Background
[0001] The present invention relates to a subsea power cable and the design of a conductor
for such a cable, especially for a cable for deep waters where the cable during the
laying of the cable is exposed to high tension.
Prior art
[0002] The document
US 2012/061123 A1 discloses an umbilical for use in the offshore production of hydrocarbons, and discloses
in particular a power umbilical for use in deep water applications.
[0003] In particular for cables to be placed in deep waters the volume and weight of the
cable is of high importance to the costs and size of equipment involved in the laying
of the cable. The metal conductor contributes significantly to the weight of the cables
and prior art solutions to reduce the weight comprise selecting lighter metals such
as aluminium for the conductor. However under high laying tension in deep water the
light metals such as pure aluminium yield and therefore the other cable elements,
mainly the armour will have to take all the laying tension. In such case not only
the conductor will be given a permanent elongation which is detrimental to the cable,
but the consequence is also damage to the cable insulation. If the conductor yields
due to high tension the conductor is elongated and thereby the diameter thereof is
reduced. This reduces the radial pressure of the conductor on the insulation, the
insulations attempt to adapt to this change is likely to result in damage to the insulation.
When the conductor yields, the tension in the cable will have to be taken by the other
cable elements (e.g. the armouring), which also may be negatively affected.
Objectives of the invention
[0004] An objective of the present invention is to provide a subsea cable with conductors
optimized with respect to conductivity, volume and weight such that the conductor
will not yield under high laying tension in deep waters. When the conductor does not
yield the risk of damaging the insulation is avoided.
[0005] Another objective is to provide a solution that allows for individual optimization
of the conductivity, weight and volume of the conductor.
[0006] These objectives are obtained by the subsea power cable according to the attached
independent claim. Further embodiments are disclosed in the dependent claims.
[0007] The present invention provides a subsea power cable comprising at least one conductor
surrounded by at least one layer of insulation and at least one layer of armouring,
wherein the conductor comprises at least a first conductor element and a second conductor
element, where the first conductor element is made of a first material and the second
conductor element is made of a second material and where the first and the second
materials are different.
[0008] The cross section of each conductor element of can be round or any other shape. The
conductor comprises at least two conductor elements but may comprise any number, from
2 - 100, preferably between 2 and 50 conductor elements or alternatively 3 or more
elements, preferably between 3-100 elements.
[0009] The conductor elements of different materials are distributed in more layers of the
conductor. In one aspect the two or more conductor elements are stranded together.
[0010] By preparing the conductor of two or more conductor elements and selecting conductor
elements made of at least two different types of materials the properties of the conductor
can be adapted to provide for optimization of the conductivity, weight and volume
of the conductor.
[0011] According to an aspect of the present subsea power cable the conductor comprises
a third conductor element made of a third material different from the first and the
second material. By using elements of three or more types of different materials the
flexibility of the construction of the conductor is further increased.
[0012] In a further aspect of the subsea power cable the conductor elements of different
materials are distributed throughout the cross-section of the conductor. In an aspect
of the subsea power cable the conductor comprises a core, a first layer surrounding
the core and a second layer surrounding the first player. To provide the conductor
with the intended conductivity at least one of the conductor elements is conductive.
[0013] The two or more different types of materials are in one aspect each a material independently
selected from the group comprising copper, copper alloys, aluminium, aluminium alloys,
steel, other metals or non-metallic materials. In one aspect the first material is
copper or a copper alloy and the second material is aluminium or an aluminium alloy.
In another aspect the first material is aluminium or an aluminium alloy and the second
material is copper or a copper alloy. These aspects can be combined in a cable comprising
a third conductor element made a third material where the third material is steel.
[0014] In a further aspect the subsea cable is a high voltage power cable. High voltage
means above 1000 V for AC or above 1500 V for DC, preferably 50 kV for AC or above
500 kV for DC or alternatively above 200 kV for AC or above 600 kV for DC In another
aspect at least one of the first, second or third material is aluminium or aluminium
alloy.
[0015] In yet another aspect the selection and distribution of conductor elements of different
materials within the conductor of the subsea power cable are such that the conductor
will not yield during the laying of the cable as the yield stress limit of the conductor
is not reached when laying at water depths of 400 - 3000 m. Alternatively when laying
at water depths below 500 m or between 600 and 2500 m.
[0016] Even when the cable laying tension is in the range of 50 tonnes or more, the conductor
of the subsea power cable will not yield.
[0017] The term "power cable" as used herein refers to any cable which at least has the
purpose of transferring electrical power. This may be the main purpose and it may
be the only purpose, the cable may however have additional purposes such as transferring
signals or fluids.
