U.S. patent application number 14/307557 was filed with the patent office on 2015-07-23 for power cable.
The applicant listed for this patent is J-Power Systems Corporation. Invention is credited to Kinya Kumagawa, Shoji Mashio, Itaru Minakawa, Satoshi ONA.
Application Number | 20150206628 14/307557 |
Document ID | / |
Family ID | 53545390 |
Filed Date | 2015-07-23 |
United States Patent
Application |
20150206628 |
Kind Code |
A1 |
ONA; Satoshi ; et
al. |
July 23, 2015 |
POWER CABLE
Abstract
A power cable includes a steel pipe coupled to a reference
potential node, three transmission cables within the steel pipe and
respectively including a conductor to transmit three-phase
alternating current power, and a return cable within the steel pipe
and coupled to the reference potential node. Each of the three
transmission cables includes a first insulating layer covering the
conductor, a metal layer covering the first insulating layer, and a
second insulating layer covering the metal layer. The three
transmission cables are twisted around a periphery of the return
cable along a longitudinal direction of the return cable, and the
metal layer is coupled to the reference potential node.
Inventors: |
ONA; Satoshi; (Tokyo,
JP) ; Mashio; Shoji; (Tokyo, JP) ; Kumagawa;
Kinya; (Tokyo, JP) ; Minakawa; Itaru; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
J-Power Systems Corporation |
Tokyo |
|
JP |
|
|
Family ID: |
53545390 |
Appl. No.: |
14/307557 |
Filed: |
June 18, 2014 |
Current U.S.
Class: |
174/27 ; 174/103;
174/70R |
Current CPC
Class: |
H01B 9/029 20130101;
H02G 15/1055 20130101; H02G 9/06 20130101 |
International
Class: |
H01B 9/02 20060101
H01B009/02; H01B 9/06 20060101 H01B009/06; H01B 9/00 20060101
H01B009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 21, 2014 |
JP |
2014-008452 |
Claims
1. A power cable comprising: a first steel pipe coupled to a
reference potential node; three first transmission cables, inserted
inside the first steel pipe, and respectively including a first
conductor to transmit three-phase alternating current power; and a
return cable inserted inside the first steel pipe and coupled to
the reference potential node, wherein each of the three first
transmission cables includes a first insulating layer covering the
first conductor, a metal layer covering the first insulating layer,
and a second insulating layer covering the metal layer, without a
shield wire, wherein the three first transmission cables are
twisted around a periphery of the return cable along a longitudinal
direction of the return cable, and wherein the metal layer is
coupled to the reference potential node.
2. The power cable as claimed in claim 1, wherein the three first
transmission cables, in a cross sectional view of the power cable,
have a positional relationship maintaining a three-fold symmetry
with respect to the return cable that is located at a center of the
three first transmission cables in the cross sectional view.
3. The power cable as claimed in claim 1, wherein the metal layer
includes a metal wrap that wraps the first insulating layer.
4. The power cable as claimed in claim 1, further comprising: a
second conductor, coupled to the reference potential node, and
twisted around the periphery of the return cable along the
longitudinal direction of the return cable, together with the three
first transmission cables.
5. The power cable as claimed in claim 1, further comprising: three
second conductors twisted around the periphery of the return cable
along the longitudinal direction of the return cable, together with
the three first transmission cables.
6. The power cable as claimed in claim 5, wherein the three second
conductors, in a cross sectional view of the power cable, have a
positional relationship maintaining a three-fold symmetry with
respect to the return cable that is located at a center of the
three second conductors in the cross sectional view.
7. The power cable as claimed in claim 5, wherein each of the three
second conductors includes a metal pipe.
8. The power cable as claimed in claim 7, further comprising: an
optic fiber arranged inside the metal pipe.
9. A power transmission system comprising: the power cable as
claimed in claim 8, wherein the power cable is coupled to a pipe
type oil filled cable that includes a second steel pipe, a second
transmission cable arranged inside the second steel pipe and
coupled to one of the three first transmission cables, and an
insulating oil covering the second transmission cable inside the
second steel pipe, and wherein the metal pipe supplies the
insulating oil of the pipe type oil filled cable via the second
steel pipe, or receives the insulating oil of the pipe type oil
filled cable via the second steel pipe.
10. A power cable comprising: a first steel pipe coupled to a
reference potential node; three first transmission cables, inserted
inside the first steel pipe, and respectively including a first
conductor to transmit three-phase alternating current power; and a
return cable inserted inside the first steel pipe and coupled to
the reference potential node, wherein each of the three first
transmission cables includes a first insulating layer covering the
first conductor, a metal layer covering the first insulating layer,
and a second insulating layer covering the metal layer, wherein the
three first transmission cables are twisted around a periphery of
the return cable along a longitudinal direction of the return
cable, wherein the metal layer is coupled to the reference
potential node, and wherein the three first transmission cables
include no shield wire between the first insulating layer and the
second insulating layer.
11. The power cable as claimed in claim 10, wherein the three first
transmission cables, in a cross sectional view of the power cable,
have a positional relationship maintaining a three-fold symmetry
with respect to the return cable that is located at a center of the
three first transmission cables in the cross sectional view.
12. The power cable as claimed in claim 10, wherein the metal layer
includes a metal wrap that wraps the first insulating layer.
13. The power cable as claimed in claim 10, further comprising: a
second conductor, coupled to the reference potential node, and
twisted around the periphery of the return cable along the
longitudinal direction of the return cable, together with the three
first transmission cables.
14. The power cable as claimed in claim 10, further comprising:
three second conductors twisted around the periphery of the return
cable along the longitudinal direction of the return cable,
together with the three first transmission cables.
15. The power cable as claimed in claim 14, wherein the three
second conductors, in a cross sectional view of the power cable,
have a positional relationship maintaining a three-fold symmetry
with respect to the return cable that is located at a center of the
three second conductors in the cross sectional view.
16. The power cable as claimed in claim 14, wherein each of the
three second conductors includes a metal pipe.
17. The power cable as claimed in claim 16, further comprising: an
optic fiber arranged inside the metal pipe.
18. A power transmission system comprising: the power cable as
claimed in claim 17, wherein the power cable is coupled to a pipe
type oil filled cable that includes a second steel pipe, a second
transmission cable arranged inside the second steel pipe and
coupled to one of the three first transmission cables, and an
insulating oil covering the second transmission cable inside the
second steel pipe, and wherein the metal pipe supplies the
insulating oil of the pipe type oil filled cable via the second
steel pipe, or receives the insulating oil of the pipe type oil
filled cable via the second steel pipe.
19. A power cable comprising: a first steel pipe coupled to a
reference potential node; three first transmission cables, inserted
inside the first steel pipe, and respectively including a first
conductor to transmit three-phase alternating current power; and a
return cable inserted inside the first steel pipe and coupled to
the reference potential node, wherein each of the three first
transmission cables includes a first insulating layer covering the
first conductor, a metal layer covering the first insulating layer,
and a second insulating layer covering the metal layer, wherein the
three first transmission cables are twisted around a periphery of
the return cable along a longitudinal direction of the return
cable, and wherein the metal layer is coupled to the reference
potential node.
20. The power cable as claimed in claim 19, wherein the metal layer
is formed by a sheathed metal having a hollow cylindrical shape.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority of Japanese Patent Application No. 2014-008452 filed on
Jan. 21, 2014, the entire contents of which are incorporated herein
by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a power cable.
[0004] 2. Description of the Related Art
[0005] An example of a conventional large-capacity power cable may
include three (3) transmission cables that are arranged so that
center axes thereof in a cross sectional view substantially
correspond to three (3) vertexes of an equilateral triangle, where
each transmission cable has a semiconductive layer at an outermost
layer portion without providing a metal layer on an outer periphery
of an insulator. A return path conductor forming a return path for
a fault current may be arranged at a center of the equilateral
triangle, to be surrounded by the three (3) transmission cables, in
order to electrically connect the conductor to the semiconductive
layer of the transmission cables. An example of such a conventional
large-capacity power cable is proposed in Japanese Laid-Open Patent
Publication No. 2007-180742.
