Patent Document

CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority of European Patent Office application No. 10163318.8 EP filed May 19, 2010, which is incorporated by reference herein in its entirety. 
       FIELD OF INVENTION 
       [0002]    The present invention relates to a generator and to a wind turbine. 
       BACKGROUND OF INVENTION 
       [0003]    Based on today&#39;s technology in direct drive generators, each coil is composed of more than one series turn while a chosen number of coils may also be connected in series. The two aforementioned selectable numbers, i.e. the number of series in turn and the number of coils connected in series, may be chosen to obtain the terminal voltage of the generator which itself may have already been chosen based on power electronics/grid requirements. In the described conventional type of winding, the series turns in each slot need to be electrically insulated from each other by a so called turn-turn insulation due to the voltage difference between the turns in series. 
         [0004]    The aforementioned turn-turn insulation used in the slot of the machines with conventional multi-turn windings, results in different disadvantages: Poor heat transfer coefficient of the insulation makes it very difficult for the main source of heat in the generator, i.e. the windings, to get cooled down through the neighbouring laminations. Using the required insulation in the slots decreases the slot space for the active material, which is usually copper, and thereby the so called fill factor. This in turn reduces the out put torque for the same current density or decreases the efficiency for the same torque. A typical value of fill factor for conventional type of winding is in the range of 70-80%. 
       SUMMARY OF INVENTION 
       [0005]    Therefore, it is a first objective of the present invention to provide a generator, where the slot fill factor is increased. It is a second objective of the present invention to provide an advantageous wind turbine. 
         [0006]    The above objectives are solved by the features of the independent claims. The depending claims define further developments of the invention. 
         [0007]    The inventive generator comprises at least one pole set. One pole set represents one phase. Each pole set comprises a number of poles. At least one conductor is turned about the poles of the particular pole set such that only half a single turn is associated to each pole. Preferably, a number of conductors which are connected in parallel are turned about the poles such that only half a single turn of each conductor is associated to each pole. 
         [0008]    Compared with a conventional coil composed of more than one series turn, the insulation between the conductors placed together in a slot of the inventive generator can significantly be reduced. Preferably, the turn-turn insulation; i.e. the insulation between series turns in a slot, is removed or only a thin insulation between parallel conductors is present. This improves the slot fill factor resulting in higher torque or efficiency. Moreover, the inventive generator provides the possibility for a better cooling of, for example, a permanent magnet generator. The inventive generator may, for example, be used in direct drive wind turbine applications. 
         [0009]    In the inventive generator single turn wave winding replaces the conventional windings. The idea is, that each phase in, for example, a three phase or multi phase generator has a single Go or Return path in each pole. In the frame work of the present invention a single Go or Return path is also designated as half a single turn. The Go and Return paths or half a single turns may form a wave configuration. For example, a single Go path may itself be composed of a number of parallel conductors. The parallel conductors return in the next pole and continue this way of distribution along the hole circumference of, for example, the stator of the generator. This gives the advantage of having less insulation in the slot. Thereby, a better cooling of the windings can be achieved and a higher slot fill factor can be realised. 
         [0010]    The generator may comprise a number of slots. Advantageously, between 5 and 25, preferably between 10 and 20, conductors may be connected in parallel in each slot, for instance in each stator slot. Assuming that the same slot dimension as for conventional multi-turn windings is used for the wave winding, 10 to 20 parallel conductors or in that range will form the winding in order to reduce the proximity and skin effect losses. The optimal number of parallel conductors to give a low value of proximity and skin effect loss can be chosen analytically or can be obtained by a simulation or can be obtained experimentally. 
         [0011]    The conductors can be transposed from one pole to another pole. This improves the elimination of extra AC losses, for example losses due to the proximity and skin effect. The conductors can be partially or fully transposed in each or every second and winding. Advantageously, the conductors may be transposed at every neighbouring pole or at every second neighbouring pole of the particular pole set. Preferably, the number of poles in a pole set may be an integer multiple of the number of the conductors connected in parallel. To have completely balance out the extra AC loss a full transposition may be used, i.e. to transpose every parallel conductor at every pole while choosing the number of poles to be in integer multiple of the number of parallel conductors in the slots. Having a different number of poles than what is mentioned will still be an option, but with some extend higher relative AC loss due to proximity effect. 
         [0012]    The inventive generator may comprise an even number of poles per pole set. In a preferred embodiment of the invention such as for a generator for a direct drive wind turbine the number of poles is equal to or above 100. For example, the generator may comprise at least 3 pole sets. Furthermore, the generator may be a direct drive generator. Generally, the generator may comprise a stator and a rotor. The stator may comprise the at least one pole set. Alternatively or additionally the rotor may comprise the at least one pole set. 
