in which superconducting conductors with each phase are
disposed to coaxially overlap in addition to the three-core integrated superconducting
cable where cores with each phase are cooperatively stranded. In this specification,
the superconducting cable is called 'triaxial cable'.
The triaxial superconducting cable disclosed in Patent Literature 1 is
configured so that a single core having superconducting conductor layers (power
transmission layers) with different phases, which coaxially overlap trebly with the
insulating layers being interposed between them, is disposed from the innermost
former to the outside in the radial direction. This cable may decrease the diameter
of the core, and so the diameter of the entire cable is somewhat reduced in
comparison to the three-phase integrated superconducting cable. However, since a
.~ neutral line (neutral layer) made of normal conduction metal should be stranded on
the outer circumference of the outer insulating layer of the core in order to cope with
zero phase current (less than several hundred amperes) and fault current generated
by three-phase unbalanced current at ordinary time, the structure and manufacturing
process of the triaxial cable are also complicated, and a high production cost is
required.
In particular, in a case where a neutral line is disposed at the outside of the
core, the neutral line generates heat since zero phase current flows through the
neutral line, and the capacity of a cooling device for cooling the heat increases,
which also increases the entire system cost. In addition, if fault current of several
ten kilo amperes flows into the cable, an electromagnetic force is generated at the
neutral line by the fault current, and the electromagnetic force damages the
insulating body, thereby deteriorating the reliability of the superconducting cable.
(Related Literatures)
(Patent Literature)
Korean Patent Publication No. 10-2008-0000671
Korean Patent Publication No. 10-2011-0091929
(Description of the Invention)
(Technical Objective to be accomplished by the Invention)
The present disclosure is directed to solving the problem of an existing
superconducting cable and providing a triaxial superconducting cable, in which
superconducting conductors with each phases coaxially overlap to configure a core
and an outer cryostat is configured with an aluminum tube having high conductivity to
be used as a neutral line which is a fault current pass circuit, without forming a
~ neutral line on the outer circumference of the core, so that the superconducting cable
is manufactured with a low production cost due to a small diameter and a simple
structure and also the reliability of the cable is improved by preventing overheating or
damage of an insulating body due to the electromagnetic force generated at the
neutral line.
(Constitution of the Invention]
In one aspect, there is provided a triaxial superconducting cable, which
includes: a cryostat having an inner cryostat and an outer cryostat coaxially disposed
with a space being interposed therebetween; and a single core disposed in the inner
cryostat of the cryostat with a space being interposed therebetween, wherein a
former is disposed at the center of the core, superconducting conductor layers with
each phase are coaxially disposed at the outer circumference of the former at an
outer side in a radial direction with insulating layers being interposed therebetween,
and the insulating layer are coaxially disposed at the outer circumference of an
outermost superconducting conductor layer, and wherein the outer cryostat of the
cryostat is made of aluminum material and configures a neutral line electrically wired
to neutral polarity (N polarity) at a superconducting cable system.
In another aspect, there is provided a triaxial superconducting cable, which
includes: a cryostat having an inner cryostat and an outer cryostat coaxially disposed
with a space being interposed therebetween; and a single core disposed in the inner
cryostat of the cryostat with a space being interposed therebetween, wherein the
core includes a former, which is disposed at a center thereof, and includes a first
phase superconducting conductor layer, a first insulating layer, a second phase
superconducting conductor layer, a second insulating layer, a third phase
superconducting conductor layer, a third insulating layer and a binder, which
"- coaxially overlap in order from the former to an outside in a radial direction, and
wherein the outer cryostat of the cryostat is made of aluminum material and
configures a neutral line electrically wired to neutral polarity (N polarity) at a
superconducting cable system.
In the triaxial superconducting cable according to the present disclosure, the
inner cryostat of the cryostat may be made of aluminum material and may be wired
to electrically earth at the superconducting cable system.
An adiabatic material may be disposed at the outer circumference of the inner
cryostat, and the adiabatic material and the outer cryostat preferably may maintain a
gap by a spacer to form the space.
A coolant may flow in the space between the inner cryostat and the insulating
layer of the core.
[Advantageous Effects]
If the triaxial superconducting cable according to the present disclosure is
used, the size of the superconducting cable may be reduced since superconducting
conductors with each phase coaxially overlap to reduce a sectional size of the cable.
In addition, if the triaxial superconducting cable according to the present
disclosure is used, an amount of superconducting wire used may be greatly reduced,
which ensures excellent economic property, since a superconducting shielding layer
is not necessary.