[0006] In the conventional power cable, the return path conductor
forming the return path for the fault current is the only conductor
through which the fault current may flow. For this reason, when the
fault current is large to a certain extent, a current exceeding a
ground-fault capacity of the power cable or the return path
conductor may flow and damage the power cable.
SUMMARY OF THE INVENTION
[0007] Embodiments of the present invention can provide a power
cable that can provide a sufficient path for the fault current.
[0008] According to one aspect of the present invention, a power
cable may include a first steel pipe coupled to a reference
potential node; three first transmission cables, inserted inside
the first steel pipe, and respectively including a first conductor
to transmit three-phase alternating current power; and a return
cable inserted inside the first steel pipe and coupled to the
reference potential node, wherein each of the three first
transmission cables includes a first insulating layer covering the
first conductor, a metal layer covering the first insulating layer,
and a second insulating layer covering the metal layer, wherein the
three first transmission cables are twisted around a periphery of
the return cable along a longitudinal direction of the return
cable, and wherein the metal layer is coupled to the reference
potential node.
[0009] Other objects and further features of the present invention
will be apparent from the following detailed description when read
in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIGS. 1A and 1B are diagrams for explaining an example of a
power cable in a first embodiment;
[0011] FIGS. 2A and 2B are diagrams for explaining a transmission
cable of the power cable in the first embodiment;
[0012] FIG. 3 is a diagram for explaining a ground-fault capacity
of the power cable in the first embodiment;
[0013] FIGS. 4A and 4B are cross sectional views for explaining a
transmission cable and an OF (Oil Filled) cable in a comparison
example;
[0014] FIG. 5 is a diagram illustrating a state in which a
plurality of power cables in the first embodiment are connected via
vaults;
[0015] FIG. 6 is a cross sectional view illustrating an example of
the power cable in a second embodiment;
[0016] FIG. 7 is a diagram for explaining the ground-fault capacity
of the power cable in the second embodiment;
[0017] FIG. 8 is a diagram illustrating in which a plurality of
power cables in the second embodiment are connected via vaults;
and
[0018] FIGS. 9A and 9B are diagrams for explaining a state in which
existing POF (Pipe type Oil Filled) cables are replaced by the
power cables in the second embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] A description will be given of the power cable in
embodiments of the present invention, by referring to the
drawings.
First Embodiment
[0020] FIGS. 1A and 1B are diagrams for explaining an example of a
power cable 100 in a first embodiment. FIG. 1A illustrates a
perspective view of power cable 100, and FIG. 1B illustrates a
cross sectional view of the power cable 100. The perspective view
illustrated in FIG. 1A illustrates a state of the power cable 100
that is cut along a plane perpendicular to a longitudinal direction
of the power cable 100.
[0021] The power cable 100 includes a steel pipe 110, transmission
cables 120R, 120Y and 120B, and a return cable 130.
[0022] The steel pipe 110 is be formed by a pipe made of iron, for
example. The transmission cables 120R, 120Y and 120B, and the
return cable 130 are inserted inside the steel pipe 110. The steel
pipe 110 is an example of a first steel pipe, and is connected to a
reference potential node. In this first embodiment, the steel pipe
110 is grounded and held at a ground potential. The steel pipe 110
is held at the reference potential, in order to use the steel pipe
110 as a return path for a fault current in a case in which the
fault current caused by ground fault or the like flows through the
transmission cables 120R, 120Y and 120B.
[0023] The steel pipe 110 may be a new, unused steel pipe, or an
old, used steel pipe. For example, when replacing an existing power
cable by the power cable 100 in this first embodiment, the steel
pipe of the existing power cable may be reused as the steel pipe
110 of the power cable 100.
[0024] More particularly, the steel pipe of the existing POF (Pipe
type Oil Filled) cable, HPFF (High Pressure Fluid Filled) cable, or
HPGH (High Pressure Gas Filled) cable, for example, after removing
the transmission cables and an insulating oil therefrom and
cleaning, may be reused as the steel pipe 110. In this first
embodiment, it is assumed for the sake of convenience that the
steel pipe of the existing POF cable is reused as the steel pipe
110. An inner diameter of the steel pipe 110 may be in a range of
100 mm to 254 mm, for example, and may be 206 mm, for example.
Alternatively, the inner diameter of the steel pipe 110 may be in a
range of 6 inches to 10 inches, for example, and may be 8 inches,
for example.
[0025] In the cross sectional view illustrated in FIG. 1B, the
transmission cables 120R, 120Y and 120B are arranged so that center
axes thereof substantially correspond to three (3) vertexes of an
equilateral triangle, and the return cable 130 is arranged at a
center of the equilateral triangle, to be surrounded by the
transmission cables 120R, 120Y and 120B. In addition, the
transmission cables 120R, 120Y and 120B, and the return cable 130
are inserted into the steel pipe 110 in a state in which the
transmission cables 120R, 120Y and 120B are twisted around the
return cable 130 along the longitudinal direction of the return
cable 130. The transmission cables 120R, 120Y and 120B may be used
to transmit power of each phase of three-phase A.C. (Alternating
Current) power. The transmission cables 120R, 120Y and 120B are
examples of three (3) first transmission cables.
[0026] For example, the transmission cables 120R, 120Y and 120B may
be categorized as red-phase, yellow-phase and blue-phase cables,
respectively, permitting identification of the cables by color. The
transmission cables 120R, 120Y and 120B have different colors for
identification, but have the same configuration. For this reason,
when not distinguishing the transmission cables 120R, 120Y and
120B, these transmission cables 120R, 120Y and 120B may also be
referred to as "transmission cables 120" in the following
description. The detailed configuration of the transmission cable
120 will be described later in conjunction with FIGS. 2A and
2B.
[0027] The return cable 130 includes a conductor 131, and a jacket
132 covering the periphery of the conductor 131. The conductor 131
is made of a metal, and for example, copper may be used as the
metal. The jacket 132 is formed by an insulating layer covering the
periphery of the conductor 131, and made of a material such as an
XLPE (Cross Linked Polyethylene), PVC (Poly-Vinyl Chloride), and
the like.
[0028] The conductor 131 of the return cable 130 is connected to
the reference potential node, similarly to the steel pipe 110. In
this first embodiment, the conductor 131 of the return cable 130 is
grounded and held at the ground potential. The conductor 131 of the
return cable 130 is held at the reference potential, in order to
use the return cable 130 as a return path for a fault current in a
case in which the fault current caused by ground fault or the like
flows through the transmission cables 120.
[0029] Next, a description will be given of the detailed
configuration of the transmission cable 120, by referring to FIGS.
2A and 2B.
[0030] FIGS. 2A and 2B are diagrams for explaining the transmission
cable 120 of the power cable 100 in the first embodiment. FIG. 2A
illustrates a cross sectional view of the transmission cable 120,
and FIG. 2B illustrates a perspective view of a triplex
formation.
[0031] As illustrated in FIG. 2A, the transmission cable 120
includes a conductor 121, a conductor screen 122, an insulating
layer 123, an insulating screen 124, a bedding 125, a metal sheath
126, and a jacket 127. In this example, the conductor screen 122,
the insulator layer 123, the insulating screen 124, the bedding
125, the metal sheath 126, and the jacket 127 respectively have a
hollow cylindrical shape covering, one by one, the conductor 121
having the solid cylindrical shape (that is, formed by a stranded
wire).
[0032] The conductor 121 is made of a metal, and for example,
copper may be used as the metal. The conductor 121 is an example of
a first conductor.
