SE539016C2 - A generator for generating electric energy from movements of sea water - Google Patents

Abstract

21 Abstract A generator for generating electric energy from kinetic energy ofmoving sea water comprises at least one first pile (4, 5) of a plu-rality of permanent magnets (6) separated by a first member (7)of magnetically permeable material, two second piles (8-10) ofsecond members (11) ofmagnetically permeable material extend-ing along two different sides of the magnet pile, a core (17-19) ofmagnetically permeable material forming a closed loop from onesecond pile to another for allowing magnetic flux to pass from themagnet pile to one second pile and back through the core, and awinding (23) of an electric conductor (21) around a section (20)of the core. The magnet pile and the second piles are movablewith respect to each other for generating a time varying magneticflux in the core transversally to the direction of this movement. (Fig 1).

Description

AND BACKGROUNDART The present invention relates to a generator for generating elec-tric energy from kinetic energy of moving sea water.

“Sea water” is to be interpreted as water present outdoors in anytype of Constellation, such as for example in oceans, lakes, riversand even dams. The movement from which kinetic energy is con-verted to electric energy in such a generator may be caused bywaves on the surface of said water or water currents of differenttypes within such sea water constellations. However, the presentinvention is particularly directed to generating electric energyfrom power of waves of sea water, which is the reason for here-inafter mainly describing the invention for that application withoutrestricting it thereto. Such wave power generators could be con-nected to a buoy that is either on the surface of the water or somemeters below the surface, and energy is extracted from the seawaves when this buoy moves.

Characterizing for wave power is that it is delivered with very lowspeeds and large forces. The speeds of movements caused bywaves where generators of this type are arranged may often bebelow 1.0 m/s and even below 0.5 m/s in wave climates withsmaller waves, such as for example in the seas surrounding Swe-den. These low speeds makes it challenging to efficiently convertenergy from sea waves to electric energy.

The most common generator type used for wave power is a lon-gitudinal flux permanent magnet synchronous generator. Thisgenerator perform poorly at low speeds by providing a weakdamping force and having large losses at these low speeds. Theweak damping force at the low speeds limits the possibilities to control the buoy movement by controlling the current in the gen-erator, since it is desirable to have large forces at low speeds toget a proper buoy control. These generators are also large andexpensive, so that a large part of the cost for a wave power planthaving such generators is the cost of the generators.

The present invention is for that sake directed to another type ofsuch generators, namely transverse magnetic flux generators, i.e.generators in which the magnetic flux caused to vary by a move-ment of moveable parts of the generator is flowing transversallyto the direction of such movement.

SUMMARY OF THE INVENTION The object of the present invention is to provide a generator forgenerating electric energy from kinetic energy of moving sea wa-ter being improved in at least some aspect with respect to suchgenerators already known.

This object is according to the invention obtained by providing agenerator according to the preamble of appended claim 1 with thefeatures of the characterizing part of that claim.

By having the total length I of the electric conductor forming thewinding by being wound around a core section < Nb4fi, in whichA is the cross section area of said section of the core enclosedby the winding, N is the number of turns of the electric conductoraround this core section and b is 1.7, 1.5, 1.4, 1.3 or 1.2, thewinding may be made considerably shorter than in known suchgenerators for delivering an alternating voltage aimed at, whichmeans that the resistance of said winding will be lower for a de-termined electric conductor used, so that even a cheaper conduc-tor, such as of Al instead of Cu, with slightly lower conductivitymay be used and still a considerably higher electric current maybe generated in the generator. This results in a high damping force already at low speeds, and that the efficiency of the gener-ation at these speeds may be increased considerably. The higherdamping force in the form of higher force density does also meanthat the generator may be made smaller for the same power ratingsaving costs. Furthermore, the high forces at low speeds makesthis generator a very useful tool for buoy control.

According to an embodiment of the invention said magnet pile,second piles and core are designed to simultaneously during op-eration of the generator gather a magnetic flux from at least threeconsecutive magnets in said magnet pile as seen in the directionof extension of this pile in said core section around which saidelectric conductor is wound. This results in a short winding with alow resistance for a certain amount of magnetic flux resulting inhigh damping forces at low speeds and by that a high power ratingat these speeds.

