Abstract:
A magnet wheel and a stator winding which are necessary for an excitation device are included in a synchronous machine. Energy is transferred to the magnet wheel through inductivity, preferably, energy to a super-conductive coil, by the excitation device. Protection against the magnetic field produced by the current in the winding head is provided in the form of a specific system which is used to reduce the corruptions of the interfering fields of stator and rotor winding.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based on and hereby claims priority to German Application No. 10 2005 047 451.9 filed on Sep. 30, 2005, the contents of which are hereby incorporated by reference. 
     BACKGROUND 
     Described below is a synchronous machine, containing a stator winding and a rotor inductance, with an excitation device for driving and monitoring the rotor inductance. 
     Specific excitation devices are provided for synchronous machines for use as electrical generators or motors. In particular in the case of machines with superconducting exciter windings, in which the current needs to be built up and reduced in a targeted manner, excitation devices including inverters, transformers and synchronous rectifiers are suitable, as are described, for example, in parallel applications by the Applicant with the same priority. 
     The installation site of such an excitation device should be as close as possible to the rotor inductance in order to minimize the losses on feed lines. In particular in the case of such superconducting windings which are constructed using HTS (high-temperature superconducting) technology, protection for the superconducting rotor inductance needs to be implemented which should be fitted as close as possible to the superconducting inductance in order to rule out the probability of breakage of the cable and the associated destruction of the superconducting rotor inductance or to keep this probability as low as possible. 
     The magnetic field produced by the currents in the winding head, on the one hand, and the stator and rotor stray field emerging from the air gap, on the other hand, are problematic for the latter excitation device. These undesirable magnetic fields can disrupt electronics located there and in particular bring the ferromagnetic materials of the transformer to saturation and therefore render them functionless. 
     An aspect of the synchronous machine is to use the available space below the stator winding head as the installation site for contactless energy and data transmission without introducing faults. In particular, it should in this case equally be possible to use a special protection concept for an advantageous use of HTS coils on the rotor. 
     SUMMARY 
     An inner (with respect to the machine construction) excitation device for electric machines with contactless energy transmission and magnetic shielding is realized. 
     Described below is a machine with superconducting windings, in particular made of HTS material. However, the design can also be applied in all known synchronous machines. 
     As a result, the disruptive external fields of stator and rotor windings are weakened in a suitable manner. Thus, a contactless energy transmission method with an inductive coupling of magnetic core materials, in particular of ferrites provided there, can be used to the full for the first time. 
     It is known from the related art that the magnetic flux density at the installation site of the excitation device is a few 10 mT. As a result of the magnetic components contained in the excitation device, such as in particular the ferrites, however, the field strength distribution is distorted in such a way that these components are magnetically saturated and therefore often, as has already been mentioned above, no longer function correctly. 
     On the other hand, required field strength distributions can be predetermined in a targeted manner and in particular the regions of the excitation device with the sensitive electronics can be freed of disruptive fields, which could impair the functioning of individual components of the electronics. 
     In a targeted development, different embodiments for the design of the shield as well as the housing are possible, a combination of variants also being possible. 
     Advantageously, the entire housing for the excitation device can be made of magnetic steel, whereby the external fields are shielded to the greatest possible extent. 
     A stationary or laminated screen made of magnetic steel can also be provided which at least partially surrounds the rotating housing of the excitation device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other aspects and advantages will become more apparent and more readily appreciated from the following description of exemplary embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a schematic, sectional illustration of an electric synchronous machine with a stator winding, rotor and excitation device including a transformer, 
         FIG. 2  is a perspective view from the front of the electric machine shown in  FIG. 1 , 
         FIG. 3  is a sectional perspective view from the front of a section of the electric machine shown in  FIG. 1  along the line III-III, 
         FIG. 4  is a partial sectional view of an alternative for the shield shown in  FIG. 1   a  partial, and 
         FIG. 5  is a partial sectional view of detail of a screen with additional elements. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference will now be made in detail to exemplary embodiments which are illustrated in the accompanying drawings, wherein like reference symbols refer to like elements throughout. 
