Transferring electrical power for subsea applications

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

generating AC power;

guiding the AC power through a cable from a first end of the cable to a second end of the cable; and

adjusting a frequency of the AC power guided through the cable in dependence of a length of the cable between the first end and the second end of the cable, wherein the frequency 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, and

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

2. The method according to claim 1 wherein the power consumption changes from 0 MW to 100 MW.

3. A method for transferring electrical power, the method comprising:

generating AC power;

guiding the AC power through a cable from a first end of the cable to a second end of the cable; and

adjusting a frequency of the AC power guided through the cable in dependence of a length of the cable between the first end and the second end of the cable, wherein the frequency is adjusted such that a second voltage changes less than a voltage 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,

the method further comprising:

supplying the AC power from the second end to the load.

4. The method according to claim 1 , wherein an absolute value of the threshold is 0.5.

5. The method according to claim 1 , wherein an absolute value of the threshold is 0.2.

6. The method according to claim 1 , wherein adjusting the frequency comprises calculating plural voltage ratio changes for plural test frequencies, for each test frequency considering at least two test power consumptions of loads in order to obtain the respective voltage ratio change,

wherein the frequency to be adjusted is selected from the plural test frequencies for which the calculated voltage ratio change is lower than the threshold.

7. The method according to claim 1 , further comprising

calculating plural input currents for plural test frequencies, the input current representing a respective current of the generated AC power supplied to the first end of the cable, and

for each test frequency, considering at least one test power consumption of a load,

wherein the frequency to be adjusted is selected from the plural test frequencies for which the input current is within a range according to a rating of the cable.

8. A method for transferring electrical power, the method comprising:

generating AC power;

guiding the AC power through a cable from a first end of the cable to a second end of the cable; and

adjusting a frequency of the AC power guided through the cable in dependence of a length of the cable between the first end and the second end of the cable, wherein the frequency between resonance peaks according to a calculated voltage ratio is selected as between a first and a second resonance peak or between the second and a third resonance peak,

wherein the frequency further depends on properties of the cable.

9. The method according to 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.

10. The method according to claim 1 , further comprising:

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

11. The method according to claim 1 , wherein the frequency of the AC power is between 10 Hz and 300 Hz,

wherein 80-100% of the cable is arranged underwater.

12. The method according to claim 1 , wherein the AC power is supplied from an AC power supply comprising a generator or a converter to the first end of the cable.

13. The method according to claim 1 , wherein the first voltage is predetermined and the second voltage is calculated for a given power consumption of the load.

14. The method according to claim 13 wherein the second voltage is calculated utilizing a model of the cable with PI-elements.

15. The method according to claim 1 , wherein the second end of the cable is between 100 m and 4000 m below sea level, and wherein the cable has a length between 100 km and 1000 km.

16. The method according to claim 1 , wherein the voltage at the cable is between 80 kV and 100 kV.

17. The method according to claim 1 , further comprising:

connecting a first reactor near the first end of the cable, connecting a second reactor near the second end of the cable, connecting plural reactors at plural locations along the cable, or combinations thereof,

further comprising, depending on the load, adjusting the frequency, the first voltage, or both when power consumption of the load increases.

18. The method according to claim 17 wherein adjusting the frequency comprises decreasing the frequency.

19. The method according to claim 1 wherein guiding comprises guiding at least partially underwater.

20. The method according to claim 1 wherein adjusting comprises adjusting the frequency of the AC power to be larger than a power grid frequency.

21. The method according to claim 20 wherein adjusting to be larger than the power grid frequency comprises adjusting to be larger than 50-60 Hz.

22. An arrangement for transferring electrical power in the sea, the arrangement comprising:

a power source operable to generate AC power;

a cable having a first end to which the AC power is supplied and being arranged to guide the AC power to a second end of the cable,

wherein the power source includes a converter configured to adjust a frequency of the AC power guided through the cable in dependence of a length of the cable between the first end and the second end of the cable to be larger than a conventional grid frequency, wherein the power source is configured to adjust the frequency 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 represents a potential difference between the first end of the cable and the reference potential.

23. An arrangement for transferring electrical power in the sea, the arrangement comprising:

a power source operable to generate AC power;

a cable having a first end to which the AC power is supplied and being arranged to guide the AC power to a second end of the cable,

wherein the power source includes a converter configured to adjust a frequency of the AC power guided through the cable in dependence of a length of the cable between the first end and the second end of the cable to be larger than a conventional grid frequency, wherein the power source is configured to adjust the frequency such that a second voltage changes less than a voltage threshold, when a power consumption of the AC power supplied to 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.

24. An arrangement for transferring electrical power in the sea, the arrangement comprising:

a power source operable to generate AC power;

a cable having a first end to which the AC power is supplied and being arranged to guide the AC power to a second end of the cable,

wherein the power source includes a converter configured to adjust a frequency of the AC power guided through the cable in dependence of a length of the cable between the first end and the second end of the cable to be larger than a conventional grid frequency, wherein the power source is configured to select the frequency between resonance peaks according to a calculated voltage ratio, the selection being between a first and a second resonance peak or between the second and a third resonance peak, wherein the frequency further depends on properties of the cable.