In addition, if the triaxial superconducting cable according to the present
disclosure is used, since an outer cryostat which must be adopted in the
superconducting cable is made of aluminum material with excellent conductivity and
the outer cryostat is wired to neutral polarity to serve as a neutral line, it is not
needed to separately strand a neutral line conductor such as a copper conductor on
~ the insulating layer at the outer circumference of the core. Therefore, the cable may
have a simple structure and ensure easy manufacture, and it is possible to prevent
the insulating body from being damaged by fault current, thereby improving the
reliability of the superconducting cable.
In addition, if the triaxial superconducting cable according to the present
disclosure is used, even when the outer cryostat generates heat due to the inflow of
unbalanced current or fault current, since adiabatic material is interposed between
the outer cryostat and the space, the heat of the outer cryostat does not influence
inner insulation and inner coolant, and accordingly it is possible to implement a
system which may have excellent efficiency and solve a heating problem of the
coolant when zero phase current or fault current flows in.
[Brief Description of Drawings]
FIG. 1 is a sectional view showing a general three-core integrated
superconducting cable;
FIG. 2 is a sectional view showing a triaxial superconducting cable according
to the present disclosure;
FIG. 3 is an equivalent circuit view of the superconducting cable shown in
FIG. 2;
FIG. 4 is a schematic diagram for illustrating the stray voltage of an aluminum
cryostat which is a neutral line of the triaxial superconducting cable according to the
present disclosure; and
FIG. 5 is a schematic diagram for comparing sectional sizes of the triaxial
superconducting cable according to the present disclosure and a general integrated
superconducting cable.
[Specific Details for the Implementation of the Invention]
8
~ Hereinafter, a preferred embodiment of the present disclosure will be
described with reference to the accompanying drawings.
FIGS. 2 and 3 show the structure of a triaxial superconducting cable
according to the present disclosure.
Referring to FIGS. 2 and 3, the triaxial superconducting cable 100 according
to the present disclosure is configured to have a core 120 in which superconducting
conductors with each electric phase coaxially overlap in a cryostat 110. In FIG. 2,
the center of the core 120 is dislocated from the center of the cryostat 110 (falling
downwards), but it is a figure showing a sectional view of an elongated cable at any
point and just intactly expresses that the core 120 goes down due to the gravity
(located at that point). According to the installation method or the curve of the cable,
the core 120 may droop down in the cryostat 110 or float in the middle at another
point.
This will be described below in more detail.
The triaxial superconducting cable 100 maintains a space in the cryostat 110
so that the core 120 is disposed therein.
The core 120 includes a former 121 at a center thereof, and superconducting
conductor layers with each phase are coaxially disposed at the outer circumference
of the former 121 at an outer side in a radial direction with insulating layers being
interposed between the superconducting conductor layers.
In the embodiment shown in FIGS. 2 and 3, the core 120 includes a first
phase (for example; A phase) superconducting conductor layer 122, a first insulating
layer 123, a second phase (for example; B phase) superconducting conductor layer
124, a second insulating layer 125, a third phase (for example; C phase)
superconducting conductor layer 126, and a third insulating layer 127, which
\~ coaxially overlap in order from the former 121 at the center to an outer side in the
radial direction. The outside of the third insulating layer 127 which is an outermost
insulating layer is surrounded by a binder 128. The binder 128 protects the
outermost insulating layer and electrically earth, and the binder 128 is made of 'metal
binder' which is generally configured with a metallic tape.
The first, second and third insulating layers 123, 125, 127 are composed of a
semi-conductive layer, an insulating layer and a semi-conductive layer, though not
distinguishably shown in the figures.
As shown in FIGS. 2 and 3, the former 121 is configured in a way that a
metallic wire (for example, a copper wire) is stranded to have a hollow forming a
space 120a at the center portion or stranded in a solid form where the inside is full
without a space.
In addition, the former 121 may be configured with a metallic pipe having the
space 120a therein. The space 120a formed at the center of the former 121 is used
as a passage for flowing a coolant 120b (see FIG. 3), and the space may also be
maintained intactly even when a coolant does not flow therein.
The cryostat 110 is coaxial with the core 120 and plays a role of protecting
the superconducting cable, namely the core 120, and maintaining the
superconducting cable in an extremely low temperature state.
For this purpose, the cryostat 110 includes an inner cryostat 111 separated
from the core 120 in the radial direction to form a space 11 Oa, and an outer cryostat
113 disposed to maintain a vacuum space 114 from the inner cryostat 111 .