According to another embodiment of the invention the cross sec-tion of the magnetically permeable material of said core sectionenclosed by said winding has rectangular, square or circularshape. Such a shape of the cross section enclosing the magneticflux, especially the circular shape, makes it possible to have ashort electric conductor for enclosing a certain magnetic fluxwhile generating a certain voltage, so that the damping force pro-vided by the generator will then be high and by that also the powergenerated by the generator even at low speeds.

According to another embodiment of the invention said magnetpile has three consecutive sections in the direction of extensionof the pile each having a plurality of permanent magnets sepa-rated by a said first member, adjacent magnet pile sections areseparated by a member of magnetically non-permeable material,that the generator comprises three said cores of magnetically per-meable material, one for each magnet pile section, configured toform a closed loop from one second pile to the other for allowing magnetic flux to pass from a said magnet pile section to one sec-ond pile and back through the core and the other second pile,each said core has a section around which an electric conductoris wound, and said members of magnetically non-permeable ma-terial separating the magnetic pile sections are dimensioned soas to displace an alternating voltage induced by said mutualmovement of the magnet pile and said second piles in each saidwinding by 120 electrical degrees with respect to the alternatingvoltage induced in the other two windings so as to generate athree-phase alternating voltage. This generator will efficientlygenerate a three-phase alternating voltage to be fed to consum-ers through possible interconnection of active rectifiers with cur-rent control, power converters and transformers.

According to another embodiment of the invention said magnetpile is immovable with respect to said core, and said second pilesare configured to be moved by being influenced by a movementof sea water. By having the permanent magnets in the non-mov-ing part all magnets may be used all the time irrespectively of themutual position of this magnet pile with respect to said secondpiles then moving, so that the number of magnets of the generatormay be reduced with respect to having the magnets in the movingpart. This results in a considerable reduction of costs for the gen-erator, since that permanent magnets used in generators of thistype are expensive.

According to another embodiment of the invention the generatorcomprises two said first magnet piles having a fixed mutual posi-tion and three said second piles having a fixed mutual position,each first magnet pile has a said second pile on two differentsides thereof, each magnet of one said magnetic pile has an op-posite direction of magnetization than the magnet of the othermagnet pile arranged directly laterally thereto with respect to thedirection of extension of the magnetic piles, and said core is form-ing a closed loop from one second pile to another second pile for allowing magnetic flux to pass from one magnet pile to a first sec-ond pile to the other magnet pile to a second second pile andback to the core and a third second pile. Such a series connectionof the two magnet piles obtained in this way results in a lowermagnetic flux for a certain damping force obtainable with respectto a parallel connection of the magnet piles, so that said core maybe given a smaller cross section and still able to take the mag-netic flux. Magnetically permeable material, normally iron, usedfor the core may by that be saved at the cost of more turns andmore material of the electric conductor of the winding. lt is pointedout that the generator may have an arbitrary amount of said mag-net piles and second piles arranged as in this embodiment of theinvention for optimizing the relationship between cost and perfor-mance of the generator.

According to another embodiment of the invention said piles havea rectilinear extension. This is a suitable extension of the pilesfor connecting the moving part to a said buoy by a linear directcoupling thereto, whereas in another embodiment of the inventionat least one first magnet pile and said second piles extend alonga circle and the movability of the first and second piles with re-spect to each other is provided by having one of them rotatablyarranged so as to be rotated by movement of sea water actingthereupon, which then requires a simple conversion from linear torotating motion for example by using a winch, when connectingthe part rotatably arranged to a said buoy.

According to another embodiment of the invention directed to theembodiment having piles with a rectilinear extension the genera-tor has two sets of at least one first magnet pile and two secondpiles, and the two sets have a first said core section around whichan electric conductor is wound in common and separate core sec-tions magnetically connecting the respective set to said first coresection. This means that the magnetic flux from both sets will beconcentrated in one and the same core section provided with saidwinding resulting in a high voltage induced per turn of the winding and by that a possibility to have a short winding with a low re-sistance and still obtain a high voltage and by that a high currentand a strong damping force.