     The drawings illustrate an electric machine which either functions as an electrical generator or as a motor. Essential to such a machine is a rotating shaft  2 , which is mounted in at least two mounts  3 ,  3 ′. 
     It can be seen from the schematic illustration in  FIG. 1  that a rotor  5  is arranged on the shaft  2 , on which rotor windings, in particular superconducting windings made of HTS material, are located, which will be clarified further below with reference to  FIGS. 2 and 3 . 
     It can furthermore be seen in  FIG. 1  that a stator winding  10  with winding heads  11 ,  11 ′ is provided opposite the rotor  5  as the rotating element. 
     Especially in  FIG. 1  an excitation device  20  is provided which is substantially formed by a fixed part  21  and a rotating part  22 . The two parts  21  and  22  have windings for voltage transformation, essentially a higher voltage being transformed to a lower voltage and the excitation device  20  being operated on the lower voltage in the moving part, i.e. on the shaft  2 . 
     In  FIG. 1 , the excitation device  20  in the form of a compact unit is located on the rotating shaft  2  and is activated by a transformer  25  for transmitting electrical power from the fixed part  21  to the rotating part  22  on the shaft  2 . The excitation device  20  contains a circuit construction with electronic component parts, of which no further details are given in this context. Since the electronic component parts are sensitive to external fields, a shield  30  is necessary, which will be described in more detail below. 
     The shield  30  can include a complete hollow cylinder, which is pushed, as a housing, over the entire excitation device  20  including the transformer  25 . The shield  30  can, however, also include individual elements, such as individual ferrite rings  31 , which can be seen with reference to  FIG. 2  below. 
     The housing or the shield  30  is advantageously made of magnetically highly conductive material, such as in particular steel. However, it can also be made of SMC (soft magnetic composite) materials, which, as a result of magnetic inclusions, realize the required magnetic properties despite being electrically very poorly conductive. These properties can also be achieved by a layer on the wall of the housing  30 , which then advantageously can be made of nonferrous material, for example carbon fiber or the like. Further details will be given on this subject in the text which follows. 
     The shield  30  can be designed not to concomitantly rotate with the shaft  2  or else to concomitantly rotate with it. The advantage of the first alternative, i.e. a non-concomitantly rotating shield, is a mechanically simpler design. With such a design, in particular no centrifugal forces which need to be absorbed result from the rotating shield. 
     In the second alternative of a concomitantly rotating arrangement of the shield, on the other hand, no disruptive eddy currents occur as a result of a synchronously revolving rotary field of the synchronous machine. 
     For the practical application, when selecting the non-concomitantly rotating or rotating arrangement of the shield the arrangement of the excitation device  20  in relation to the stator winding  10  is taken into consideration. In particular when the excitation device is arranged directly below the winding heads  11 , a concomitantly rotating arrangement is preferred. Otherwise, the stationary arrangement of the shield is to be selected as being advantageous. 
     In a specific arrangement as shown in  FIG. 4 , which is formed by modifying  FIG. 1 , a cavity  44  is introduced into a shaft  4  in the end region  41 , with the result that an inner, already magnetically shielded free space is formed for the magnetically sensitive excitation electronics. 
     The latter is expedient in particular in the case of machines with a high power in which the shaft has a sufficiently large diameter. In the case of smaller diameters, the shaft  2  from  FIG. 1  can be extended in the end region and can be in the form of a hollow cylinder  41  with the inner free space  44 . For this case, the mount  2 ′ needs to be changed, while the fixed part of the excitation device  20  with the transformer windings of the transformer  25  remains substantially the same. 
     A receptacle for the complete excitation device  20  with the associated electronics can be provided in the free space  44  of the extended part  41  of the shaft  4 . It is particularly advantageous here that, in the case of a shaft made of magnetic material, which is equally used as a magnetic shield, the centrifugal forces are kept markedly lower since an arrangement of the excitation electronics close to the axis can result in a diameter of the excitation device which is overall reduced in comparison with that in  FIG. 1 . 
