Abstract:
The invention concerns an electric generator ( 10 ) allowing the conversion of mechanical energy to electrical energy. 
     The invention is characterized by the fact that the electric generator comprises at least:
       a first axial flow electrical machine ( 100 ) comprising a first rotor ( 102 ) mounted in rotation about a first axis and surrounding a first stator ( 104 );   a second axial flow electrical machine ( 200 ) comprising a second rotor ( 202 ) coaxial to the first rotor and surrounding a second stator ( 204 );   first azimuthal securing means ( 12 ) to secure together the first and second rotors so that the first and second rotors can be simultaneously set in rotation about the first axis.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject of the present invention is an electric generator allowing the conversion of mechanical energy to electrical energy. 
         [0002]    In its main application the electric generator is used for converting the mechanical energy of a wind turbine. However, the electric generator can also be used in numerous other sectors, such as electricity power stations grouped with a steam turbine or gas turbine, or in hydraulic power stations. 
         [0003]    In the remainder of the application, the advantages are detailed of an electric generator comprising at least one electrical machine, the electrical machine being an axial flow alternator able to be integrated in a wind turbine. 
         [0004]    On the basis of this example, persons skilled in the art will easily infer the adaptations required to produce the electric generator for other applications such as those aforementioned. 
         [0005]    For several years, the dimensions of wind turbines and in particular the diameter of their blades have undergone considerable increase to obtain very high electric power without multiplying the number of wind turbines. Thereafter the electrical machines equipping these wind turbines have become increasingly more voluminous. 
         [0006]    These changes to the size of electrical machines require the adapting of production tooling, complicate installation and maintenance, increase manufacturing and installation costs and accentuate the visual impact of such devices. 
         [0007]    One solution is proposed in document FR 2 926 935 held by the applicant, which describes an electrical machine comprising a rotor surrounding a stator, the rotor and stator both being formed of different sections joined to one another. The structure of the rotor and of the stator therefore allows electrical machines to be produced of varying size, using one and the same production tooling, and being easier to install than electrical machines of same size comprising a rotor and stator each formed of a single piece. 
         [0008]    However this solution does not solve all the problems previously mentioned amongst which the visual impact of wind turbines of large size. 
       SUBJECT AND SUMMARY OF THE INVENTION 
       [0009]    It is the objective of the present invention to propose an electric generator allowing very high electrical power to be obtained without a significant increase in the dimensions of the electric generator. This objective is reached through the fact that the invention concerns an electric generator allowing the conversion of mechanical energy to electrical energy, the electric generator at least comprising:
       a first axial flow electrical machine comprising a first rotor mounted in rotation about a firs axis and surrounding a first stator to generate a first magnetic flow;   a second axial flow electrical machine comprising a second rotor separate from the first rotor, which is coaxial to the first rotor and surrounds a second stator to generate a second magnetic flow;   first azimuthal securing means to join the first and second rotors so that the first and second rotors can be simultaneously placed in rotation about the first axis for the simultaneous generation of the first and second magnetic flows.       
 
         [0013]    This device therefore allows the accumulation of the electric powers generated by the first and second electrical machines, to obtain greater electrical energy than would be obtained by an electric generator only comprising one of the first and second electrical machines. 
         [0014]    By azimuthal is meant the direction perpendicular both to the axial direction of the first and second rotors, defined by the first axis about which the first and second rotors are rotatably mounted, and to the radial direction of the first and second rotors, defined by one of the radii of one of the first and second rotors. Azimuthal joining has the effect that the first and second rotors cannot rotate relative to one another about their axial directions. Said otherwise, azimuthal joining of two rotors prevents relative azimuthal movement between these two rotors. The rotation of one of the rotors therefore causes the rotation of the other. 
         [0015]    Since the first and second rotors are secured to one another, they are set in rotation simultaneously, for example but not limited thereto by the hub of a wind turbine. 
         [0016]    In addition, the complexity of the manufacture of the electric generator of the present invention is similar to that of the manufacture of each of the first and second electrical machines; its manufacturing cost is equal to or slightly higher than the manufacturing costs of the first and second electrical machines. 
         [0017]    Its installation and maintenance are significantly simplified compared with an electric generator generating similar electrical power and comprising a single electrical machine, the dimensions of this single electrical machine being substantially larger than those of each of the first and second electrical machines forming the generator of the present invention. 
         [0018]    In the event of faulty functioning of one or other of the electrical machines, the electric generator of the present invention is able to continue generating electric energy, the electric generator thereby remaining available. This characteristic is particularly advantageous when the electric generator is used to equip a wind turbine installed in areas having difficult access, in open sea for example, the servicing time to repair the faulty element then possibly being particularly lengthy. 
         [0019]    The radial bulk of the electric generator of the present invention is the same as that of an electrical machine of larger size. 
         [0020]    By radial bulk of the generator is meant the span defined by the first and second electrical machines in a plane perpendicular to the first axis. 
