METHOD FOR INSTALLING AN OFFSHORE INSTALLATION

Abstract

A method for installing an offshore installation is provided, the method including: a) providing a pipe for connecting the offshore installation with another offshore installation or an onshore installation; b) arranging an electrical cable inside the pipe; c) determining a level at or above the seabed, wherein the pipe includes a first portion arranged below the determined level and a second portion arranged above the determined level, and wherein the electrical cable is arranged inside the pipe so as to form a gap with an inner wall of the pipe along the first and second portion; d) determining an amount of cooling liquid such that, when the cooling liquid has a first temperature, the cooling liquid fills the gap along the first portion of the pipe, wherein the second portion of the pipe is free of the cooling liquid, and when the cooling liquid cools the electrical cable.

Claims

1. A method for installing an offshore installation, the method comprising: a) providing a pipe for connecting the offshore installation with another offshore installation or an onshore installation; b) arranging an electrical cable inside the pipe; c) determining a level at or above the seabed, wherein the pipe comprises a first portion arranged below the level and a second portion arranged above the determined level, and wherein the electrical cable is arranged inside the pipe to form a gap with an inner wall of the pipe along the first portion and second portion; d) determining an amount of cooling liquid such that; when the cooling liquid has a first temperature, the cooling liquid fills the gap along the first portion of the pipe, wherein the second portion the pipe is free of the cooling liquid, and when the cooling liquid cools the electrical cable and has a second temperature higher than the first temperature, it is expanded from the first portion into the second portion, filling the gap along the first portion and the second portion of the pipe and; and e) providing the determined amount of the cooling liquid inside the pipe.

2. The method according to claim 1, wherein the level is a sea level at the offshore installation, a level of the seabed below the offshore installation or a level between the sea level and the seabed level.

3. The method according to claim 1, wherein the level is a level at or below which an outside temperature of the pipe is high enough so that the cooling liquid inside the first portion of the pipe is not freezing.

4. The method according to claim 1, wherein the cooling liquid has the first temperature during a state in which no power is transmitted through the electrical cable.

5. The method according to claim 1, wherein the cooling liquid has the second temperature during a state in which power is transmitted through the electrical cable.

6. The method according to claim 1, wherein the determined amount of the cooling liquid is provided inside the pipe in step e) by filling the amount of the cooling liquid into the pipe.

7. The method according to claim 1, further comprising filling a larger amount than the amount of the cooling liquid into the pipe, and wherein the amount of the cooling liquid is provided in step e) inside the pipe by draining an excess amount of the cooling liquid from the pipe.

8. The method according to claim 7, wherein the electrical cable is arranged inside the pipe in step b) by pushing the electrical cable by the cooling liquid, thereby filling the larger amount of the cooling liquid into the pipe.

9. The method according to claim 7, wherein the excess amount of the cooling liquid is drained from the pipe by a pump or by pressurized air.

10. The method according to claim 7, wherein the pipe is ventilated during the draining of the excess amount of the cooling liquid from the pipe.

11. The method according to claim 10, wherein the pipe is ventilated by a ventilation element arranged at a free end of the second portion of the pipe, the ventilation element including a floater.

12. The method according to claim 7, wherein the amount of the cooling liquid or the larger amount of the cooling liquid is filled into the pipe through an access port of the pipe.

13. The method according to claim 12, wherein the excess amount of the cooling liquid is drained from the pipe through the access port of the pipe.

14. The method according claim 1, wherein one or both of the offshore installation and the other offshore installation is/are an energy generating installation, a wind turbine, a substation of a wind farm, a tidal power facility, an oil rig and/or a gas rig.

15. The method according to claim 1, wherein the cooling liquid is water, seawater, a brine solution and/or a glycol aqueous solution.