[0033] The conductor screen 122 is formed by a semiconductive tape
having heat resistance, and a resin layer including carbon powder,
and is wound around the periphery of the conductor 121. For
example, nylon or polyester may be used as the semiconductive tape
having heat resistance, and for example, EEA
(Ethylene-Ethylacrylate Copolymer) resin may be used as the resin
layer including carbon powder.
[0034] The insulating layer 123 is provided to insulate the
conductor 121. The insulating layer 123 may be formed by injection
molding using XLPE (Crosslinked Poly-Ethylene), for example. In
this example, it is assumed that XLPE is used for the insulating
layer 123, however, a material other than XLPE may be used for the
insulating layer 123 as long as the material is insulative and heat
resistant.
[0035] The insulating screen 124 is formed by a resin layer
including carbon powder, and is wound around the periphery of the
insulating layer 123. For example, EEA resin may be used as the
resin layer including carbon powder.
[0036] The bedding 125 is the so-called bedding tape, and is wound
around the insulating screen 124.
[0037] The metal sheath 126 is formed by a metal tape that covers
the periphery of the bedding 125 along a longitudinal direction of
the transmission cable 120. An adhesive layer on this metal tape is
bonded to the jacket 127. For example, copper laminated tape may be
used as the metal sheath 126. The metal sheath 126 is an example of
a metal layer, and is also an example of a metal wrap.
[0038] The metal sheath 126 is provided to achieve electrostatic
shielding and electromagnetic induction shielding, and to ensure a
path for the fault current to flow.
[0039] The electrostatic shielding covers the periphery of the
conductor 121 by a metal member in order to suppress a high voltage
from being induced on the ground side due to the electrostatic
capacitance between the conductor 121 and the ground, in a case in
which a high voltage is applied to the conductor 121.
[0040] The electromagnetic induction shielding covers the periphery
of the conductor 121 by a metal member in order to suppress
formation of a magnetic field caused by electromagnetic induction
that is generated by a closed loop created by the conductor 121 and
the ground, in a case in which the fault current is generated.
[0041] The metal sheath 126 covers the outer periphery of the
conductor 121 via the conductor screen 122, the insulating layer
123, the insulating screen 124, and the bedding 125. Hence, the
magnetic field generated due to a current flowing through the
conductor 121 is canceled by the current induced by the metal
sheath 126.
[0042] In addition, the metal sheath 126 is connected to the
reference potential node, similarly to the steel pipe 110 and the
return cable 130 as described above in conjunction with FIGS. 1A
and 1B. In this first embodiment, the metal sheath 126 is grounded
and is held at the ground potential, for example. Because the metal
sheath 126 is held at the reference potential, the metal sheath 126
can function as a path for a fault current to flow in a case in
which the fault current caused by ground fault or the like flows
through the transmission cables 120.
[0043] The jacket 127 is formed by an insulating layer covering the
periphery of the metal sheath 126, for example, polyethylene may be
used for the insulating layer. An outer peripheral surface of the
jacket 127 can be distinguished amongst the transmission cables
120R, 120Y and 120B by emboss or the like identifying the
red-phase, yellow-phase and blue-phase.
[0044] The transmission cables 120R, 120Y and 120B having the
configuration described above in conjunction with FIGS. 1A and 1B
are twisted around the center, return cable 130 along the
longitudinal direction of the power cable 100, as illustrated in
FIG. 2B. The twisted configuration of the three (3) transmission
cables 120R, 120Y and 120B may be referred to as the "triplex
formation".
[0045] According to the triplex formation of the transmission
cables 120R, 120Y and 120B, the transmission cables 120R, 120Y and
120B are twisted around the center, return cable 130, while
maintaining rotational symmetry of order three (3), that is,
three-fold symmetry, in the cross sectional view illustrated in
FIG. 1B. The triplex formation has small expansion and contraction
along the longitudinal direction of the transmission cables 120R,
120Y and 120B of the power cable 100, and enables easy fixing
within a vault (or manhole) as will be described later. The
positional relationship of the transmission cables 120R, 120Y and
120B having the three-fold symmetry in the cross sectional view is
not limited to the perfect three-fold symmetry. It is assumed that
the transmission cables 120R, 120Y and 120B have the three-fold
symmetry in the cross sectional view even when a positional error
occurs due to inconsistencies in the twisting and the like of the
transmission cables 120R, 120Y and 120B around the return cable
130.
[0046] In this first embodiment, in a state in which the
transmission cables 120R, 120Y and 120B having the triplex
formation are arranged along the outer periphery of the return
cable 130, the transmission cables 120R, 120Y and 120B and the
return cable 130 are arranged inside the steel pipe 110 as
illustrated in FIGS. 1A and 1B.
[0047] The power cable 100 described above in this first embodiment
transmits three-phase A.C. power by the transmission cables 120R,
120Y and 120B illustrated in FIGS. 1A and 1B. For example, a rated
capacity of the power cable 100 is 250 MVA (138 kV, 1045 A).
However, this rated capacity is merely an example, and the rated
capacity may vary depending on laying conditions, such as the
temperature and a burying depth of steel pipe 110.
[0048] For example, the power cable 100 has a length of 487.68 m
(1600 feet), and a plurality of such power cables 100 are connected
in series upon use. In this case, the transmission cables 120R,
120Y and 120B of each power cable 100 are connected to the
corresponding transmission cables 120R, 120Y and 120B of another
power cable 100 so that the color phases match. Connecting the
transmission cables 120R, 120Y and 120B of each power cable 100 to
the corresponding transmission cables 120R, 120Y and 120B of
another power cable 100 so that the color phases match means that
the conductors 121 of the transmission cables 120R are connected,
the conductors 121 of the transmission cables 120Y are connected,
and the conductors 121 of the transmission cables 120B are
connected, between two adjacent power cables 100 that are connected
in series. In this case, with regard to the metal sheaths 126 of
the transmission cables 120R, 120Y and 120B of the two adjacent
power cables 100 that are connected in series, the metal sheaths
126 of the same color phase may be connected, or the metal sheath
126 may be grounded at each power cable 100.
[0049] In addition, the power cable 100 may be used as a new
replacement power cable when replacing a part of a plurality of
existing power cables that are connected in series. For example,
the power cable 100 may be used to replace one of the plurality of
existing power cables that are connected in series. In this case,
when the existing power cable to be removed has a steel pipe
similar to the steel pipe 110 and the transmission cables 120R,
120Y and 120B and the return cable 130 can be inserted into this
steel pipe, this steel pipe of the existing power cable to be
removed may be used as the steel pipe 110.
[0050] In the above described case, the conductors 121 of the
transmission cables 120R, 120Y and 120B of the power cable 100 may
be connected to the conductors of the corresponding transmission
cables of the existing power cables at both ends of the power cable
100 so that the color phases match. Further, the metal sheaths 126
of the transmission cables 120R, 120Y and 120B may be grounded in
this case.
[0051] Next, consideration will be given of ground-fault capacities
of the steel pipe 110 of the power cable 100, the metal sheaths 126
of the transmission cables 120R, 120Y and 120B, and the return
cable 130. When an insulator breakdown occurs in the transmission
cables 120R, 120Y or 120B of the power cable 100, the metal sheath
126 or the return cable 130 included in the transmission cable 120
in which the insulator breakdown occurs may melt, and a fault
current may flow through the steel pipe 110.
[0052] In such a case, the fault current flows from the steel pipe
110 of the power cable 100 in which the insulator breakdown occurs
to the steel pipe 110, the metal sheaths 126 and the return cables
130 of an adjacent power cable 100 that is connected in series to
the power cable 100.
[0053] Accordingly, the steel pipe 110, the metal sheath 126, and
the return cable 130 of the power cable 100 respectively need to
have a ground-fault capacity to a certain extent at least greater
than or equal to a fault current dividing ratio. The ground-fault
capacities are determined by amounts of current that can flow
through the steel pipe 110, the metal sheath 126, and the return
cable 130 that may form the path for the fault current to flow.