         [0021]    Preferably, the first and second rotors respectively surround the first and second stators circumferentially. 
         [0022]    In other words, the first and second rotors extend along the respective circumference of the first and second stators, surrounding the same. 
         [0023]    It will therefore be understood that the first and second rotors each define an annular cavity or housing configured to receive the first and second stators respectively. 
         [0024]    The annular housings thus defined by the first and second rotors are joined together by the first azimuthal securing means. 
         [0025]    Preferably, the first and second electrical machines are identical, so that the complexity of the manufacture of the electric generator is thereby further reduced. The radial bulk of the electric generator is then the radial bulk of an electric generator only comprising a single electrical machine. 
         [0026]    Advantageously, the first and second electrical machines are able to implement different technologies, to reduce the probability that the electrical machines may simultaneously develop a fault. 
         [0027]    The invention is described below in a series of variants of embodiment which can be considered alone or in combination with one or more of the others. 
         [0028]    Advantageously, the first and second rotors each comprise first and second walls, arranged either side of the first and second stators respectively, which define a first and second annular housing respectively in which the first and second stators are housed, the second wall of the first rotor and the first wall of the second rotor being arranged facing one another and the first azimuthal securing means being configured to join together the second wall of the first rotor and the first wall of the second rotor in an azimuthal direction. Azimuthal coupling is therefore obtained between the first and second rotors. 
         [0029]    It will therefore be understood that in the electrical machines of the electric generator of the present invention, each stator is arranged between the first and second walls of the corresponding rotor, the first and second walls of each of the rotors defining a circumferential housing. It will also be understood that the first and second electrical machines are placed side by side, and that they are secured to one another by cooperation of their adjacent walls. It is therefore understood that in a plane containing the first axis the electric generator has an axis of symmetry positioned between the second wall of the first machine and the first wall of the second machine. 
         [0030]    With this arrangement, it is sufficient that one of the electrical machines is driven in rotation about the first axis so that it will cause the other electrical machine also to be driven in rotation about the first axis. 
         [0031]    Additionally, with this arrangement, it will be understood that the structure of the stators need not be modified so that they can be mounted on the electric generator of the present invention, thereby avoiding the generation of additional costs for the manufacture and assembly thereof. Also, it will be understood that the first securing means are mounted on the outer surface of the adjacent walls of the first and second rotors, so that the inner structure of the rotors and the functioning of the electrical machines are not modified by the joining of the first and second electrical machines. 
         [0032]    By outer surface of the walls is meant the surface of the rotor walls opposite the surface arranged facing the first and second stator with which the first and second rotors respectively cooperate. 
         [0033]    Preferably the first and second walls of the first and second rotors are of annular shape. 
         [0034]    Advantageously the first and second walls of the first and second rotors are in the shape of coaxial discs. 
         [0035]    Preferably the first and second stators are also coaxial discs. 
         [0036]    Advantageously the first and second stators are coaxial to the first and second rotors. 
         [0037]    Preferably, the first azimuthal securing means also form axial securing means configured to couple together the first and second rotors along the first axis. In other words, they prevent any axial movement between the first and second rotors. The only degree of freedom is radial movement which is only permitted during mounting and dismounting operations of the electric generator of the present invention. 
         [0038]    Advantageously, the first azimuthal securing means comprise a sliding connection enabling radial movement of the second wall of the first rotor relative to the first wall of the second rotor when assembling the electric generator. 
         [0039]    With this arrangement, it will be understood that the first and second rotors are secured together via radial translation along an axis perpendicular to the first axis, so that the axial space required for assembling of the electric generator is equal to the axial space taken up the electric generator once it has been mounted. 
         [0040]    By axial space is to be understood the portion of the first axis along which the first and second electrical machines are arranged in the electric generator of the present invention. 
         [0041]    It will therefore be understood that the first azimuthal securing means are moved radially relative to the first and second rotors in order to assemble the electric generator of the present invention. The use of a sliding connection therefore ensures a maintained constant gap between the first and second rotors 
         [0042]    Preferably the sliding connection comprises an outer slide formed on one of the walls from among the second wall of the first rotor and the first wall of the second rotor, and an inner slide formed on the other of the walls from among the second wall of the first rotor and the first wall of the second rotor, the inner and outer slides being configured so that the inner slide slides in the outer slide at the time of assembling the electric generator. 
         [0043]    It will therefore be understood that the second wall of the first rotor and the first wall of the second rotor comprise outer and inner slides formed on their outer surface so that it is possible to secure the two walls to one another. With this arrangement, the manufacturing of the rotors is identical to that of a rotor intended to equip an electric generator only comprising a single electrical machine, the inner and outer slides simply having to be added and secured onto the outer surfaces of the rotors. 
         [0044]    Advantageously, the slide connection has a dovetail-shaped profile. 
         [0045]    By dovetail is meant a slide connection which comprises a tenon of trapezoid shape engaging in a groove of same shape to ensure the sliding connection. 
