FIELD
[0001] The present application relates to the technical field of submarine cables, particularly,
relates to multicore DC submarine cables and production method thereof.
BACKGROUND
[0002] This part is intended to provide a background or context for the embodiments of the
present application stated in claims. The description here is not to be recognized
as prior art because it is included in this part.
[0003] DC submarine cables are configured for connecting to converter equipment at both
ends of a DC transmission system, and supporting submarine cable accessories to build
a complete underwater or terrestrial transmission line system. Large capacity and
long-distance transmission are often found as features. The required conductor cross-section
is large. Therefore, existing DC submarine cables are mostly designed with single
core submarine cable structure. The existing submarine cable adopts a large section
single core structure, resulting in high project cost, and long project cycle. Additionally,
when an optical unit needs to be added in a single core DC submarine cable, the optical
unit needs to be in an armored layer of the single core DC submarine cable, or an
optical fiber filling layer needs to be added separately in the cable. Placing the
optical unit in the armored layer increases the risk of damage to the optical fiber
unit. Adding the optical fiber filling layer separately will increase the cost of
DC submarine cable raw materials, and reduce the transmission capacity of the submarine
cable due to the addition of thermal insulation materials.
[0004] Generally, a pseudo bipolar DC submarine cable transmission system consists of two
polar submarine cables. If one of the two polar submarine cables fails, the whole
circuit will not operate normally. In a true bipolar DC submarine cable transmission
system, a return submarine cable is added in the system. The true bipolar DC submarine
cable transmission system is composed of three electrical paths to form a circuit.
When one polar submarine cable fails, another polar submarine cable can form a circuit
with the help of the return submarine cable, maintaining half of the transmission
capacity. At present, in order to avoid an overall outage after the failure of one
of the two polar submarine cables in the pseudo bipolar DC submarine cable transmission
system, another standby polar submarine cable is also added in the pseudo bipolar
DC submarine cable transmission system. When a fault occurs in one polar submarine
cable, the polar submarine cable can be converted to the standby submarine cable,
and the circuit can be reconstructed by the other polar submarine cable and the standby
submarine cable.
[0005] When building a DC submarine cable transmission system, the main cost includes costs
of converter systems, submarine cables, and submarine cable construction. A key content
of the submarine cable construction is submarine cable laying. In the conventional
single core structure of existing DC submarine cables, two or three DC submarine cables
in each circuit need to be laid separately, which will increase the construction period
and the cost of the construction ship. In order to solve the problem of high cost,
the existing solution in the field is to use a construction ship equipped with two
independent turntables to lay two single core DC submarine cables at the same time,
bind them at the same time, and complete the construction at one time to save time
and cost. However, no successful experience and case for manufacturing and using three
single core DC submarine cables is known. Additionally, the bundling and laying scheme
has high requirements for the construction ship, which requires the special multi
turntable construction ship and the completion of the transformation and upgrading
of auxiliary equipment. High costs are involved, which is not conducive to large-scale
promotion.
SUMMARY
[0006] The present application discloses a multi-core direct-current submarine cable, including
a structure in which two identical polar electric units and an additional electric
unit assembly are integrated into a cable and are fully armored. An outer diameter
of the cross-section of the additional electric unit assembly is the same as an outer
diameter of the cross-section of each polar electric unit. Filling strips are arranged
between the internal polar electric unit and the additional electric unit assembly,
so as to reduce the material cost and the laying cost, and give roundness to the cabling
of cores with different size.
[0007] The present application also discloses a stranding equipment of the multi-core direct-current
submarine cable. The stranding equipment can achieve stable operation for the multi-core
direct-current submarine cables by setting counterweights on a turntable.
[0008] The present application also discloses a production method of the multi-core direct-current
submarine cable. The stranding equipment is used to squeeze together two polar electric
units and additional electric unit assembly with the help of gravity, so as to achieve
stranding of the multi-core direct-current submarine cable stably and efficiently.
[0009] The present application discloses a multi-core direct-current submarine cable, the
multi-core direct-current submarine cable includes two identical polar electric units,
additional electric unit assembly, several filling strips, a belt, a cushion layer,
an armored layer, and an outer protective layer. An outer diameter of the cross-section
of the additional electric unit assembly is the same as an outer diameter of the cross-section
of each polar electric unit. The two polar electric units are squeezed and twisted
together with the additional electric unit assembly, and are sequentially provided
with the belt, the cushion layer, the armored layer and the outer protective layer
wrapped around same. A plurality of the filling strips is arranged in gaps between
the two polar electric units, the additional electric unit assembly, and the belt.
