WO2002093715A1

WO2002093715A1 - Electric power generation system

Info

Publication number: WO2002093715A1
Application number: PCT/SE2002/000932
Authority: WO
Inventors: Li Ming; Peter Löfgren; Gang Zhou; Rongsheng Liu
Original assignee: Abb Ab
Priority date: 2001-05-15
Filing date: 2002-05-15
Publication date: 2002-11-21
Also published as: SE0101727D0

Abstract

An electric power generation system including at least one submerged water turbine (17) that is driven by an underwater current (20), at least one electric generator (10) and mechanical transmission means (16) interconnecting them, where said at least one generator is enclosed within a fluid-tight casing (11) and contains an induction winding (30) incorporating an electric conductor (31) surrounded by an insulation system comprising an semiconducting layer (32) surrounding said conductor and compressed gas surrounding said semiconducting layer (34), said compressed gas providing electric insulation and facilitating better cooling of said generator.

Description

Electric power generation system

TECHNICAL FIELD

The present invention relates to an electric power generation system and a method for generating electric power. More particularly, the present invention concerns a system and a method for efficiently converting the kinetic energy of underwater currents, such as ocean currents, like the Gulf Stream, diurnal tide streams, and river currents into electric power.

BACKGROUND OF THE INVENTION

Underwater currents, existing at a depth of 20-200 m below water level, for example sea-level, as distinguished from wind and solar activity, are of a relatively steady and predictable nature and they are only slightly influenced by the weather. Due to the much greater density of water compared with air (the density of water is about 800 times greater than the density of air), much lower underwater current velocities are needed to give the same power density, i.e. power per unit area of flow. Underwater currents contain a large amount of energy (up to 65 kW/m²) that can be harnessed using devices that convert their kinetic energy into electric power. An advantage of such devices as compared with a wind power plant is that there is no environmental impact such as visual or acoustic intrusion.

Devices that convert the kinetic energy of underwater currents into electric power comprise rotary means, such as a propeller, that is located in an underwater current and which turns in response thereto. The rotation of the rotary means is utilized to mechanically rotate the shaft/rotor of an electric generator to produce a substantially constant electric output. Electric power from a water-based generator can be transmitted through electric cables to a power transmission network on land or to a water-based infrastructure such as an oil or gas platform.

WO 97/45921 describes a rotating electric machine including an induction winding containing an electric conductor enclosed within an insulation system comprising a first semiconducting layer, which is provided with a surrounding solid insulation layer and a second semiconducting layer that encases the solid insulation layer. The use of such an induction winding, in the stator winding of a rotating electric machine, allows the voltage of the rotating electric machine to be increased to such a level that it can be connected directly to a power network without the need of an intermediate transformer. Consequently this leads to savings in both economic terms and with regards to space requirements for installations comprising a rotating electric machine as a transformer constitutes an extra cost and reduces the total efficiency of the system. Such electric machines generally operate at high voltages i.e. voltages exceeding 10kV, typically in the range 36kV up to 800kV or higher.

The induction windings of such rotating electric machines require a relatively thick insulation system due to the high voltage. The insulation system provides the desirable electric insulation but, because electric insulation materials are generally also good thermal insulators, it also unavoidably provides good thermal insulation. A thick insulation system around the machine's induction winding hinders heat from being dissipated from the winding's electric conductor. During the rotating machine's use, heat is generated inside the machine's magnetic core and induction winding. The rotating machine's components have to be cooled to ensure their optimum performance and prolonged lifetime. The thick insulation system also entails an increased radius of curvature of the induction winding, which in turn results in an increased size of the winding overhang. WO 00/74214 A1 concerns the cooling of a high-voltage rotating electric machine of the type previously described. It relates to the utilization of the same kinetic-energy-carrying-medium that drives the rotating electric machine to cool at least part of said machine by allowing said medium to flow into contact and past the machine's magnetic core, induction winding and electric connections. The use of such a rotating electric machine to generate electric energy from underwater currents might be apparent to a person skilled in the art however there are many practical problems that would need to be solved. The machine's components need to withstand the corrosive underwater environment and be adapted to withstand the pressure that the submerged rotating electric machine would be exposed to. Suitable coatings would need to be applied to protect the rotating electric machine's components from water or moisture and the waterproofed generator would need to be cleaned frequently to prevent the build up of any fouling solid matter that may hinder its performance. Maintenance and repair work cannot reasonably be done underwater in an area of very high underwater currents and so the generator would frequently have to be raised to water level to be cleaned.