         [0046]    The sliding of the slides one in the other also provides for simplified mounting of the electric generator of the present invention, once the inner slide is engaged in the outer slide, the user only having to translate the slides in relation to each other. 
         [0047]    Advantageously, one of the first and second rotors is composed of at least two sections and of assembly means allowing the joining of the two sections to each other, the first azimuthal securing means being arranged on at least one of the sections. 
         [0048]    With this arrangement, it is possible to manufacture and transport the different sections of the rotor separately, the assembling together of the sections possibly being performed at the mounting site of the electric generator of the present invention. 
         [0049]    Additionally, the use of sections to form the rotor also allows electrical machines of varying sizes to be produced, and in particular of large size using one same production tooling. 
         [0050]    Preferably the two rotors are composed of at least two sections. 
         [0051]    Advantageously, the two rotors comprise the same number of sections. 
         [0052]    Advantageously, each section of the first rotor can be secured by azimuthal securing means to one of the sections of the second rotor. 
         [0053]    Preferably, the electric generator also comprises attachment means to secure the first and second stators. 
         [0054]    With this configuration, the gap between the stators is kept constant. 
         [0055]    Advantageously, the electric generator also comprises a third axial flow electrical machine comprising a third rotor coaxial to the first rotor and surrounding a third stator to generate a third magnetic flow, and second azimuthal securing means to secure the third rotor to one of the first and second rotors so that the first, second and third rotors can be simultaneously set in rotation about the first axis to generate the first, second and third magnetic flows simultaneously. 
         [0056]    The third rotor therefore defines a third annular housing configured to receive the third stator, the third annular housing being connected to one of the first and second annular housings by the second azimuthal securing means. 
         [0057]    It will be understood that all the advantages detailed previously for an electric generator comprising a first and second electrical machine remain true for the case in which the electric generator comprises three electrical machines. It is within easy reach of persons skilled in the art, from the structure of the electric generators described in this application, to infer the structure of an electric generator which may comprise four, five or more electrical machines. It is therefore easily possible to have an electric generator of the desired power by associating a suitable number of electrical machines. 
         [0058]    The invention also concerns a wind turbine comprising a tower and hub mounted in rotation relative to the tower about an axis of rotation, the hub being driven in rotation by a spinner, the wind turbine also comprising an electric generator according to the present invention, the first and second rotors being mounted in rotation about the axis of rotation. 
         [0059]    Advantageously, at least one of the first and second rotors comprises securing means configured to secure the said at least one of the first and second rotors to the hub. 
         [0060]    With this configuration it will be understood that the spinner, via the securing means, drives the first and rotors in rotation. Therefore the electric power produced by the wind turbine of the present invention, obtained by combining the first and second electrical machines, is substantially higher than the power that would be produced by a wind turbine of same size of which the electric generator only comprises one of the first and second electrical machines. 
         [0061]    Preferably the wind turbine comprises a flange connecting the hub to at least one of the electrical machines, perforations being made in the flange to allow ventilation of the electrical machines. 
         [0062]    Advantageously, the wind turbine comprises a ventilation system comprising at least one ventilation module formed of a fan and motor. 
         [0063]    Preferably, the ventilation system comprises at least as many ventilation modules as there are electrical machines. 
         [0064]    With this configuration, it will be understood that each of the ventilation modules is intended to ventilate separately one of the electrical machines. The configuration of the ventilation system therefore allows some ventilation modules to be placed in operation selectively to ventilate at least one of the electrical machines. 
         [0065]    Advantageously, each electrical machine comprises a power converter configured to transfer the electric power generated by the electrical machines onto the electricity grid allowing the conveying of electric energy to consumers. 
         [0066]    Advantageously, the wind turbine of the present invention comprises a selection system configured to set in operation independently each of the power converters of the electric generator. 
         [0067]    It will therefore be understood that it is possible to optimise the yield of the electric generator, for example when wind power is low, by only setting in operation some power converters. The selection system also allows the production time of electric energy to be distributed over the different electric machines so as to manage the wear thereof. 
         [0068]    More generally it will be understood that the electric generator of the present invention comprises numerous modular factors: several electrical machines can be combined with one another within one same electric generator, the different electrical machines can be of same or different size and power or have same or different properties, or they can apply same or different technologies, the rotors can be composed of several sections, the stators can also be composed of several separate parts intended to be assembled, the ventilation system comprises several ventilation modules, each electrical machine is associated with a separate power converter, . . . . 
         [0069]    It will therefore be understood that starting from elementary components such as the rotor sections, stator elements, ventilation modules, power converters, . . . , it is possible to produce a wind turbine which meets all types of power and size requirements. As detailed in the foregoing when describing the electric generator comprising first and second electrical machines, said modular structure has multiple advantages regarding cost and complexity of manufacture, the transport of components of the wind turbine to the assembly site, the dimensions of the assembled wind turbine, the maintenance thereof, its capacity to generate electric energy continuously, despite unfavourable outside conditions or faulty elements, . . . . 