[0018] High cable laying tension is used here to refer to tensions which may expose the
conductor to a stress which exceeds the yield stress of the traditional conductor
material. Typically such critical laying tension could be in the range 50 tonnes,
but the critical tension will depend on different parameters of the cable design,
such as conductor size, the armour design etc.
[0019] The present invention is especially applicable for power cables to be laid at large
water depths such as 400 m - 3000 m, 600-2500 m or 400-2000 m.
[0020] The term "alloy" as used in copper alloy, aluminium alloy and other alloys refers
to a metal alloy which comprises the mentioned metal in an amount of between 50 and
99 w/w %.
[0021] The term "different" as used herein referring to the first, second and optionally
more materials being different, is to be understood as describing solutions where
the pure metal component or the main metal of the metal alloy is different such as
one component is made of copper or copper alloy and the other is made of aluminium
or aluminium alloy. Different also includes the situation with one metallic conductor
element and one non metallic conductor element. Different also describes the situation
where the two conductor elements are made of a pure metal and an alloy of the same
pure metal or two different alloys of the same metal. For a pure metal and an alloy
thereof of two alloys or the same metal to be different the materials have a difference
in yield stress limit of at least 1 %, preferably at least 3 % more preferably at
least 10%.
Brief description of the drawings
[0022] The present invention will be described by reference to the enclosed figures which
are schematic illustrations of the present invention. All the figures illustrate cross-sectional
views.
Figure 1 illustrates the configuration of a subsea power cable according to the present
invention.
Figure 2 illustrates a second alternative configuration of the conductor for a subsea
power cable according to the present invention.
Figure 3 illustrates an example configuration of a conductor not forming part of to
the invention.
Figure 4 illustrates a fourth alternative configuration of the conductor.
Figure 5 illustrates a fifth alternative configuration of the conductor.
Principal description of the invention
[0023] Figure 1 illustrates the cross-section of a subsea power cable 1 according to the
present invention. The power cable comprises a conductor 1 surrounded by a layer of
insulation 20. Surrounding the insulation is an optional metal sheath 30. Surrounding
the metal sheath 30 is an armouring layer 40 and outside of that is an outer serving
50. Subsea power cables are well known in the art and may comprise additional layers
than the layers disclosed here. Further the conductor, insulation layer and the armouring
layer may consist of one or more layers of material.
[0024] The armouring may comprise wires stranded or helically wound around the core of the
cable. It is well known to include more than one layer of armouring around the core
at different lay lengths and/or directions.
[0025] The present invention relates to providing a new conductor for an armoured subsea
power cable. Accordingly the present invention is not limited to a specially structure
of the layers surrounding the conductor other than that the structure comprises armouring
in the form of wires or bands of metal or fibre reinforced polymers. However, if the
conductor yields under high tension not only the conductor will be given a permanent
elongation which is detrimental to the cable, but the consequence is also damage to
the cable insulation.
[0026] The embodiment of the conductor 10 illustrated on figure 1 comprises an central wire
11 and a first inner layer and a second surrounding the first layer. In certain cables
the central wire will not exist, but will form an oil channel as the first layer is
self supported or supported by a tube or other kind of support. The first layer is
made up of conductor elements 15a and 15b aligned around the central wire. The second
layer is made up of conductor elements 12a and 12b aligned around the outer surface
of the first layer. In the illustrated embodiment the central wire 11, the conductor
elements 12b and 15b are all made of a first conducting material whereas the conductor
elements 12a and 15a are made of a second conducting material different from the first
conducting material. In the embodiment on figure 1 the elements of different materials
within each layer are evenly distributed, every second element in each layer is made
of the same material.
[0027] The first and second conductive material are selected from the group comprising copper,
copper based alloys, aluminium, aluminium alloys, steel, other conductive metals,
and other conductive or non-conductive materials.
[0028] Figure 2 illustrates an alternative embodiment of the conductor 10 for an armoured
subsea cable according to the present invention. In this embodiment the conductor
comprises a central wire and three layers of conducting elements 15a, 15b, 12a, 12b,
18a and 18b arranged around the core. In the illustrated embodiment the central wire
11, the conductor elements 12b and 15b are all made of a first conducting material
whereas the conductor elements 12a and 15a are made of a second conducting material
different from the first conducting material. In the embodiment on figure 2 the elements
of different materials within the first and the second layer are evenly distributed,
every second element in each layer is made of the same material. In the third layer
the number of elements 18a of the second material is less than the number of conducting
elements 18b of the first material. According to this embodiment the conductor comprises
layers with different ratio of the different materials.
[0029] In this embodiment the first and second conductive material are selected from the
group comprising copper, copper based alloys, aluminium, aluminium alloys, steel,
other conductive metals, and other conductive or non-conductive materials.