SUMMARY OF THE INVENTION

It is an object of this invention to provide an efficient, environmentally friendly, cost-efficient electric power generation system to provide energy from a sustainable source for both small and large-scale applications.

This and other objects of the invention are achieved by utilizing an electric power generation system including at least one submerged water turbine that is driven by underwater currents, at least one electric generator and mechanical transmission means interconnecting them. Said at least one turbine may be of the axial- or cross-flow type. Said at least one generator is enclosed within a fluid-tight, pressurized casing and contains an induction winding incorporating an electric conductor surrounded by an insulation system comprising a semiconducting layer surrounding said conductor and compressed gas, said compressed gas providing electric insulation and facilitating cooling of said at least one generator. Compressed gas meaning gas having a pressure greater than 1 bar.

In a preferred embodiment of the invention a solid insulation layer surrounds said semiconducting layer, said solid insulation layer becoming surrounded by compressed gas when said casing is pressurized. The semiconducting layer and the solid insulation layer provide protection and mechanical reinforcement that that limit damage to the electric conductor as it is being wound into position. In a further embodiment of the invention said electric cable comprises additional reinforcement means, such as a thin layer or coating, applied around said solid insulation layer. The compressed gas fills the gap between the induction winding's solid insulation layer and the walls of the stator slots through which it is wound. Depending on the gas pressure, said gap can have a breakdown voltage equal to or much higher than the solid insulation layer. For example if a gap (1-30mm) is filled with air at a pressure of 10 bar, a breakdown strength of up to 20 kV/mm could be reached. This compressed gas-filled gap provides good electric insulation, which means that a much thinner solid insulation layer can be used in said induction winding. This leads to a much thinner cable having a much smaller radius of curvature, giving rise to a decreased size of winding overhang.

Another very important advantage of said induction winding is that a thinner solid insulation layer provides less thermal insulation. The compressed gas surrounding said solid insulation layer dissipates heat transferred from the induction winding's electric conductor through the thin solid insulation layer to the surroundings more readily via conduction, radiation and convection. Heat is transferred from the generator's components to the surrounding compressed gas enclosed in the casing and then from the casing to the surroundings.

In a preferred embodiment of the invention said at least one generator is located below water level and water flowing past the casing is used to cool the casing. Having the more effective cooling system according to the present invention enables the said at least one generator to be run at a much higher power output. In another preferred embodiment of the invention a submerged generator's casing is pressurized to a pressure equal to or greater than the pressure acting on the outside of said casing. In another embodiment of the invention said casing is pressurized to a pressure less than the pressure acting on the outside of the casing to facilitate sealing of the generator casing. Enclosing said at least one generator in a fluid tight, waterproofed casing eliminates the need to waterproof said submerged generator's components. In yet another embodiment the casing is pressurized to a pressure that provides the desired breakdown strength of the compressed gas insulation layer around said induction winding.

According to preferred embodiments of the invention said compressed gas is compressed at least one of the following: nitrogen, SF₆ or air and said casing is pressurized to a pressure in the range of 2-10 bar. In another preferred embodiment said induction winding further comprises an outer enclosing layer positioned between said induction winding and the stator slot walls, said outer enclosing layer enclosing a layer of compressed gas around said solid insulation layer. In a preferred embodiment of the invention said outer enclosing layer is semiconducting. In a further embodiment of the invention said outer enclosing layer is applied to the walls of the stator through which the induction winding is wound in order to eliminate local concentrations in the electric field around non-uniformities or protrusions on the surface of the stator walls. In a preferred embodiment of the invention, said induction winding is held in place by supporting means that hold said induction winding in place substantially in the centre of the stator slot through which it is wound. Said supporting means comprise for example a fibre of insulating material wound around said induction windings solid insulation layer or spacers having a long discharge distance positioned between said solid insulation layer and the stator slot walls. Said supporting means have the resilience to withstand the induction winding's tendency to vibrate when subjected to currents having a certain frequency and its changes in dimension due to thermal expansion.

According to preferred embodiments of the invention said electric conductor has a circular cross-section and is located in stator slot having a circular cross-section or an elliptical cross-section to optimize the electric field distribution. According to another embodiment of the invention, said electric conductor has a rectangular cross-section and is located in a stator slot having a rectangular cross-section.

Said at least one generator can be connected directly to a transmission or distribution network having a high voltage (higher than 10kV), via coupling elements, without requiring a step-up transformer that decreases the total efficiency of the system, consequently leading to savings in both economic terms and with regards to space requirements.