[0010] Preferably, the additional electric unit assembly includes an additional electric
unit and at least one additional filling strip arranged at a side of the additional
electric unit.
[0011] Preferably, the additional electric unit assembly includes two semicircular additional
filling strips. The two semicircular additional filling strips are arranged on two
sides of the additional electric unit, and the two semicircular additional filling
strips form a substantially circular overall shape.
[0012] Preferably, after the two additional filling strips cooperate with the additional
electric unit to give roundness, gaps are formed at an upper end and a lower end.
[0013] Preferably, the additional filling strip is located at the side where the additional
electric unit is far away from the two polar electric units or between the additional
electric unit and the two polar electric units.
[0014] Preferably, when the multi-core direct-current submarine cable is used in a pseudo
bipolar DC transmission system, and transmission capacity of the additional electric
unit assembly and the polar electric unit assembly is required to be the same, the
additional electric unit assembly includes the additional electric unit with the same
structure as the polar electric unit, and a sectional area of the conductor of the
additional electric unit is the same as that of the polar electric unit.
[0015] Preferably, when the multi-core direct-current submarine cable is used in a true
bipolar DC transmission system, the additional electric unit assembly includes an
additional electric unit with the same structure as the polar electric unit, and the
sectional area of the conductor of the additional electric unit is the same as the
sectional area of the conductor of the polar electric unit.
[0016] Preferably, the additional electric unit assembly includes three additional electric
units cabled together, and filling strips are arranged inside.
[0017] The application discloses a stranding equipment of the multi-core direct-current
submarine cables, the stranding equipment is configured for stranding the multi-core
direct-current submarine cables. The stranding equipment of the multi-core direct-current
submarine cables includes a first platform, a second platform, a counterweight plate,
a central shaft, two polar electric unit turntables, an additional electric unit turntable,
at least one auxiliary turntable, a first traction wrapping assembly, a first stranding
mold, a second traction wrapping assembly, a second stranding mold, and a steering
wheel. The two polar electric units are respectively mounted in the two polar electric
unit turntables. The auxiliary turntable is arranged at a side of the additional electric
unit turntable. The counterweight plate, the first platform, and the second platform
are all parallel and arranged from bottom to top. The central shaft is perpendicular
to a middle portion of the counterweight plate. The two polar electric unit turntables
and the additional electric unit turntable are uniformly arranged on the counterweight
plate. The first traction wrapping assembly is arranged on the first platform, and
the first stranding mold is arranged at a bottom of the first traction wrapping assembly.
The second traction wrapping assembly is arranged on the second platform, and the
second stranding mold is arranged at a bottom of the second traction wrapping assembly.
The steering wheel is arranged on the second platform, and the steering wheel abuts
the second traction wrapping assembly. A plurality of counterweights are arranged
on the counterweight plate at a position vertically corresponding to the additional
electric unit turntable. A counterweight is arranged on a side of the first platform
away from the first traction wrapping assembly.
[0018] The production method of the multi-core direct-current submarine cable, applied in
the stranding equipment of the multi-core direct-current submarine cable, includes
the following steps:
- (A) The two polar electric unit turntables and the additional electric unit turntables
rotate counterclockwise around the central shaft at angular velocity ω1; the polar
electric unit rotary turntables, the additional electric unit turntable, and the auxiliary
turntable rotate clockwise synchronously at an angular speed ω2, the first platform
rotates counterclockwise synchronously at an angular speed ω3, wherein ω1=ω2=ω3;
- (B) Synchronously, the first traction wrapping assembly vertically pulls the additional
electric unit or the additional electric unit and the additional filling strip at
a speed v 1, the additional electric unit assembly is assembled at the first stranding
mold and bound firmly, the second traction wrapping assembly vertically pulls the
additional electric unit assembly and the two polar electric units at a speed v2,
and the second stranding mold is a point of convergence to form an integral circular
structure, wherein v1=v2;
- (C) Synchronously, the integral circular structure is filled with and rounded by the
filling strips, and the second traction wrapping assembly is configured to be bound
firmly to complete the wrapping;
- (D) After the belt binding is completed, the production process of the armored layer
and the outer protective layer through the steering wheel is entered.