         [0070]    In addition, the invention also concerns a method for mounting a wind turbine according to the present invention, the wind turbine comprising a first and second electrical machine, the method comprising a step during which the first electrical machine is mounted on the wind turbine, followed by a step during which the second stator is mounted on the wind turbine, followed by a step during which the second rotor is mounted around the second stator and is secured to the first rotor. 
         [0071]    Advantageously, it is therefore possible to replace one of the constituent elements of one of the first and second machines without dismounting the assembly formed by the first and second electrical machines. 
         [0072]    Advantageously, the first and second electrical machines can be mounted together in accordance with the method, before the assembly formed by the first and second electrical machines is mounted on the wind turbine, for example to carry out testing thereof. 
         [0073]    Finally, the invention concerns a method for assembling a wind turbine of the present invention, the wind turbine comprising a first, a second and a third electrical machine, the method comprising a step during which the first electrical machine is mounted on the wind turbine, followed by a step during which the second stator is mounted on the wind turbine, followed by a step during which the third electrical machine is mounted on the wind turbine, followed by a step during which the second rotor is mounted around the second stator and is secured to the first and third rotors. 
         [0074]    Advantageously the first, second and third electrical machines can be mounted together according to the method before the assembly formed by the three electrical machines is mounted on the wind turbine. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0075]    Other characteristics and advantages of the invention will become more clearly apparent and complete on reading the following description of one preferred embodiment given as a non-limiting example and with reference to the appended drawings in which: 
           [0076]      FIG. 1  schematically illustrates an example of an electric generator according to the present invention, the electric generator comprising a first and second electrical machine; 
           [0077]      FIG. 2  schematically illustrates the first and second electrical machines of the electric generator in  FIG. 1 , seen from overhead; 
           [0078]      FIGS. 3 and 4  schematically illustrate part of the first and second electrical machines of the electric generator in  FIG. 1 ; 
           [0079]      FIG. 5  schematically illustrates a step in the mounting of the electric generator in  FIG. 1 ; 
           [0080]      FIG. 6  schematically illustrates a wind turbine comprising the electric generator in  FIG. 1 ; and 
           [0081]      FIG. 7  schematically illustrates an example of an electric generator according to the invention, the electric generator comprising a first, a second and a third electrical machine. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0082]    In the example illustrated in  FIG. 1 , the electric generator  10  of the invention has a first axial flow electrical machine  100  formed by a first rotor  102  mounted in rotation about a first axis X and surrounding a first stator  104 . The electric generator  10  also has a second axial flow electrical machine  200  formed by a second rotor  202  also mounted in rotation about a first axis X and surrounding a second stator  204 . 
         [0083]    As illustrated in  FIG. 1 , the first rotor  102  has a U-shaped profile, but is not limited thereto; the first rotor  102  particularly comprises first  106  and second  108  walls arranged either side of the first stator  104 . The first rotor  102  further comprises a first upper edge  110  which connects the first  106  and second  108  walls. 
         [0084]    The first  106  and second  108  walls of the first rotor  102  each have an annular shape and define a first annular housing configured to receive the first stator  104 . 
         [0085]    It will therefore be understood that the first rotor  102  surrounds the first stator  104  circumferentially. In other words, the first rotor  102  extends along the circumference of the first stator  104  so as to surround the latter. 
         [0086]    Similarly the second rotor  202  has a U-shaped profile but is not limited thereto; the second rotor  202  in particular comprises first  206  and second  208  walls arranged either side of the second stator  204  and connected by a second upper edge  210 . 
         [0087]    Therefore, in similar manner to the first electrical machine  100 , the first  206  and second  208  walls of the second rotor  202  are each of annular shape, and define a second annular housing configured to receive the second stator  204 . 
         [0088]    In other words, second rotor  202  surrounds the second stator  204  circumferentially. 
         [0089]    Without departing from the scope of the present invention, the first and second walls  106 ,  108 ,  206 ,  208  and the upper edges  110 ,  210  of each of the first and second rotors  102 ,  202  could form a single part having a profile such that it surrounds the first  104  and second  204  stators respectively. 
         [0090]    The electric generator  10  of the present invention also comprises first securing means  12  arranged between the second wall  108  of the first electrical machine  100  and the first wall  206  of the second electrical machine  200 , which will be described in more detail in particular in the description of  FIG. 2 . 
         [0091]    It will be understood that the first securing means  12  are configured to join the first and second circumferential housings defined by the first  102  and second  202  rotors respectively. 
         [0092]    The electric generator  10  also comprises first connecting means  14  arranged between the first  100  and second  200  electrical machines. As illustrated in  FIG. 1 , the upper end  15  of the first connecting means  14  is arranged between the first  104  and second  204  stators and comprises attaching means  16  configured to secure the first  104  and second  204  stators. 
         [0093]    The median portion of the first connecting means  14  comprises a perforation  18 , and the lower portion thereof  20  comprises first  22  and second  24  attaching elements. 