[0054] In the case of a power cable 100 in which the insulator
breakdown occurs but the metal sheath 126 or the return cable 130
of the power cable 100 does not melt, the fault current may still
flow through the steel pipe 110, the metal sheath 126, and the
return cable 130 that may form the path for the fault current to
flow.
[0055] However, even in such a case, the fault current flows
through the steel pipe 110, the metal sheath 126, and the return
cable 130 of an adjacent power cable 100. Hence, the ground-fault
capacities are evaluated based on amounts of current that can flow
through the steel pipe 110, the metal sheath 126, and the return
cable 130 of the adjacent power cable 100 that is adjacent to the
power cable 100 in which the insulator breakdown occurs but the
metal sheath 126 or the return cable 130 of the power cable 100
does not melt.
[0056] FIG. 3 is a diagram for explaining the ground-fault capacity
of the power cable 100 in the first embodiment. In FIG. 3, a
comparison example of the power cable is also considered, in which
the return cable 130 is omitted from the power cable 100 in this
first embodiment. In the following, the amount of current flowing
through the power cable 100 in this first embodiment and the amount
of current flowing through the power cable in the comparison
example are compared to the respective ground-fault capacities. The
current value in FIG. 3 is represented by kA (kilo-Amperes).
[0057] For example, the ground-fault capacities of the steel pipe
110, the metal sheath 126, and the return cable 130 that are used
are computed under a precondition that the steel pipe 110, the
metal sheath 126, and the return cable 130 have predetermined cross
sectional areas and that the current flows for 0.25 second.
[0058] The ground-fault capacities of the steel pipe 110, the metal
sheath 126, and the return cable 130 are 60 kA, 15.6 kA, and 15.3
kA, respectively. The computed ground-fault capacity of the steel
pipe 110 is 60 kA or greater, however, it is assumed for the sake
of convenience that the computed ground-fault capacity of the steel
pipe 110 is 60 kA. In addition, the ground-fault capacity of the
metal sheath 126 exists for each of the transmission cables 120R,
120Y and 120B, and the metal sheaths 126 of the transmission cables
120R, 120Y and 120B are represented as "metal sheath 126(R)",
"metal sheath 126 (Y)" and "metal sheath 126 (B)" in FIG. 3.
[0059] Therefore, for up to a time of 0.25 second, the steel pipe
110, the metal sheath 126, and the return cable 130 can allow
currents amounting to 60 kA, 15.6 kA and 15.3 kA to flow,
respectively.
[0060] In the following description, it is assumed that, in the
case in which the steel pipe 110, the metal sheath 126, and the
return cable 130 have the ground-fault capacities described above,
a current of 60 kA flows through the transmission cables 120R, 120Y
and 120B for 0.25 second, and the fault current is generated in the
transmission cable 120R. Further, in the following description, the
phase in which the fault current is generated may also be referred
to as a "fault-phase".
[0061] In this first embodiment, the current flowing through the
steel pipe 110 of the power cable 100 is 17.9 kA, and the current
flowing through the fault-phase metal sheath 126 (R) is 15.0 kA.
The current flowing through each of the metal sheaths 126 (Y) and
126 (B) of phases other than the fault-phase is 8.2 kA, and the
current flowing through the return cable 130 is 15.3 A.
[0062] Accordingly, the amounts of current flowing through the
steel pipe 110, the metal sheaths 126 (R), 126 (Y) and 126 (B), and
the return cable 130, respectively, are the respective ground-fault
capacities or less. Hence, it is confirmed that the power cable 100
in this first embodiment can ensure a sufficient path for the fault
current to flow.
[0063] On the other hand, in a case in which a current of 60 kA
flows through the transmission cables 120R, 120Y and 120B of the
power cable in the comparison example including no return cable 130
for 0.25 second, and the fault current is generated in the
transmission cable 120R, the current flowing through the steel pipe
110 is 23.4 kA, and the current flowing through the fault-phase
metal sheath 126 (R) is 18.4 kA. The current flowing through each
of the metal sheaths 126 (Y) and 126 (B) of phases other than the
fault-phase is 11.9 kA.
[0064] Accordingly, in the case of the power cable in the
comparison example, the amount of current flowing through the
fault-phase metal sheath 126 (R) exceeds its ground-fault capacity,
and it is confirmed that a sufficient path for the fault current to
flow cannot be ensured by the power cable in the comparison
example.
[0065] According to this first embodiment, it is possible to
provide the power cable 100 that ensures a sufficient path for the
fault current to flow, by including the transmission cables 120R,
120Y and 120B having the triplex formation in which the
transmission cables 120R, 120Y and 120B are twisted around the
periphery of the return cable 130 along the longitudinal direction
of the return cable 130, with the return cable 130 arranged at the
center of the transmission cables 120R, 120Y and 120B.
[0066] In addition, each of the transmission cables 120R, 120Y and
120B includes the conductor 121, the conductor screen 122, the
insulating layer 123, the insulating screen 124, the bedding 125,
the metal sheath 126, and the jacket 127 described above.
[0067] For example, when replacing the existing power cable by the
power cable 100 in this first embodiment, the the transmission
cables of the existing power cable may include a shield. Hence, a
description will be given of the transmission cable in the
comparison example, by referring to FIGS. 4A and 4B.
[0068] FIGS. 4A and 4B are cross sectional views for explaining a
transmission cable 20 and an OF (Oil Filled) cable 40 in the
comparison example. FIG. 4A illustrates a cross section of the
transmission cable 20, corresponding to the cross section of the
transmission cable 120 illustrated in FIG. 2A.
[0069] The transmission cable 20 includes a conductor 21, a
conductor screen 22, an insulating layer 23, an insulating screen
24, a bedding 25, a shield 30, a metal sheath 26, and a jacket 27.
The conductor 21, the conductor screen 22, the insulating layer 23,
the insulating screen 24, the bedding 25, the metal sheath 26, and
the jacket 27 of the transmission cable 20 in the comparison
example correspond to the conductor 121, the conductor screen 122,
the insulating layer 123, the insulating screen 124, the bedding
125, the metal sheath 126, and the jacket 127 of the transmission
cable 120 in this first embodiment, respectively, and a detailed
description thereof will be omitted.
[0070] An outer diameter of the jacket 27 of the transmission cable
20 is equal to an outer diameter of the jacket 127 of the
transmission cable 120. Because the transmission cable 20 includes
the shield 30 between the bedding 25 and the metal sheath 26, the
conductor 21 has a size smaller than that of the conductor 121 of
the transmission cable 120.
[0071] The shield 30 is formed by a metal wire member, and is held
at the ground potential (reference potential) together with the
metal sheath 26. For example, the metal wire member has a
configuration in which a large number of conductors having a
diameter on the order of approximately 1 mm to 2 mm are wound
around the bedding 25. The shield 30 is provided to achieve
electrostatic shielding and electromagnetic induction shielding,
and to ensure a path for the fault current to flow.
[0072] On the other hand, the OF cable 40 illustrated in FIG. 4B
for the POF cable includes a conductor 41, a conductor screen 42,
an insulating layer 43, an insulating screen 44, and a bedding
45.
[0073] The conductor 41, the conductor screen 42, the insulating
layer 43, the insulating screen 44, and the bedding 45 of the OF
cable 40 correspond to the conductor 121, the conductor screen 122,
the insulating layer 123, the insulating screen 124, and the
bedding 125 of the transmission cable 120 in this first embodiment,
respectively, and a detailed description thereof will be omitted.
In the OF cable 40, the conductor screen 42, the insulating layer
43, the insulating screen 44, and the bedding 45 are made of paper.
In the existing POF cable, the OF cable 40 is provided within a
steel pipe, and an insulating oil is provided within the steel
pipe, so that the steel pipe functions as the metal sheath 126 and
the jacket 127 of the transmission cable 120 of this first
embodiment.