         [0013]    In the proposed type of single turn winding, the number of poles may be equal to the sum of Go and Return paths of each phase winding. This means, that the number of poles may be equal to the sum of the half a single turns. 
         [0014]    The inventive wind turbine comprises an inventive generator as previously described. The inventive wind turbine has the same advantages as the inventive generator. 
         [0015]    In the present invention, the series turns in the slot are replaced by effectively half a single turn which needs much less thinner insulation. This is caused by a less voltage difference between the series turns in one slot in the inventive generator. Taking the advantage of having less insulation for conductors and all the following improvement of the generator performance, some draw backs like high extra AC loss due to proximity and skin effect are reduced by transposing the conductors in an efficient way. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    Further features, properties and advantages of the present invention will become clear from the following description of an embodiment in conjunction with the accompanying drawings. All mentioned features and properties are advantageous alone or in any combination with each other. 
           [0017]      FIG. 1  schematically shows a wind turbine. 
           [0018]      FIG. 2  schematically shows a comparative illustration of multi-turn and single turn wave windings for one phase and four poles. 
           [0019]      FIG. 3  schematically shows part of a single turn wave windings of the lower part of  FIG. 2  in a perspective view. 
           [0020]      FIG. 4  schematically shows the AC loss factor dependency for single turn winding of the number of parallel, fully transposed conductors. 
           [0021]      FIG. 5  schematically shows an arrangement of fully transposed  5  parallel conductors belonging to one phase. 
           [0022]      FIG. 6  schematically shows the insulation between parallel conductors associated to a pole. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0023]    An embodiment of the present invention will now be described with reference to  FIGS. 1 to 6 . 
         [0024]      FIG. 1  schematically shows a wind turbine  71 . The wind turbine  71  comprises a tower  72 , a nacelle  73  and a hub  74 . The nacelle  73  is located on top of the tower  72 . The hub  74  comprises a number of wind turbine blades  75 . The hub  74  is mounted to the nacelle  73 . Moreover, the hub  74  is pivot-mounted such that it is able to rotate about a rotation axis  79 . A generator  76  is located inside the nacelle  73 . The wind turbine  71  is a direct drive wind turbine. 
         [0025]      FIG. 2  schematically shows a comparative illustration of multi-turn and single turn wave windings for one phase and four poles. The upper part of  FIG. 2  shows the distributed winding with slots per pole and phase equal to 1 for a 3-phase machine, phases A, B and C. A, B and C correspond to Go direction of the phases and A′, B′ and C′ correspond to Return direction, i.e. opposite direction, of the phases. 
         [0026]    In the middle part of  FIG. 2  two poles  4  representing the first phase are shown. Each of the poles  4  comprises a number of conductor windings  5  with multiple-turns per pole  4 . The strokes  6  indicate the more than one series turns. The conductors  5  are connected in series. This is indicated by the dashed line  7 . Due to the series turns each of the poles  4  or coils comprises a number of Go paths  17  and a number of Return paths  18 . 
         [0027]    The lower part of  FIG. 2  schematically shows the inventive single turn wave windings for one phase of an inventive generator. The pole set belonging to the first phase A comprises a number of poles  4 , from which four poles  4   a ,  4   b ,  4   c  and  4   d  are shown. Generally, the poles  4  may comprise a lamination. 
         [0028]    Each pole  4  comprises a right side  10 , a left side  11 , a front side  12  and a back side  13 . A conductor  8  is wave-like turned about the poles  4 . The conductor  8  comprises a first half turn  8   a , a second half turn  8   b , a third half turn  8   c  and a fourth half turn  8   d . The first half turn  8   a  represents a Return path A′, the second half turn  8   b  represents a Go path A, the third half turn  8   c  represents a Return path A′ and the fourth half turn  8   d  represents a Go path A. 
         [0029]    The first half turn  8   a  proceeds along the right side  10  of the first pole  4   a  and proceeds further along the back side  13  of the first pole  4   a . Then it proceeds further along the left side  11  of the first pole  4   a  and at the same time along the right side  11  of the second pole  4   b . This means, that the conductor passes a slot between the first pole  4   a  and the second pole  4   b . Then the conductor  8  further proceeds along the front side  11  of the second pole  4   b , then along the left side  11  of the second pole  4   b  and at the same time along the right side  10  of the third pole  4   c . The conductor  8  further proceeds along the back side  13  of the third pole  4   c  and along the left side of the third pole  4   c  and at the same time along the right side  10  of the fourth pole  4   d.    