An adiabatic material 112 is disposed at the outer circumference of the inner
cryostat 111 to shield heat. The inner cryostat 111 and the outer cryostat 113
maintain a gap by the spacer 115. In other words, in a case where the adiabatic
\,. layer 112 is formed at the inner cryostat 111 , the spacer 115 is disposed between the
adiabatic material 112 and the outer cryostat 113.
A coolant 11 Ob (see FIG. 3) may flow in the space 11 Oa between the inner
cryostat 111 and the core 120 in order to assist cooling.
The inner cryostat 111 and the outer cryostat 113 are made of a corrugated
pipe spirally corrugated.
In the present disclosure, the outer cryostat 113 is particularly made of an
aluminum (AI) tube with excellent conductivity and is electrically wired as a neutral
line (N polarity) (neutral conductor) at a superconducting cable system.
Along with it, the inner cryostat 111 may be also made of an aluminum tube,
and the inner cryostat 111 is wired to electrically earth.
In the superconducting cable system, since the inner cryostat 111 directly
contacts extremely low temperature fluid (for example, liquid nitrogen) at a terminal
and connection box, the inner cryostat 111 is not used as a neutral line but used as
an earth line, and the outer cryostat 113 in a normal temperature state is used as a
neutral line at ordinary time and configured as a fault current pass circuit when a fault
occurs, instead of the inner cryostat 111. In a case where an earth wire is provided
separately, the inner cryostat 111 may be made of a stainless steel tube which is
frequently used for extreme low temperature.
In the superconducting cable of the present disclosure, if electric current is
applied to the superconducting layer of each phase, voltage is induced to the outer
cryostat 113 made of aluminum due to the influence of a magnetic field generated by
the current, and a circulating current (shield current) flows in the outer cryostat 113
made of aluminum due to the corresponding stray voltage.
However, in a case where superconducting conductors with three phases are
""-' disposed to coaxially overlap as in the present disclosure, as shown in FIG. 4,
electric current does not flow in the outer cryostat 113 made of aluminum. In FIG. 4,
'r' represents the distance from the conductor to the outer cryostat 113.
Since the triaxial superconducting cable 100 according to the present
disclosure is configured so that superconducting conductors with each phase
coaxially overlap, its sectional size may be reduced in comparison to an existing
three-core integrated superconducting cable 2.
FIG. 5 is a diagram for comparing actual sectional sizes of an existing threecore
integrated superconducting cable 2 and the triaxial superconducting cable 100
according to the present disclosure, which have the same capacity, and it is possible
to judge how much the superconducting cable according to the present disclosure
may reduce its size.
In addition, since the existing three-core integrated superconducting cable 2
should further include a superconducting shielding layer 24 for the core with each
phase, a large amount of superconducting wire is required. However, the
superconducting cable 100 of the present disclosure does not need a
superconducting shielding layer, and so an amount of superconducting wire used
may be reduced by half in comparison to the three-core integrated superconducting
cable 2, thereby ensuring excellent economic property.
In the existing three-core integrated superconducting cable, a copper
conductor should be wound around the outer circumference of the core with each
phase to playa role of a neutral line and a role of a fault current pass circuit.
Similarly, in a case of an existing coaxial superconducting cable, a neutral line
conductor such as a copper conductor should be wound around an outermost
insulating layer. In the existing superconducting cable, since the cryostat is made of
\~ a stainless steel tube generally used for extremely low temperature, it is impossible
to use the cryostat as a conductor. For this reason, it is not impossible to use the
cryostat as an ordinary neutral line or a fault current pass circuit, and so a neutral line
conductor should be separately stranded on each core. The existing cable where a
neutral line conductor should be stranded on each core has a complex structure, and
its manufacturing process is also complicated and difficult.
In addition, in a case where a neutral line conductor made of a normal
conduction metal such as copper is stranded on the outside of the insulating layer,
similar to both of the existing cables described above, if a fault current of several ten
kA flows in the cable, an electromagnetic force is generated at the neutral line by the
fault current, which may damage the insulating body.
However, in a case of the triaxial superconducting cable 100 of the present
disclosure, since the outer cryostat 110 essentially required for the superconducting
cable is made of aluminum material with excellent conductivity and is wired to neutral
polarity to serve as a neutral line, it is not needed to separately strand a neutral line
conductor on the outermost insulating layer 127 of the core 120. Therefore, the
cable may have a simple structure and be manufactured easily, and it is possible to
prevent the insulating body from being damaged by a fault current, which improves
the reliability of the superconducting cable.