According to a preferred embodiment of the invention said at least one submerged turbine is located within a duct that is adapted to channel the underwater current flow through the turbine to maximize its output. In a further preferred embodiment said duct comprises a filter to separate solid matter, such as seaweed and sea-life, from the water passing through said at least one turbine. In yet another preferred embodiment, the filter is adapted to channel the flow of water through said at least one turbine and create a swirl in the water passing through it to improve the performance of said at least one turbine.

In a preferred embodiment means are provided to locate said at least one submerged generator downstream of said at least one connected turbine. Said at least one generator has a hydrodynamic design to align said at least one turbine to new underwater current flow directions and to minimize turbulence on said at least one turbine. In yet another preferred embodiment said at least one generator is mounted on a rotatable hydrodynamically shaped navigation support. This enables the generator to adapt its orientation to the direction of flow of the water in which it is located automatically to take maximum advantage of the direction of flow of the underwater current. This is advantageous as the direction of an underwater current may vary, with the time of day or with the tides for example.

According to another preferred embodiment the navigation stand comprises a mobile clamp that enables the turbine to be moved vertically either into the path of the strongest underwater current, away from a turbulent current or up to the surface for maintenance purposes. Such positioning can be controlled by means of a control system responding to signals from sensors placed on or around the electric power generation system to regulate the operation of the system's components in a predetermined response to various conditions. For example a sensor could be used to disable or discontinue operation at any time by selectively disengaging/closing off turbines. In a preferred embodiment of the invention the generator covers less than 1/4, advantageously less than 1/8 and preferably less than 1/16 of the turbine flow area so as not to cause a flow shadow behind said generator. According to further embodiments of the invention said at least one generator is located at or above water level and is connected to at least one water turbine via a substantially vertical drive shaft. In such embodiments a waterproofed casing is then only necessary for generators that are exposed to salt water and precipitation. Said at least one generator is housed within or mounted on a water-based infrastructure which may comprise at least one of the following: a wind power plant comprising a single wind turbine or a plurality of wind turbines, a tidal wave plant or a solar power plant. This is advantageous in that the underwater current driven generator can be utilized at times when there is a lull in wind, tidal or solar power, when the wind is not blowing or the sun is nor shining for example. In this way the electric energy generation system of the present invention can be integrated with other power plants to allow electric energy to be produced continuously. According to another embodiment of the invention, said electric energy generation system can be mounted on a travelling vessel.

In a preferred embodiment of the invention the electric energy generation system comprises means to raise said at least one turbine to water level independently of said at least one generator (which can have a diameter of about 5m) to facilitate maintenance and repair work. In another preferred embodiment means are provided to raise said at least one generator and said at least one turbine to water level simultaneously.

It is estimated that an electric power generation system according to the present invention comprising a turbine with a diameter of 15-20m, located in an underwater current having a velocity between 0.3-5.0 ms^'\ such as those existing along the Scandinavian coasts, and operating at an efficiency of 35% could generate up to 6.9 megawatts electric power.

The above and other objects, features and advantages of the present invention will become more apparent from the following description and the appended claims, taken in conjunction with the accompanying drawing. BRIEF DESCRIPTION OF THE DRAWING

A greater understanding of the present invention may be obtained by reference to the accompanying drawing, when considered in conjunction with the subsequent description of the preferred embodiments, in which

figure 1 shows a schematic diagram of a generator according to a preferred embodiment of the present invention,

figure 2 shows a schematic diagram of a generator according to another preferred embodiment of the present invention,

figure 3 depicts an induction winding for use in an electric power generation system according to a preferred embodiment of the present invention,

figure 4 illustrates schematically an axial end-view of a sector of the stator in a generator according to a preferred embodiment of the present invention, and

figure 5 shows possible configurations of an electric power generation system according to preferred embodiments of the present invention.

It should be noted that the components of the electric energy generation systems shown in the figures are not drawn to scale.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 shows a submerged generator 10 enclosed in a fluid-tight casing 11 , that is pressurized. The pressure inside the casing 13 is either the same as the pressure acting on the outside of the casing or slightly lower. The generator 10 comprises a stator 14 that incorporates an induction winding 30 and a rotor 15. The rotor is driven by a water turbine 17 via a shaft 16 and optionally a gearbox 21 if required. The generator in its pressurized fluid tight casing 11 is mounted on a rotatable navigation stand 12. The turbine is automatically aligned with the underwater current flow with the aid of a rudder 13 that is mounted on the rear of the fluid tight casing 11. The generator is connected directly to a power grid for example via a rectifier.