[0074] According to the transmission cable 120 in this first
embodiment, the metal sheath 126 provides a sufficient
electrostatic shielding property, and the metal sheath 126 and the
return cable 130 provide a sufficient electromagnetic induction
shielding property. For this reason, in a case in which the
existing POF cable has a configuration in which the OF cable 40 is
included inside the steel pipe 110, for example, the steel pipe 110
can be reused when making repairs, for example. In this case, when
laying the power cable 100, the transmission cables 120R, 120Y and
120B, and the return cable 130 may be inserted inside the steel
pipe 110, instead of using a configuration in which a bundle of
three (3) transmission cables 20 are included.
[0075] The transmission cable 120 in this case has an outer
diameter equal to that of the transmission cable 20, however, the
transmission cable 120 includes no shield 30. For this reason, the
diameter of the conductor 121 in the transmission cable 120 can be
made larger than that of the conductor 21 in the transmission cable
20, to thereby improve the transmission capacity.
[0076] In addition, in a case in which the existing power cable is
the POF cable, it is possible to replace the power cable by the
power cable 100 having a high adaptability to the environment
without using insulating oil. As a result, it is possible to
simultaneously improve the transmission capacity and ensure high
adaptability to the environment. High adaptability to the
environment means that it is environmentally-friendly or
ecological.
[0077] Next, a description will be given of a state in which a
plurality of power cables 100 are connected via vaults, by
referring to FIG. 5.
[0078] FIG. 5 is a diagram illustrating the state in which a
plurality of power cables 100A, 100B and 100C in the first
embodiment are connected via manholes 50A, 50B and 50C. FIG. 5
illustrates the plurality of power cables 100A, 100B and 100C which
are identical to the power cable 100 described above. For this
reason, when not distinguishing the power cables 100A, 100B and
100C, these power cables 100A, 100B and 100C may also be referred
to as "power cables 100" in the following description.
[0079] In FIG. 5, only the steel pipe 110, the conductor 121 and
the metal sheath 126 of the transmission cables 120R, 120Y and
120B, and the return cable 130 of the power cable 100 are
illustrated. The conductors 121 and the metal sheaths 126 of the
transmission cables 120R, 120Y and 120B are respectively
represented as conductors 121R, 121Y and 121B and metal sheaths
126R, 126Y and 126B, respectively.
[0080] When not distinguishing the conductors 121R, 121Y and 121B
and the metal sheaths 126R, 126Y and 126B of the transmission
cables 120R, 120Y and 120B, these conductors 121R, 121Y and 121B
and these metal sheaths 126R, 126Y and 126B may also be referred to
as "conductors 121" and "metal sheaths 126", respectively, in the
following description.
[0081] The vaults 50A, 50B and 50C have the same configuration, and
thus, when not distinguishing the vaults 50A, 50B and 50C, these
vaults 50A, 50B and 50C may also be referred to as "vaults 50" in
the following description.
[0082] The vault 50 includes a housing 51, joints 52R, 52Y and 52B,
cables 54, 54A, 55R, 55Y, 55B, 56R, 56Y and 56B, and a link box 53
as a connecting location, for example.
[0083] The housing 51 is formed by a concrete, for example, and
accommodates connecting parts of the mutually adjacent power cables
100 that are to be connected. The connecting parts include the
joints 52R, 52Y and 52B, the link box 53, and the cables 54, 54A,
55R, 55Y, 55B, 56R, 56Y and 56B.
[0084] The joint 52R includes a connecting part 57A, an insulating
part 57B, and a connecting part 57C. The joints 52Y and 52B have
configurations similar to that of the joint 52R. The connecting
parts 57A and 57C are formed by a metal connecting member,
respectively, and connect the conductors 121R of the mutually
adjacent power cables 100A and 100B, but do not connect the metal
sheaths 126 of the mutually adjacent power cables 100A and 100B.
The metal sheaths 126 of the mutually adjacent power cables 100A
and 100B are insulated by the insulating part 58B inside the joint
52R.
[0085] The cable 55R is connected to the connecting part 57A of the
joint 52R, and the cable 56R is connected to the connecting part
57C of the joint 52R. The cables 55R and 56R are connected via a
connecting part 53A of the link box 53. The connecting part 53A of
the link box 53 is grounded, and the metal sheath 126 is held at
the ground potential via the connecting part 53A of the link box
53.
[0086] The joints 52Y and 52B have a configuration similar to that
of the joint 52R. Hence, constituent elements of the joints 52Y and
52B are designated by the same reference numerals as the
constituent elements of the joint 52R, except that the subscript
"R" is replaced by "Y" and "B", respectively.
[0087] As described above, the link box 53 includes the connecting
part 53A that is held at the ground potential. The connecting part
53A connects the cables 55R, 55Y and 55B to the cables 56R, 56Y and
56B, respectively, and also hold the cables 55R, 55Y and 55B and
the cables 56R, 56Y and 56B to the ground potential. Further, the
cable 54A that branches from the cable 54 is also connected to the
connecting part 53A, and the connecting part 53A holds the steel
pipe 110 and the return cable 130 to the ground potential.
[0088] The cable 54 connects the steel pipes 110 of the mutually
adjacent power cables 100A and 100B. In addition, the return cable
130 is also connected to the cable 54. For this reason, the cable
54 also connects the return cables 130 of the mutually adjacent
power cables 100A and 100B.
[0089] The cable 54A branches from an intermediate part of the
cable 54, and the cable 54A is connected to the connecting part 53A
of the link box 53. Because the connecting part 53A of the link box
53 is held at the ground potential, the steel pipe 110 and the
return cable 130 are held at the ground potential via the
connecting part 53A of the link box 53.
[0090] The cable 55R connects the connecting part 57A of the joint
52R and the connecting part 53A of the link box 53. The cable 56R
connects the connecting part 57C of the joint 52R and the
connecting part 53A of the link box 53. The cables 55R and 56R are
mutually connected via the connecting part 53A, and are held at the
ground potential.
[0091] The cables 55Y and 56Y and the cables 55B and 56B have
configurations similar to those of the cables 55R and 56R. Hence,
constituent elements of the cables 55Y and 56Y and the cables 55B
and 56B are designated by the same reference numerals as the
constituent elements of the cables 55R and 56R, except that the
subscript "R" is replaced by "Y" and "B", respectively.
[0092] The connecting relationship of the mutually adjacent power
cables 100B and 100C is similar to that of the mutually adjacent
power cables 100A and 100B described above, and the mutually
adjacent power cables 100B and 100C are similarly connected via the
vault 50.
[0093] A case will be considered in which the insulator breakdown
occurs in the transmission cable 120R illustrated in FIG. 1B of the
power cable 100A including the conductor 121R, when the power
cables 100A, 100B and 100C are connected in series as described
above.
[0094] In this case, the fault current generated in the
transmission cable 120R flows to the steel pipe 110 via the metal
sheath 126R or the return cable 130 of the power cable 100A, and
flows through the cable 54 as indicated by an arrow A. Further, a
part of the fault current flows to the steel pipe 110 and the
return cable 130 of the power cable 100B via the cable 54 as
indicated by an arrow B, and the remaining part of the fault
current flows to the connecting part 53A via the cable 54A. The
current flowing to the connecting part 53A flows to the metal
sheaths 126R, 126Y and 126B of the power cable 100B, via the cables
56R, 56Y and 56B.
[0095] Accordingly, the fault current generated by the insulator
breakdown in the transmission cable 120R of the power cable 100A
flows through the steel pipe 110 of the power cable 100A, and
branches to the steel pipe 110, the metal sheaths 126R, 126Y and
126B, and the return cable 130 of the power cable 100B, via the
cables 54, 54A, 56R, 56Y and 56B.
[0096] As described above in conjunction with FIG. 3, the steel
pipe 110, the metal sheaths 126 (126R, 126Y and 126B), and the
return cable 130 of the power cable 100 provide a path with a
sufficient capacity for the fault current to flow.