[0019] Compared with the prior art, the multi-core direct-current submarine cable and the
production method disclosed in the present application have the following advantages:
the multi-core direct-current submarine cable saves required raw material costs under
the same conductor cross-section and insulation structure design, and have better
market value. It is conducive to laying a single circuit DC submarine cable line at
one time during the construction of submarine cable project, saving a lot of laying
costs. Problem of roundness of electric units with different outer diameters is effectively
solved. The stranding equipment of the multi-core direct-current submarine cable improves
the stability of the stranding equipment by setting a counterweight turntable and
counterweights. The multi-core direct-current submarine cable production method can
achieve stable stranding of the multi-core direct-current submarine cable, and can
improve the production efficiency.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Many aspects of the disclosure can be better understood with reference to the following
drawings. The drawings in the following description are some embodiments of the present
disclosure. For those of ordinary skill in the art, other drawings can be obtained
based on these drawings without creative work.
FIG. 1 is a cross-sectional view of a multi-core direct-current submarine cable of
the present application.
FIG. 2 is a cross-sectional view of a polar electric unit of the multi-core direct-current
submarine cable in the present application.
FIG. 3 is a cross-sectional view of an additional electric unit assembly of the multi-core
direct-current submarine cable in the present application.
FIG. 4 is a cross-sectional view of a first variant of the multi-core direct-current
submarine cable of the present application.
FIG. 5 is a cross-sectional view of a second variant of the multi-core direct-current
submarine cable of the present application.
FIG. 6 is a cross-sectional view of the third variant of the multi-core direct-current
submarine cable of the present application.
FIG. 7 is a schematic view of a stranding equipment of multi-core direct-current submarine
cable in the present application.
FIG. 8 is a top view of turntable rotation of the stranding equipment of multi-core
direct-current submarine cable of the present application.
FIG. 9 is a top view of turntable rotation of a variant of the stranding equipment
of multi-core direct-current submarine cable of the present application.
FIG. 10 is flow chart of the production method of multi-core direct-current submarine
cable in the present application.
Description of main components or elements:
[0021]
Polar electric unit 11, 12
Conductor 111
Inner semiconducting shielding layer 112
Extruded insulating layer 113
Outer semiconducting shielding layer 114
Semiconducting water-blocking layer 115
Metal shielding layer 116
Plastic sheath 117
Additional electric unit assembly 13
Additional electric unit 131
Additional filling strip 132
Optical unit 14, 133C
Filling strip 15
belt 161
Cushion layer 162
Armored layer 163
Outer protective layer 164
First platform 1
Second platform 2
Counterweight plate 3
Polar electric unit turntable 10
Center shaft 20
Additional electric unit turntable 30
Counterweight 301
Twisting center 302
Auxiliary turntable 31
First traction wrapping assembly 32
First stranding mold 321
Counterweight 322
Second traction wrapping assembly 40
Second stranding mold 401
Steering wheel 50.
DETAILED DESCRIPTION
[0022] In order to better understand the above purposes, features and advantages of embodiments
of the application, the application is described below in combination with the drawings
and specific embodiments. It should be noted that, in the case of no conflict, the
features in the embodiments of the present application can be combined with each other.
[0023] Many specific details are described in the following description to understand the
embodiments of the application. The described embodiments are only part of the embodiments
of the application, not all of them.
[0024] Unless otherwise defined, all technical and scientific terms used herein have the
same meanings as those commonly understood by those skilled in the technical field
belonging to the embodiments of the application. The terms used in the specification
of the application herein are only for the purpose of describing specific embodiments,
and are not intended to limit embodiments of the application.
[0025] The following specific embodiments will further explain the embodiments of the application
in combination with the above drawings.