The water turbine 17 is located in an underwater current 20. Water flows through a filter 19 that is adapted to guide the flow of water through said at least one turbine and create a swirl in the water passing through it to increase the performance of said at least one turbine. Said filter also removes solid matter such as seaweed from the water passing through it, which is then channelled through a duct 18 past the water turbine 17. The navigation base 12 is either anchored to the sea/river bed or mounted on an underwater infrastructure.

The rudder 13 keeps the turbine automatically aligned with the direction of the underwater current flow. However if the distance between the navigation base 12 and the centre of force acting on the rudder L₂ is too short compared to the distance between the navigation base and the centre of force acting on the turbine, l_ι, and the turbine diameter, d, (that can be 20m or greater), stability problems can occur. In the worst case the whole generator might turn around and the turbine could start to rotate backwards. To achieve a stable configuration the rudder must be long enough to make the system stable.

Figure 2 shows a configuration that renders a rudder to control the direction of a generator unnecessary. The generator in its fluid-tight, I I hydrodynamically shaped casing 11 is located downstream of a water turbine 17 said turbine being oriented to face the underwater current with its plane of rotation normal to the direction of the flow. A filter 19 is attached to said casing 11 to prevent solid matter reaching the turbine 17. No rudder is needed since , and d are in practice always larger than L₂. The shape of the casing minimizes turbulence on the turbine. In a preferred embodiment of the invention said generator in it's casing is mounted on a hydrodynamically shaped navigation support that minimizes the drag on the support stand and the resulting wake. In a preferred embodiment of the invention the generator covers less than 1/16 of the turbine flow area so as not to cause a flow shadow behind said generator.

Figure 3a shows an induction winding 30 inside the slot 44 of a stator 42. The induction winding comprises an electric conductor 31 , made up of circular strands for example, enclosed in a semiconducting layer 32, that is surrounded by a solid insulation layer 33 and compressed air 34. The solid insulation layer 33 comprises for example a thermoplastic such as low/high-density polyethylene, polypropylene, polybutylene, Teflon™, polyvinylchloride or mica, cross-linked material such as cross-linked polyethylene or rubber for example ethylene-propylene rubber or silicone rubber. The semiconducting layer 32 comprises the same or a similar material as the solid insulation layer but contains conducting material for example carbon black.

Fig 3b shows an induction winding 30 according to the present invention held in place in a stator slot 44 by supporting means 36. The induction winding comprises an enclosing outer layer 35 located between the induction winding's solid insulation layer and stator slot walls, enclosing a layer of compressed air 34 around said solid insulation layer. Fig 3c shows an induction winding 30 held in place at the centre of a stator slot 44, through which it is wound, by spacers 37 comprising electric insulation material.

Figure 4 depicts schematically an axial end-view of a sector of the stator of a generator according to the present invention. The sector shows a segment 42 of the stator and a segment 41 of the rotor with a rotor pole 40. From a yoke portion 42 of the core situated radially outermost, a number of teeth 43 extend radially inwards towards the generators rotor 41. The teeth are separated by slots 44 in which the stator's induction winding is arranged. Only the electric conductor of the induction winding 30 has been shown for clarity. Compressed gas 34 fills the stator slots 44. Each slot 44 has varying cross-section with alternating wider parts 45 and narrower parts 46. The wider parts 45 are substantially circular and surround the induction winding lead-throughs. The narrower parts serve to radially position each induction winding lead-through. The cross-section of the slot 44 as a whole becomes slightly narrower in the direction radially inwards. This is because the voltage in the induction winding lead-throughs is lower the closer they are situated to the radially inner part of the stator. Narrower cable lead-throughs can therefore be used here, whereas increasingly wider cable lead-throughs are required further out. In the embodiment shown, induction windings of three different dimensions are used, arranged in three correspondingly dimensioned sections 47, 48, 49 of the slots 44. The induction winding is held in place with supporting means.

By using an induction winding according to the present invention in the stator winding the voltage of the generator can be increased to such a level that it can be connected directly to a power network without the need of an intermediate transformer. Consequently, the solution according to the present invention leads to savings in both economic terms and with regards to space requirements for installations comprising such a generator. Figure 5a shows generator driven by a plurality of turbines 17 to maximize kinetic energy extraction from the underwater current. The turbines are connected to the generator by mechanical transmission means 16. The generator 10 is located under water level 50 and is integrated within the supporting structure of a wind turbine 51. Mounting the generator on an existing infrastructure reduces the installation cost and its integration with a wind power plant will increase the total power generation output of that plant. In a preferred embodiment of the invention means are provided to raise the generator to water level to facilitate maintenance and repair work.