[0030] Figure 3 illustrates an example of a conductor for an armoured subsea cable. In this
example the conductor comprises a central wire and two layers of conducting elements
15a, and 12b arranged around the core. In the illustrated embodiment the central wire
11 and the conductor elements 12b are all made of a first conducting material whereas
the conductor elements 15a are made of a second conducting material different from
the first conducting material. In the example on figure 3 the elements of different
materials are arranged as layers of a second material arranged between the core and
a second layer of a first material. Although the layers are illustrated as consisting
of a number of separate elements arranged as a surrounding layer it is equally possible
to prepare one or more of the layers as one single element.
[0031] In this example the first and second conductive material are selected from the group
comprising copper, copper based alloys, aluminium, aluminium alloys, steel, other
conductive metals, and other conductive materials.
[0032] Figure 4 illustrates a fourth embodiment of a conductor for an armoured subsea cable
according to the present invention. In this embodiment the conductor comprises a central
wire and two layers of conducting elements 15a, 15b, 15c and 12a,12b, 12c arranged
around the core. In the illustrated embodiment the central wire 11 and the conductor
elements 12b and 15b are all made of a first conducting material whereas the conductor
elements 12a and 15a are made of a second conducting material different from the first
conducting material and the conducting elements 12c and 15c are made of a third conducting
material different from the first and the second conducting material. In the embodiment
on figure 4 the elements of three different materials are evenly distributed in each
layer.
[0033] In this embodiment the first, second and third conductive material are selected from
the group comprising copper, copper based alloys, aluminium, aluminium alloys, steel,
other conductive metals, and other conductive or non-conductive materials.
[0034] Figure 5 illustrates a fifth embodiment of a conductor for an armoured subsea cable
according to the present invention. In this embodiment the conductor comprises a central
wire and two layers of conducting elements 15a, 15b and 12a, 12b arranged around the
core. In the illustrated embodiment the conductor elements 12b and 15b are all made
of a first conducting material whereas the central wire 11a and the conductor elements
12a and 15a are made of a second conducting material different from the first conducting
material. In the embodiment on figure 5 the conducting elements each have a circular
cross-section. The elements conductor may be stranded together.
[0035] In this embodiment the first and second conductive material are selected from the
group comprising copper, copper based alloys, aluminium, aluminium alloys, steel,
other conductive metals, and other conductive or non-conductive materials.
[0036] A person skilled in the art will appreciate the different embodiments illustrated
in the figures 1-2 and 4-5 may be free combined providing conductors comprising at
least two conductor elements of different materials joint to form one conductor, wherein
the cross-sectional structure of each conductor element may be freely selected.
1. Subsea power cable (1) comprising a conductor (10) surrounded by at least one layer
of insulation (20) and at least one layer of armouring (40), the conductor (10) comprising
at least a first conductor element (12b, 15b) and a second conductor element (12a,
15a), where the first conductor element (12b, 15b) is made of a first material and
the second conductor element (12a, 15a) is made of a second material and where the
first and the second materials are different, characterized in that the conductor (10) comprises a core, a first layer surrounding the core and a second
layer surrounding the first layer, the first layer and the second layer each being
made of first conductor elements and second conductor elements.
2. Subsea power cable according to claim 1, wherein the conductor (10) comprises a third
conductor element (12c, 15c) made of a third material different from the first and
the second material.
3. Subsea power cable according to claim 1 or 2, wherein the conductor elements of different
materials are distributed throughout the cross-section of the conductor.
4. Subsea power cable according to any one of the previous claims, wherein the two or
more different types of materials are each a material independently selected from
the group comprising copper, copper alloys, aluminium, aluminium alloys, steel, other
metals or non-metallic materials.
5. Subsea power cable according to claim 4, wherein the first material is copper or a
copper alloy and the second material is aluminium or an aluminium alloy.
6. Subsea power cable according to claim 4, wherein the first material is aluminium or
an aluminium alloy and the second material is copper or a copper alloy.
7. Subsea power cable according to claim 2 and claim 5 or6, wherein the third material
is steel.
8. Subsea power cable according to any one of the previous claims, wherein the subsea
power cable is a high voltage subsea power cable.
9. Subsea power cable according to any one of the previous claims, wherein al least one
of the first, second or third material is aluminium or aluminium alloy.