[0097] For this reason, even when the fault current is generated
due to the insulator breakdown in the transmission cable 120, it is
possible to suppress the currents flowing through the steel pipe
110, the metal sheaths 126 (126R, 126Y and 126B), and the return
cable 130 from exceeding the respective ground-fault capacities
thereof, and provide the power cable 100 in which a sufficient path
is ensured for the fault current to flow.
Second Embodiment
[0098] FIG. 6 is a cross sectional view illustrating an example of
a power cable 200 in a second embodiment. The cross section of the
power cable 200 illustrated in FIG. 6 corresponds to the cross
section of the power cable 100 illustrated in FIG. 1B.
[0099] The power cable 200 illustrated in FIG. 6 includes a steel
pipe 110, transmission cables 120R, 120Y and 120B, a return cable
130, and three pipes 241, 242 and 243. In other words, the power
cable 200 has a configuration in which the pipes 241, 242 and 243
are additionally provided with respect to the power cable 100 in
the first embodiment. Parts other than the pipes 241, 242 and 243
of the power cable 200 are the same as those corresponding parts of
the power cable 100 in the first embodiment, and a description
thereof will be omitted by designating the same parts by the same
reference numerals.
[0100] In the cross sectional view of FIG. 6, the pipe 241 is
arranged between the transmission cables 120Y and 120B, the pipe
242 is arranged between the transmission cables 120B and 120R, and
the pipe 243 is arranged between the transmission cables 120R and
120Y. In addition, the pipes 241, 242 and 243 are twisted along the
longitudinal directions of the transmission cables 120R, 120Y and
120B, in a manner similar to the transmission cables 120R, 120Y and
120B.
[0101] More particularly, in a state arranged between the
transmission cables 120Y and 120B, the pipe 241 is twisted along
the longitudinal directions of the transmission cables 120Y and
120B along the outer peripheries of the transmission cables 120Y
and 120B.
[0102] Similarly, in a state arranged between the transmission
cables 120B and 120R, the pipe 242 is twisted along the
longitudinal directions of the transmission cables 120B and 120R
along the outer peripheries of the transmission cables 120B and
120R. In addition, in a state arranged between the transmission
cables 120R and 120Y, the pipe 243 is twisted along the
longitudinal directions of the transmission cables 120R and 120Y
along the outer peripheries of the transmission cables 120R and
120Y.
[0103] The pipes 241, 242 and 243 are arranged in a triplex
formation around the return cable 130 located at their center, and
are twisted around the transmission cables 120R, 120Y and 120B that
are also arranged in the triplex formation and twisted.
[0104] The pipes 241, 242 and 243 maintain the three-fold symmetry
in the cross sectional view by the triplex formation around the
return cable 130 located at their center, and are twisted around
the return table 130.
[0105] The pipes 241, 242 and 243 are examples of a second
conductor, and are connected to the reference potential node. In
this second embodiment, the pipes 241, 242 and 243 are grounded,
for example, and are held at the ground potential. The pipes 241,
242 and 243 are held at the reference potential in order to provide
a path for the fault current to flow by the pipes 241, 242 and 243
in a case in which the fault current is generated in the
transmission cable 120 due to ground-fault or the like.
[0106] The pipes 241, 242 and 243 have the same configuration.
Outer peripheries of pipe parts 241A, 242A and 243A of the pipes
241, 242 and 243 are covered by jackets 241B, 242B and 243B,
respectively.
[0107] The pipe parts 241A, 242A and 243A are hollow along the
longitudinal directions thereof, and are made of aluminum, for
example, in this second embodiment. However, the pipe parts 241A,
242A and 243A may be formed by metal pipes other than aluminum
pipes.
[0108] The jackets 241B, 242B and 243B are insulating layers
covering the peripheries of the pipe parts 241A, 242A and 243A,
respectively, and are made of polyethylene, for example.
[0109] In addition, optic fibers 244, 245 and 246 are inserted into
the pipe parts 241A, 242A and 243A, respectively. The optic fibers
244, 245 and 246 may include optic fiber parts 244A, 245A and 246A
that are covered by plastic pipes 244B, 245B and 246B,
respectively. For example, the optic fiber parts 244A, 245A and
246A may be formed by air-blown fibers, and the plastic pipes 244B,
245B and 246B may be formed by pipes designed for the air-blown
fibers.
[0110] By arranging the optic fibers 244, 245 and 246 inside the
pipe parts 241A, 242A and 243A, respectively, the pipes 241, 242
and 243 can be used as a path for the fault current to flow, and
also as an information communication network using the optic fibers
244, 245 and 246.
[0111] Because the pipes 241, 242 and 243 are inserted inside the
steel pipe 110 together with the transmission cables 120R, 120Y and
120B, and the return cable 130, the pipes 241, 242 and 243
desirably have a diameter that is adjusted so that the pipes 241,
242 and 243 do not protrude on the outer side of the transmission
cables 120R, 120Y and 120B along the radial direction relative to
the center where the return cable 130 is located.
[0112] In addition, when connecting a plurality of power cables
200, the pipes 241, 242 and 243 of the adjacent power cables 200
may be connected, or the plastic pipes 244B, 245B and 246B may be
inserted through the pipes 241, 242 and 243 of the adjacent power
cables 200, in order to lay the optic fiber parts 244A, 245A and
246A.
[0113] Next, consideration will be given of ground-fault capacities
of the steel pipe 110 of the power cable 200, the metal sheaths 126
of the transmission cables 120R, 120Y and 120B, the return cable
130, and the pipes 241, 242 and 243. When an insulator breakdown
occurs in the transmission cables 120R, 120Y and 120B of the power
cable 200, the metal sheath 126, the return cable 130, or the pipes
241, 242 and 243 included in the power cable 200 in which the
insulator breakdown occurs may melt, and a fault current may flow
through the steel pipe 110.
[0114] In such a case, the fault current flows from the steel pipe
110 of the power cable 200 in which the insulator breakdown occurs
to the steel pipe 110, the metal sheaths 126, the return cables
130, and the pipes 241, 242 and 243 of an adjacent power cable 200
that is connected in series to the power cable 200.
[0115] Accordingly, the steel pipe 110, the metal sheath 126, the
return cable 130, and the pipes 241, 242 and 243 of the power cable
200 respectively need to have a ground-fault capacity to a certain
extent. The ground-fault capacities are determined by amounts of
current that can flow through the steel pipe 110, the metal sheath
126, the return cable 130, and the pipes 241, 242 and 243 that may
form the path for the fault current to flow.
[0116] In the case of a power cable 200 in which the insulator
breakdown occurs but the metal sheath 126, the return cable 130, or
the pipes 241, 242 and 243 of the power cable 200 do not melt, the
fault current may still flow through the steel pipe 110, the metal
sheath 126, the return cable 130, and the pipes 241, 242 and 243
that may form the path for the fault current to flow.
[0117] However, even in such a case, the fault current flows
through the steel pipe 110, the metal sheath 126, the return cable
130, and the pipes 241, 242 and 243 of an adjacent power cable 200.
Hence, the ground-fault capacities are evaluated based on amounts
of current that can flow through the steel pipe 110, the metal
sheath 126, the return cable 130, and the pipes 241, 242 and 243 of
the adjacent power cable 200 that is adjacent to the power cable
200 in which the insulator breakdown occurs but the metal sheath
126, the return cable 130, or the pipes 241, 242 and 243 of the
power cable 200 do not melt.
[0118] FIG. 7 is a diagram for explaining the ground-fault capacity
of the power cable 200 in the second embodiment. In the following,
the amounts of current flowing through the power cable 200 in this
second embodiment are compared to the respective ground-fault
capacities. The current value in FIG. 7 is represented by kA
(kilo-Amperes), and FIG. 7 uses the same designations as those used
in FIG. 3.