Figure 5b shows a generator 10 located at or above water level 50 within a wind power plant infrastructure 51 to make the generator more accessible for maintenance or repair work.

Figure 5c shows a floating platform 53 that houses a generator 10 within a fluid tight casing 11. Turbines 17 are located at a predetermined required depth below the water surface 50 and are connected by mechanical transmission means 16 to a submerged generator 10. This installation is securely anchored or moored so as to be able to withstand the considerable drag forces that it experiences when in operation. This installation can be used to generate electricity to charge batteries, located within the floating platform, which can serve solely to provide light or telecommunication signals to assist navigation.

Figure 5d shows a sub-sea station comprising a turbine housed in a fluid- tight casing 11 connected by mechanical transmission means to a turbine located in an underwater current 20. The generator is mounted on a navigation base that is moored on a sea/river-bed 21 or an underwater infrastructure 21. In embodiments such as that shown in figure 5d, where the generator casing is in direct contact with the water it needs to be waterproofed by making it from a corrosion-resistant material or by coating the casing with a polymer such as high-density polyethylene, polypropylene or an aliphatic polyketone.

Figure 5e shows a vertical axis turbine 17 mounted on a gravitation foundation 52, located on a sea/river bed 21 , which houses a generator 10. The generator 10 is connected by mechanical transmission means 16 to said turbine 17. The turbine is positioned in the path of an underwater current 20. This infrastructure must be firm enough to withstand moments from the thrust on the turbine. It can be built at a nearby dock, taken to the site at which the electπc power generation system is to be located and filled with sand for example until it sinks into place.

Figure 5f illustrates an electric power generation system comprising two horizontal axis turbines 17 to increase the system's power output, which are located in the path of an underwater current 20 which in figure 5f flows perpendicularly into the plane of the page. A generator 10 is located within a gravitation foundation 52. The system comprises means 54 such as a rudder that orients the turbine blades so as to extract maximum kinetic energy from the underwater current.

Figure 5g illustrates a generator 10 mounted on a travelling ship 55. The generator is connected by mechanical means 16 to at least one turbine 17 that is located in below water level 50.

While only certain preferred features of the present invention have been illustrated and described, many modifications and changes will be apparent to those skilled in the art. It is therefore to be understood that all such modifications and changes of the present invention fall within the scope of the claims.

Claims

1. An electric power generation system including at least one submerged water turbine (17) that is driven by an underwater current (20), at least one electric generator (10) and mechanical transmission means (16) interconnecting them, characterized in that said at least one generator (10) is enclosed within a fluid tight, pressurized casing (11 ) and contains an induction winding (30) incorporating an electric conductor (31 ) surrounded by an insulation system comprising a semiconducting layer (32) surrounding said conductor and compressed gas (34) surrounding said semiconducting layer, said compressed gas providing electric insulation and facilitating cooling of said at least one generator (10).

2. A system according to claim 1 , characterized in that said insulation system comprising a semiconducting layer (32) surrounding said conductor, a solid insulation layer (33) surrounding said semiconducting layer and compressed gas (34) surrounding said solid insulation layer, said compressed gas providing electric insulation and facilitating cooling of said at least one generator (10).

3. A system according to any of claims 1 or 2, characterized in that said compressed gas (34) is at least one of the following: air, nitrogen, SF₆.

4. A system according to any preceding, characterized in that said pressurized casing (11 ) is pressurized to a pressure in the range of 2-10 bar.

5. A system according to any preceding claims, characterized in that said induction winding (30) comprises reinforcement means.

6. A system according to any preceding claims, characterized in that said induction winding (30) comprises an outer enclosing layer (35) that encloses the induction winding's compressed gas (34) around said induction winding (33).

7. A system according to claim 6, characterized in that said outer enclosing layer (35) is a semiconducting layer.

8. A system according to any of preceding claims, characterized in said electric conductor has a circular cross-section.

9. A system according to any of claims 1 -7, characterized in said electric conductor has a rectangular cross-section.

10. A system according to claim 8, characterized in said electric conductor having a circular cross-section is located inside an enclosure having a substantially circular cross-section.

1 1 . A cable according to claim 8, characterized in said electric conductor having a circular cross-section is located inside an enclosure having a substantially elliptical cross-section.