According to another embodiment of the invention constituting afurther development of the embodiment last mentioned the pilesof one set are arranged to extend in parallel with the piles of theother set, and said core has a H-like shape as seen in the direc-tion of extension of said piles with the web of said H formed by asaid first core section provided with said winding separating thepiles of the two sets from each other and the legs of the H havethe two ends connecting to one set of piles each. The H-shapemakes the generator with core and piles symmetric and the wind-ing may be applied around one core section being in common totwo parallel magnetic circuits.

According to another embodiment of the invention said first mag-net pile has a plurality of permanent magnets arranged side byside in a row in the direction perpendicular to the extension of thepile and to the direction this pile is facing a said second pile witha said first member separating each such row of permanent mag-nets, an elongated rigid element extends along the extension ofthe magnet pile on each side thereof corresponding to oppositeends of said rows of permanent magnets, stabilizing rods pene-trate through said first members transverse to the extension ofthe magnet pile from one said elongated element to the other forconnecting these elements to each other while bearing under pre-tension against opposite sides of the magnet pile. This construc-tion of the magnet pile makes it possible to obtain a sufficientstiffness even to withstand magnetic forces from the magnetstending to bend the structure even if the structure of the magnetpile is long and thin.

According to another embodiment of the invention said stabilizingrods are provided with a bolt joint to be tightened for pressingsaid elongated elements against the sides of said magnet pile, and according to another embodiment of the invention each saidmagnet pile has at least one beam of an electrically insulatingmaterial extending in the direction of extension of the pile whiledividing said row of permanent magnets so as to stabilize themagnet pile. The network of stabilizing rods and beam or beamswill then form a grate that will be very stiff without disturbing theelectromagnetic performance of the generator. This is ensured byhaving the elongated elements and/or stabilizing rods made of orcoated by an electrically insulating material according to anotherembodiment of the invention.

The invention also relates to a plant for generating electric powerfrom kinetic energy of moving sea water provided with at leastone generator according to the invention. The advantages andadvantageous features of such a plant appear clearly from theabove discussion of the different embodiments of a generator ac-cording to the invention.

Further advantages and advantageous features of the inventionappear from the description following below.

BRIEF DESCRIPTION OF DRAWINGS With reference to the appended drawings, below follows a specificdescription of embodiments of the invention cited as examples. ln the drawings: Fig1 is a simplified perspective view illustrating vitalparts of a generator according to a first embodi-ment of the invention, Fig 2 is a simplified view of the generator shown in Fig 1 from above, Figs 3 and 4 Figs 5 and 6 Fig 7 Fig 8 Fig 9 Fig 10 are Simplified views illustrating how the generatorshown in Fig 1 works, are graphs of force density versus speed andpower density versus speed for a generator accord-ing to the present invention in comparison to aknown conventional generator with a longitudinalmagnetic flux, is a simplified side elevation of a magnet pile of thegenerator shown in Fig 1, is a view corresponding to that in Fig 7 of the mag-net pile from above, is a simplified view corresponding to Fig 3 and 4 ofa part of a generator according to a second embod-iment of the invention, and is a simplified perspective view of a part of a gen-erator according to a third embodiment of the in-venüon.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OFTHE INVENTION A generator according to a first embodiment of the invention isschematically and very simplifiedly illustrated in a perspectiveview in Fig 1. lt is shown how the generator 1 is connected to abuoy 2 located at the surface of a sea 3 for being moved by seawaves and by that also move a movable part of the generator forgenerating electric energy from the kinetic energy of the buoy 2.

The general construction of the generator shown in Fig 1 will beexplained while at the same time also making reference to Figs 2-4. The generator has two first piles 4, 5 of a plurality of perma-nent magnets 6 with magnetization in the direction in extensionof the pile. Adjacent magnets are separated by a first member 7of magnetically permeable material and have opposite magneti-zation direction. “Magnetically permeable material” is in this dis-closure defined to be a material which has a relative permeabilityof more than 50 in any direction at a magnetic flux density of 0.5T. The two magnet piles 4, 5 have a fixed mutual position by beinginterconnected in a suitable way not shown, and each magnet ofone magnet pile has an opposite direction of magnetization thanthe magnet of the other magnet pile arranged directly laterallythereto with respect to the direction of extension of the magnetpiles, which appears from Figs 3 and 4.

