Patent Publication Number: US-2011075797-A1

Title: Device for a computer tomography gantry for transfering contactlessly electrical energy

Description:
FIELD OF THE INVENTION 
     The present invention relates to a device for a computer tomography gantry for transferring contactlessly electrical energy from a stationary part of the gantry to a rotary part of the gantry and a computer tomography gantry comprising such a device and a method for transferring contactlessly electrical energy from a stationary part of a computer tomography gantry to a rotary part of the gantry. 
     BACKGROUND OF THE INVENTION 
     Usually, power transformers of computer tomography gantries are operated with high frequency. The high frequency operation renders the possibilty to reduce size and weight of the energy storing devices (capacitors, inductors, transformers) used in the system. Usually, E-cores are used for the transformers in order to avoid external leakage flux. Thus, a long winding path first clockwise and then counterclockwise along the circumference will cause high values of inductances. Using a resonant converter system, the resulting leakage inductance of the transformer must be low in order to transmit the required power level. When high power transmissions for the rotary part of the gantry is required, a plurality of inverters will be used. In this case, each of the inverters generates a fraction of the totally required power to transfer to the rotary part of the gantry. With respect to manufacturing tolerances and temperature influences, the components of the inverters as well as the characteristics of the transformers are different. Thus, the fractions of power, which are transferred by the different inverters are not equal. This leads to an unequal workload of the different inverters. As a result thereof cogging forces will occur and thus the rotary part of the gantry could be bent during rotation of the rotary part of the gantry. 
     SUMMARY OF THE INVENTION 
     It would be desirable to provide an improved device for balancing the workload of the different inverters, which supply the power transformer. As a result thereof cogging forces and bending of the rotary part of the gantry would be avoided. This would lead to a longer lifetime of the power transformer of the computer tomography gantry and the gantry itself. 
     The invention provides a device for a computer tomography gantry for transferring contactlessly electrical energy from a stationary part of the gantry to a rotary part of the gantry, wherein the device comprises a first power transformer, a second power transformer, wherein the first and the second power transformers are adapted for transferring the electrical energy, wherein the first power transformer comprises a first winding out of the group consisting of a first set of primary windings and a first set of secondary windings of the first power transformer, wherein the second power transformer comprises a second winding out of the group consisting of a second set of primary windings and a second set of secondary windings of the second power transformer, wherein the first set of primary windings and the second set of primary windings being adapted to be mounted on the stationary part of the gantry, wherein the first set of secondary windings and the second set of secondary windings being adapted to be mounted on the rotary part of the gantry, wherein the device is adapted to balance the currents of the first winding and the second winding. 
     The balancing of the different currents of the single windings is important with respect to the aim of a equally rotation without fluctuations. Fluctuations of the rotation would lead to uncontrollable vibrations. In a worst case scenario these vibrations could lead to damages to the computer tomography gantry. 
     The invention provides also a computer tomography gantry comprising a device according to one of the claims  1  to  13 . 
     Further, the invention provides a method for transferring contactlessly electrical energy from a stationary part of a computer tomography gantry to a rotary part of the gantry, comprising the steps of balancing currents with the help of a device according to one of the claims  1  to  13 . 
     Further embodiments are incorporated in the dependent claims. 
     According to the present invention it is provided a device, wherein the first winding and the second winding are magnetically coupled in such a way that the device is adapted to balance the currents of the first winding and the second winding. 
     This arrangement balances the currents without requiring additional components such as an additional current compensating choke. It is only necessary to couple the magnetic relevant areas of windings with different currents. The common magnetic flux would result in a balancing of the different currents. 
     According to an exemplary embodiment it is provided a device, further comprising a current balancing transformer, which is arranged in such a way so that being adapted for balancing the currents of the first winding and the second winding. The term current balancing transformer corresponds to the term current balancing choke. The current balancing choke is a special variation of a transformer. 
     It is also possible to arrange discrete elements to balance the currents of the different windings. These elements generate an additional magnetic coupling between the different windings. This magnetic coupling leads to the balance of the currents. This embodiment is advantageously because of the fact that a special arrangement of the windings of the transformer is not necessary. Further, the additional element, the current balancing choke/transformer are available in every size and requirements. 
     According to the present invention it is provided a device, wherein the first winding is a first primary winding of the first power transformer and the second winding is a second primary winding of the second power transformer, so that the device is adapted for balancing the currents of the first primary winding and the second primary winding. 
     According to an exemplary embodiment it is provided a device, wherein the first winding is a first secondary winding of the first power transformer and the second winding is a second secondary winding of the second power transformer, so that the device is adapted for balancing the currents of the first secondary winding and the second secondary winding. 