         [0094]    As illustrated in  FIG. 1 , the electric generator  10  also comprises first  26  and second  28  bearings. The upper portion of the first bearing  26  is secured to the second wall  108  of the first rotor  102  of the first electrical machine  100  via first securing means  29 ; the lower portion of the first bearing  26  is secured to the upper end  15  of the first connecting means  14  via second securing means  30 . 
         [0095]    The upper portion of the second bearing  28  is secured to the lower end  20  of the first connecting means  14  via second attaching elements  24 ; the lower portion of the second bearing  28  comprises coupling means  31 . 
         [0096]    As illustrated in the different Figures, the first and second  29 ,  30  securing means, the first and second  22 ,  24  attaching elements and the coupling means  31  can be formed of bolts; they may also be formed of any other means allowing the securing together of several elements without departing from the scope of the invention. 
         [0097]    Finally, the electric generator  10  comprises attaching means  33  mounted both on the first wall  106  of the first rotor  102  of the first electrical machine  100  and on the second bearing  28  via coupling means  31 . 
         [0098]      FIG. 2  gives a detailed illustration of the first azimuthal securing means  12 . 
         [0099]    In this Figure in which the first  102  and second  202  rotors are illustrated from above, it can be seen that the first azimuthal securing means  12  are formed of an outer slide  32  and inner slide  34 . 
         [0100]    The outer slide  32  is formed by first  36  and second  38  lateral portions, both formed on the first wall  206  of the second rotor  202 . The space formed between the first  36  and second  38  lateral portions defines a housing having a trapezoid-shaped profile. 
         [0101]    The inner slide  34  is formed by a first  40  and second  42  side, both formed on the second wall  108  of the first rotor  102  and which define a section of trapezoid shape configured to be contained in the housing defined by the outer slide  32 . The inner slide  34  could also be formed of a single part defining a section of trapezoid shape without departing from the scope of the invention. It will therefore be understood that the shape of the inner  34  and outer  32  slides is such that the inner slide  34  is able to slide in the outer slide  32  in longitudinal direction L, the longitudinal direction L being defined by the lateral portions  36 ,  38  and the sides  40 ,  42  parallel to one another. 
         [0102]    As can be seen in  FIG. 2 , the lateral portions  36 ,  38  and the sides  40 ,  42  project from the first wall  206  of the second rotor  202  and the second wall  108  of the first rotor  102  respectively; for example but not limited thereto the lateral portions  36 ,  38  and the sides  40 ,  42  are secured by screwing or any other securing device onto the first wall  206  of the second rotor  202  and onto the second wall  108  of the first rotor  102 . 
         [0103]    It can therefore be seen that the first azimuthal securing means  12  have a dovetail-shaped profile. 
         [0104]    It could also be contemplated, without departing from the scope of the present invention, that the first azimuthal securing means  12  could have a profile of different shape, or that the electric generator  10  could have an inner slide  34  and outer slide  32  respectively formed on the first wall  206  of the second rotor  202  and on the second wall  108  of the first rotor  102 . 
         [0105]    It will therefore be understood that the first azimuthal securing means  12  comprise a slide connection in a longitudinal direction L, which forms a radial direction of the first  102  and second  202  rotors, the slide connection being formed by the inner slide  34  and outer slide  32  configured to slide in one another when mounting the electric generator  10  of the present invention, so as to secure the first  102  and second  202  rotors. 
         [0106]      FIGS. 3 and 4  illustrate part of the first  100  and second  200  electrical machine of the electric generator  10  of the present invention. 
         [0107]    As illustrated in  FIG. 3 , the first rotor  102  is formed of several sections  112 ,  112 ′ which comprise assembly orifices  114 ,  114 ′ formed on the upper edges  110 ,  110 ′ for assembling of the sections  112 ,  112 ′, via assembly means such as screws, but not limited thereto, passed through the assembly orifices  114 ,  114 ′. Any other assembly means could also be envisaged without departing from the scope of the present invention. 
         [0108]    The first and second walls  106 ,  108  of the first rotor  102  each define an inner surface and outer surface, the inner surfaces of the first and second walls  106 ,  108  being arranged facing one another and surrounding the first stator  104 . As illustrated in  FIG. 3 , magnetizing areas  116  are arranged on the inner surfaces of the walls  106 ,  108 , these magnetizing areas  116  forming the inductor portion of the magnetic circuit of the first electrical machine  100 . 
         [0109]    For example, but not limited thereto, the magnetizing areas  116  are formed by the superimposition of permanent magnets. It could also be envisaged without departing from the scope of the present invention, that the inductor portion of the magnetic circuit of the first electrical machine  100  is formed of any other element such as coils for example. 
         [0110]    As illustrated in  FIG. 3 , the first  40  and second  42  sides of the inner slide  34  are formed on the outer surface of the second wall  108 . Also, first matching means  118  are arranged on the outer surface of the second wall  108 . 