The generator also has three second piles 8-10 of second mem-bers 11 of magnetically permeable material, in which each firstmagnet pile has a second pile 8-10 on each side thereof. Adjacentsecond members 11 of each second pile have a mutual distancecorresponding to twice the distance of two consecutive first mem-bers 7 of the magnet piles 4, 5, and the three second piles havea fixed mutual position by being connected to each other as sche-matically illustrated by a connecting member 12 in Fig 1. Eachsecond member 11 of one second pile is as seen in the pile ex-tension direction arranged at equal distance to two consecutivesecond members of the second pile located next to this secondpile.

Each magnet pile 4, 5 has in this embodiment three consecutivesection 13-15 in the direction of extension of the pile each havinga plurality of permanent magnets separated by a said first mem-ber 7, and adjacent magnet pile sections are separated by a mem-ber 16 of magnetically non-permeable material. The generatorhas three cores 17-19 of magnetically permeable material eachforming a closed loop from one second pile 8 to another 10 forallowing magnetic flux to pass from the magnet piles 4, 5 throughthe second piles 8-10 and back through the core. Each core has a section 20 around which an electric conductor 21 is wound byfor example in the order of 200 turns.

The magnet piles 4, 5 and the second piles 8-10 are movablyarranged with respect to each other by having the magnet pilesarranged immovable with respect to the cores and the secondpiles configured to be moved by being influenced by a movementof sea water as simplifiedly illustrated in Fig 1 by a connection ofa line 22 to the connecting member 12. Such a mutual movementof the second piles and the magnet piles along the extension ofthese piles will generate a time varying magnetic flux in the corestransversally to the direction of this mutual movement and an al-ternating voltage in the windings 23. The members 16 of magneti-cally non-permeable material separating magnet pile sections aredimensioned to displace an alternating voltage induced by saidmutual movement of the magnet piles and the second piles ineach said winding by 120 electrical degrees with respect to thealternating voltage induced in the other two windings so as togenerate a three-phase alternating voltage.

The generator according to this embodiment of the invention hastwo sets 24, 25 of two magnet piles and three second piles, andthe two sets have a first core section 20 around which an electricconductor 21 is wound in common and separate core sections 26-29 magnetically connecting the respective set to said first coresection. The two sets 24, 25 of piles have a rectilinear extensionand extend in parallel with each other. Each core has a H-likeshape as seen in the direction of extension of the piles as seenin Fig 2 with a web of the H formed by a first core section 20separating the piles of the two sets from each other and the legsof the H have each two ends connecting to one set of piles each.

How the magnetic flux through the cores is brought to be varyingwith time is schematically illustrated through Figs 3 and 4. lt isshown how the magnetic flux from the permanent magnets will 11 find a way through the first members of these piles and the sec-ond members of the second piles and further in said closed loopthrough the core in one direction when the second piles have aposition shown in Fig 3 with respect to the magnet piles 4, 5 andhow the magnetic flux direction has changed to be the oppositewhen the second piles have been moved from the position shownin Fig 3 to the position shown in Fig 4. The magnet piles may becalled “flux concentrators” by having the magnets directed to-wards each other with a said first member 7 therebetween. Thismeans that the magnetic flux density out from the first members7 is normally higher than the magnetic flux density through themagnets, since the first members have normally a smaller surfacethan the permanent magnets.

The total length I of the electric conductor 21 of each winding 23is much shorter than in conventional generators of this type perunit induced voltage and will by that have a much lower windingresistance. More exactly, this total length I is < Nb4fi, in whichA is the cross section area of said first core section 20 enclosedby the winding, N is the number of turns of the electric conductoraround this core section and b is here with a first core sectionwith the cross section of a circular shape as low as 0.9 (I = 0.88-4Nfifor a circular cross section and I = 4Nx/Ã for a square crosssection for the case only of one winding layer). This lower re-sistance results in a higher current possible for a certain voltageinduced in the windings, so that a higher damping force may beobtained and by that more electric power may be generated at agiven speed of movement of said buoy 2 and by that the secondpiles.