     According to an exemplary embodiment it is provided a device, wherein the first and the second power transformers are adapted to be operated with currents of a high frequency, such that the power transformers are adapted to transfer energy in a high frequency. 
     In order to transfer the immense electrical energy, which is required from the components on the rotary part of the gantry, it is necessary to use a high frequency application. Therefore, it is advantageously to adapt the device according to the inventive concept to the requirements of a high frequency application. 
     According to an exemplary embodiment it is provided a device, further comprising an inverter, wherein the inverter is adapted to be connected with the first and the second power transformer such that the inverter feeds the first and the second power transformer with electrical energy. 
     According to an exemplary embodiment it is provided a device, further comprising a rectifier, wherein the rectifier is adapted to be connected with the first and the second power transformer such that the rectifier rectifies the output voltage of the first and the second power transformer. 
     Especially, the problem of current balancing is on hand in case of only one single inverter, which supplies the primary windings, or in case of only one single rectifier, which rectifies the voltages at the secondary side of the transformer. In both cases there is no possibility to adjust the different currents, because the inverter/rectifier can only influence the common current of all windings of the primary or the secondary side of the transformer. Therefore, the solution provided by this invention is especially advantageously with respect to the above-mentioned situations. 
     According to an exemplary embodiment it is provided a device, wherein the device further comprises a third power transformer, a fourth power transformer, wherein the first power transformer is adapted to be supplied by a first inverter, wherein the second power transformer is adapted to be supplied by a second inverter, wherein the third power transformer is adapted to be supplied by a third inverter, wherein the fourth power transformer is adapted to be supplied by a fourth inverter, wherein the first inverter is arranged close to the second inverter, wherein the third inverter is arranged close to the fourth inverter, wherein the first inverter is supplied by a mains input stage via a first supply line, wherein the second inverter is supplied by the mains input stage via a second supply line, wherein the third inverter is supplied by the mains input stage via a third supply line, wherein the fourth inverter is supplied by the mains input stage via a fourth supply line, wherein the first supply line is considerably shorter than the second supply line, wherein the third supply line is considerably shorter than the fourth supply line. 
     According to another exemplary embodiment it is provided a device, wherein a winding out of a group consisting of the first set of primary windings and the first set of secondary windings of the first power transformer and the second set of primary windings and the second set of secondary windings of the second power transformer is arranged in a circular arc. 
     According to another exemplary embodiment it is provided a device, comprising a first power transformer with a first winding out of a group consisting of the first set of primary windings and the first set of secondary windings, a second power transformer with a second winding out of a group consisting of the second set of primary windings and the second set of secondary windings, a third power transformer with a third winding out of a group consisting of the third set of primary windings and the third set of secondary windings, a fourth power transformer with a fourth winding out of a group consisting of the fourth set of primary windings and the fourth set of secondary windings, wherein the first, the second, the third and the fourth windings are arranged in four circular arcs. 
     According to another exemplary embodiment it is provided a device, comprising a first power transformer with a first primary winding, a second power transformer with a second primary winding, a third power transformer with a third primary winding, a fourth power transformer with a fourth primary winding, a first current balancing transformer, wherein a winding of the first current balancing transformer is wound around a part of the first primary winding and around a part of the second primary winding, so that the first current balancing transformer is adapted for balancing the currents of the first and second primary windings,a second current balancing transformer, wherein a winding of the second current balancing transformer is wound around a part of the second primary winding and around a part of the third primary winding, so that the current balancing transformer is adapted for balancing the currents of the second and third primary windings,a third current balancing transformer, wherein a winding of the third current balancing transformer is wound around a part of the third primary winding and around a part of the fourth primary winding, so that the current balancing transformer is adapted for balancing the currents of the third and fourth primary windings. 
     According to another exemplary embodiment it is provided a device, comprising a first power transformer with a first secondary winding, a second power transformer with a second secondary winding, a third power transformer with a third secondary winding, a fourth power transformer with a fourth secondary winding, a first current balancing transformer, wherein a winding of the first current balancing transformer is wound around a part of the first secondary winding and around a part of the second secondary winding, so that the first current balancing transformer is adapted for balancing the currents of the first and second secondary windings,a second current balancing transformer, wherein a winding of the second current balancing transformer is wound around a part of the second secondary winding and around a part of the third secondary winding, so that the current balancing transformer is adapted for balancing the currents of the second and third secondary windings, and a third current balancing transformer, wherein a winding of the third current balancing transformer is wound around a part of the third secondary winding and around a part of the fourth secondary winding, so that the current balancing transformer is adapted for balancing the currents of the third and fourth secondary windings. 
     It may be seen as a gist of the present invention to provide a possibilty to balance currents, which are supplied by inverters to windings of transformers. The corresponding windings of the transformer can be primary windings or secondary windings or both (the primary windings and the secondary windings can be balanced). This leads to the result that the workload for different inverters/windings are equal. Therefore, asymmetrical workload is avoided, which results in the prevention of bending of the computer tomography gantry. 
     It should be noted that the above features may also be combined. The combination of the above features may also lead to synergetic effects, even if not explicitly described in detail. 
     These and other aspects of the present invention will become apparent from and elucidated with reference to the embodiments described hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention will be described in the following with reference to the following drawings. 
         FIG. 1  shows a part of a computer tomography gantry, 
         FIG. 2  shows a part of a transformer, 
         FIG. 3  shows a part of a transformer with four inverters, 
         FIG. 4  shows a part of a transformer with four inverters, 
         FIG. 5  shows a part of a transformer with current balancing chokes, 
         FIG. 5A  shows a part of a transformer with four inverters, 
         FIG. 5B  shows a part of a transformer with two current balancing chokes, 
         FIG. 5C  shows a part of a transformer with three current balancing chokes, 
         FIG. 6  shows a part of a transformer with three current balancing chokes, 
         FIG. 7  shows a diagram of a part of a computer tomography gantry, 
         FIG. 8  shows a part of a transformer, 
         FIG. 9  shows a part of a transformer, 
         FIG. 10  shows rectifiers, 
         FIG. 11  shows a part of a transformer, 
         FIG. 12  shows a part of a transformer with six rectifiers, 
         FIG. 13  shows a part of a transformer, 
         FIG. 14  shows a part of a transformer, 
         FIG. 15  shows a computer tomography gantry. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     The system described herein focuses on a system for contactlessly energy transmission, which provides energy transfer to a rotating dish, i.e. a rotating part of a computer tomography gantry. Further, an arrangement of windings is described, which provides the balancing of currents in different windings. 
     In this invention a rotary transformer is shown, which provides the use of high frequency operation and minimized amount of magnetic material. Further, it is avantageously that the losses in the windings according to the inventive concept will be reduced, especially with high frequencies. The major problems which are solved by this invention is an unequal flux distribution along the circumference of the rotary transformer and an unequal power transmission when the power transformer of the gantry comprises a plurality of primary or secondary windings. 
       FIG. 1  shows a part of a computer tomography gantry  101 , with a stationary part  102 . It is depicted two stationary parts of the transformer  103 ,  104  and a rotary part of the transformer  105 . The stationary parts of the transformer  103 ,  104  are supplied by an inverter  106  with the help of a supply line  107 . 
       FIG. 1  shows essential elements of a computer tomography gantry  101 , wherein a contactless energy transmission from the stationary part of the gantry  102  to the rotary part of the gantry  105  is applied. The system  101  consists of a frame  102  and a rotating part of the gantry  105 , wherein the rotary part of the gantry is mounted by bearings. The primary side of a power transformer  103 ,  104  is arranged at the stationary part of the gantry  102 . The secondary part of the transformer  105  is arranged at the stationary part of the gantry. The power transformer is used to transfer electrical energy from the stationary part of the gantry to the rotary part of the gantry. There can be also an auxiliary transformer, which is arranged in a similar way, to transmit electrical energy for auxiliary units, which are located on the rotating part of the gantry. It is also possible to arrange several power transformers to transmit electrical energy. 
     It is depicted only one inverter  106 , which supplies the electrical energy to the gantry. It is also possible to use a plurality of inverters  106 , in order to distribute the workload on several inverters  106 . In this case the inverters  106  can be equipped with smaller, cheaper electronical elements. 
       FIG. 2  shows a part of a transformer  212  with windings  208 ,  209 ,  210  and  211 . The part of the transformer  212  belongs to the stationary part of the transformer, which is connected with the stationary part of the gantry  206 . The different primary windings  208 ,  209 ,  210  and  211  of the transformer  212  are supplied by two inverters  202 ,  203 , wherein a mains supply unit  201  feeds the two inverters  202  and  203 . The four different windings  208 ,  209 ,  210  and  211  are supplied with the help of supply lines  204  and  205 . The four different windings  208 ,  209 ,  210  and  211  are adapted to induce a magnetic flux in the core  207 . The core  207  is usually E-shaped. 
       FIG. 3  shows a part of a transformer, wherein the part of the transformer is the stationary part of the transformer, which is connected with the stationary part of the gantry  310 . The four different primary windings  306 ,  307 ,  308  and  309  are supplied by four different inverters  302 ,  303 ,  304  and  305 . These four inverters  302 ,  303 ,  304  and  305  will be fed by a mains input stage  301 . In this case every different winding  306 ,  307 ,  308  and  309  is supplied by a different inverter  302 ,  303 ,  304  and  305 . Every different inverter  302 ,  303 ,  304  and  305  enables an user to adjust the currents to the different physical characteristics of the primary windings  306 ,  307 ,  308  and  309 . According to this it is possible to supply the different primary windings  306 ,  307 ,  308  and  309  with the same currents, because the four different currents for the four different windings  306 ,  307 ,  308  and  309  can be adjusted separately. 
       FIG. 3  depicts four inverters  302 ,  303 ,  304 ,  305 . Typically the inverters  302 ,  303 ,  304 ,  305  are located around the circumference of the power transformer. Other numbers of inverters are also realizable. 
     Due to mechanical tolerances the inductances of each winding  306 ,  307 ,  308 ,  309  on the primary side of the contactless power transformer will be different. Thus, the current in each winding  306 ,  307 ,  308 ,  309  and the flux induced by each winding  306 ,  307 ,  308 ,  309  will be different. This will cause unequal power transmission to the stationary side of the gantry during rotation of the rotary part of the gantry. Furthermore, cogging forces will occur and thus the rotating part of the gantry could be bent during rotation. 
     To overcome the bending of the rotating part of the gantry and to achieve identical current distribution in the primary windings  306 ,  307 ,  308 ,  309 , the current in each winding  306 ,  307 ,  308 ,  309  must be identical. In case the currents in each winding  306 ,  307 ,  308 ,  309  is identical the flux induced by the windings  306 ,  307 ,  308 ,  309  will be identical at each rotational angle. Identical currents can be achieved with the help of current balancing chokes. 
       FIG. 4  shows a part of the stationary part of the transformer  401 . The different four primary windings  407 ,  408 ,  409  and  410  are supplied by four different inverters  402 ,  403 ,  405  and  406 . These four inverters  402 ,  403 ,  405 ,  406  are fed by a mains input stage  404 . 
       FIG. 5  shows a part of a transformer  501 . It is shown four different primary windings  506 ,  507 ,  508  and  509 . The primary winding  506  is supplied by the inverter  503 , the primary winding  507  is supplied by the inverter  510 , the primary winding  508  is supplied by the inverter  511 , the primary winding  509  is supplied by the inverter  504 . The inverters  503 ,  504 ,  510  and  511  are fed by a mains input stage  502 . The four inverters  503 ,  504 ,  510  and  511  are supplied by supply lines  514  and  515 . The arrangement of the supply lines  514  and  515  is such that the part of the supply line  515  which leads to the inverter  504  also supplies the inverter  510 . The supply line  515  supplies the inverter  503  as well as the inverter  511 . The currents of the inverter  503  and the inverter  504  will be balanced by a current balancing choke  505 , such as the currents which are in the primary windings  506  and  509  are equal. The current balancing choke  505  is an additional discrete separate element, which has to be added. The currents of the inverters  510  and  511  by which the primary windings  507  and  508  are supplied will be balanced by a current balancing choke  512 . As a result thereof, the currents of the primary windings  507  and  508  are equal. In order to adjust all four currents in the primary windings  506 ,  507 ,  508  and  509 , it is necessary to insert a third current balancing choke  513 . In order to enabling the addition of a third current balancing choke  513 , it is also necessary to arrange two primary windings  508 ,  509  or the primary windings  506 ,  507  in a special way. It is also possible to balance the currents of the stationary part of the transformer by balancing the currents of the primary windings  506  and  507 . A third possibility would be to balance the currents of the primary windings  506  and  508  and a fourth possibility would be the balancing of the currents  507  and  509 . 
     The  FIGS. 5A ,  5 B and  5 C show also the same arrangement of four different primary windings and four different inverters which supply the four different primary windings. 
       FIG. 5A  differs from the  FIG. 5  by the different arrangement of supply lines  516  and  517 . In  FIG. 5A  the supply line  516  supplies the inverter  520  and the inverter  521 . This is the same arrangement as in  FIG. 5  according to the supply line  514 . The difference is the arrangement of the supply line  517 . In  FIG. 5A  the supply line  517  supplies at first the inverter  522  and then the inverter  519 . The difference to the  FIG. 5  is that the supply line  517  does not run at first to the inverter  519  and then to the inverter  522 . According to this the length of the part of the supply line  516  which leads to the inverter  520  is considerably short in comparison with the part of the supply line  516  which leads to the inverter  521 . The length of the part of the supply line  517 , which leads to the inverter  522  is short in comparison with the length of the part of the supply line  517 , which leads to the inverter  522 . Therefore, as a result thereof, the length of the supply lines to the inverter  519  and  520  are considerably different. The same for the pair of inverters  521 ,  522 , wherein the length of the supply lines  516 ,  517  are considerably different also. 
       FIG. 5B  shows the same arrangement of supply lines and inverters. With respect to the fact, that along a supply line  529 ,  531  there is a voltage decrease it is obvious, that the pairs of inverters  523 ,  528  as well as the pair of inverter  526  and  527  are supplied with considerably different voltages due to the fact that the length of supply lines are considerably different. Therefore, the currents which will be fed to the primary windings of the pairs of inverters are also different because of the voltage decrease along the supply lines, which are considerably different. Therefore, it is a considerable difference of the currents of the pair of inverters  523 ,  528  as well as the pair of the inverter  526 ,  527 . Therefore, two points of considerably difference of currents are enforced at the output of the pairs of inverters  523 ,  528  and  526 ,  527 . Therefore, the current balancing choke  524  as well as the current balancing choke  525  are placed at very useful sites in the arrangement of the primary windings and their feeding inverters. Resulting from the both current balancing chokes at very favourable sites of the arrangement, the difference of the currents of the pairs of the two primary windings is not considerably different. This leads to the fact, that a third current balancing choke (as described above in  FIG. 5 ) can be omitted. 
     The  FIG. 5C  shows a part of the computer tomography gantry, wherein the mains input stage  538  supplies the inverters  532 ,  539 ,  535  and  536  in the same manner as in the arrangement of the  FIG. 5B . There are also two current balancing chokes  533  and  534 . The difference of the  FIG. 5C  in comparison with the  FIG. 5B  is the arrangement of a third current balancing choke  541 . The third current balancing choke  541  is arranged in order to balance the currents of the primary windings  542  and  543 . In order to receive the same value of current in all four primary windings  542 ,  543 ,  544  and  545 . It is also possible to balance the currents of the primary windings  542  and  544  to arrive at four identical currents in the four primary windings  542 ,  543 ,  544 ,  545 . Another possibility with the same result would be the balancing of the currents of the primary windings  545  and  543 . 
       FIG. 6  shows an arrangement of four primary windings  601 ,  602 ,  603  and  604 . The primary winding  602  is supplied by the supply line  607 , the primary winding  601  is supplied by the supply line  605 , the primary winding  603  is supplied by the supply line  608 . The primary winding  604  is supplied by the supply line  606 . All four supply lines  607 ,  608 ,  605  and  606  are fed by one single inverter  612 . According to the fact that four primary windings  601 ,  602 ,  603  and  604  are supplied by one single inverter  612  it is not possible to adjust all four currents in the primary windings  601 ,  602 ,  603  and  604  such that the value of the currents are equal without further arrangements. The value of the currents of the different primary windings  601 ,  602 ,  603  and  604  depends on the physical characteristics of the primary windings  601 ,  602 ,  603  and  604 . In order to adjust the currents of the four different primary windings  601 ,  602 ,  603  and  604  it is therefore necessary to balance the different currents. Therefore, the currents in the supply lines  607  and  608  are balanced by a current balancing choke which is realized by magnetic coupling with the help of the inductances  614  and  615 . The currents in the supply lines  608  and  606  is balanced with the help of a current balancing choke, which is realized by the inductances  616  and  617 . The currents in the supply lines  605  and  606  is balanced with the help of a current balancing choke which is realized by the inductances  618  and  619 . With the help of the current balancing chokes  614 ,  615 ,  616 ,  617 ,  618  and  619  it is guaranteed that the four different primary windings  601 ,  602 ,  603  and  604  have the same value of current. 
       FIG. 7  shows the arrangement of current balancing chokes  705  at the secondary side of a power transformer.  FIG. 7  shows schematically a part of a computer tomography gantry. It is shown an inverter  701 , which transforms a DC voltage into a switched DC voltage. This switched voltage is supplied to a resonant circuit  702  with a capacitor and an inductance, wherein in this special case four different inverters  701  supply four different resonant circuits  702 , which lead to four different currents which are fed to four different primary windings, which are galvanically isolated. In order to adjust the four different currents a current balancing choke  703  is implemented. The transformer  704  transforms the input voltage and supplies his output voltage to a further transformer  706 , which is adapted to transform the voltage into a higher voltage. It is also implemented between the first transformer and the second transformer a current balancing choke  705  in order to adjust the two different currents at the secondary side of the transformer  704 . The output voltage of the second transformer  706  is rectified and smoothened by an unit  707 . The output of the unit  707  will be supplied to an unit on the rotary part of the computer tomography gantry, which is schematically depicted by a capacitor  708 . 
     The current balancing chokes (transformers)  705  are located between the secondary windings of the first transformer and the successive rectifier  707  or a further transformer  706 . If identical currents in all primary windings are achieved and identical currents in the secondary windings are achieved the transferred power and the resonance frequency are independent from the angular position of the power transformer. 
       FIG. 8  shows a part of the primary side of the transformer of a computer tomography gantry. The primary side of the transformer comprises three different primary windings  802 ,  805  and  807 . The primary winding  802  is supplied by the inverter  801 , the primary winding  805  is supplied by the inverter  804 , the primary winding  807  is supplied by the inverter  806 . The arrangement of the primary windings is symmetrically with respect to the center lines  809  and  808 . It is also depicted the core  803  of the primary side of the transformer, wherein the core  803  has an E-shaped form. 
     Exemplarily, it is shown three inverters  801 ,  804 ,  806  at the primary side of the power transformer. Each of the inverters  801 ,  804 ,  806  is connected to a single primary winding  802 ,  805 ,  807 . Each of the winding  802 ,  805 ,  807  covers a fraction of the core  803 . Other arrangements with more primary windings or only two or only one winding are also realisable. 
       FIG. 9  shows a secondary part of a transformer for a computer tomography gantry  906 . It is depicted a secondary part of the transformer with only one secondary winding  901 , wherein the winding  901  is connected with a rectifier  902 . The rectifier  902  rectifies an output voltage of the transformer. The arrangement is symmetrically with respect to the center lines  903  and  905 . The secondary winding  901  is arranged in such a way that it can induce a magnetic flux in the core  904 . The core  904  is E-shaped. 
       FIG. 10  shows three schematically diagrams of different electronic elements. The diagram  1001  represents an unit for rectifying. The element  1002  represents an unit which comprises diodes and switches. The element  1004  represents a transformer and the element  1003  represents a rectifier.  FIG. 10  shows electronic loads, which can be connected to the secondary side of the power transformer. These loads can be used as alternatives to the rectifier, depicted in  FIG. 9  ( 902 ). 
       FIG. 11  shows the secondary side of a transformer  1108 . The secondary side of the transformer  1108  comprises two different secondary windings  1101  and  1104 . These two different windings  1101  and  1104  will be supplied to two different rectifiers  1102  and  1103 . The arrangement is symmetrically with respect to the center lines  1106  and  1107 . The secondary windings  1101  and  1104  are embedded in a core  1105 . The core  1105  is typically designed in an E-shape form. 
       FIG. 12  shows a part of the primary side of a transformer  1216 . It is depicted six different primary windings  1202 ,  1204 ,  1207 ,  1211 ,  1212  and  1215 . The primary winding  1202  is supplied by an inverter  1201 , the primary winding  1204  is supplied by the inverter  1203 , the primary winding  1207  is supplied by the inverter  1206 , the primary winding  1211  is supplied by the inverter  1210  and the primary winding  1212  is supplied by the inverter  1213 . The six primary windings  1202 ,  1204 ,  1207 ,  1211 ,  1212  and  1215  can be galvanically isolated and have six different currents. In order to adjust the six different currents the six galvanically isolated primary windings are magnetically coupled with the help of a special arrangement. The primary winding  1202  is magnetically coupled with the primary winding  1204  and the primary winding  1214  with the help of a special arrangement, wherein a common magnetically flux results by overlapping windings. The primary winding  1204  is coupled with the primary winding  1207 . The primary winding  1207  is coupled with the primary winding  1211 . The primary winding  1211  is magnetically coupled with the primary winding  1212 . The primary winding  1212  is magnetically coupled with the primary winding  1212 . The primary winding  1212  is magnetically coupled with the primary winding  1215 . With the help of the special arrangement of the primary windings  1202 ,  1204 ,  1207 ,  1211 ,  1212  and  1215  it is possible to adjust the different currents without the help of discrete, separated components such as current balancing chokes. 
     Due to mechanical tolerances the inductances of each of the winding  1202 ,  1204 ,  1207 ,  1211 ,  1212 ,  1215  around the circumference on the primary side of the contactless power transformer will be different. Thus, the current and the flux, which is induced by a winding  1202 ,  1204 ,  1207 ,  1211 ,  1212 ,  1215 , in each segment will be different. This will cause unequal power transmitted to the secondary side of the power transformer during the rotation of the secondary part of the gantry. Furthermore, cogging forces will occur and thus the rotating gantry could be bent during rotation. To overcome the bending of the rotating part of the gantry and to achieve identical current distribution in the primary windings  1202 ,  1204 ,  1207 ,  1211 ,  1212 ,  1215  around the circumference, the current in each of the windings must be identical. When the current in each of the windings  1202 ,  1204 ,  1207 ,  1211 ,  1212 ,  1215  is identical the flux generated along the circumference will be identical at each rotational angle. 
     Exemplarily,  FIG. 12  shows six inverters  1203 ,  1206 ,  1210 ,  1213 ,  1214 ,  1201 , which feed six primary windings  1202 ,  1204 ,  1207 ,  1211 ,  1212 ,  1215 . Other numbers of inverters are also realisable. According to the inventive concept neighbouring windings are overlapping in a symmetric way. The magnetic coupling between neighbouring windings in these overlap regions provides the functionality of current balancing chokes but without using additional separate discrete components. 
       FIG. 13  shows a part of a transformer  1310 . This part of a transformer could be a part of the primary side of the transformer as well as a part of the secondary side of the transformer. It is depicted six different galvanically isolated windings  1301 ,  1302 ,  1303 ,  1309 ,  1308  and  1307 . The windings  1301 ,  1302 ,  1303 ,  1309 ,  1308  and  1307  are magnetically coupled in such a way that alone with the help of the special arrangement a current balancing effect on the six windings is achieved. The winding  1301  is magnetically coupled with the windings  1302  and the winding  1303 . The winding  1308  is magnetically coupled with the winding  1309  and the winding  1302 . The winding  1307  is magnetically coupled with the winding  1309  as well as with the winding  1303 . The six different windings  1301 ,  1302 ,  1303 ,  1307 ,  1308  and  1309  are embedded in a core  1306 . The core  1306  is typically E-shaped. The arrangement is symmetrically with respect to the center lines  1304  and  1305 . 
       FIG. 13  shows a winding arrangement, which represents an alternative to that depicted in  FIG. 12 . The advantage of this configuration is that the windings  1301 ,  1302 ,  1303 ,  1307 ,  1308 ,  1309  leave the area of the core  1306  only at two different places. This leads to advantages with respect to construction and maintenance of the power transformer. 
       FIG. 14  shows details of the arrangement depicted in  FIG. 13 . The  FIG. 14  shows a part of the transformer  1403 . The part of the transformer  1403  could be a part of the primary side of the transformer as well as a part of the secondary side of the transformer. It is shown the magnetically couplement of different galvanically isolated windings  1401 ,  1402  and  1405 . The winding  1401  is magnetically coupled with the winding  1402  with the help of a common magnetic flux. The windings  1402  and the winding  1405  are coupled with a common magnetic flux with the help of overlapping areas, which comprise a magnetic flux. The windings  1401 ,  1402  and  1405  are embedded in a core  1404 . The core  1404  is typically E-shaped. 
       FIG. 15  shows an exemplary embodiment of a computer tomography gantry  91  arrangement. The gantry  91  comprises a stationary part  92  connected to a high frequency power source  98  and a rotary part  93  adapted to rotate relative to the stationary part  92 . An X-ray source  94  and an X-ray detector  95  are attached to the rotary part  93  at opposing locations such as to be rotatable around a patient positioned on a table  97 . The X-ray detector  95  and the X-ray source  94  are connected to a control and analysing unit  99  adapted to control the X-ray detector  95  and the X-ray source and to evaluate the detection results of the X-ray detector  95 . 
     It should be noted that the term ‘comprising’ does not exclude other elements or steps and the ‘a’ or ‘an’ does not exclude a plurality. Also elements described in association with the different embodiments may be combined. 
     It should be noted that the reference signs in the claims shall not be construed as limiting the scope of the claims. 
     LIST OF REFERENCE SIGNS 
       91  Computer tomography gantry, 
       92  Stationary part of the gantry, 
       93  Rotary part of the gantry, 
       94  X-ray source, 
       95  X-ray detector, 
       97  Table, 
       98  High frequency power source, 
       99  Control and analysing unit, 
       101  Computer tomography gantry, 
       102  Part of a computer tomography gantry, 
       103  Stationary part of a transformer, 
       104  Stationary part of a transformer, 
       105  Rotary part of a transformer, 
       106  Inverter, 
       107  Supply line, 
       201  Mains input stage, 
       202  Inverter, 
       203  Inverter, 
       204  Supply line, 
       205  Supply line, 
       206  Stationary part of a gantry, 
       207  Core, 
       208  Primary winding, 
       209  Primary winding, 
       210  Primary winding, 
       211  Primary winding, 
       301  Mains input stage, 
       302  Inverter, 
       303  Inverter, 
       304  Inverter, 
       305  Inverter, 
       306  Primary winding, 
       307  Primary winding, 
       308  Primary winding, 
       309  Primary winding, 
       310  Part of a computer tomography gantry, 
       401  Part of a computer tomography gantry, 
       402  Inverter, 
       403  Inverter, 
       404  Mains input stage, 
       405  Inverter, 
       406  Inverter, 
       501  Part of a computer tomography gantry, 
       502  Mains input stage, 
       503  Inverter, 
       504  Inverter, 
       505  Current balancing choke, 
       506  Primary winding, 
       507  Primary winding, 
       508  Primary winding, 
       509  Primary winding, 
       510  Inverter, 
       511  Inverter, 
       512  Current balancing choke, 
       513  Current balancing choke, 
       519  Inverter, 
       520  Inverter, 
       521  Inverter, 
       522  Inverter, 
       516  Supply line, 
       517  Supply line, 
       518  Mains input stage, 
       523  Inverter, 
       524  Current balancing choke, 
       525  Current balancing choke, 
       526  Inverter, 
       527  Inverter, 
       528  Inverter, 
       529  Supply line, 
       530  Mains input stage, 
       531  Supply line, 
       532  Inverter, 
       533  Current balancing choke, 
       534  Current balancing choke, 
       535  Inverter, 
       536  Inverter, 
       537  Supply line, 
       538  Mains input stage, 
       539  Inverter, 
       540  Supply line, 
       541  Current balancing choke, 
       542  Primary winding, 
       543  Primary winding, 
       544  Primary winding, 
       545  Primary winding, 
       601  Primary winding, 
       602  Primary winding, 
       603  Primary winding, 
       604  Primary winding, 
       605  Supply line, 
       606  Supply line, 
       607  Supply line, 
       608  Supply line, 
       609  Cross-section, 
       610  Core, 
       611  Cross-section of the primary winding  604 , 
       612  Inverter, 
       613  Supply line, 
       614  Inductance of a current balancing choke, 
       615  Inductance of a current balancing choke, 
       616  Inductance of a current balancing choke, 
       617  Inductance of a current balancing choke, 
       618  Inductance of a current balancing choke, 
       619  Inductance of a current balancing choke, 
       701  Power switching unit, 
       702  Resonant circuit, 
       703  Current balancing choke, 
       704  Transformer, 
       705  Current balancing choke, 
       706  Transformer, 
       707  Rectifier, 
       708  Capacitor, 
       801  Inverter, 
       802  Winding, 
       803  Core, 
       804  Inverter, 
       805  Winding, 
       806  Inverter, 
       807  Winding, 
       808  Center line, 
       809  Center line, 
       901  Winding, 
       902  Rectifier, 
       903  Center line, 
       904  Core, 
       905  Center line, 
       906  Part of a transformer, 
       1001  Rectifier, 
       1002  Diode and switch, 
       1003  Rectifier, 
       1004  Transformer, 
       1101  Winding, 
       1102  Rectifier, 
       1103  Rectifier, 
       1104  Winding, 
       1105  Core, 
       1106  Center line, 
       1107  Center line, 
       1108  Part of a transformer, 
       1201  Inverter, 
       1202  Winding, 
       1203  Inverter, 
       1204  Winding, 
       1205  Core, 
       1206  Inverter, 
       1207  Winding, 
       1208  Center line, 
       1209  Center line, 
       1210  Inverter, 
       1211  Winding, 
       1212  Winding, 
       1213  Inverter, 
       1214  Inverter, 
       1215  Winding, 
       1216  Part of a transformer, 
       1301  Winding, 
       1302  Winding, 
       1303  Winding, 
       1304  Center line, 
       1305  Center line, 
       1306  Core, 
       1307  Winding, 
       1308  Winding, 
       1309  Winding, 
       1310  Part of a transformer, 
       1401  Winding, 
       1402  Winding, 
       1403  Part of a transformer, 
       1404  Core, 
       1405  Winding.