[0119] For example, the ground-fault capacities of the steel pipe
110, the metal sheath 126, the return cable 130, and the pipes 241,
242 and 243 that are used are computed under a precondition that
the steel pipe 110, the metal sheath 126, the return cable 130, and
the pipes 241, 242 and 243 have predetermined cross sectional areas
and that the current flows for 0.25 second.
[0120] The ground-fault capacities of the steel pipe 110, the metal
sheath 126, and the return cable 130 are 60 kA, 15.6 kA, and 15.3
kA, respectively, which are the same as those illustrated in FIG. 3
for the first embodiment. The computed ground-fault capacities of
the pipes 241, 242 and 243 are all 20 kA.
[0121] Therefore, for up to a time of 0.25 second, the steel pipe
110, the metal sheath 126, the return cable 130, and the pipes 241,
242 and 243 can allow currents amounting to 60 kA, 15.6 kA, 15.3
kA, and 20 kA to flow, respectively.
[0122] In the following description, it is assumed that, in the
case in which the steel pipe 110, the metal sheath 126, the return
cable 130, and the pipes 241, 242 and 243 have the ground-fault
capacities described above, a current of 60 kA flows through the
transmission cables 120R, 120Y and 120B for 0.25 second, and the
fault current is generated in the transmission cable 120R. Further,
in the following description, the phase in which the fault current
is generated may also be referred to as a "fault-phase".
[0123] In this second embodiment, the current flowing through the
steel pipe 110 of the power cable 200 is 8.4 kA, and the current
flowing through the fault-phase metal sheath 126 (R) is 10.4 kA.
The current flowing through each of the metal sheaths 126 (Y) and
126 (B) of phases other than the fault-phase is 4.4 kA, and the
current flowing through the return cable 130 is 9.0 A. These
amounts of current are reduced compared to the corresponding
amounts of current flowing in the power cable 100 described above
in the first embodiment. It may be regarded that the amounts of
current are reduced in this second embodiment due to the additional
provision of the pipes 241, 242 and 243.
[0124] The currents flowing through the pipes 241, 242 and 243 are
4.6 kA, 12.6 kA and 11.6 kA, respectively. It may be regarded that
a distribution is generated in the amounts of current flowing
through the pipes 241, 242 and 243 due to the positional
relationship of the pipes 241, 242 and 243 with respect to the
fault-phase. The currents flowing through the pipes 241, 242 and
243 are considerably lower than the corresponding ground-fault
capacities which are 20 kA.
[0125] Accordingly, the amounts of current flowing through the
steel pipe 110, the metal sheaths 126 (R), 126 (Y) and 126 (B), the
return cable 130, and the pipes 241, 242 and 243, respectively, are
the respective ground-fault capacities or less. Hence, it is
confirmed that the power cable 200 in this second embodiment can
ensure a sufficient path for the fault current to flow.
[0126] According to this second embodiment, it is possible to
provide the power cable 200 that ensures a sufficient path for the
fault current to flow, by including the transmission cables 120R,
120Y and 120B having the triplex formation, and the pipes 241, 242
and 243 having the triplex formation. The transmission cables 120R,
120Y and 120B, and the pipes 241, 242 and 243, are respectively
twisted around the periphery of the return cable 130 along the
longitudinal direction of the return cable 130 by the triplex
formations thereof, with the return cable 130 arranged at the
center of the transmission cables 120R, 120Y and 120B and the pipes
241, 242 and 243.
[0127] In addition to being used as the path for the fault current
to flow, the pipes 241, 242 and 243 can be used as the information
communication network through the optic fibers 244, 245 and 246. Of
course, the insides of the pipes 241, 242 and 243 may be maintained
in the hollow state, without arranging the optic fibers 244, 245
and 246 (including the optic fiber parts 244A, 245A and 246A, and
the plastic pipes 244B, 245B and 246B) inside the pipes 241, 242
and 243, respectively.
[0128] The optic fibers 244, 245 and 246 may be utilized to form a
fiber-optic DTS (Distributed Temperature Sensing) system, such as
OPTHERMO (registered trademark). The fiber-optic DTS system can
measure the temperature distribution along the optic fibers for
several tens of kilometers in real-time, for example, using the
optic fibers 244, 245 and 246 themselves as temperature
sensors.
[0129] In addition, in a case in which a POF cable is connected to
one end or both ends of one or a plurality of power cables 200 in
order to replace an existing POF cable by the power cable 200, it
is possible to utilize the internal spaces within the pipe parts
241A, 242A and 243A as flow passages for the insulating oil,
instead of arranging the optic fibers 244, 245 and 246 (including
the optic fiber parts 244A, 245A and 246A, and the plastic pipes
244B, 245B and 246B) inside the pipes 241, 242 and 243,
respectively. The flow passage for the insulating oil of the
adjacent POF cable can be formed by flowing the insulating oil
inside the pipe parts 241A, 242A and 243A, as will be described
later in conjunction with FIGS. 9A and 9B. Further, the
transmission cable 120 can be cooled by flowing a cooling liquid
(for example, water) inside the pipes 241, 242 and 243.
Accordingly, each of the pipes 241, 242 and 243 may function to
provide a path or passage for the composite optic fiber, cooling,
and oil.
[0130] Next, a description will be given of a state in which a
plurality of power cables 200 are connected via a vault, by
referring to FIG. 8.
[0131] FIG. 8 is a diagram illustrating the state in which a
plurality of power cables 200A, 200B and 200C in the second
embodiment are connected via vaults 250A, 250B and 250C. FIG. 8
illustrates the plurality of power cables 200A, 200B and 200C which
are identical to the power cable 200 described above. For this
reason, when not distinguishing the power cables 200A, 200B and
200C, these power cables 200A, 200B and 200C may also be referred
to as "power cables 200" in the following description.
[0132] In FIG. 8, only the steel pipe 110, the conductor 121 and
the metal sheath 126 of the transmission cables 120R, 120Y and
120B, the return cable 130, and the pipes 241, 242 and 243 of the
power cable 200 are illustrated. The conductors 121 and the metal
sheaths 126 of the transmission cables 120R, 120Y and 120B are
respectively represented as conductors 121R, 121Y and 121B and
metal sheaths 126R, 126Y and 126B, respectively. The vaults 250A,
250B and 250C have the same configuration, and thus, when not
distinguishing the vaults 250A, 250B and 250C, these vaults 250A,
250B and 250C may also be referred to as "vaults 250" in the
following description.
[0133] The vault 250 has the same configuration as the vault 50 in
the first embodiment illustrated in FIG. 5, except that the joints
52R, 52Y and 52B are replaced by joints 252R, 252Y and 252B,
respectively. Since other parts of the vault 250 are the same as
the corresponding parts of the vault 50, those parts in FIG. 8 that
are the same as those corresponding parts in FIG. 5 are designated
by the same reference numerals, and a description thereof will be
omitted.
[0134] The joints 252R, 252Y and 252B have the same configuration,
and thus, a description will be given only with respect to the
configuration of the joint 252R.
[0135] The joint 252R includes a connecting part 57A, an insulating
part 57B, a connecting part 57C, and projecting parts 58A and 58B.
The connecting parts 57A and 57C, and the insulating part 57B have
the same configurations as those of the joint 52R.
[0136] The projecting parts 58A and 58B are provided on the
connecting parts 57A and 57C, respectively. The projecting parts
58A and 58B project to the outer side of the connecting parts 57A
and 57C, respectively, and are made of a metal, similarly to the
connecting parts 57A and 57C.
[0137] The pipe 241 of the power cable 200A is connected to the
connecting part 57A, and the pipe 241 of the power cable 200B is
connected to the connecting part 57C. Hence, the pipe 241 is held
at the ground potential.
[0138] The connections at the joints 252Y and 252B are similar to
that at the joint 252R. The joint 252Y connects the pipe 241 of the
power cable 200A and the pipe 241 of the power cable 200B. The
joint 252B connects the pipe 241 of the power cable 200A and the
pipe 241 of the power cable 200B.
[0139] The connecting relationship of the mutually adjacent power
cables 200B and 200C is similar to that of the mutually adjacent
power cables 200A and 200B described above, and the mutually
adjacent power cables 200B and 200C are similarly connected via the
vault 250.
[0140] A case will be considered in which the insulator breakdown
occurs in the transmission cable 120R illustrated in FIG. 6B of the
power cable 200A including the conductor 121R, when the power
cables 200A, 200B and 200C are connected in series as described
above.
[0141] In this case, the fault current generated in the
transmission cable 120R flows to the steel pipe 110 via the metal
sheath 126R, the return cable 130, or the pipes 241, 242 and 243 of
the power cable 200A, and flows through the cable 54 as indicated
by an arrow A. Further, a part of the fault current flows to the
steel pipe 110 and the return cable 130 of the power cable 200B via
the cable 54 as indicated by an arrow B, and the remaining part of
the fault current flows to the connecting part 53A via the cable
54A. The current flowing to the connecting part 53A flows to the
metal sheaths 126R, 126Y and 126B and the pipes 241, 242 and 243 of
the power cable 200B, via the cables 56R, 56Y and 56B.
[0142] Accordingly, the fault current generated by the insulator
breakdown in the transmission cable 120R of the power cable 200A
flows through the steel pipe 110 of the power cable 200A, and
branches to the steel pipe 110, the metal sheaths 126R, 126Y and
126B, the return cable 130, and the pipes 241, 242 and 243 of the
power cable 200B, via the cables 54, 54A, 55R, 55Y, 55B, 56R, 56Y
and 56B.
[0143] As described above in conjunction with FIG. 7, the steel
pipe 110, the metal sheaths 126 (126R, 126Y and 126B), the return
cable 130, and the pipes 241, 242 and 243 of the power cable 200
provide a path with a sufficient capacity for the fault current to
flow. Compared to the power cable 100 in the first embodiment, the
capacity of the path for the fault current to flow in the power
cable 200 in this second embodiment can be increased by
approximately 50%.
[0144] For this reason, even when the fault current is generated
due to the insulator breakdown in the transmission cable 120, it is
possible to suppress the currents flowing through the steel pipe
110, the metal sheaths 126 (126R, 126Y and 126B), the return cable
130, and the pipes 241, 242 and 243 from exceeding the respective
ground-fault capacities thereof, and provide the power cable 200 in
which a sufficient path is ensured for the fault current to
flow.
[0145] Although the pipes 241, 242 and 243 are used in this second
embodiment, it is possible to use conductors or wires in place of
the pipes 241, 242 and 243. In addition, only one or two of the
pipes 241, 242 and 243 may be provided.
[0146] Next, a description will be given of a case in which an
existing POF cable is replaced by the power cable 200, in order to
provide a flow passage for the insulating oil, by flowing the
insulating oil of the POF cables at both ends of the power cable
200 inside the pipes 241, 242 and 243 of the power cable 200.
[0147] FIGS. 9A and 9B are diagrams for explaining a state in which
the existing POF cables are replaced by the power cables 200A and
200B in the second embodiment. For the sake of convenience, FIGS.
9A and 9B illustrate only one transmission cable 120 and one pipe
241 and the steel pipe 110 with respect to the power cables 200A
and 200B.
[0148] In addition, it is assumed in FIGS. 9A and 9B that each of
POF cables 70A, 70B, 70C and 70D include three (3) OF cables 40
inserted into the steel pipe 110 thereof, and that the insulating
oil is provided inside this steel pipe 110. The OF cable 40 is the
OF cable 40 in the comparison example illustrated in FIG. 4B. For
the sake of convenience, FIGS. 9A and 9B illustrate only the steel
pipe 110 and one OF cable 40 with respect to each of the POF cables
70A, 70B, 70C and 70D. In addition, because the POF cable may
function as an oil line, the steel pipe 110 thereof may be treated
as an oil line.
[0149] In FIG. 9A, the transmission cables 120 of the power cables
200A and 200B are connected between the OF cable 40 of the POF
cable 70A and the OF cable 40 of the POF cable 70B, via joints 80A
and 80B. The OF cables 40 of the POF cables 70C and 70D are
connected on the right side of the OF cable 40 of the POF cable
70B, via joints 80D and 80E. The transmission cables 120 of the
power cables 200A and 200B are connected via a joint 80B.
[0150] The steel pipe 110 of the POF cable 70A, the pipes 241 of
the power cables 200A and 200B, and the steel pipes 110 of the POF
cables 70B, 70C and 70D are connected via joints 72. With regard to
the pipe 241, the pipe parts 241A of the pipe 241 is connected to
the steel pipe 110. Actually, there are three (3) pipes 241, 242
and 243, and thus, there are three (3) pipe parts 241A, 242A and
243A. Hence, the three (3) pipe parts 241A, 242A and 243A are
actually merged at the joint 72 and connected to the steel pipe
110. A part of the joint 80A may be formed by one joint 72, and a
part of the joint 80C may be formed by another joint 72.
[0151] In addition, a terminating part 90A is connected on the left
side of the POF cable 70A, and a terminating part 90B is connected
on the right side of the POF cable 70D. An oil supply device 90E is
connected to the steel pipe 110 of the POF cable 70A, and an oil
supply device 90F is connected to the steel pipe 110 of the POF
cable 70D.
[0152] The joint 80B is a connecting part similar to the vaults
250A through 250C illustrated in FIG. 8. The terminating parts 90A
and 90B are connected to a supply source or a supply destination of
the power. The terminating parts 90A and 90B are also connected to
the oil supply device, in order to manage and adjust the pressure
of the insulating oil and the like inside the POF cables 70A
through 70D.
[0153] When laying the power cables 200A and 200B, the two (2) POF
cables that existed between the POF cables 70A and 70B before the
replacement are replaced by the power cables 200A and 200B as
illustrated in FIG. 9A.
[0154] In this case, the replacement by the power cables 200A and
200B, and the provision of the flow passage for the insulating oil
between the POF cables 70A and 70B can be achieved simultaneously,
by connecting the pipes 241 of the power cables 200A and 200B to
the steel pipes 110 of the POF cables 70A and 70B.
[0155] Further, in FIG. 9B, the POF cable 70A, the joint 80A, the
power cable 200A, the joint 80B, the power cable 200B, the joint
80C, and a power cable 270E are connected to the terminating part
90A. The power cable 270E is a dry type power cable that does not
use insulating oil. The power cable 270E is an example of a line or
path that is set up at a location where no steel pipe 110 is
provided, or at a location where the line or path is not provided
inside the steel pipe 110.
[0156] An oil line 90C branches from the joint 80C, and connects to
an existing oil supply device 90D, for example.
[0157] FIG. 8B illustrates a case in which the connection of the
plurality of POF cables, the oil supply device 90D, and the power
cable 270E that are connected on the right side of the POF cable
70A in a power transmission system before the replacement is
modified, by replacing the POF cables other than the POF cable 70A
by the power cables 200A and 200B, and reconnecting the modified
power transmission system to the existing oil supply device
90D.
[0158] In the power transmission system illustrated in FIG. 9B, the
power is transmitted between the terminating part 90A and the power
cable 270E. In addition, the oil supply device 90D manages and
adjusts the pressure and the like of the insulating oil in the
steel pipe 110 of the POF cable 70A, via the pipes 241 of the power
cables 200A and 200B and the oil line 90C.
[0159] According to the power cable 200 in this second embodiment,
the pipes 241, 242 and 243 can be utilized as the flow path for the
insulating oil, and can be used to replace a part of the existing
POF cable.
[0160] According to the embodiments described above, the power
cable can provide a sufficient path for the fault current.
[0161] Further, the present invention is not limited to these
embodiments, but various variations and modifications may be made
without departing from the scope of the present invention.
* * * * *