         [0111]    The first stator  104  is formed by a first rim of which one portion  120  is illustrated in  FIG. 3 ; the portion  120  comprises radial notches  122  in which first active modules are inserted  124 . 
         [0112]    The first active modules  124  form the induced part of the magnetic circuit of the first electrical machine  100 . 
         [0113]    It will therefore be understood from  FIG. 3 , that the first rim of the first stator  104  is advantageously formed of at least two portions  120 , the portions  120  able to be easily assembled at the mounting site of the electric generator  10  using conventional operations for those skilled in the art such as welding or riveting for example. 
         [0114]    It will also be understood that the shape of the sections  112 ,  112 ′ of the first rotor  102  makes it possible easily and precisely to position the inducing part in relation to the induced part of the first stator  104 . 
         [0115]    Finally it will be understood that the assembling of the portions  120  of the first rim of the first stator  104  defines a disc the centre of which has an orifice for mounting of the first stator  104  in free rotation. The assembling of the sections  112 ,  112 ′ of the first rotor  102  defines a cylinder portion having an outer diameter of same or even slightly larger size than the disc formed by the first stator  104 , the cylinder portion formed by the first rotor  102  comprising two lateral edges arranged perpendicular to the cylinder surface and configured to be arranged either side of the radial end of the disc formed by the first stator  104 . 
         [0116]    Similarly, and as illustrated in  FIG. 4 , the second rotor  202  is formed of several sections  212 ,  212 ′ comprising assembly orifices  214 ,  214 ′. The first and second walls  206 ,  208  each comprise an inner surface and an outer surface, magnetization areas  216  being arranged on the inner surfaces of the walls  206 ,  208 . 
         [0117]    As illustrated in  FIG. 4 , the first  36  and second  38  lateral portions of the outer slide  32  are formed on the outer surface of the first wall  206 . In addition, second matching means  218  are arranged on the outer surface of the first wall  206 . 
         [0118]    The second stator  204  is formed of a second rim, of which one portion  220  is illustrated in  FIG. 4 ; the portion  220  comprises second radial notches  222  in which second active modules  224  are inserted. 
         [0119]    It will be understood from  FIGS. 3 and 4  that the sides  40 ,  42  and the lateral portions  36 ,  38  are respectively arranged symmetrically in relation to a first R 1  and second R 2  radius of the first  102  and second  202  rotors. 
         [0120]      FIG. 5  illustrates a mounting step of the electric generator  10 . 
         [0121]    Initially the first connecting means  14  are mounted on the second bearing  28 , via cooperation between second attaching elements  24  and the upper part of the second bearing  28 . 
         [0122]    The portions  120  of the first rim of the first stator  104  are then mounted on the upper end  15  of the first connecting means  14 , and the first bearing  26  is also mounted, for example but not limited thereto by welding or riveting, on the upper end  15  of the first connecting means  14 . 
         [0123]    As detailed previously in connection with  FIG. 3 , the sections  112 ,  112 ′ of the first rotor  102  are then mounted around the first stator  104 , the sections  112 ,  112 ′ being secured via their assembly orifices  114 ,  114 ′ and assembly means, and the radial engaging of the sections  112 ,  112 ′ around the first stator  104  is limited by the presence of the first bearing  26 ; in particular, the first securing means  29  allow the securing together of the second wall  108  of the first rotor  102  and the first bearing  26 . 
         [0124]    Next, the portions  220  of the second rim of the second stator  204  are mounted on the attaching means  16  of the upper end  15  of the connecting means  14 . In particular, the attaching means  16  define a first and second longitudinal end, the first and second stators  104 ,  204  being respectively mounted on each of the longitudinal ends, the first bearing  26  being mounted between the two longitudinal ends. 
         [0125]    Thereafter and as illustrated in  FIG. 5 , the sections  212 ,  212 ′ of the second rotor  202  are moved radially relative to the sections  112 ,  112 ′ of the first rotor  102 . 
         [0126]    For example, but not limited thereto, the first and second rotors  102 ,  202  each comprise the same number of sections, each section  112 ,  112 ′,  212 ,  212 ′ comprising first azimuthal securing means  12  and each section  112 ,  112 ′ of the first rotor  102  being configured to cooperate with a section  212 ,  212 ′ of the second rotor  202 . 
         [0127]    It could also be contemplated, without departing from the scope of the invention, that the first  102  and second  202  rotors do not comprise the same number of sections or that the matching of the sections of the first and second rotors  102 ,  202  is only performed by some of their sections. 
         [0128]    It will therefore be understood, as illustrated in particular in  FIG. 5 , that the section  220  of the second rotor  202  is arranged above the second stator  204 , the first and second walls  206 ,  208  being arranged on each side of the second stator  204 , and the first wall  206  of the second rotor  202  is arranged facing the second wall  108  of the first rotor  102 , the lower end  37  of the outer slide  32  formed on the second rotor  202  being arranged opposite, even slightly above the upper end  39  of the inner slide  34  formed on the first rotor  102 . The second rotor  202  can then be moved radially relative to the first rotor  102 , when mounting or dismounting the electric generator  10 , so that the outer slide  32  slides around the inner slide  34 . In this position in which the outer  32  and inner  34  slides cooperate, there is merging of the first R 1  and second R 2  radii. 
         [0129]    The second rotor  202  is therefore moved radially in relation to the first rotor  102  until the first  118  and second  218  matching means are arranged opposite one another to match the first  102  and second  202  rotors. For example and not limited thereto, the matching means  118 ,  218  can be formed by threaded holes and bolts, rivets or any other device allowing the matching of the first and second  102 ,  202  rotors. It could also be envisaged, without departing from the scope of the present invention, that there is an abutment on the first azimuthal securing means  12  allowing the limiting of radial movement of the second wall  108  of the first rotor  102  relative to the first wall  206  of the second rotor  202 . 
         [0130]    It will therefore be understood that the first azimuthal securing means  12  have the effect that the first  102  and second  202  rotors are unable to rotate in relation to one another about the first axis X. 
         [0131]    It will also be understood that the shape of the first azimuthal securing means  12 , described in particular with reference to  FIG. 2 , is such that the first azimuthal securing means  12  prevent any axial movement relative to the first axis X between the first  102  and second  202  rotors, thereby making it possible to maintain constant the distance separating the first  102  and second  202  rotors. It therefore appears that the first azimuthal securing means  12  also form axial securing means. 
         [0132]    Without departing from the scope of the present invention, an electric generator  10  can also be envisaged of which the second rotor  202  is secured onto the first bearing  26 , the second rotor  202  therefore not necessarily comprising matching means to allow the second rotor  202  to be matched directly with the first rotor  102 . 
         [0133]      FIG. 6  illustrates a wind turbine  50  comprising a hub  52  mounted in rotation about the first axis X, and a spinner  54  to drive the hub  52  in rotation about the first axis X; also, the first  100  and second  200  electrical machines are mounted in the wind turbine  50 . As illustrated in  FIG. 6 , the first and second stators  104 ,  204  and the first and second rotors  102 ,  202  are coaxial to one another, the first and second  102 ,  202  rotors both being mounted in rotation about the first axis X. 
         [0134]    The attaching means  33  mounted on the first wall  106  of the first rotor  102  are also mounted on the hub  52 . It will therefore be understood that when the spinner  54  drives the hub  52  in rotation about the first axis X, it also drives the first rotor  102  in rotation about the first axis X, via the attaching means  33 . Subsequently, since the first and second rotors  102 ,  202  are secured by the first azimuthal securing means  12 , the second rotor  202  is simultaneously driven in rotation about the first axis X. 
         [0135]    For example but not limited thereto the attaching means  33  are formed of a plate or metal sheet of which the lower and is attached to the hub  52  and to the second bearing  28 , for example by clamping the lower end of the metal sheet between the hub  52  and the second bearing  28 . 
         [0136]    As can be seen on examining  FIG. 6 , the wind turbine  50  is also formed of a frame  55  secured to a tower  57  on which the hub  52  is mounted in rotation. The first and second stators  104 ,  204  are mounted firstly on the frame  55  of the wind turbine via first attaching elements  22  mounted on the lower end  20  of the first connecting means  14 , and secondly on the first and second bearings  26 ,  28 ; they are not driven in rotation about the axis X. Therefore via respective cooperation between the induced part of the first and second stators  104 ,  204  stators and the inducing part of the first and second rotors  102 ,  202 , the first and second electrical machines  100 ,  200  respectively generate first and second magnetic flows. 
         [0137]    As illustrated in  FIG. 6 , the wind turbine  50  also comprises a ventilation system  56  which comprises at least one ventilation module  58  formed of a fan and motor. The ventilation system  56  also comprises an aeration duct  60  directed towards the perforation  18  formed in the median portion of the first connecting means  14 . 
         [0138]    Therefore and as shown by the arrows illustrating the cycle in  FIG. 6 , the ventilation system  56  allows the diffusing of a fluid e.g. air of temperature T 1  in the first and second electrical machines  100 ,  200 . The operation of the first and second electrical machines  100 ,  200  and in particular the rotation of the first  102  and second  202  rotors, tends to raise the temperature of the fluid which is then directed at temperature T 2 , towards the ventilation system  56 . Through heat exchange with the environment outside the wind turbine  50 , the temperature of the fluid is lowered to temperature T 1 , before the fluid is again directed into the aeration duct  60  towards the first and second electrical machines  100 ,  200 . 
         [0139]    As detailed in particular with reference to  FIGS. 3 and 4 , the first  100  and second  200  electrical machines have a modular structure and in particular comprise several sections  112 ,  112 ′,  212 ,  212 ′ forming the first  102  and second  202  rotors, and several portions  120 ,  220  forming the rims of the first  104  and second  204  stators. The first connecting means  14  subsequently define a circular shape coaxial with the stators  104 ,  204  and may also, but not limited thereto, be formed of a plurality of elements arranged between the first  100  and second  200  electrical machines. It will also be understood that the perforations  18  formed in the median part of the first connecting means  14  are not necessarily distributed homogeneously over the entire circular shape defined by the first connecting means  14 . For example and not limited thereto, at some positions of the circular shape defined by the first connecting means  14 , the median portion may not be perforated. Therefore the ventilation system  56  allows the ventilation of the first  100  and second  200  electrical machines, the perforations  18  formed in the first connecting means  14  directing the fluid towards the first machine  100 , whereas the positions of the circular shape defined by the first connecting means  14  in which no perforation is formed direct the fluid towards the second electrical machine  200 . 
         [0140]    In addition, the ventilation system  56  may be formed of several ventilation modules  58 . For example and not limited thereto, to allow homogenous ventilation of the electrical machines  100 ,  200 , the same number of ventilation modules  58  may be intended for the ventilation of the first  100  and second  200  electrical machines. 
         [0141]    It will therefore be understood that the first connecting means  14  indirectly connect the hub  52  to the first and second electrical machines,  100 ,  200  and form a flange in which perforations  18  are made to allow ventilation of the electrical machines  100 ,  200 . 
         [0142]    As detailed in the foregoing, the first and second rotors  102 ,  202  and the first and second stators  104 ,  204  are respectively formed of permanent magnets arranged around active modules. It will also be understood that the structure of the first and second electrical machines  100 ,  200  of the present invention is identical. Nevertheless, it could just as well be envisaged without departing from the scope of the invention that in the electric generator  10  either one of the first and second electrical machines  100 ,  200 , or both, has induced and inducing parts of different structure; for example and not limited thereto one of the electrical machines  100 ,  200  could comprise a coiled rotor. 
         [0143]      FIG. 7  illustrates another embodiment of the electric generator  10  according to the present invention which, in addition to the first and second electrical machines  100 ,  200 , comprises a third electrical machine  300  formed by a third rotor  302  coaxial to the first rotor  102  and surrounding a third stator  304 . In addition, the electric generator  10  also comprises a third bearing  62  and second connecting means  66 . 
         [0144]    Similar to the first  100  and second  200  electrical machines previously described, the third rotor  302  of the third electrical machine  300  comprises first  306  and second  308  walls both of annular shape, which define a third annular housing configured to receive the third stator  304 . The third stator  304  is therefore surrounded by the third rotor  302  circumferentially. 
         [0145]    As illustrated in  FIG. 7 , the first  100  and third  300  electrical machines are arranged symmetrically either side of the second electrical machine  200 . 
         [0146]    It will be understood that to mount the electric generator  10  such as illustrated in  FIG. 7 , in similar manner to the mounting previously described, the first electrical machine  100  and the second stator  204  are mounted on the first connecting means  14 . The second connecting means  66  are then mounted on the second stator  204 , the lower end of the second connecting means  66  being attached to the frame  55 . The third electrical machine  300  is then mounted on the second connecting means  66 , the first wall  306  of the third rotor  302  being mounted on the third bearing  62 , whilst the third stator  304  is mounted on the upper end of the second connecting means  66 . 
         [0147]    The second rotor  202  is then engaged between the first  100  and third  300  electrical machine, second azimuthal securing means  68  being formed on the second wall  208  of the second electrical machine  200  and on the first wall  306  of the third electrical machine  300 . 
         [0148]    It will therefore be understood that the second azimuthal securing means  68  are configured to join together the second and third annular housings defined by the second  202  and third  302  rotors respectively. 
         [0149]    Therefore, and in similar manner to the foregoing description with reference in particular to  FIG. 6 , the spinner  54  drives the hub  52  in rotation about a first axis X, so that the first rotor  102  rotor is driven in rotation about the first axis X via attaching means  33 . Subsequently, the second  202  and third  302  rotors being secured to the first rotor  102  by the first  12  and second  68  azimuthal securing means, they are simultaneously driven in rotation about the first axis X. Since the first  104 , second  204  and third  304  stators are not driven in rotation about the first axis X, through respective cooperation between the induced part of the first, second and third stators  104 ,  204 ,  304  and the inducing part of the first, second and third rotors  102 ,  202 ,  302 , the first, second and third electrical machines  100 ,  200 ,  300  machines respectively generate a first, second and third magnetic flow. 
         [0150]    The foregoing detailed characteristics regarding the structure of the first and second electrical machines  100 ,  200  evidently apply to the third electrical machine  300 . In particular, perforations can be made in the second connecting means  66  to enable the ventilation system  56  to ventilate the first, second and third electrical machines  100 ,  200 ,  300 . 
         [0151]    The entire foregoing description is given as an example and therefore does not limit the invention. 
         [0152]    In particular, although the invention is particularly detailed for electric generators comprising two or three electrical machines, it can be extended directly and obviously to a higher number of electrical machines.