Meanwhile, in a case of a three-phase power transmission cable, for example,
power imbalance may occur among phases (A phase, B phase and C phase) due to
the variation of a load at a power receiving party. Since the zero phase current
flows along the neutral line as much as the imbalance (the difference in power),
Joule heat is generated at the neutral line. In addition, when fault current flows in,
the neutral line generates more heat.
However, in a case of an existing three-core integrated superconducting
cable where the neutral line conductor 25 is stranded on the outer circumference of
the core 20 with each phase, or in a case of an early coaxial superconducting cable
where a neutral line conductor is stranded on the outermost portion of the core 120,
the neutral line conductor contacts or is directly adjacent to a coolant (for example;
liquid nitrogen (LN2)). Therefore, if heat is generated at the neutral line conductor
by the unbalanced current or fault current, the coolant (extremely low temperature
fluid) is heated, thereby deteriorating power transmission efficiency. In addition, in
order to prepare the heating of the coolant, the superconducting cable system has a
burden of further cooling the coolant.
However, if the outer cryostat 113 of the cryostat 110 is set as the neutral line
instead of the inner cryostat 111 directly contacting the coolant as in the preferred
embodiment of the superconducting cable according to the present disclosure, even
when the outer cryostat 113 generates heat due to the introduction of unbalanced
current or fault current, since the adiabatic material 112 is interposed between the
outer cryostat 113 and the space 11 Oa, the heat of the outer cryostat 113 does not
influence the coolant in the space 11 Oa.
While the exemplary embodiments have been shown and described, it will be
understood by those skilled in the art that various changes in form and details may
be made thereto without departing from the spirit and scope of the present disclosure
as defined by the appended claims.
[EXPLANATION ON CHIEF REFERENCE NUMERALS OF DRAWINGS]
100: triaxial superconducting cable 110: cryostat
110a: space 111: inner cryostat
112: adiabatic material 113: outer cryostat
t'-f
115: spacer
120a:space
114: space
120: core
121: former
122: first phase superconducting conductor layer
123: first insulating layer
124: second phase superconducting conductor layer
125: second insulating layer
126: third phase superconducting conductor layer
127: third insulating layer
128: binder
J.5

We claim:
A triaxial superconducting cable, comprising:
a cryostat (110) having an inner cryostat (111) and an outer cryostat (113)
coaxially disposed with a space (114) being interposed therebetween; and
a single core (120) disposed in the inner cryostat (111) of the cryostat (110)
with a space (11 Oa) being interposed therebetween,
wherein a former (121) is disposed at the center of the core (120),
superconducting conductor layers with each electric phase are coaxially disposed at
the outer circumference of the former (121) at an outer side in a radial direction with
insulating layers being interposed therebetween, and the insulating layer are
coaxially disposed at the outer circumference of an outermost superconducting
conductor layer, and
wherein the outer cryostat (113) of the cryostat (110) is made of aluminum
material and configures a neutral line electrically wired to neutral polarity (N polarity)
at a superconducting cable system.
(Claim 2)
A triaxial superconducting cable, comprising:
a cryostat (110) having an inner cryostat (111) and an outer cryostat (113)
coaxially disposed with a space (114) being interposed therebetween; and
a single core (120) disposed in the inner cryostat (111) of the cryostat (110)
with a space (11 Oa) being interposed therebetween,
wherein the core (120) includes a former (121), which is disposed at a center
thereof, and includes a first phase superconducting conductor layer (122), a first
insulating layer (123), a second phase superconducting conductor layer (124), a
second insulating layer (125), a third phase superconducting conductor layer (126), a
third insulating layer (127) and a binder (128), which coaxially overlap in order from
the former (121) to an outside in a radial direction, and
wherein the outer cryostat (113) of the cryostat (110) is made of aluminum
material and configures a neutral line electrically wired to neutral polarity (N polarity)
at a superconducting cable system.
(Claim 3)
The triaxial superconducting cable according to claim 1 or 2,
wherein the inner cryostat (111) of the cryostat (110) is made of aluminum
material and is wired to electrically earth at the superconducting cable system.
(Claim 4)
The triaxial superconducting cable according to claim 1 or 2,
wherein an adiabatic material (112) is disposed at the outer circumference of
the inner cryostat (111), and the adiabatic material (112) and the outer cryostat (113)
maintain a gap by a spacer (115) to form the space (114).
(Claim 5)
The triaxial superconducting cable according to claim 1 or 2,
wherein a coolant flows in the space (11 Oa) between the inner cryostat (111)
and the insulating layer (127) of the core (120).
Dated this
The Controller of Patent
The Patent Office
At New Delhi
day of November, 2012
(l~
Garima Sahney
(Agent for the Applicant)