1. Unterseestromkabel (1), umfassend einen Leiter (10), der von mindestens einer Isolierschicht
(20) und mindestens einer Panzerschicht (40) umschlossen ist, wobei der Leiter (10)
mindestens ein erstes Leiterelement (12b, 15b) und ein zweites Leiterelement (12a,
15a) umfasst, wobei das erste Leiterelement (12b, 15b) aus einem ersten Material besteht
und das zweite Leiterelement (12a, 15a) aus einem zweiten Material besteht, und wobei
das erste und zweite Material unterschiedlich sind, dadurch gekennzeichnet, dass der Leiter (10) einen Kern, eine den Kerm umschließende erste Schicht und eine die
erste Schicht umschließende zweite Schicht umfasst, wobei die erste und zweite Schicht
jeweils aus ersten und zweiten Leiterelementen bestehen.
2. Unterseestromkabel nach Anspruch 1, wobei der Leiter (10) ein drittes Leiterelement
(12c, 15c) aus einem dritten Material umfasst, das sich vom ersten und zweiten Material
unterscheidet.
3. Unterseestromkabel nach Anspruch 1 oder 2, wobei die Leiterelemente aus unterschiedlichen
Materialien durch den ganzen Querschnitt des Leiters verteilt sind.
4. Unterseestromkabel nach einem der vorstehenden Ansprüche, wobei die zwei oder mehr
unterschiedlichen Materialarten jeweils ein Material sind, das unabhängig aus folgender
Gruppe gewählt ist: Kupfer, Kupferlegierungen, Aluminium, Aluminiumlegierungen, Stahl,
sonstige mEtalle oder nichtmetallische Stoffe.
5. Unterseestromkabel nach Anspruch 4, wobei das erste Material Kupfer oder eine Kupferlegierung
ist und das zweite Material Aluminium oder eine Aluminiumlegierung ist.
6. Unterseestromkabel nach Anspruch 4, wobei das erste Material Aluminium oder eine Aluminiumlegierung
ist und das zweite Material Kupfer oder eine Kupferlegierung ist.
7. Unterseestromkabel nach Anspruch 2 und Anspruch 5 oder 6, wobei das dritte Material
Stahl ist.
8. Unterseestromkabel nach einem der vorstehenden Ansprüche, wobei das Unterseestromkabel
ein Hochspannungs-Unterseestromkabel ist.
9. Unterseestromkabel nach einem der vorstehenden Ansprüche, wobei mindestens eines des
ersten, zweiten oder dritten Materials Aluminium oder eine Aluminiumlegierung ist.
1. Câble d'alimentation sous-marin (1) comprenant un conducteur (10) entouré par au moins
une couche d'isolation (20) et au moins une couche d'armure (40), le conducteur (10)
comprenant au moins un premier élément conducteur (12b, 15b) et un deuxième élément
conducteur (12a, 15a), où le premier élément conducteur (12b, 15b) est constitué d'un
premier matériau et le deuxième élément conducteur (12a, 15a) est constitué d'un deuxième
matériau et où les premier et deuxième matériaux sont différents, caractérisé en ce que le conducteur (10) comprend une âme, une première couche entourant l'âme et une deuxième
couche entourant la première couche, la première couche et la deuxième couche étant
chacune constituées de premiers éléments conducteurs et de deuxièmes éléments conducteurs.
2. Câble d'alimentation sous-marin selon la revendication 1, dans lequel le conducteur
(10) comprend un troisième élément conducteur (12c, 15c) constitué d'un troisième
matériau différent du premier et du deuxième matériau.
3. Câble d'alimentation sous-marin selon la revendication 1 ou 2, dans lequel les éléments
conducteurs de différents matériaux sont répartis dans l'ensemble de la section transversale
du conducteur.
4. Câble d'alimentation sous-marin selon l'une quelconque des revendications précédentes,
dans lequel les deux ou plus de deux types de matériaux différents sont chacun un
matériau indépendamment choisi dans le groupe comprenant le cuivre, des alliages de
cuivre, l'aluminium, des alliages d'aluminium, l'acier, d'autres métaux ou matériaux
non métalliques.
5. Câble d'alimentation sous-marin selon la revendication 4, dans lequel le premier matériau
est le cuivre ou un alliage de cuivre et le deuxième matériau est l'aluminium ou un
alliage d'aluminium.
6. Câble d'alimentation sous-marin selon la revendication 4, dans lequel le premier matériau
est l'aluminium ou un alliage d'aluminium et le deuxième matériau est le cuivre ou
un alliage de cuivre.
7. Câble d'alimentation sous-marin selon la revendication 2 et la revendication 5 ou
6, dans lequel le troisième matériau est l'acier.
8. Câble d'alimentation sous-marin selon l'une quelconque des revendications précédentes,
le câble d'alimentation sous-marin étant un câble d'alimentation sous-marin à haute
tension.
9. Câble d'alimentation sous-marin selon l'une quelconque des revendications précédentes,
dans lequel au moins l'un parmi le premier, le deuxième ou le troisième matériau est
l'aluminium ou un alliage d'aluminium.