Description

BRIEF DESCRIPTION

[0078] Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

[0079] FIG. 1 shows an offshore wind farm according to an embodiment;

[0080] FIG. 2 shows a detailed view of a portion II of a wind turbine of the offshore wind farm of FIG. 1, the wind turbine being connected by a pipe with another wind turbine of the wind farm of FIG. 1, the pipe containing inside an electrical cable and cooling liquid at a first temperature;

[0081] FIG. 3 shows an embodiment of arranging the electrical cable inside the pipe of FIG. 2;

[0082] FIG. 4 shows a view similar to FIG. 2 but with an excess amount of the cooling liquid drained from the pipe;

[0083] FIG. 5 shows a view similar to FIG. 4 but with the cooling liquid heated to a second temperature and expanded inside the pipe;

[0084] FIG. 6 shows a perspective view of a vent system configured to be arranged at the pipe;

[0085] FIG. 7 shows a partial side view of the vent system of FIG. 6;

[0086] FIG. 8 shows a detailed view of a ventilation element of the vent system of FIG. 6 in two different states;

[0087] FIG. 9 shows a flowchart illustrating a method for installing the wind turbine of FIG. 1 according an embodiment;

[0088] FIG. 10 shows a first aspect of step S5 of the method of FIG. 9; and

[0089] FIG. 11 shows a second aspect of step S5 of the method of FIG. 9.

DETAILED DESCRIPTION

[0090] FIG. 1 shows an offshore wind farm 1 according to an embodiment. The offshore wind farm 1 comprises several offshore wind turbines. As an example, an offshore wind turbine 2 and another offshore wind turbine 3 of the wind farm 1 are shown in FIG. 1. In addition, an onshore wind turbine 3′ is shown in FIG. 1.

[0091] Each of the wind turbines 2 and 3 comprises a rotor 4 connected to a generator (not shown) arranged inside a nacelle 5. The nacelle 5 is arranged at the upper end of a tower 6 of the wind turbine 2, 3. The tower 6 is erected on a foundation 7 such as a monopile or tripile. The foundation 7 is connected to and/or driven into the seabed 8 and extends above the sea water 9. The tower 6 can be erected directly on the foundation 7, or the tower 6 can be connected to a transition piece (not shown) and the transition piece is erected on the foundation 7.

[0092] During operation of the wind turbine 2, 3, the wind's kinetic energy is converted into electrical energy by the generator in the nacelle 5. The power generated in the generator is transmitted via an interior power cable to a switch gear (not shown) in a lower part of the tower 6 or in the transition piece. The generated power is transmitted from the switch gear via a further interior power cable to a hang-off zone 10 (FIG. 2) of the lower part of the tower 6 or the transition piece. For an electrical connection from the hang-off zone 10 onward, electrical transmission means are required to connect the interior power cable of the wind turbine 2 to another offshore installation 3 or an onshore installation 3′.

[0093] In the following an improved method for installing an offshore installation such as the wind turbine 2, is described with respect to FIGS. 2 to 11. In particular, a method for installing an electrical connection between the wind turbine 2 and the other offshore wind turbine 3 is described. Although not described in the following, the method can also be applied for installing an electrical connection between the wind turbine 2 and the onshore wind turbine 3′.

[0094] In step S1 of the method, a pipe 11 is provided for connecting the wind turbine 2 with the wind turbine 3.

[0095] The pipe 11 is, in particular, long enough to connect the wind turbine 2 with the wind turbine 3. The pipe 11 has, for example, a length of several kilometers and/or has any other length required to connect the wind turbines 2 and 3 with each other. The pipe 11 is a flexible tube made, for example, of plastic. The pipe 11 is, for example, steel armored.

[0096] For providing the pipe 11, the seabed 8 is trenched between the wind turbine 2 and the other wind turbine 3. The pipe 11 is, for example, provided by unwinding the pipe 11 from a drum (not shown) arranged on a vessel (not shown), lowering the pipe 11 from the vessel and laying it into the trench. Instead of the vessel, the pipe 11 could also be supplied by a seabed vehicle (not shown).

[0097] The pipe 11 is then connected to the wind turbine 2 and the other wind turbine 3. In the following, the connection of the pipe 11 to the wind turbine 2 is described in detail. The connection of the pipe 11 to the other wind turbine 3 may be performed in a similar manner. The pipe 11 is, in particular, connected to a portion of the wind turbine 2 which is above the level 9′ of the sea water 9.