         [0030]    In this wave-like configuration the first half a turn  8   a  is associated to the first pole  4   a , the second half a turn  8   b  is associated to the second pole  4   b , the third half a turn  8   c  is associated to the third pole  4   c  and the fourth half a turn  8   d  is associated to the fourth pole  4   d .  FIG. 3  schematically shows part of the single turn wave windings of the lower part of  FIG. 2  in a perspective view. The poles  4  are separated from each other by slots  19 . 
         [0031]    A number of conductors  8  are connected in parallel and are turned about the poles in such a way that only half a single turn of each conductor is associated to each pole, as shown in the lower part in  FIG. 2  and in  FIG. 3 . The optimal number of parallel conductors to give a low value of proximity and skin effect loss can be chosen analytically or experimentally or by simulation. An example is shown in  FIG. 4 . 
         [0032]      FIG. 4  schematically shows the AC loss factor for single turn windings versus the number of parallel conductors which are always assumed to be fully transposed. The x-axis represents the number N of parallel and fully transposed conductors. The y-axis represents the AC loss factor L for a single turn winding in arbitrary units. The AC loss factor is caused by proximity and skin effect losses. The obtained curved  14  in  FIG. 4  shows a maximum AC loss factor for about two parallel conductors. With a further increasing number of parallel conductors the AC loss factor decreases nearly exponentially. For eight and more parallel conductors the AC loss factor L decreases only minimally. The curve  14  shows for ten and more parallel conductors a nearly straight line which is nearly parallel to the x-axis. This means, that the optimal number of parallel conductors to give a low value of proximity and skin effect loss is ten and more. 
         [0033]      FIG. 5  schematically shows an arrangement of fully transposed  5  parallel conductors belonging to one phase. In the shown arrangement the first pole  21  is followed by a second pole  22 , followed by a third pole  23 , followed by a fourth pole  24 , which is followed by a fifth pole  25  and so forth. Each of the poles  21 ,  22 ,  23 ,  24  and  25  comprises an upper side  15  and a bottom side  16 . The different conductors are designated by numbers  1  to  5 . Each pole  21 ,  22 ,  23 ,  24  and  25  comprises five positions, a first position  31 , a second position  32 , a third position  33 , a fourth position  34  and a fifth position  35 , which follow each other from the upper side  15  to the bottom side  16 . 
         [0034]    In the first pole  21  the first conductor  1  is located at the first position  31 , the second conductor  2  is located at the second position  32 , the third conductor  3  is located at the third position  33 , the fourth conductor  4  is located at the forth position  34  and the fifth conductor  5  is located at the fifth position  35 . 
         [0035]    In the second pole  22  the next half a turn of the first conductor  1  changes to the second position  32 , the next half a turn of the second conductor  2  changes to the third position, the next half a turn of the third conductor  3  changes to the fourth position  34  and the next half a turn of the fourth conductor  4  changes to the fifth position  35 . The next half a turn of the fifth conductor  5  changes from the fifth position  35  in the first pole  21  to the first position  31  in the second pole  22 . This pattern is continued for the next poles as shown in  FIG. 5 . By arranging the conductors as shown in  FIG. 5  the 5 parallel conductors are completely transposed. 
         [0036]    In the present embodiment the generator comprises three phases, which means that it comprises three pole sets. Each pole set comprises ten poles. The pattern which is shown in  FIG. 5  is cyclically repeated for the other 5 poles which are not shown in  FIG. 5 . Generally, the generator comprises a rotor  26 , a stator  27  and an airgap  28  between the rotor  26  and the stator  27 . The stator  27  comprises the poles shown in  FIG. 5 . Alternatively, the rotor  26  may comprise the poles shown in  FIG. 5 . 
         [0037]      FIG. 6  schematically shows as an example the insulation between the parallel conductors  55  of a pole  53 . The conductors are numbered from  1  to  5 . They are connected in parallel, as previously described. Because of the connection in parallel and the parallel assembly none or only very thin conductor insulation  55  is necessary between the different conductors. 
         [0038]    Generally, the generator  76  can comprise an inner stator, which means that the stator is located radially inside of the rotor of the generator related to the rotation axis  79  of the rotor. Alternatively, the generator can comprise an outer stator, which means that the stator is located radially outside of the rotor of the generator related to the rotation axis  79  of the rotor. In both cases the rotor and/or the stator can comprise the described single turn wave winding. 
         [0039]    Based on the described transposed single turn wave winding configuration, it is theoretically clear that the parallel conductors in the slot may need no insulation or only some varnish as there is none or very small voltage difference between these parallel conductors. 
         [0040]    Furthermore, using the described single turn wave-like winding the manufacturing of the coils and the winding process becomes significantly easier and less costly than for conventional multi-turn windings.

Technology Category: 5