Transformer with a casting embedding a winding arrangement and method of manufacturing a winding arrangement for a transformer

1. A transformer, comprising:

a transformer core having a core leg having a longitudinal axis;

a low voltage winding arranged around the core leg, the low voltage winding extending along a first length in the direction of the longitudinal axis;

a high voltage winding arranged around the low voltage winding, the high voltage winding extending along a second length in the direction of the longitudinal axis, wherein the second length is shorter than the first length; and

a casting embedding the low voltage winding and the high voltage winding, wherein the casting has a recess, wherein the recess is provided at a radial location of the high voltage winding, and wherein the recess extends in the direction of the longitudinal axis,

the recess occupying at least partly a space provided by the second length being shorter than the first length; and

the recess providing for a surface having a normal extending substantially in the direction of the longitudinal axis and the surface is a flat annular surface at a radial location of the high voltage winding.

2. The transformer of claim 1 , further comprising a coil block embedded in the casting, wherein the coil block is provided between the recess and the high voltage winding.

3. The transformer of claim 2 , wherein the coil block is arranged and configured for providing a vertical support of the high voltage winding.

4. The transformer of claim 3 , wherein the coil block is arranged and configured for providing a vertical support of the high voltage winding during embedding the low voltage winding and the high voltage winding in the casting.

5. The transformer of claim 1 , wherein the recess is provided at a first end of the casting, and wherein the casting has a further recess provided at a second end of the casting wherein the second end is opposite the first end.

6. The transformer of claim 5 , wherein the further recess occupies at least partly a space provided by the second length being shorter than the first length.

7. The transformer of claim 5 , wherein an axial extent of the recess and the further recess plus the second length is at least approximately equal to the first length.

8. The transformer of claim 5 , wherein an axial extent of the recess and/or the further recess are chosen such that a first surplus axial extent of the casting at the radial location of the high voltage winding over the second length is larger than a second surplus axial extent of the casting at the radial location of the low voltage winding over the first length.

9. The transformer of claim 5 , wherein the further recess provided at the second end is symmetric to the recess provided at the first end with respect to a symmetry plane extending perpendicular through the longitudinal axis.

10. The transformer of claim 1 , wherein the casting is made of an insulating material.

11. The transformer of claim 10 , wherein the insulating material comprises an insulating resin.

12. The transformer of claim 1 , wherein the transformer is symmetric with respect to a plane which comprises the longitudinal axis.

13. The transformer of claim 1 , wherein the transformer is a medium frequency transformer.

14. The transformer of claim 13 , wherein the medium frequency transformer is a dry-cast medium frequency transformer.

15. Method of manufacturing a winding arrangement for a transformer, the method comprising:

arranging a low voltage winding around a substantially vertical axis such that the low voltage winding extends along a first length in the direction of the substantially vertical axis;

arranging a high voltage winding around the low voltage winding such that the high voltage winding extends along a second length in the direction of the substantially vertical axis, wherein the second length is shorter than the first length;

providing a casting mold surrounding the low voltage winding and the high voltage winding, wherein the casting mold has a bottom wall, wherein at a radial location of the high voltage winding the bottom wall has an axial projection; wherein the axial projection is essentially horizontal for providing a horizontal surface of recess, wherein the recess occupies at least partly a space provided by the second length being shorter than the first length; and

embedding the low voltage winding and the high voltage winding in an insulating material by casting the insulating material into the casting mold.

16. The method of claim 15 , further comprising placing a coil block on the bottom wall of the casting mold at the radial location of the high voltage winding prior to arranging the high voltage winding around the low voltage winding.

17. The method of claim 15 , wherein the casting mold has a top wall, wherein the top wall has an axial indentation at a radial location of the high voltage winding.

18. The method of claim 17 , wherein the axial indentation is symmetric to the axial projection with respect to a symmetry plane extending perpendicular through the substantially vertical axis.

19. The method of claim 17 , wherein the axial indentation is at the radial location of the further recess.

20. The method of claim 17 , wherein the axial indentation comprises a horizontal surface of the further recess.