[0098] FIG. 2 shows a detailed view II of the wind turbine 2 of FIG. 1. In FIG. 2 a lower part of the tower 6 including the hang-off zone 10 and the foundation 7 of the wind turbine 2 is shown. The free end 12 of the pipe 11 is, in particular fixedly, connected to the hang-off zone 10 of the wind turbine 2. Furthermore, the other free end 13 (FIG. 1) of the pipe 11 is, in particular fixedly, connected to a hang-off zone (not shown) of the other wind turbine 3.

[0099] In step S2 of the method, an electrical cable 14 (FIG. 2) is arranged inside the pipe 11. The electrical cable 14 is, in particular, arranged inside the pipe 11 by inserting it into one end (e.g., the free end 12) of the pipe 11 and pulling or pushing it to the other end (e.g., the other free end 13, FIG. 1) of the pipe 11. The electrical cable 14 is, for example, unwound from a cable drum, such as the cable drum 15 shown in FIG. 3.

[0100] FIG. 3 shows an example of arranging the electrical cable 14 inside the pipe 11 by pushing the electrical cable 14 by a cooling liquid 16, such as water and/or sea water, through the pipe 11. As shown in FIG. 3, an adapter 17 is connected to the free end 12 of the pipe 11. The adapter 17 provides on one side thereof a liquid-tight connection with the pipe 11 and comprises on the other side thereof both an opening 18 for the electrical cable 14 and a separate liquid inlet port 19. A free end 20 of the electrical cable 14 is connected to a plug 33 and inserted into the opening 18 of the pipe 11. The cooling liquid 16 is filled with high pressure into the liquid inlet port 19 and pushes, via the plug 33, the electrical cable 14 through the pipe 11 until the electrical cable 14 emerges at the other free end 13 (FIG. 1) of the pipe 11. While being pushed through the pipe 11, the electrical cable 14 is continuously unwound from the cable drum 15 and guided by guiding means 32 towards the opening 18.

[0101] In the example of FIG. 3, the pipe 11 is filled during arranging of the electrical cable 14 with the cooling liquid 16.

[0102] As shown in FIG. 2, the electrical cable 14 arranged inside the pipe 11 forms a gap 21 with an inner wall of the pipe 11. FIG. 2 shows a state in which the gap 21 of the pipe 11 is completely filled, i.e. along the entire length of the pipe 11, with the cooling liquid 16.

[0103] In step S3 of the method, a level 22 at or above the seabed 8 is determined such that the cooling liquid 16 in the pipe 11 is not freezing below this level 22. In other words, the level 22 is a level at or below which a temperature outside of the pipe 11 is high enough so that the cooling liquid 16 inside the pipe 11 and below this level 22 is not freezing.

[0104] The level 22 is determined based on weather and environmental conditions at the wind turbine 2. In the example of FIG. 2, it is determined that a minimum temperature of the sea water 9 is below zero degree Celsius. The sea water 9 contains, for example, sea ice. Thus, the cooling liquid 16 in a portion of the pipe 11 surrounded by the sea water 9 is at the risk of freezing in this example. Therefore, the level 22 has been determined here to be the level 8′ of the seabed 8.

[0105] The pipe 11 comprises a first portion 23 arranged below the determined level 22 and a second portion 24 arranged above the determined level 22.

[0106] In step S4 of the method, an amount 25 (FIG. 4) of the cooling liquid 16 is determined such that, when the cooling liquid 16 has a first temperature T1, the cooling liquid 16 having the amount 25 fills the gap 21 only along the first portion 23 of the pipe 11 but not along the second portion 24 of the pipe 11. The second portion 24 of the pipe 11 in FIG. 4 is free of the cooling liquid 16 and is filled with air.

[0107] The first temperature T1 is, for example, a temperature of the cooling liquid 16 in a state in which the wind turbine 2 is not generating power and is, therefore, not transmitting power through the electrical cable 14. The state in which the wind turbine 2 is not transmitting power through the electrical cable 14 is, for example, a state in which no wind is blowing or a state in which the rotor 4 has been blocked for safety reasons because winds are too strong.