       FIGS. 2 and 3  show the external design of the above-described machine. In particular in the view of the section in  FIG. 3 , the rotor  5  on the rotating shaft  2  can be seen, on which rotor the rotor winding, in particular a superconducting coil  6  made of HTS material, is located. 
       FIG. 2  only provides an overall indication of the excitation electronics with which the transmission of the input or output of energy, on the one hand, and the control of the superconducting coil  6  in the cold region, on the other hand, are ensured. 
     It is essential that when the component parts which belong to the excitation device outside or possibly inside a machine shaft are fitted, the shield realizes a housing, which surrounds all of the components. Specifically in  FIG. 1 , this housing can be replaced easily and as a result is more reliable and space-saving in comparison with separate housings, as are provided in the related art alternatively within the cold region, warm region and outside the entire machine housing. As a result of the compact arrangement, in this case in particular the feed lines can be reduced. 
     With the alternative shown in  FIG. 4  which has already been explained above, a design of the electric machine which is essentially identical apart from the excitation region and corresponds to  FIG. 1  results. A separate housing is in this case superfluous. Instead, it is essential that the machine shaft is extended in the region facing the exciter and accommodates the excitation device in its free space. 
     The hollow-cylindrical shaft part, as long as it is made of magnetically conductive material as is the shaft, can therefore form the shield for the excitation electronics equally in addition to accommodating the excitation device in  FIG. 4 . A particularly compact design of the machine is therefore possible. 
     In  FIG. 5 , elements  31 ,  31 ′, . . . for flux guidance in the radial direction are introduced in a hollow cylinder  30 ′ acting as the shield. Such elements  31 ,  31 ′, . . . are realized by webs or disks on a material with good magnetic conductivity and are arranged at a distance within the hollow cylinder  30 ′ with a minimum radial air gap. 
     With such an arrangement, a magnetic field is kept away from the interior of the hollow cylinder, in which the excitation electronics with component parts which are sensitive to magnetic fields are located, in a suitable manner. In particular when diametric fields are critical, the strength of the outer shield  30 ′ can therefore be reduced. 
     When using flat disks as the field guidance elements, advantageously line bushings for the components of the excitation electronics are provided in the interior of the cylinder. 
       FIG. 5  shows individual lines of force. The specific arrangement shown in  FIG. 5  therefore acts as a flux concentrator, with which the field strength distribution of the magnetic fields can be influenced in a desirable manner. 
     In  FIGS. 1 to 5 , the material of the shield  30  is in each case magnetically conductive steel. An alternative material with high permeability and low anisotropic electric conductivity is also provided, for example, by so-called soft magnetic composites (SMC). Such compound materials are in particular capable of being sintered and therefore can easily be brought into the desired form. 
     Alternatively, the shield can contain an outer covering, made of magnetically nonconductive material, on which the actual magnetic shield is formed by coating it with a material of high permeability. In this case, the outer covering can be made of corrosion-resistant material, for example stainless steel, the coating of the material of high permeability being located in particular on the inside. 
     Finally, it is also possible to use an outer covering of magnetically nonconductive material for the shield, with the actual magnetic shield being formed by rings made of a material of high permeability, for example Mu metal. 
     The system also includes permanent or removable storage, such as magnetic and optical discs, RAM, ROM, etc. on which the process and data structures of the present invention can be stored and distributed. The processes can also be distributed via, for example, downloading over a network such as the Internet. The system can output the results to a display device, printer, readily accessible memory or another computer on a network. 
     A description has been provided with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the claims which may include the phrase “at least one of A, B and C” as an alternative expression that means one or more of A, B and C may be used, contrary to the holding in  Superguide v. DIRECTV,  358 F3d 870, 69 USPQ2d 1865 (Fed. Cir. 2004).