The graph of Fig 5 illustrates how the force per m2 active area(the active area is the air gap area on both sides of each magnetpile and here calculated to be height x width x 2 for each magnetpile. The total active area of the generator is the sum of the activearea of all magnet piles) obtainable by a generator according tothe invention (solid line) is depending upon said speed of the 12 movement compared to a conventional typical longitudinal fluxpermanent magnet synchronous generator (dashed line). lt ap-pears that a generator according to the invention has a maximumdamping force being high (60 kN/m2) already at a speed of lessthan 0.1 m/s, whereas this force is much lower for the conven-tional machine, especially for the low speeds normal for waterslike the ones surrounding Sweden. For such speeds the dampingforce per square meter active area (the shear stress) of the gen-erator according to the invention may be as much as 10 timeshigher, which then also results in an electric power per squaremeter active area generated by the generator according to theinvention being that much higher (as illustrated in Fig 6), sincethe power is said damping force multiplied with the speed. Evenfor a speed of 0.7 m/s that power per square meter will be five toten times higher than for the conventional generator. lt appears from Fig 1 that each magnet pile 4, 5 has a plurality ofpermanent magnets arranged side by side in a row in the directionperpendicular to the extension of the pile and to the direction thispile is facing the second piles next thereto with a first member 7separating each such row of permanent magnets. This way ofar-ranging permanent magnets and first members in a magnet pilewill result in magnetic forces trying to bend the structure, and howthe structure of the magnetic piles are constructed for being sta-bile will now be described while making reference to Figs 7 and8. An elongated rigid element 30, 31 of electrically insulating ma-terial or coated by such a material extends along the extension ofthe magnet pile on each side thereof corresponding to oppositeends of said rows of permanent magnets for example of neodym-ium and separated by laminated iron. These two rigid elementsare interconnected by stabilizing rods 32 also of electrically insu-lating material or coated by such a material penetrating throughthe first members transverse to the extension of the magnet pile.The stabilizing rods are provided with a bolt joint 33 to be tight-ened for pressing the elongated elements 30,31 against the sides 13 of the magnet pile. Each magnet pile has also beams 34 of elec-trically insulating material or coated by such a material extendingin the direction of extension of the pile while dividing the rows ofpermanent magnets and stabilizing the magnet pile. The problemto get the long-thin structure sufficiently stiff to withstand mag-netic forces is obtained by this network of stabilizing rods andbeams forming a grate that will be very stiff without disturbing theelectromagnetic performance of the generator, since the materialof this grate will be electrically insulated with respect to the restof the piles and not form any electrically conducting loops therein.The second piles are held together in a similar way by elongatedrigid elements 35, 36 of electrically insulating material on eachside thereon.

Fig 9 is a view corresponding to Figs 3 and 4 of a part of a gen-erator according to a second embodiment of the invention differ-ing from the one shown in Fig 1 mainly by having only one magnetpile 40 and two second piles 41, 42. The function of this generatorwill be the same as for the generator shown in Fig 1. An ad-vantage of having more than one magnet pile connected in seriesas in the first embodiment is that the same magnetic flux will beobtained in the core, so that this has not to have a greater crosssection requiring more material to be used, but the magnetic forceand by that the damping force of the generator will still be higher.

A part of a generator according to a third embodiment of the in-vention is schematically illustrated in Fig 10, and this has a firstmagnet pile 50 and second piles 51, 52 extending along a circle.The movability of the magnet pile and the second piles with re-spect to each other is provided by having the magnet pile rotata-bly arranged so as to be rotated by movement of sea water actingthereupon by a suitable connection thereof to a buoy or the likethrough a transmission which may convert a linear motion to arotating motion, so that the magnet pile is the rotor and the restthe stator of the generator. Otherwise, the function of this gener-ator will be similar to that of the generator shown in Fig 1 and 14 described above with a time varying magnetic flux directed trans-versal to the extension of the magnetic pile, which is here accord-ing to a circle arc. Thus, pile is in this disclosure defined as anarrangement of pieces directly or indirectly superimposed andhaving an arbitrary extension.