[0026] Referring to FIG. 1, a multi-core direct-current submarine cable of the present application
includes two identical polar electric units 11 and 12, an additional electric unit
assembly 13, several optical units 14, several filling strips 15, a belt 161, a cushion
layer 162, an armored layer 163, and an outer protective layer 164. An outer diameter
of the cross-section of the additional electric unit assembly 13 is the same as outer
diameter of the cross-sections of the polar electric units 11 and 12 to improve roundness
after cabling. The two polar electric units 11 and 12 are twisted together with the
additional electric unit assembly 13, and are sequentially provided with the belt
161, the cushion layer 162, the armored layer 163, and the outer protective layer
164 wrapped around same. Several optical units 14 are arranged in gaps between the
two polar electric units 11 and 12, the additional electric unit assembly 13, and
the belt 161, and several filling strips 15 are arranged in gaps between the two polar
electric units 11 and 12, the additional electric unit assembly 13, and the belt 161.
[0027] Referring to FIG. 2, the polar electric unit 11 includes a conductor 111, an inner
semiconducting shielding layer 112, an extruded insulating layer 113, an outer semiconducting
shielding layer 114, a semiconducting water-blocking layer 115, a metal shielding
layer 116, and a plastic protective layer 117, which are sequentially wrapped from
the inside to the outside. The structural dimensions of the polar electric unit 12
and of the polar electric unit 11 are the same. A main function of the polar electric
units 11 and 12 is to form a direct-current (DC) transmission circuit, which can transmit
electrical energy. When the polar electric units 11 and 12 are in normal operation,
the additional electric unit assembly 13 is not required to work.
[0028] The additional electric unit assembly 13 includes an additional electric unit 131.
In a true bipolar DC transmission system, a main function of the additional electric
unit 131 is to transmit a return current for the other polar electric unit when one
of the polar electric units fails. In the present application, a conductive sectional
area of the additional electric unit 131 (recorded as S
additional) is the same as that of the polar electric unit (recorded as S
polar), that is, S
additional = S
polar. Preferably, a thickness of an insulation layer of the additional electric unit (recorded
as d
additional) is 30% of a thickness of an insulation layer of the polar electric unit (recorded
as d
polar), that is, d
additional=30%×d
polar. In a pseudo bipolar DC transmission system, a main function of the additional electric
unit 131 is to provide functionality of the circuit with the other polar electric
unit when one of the polar electric units fails, so as to maintain normal operation
of the system. At this time, the design of the conduct sectional area and the thickness
of the insulation layer of the additional electric unit 131 depends on the transmission
capacity that the system requires of the additional electric unit. When the transmission
capacity that the additional electric unit 131 is required to achieve is the same
as that of the polar electric unit, S
additional = S
polar, and d
additional =d
polar. At this time, the structural composition and size of the additional electric unit
are completely consistent with those of the polar electric unit.
[0029] In the pseudo bipolar DC transmission system, when the system sets the transmission
capacity reserved by the additional electric unit 131 at less than the transmission
capacity of the polar electric units 11 and 12, the size of the additional electric
unit 131 is inconsistent with that of the polar electric units 11 and 12, and the
additional electric unit assembly 13 needs to add additional filling strips to keep
the outer diameter of the cross-section of the additional electric unit assembly 13
the same as the sectional size of the polar electric units 11 and 12. Referring to
FIG. 3, the additional electric unit assembly 13 includes two semicircular additional
filling strips 132. Two additional filling strips 132 are arranged on two sides of
the additional electric unit 131, and the two additional filling strips 132 form an
approximately round shape. D, shown in FIG. 3, is the approximate outer diameter,
and D is the same as the outer diameter of the cross-section of the polar electric
units 11 and 12, so as to cooperate with the two polar electric units to improve the
roundness of the entire package submarine cable after cabling. In order to maintain
a margin of deformation after adding the two additional filling strips 132, two additional
filling strips 132 are designed to cooperate with the additional electric unit 131
to lend roundness, and gaps are formed at an upper end and a lower end, that is, the
gap is marked as d in FIG. 3, and preferably d is 10mm. In order to avoid deformation
of the additional electric unit 131 caused by excessive pressure when tightening the
two additional filling strips 132 on the additional electric unit 131 during the stranding
process, a radian inside the additional filling strip 132 is designed to be according
to the outer diameter of the additional electric unit 131, and fitting angle α between
the inner arc of the additional filling strip 132 on both sides and the outer diameter
of the additional electric unit 131 is defined as 120 °.
[0030] Referring to FIG. 4, a first variant of the multi-core direct-current submarine cable
in the application is shown. The difference is that the additional electric unit assembly
13A includes an additional electric unit 131A and an additional filling strip 132A.