[0108] During operation of the wind turbine 2, power is transmitted through the electrical cable 14 and is, thus, heating up the electrical cable 14. The cooling liquid 16 in the gap 21 of the pipe 11 cools the electrical cable 14. During the cooling process, the cooling liquid 16 heats up to a second temperature T2 and expands.

[0109] The amount 25 of the cooling liquid 16 is further determined in step S4 such that, when the cooling liquid 16 cools the electrical cable 14 and, therefore, has the second temperature T2, it is expanded from the first portion 23 into the second portion 24. Due to this expansion, the cooling liquid 16 fills the gap 21 along the first and second portions 23, 24 of the pipe 11, as shown in FIG. 5. As the cooling liquid 16 is heated here by the power transmitting electrical cable 14, there is no risk of freezing of the cooling liquid 16 in the second portion 24.

[0110] In step S5 of the method, the determined amount 25 of the cooling liquid 16 is provided inside the pipe 11. In a first aspect of the embodiment (FIG. 10), the method comprises the step S2′ of filling a larger amount 26 than the determined amount 25 into the pipe 11, and step S5 comprises the step S5′ of draining the excess amount from the pipe 11.

[0111] In the example shown in FIGS. 2 to 5, the pipe 11 has been filled (S2′) already with a larger amount 26 (FIG. 2) than the determined amount 25 (FIG. 4) of cooling liquid 16 during step S2. Therefore, in this example, the determined amount 25 of the cooling liquid 16 is provided in step S5 by draining (S5′) the excess amount of the cooling liquid 16, i.e. the amount by which the larger amount 26 is in excess of the determined amount 25.

[0112] The pipe 11 comprises at its free end 12, for example, a vent system 27, as shown in FIGS. 6 to 8. FIG. 6 shows a perspective view of the vent system 27. The vent system 27 of FIG. 6 is configured to serve, as an example, four pipes 11. FIG. 7 shows the vent system 27 in a partial side view along with one pipe 11, and FIG. 8 shows a ventilation element 28 of the vent system 27 in two different states.

[0113] The vent system 27 comprises for each pipe 11 an access port 29 for draining and/or filling of the cooling liquid 16. Further, the vent system 27 comprises the ventilation element 28 fluidly connected to each access port 29 for ventilating the pipe 11 during draining of the cooling liquid 16 and/or during expansion of the cooling liquid 16.

[0114] The excess amount of the cooling liquid 16 is drained from the pipe 11 by connecting a hose (not shown) via a pump and a liquid flow meter (not shown) with the access port 29 of the vent system 27. The cooling liquid 16 is drained by the pump from the pipe 11 and through the hose, for example, into a tank (not shown) or into the sea. The cooling liquid 16 is drained until the drained amount, as measured by the liquid flow meter, is the excess amount.

[0115] As shown in FIG. 8, the ventilation element 28 comprises a floater 30. As shown in the bottom view of FIG. 8, when the pipe 11 is completely filled with the cooling liquid 16, the floater 30 seals the ventilation element 28 to prevent cooling liquid 16 from leaking through the ventilation element 28. When the cooling liquid 16 is drained from the pipe 11, the floater 30 sinks and does not seal the ventilation element 28 any more so that air 31 can be drawn in, as shown in the top view of FIG. 8.

[0116] For example, the level 22 may also be the level 9′ of the sea water 9 or a level between the sea water level 9′ and the seabed level 8′.

[0117] For example, the arranging of the electrical cable 14 may not include filling of the cooling liquid 16 into the pipe 11. Then, in a second aspect of the embodiment (FIG. 11), step S5 of providing the determined amount 25 of the cooling liquid 16 into the pipe 11 may comprise the step S5″ of filling the determined amount 25 of the cooling liquid 16 into the pipe 11. Thus, in the second aspect, the correct amount of the cooling liquid 16 is directly filled into the pipe 11 without the need to drain an excess amount.

[0118] Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

[0119] For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements.