Abstract:
The invention relates to a synchronous generator of a gearless wind power plant, comprising an external rotor and a Stator, wherein the synchronous generator has a generator outside diameter and the Stator has a Stator outside diameter, and a ratio of the stator outside diameter to the generator outside diameter is greater than 0.86, in particular greater than 0.9, and in particular greater than 0.92.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The invention concerns a synchronous generator of a gearless wind power installation. The invention also concerns a gearless wind power installation. 
         [0003]    2. Description of the Related Art 
         [0004]    Wind power installations are generally known, they generate electric energy from the energy of the wind. Usually a so-called horizontal-axis wind power installation is used for that purpose, as shown for example in  FIG. 1 . It has an aerodynamic rotor which, driven by the wind, rotates about a substantially horizontal axis and in so doing drives a generator. Particularly reliable wind power installations are of a gearless design so that the aerodynamic rotor is coupled directly to the generator, namely the electrodynamic rotor of the generator. The aerodynamic rotor and the electrodynamic rotor which for the avoidance of misunderstanding is referred to hereinafter as the rotor member rotate in that case at the same speed. For that purpose, at any event for wind power installations involving high levels of power which nowadays are in the megawatt range, corresponding synchronous generators of a large structural configuration, namely in particular with a large air gap diameter, are required. In other words, an air gap diameter is correspondingly greater and thus the structural configuration of the synchronous generator overall is correspondingly greater, the greater the amount of power that the synchronous generator is to generate. 
         [0005]    The size of a generator however cannot be increased just as desired. In particular, transport conditions on public roads limit the structural size of a generator. 
         [0006]    The wind power installation which at the present time is the most powerful in the world, the E126 from ENERCON GmbH, has an air gap diameter of 10 m and solves the transport problem in that both the rotor member and also the stator of the generator are respectively subdivided into four segments which are assembled only at or in the proximity of the location for erection of the wind power installation. Such a procedure however can be complicated and expensive and presupposes particular precautions in order to reduce risks of error, in particular at a separation location. It would also be desirable to reduce the complication and expenditure involved in assembly. 
         [0007]    The German Patent and Trade Mark Office searched the following state of the art in the priority application: DE 44 02 184 A1, DE 196 36 591 A1, DE 199 23 925 A1 and DE 10 2004 018 758 A1. 
       BRIEF SUMMARY 
       [0008]    One or more embodiments of the present invention may address one or more of the above-mentioned problems. In particular in one embodiment there is provided a generator for a gearless wind power installation, which can be transported with as few problems as possible and which can be installed at the lowest possible level of complication and expenditure when erecting a wind power installation. The invention seeks to propose at least an alternative solution. 
         [0009]    According to one embodiment of the invention there is proposed a synchronous generator of a gearless wind power installation includes an external rotor member and a stator around which the external rotor member rotates as desired. The synchronous generator has a generator outside diameter and the stator has a stator outside diameter. It is proposed that the synchronous generator is so constructed that a ratio of the stator outside diameter to the generator outside diameter is greater than 0.86. It is thus proposed that the air gap of a synchronous generator for a gearless wind power installation is disposed as far outwardly as possible. The synchronous generator is therefore correspondingly constructed such that the air gap is disposed as far outwardly as possible and accordingly the external rotor member is as narrow as possible so that said ratio of the stator outside diameter to the generator outside diameter is more than 0.86. 
         [0010]    It is to be noted in that respect that, in a synchronous generator of the external rotor member type which is proposed here, the stator outside diameter basically corresponds to the air gap diameter. In this respect, the basic configuration adopted is in principle a cylindrical configuration both for the stator and also the rotor member and in particular the air gap. Disregarding the thickness of the air gap, the air gap diameter corresponds to the stator outside diameter. 
         [0011]    Particularly preferably the air gap is displaced outwardly to such an extent that the ratio of the stator outside diameter to the generator outside diameter is greater than 0.9. Still more preferably the synchronous generator is so constructed that the ratio of the stator outside diameter to the generator outside diameter is greater than 0.92. 
         [0012]    The proposed use of an external rotor member already permits such an advantageous ratio. Due to the construction involved more specifically the rotor member poles or in their actual physical configuration the rotor member pole shoes with the corresponding exciter windings if an externally excited synchronous generator is used can be reduced in their radial extent to a very small amount. As a result it is possible for the air gap to be displaced outwardly as far as possible. At the same time this means that the stator has room in order to advantageously design the stator windings. Further space in the interior of the stator can be used, as will also be described hereinafter in respect of some embodiments by way of example. 
         [0013]    In an embodiment it is proposed that the stator has a radial support structure which extends radially inwardly and is adapted for fixing to an axle mounting extending axially through the stator. Thus the space in the interior of the stator is advantageously used for a stable structure for the stator. In that respect, the underlying construction involves an axle journal mounting which upon appropriate installation of the generator extends centrally through the stator. Such an axle mounting is a stable, in particular tubular element which is fixedly secured in a machine carrier and can be for example a ferrous casting. The support structure thus extends from the stator lamination assembly carrying the stator winding substantially from the air gap radially inwardly to that axle mounting on which it can be fixedly secured with a suitable annular flange. 
         [0014]    It is preferably proposed that the stator has radial and axial cooling passages. The radial cooling passages are provided for radially supplying cooling air to the stator, namely in particular to the lamination assembly of the stator. The axial cooling passages then guide the radially supplied cooling air for cooling the stator along the latter, in particular through the stator lamination assembly and/or between rotor member poles. In particular the cooling air which is radially supplied in an adequate amount is divided for axially guiding same, namely in an axial forward direction which in proper operation of the wind power installation is in opposite relationship to the wind, and in a rearward direction, that is to say basically in the direction of the wind. 
         [0015]    That also provides that the space in the interior of the stator is put to advantageous use. In that respect the use of that space permits a supply of a large volume of cooling air. If it is then divided in a forward direction and a rearward direction it appropriately flows from such a division location only over half the stator length, relative to the axial direction. Accordingly the stator can be well cooled and have long cooling paths, in respect of which cooling air, when reaching the end of such a cooling path, has already heated up to such an extent that its cooling capability is considerably reduced, are avoided. 
         [0016]    It is also desirable for cooling air to be supplied radially over the entire axial extent of the stator. The radial cooling passages are thus of a width corresponding to the length of the stator. That permits the option of a large-volume cooling flow when the cooling air is supplied radially, and this avoids cooling air flow losses. 
         [0017]    It is also desirable for the radial support structure to be so designed that it provides the radial cooling passages. In that way it is possible in principle to use the entire space within the stator for the supply of cooling air. For that purpose the support structure can have a few substantially radially extending support plates. Preferably plates are used, of which some extend radially and axially and others extend radially and transversely relative to a longitudinal axis, namely the axis of rotation of the synchronous generator. Those plate can be so assembled that they can reliably carry the stator, namely in particular the stator lamination assembly, and at the same time guide cooling air radially in the direction towards the stator lamination assembly. If the structure overall is so designed that the internal space in the stator is substantially available for that radial supply of cooling air, it is possible to guarantee a large-volume cooling air flow which in return achieves a low cooling air flow speed and accordingly makes only low demands in respect of the aerodynamics of the radial cooling passages. 
         [0018]    According to a further configuration it is proposed that the synchronous generator is encapsulated. In particular it is proposed that the external rotor member of the synchronous generator is encapsulated. That makes it possible to achieve a compact structure which is also advantageous for handling for transport purposes. An advantageous structure such that the air gap is displaced radially outwardly as far as possible makes it possible to achieve an increase in generator power without an increase in outside dimensions. An increase in power is thus possible without increasing the overall dimension of the generator so that as far as possible the generator can be transported in one piece from a production factory to the erection location. An encapsulated construction can thus already be achieved in the factory and the generator can advantageously be transported in encapsulated fashion. That overall facilitates construction of the installation. 
         [0019]    In particular for that purpose the rotor member, namely the external rotor member, can have a rotor member bell which more specifically encloses the rotor member in the fashion of a bell or as a cover. In that respect, inspection openings are provided in the bell for maintenance of the synchronous generator. Such inspection openings are openings which in particular can also be opened at an end of the rotor member bell to view the condition of the synchronous generator and possibly also to carry out minor repairs or the like. 
         [0020]    Preferably the synchronous generator is separately excited. Thus the rotor member, namely the external rotor member, has many rotor member poles with exciter windings, by which a current for exciting the rotor member poles and thus the rotor member is controlled. Those rotor member poles are in particular in the form of pole shoes or pole shoe bodies with an exciter winding, which are carried at a support ring of the rotor member. That structure is thus so adapted in construction that it is particularly slender and is thus of a minimum possible thickness in the radial direction. As a result the air gap can be displaced radially outwardly as far as possible. 
         [0021]    Preferably the synchronous generator is in the form of a ring generator. A ring generator describes a structural form of a generator, in which the magnetically effective region is arranged substantially on a ring region concentrically around the axis of rotation of the generator. In particular the magnetically effective region, more specifically of the rotor member and the stator, is arranged only in the radially outer quarter of the generator. That configuration in the form of a ring generator also provides a possibility of the air gap being displaced radially as far outwardly as possible or it simplifies attaining such a structure. 
         [0022]    Preferably there is proposed a slowly operating synchronous generator which has at least 48 stator poles. Thus, even with a low speed of rotation, it is possible to generate an alternating current at a comparatively high frequency. Accordingly it is preferably proposed that there are provided at least 72 stator poles, wherein still more preferably even more stator poles are used, in particular at least 192 stator poles. 
         [0023]    It is also desirable for the synchronous generator to be in the form of a 6-phase generator, more specifically a generator having two 3-phase systems which in particular are displaced relative to each other through about 30 degrees. Such a configuration is particularly advantageous for generating a 6-phase current which as a result is highly suited to rectification and due to the principle involved already causes a lesser degree of harmonics upon rectification. 
         [0024]    It is further proposed that a continuous winding be provided for the stator, more specifically in particular a continuous line or a continuous line system for each phase. In the case of the 6-phase generator, that is to say with twice 3-phases therefore a total of six line systems would be implemented. The placement of such six line systems without interruption for the entire stator which can preferably be of an outside diameter of 4.5 m is extremely complicated and expensive but leads to a highly reliable stator and thus also a correspondingly reliable generator because this dispenses with connecting locations which could otherwise come loose in operation. 
         [0025]    In a further embodiment it is proposed that the stator is carried on an axial mounting, in particular on an axle journal mounting. That axial mounting, in particular the axle journal mounting, extends axially through the stator and the external rotor member, more specifically centrally along the axis of rotation of the external rotor member and thus at the same time the central axis of the stator. In addition the external rotor member is preferably supported on a first and a second bearing connected to that mounting, wherein both bearings are arranged in the axial direction at one side of the stator, in particular in such a way that the one bearing is arranged in the axial direction between the other bearing and the stator. The rotor member is thus carried by those two bearings so that it is held in cantilever relationship in the region of the stator. 
         [0026]    In other words the stator is fixedly secured to the mounting by those two axially spaced bearings so that the external rotor member extends over the stator and is carried on one side of the stator on the two bearings. That therefore gives an extremely stable structure which in that respect is comparatively easy to build. The use of two bearings, namely both on one side of the stator, is particularly well suited for carrying tilting forces which could be applied in particular by a wind load on the rotor blades by way of a rotor hub towards the external rotor member. It is to be noted that one or both of the bearings can also be arranged spaced at a greater distance from a fixing of the stator on the mounting or an axle journal. A spacing which is as large as possible between the two bearings also enhances the capability of carrying tilting forces. 
         [0027]    Preferably there is proposed a synchronous generator which is characterized in that there is provided at least one blower ( 309 ), in particular in the support structure of the stator, to blow air for cooling purposes radially outwardly through the stator lamination assembly ( 658 ). The air flow is thus deliberately directed outwardly and can firstly cool the stator. 
         [0028]    In a further embodiment it is proposed that the external rotor member has cooling openings towards the air gap so that a part of the cooling air flows from the air gap ( 206 ) further outwardly through the external rotor member ( 304 ) and between rotor member poles, in particular rotor member pole shoes ( 32 A), of the external rotor member, along exciter windings of the external rotor member in order thereby to cool the rotor member pole shoes, in particular their exciter windings. 
         [0029]    Thus at least in accordance with a preferred embodiment, there is proposed a large slowly operating synchronous generator which has a separately excited rotor member. It is cooled in specifically targeted fashion by at least one blower in the support structure of its stator. In that case the cooling air is blown radially outwardly by the blower, that is to say it is urged outwardly, and thus firstly cools the stator, in particular the stator lamination assembly, through which the cooling air flows outwardly to the air gap. The cooling air thus flows further through the air gap and in so doing cools the stator and the external rotor member. In addition a part of the cooling air which in the meantime has already been at least somewhat heated flows outwardly through openings in the external rotor member. As a result the exciter windings of the external rotor member can be reached and cooled, which otherwise are not in direct contact with the air gap. 
         [0030]    The structure of this gearless, separately excited, slowly operating generator in the form of an external rotor member means that it is also possible to achieve such cooling of the external rotor member. The external rotor member structure also provides in the region of the pole shoes of the rotor member an intermediate space which permits such cooling. 
         [0031]    Preferably the synchronous generator is so designed and sized that the stator outside diameter is at least 4.4 m, preferably at least 4.5 m and in particular at least 4.6 m, in particular with a generator outside diameter of 5 m. There is thus proposed a synchronous generator which with an outside diameter of 5 m still permits transport on public roads and in that respect is of a stator outside diameter that is as large as possible and can thus afford a nominal power which is as great as possible. 
         [0032]    In addition there is proposed a wind power installation having a synchronous generator according to at least one of the above-described embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0033]    The invention will now be described by way of example hereinafter by means of embodiments with reference to the accompany Figures. 
           [0034]      FIG. 1  shows a perspective view of a wind power installation, 
           [0035]      FIG. 2  shows a side view in section of a generator of internal rotor member type, 
           [0036]      FIG. 3  shows a side view in section of a generator of external rotor member type, 
           [0037]      FIG. 4  shows a perspective view of a generator similar to  FIG. 3 , 
           [0038]      FIG. 5  shows a further perspective view of a generator as shown in  FIG. 4 , 
           [0039]      FIG. 6  shows a perspective view of a generator according to the invention in a further embodiment, 
           [0040]      FIG. 7  shows a perspective sectional view of the  FIG. 6  generator, 
           [0041]      FIG. 8  shows another view of the  FIG. 7  generator, 
           [0042]      FIG. 9  shows a diagrammatic view on an enlarged scale of a portion of a generator, 
           [0043]      FIG. 10  shows a diagrammatic view on an enlarged scale of a portion of a generator, 
           [0044]      FIG. 11  diagrammatically shows a portion of a rotor of an external rotor member together with a portion of a rotor of an internal rotor member, and 
           [0045]      FIG. 12  diagrammatically shows a sectional side view of a generator fixed to a support structure. 
       
    
    
     DETAILED DESCRIPTION 
       [0046]      FIG. 1  shows a wind power installation  100  comprising a pylon  102  and a pod  104 . Arranged at the pod  104  is a rotor  106  having three rotor blades  108  and a spinner  110 . In operation the rotor  106  is caused to rotate by the wind and thereby drives a generator in the pod  104 . 
         [0047]      FIG. 2  shows a generator  201  of internal rotor member type and thus an externally disposed stator  202  and a rotor member  204  which is disposed inwardly in relation thereto. The air gap  206  is between the stator  202  and the rotor member  204 . The stator  202  is carried on a stator carrier  210  by way of a stator bell  208 . The stator  202  has stator lamination assemblies  212  which carry windings, of which winding heads  214  are shown. Basically the winding heads  214  show the winding wires which are laid from a stator groove into the next stator groove. The stator lamination assemblies  212  of the stator  202  are fixed to a support ring  216  which can also be viewed as part of the stator  202 . The stator  202  is fixed to a stator flange  218  of the stator bell  208  by means of that support ring  216 . The stator bell  208  carries the stator  202  by way thereof. In addition the stator bell  208  can provide blowers for cooling purposes, that are arranged in the stator bell  208 . By virtue thereof air for cooling purposes can also be urged through the air gap  206  in order thereby to cool in the region of the air gap. 
         [0048]      FIG. 2  also shows the outside periphery  220  of the generator  201 . Only handling tongues  222  project therebeyond, which however does not cause any problem as they are not present over the entire periphery. 
         [0049]    Adjoining the stator carrier  210  is an only partly shown axle journal  224 . The rotor member  204  is supported on the axle journal  224  by way of two rotor member bearings  226  of which only one is shown. For that purpose the rotor member  204  is fixed to a hub portion  228  which is also connected to rotor blades of the aerodynamic rotor so that the rotor blades, moved by the wind, can rotate the rotor member  204  by way of that hub portion  228 . 
         [0050]    In this arrangement the rotor member  204  has pole shoe bodies with exciter windings  230 . Towards the air gap  206 , at the exciter windings  230 , it is still possible to see a part of the pole shoe  232 . To the side remote from the air gap  206 , that is to say inwardly, the pole shoe  232  with the exciter winding that it carries is fixed to a rotor member support ring  234  which in turn is fixed to the hub portion  228  by means of a rotor member carrier  236 . The rotor member support ring  234  is basically a continuous solid portion in the form of cylindrical configuration. The rotor member carrier  236  has a plurality of struts. 
         [0051]    It will be seen from  FIG. 2  that the radial extent of the rotor member  204 , namely from the rotor member support ring  234  to the air gap  206 , is markedly less than the radial extent of the stator  202 , namely from the air gap  206  to the outer periphery  220 . 
         [0052]    In addition the Figure shows a spacing length  238  which approximately describes a mean spacing of a rotor member mounting  250  relative to a stator mounting  252 . The length  238  is a dimension for influencing the air gap in the generator structure by virtue of external forces. With the generator shown in  FIG. 2  that axial spacing length is comparatively great and thus shows that a very rigid construction of stator and rotor member is necessary in order to also ensure in operation a uniform spacing between the stator and the rotor member. 
         [0053]    The generator  301  in  FIG. 3  is of the external rotor member type. Accordingly the stator  302  is disposed inwardly and the rotor member  304  outwardly. The stator  302  is carried by a central stator support structure  308  on the stator carrier  310 . A blower  309  is shown in the stator support structure  308  for cooling purposes. The stator  302  is thus centrally supported, which can greatly enhance stability. In addition it can be cooled from the interior by the blower  309  which only characteristically represents further blowers. In this construction the stator  302  is accessible from the interior. Cooling air is urged outwardly by the blower. 
         [0054]    The rotor member  304  has an outwardly disposed rotor member support ring  334  which is fixed to a rotor member carrier  336  which can also be referred to as the rotor member bell  336  and is carried by the carrier or the bell on the hub portion  328  which in turn is mounted on an axle journal  324  by way of two rotor member bearings of which one rotor member bearing  326  is shown. 
         [0055]    By virtue of the interchanged arrangement of the stator  302  and the rotor member  304  this configuration gives an air gap  306  which is of a larger diameter than the air gap  206  in  FIG. 2  of the generator  201  of internal rotor member type. 
         [0056]      FIG. 3  also shows an advantageous arrangement of a brake  340  which if required can stop the rotor member  304  by way of a brake disc  342  connected to the rotor member  304 . 
         [0057]      FIG. 3  also shows an axial spacing length  338  which also describes a mean spacing of the rotor member mounting  350  relative to a stator mounting  352 . Here that length  338  is markedly reduced in comparison with the axial spacing length  238  shown in the generator of the internal rotor member type illustrated in  FIG. 2 . The axial spacing length  238  in  FIG. 2  also determines a mean spacing between the two support structures for the stator  202  on the one hand and the rotor member  204  on the other hand. The shorter such an axial support length  238  or  338  respectively is, the correspondingly greater is the air gap stability which can be achieved, in particular also stability in respect of tilting between the stator and the rotor member. 
         [0058]    The outside diameter  344  of the outer periphery  320  is identical in both the generators illustrated in  FIGS. 2 and 3 . The outer periphery  220  of the generator  201  in  FIG. 2  thus also involves the outside diameter  344 . In spite of the same outside diameter  344 , the structure shown in  FIG. 3  illustrating the generator  301  of the external rotor member type makes it possible to achieve a larger air gap diameter for the air gap  306  relative to the air gap  206  in  FIG. 2 . 
         [0059]    The basic structure of an encapsulated generator  401  according to one embodiment the invention can be seen from the perspective view in  FIG. 4 .  FIG. 4  also shows a stator carrier  410 , in particular its flange. That stator carrier  410  carries the stator. The illustrated carrier flange  450  is provided for fixing to a machine carrier which more specifically is fixedly arranged as required on a pod of a wind power installation. The stator carrier  410  carries the stator of the generator  401  and is also referred to as the axle journal mounting because that axle journal mounting is fixed with its one side, namely the carrier flange  450 , to the machine carrier, while at its other side which is not shown in  FIG. 4  it is fixedly connected to an axle journal. Such an axle journal carries or supports the aerodynamic rotor. 
         [0060]    The stator carrier  410  or the axle journal mounting  410  can be interpreted as being part of the generator  401 . 
         [0061]      FIG. 4  also shows brakes  440  which also mark the transition from the external rotor member  404  to the inwardly disposed stator  402 . In this case the brakes  440  are fixed to an annular stator disc  446  and from there can brake the rotor member  404  at its brake disc  442 . The annular stator disc  446  is substantially fixed to the carrier flange  450 . 
         [0062]      FIG. 5  shows a further view of the generator  401  and essentially shows the encapsulated rotor member  404 . In addition in the perspective view in  FIG. 5 , of the stator carrier  410  or the axle journal mounting  410 , it is possible to see an axle journal flange  452  to which an axle journal is mounted in ordinary use. This also makes it clear that the axle journal mounting  410  or the stator carrier  410  can be interpreted as being part of the generator  401 , which moreover applies not only for that embodiment, because it will be clearly seen from  FIGS. 4 and 5  that the generator  401  with that stator carrier  410  does in any case form a spatially clearly predetermined arrangement. 
         [0063]      FIG. 6  shows a generator  601  which is of a similar structure to the generator  401  and the generator  301 . The generator  601  differs from the generator  401  in  FIGS. 4 and 5  substantially in that a stator carrier or an axle journal mounting is not shown, although this not an important consideration in terms of the view. In addition  FIG. 6  shows an inspection opening  656  through which it is possible to look into the rotor member  604  to be able to perform any maintenance or checking operations on the rotor member  604 . In addition the stator  602  can also be at least partially examined and assessed through that inspection opening  656 . The inspection opening  656  is shown for illustrative purposes in  FIG. 6 . If required however and having regard to the remaining stability of the illustrated encapsulation of the rotor member  604  further inspection openings  656  are preferably also to be provided. For examining and assessing just the stator  602 , one inspection opening  656  could suffice, which as required can be turned to the corresponding location of the stator  602 . For examining the rotor member  604  however it may be advantageous to provide a plurality of such inspection openings  656 . 
         [0064]    The view in  FIG. 7  shows a part of the structure of the inwardly disposed stator  602 . It has a stator lamination assembly  658  which is wound thereon, as indicated by the winding heads  660 . Towards the axis of rotation the stator  602  has a radial support structure  662 . The radial support structure  662  substantially includes two radial guide plates which extend radially outwardly and in that respect are arranged perpendicularly to the axis of rotation of the generator  601 . Those radial guide plates  664  can fix the stator  602 , in particular the stator lamination assembly  658 , with its windings, on a stator carrier or an axle journal mounting as shown for example in  FIG. 4  and identified by reference  410 . At the same time the guide plates  664  can pass air as cooling air to the stator lamination assembly  658 . 
         [0065]    In that way the stator lamination assembly  658  and also the windings therein, which are indicated by the winding heads  660 , can be cooled. Radially outwardly adjoining the stator lamination assembly  658  is the rotor member  604  with its pole shoes  632 . An air gap  606  is provided between the stator lamination assembly  658  and the pole shoes  632 , the air gap being visible only as a line in  FIG. 7 . 
         [0066]    The perspective view in  FIG. 8  also illustrates the structure of the stator  602  with its radial support structure  662  with the two radial guide plates  664 . In this respect it is possible to see further inspection openings  656 ′ which are also provided for assessing and maintaining both the stator  602  and also the rotor member  604 . In that respect the inspection openings  656 ′ are arranged in a radial rotor plate  666  and allow a view on to the pole shoes  632  of the rotor member and in particular the winding heads  660  at the machine carrier side. 
         [0067]    In that arrangement the radial rotor plate  666  is such that a brake disc  642  can also be carried. 
         [0068]      FIGS. 9 and 10  show a partial view illustrating cooling flows in different generator types, namely a generator  901  of the internal rotor member type in  FIG. 9  and a generator  1001  of external rotor member type in  FIG. 10 . The portion in  FIG. 9  approximately corresponds to the portion of a generator  201  as shown in  FIG. 2 ,  FIG. 9  showing a somewhat different embodiment. The portion in  FIG. 10  approximately corresponds to the portion of a generator  301  as shown in  FIG. 3 ,  FIG. 10  showing a somewhat different embodiment. 
         [0069]    Referring to  FIG. 9  radial cooling flows  970  flow substantially on both sides—with respect to the view in  FIG. 9  of the rotor  904  outwardly towards the stator lamination assembly  958  and the winding heads  960 . An axial cooling flow  972  is formed only in one direction and thus has to completely cool in the axial direction both the stator lamination assembly  958  and also the rotor member pole shoes  932 . The cooling path is therefore comparatively long and a feed of cooling air is effected substantially by way of one of the radial cooling flows  970 . 
         [0070]    The generator  1001  of external rotor member type guides cooling air radially to the stator lamination assembly  1058  by way of radial cooling flows  1070  basically over the full width of the stator  1002 , and from the stator lamination assembly the cooling air is possibly further guided by way of cooling passages (not shown) to rotor member pole shoes  1032 . The cooling air can cool the rotor member  1004  and the stator  1002  in two directions as an axial cooling flow  1072 . Therefore a great deal of cooling air can be supplied, more specifically over the full width of the stator  1002 —in relation to the view in FIG.  10 —or over the full axial length of the stator  1002 . In that case the radially supplied cooling air of the radial cooling flows  1070  can split up upon reaching approximately the air gap  1006  so that the stator  1002  and the rotor member  1004  only have to be respectively axially cooled by a cooling flow in respect of half thereof. The heating distance of the respective cooling flow is thus halved. 
         [0071]    The comparison between  FIGS. 9 and 10  also illustrates the position and the space requirement of the stator winding heads  960  of the generator  901  in  FIG. 9  for the case of an internal rotor member and the stator winding heads  1060  of the generator  1001  in  FIG. 10  for the external rotor member on the other hand. 
         [0072]    The radial and axial cooling flows  1070  and  1072  shown in  FIG. 10  can be produced for example by a blower like for example the blower  309  shown in the generator  301  in  FIG. 3 . Such a blower of which a plurality can also be provided can for example urge cooling air between the two radial guide plates  1064  so that cooling air is guided radially outwardly between the two radial guide plates  1064 . In addition, a cooling flow can result in the radial direction, due to another feed of cooling air to the stator. When the cooling flow arrives at the stator lamination assembly  1058  or the pole shoes  1032  or substantially in the region of the air gap  1006  it can be diverted into an axial flow. Suitable cooling passages can be provided distributed over the stator lamination assembly  1058  for further passing radial cooling air  1070  through the stator  1002 . Cooling air can flow substantially along between pole shoes  1032  in the axial direction and can also flow axially through the air gap  1006 . A partly axial flow of cooling air is also possible in parts of the stator lamination assembly  1058 , namely in particular in winding grooves, insofar as windings disposed therein have left a free space, for example by virtue of cooling passages, which are disposed in the windings. A further path of cooling air can be through passages which extend within the lamination assembly. Quite apart therefrom it is pointed out that the radial cooling flows  1070  and axial cooling flows  1072  indicated by arrows are to be interpreted as a diagrammatic view. A part of the cooling air can flow radially outwardly from the air gap  1006  through openings in the rotor member  1004 , namely the external rotor member  1004 , and can thereby better cool the external rotor member  1004 , although those flow portions are not shown in  FIG. 10 . 
         [0073]      FIG. 11  is a diagrammatic view showing in a portion of the structure pole shoes  32 A of an external rotor member  4 A together with pole shoes  32 B of an internal rotor member  4 B combined together in one view. In this assembly the illustrated arrangement is not part of a functioning machine. 
         [0074]    Rather,  FIG. 11  is intended to clearly illustrate the difference in the pole shoe arrangement of an external rotor member  4 A of a separately excited synchronous generator relative to the pole shoe arrangement of an internal rotor member  4 B of a synchronous generator.  FIG. 11  also shows an air gap  6 AB as an orientation guide. The internal rotor member  4 B extends from the air gap  6 AB inwardly, with the consequence that the pole shoes  32 B converge from the air gap  6 AB. In that case the intermediate spaces  48 B decrease and the pole shoes  32 B basically converge towards each other. This means that the winding space of the pole shoes  32 B is restricted and also space for possible cooling flows is reduced. It is pointed out that  FIG. 11  shows a view in the axial direction, that is to say viewing along the axis of rotation. 
         [0075]    On the other hand the pole shoes  32 A of the external rotor member  4 A diverge radially outwardly from the air gap  6 AB. Accordingly there is a great deal of intermediate space  48 A between the pole shoes  32 A. That effect can also be put to use structurally and it becomes possible for the radial extent of the rotor member pole shoes and thus basically the radial extent of the rotor member to be reduced. That represents a possible measure—in principle for the various embodiments—for the air gap to be placed as far outwardly as possible in order thereby to still further increase or optimize its efficiency, with a given structural size, in particular a given generator outside diameter. 
         [0076]    The view of the external rotor member  4 A in  FIG. 11  shows the intermediate spaces  48 A for which it is also proposed that they are used to guide cooling air. 
         [0077]      FIG. 12  diagrammatically shows a generator in an embodiment in an installed condition. Provided there is a machine carrier  1209  to which there is fixed a stator carrier  1210  to which an axle journal  1224  is in turn fixed. Of the generator  1201  the stator  1202  is fixed to the stator carrier  1210 . The machine carrier  1209 , the stator carrier  1210 , the axle journal  1224  and the stator  1202  are thus connected to provide a rigid stationary element, apart from the possibility of azimuth adjustment of the entire illustrated structure. 
         [0078]    The externally disposed rotor member  1204  is fixed to a rotor hub  1228  by way of a rotor carrier  1236 . The hub portion  1228  is mounted rotatably on the axle journal  1224  by way of a first and a second rotor bearing  1226  and  1227  respectively. The large axial spacing between the first and second rotor bearings  1226  and  1227  affords a high level of tilting stability for the rotor member  1204 . 
         [0079]    The Figure also shows an axial spacing length e corresponding to the spacing length  338  in  FIG. 3 . This describes a mean spacing in the axial direction from the rotor carrier  1236  to a stator mounting  1252 . By the provision of an external rotor member generator and thus an inwardly disposed stator  1202  the stator  1202 , as viewed in the axial direction, can be fixedly secured centrally on the stator carrier  1210  so that the illustrated spacing length e is comparatively short. Together with the large spacing and the tilting stability resulting therefrom it is possible to achieve a particularly stable structure. 
         [0080]    The rotor member  1204  also has a peripherally extending brake disc  1242  which in operation rotates together with the rotor member  1204 . A brake  1240  is correspondingly provided for braking or arresting purposes. 
         [0081]    It can also be seen from  FIG. 12  that there is a great deal of space for cooling medium, in particular cooling air, to be caused to flow against the stator  1202  from the interior. Inter alia such a cooling medium can also flow within the illustrated stator mounting  1252  to the stator, in particular in the region of the stator windings  1230 . In addition the radially guided cooling air can be used for cooling the rotor poles  1231  of the exciter winding. 
         [0082]    In principle it is therefore possible, in comparison with a separately excited internal rotor member generator, to increase the air gap diameter with the same overall outside diameter. If, in the case of internal rotor member generators, the ratio of air gap diameter to overall outside diameter is limited to below a value of 0.86, it now becomes possible to increase that ratio even with a separately excited external rotor member. It is now possible to implement a ratio of 0.86 to 0.94. In addition, in an encapsulated design, there is sufficient space for the stator winding heads. In that respect this gives good accessibility to the stator winding heads, in the case of an encapsulated design configuration. 
         [0083]    In the case of an external rotor member generator it is easily possible to provide for a through flow of air over the entire stator lamination assembly, with a supply of air within the outside dimensions. 
         [0084]    With a separately excited external rotor member generator as is proposed, in comparison with an internal rotor member generator involving the same air gap diameter, it is possible to implement a larger lamination assembly in the poles, more exciter windings and more cooling air between the pole assemblies. 
         [0085]    Disadvantages in the state of the art such as a small air gap diameter with comparable outside dimensions, difficult or practically impossible accessibility to the stator winding head in an encapsulated structure and limited air cooling options can be at least partially addressed by one or more embodiments of the proposed invention. It is thus possible to achieve better utilization of material, better cooling and accordingly a higher level of generator power or lower generator power loss. 
         [0086]    At the same time the transport dimensions are kept small, in particular it is possible to observe maximum transport dimensions for transport on public roads. It is possible to achieve an improvement of cooling of the generator and accordingly a higher level of generator power or at least a low level of generator power loss can be achieved. 
         [0087]    With a proposed separately excited external rotor member generator, in comparison with known internal rotor member generators involving the same air gap diameter, it is possible to achieve a larger lamination assembly, more exciter winding and more cooling air between the pole assemblies or poles. 
         [0088]    The various embodiments described above can be combined to provide further embodiments. All of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet are incorporated herein by reference, in their entirety. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications and publications to provide yet further embodiments. 
         [0089]    These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.