Method and apparatus for transferring electrical power for subsea applications

1. A method for transferring electrical power in the sea, the method comprising:

generating AC power;

guiding, at least partially underwater, the AC power through a cable from a first end of the cable to a second end of the cable;

wherein a first reactor is connected adjacent to the first end of the cable;

wherein a second reactor is connected adjacent to the second end of the cable;

wherein inductances of the first reactor and inductances of the second reactor are selected to at least partially compensate for reactive power generated in the cable;

wherein the inductances of the first reactor and second reactor are adjusted to avoid resonances close to a frequency of the AC power; and

adjusting the frequency of the AC power such that a voltage ratio between a second voltage and a first voltage changes less than a threshold, when a power consumption of a load connected to the second end of the cable changes from a first value to a second value;

wherein the second voltage is indicative of a potential difference between the second end of the cable and a reference potential;

wherein the first voltage is indicative of a potential difference between the first end of the cable and the reference potential.

2. The method of claim 1 , wherein one or more additional reactors is connected along the cable between the first end of the cable and the second end of the cable.

3. The method of claim 2 , wherein the inductances of the first reactor and the inductances of the second reactor, wherein the inductances of the one or more additional reactors, or wherein the inductances of the first reactor, the inductances of the second reactor, and the inductances of the one or more additional reactors are each selected based on a frequency of the AC power and a property of the cable.

4. The method of claim 2 , wherein the first reactor and the second reactor, wherein the one or more additional reactors, or wherein the first reactor, the second reactor, and the one or more additional reactors are connectable and disconnectable from the cable.

5. The method of claim 2 , wherein at least one of the first reactor, the second reactor, and the one or more additional reactors comprises an active filter, a passive filter, or an active filter and a passive filter.

6. The method of claim 2 , wherein the first reactor and the second reactor, wherein the one or more additional reactors, or wherein the first reactor, the second reactor, and the one or more additional reactors provide reactive compensation for 16.7 Hz or 50 Hz.

7. The method of claim 1 , wherein the adjusting of the frequency comprises:

calculating a plurality of voltage ratio changes;

considering at least two test power consumptions of loads for each test frequency of a plurality of test frequencies in order to obtain a respective voltage ratio change; and

selecting the frequency to be adjusted from the plurality of test frequencies having a calculated voltage ratio change that is lower than the threshold.

8. The method of claim 1 , further comprising:

calculating a plurality of input currents, wherein each input current of the plurality of input currents represents a respective current of the generated AC power supplied to the first end of the cable;

considering at least one test power consumption of a load for each test frequency of a plurality of test frequencies; and

selecting the frequency to be adjusted from the plurality of test frequencies having an input current that is within a range determined by a rating of the cable.

9. The method of claim 1 , further comprising:

selecting a frequency between resonance peaks of a calculated voltage ratio curve, wherein the frequency depends on a property of the cable.

10. The method of claim 1 , further comprising:

transforming a voltage of the AC power to a higher voltage and supplying the transformed voltage to the first end of the cable;

transforming the AC power guided through the cable at the second end of the cable and supplying the transformed AC power to a load; or

transforming the voltage of the AC power to the higher voltage, supplying the transformed voltage to the first end of the cable, transforming the AC power guided through the cable at the second end of the cable, and supplying the transformed AC power to the load.

11. The method of claim 1 , wherein:

a frequency of the AC power is between 10 Hz and 300 Hz;

at least a portion of a length of the cable is arranged underwater; and

the AC power is supplied from a AC power supply to the first end of the cable.

12. The method of claim 1 , further comprising:

adjusting the frequency, the first voltage, or the frequency and the first voltage based on the load;

wherein the adjusting comprises decreasing the frequency when power consumption of the load increases;

wherein the first voltage is predetermined;

wherein the second voltage is calculated for a given power consumption of the load using a model of the cable comprising a plurality of PI-elements;

wherein the second end of the cable is between 1000 m and 4000 m below sea level;

wherein the cable has a length between 100 km and 1000 km; and

wherein the voltage at the cable is between 80 kV and 100 kV.

13. The method of claim 1 , wherein between 3 and 60 additional reactors are connected along the cable between the first end and the second end.

14. The method of claim 1 , wherein the voltage ratio between the second voltage and the first voltage changes less than the threshold when the power consumption of the load connected to the second end of the cable changes from 0 MW to 100 MW.

15. The method of claim 7 , further comprising:

calculating a plurality of input currents, wherein each input current of the plurality of input currents represents a respective current of the generated AC power supplied to the first end of the cable;

considering at least one test power consumption of a load for each test frequency of the plurality of test frequencies; and

selecting the frequency to be adjusted from the plurality of test frequencies having an input current that is within a range determined by a rating of the cable.

16. The method of claim 1 , further comprising:

selecting a frequency between a first resonance peak and a second resonance peak of a calculated voltage ratio curve or between a second resonance peak and a third resonance peak of the calculated voltage ratio curve;

wherein the frequency depends on a cross-sectional size of the cable, a material of the cable, or the cross-sectional size and the material of the cable.

17. The method of claim 1 , wherein a frequency of the AC power is between 50 Hz and 150 Hz.

18. The method of claim 1 , wherein a frequency of the AC power is different than 50 Hz.

19. The method of claim 11 , wherein:

at least 80% and up to 100% of the length of the cable is arranged underwater; and

the AC power is supplied to the first end of the cable from a generator or a converter.

20. The method of claim 12 , wherein the cable has a length between 200 km and 600 km.

21. An apparatus configured to transfer electrical power in the sea, the apparatus comprising:

a power supply configured to generate AC power;

a cable configured to guide, at least partially underwater, the AC power through the cable from a first end of the cable to a second end of the cable;

a first reactor connected adjacent the first end of the cable; and

a second reactor connected adjacent the second end of the cable;

wherein inductances of the first reactor and inductances of the second reactor are selected to at least partially compensate for reactive power generated in the cable;

wherein the inductances of the first reactor and second reactor are adjusted to avoid resonances close to a frequency of the AC power; and

wherein the frequency of the AC power is adjusted such that a voltage ratio between a second voltage and a first voltage changes less than a threshold, when a power consumption of a load connected to the second end of the cable changes from a first value to a second value; wherein the second voltage is indicative of a potential difference between the second end of the cable and a reference potential; wherein the first voltage is indicative of a potential difference between the first end of the cable and the reference potential.