The additional filling strip 132A is arranged at a side of the additional electric
unit 131A away from the polar electric units 11 and 12. The additional electric unit
131A is in contact with the additional filling strip 132A and two polar electric units
11 and 12, and being held at three points the position is stable. There is no mandatory
requirement for the contact area and angle between the additional filling strip 132A
and the additional electric unit 131A. Both sides of the additional filling strip
132A are required to be tightened and pressed under by the adjacent filling strip
15 to ensure no large displacement. The first variant simplifies the structure of
the additional electric unit assembly 13A, and uses a single side filling strip to
replace two semi-circular composite filling strips to improve the overall cabling
roundness.
[0031] Referring to FIG. 5, a second variant of the multi-core direct-current submarine
cable in the present application is shown. The difference is that the additional electric
unit assembly 13B includes an additional electric unit 131B and an additional filling
strip 132B. The additional filling strip 132B is arranged between the additional electric
unit 131B and the polar electric units 11 and 12. Both sides of the additional filling
strip 132B must be tightened and pressed under by the adjacent filling strip 15 to
ensure there is no large displacement. The second variant simplifies the structure
of the additional electric unit assembly 13A, and has the advantage that the center
of gravity of the submarine cable is closer to the geometric center after cabling,
which is conducive to later storage and construction process.
[0032] Referring to FIG. 6, a third variant of the multi-core direct-current submarine cable
in the present application is shown. The difference is that the additional electric
unit assembly 13C is a three core pre-cabling structure. The additional electric unit
assembly 13C includes three additional electric units 131C after cabling, and the
filling strip 132C is set inside. After that, the additional electric unit assembly
13C conducts secondary cabling with two polar electric units 11 and 12. The sum of
the sectional areas of the conductors of the three additional electric units 131C
is the same as that of the polar electric units 11 and 12. Several optical units 133C
can also be added to the additional electric unit assembly 13C, increasing optical
fiber monitoring and communication channels. The third variant divides the separate
additional power unit into three independent power units, which can flexibly control
the number of connected cores in coordination with the transmission system, and adjust
the load capacity of the additional power unit as required, making adjustment flexible
and convenient.
[0033] Referring to FIG. 7 and FIG. 8, the present application discloses a stranding equipment
of multi-core direct-current submarine cable, including a first platform 1, a second
platform 2, a counterweight plate 3, a central shaft 20, two polar electric unit turntables
10, an additional electric unit turntable 30, two auxiliary turntables 31, a first
traction winding assembly 32, a first traction winding mold 321, a second traction
winding assembly 40, a second winding mold 41, and a steering wheel 50. The polar
electric units 11 and 12 are respectively mounted in two polar electric unit turntables
10, the additional electric unit 131 is mounted in the additional electric unit turntable
30, and two additional filling strips 132 are respectively mounted in two auxiliary
turntables 31. The counterweight plate 3, the first platform 1 and the second platform
2 are parallel and arranged from bottom to top and are positioned coaxially, the central
shaft 20 is arranged to be perpendicular to a middle portion of the counterweight
plate 3. The two polar electric unit turntables 10 and the additional electric unit
turntable 30 are uniformly arranged on the counterweight plate 3 and surround the
central shaft 20. The two auxiliary turntables 31 are symmetrically arranged on both
sides of the additional electric unit turntable 30, the first traction wrapping assembly
32 is arranged on the first platform 1, and the first twisted mold 321 is arranged
at the bottom of the first traction wrapping assembly 32. The second traction wrapping
assembly 40 is arranged on the second platform 2, and the second stranding mold 41
is arranged at the bottom of the second traction wrapping assembly 40. The steering
wheel 50 is arranged on the second platform 2, and the steering wheel 50 abuts the
second traction wrapping assembly 40.
[0034] In the structure of the multi-core direct-current submarine cable in the present
application, the weight per unit length of the additional electric unit 131 will be
less than the weight per unit length of the polar electric units 11 and 12, causing
uneven weight distribution on the counterweight plate 3. Therefore, a plurality of
counterweights 301 are arranged on the counterweight plate 3 at a position perpendicular
to the additional electric unit turntable 30, and the counterweight 301 is weighted
according to the difference in weight between the sum of the weights of the additional
electric unit turntable 30, the auxiliary turntable 31, and the load, and the polar
electric unit turntable 10 and the load, to avoid the problem of the center of gravity
not being in the geometric center during the cabling process, this also ensures balance
in the vertical rotation of the stranding equipment. For the same reason, the counterweight
322 is arranged on a side of the first platform 1 where the first traction wrapping
assembly 40 is not set, to further maintain balance of the stranding device. It is
worth noting that the weight difference are recalculated and the counterweight possibly
adjusted after production of each kilometer of stranding.