The different members of magnetically permeable material in agenerator according to the invention, such as said first and sec-ond members and said cores are formed by laminate structuresof a plurality of thin laminate pieces, typically of a thickness of0.1 - 0.5 mm, separated by a thin insulating layer so as to keepeddy current losses at low levels.

The invention is of course not in any way restricted to the embod-iments described above, but many possibilities to modificationsthereof will be apparent to a person with ordinary skill in the artwithout departing from the scope of invention as defined in theappended claims.

Although it is shown that the two second piles arranged next to amagnet pile extend along opposite sides thereof, this is not nec-essary, but they do only have to extend along two different sidesof the magnet pile to form a double-sided generator to which thepresent invention is directed. “a mutual distance corresponding to twice the distance of twoconsecutive first members” is in this disclosure to be interpretedto cover mutual distances deviating slightly from twice said dis-tances, such as by for example a couple of mm as long as thefunction will be the same with respect to the magnetic flux throughconsecutive such first members. The distance may for instancedeliberately be made 1 mm larger than “twice”, which means thatthe performance is lowered slightly since the maximum magneticflux will not hit all first members simultaneously, but vibrations ofcomponents of the generator may by that be lowered. The samereasoning is also applicable to the use of “equal” as used in this disclosure with respect to the arrangement of said second mem-bers in the second piles.

The magnet piles and the second piles may be movably arrangedwith respect to each other in other ways than described above.The buoy may be secured to the stator (core), which is typicallythe case if the generator is integrated in the buoy, and the secondpiles will then instead be secured to the sea bottom.

Claims (5)

16 Claims

1. A generator for generating electric energy from kinetic energyof moving sea water comprising: o at least one first pile (4, 5, 40, 50) of a plurality of per-manent magnets (6) with magnetization in the directionof extension of the pile, adjacent magnets being sepa-rated by a first member (7) of magnetically permeablematerial and having opposite magnetization directions, o two second piles (8-10, 41, 42, 51, 52) of second mem-bers (11) of magnetically permeable material extendingalong two different sides of the first magnet pile, adja-cent second members of each second pile having a mu-tual distance corresponding to twice the distance of twoconsecutive first members (7) of the first magnet pile,said second piles (8-10, 41, 42, 51, 52) having a fixedmutual position and each said second members (11) ofone second pile being as seen in the pile extension di-rection arranged at equal distance to two consecutivesecond members of the other second pile, o a core (17-19) of magnetically permeable material form-ing a closed loop from one second pile to the other forallowing magnetic flux to pass from the first magnet pileto one second pile and back through the core and theother second pile, and o a winding (23) of an electric conductor (21) around asection (20) of said core, the first magnet pile (4, 5, 40, 50) and the second piles (8-10, 41, 42, 51, 52) being movably arranged with respect toeach other by one of them being configured to be moved bymovement of sea water for obtaining a mutual movement ofthe first magnet pile and the second piles along the extensionof these piles and by that generating a time varying magneticflux in said core (17-19) transversally to the direction of this 17 mutual movement and an alternating voltage in said winding(23). characterized in that the total length I of the electric conduc-tor (21) of said winding (23) is < Nb4x/Ä, in which A is thecross section area of said section (20) of the core enclosedby said winding, N is the number of turns of the electric con-ductor around said core section, and b is 1.7, 1.5, 1.4, 1.3 or1.

2. A generator according to claim 1, characterized in that saidmagnet pile (4, 5, 40, 50), second piles (8-10, 41, 42, 51, 52)and core (17-19) are designed to simultaneously during op-eration of the generator gather a magnetic flux from at leastthree consecutive magnets (6) in said magnet pile (4, 5,40,50) as seen in the direction of extension of this pile in saidcore section (20) around which said electric conductor (21)is wound. A generator according to claim 1 or 2, characterized in thatthe cross section of the magnetically permeable material ofsaid core section (20) enclosed by said winding (23) has arectangular, square or circular shape. A generator according to any of the preceding claims, iacterized in that said magnet pile (4, 5, 40, 50) has threeconsecutive sections (13-15) in the direction of extension ofthe pile each having a plurality of permanent magnets (6)separated by a said first member (7), that adjacent magnetpile sections are separated by a member (16) of magneticallynon-permeable material, that the generator comprises threesaid cores (17-19) of magnetically permeable material, onefor each magnet pile section (13-15), configured to form aclosed loop from one second pile(8-10, 41,42, 51, 52)totheother for allowing magnetic flux to pass from a said magnetpile section to one second pile and back through the core and 18 the other second pile, that each said core has a section (20)around which an electric conductor (21) is wound, and thatsaid members of magnetically non-permeable material sepa-rating the magnetic pile sections are dimensioned so as todisplace an alternating voltage induced by said mutual move-ment of the magnet pile and said second piles in each saidwinding (23) by 120 electrical degrees with respect to the al-ternating voltage induced in the other two windings (23) soas to generate a three-phase alternating voltage. A generator according to any of the preceding claims, char- acterized in that said magnet pile (4, 5, 40, 50) is immovablewith respect to said core (17-19), and that said second piles(8-10, 41, 42, 51, 52) are configured to be moved by beinginfluenced by a movement of sea water. A generator according to any of the preceding claims, char- acterized in that it comprises two said first magnet piles (4,5) having a fixed mutual position and three said second piles(8-10) having a fixed mutual position, that each first magnetpile has a said second pile on two different sides thereof, thateach magnet (6) of one said magnetic pile has an oppositedirection of magnetization than the magnet of the other mag-net pile arranged directly laterally thereto with respect to thedirection of extension of the magnetic piles (4, 5), and thatsaid core is forming a closed loop from one second pile (8)to another second pile (9) for allowing magnetic flux to passfrom one magnet pile to a first second pile to the other mag-net pile to a second second pile and back to the core (17-19)and a third second pile (10). A generator according to any of the preceding claims, char- acterized in that said piles (4, 5, 40, 8-10, 41, 42) have arectilinear extension. 10. 11. 19 A generator according to claim 7, characterized in that it hastwo sets (24, 25) of at least one first magnet pile (4, 5) andtwo second piles (8-10), and that the two sets have a firstsaid core section (20) around which an electric conductor(21) is wound in common and separate core sections (26-29)magnetically connecting the respective set to said first coresecüon. A generator according to claim 8, characterized in that thepiles of one set (24) are arranged to extend in parallel withthe piles of the other set (25), and that said core (17-19) hasa H-like shape as seen in the direction of extension of saidpiles with the web of said H formed by a said first core section(20) provided with said winding (23) separating the piles ofthe two sets from each other and the legs of the H have thetwo ends connecting to one set of piles each. A generator according to any of claims 1-6, characterized inthat said at least one first magnet pile (50) and said secondpiles (51, 52) extend along a circle and the movability of thefirst and second piles with respect to each other is providedby having one of them rotatably arranged so as to be rotatedby movement of sea water acting thereupon. A generator according to any of the preceding claims, macterized in that said first magnet pile (4, 5) has a pluralityof permanent magnets (6) arranged side by side in a row inthe direction perpendicular to the extension of the pile and tothe direction this pile is facing a said second pile with a saidfirst member (7) separating each such row of permanentmagnets, that an elongated rigid element (30, 31) extendsalong the extension of the magnet pile (4, 5) on each sidethereof corresponding to opposite ends of said rows of per-manent magnets, that stabilizing rods (32) penetrate throughsaid first members (7) transverse to the extension of the mag-net pile from one said elongated element (30, 31) to the other 12. 1

3. 1

4. 1

5. for connecting these elements to each other while bearingunder pretension against opposite sides of the magnet pile(4, 5). A generator according to claim 11, characterized in that saidstabilizing rods (32) are provided with a bolt joint (33) to betightened for pressing said elongated elements (30, 31)against the sides of said magnet pile (4, 5). A generator according to claim 11 or 12, characterized inthat each said magnet pile (4, 5) has at least one beam (34)of an electrically insulating material extending in the directionof extension of the pile while dividing said row of permanentmagnets so as to stabilize the magnet pile. A generator according to any of claims 11-13, characterizedin that said elongated elements (30, 31) and/or stabilizingrods (32) are made of or coated by an electrically insulatingmaterial. A plant for generating electric power from kinetic energy ofmoving sea water, characterized in that it has at least onegenerator (1) according to any of claims 1-14.