Abstract:
The invention relates to a traction transformer for railbound vehicles comprising: an insulating liquid filled enclosure, at least two windings contained in the enclosure, a transformer core, mounting means for mounting the transformer to the railbound vehicle, wherein the transformer core is arranged outside the enclosure, and wherein the mounting means are attached to the transformer core.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to the field of traction transformers for electric railway vehicles. It refers to a traction transformer as described in the preamble of claim  1  and  2 . 
       RELATED ART 
       [0002]    In electric railway propulsion vehicles such as locomotives or rail coaches, the traction transformer is a crucial piece in the traction chain. If the traction transformer fails, the train is immobilised and a track section is blocked. The traction transformer is the main transformer on the railbound vehicle and provides energy from the catenary to the propulsion motor and for all on board systems. Traction transformers have to accommodate different input frequencies and voltage (ranging from as high as 50 Hz down to 16.7 Hz and rated up to 25 kV) while being suitable for multiple AC asynchronous motor and DC converters and motors with varying harmonics mitigation filtering requirements. To provide high-power conversion the traction transformer need to be designed with a substantial size and weight. A traction transformer is designed to withstand all occurring mechanical vibrations, shocks and acceleration forces of a railway propulsion vehicle. 
         [0003]    The traction transformer is usually placed outside the main casing of the traction vehicle, i.e. underfloor or on the roof top where space is limited because of the maximal allowable vehicle height or the available space between underfloor and rail. Tractions transformers may also be placed inside the main casing end prevail similar space limitations. Further, due to considerable weight of the transformer care has to be taken if roof top or underfloor installations are demanded. 
         [0004]    The first traction transformers have been constructed with dry in or air insulations causing frequent failures as flashovers and electrical discharges during operation. The failures are caused by dust or humidity to which the transformer was exposed. 
         [0005]    Nowadays conventional state of the art traction transformers for electric railway propulsion vehicles are by the type of insulation and cooling oil-immersed transformers to meet the requirements. Oil being a very good heat transfer medium and a good electrically insulating material compared to air, when a high power density is needed. The windings and the core of oil-immersed transformers are completely encased in a tank which is filled with the transformer oil. The tank has therefore appropriate means on its outer side for mounting it to the propulsion vehicle. Such means for mounting are beams, plates etc. which are welded to the tank (housing) of the traction transformer and must take the full weight of tank, transformer and transformer oil. Consequently the tank must have a substantial wall thickness and must be made of heavy weight material as steel to provide the mechanical stability. 
         [0006]    Document GB874730 discloses an oil-immersed transformer device for railway propulsion vehicle including the main transformer disposed in transformer tank. The transformer which delivers the required voltage levels for the propulsion is mounted in the transformer tank. The transformer tank is filled with oil. The tank is mounted under the floor of the railway vehicle. 
         [0007]    WO2014086948 A2 discloses a transformer for traction applications with windings immersed in an oil filled enclosure. The closed loop core extends through the inner of a central inner cylinder element which forms part of the enclosure and is therefore of contact with oil. 
         [0008]    It is an object of the present invention to provide a compact traction transformer design which allows a reduced size and weight while maintaining the required power density. 
       SUMMARY OF THE INVENTION 
       [0009]    This object has been achieved by traction transformer according to claim  1  and  2 . 
         [0010]    Further embodiments of the present invention are indicated in the depending sub-claims. 
         [0011]    According to a first aspect, a traction transformer for railbound vehicles is provided, comprising:
       an insulating liquid filled enclosure,   at least two windings contained in the enclosure,   a transformer core,   mounting means for mounting the transformer to the railbound vehicle, wherein the transformer core is arranged outside the enclosure, and wherein the mounting means are attached to the transformer core.       
 
         [0016]    One idea of the above traction transformer is that the windings are housed in the enclosure and the transformer core can pass through the enclosure without being in contact with the insulating liquid and therewith allowing to attach the mounting means directly to the transformer core for mounting the transformer to the railbound vehicle. With other words, the mounting means and the transformer core are directly connected and are in direct physical contact. Forces acting on the railbound vehicle are transmitted directly to the transformer core via the mounting means. On the other hand forces acting on the transformer are transmitted directly from the transformer core to the railbound vehicle via the mounting means. The transformer allows reducing the quantity of insulting liquid filled in the enclosure and simplifying the mechanical structure of the enclosure. Hence, the above traction transformer has reduced size and weight. 
         [0017]    Furthermore, the enclosure of the traction transformer is attached to the transformer core by at least two support elements. 
         [0018]    It may be provided that the mounting means are solely fixed to the transformer core ( 40 ) of the traction transformer. In this way other parts of the transformer, in particular the enclosure of the transformer is not used for fixation of the mounting means. Thereby less quantity of material and more lightweight material can be used for all parts do not contribute to the fixation of the mounting means. Such reduces the total weight of the traction transformer. 
         [0019]    Furthermore, the enclosure may be formed by at least one cylindrical inner housing and by a cylindrical outer housing partially surrounding the at least one cylindrical inner housing, wherein an enclosed volume of the enclosure between the at least one cylindrical inner housing and the cylindrical outer housing is filled with the insulating liquid and wherein portions of the transformer core extend through the at least one cylindrical inner housing. The windings enclose the inner cylindrical housing and are supported by the outside surface of the inner cylindrical housing. 
         [0020]    It may be provided that a first cover and a second covers are arranged at axial ends of the enclosure. The enclosure is clamp ed between the at least two support elements pressing at the axial ends onto the first and onto the second cover. 
         [0021]    The first cover and the second cover are liquid-tight sealed to the axial ends of the enclosure. Both covers have at least one opening which matches to a diameter of the at least one cylindrical inner housing, in this way a hollow cylinder is formed which contains the insulating liquid. Typically the limbs as part of the transformer core extend through the passage of the hollow cylinder. The liquid-tight sealing may be formed by a glued joint, a gasket or by welding. 
         [0022]    Furthermore, the, traction transformer is of core-type which means two yokes and two limbs form the core loop. To each of the limbs at least one winding is attached. The yokes extend outside at both axial ends of the enclosure to which the mounting means are fixed. 
         [0023]    As the main function of the enclosure is to servers a tank for the insulating liquid and does not serve as fixation of the mounting means, it may be made of a lightweight material. Preferred enclosure materials may be types of glass fiber, epoxy based composite or aluminum. 
         [0024]    In may be provided that the mounting means is a mounting frame having sidebars which run in parallel. The sidebars are fixed to the yokes and run parallel to the yoke direction. 
         [0025]    Furthermore, stiffening elements may be comprised to absorb forces along the yoke direction and therewith along the moving direction of the railway vehicle. The stiffening elements are attached to the side bars of the frame and to the portion of the transformer which extends through the cylindrical inner housing. 
         [0026]    It may be provided the at least two support elements are adapted to the shape of the first cover and the second cover. Those shaped support elements prevent escaping of magnetic stray fields in an axial direction of the windings and the core limbs. Parasitic effects of the stray field to neighboring ferromagnetic parts of the railway vehicle and to the rail causing eddy currents and other losses are reduced. 
         [0027]    It may be provided that the enclosure has an eight-shaped cross section perpendicular to the axial direction of the windings. This cross section advantageously improves the mechanical stability of the cylindrical outer housing and therewith of the full enclosure and at the same time reduces the enclosed volume and therewith the quantity of the insulating liquid needed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]    Embodiments will be described in more detail in conjunction with the accompanying drawings, in which: 
           [0029]      FIG. 1  shows a railbound vehicle with a traction transformer attached underneath the floor of the vehicle casing; 
           [0030]      FIG. 2 a    shows a perspective view of a traction transformer for horizontal mounting; 
           [0031]      FIG. 2 b    shows a side view of the traction transformer; 
           [0032]      FIG. 2 c    shows another side view of the traction transformer; 
           [0033]      FIG. 2 d    shows-a section view of the traction transformer according to the invention; 
           [0034]      FIG. 3  shows perspective view of a traction transformer for vertical mounting. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0035]    Reference will now be made in detail to the embodiments, one or more examples of which are illustrated in the figures. Each examples provided by way of explanation, and is not meant as a limitation of the invention. Within the following description of the figures, the same reference numbers refer to the same components. Generally, only the differences with respect to individual embodiments are described. 
         [0036]      FIG. 1  schematically shows a railbound vehicle  1  equipped with traction transformer  10  attached underneath the floor of the vehicle casing. In other configurations the transformer may be attached on the roof top of the vehicle or maybe attached in the machine room inside the vehicle casing. 
         [0037]    In the following a first embodiment of the traction transformer is described in conjunction with the views according to  FIGS. 2 a    to  2   d.  The traction transformer  10  comprises an enclosure  20  filled with insulating liquid  205 . The insulating liquid typically comprises mineral oil, silicon oil, synthetic or vegetable oil and serves for electrical isolation of the windings and for pooling of the windings. 
         [0038]    The enclosure  20  is formed by two cylindrical inner housings  201 ,  202  and by a cylindrical outer housing  203  surrounding the two cylindrical inner housings  201 ,  202 . Each of the cylindrical inner housings  201 ,  202  has an annular cross section and has a cylinder axis which is substantially parallel to the cylinder axis of the outer housing  203 , which is the axial direction Y as indicted in  FIG. 2   d.  The axial direction Y is also the axial direction of the windings  30 ,  31 . The cylindrical inner housings  200 ,  201  may also be shaped with different cross-sections (across the axial direction Y thereof). 
         [0039]    Each of both axial ends of the enclosure  20  is closed by a first and a second cover  206 ,  207  respectively. The first and the second cover  206 ,  207 , the two cylindrical inner housing  201 ,  202 , and the cylindrical outer housing  203  form an enclosed volume which is filled with the insulating liquid  205  in particular with transformer oil. The windings  30 ,  31  which are accommodated in the enclosure are completely immersed in the transformer oil. Therefore the first and the second cover  206 ,  207  are liquid-tight sealed to the cylindrical outer housing  203  and to the two cylindrical inner housings  201 ,  202 . The sealing can be made by a glued joint. Alternatively, the sealing may be made by a gasket or by a type of welding, 
         [0040]      FIG. 2 d    is a section view of  FIG. 2 b    taken along the A-A line of the traction transformer  10  according to the first embodiment and shows two circular openings  208 ,  209  in the first and the second cover  207 ,  208  respectively which openings  208 ,  209  match to the inner diameter of the cylindrical inner housing  201 . Two further openings are provided and matching to the inner diameter of the cylindrical inner housing  202 . 
         [0041]    The two limbs  403 ,  404  of transformer core  40  extend through the two cylindrical inner housings  201 ,  201  and therewith through the two windings  30 ,  31 . The limbs  403 ,  404  are bridged by the two transformer yokes  401 ,  402  at the axial ends of the enclosure  20 . In this way a core-type transformer is realized with the windings  30 ,  31  solely immersed in the transformer oil. The transformer core  40  is outside the enclosure and therefore not in contact with transformer oil and may be called by air. 
         [0042]    The windings  30 ,  31  are wound around the respective cylindrical inner housing  201 ,  202 . The conductors of the winding  30 ,  31  can be wire-like, such as a coil of metal wire, e. g. copper wire, or plate-like, coated with an electrical insulation layer, and are spirally wound around the cylindrical inner housings  201 ,  202 . The winding  30  may act as a primary winding and the winding  31  may act as a secondary winding of the traction transformer  10  or vice versa. 
         [0043]    To avoid a short circuit, the two cylindrical inner housings  201 ,  202  must not act as a turn of a parasitic secondary coil. Hence, both inner housings  201 ,  202  are made of electric insulating material for example an epoxy based composite. 
         [0044]    For the horizontal mounting of the traction transformer  10  to the railbound vehicle  1  the plane spanned by the X-Y directions is substantially parallel to the roof or to the underfloor of the railbound vehicle  1 . 
         [0045]    As can be seen from the  FIGS. 2 a  to 2 d   , the transformer core  410  is fixed to the mounting means  50  which are embodied as mounting frame. The frame allows a mounting of the transformer  10  onto the roof top or underneath the floor of the train and has two parallel side bars  501 ,  502  which are welded together by two transverse bars. The side bars  501 ,  502  are aligned along the train and along the moving direction of the train which is indicted as X-direction. By fixation of the transformer core  40  directly to the frame and therewith to the railbound vehicle the heaviest part beside the windings of the transformer is used for fixation and advantageously acceleration forces or vibrations from train vehicle can be transmitted directly to the transformer core. Such simplifies the mechanical construction of the traction transformer  10  and in particular the construction of its enclosure  20 . 
         [0046]    The traction transformer  10  is fixed to the frame solely by means of the transformer core  40  which rests on the side bars  501 ,  502  of the frame. In particular the transformer yokes  401 ,  402  and the ends of the transformer limbs  403 ,  404  which protrude beyond the axial ends of the enclosure  20  rest on top of the side bars  501 ,  502 . In other embodiments it may be provided that the frame rest on top of the transformer core  40 . 
         [0047]    The fixation between the transformer core  40  and the side bars  601 ,  502  is made by screw joints. To provide a high rigidity and stability between the core  40  and the frame, the transformer core  40  is of stack-lap type in which one or several layers of the limbs  403 ,  403  overlap with one or several layers of the yokes  401 ,  402  as it is indicated in  FIG. 2   d.  8 through-holes are provided in the transformer core  40 , of which four are made at the four corners of the transformer core  40  in the overlapping region of limbs  403 ,  404  and the yokes  401 ,  402 . When the transformer core  40  is mounted to the frame by screws then also the limbs are screwed together with the yokes  401 ,  402 . The yokes  401 ,  402  are oriented parallel to the side bars  501 ,  502  and therewith along the X-direction. 
         [0048]    The frame is mounted by four curved legs to the railbound vehicle  1  which are welded to the ends of the side bars  501 ,  502 . 
         [0049]    As can be seen from the  FIGS. 2 a    to  2   d,  the enclosure  20  is fixed to the transformer core  40  by four support elements  60 ,  61 ,  62 ,  63  which are angled and in which two of them  60 ,  62  are arranged on the top of the transformer core  40  at the axial ends of the enclosure  20  and wherein the two other angled support elements  61 ,  63  are arranged at the bottom side of the transformer core  40  at the axial ends of the enclosure  20 . 
         [0050]    Each of the angled support elements  60 ,  61 ,  62 ,  63  is screwed by one of its two legs directly to the transformer core  40 , whereas the enclosure  20  is clamped between the other legs. Latter ones press at the axial ends onto the first and second cover  206 ,  207 . The support element  60  on the top of transformer core  40  and the support element  61  on the bottom side of the transformer core  40  have adjusting screws to set the contact force for damping the enclosure  20 . The adjusting screws are fixed on the leg of the support element  60 ,  6 l which presses against first  206  or the second cover  207 . 
         [0051]    Each of the yokes  401 ,  402  of the traction transformer  10  is screwed together with the respective side bar  501 ,  502  of the frame, with the respective support element  60 ,  61 ,  62 ,  63  on the top of the transformer core and with the respective support element on the bottom side of the transformer  10 . The screw joint is arranged perpendicular to the axial direction Y of the windings. 
         [0052]    The support elements  60 ,  61   62 ,  63  may be adapted partially or full to the shape of cover first  206  or the second cover  207  (not shown) so as to prevent escaping of the magnetic flux in axial direction Y of the windings. In this way shaped support elements  60 ,  61 ,  62 ,  63  act as shielding and prevent a distraction of the unwanted magnetic stray field to the environment, in particular to the railbound vehicle or the rails. 
         [0053]    The traction transformer  10  may be provided with stiffening dements  70 ,  71 ,  72 ,  73  to absorb acceleration forces along the moving direction of the railbound vehicle  1 . The stiffening elements  70 ,  71 ,  72 ,  73  are attached to top of the side bars  501 ,  502  and along the X-direction. The fixation may be made by a screw joint as shown for stiffing element  70  in  FIG. 2 b    or may be welded to the side bars,  501 ,  502  as it is exemplarily indicated for the stiffing element  71  in  FIG. 2   b.  The&#39;stiffening elements  70 ,  71 ,  72 ,  73  are positioned before and after the parts of the transformer core  40  which extend beyond the axial ends of the housing  20 , which are the yokes  401 ,  402 . 
         [0054]    Additional stiffening element may also be attached to the support elements  60 ,  61 ,  62 ,  63  to absorb acceleration forces and are welded thereto. These additional stiffening elements are positioned also before and after the yokes  401 ,  402 , may be screwed to the transformer core  40  and prevent an unwanted movement of the transformer core  40  along the X-direction. 
         [0055]      FIG. 3  shows a further embodiment of a traction transformer  11  for vertical mounting to the railbound vehicle, suitable to be mounted for example in the machine-room of the vehicle. 
         [0056]    The transformer core  40  is fixed to the mounting means  50  which are also embodied as a mounting frame. In difference to the embodiment according to the  FIGS. 2 a  to 2 d    the transformer  11  and the mounting means  50  are turned by 90° in a upright position. With other words, the plane spanned by the X-Y directions is substantially perpendicular oriented to the floor of the railbound vehicle and therefore the axis of the windings are oriented vertically. The side bars  501 ,  502  are welded together with two H-bars which run traverse between the side bars  501 ,  502  and form the frame. 
         [0057]    The cylindrical outer housing  203  has an eight-shaped cross section which provides a higher mechanical stability to the enclosure  20  as compared to a normal cylindrical shaped housing. Thus, a more lightweight material like aluminum instead of steel can be used as material for the cylindrical outer housing  203 . The cylindrical outer housing  203  can be made of aluminum which further shows a good heat conductivity compared to steel and improves the heat dissipation from the traction transformer  11  to its environment. It may be also provided to use lightweight material which is electric insulating as for example an epoxy composite, if the heat dissipation over the cylindrical outer housing  203  is not of importance for the design of the traction transformer  11 . 
         [0058]    The traction transformer  11  has two legs which are welded to the ends of the side bars  501 ,  502  at the same axial end of the enclosure  20  to mount the transformer in a vertical position to the railbound vehicle  1 . 
       REFERENCE LIST 
       [0000]    
       
           1  railbound vehicle 
           10 ,  11  traction transformer 
           20  enclosure 
           30 ,  31  windings 
           40  transformer core 
           50  mounting means 
           60 ,  61 ,  62 ,  63  support elements 
           70 ,  71 ,  72 ,  73  stiffening elements 
           201 ,  202  cylindrical inner housing 
           203  cylindrical outer housing 
           205  insulating liquid 
           206 ,  207  first and second covers 
           208 ,  209  openings in the first and second cover 
           401 ,  402  transformer yokes 
           403 ,  404  transformer limbs 
           501 ,  502  sidebars 
           600  adjustment screw 
         X axial direction of the yoke, direction of the side bars 
         Y axial direction of the windings and of the cylindrical inner housings