[0035] For the first and second variants of multi-core direct-current submarine cables,
it is only necessary to install additional filling strip 132A or 132B in the auxiliary
turntable 31 on one side.
[0036] For the third variant of the multi-core direct-current submarine cable, the stranding
equipment of the multi-core direct-current submarine cable is shown in FIG. 9, which
includes three additional electric unit turntables 30A. The three additional electric
unit turntables 30A need to first rotate counterclockwise around the stranding center
302A to complete a primary stranding. During the primary stranding process, each additional
electric unit 131C rotates clockwise to eliminate axial torsion of the cable itself.
In synchronization, the twisted additional electric unit 131C and the two polar electric
units 11 and 12 rotate counterclockwise around the central shaft 20 to complete a
secondary stranding. During the secondary stranding process, each polar electric unit
rotates clockwise prevent axial torque of the cable, wherein ω1 = ω2. Other working
processes of the third variant are the same as the original scheme.
[0037] Referring to FIG. 10, the present application also discloses a production method
of multi-core direct-current submarine cable, which is configured to prepare the multi-core
direct-current submarine cable, and is applied in the stranding equipment of multi-core
direct-current submarine cable, the production method includes the following steps:
- (A) The polar electric unit turntables 10 and additional electric unit turntable 30
rotate counterclockwise around the center shaft 20 at an angular velocity ω1; at the
same time, the polar electric unit turntables 10, the additional electric unit turntable
30 and the auxiliary turntable 31 are synchronized and rotate clockwise at an angular
velocity ω2, to prevent axial torque of cable core; at the same time, the first platform
1 rotates counterclockwise synchronously at an angular velocity ω3; wherein ω1=ω2=ω3
;
- (B) Synchronously, the first traction wrapping assembly 32 exerts a vertical pull
on the additional electric unit 131 or on the additional electric unit and the additional
filling strip at a speed v1, the additional electric unit assembly 13 shown in FIG.
3 is assembled at the first stranding mold 321 and bound firmly; at the same time,
the second traction wrapping assembly 40 vertically pulls the additional electric
unit assembly 13 and two polar electric units 11 and 12 after wrapping at a speed
v2, and the second stranding mold 41 is the point of convergence, to form an integral
circular structure; wherein v1=v2;
- (C) Synchronously, the integral circular structure is filled with and rounded by filling
strip 15, and the wrapping assembly 40 is configured to bind the integral circular
structure firmly to complete the wrapping.
- (D) After the belt binding is completed, the subsequent production process of the
armored layer and the outer protective layer through the steering wheel 50 is entered.
[0038] The above embodiments are only used to describe the technical solution of the embodiments
of the application, not the limitations. Although the embodiments of the application
have been described in detail with reference to the above preferred embodiments, ordinary
technicians in the art should understand that the technical solution of the embodiments
of the application can be modified or replaced equivalently, which should not be divorced
from the spirit and scope of the technical solution of the embodiments of the application.
1. A multi-core direct-current submarine cable, characterized in that, comprising two identical polar electric units, an additional electric unit assembly,
several filling strips, a belt, a cushion layer, an armored layer, and an outer protective
layer, an outer diameter of the cross-section of the additional electric unit assembly
is the same as an outer diameter of the cross-section of each polar electric unit;
the two identical polar electric units are squeezed and twisted together with the
additional electric unit assembly, and are sequentially provided with the belt, the
cushion layer, the armored layer and the outer protective layer wrapped around same;
a plurality of the filling strips is arranged in gaps between the two identical polar
electric units, the additional electric unit assembly, and the belt.
2. The multi-core direct-current submarine cable of claim 1, characterized in that, the additional electric unit assembly includes an additional electric unit and at
least one additional filling strip arranged at a side of the additional electric unit.