12. A cable according to claim 9, characterized in said electric conductor having a rectangular cross-section is located inside an enclosure having a substantially rectangular cross-section

13. A system according to any preceding claims, characterized in that said at least one submerged turbine (17) is located within a duct (18) that is adapted to guide the underwater current flow through said turbine to maximize its efficiency.

14. A system according to any preceding claims, characterized in that said duct (18) comprises a filter (19) to separate solid matter from the water passing through said at least one turbine (17).

15. A system according to any claim 14, characterized in that said filter (19) is adapted to guide the flow of water through said at least one turbine (17) and create a swirl in the water passing through it to increase the performance of said at least one turbine (17).

16. A system according to any of the preceding claims, characterized in that said at least one generator (10) is located below water level (50).

17. A system according to claim 16, characterized in that said fluid tight casing (11) is pressurized to a pressure equal to the pressure acting on the outside of the casing.

18. A system according to claim 16, characterized in that said fluid tight casing (11 ) is pressurized to a pressure greater than the pressure acting on the outside of the casing.

19. A system according to claim 16, characterized in that said fluid tight casing (11 ) is pressurized to a pressure less than the pressure acting on the outside of the casing.

20. A system according to claim 16, characterized in that said fluid tight casing (11 ) is pressurized to a pressure that provides the desired breakdown strength of compressed gas (34) surrounding said solid insulation layer (33).

21. A system according to claims 16-21 , characterized in that it comprises means adapted to locate said at least one turbine (17) downstream of said at least one generator (10).

22. A system according to claim 21 , characterized in that said at least one generator (10) has a hydrodynamic design to minimize turbulence on said at least one turbine (17).

23. A system according to any of claims 21 or 22, characterized in that said at least one generator (10) covers less than 1/4, advantageously less than 1/8, and preferably less than 1/16 of the turbine flow area.

24. A system according to any of claims 16-23, characterized in that said at least one generator's casing (1 1 ) is designed so as to automatically align said at least one turbine (17) to new flow directions of said underwater currents (20) downstream of said at least one generator.

25. A system according to claims 22-24, characterized in that said hydrodynamically shaped generator casing (1 1 ) is mounted on a hydrodynamically shaped rotatable navigation support (12).

26. A system according to claim 25, characterized in that said navigation support comprises a mobile clamp that allows the said at least one turbine to be moved to different positions along said navigation support.

27. A system according to any of claims 16-26, characterized in that said system comprises means to raise said at least one generator (10) to water level to facilitate maintenance and repair work.

28. A system according to any of claims 16-26, characterized in that said system comprises means to raise said at least one turbine (17) to water level to facilitate maintenance and repair work.

29. A system according to any of claims 16-26, characterized in that said system comprises means to raise said at least one generator (10) and said at least one turbine (17) to water level (50) simultaneously to facilitate maintenance and repair work.

30. A system according to any of claims 1-15, characterized in that said at least one generator (10) is located at water level (50).

31. A system according to any of claims 1-15, characterized in that said at least one generator (10) is located above water level (50).

32. A system according to any preceding claims, characterized in that said at least one turbine (17) is an axial-flow turbine.

33. A system according to any of claims 1-31 , characterized in that said at least one turbine (17) is a cross-flow turbine.

34. A system according to any preceding claims, characterized in that said system is mounted on a water-based infrastructure (51 , 52, 53).

35. A system according to claim 34, characterized in that said water-based infrastructure is a wind power plant.

36. A system according to claim 34, characterized in that said water- based infrastructure comprises a tidal wave power plant.

37. A system according to claim 34, characterized in that said water- based infrastructure comprises a solar power plant.

38. A system according to claim 34, characterized in that said water- based infrastructure comprises a travelling vessel (55).

39. A system according to any of the preceding claims, characterized in that said electric power generation system comprises a control system that regulates the operation of the electric power generation system's components in a predetermined response to various conditions.

40. A system according to any of the preceding claims, characterized in that said at least one generator (10) is adapted to be connected directly to a high voltage power network without the use of an intermediate transformer.

41 . A method for generating electricity utilizing a system according to any preceding claims, characterized in that it comprises the steps of installing a water turbine (17) in an underwater current (20) and connecting said at least one turbine (17) by mechanical transmission means (16) to at least one electric generator (10).

42. A method for providing an electric generator (10) according to claim 1 with an induction winding (30), characterized in that it comprises the step of holding said induction winding in place with supporting means

(36, 37).

43. Use of electric power generation system according to any of claims 1 - 40 or a method according to any of claims 41 or 42 to generate electricity continuously.