3. The multi-core direct-current submarine cable of claim 2, characterized in that, the additional electric unit assembly includes two semicircular additional filling
strips, the two semicircular additional filling strips are arranged on two sides of
the additional electric unit, and the two semicircular additional filling strips form
a substantially circular overall shape.
4. The multi-core direct-current submarine cable of claim 3, characterized in that, after the two additional filling strips cooperate with the additional electric unit
to give roundness, gaps are formed at an upper end and a lower end.
5. The multi-core direct-current submarine cable of claim 2, characterized in that, the additional filling strip is located at the side where the additional electric
unit is far away from the two polar electric units or between the additional electric
unit and the two polar electric units.
6. The multi-core direct-current submarine cable of claim 1, characterized in that, when the multi-core direct-current submarine cable is applied to a pseudo bipolar
DC transmission system, and transmission capacity of the additional electric unit
assembly and the polar electric unit assembly is required to be the same, the additional
electric unit assembly includes the additional electric unit with the same structure
as the polar electric unit, and a sectional area of the conductor of the additional
electric unit is the same as that of the polar electric unit.
7. The multi-core direct-current submarine cable of claim 1, characterized in that, when the multi-core direct-current submarine cable is applied to a true bipolar
DC transmission system, the additional electric unit assembly includes an additional
electric unit with the same structure as the polar electric unit, and the conductor
sectional area of the additional electric unit is the same as the sectional area of
the conductor of the polar electric unit.
8. The multi-core direct-current submarine cable of claim 1, characterized in that, the additional electric unit assembly includes three additional electric units cabled
together, and filling strips are arranged inside.
9. A stranding equipment of multi-core direct-current submarine cables, configuring for
stranding the multi-core direct-current submarine cables as claimed in any one of
the claims 1 to 7, the stranding equipment of multi-core direct-current submarine
cables comprising a first platform, a second platform, a counterweight plate, a central
shaft, two polar electric unit turntables, an additional electric unit turntable,
at least one auxiliary turntable, a first traction wrapping assembly, a first stranding
mold, a second traction wrapping assembly, a second stranding mold, and a steering
wheel; the two polar electric units are respectively mounted in the two polar electric
unit turntables; the auxiliary turntable is arranged at a side of the additional electric
unit turntable; the counterweight plate, the first platform and the second platform
are all parallel and arranged from bottom to top; the central shaft is perpendicular
to a middle portion of the counterweight plate; the two polar electric unit turntables
and the additional electric unit turntable are uniformly arranged on the counterweight
plate; the first traction wrapping assembly is arranged on the first platform, and
the first stranding mold is arranged at a bottom of the first traction wrapping assembly;
the second traction wrapping assembly is arranged on the second platform, and the
second stranding mold is arranged at a bottom of the second traction wrapping assembly;
the steering wheel is arranged on the second platform, and the steering wheel abuts
the second traction wrapping assembly; a plurality of counterweights are arranged
on the counterweight plate at a position vertically corresponding to the additional
electric unit turntable; a counterweight is arranged on a side of the first platform
away from the first traction wrapping assembly.
10. A production method of multi-core direct-current submarine cable, applied in the stranding
equipment of multi-core direct-current submarine cable as claimed in claim 9, the
production method comprising the following steps:
(A) the two polar electric unit turntables and the additional electric unit turntables
rotate counterclockwise around the central shaft at angular velocity ω1; the polar
electric unit rotary turntables, the additional electric unit turntable and the auxiliary
turntable rotate clockwise synchronously at an angular speed ω2, the first platform
rotates counterclockwise synchronously at an angular speed ω3, wherein ω1=ω2=ω3;
(B) synchronously, the first traction wrapping assembly vertically pulls the additional
electric unit or the additional electric unit and the additional filling strip at
a speed v1, the additional electric unit assembly is assembled at the first stranding
mold and bound firmly, the second traction wrapping assembly vertically pulls the
additional electric unit assembly and the two polar electric units at a speed v2,
and the second stranding mold is a point of convergence to form an integral circular
structure, wherein v1=v2;
(C) synchronously, the integral circular structure is filled with and rounded by the
filling strips, and the second traction wrapping assembly is configured to be bound
firmly to complete the wrapping;
(D) after the belt binding is completed, the production process of the armored layer
and the outer protective layer through the steering wheel is entered.