Transformer comprising winding

1. A transformer comprising:

a core; and

at least one winding wound around a winding axis extending along a limb of the core, said winding terminating in an axial end surface extending in a direction perpendicular to said winding axis, said transformer comprising a ring comprising magnetic material, said ring being located outside said winding and adjacent to said axial end surface, wherein a projection of said ring, along said winding axis, onto said winding, covers at least a part of, preferably all of, said axial end surface,

wherein the core comprises a yoke, said yoke extending radially across the ring, at one or more crossing locations, from a radial inside of the ring to a radial outside of the ring, wherein said ring comprises a set of magnetic metal components, said magnetic metal components being distributed about the winding axis and electrically insulated from each other, wherein heights along the winding axis of respective ones of the magnetic metal components varies about the winding axis such that magnetic metal components at the crossing location(s) have lower height along the winding axis than the heights of magnetic metal components further away from the crossing location(s).

2. A transformer according to claim 1 , wherein the magnetic metal components are electrically conductive.

3. A transformer according to claim 1 , wherein the heights of the magnetic metal components such that leakage flux is guided to the limb and yoke rather than to any other magnetic structure around each respective magnetic metal component.

4. The transformer according to claim 1 , wherein said ring comprises a plurality of magnetic metal sheets, each magnetic metal sheet extending in a height direction and having a magnetic metal sheet height, extending in a length direction and having a magnetic metal sheet length and extending in a width direction and having a magnetic metal sheet width, wherein said magnetic metal sheet width is smaller than each one of said magnetic metal sheet height and said magnetic metal sheet length, said ring extending in a radial direction from an inner radial portion to an outer radial portion of said ring, each magnetic metal sheet being oriented in said ring such that: said height direction coincides with said winding axis and said length direction extends along a direction from said inner radial portion to said outer radial portion of said ring.

5. The transformer according to claim 4 , wherein each magnetic metal sheet being oriented in said ring such that: said length direction extends along said radial direction.

6. The transformer according to claim 4 , wherein at least the magnetic metal sheets of a first subset of the magnetic metal sheets have a magnetic metal sheet length which extends from the inner radial portion of said ring to the outer portion of said ring).

7. The transformer according to claim 6 , wherein the metal steel sheets of a second subset of the magnetic metal sheets have a magnetic metal sheet length which does not extend from the inner radial portion of said ring to the outer portion of said ring.

8. The transformer according to claim 1 , wherein said ring has an outer periphery having a cross-section in a direction coinciding with said winding axis which is rounded.

9. The transformer according to claim 1 , wherein said ring comprises conductive elements being electrically connected to said winding.

10. The transformer according to claim 1 , wherein an electrically conductive layer encloses said ring.

11. The transformer according to claim 10 , wherein an electrical insulation layer encloses said electrically conductive layer.

12. The transformer according to claim 1 , wherein said winding also terminates in an additional axial end surface opposite to said axial end surface as seen along said winding axis, and said transformer comprises an opposing ring comprising magnetic material, said opposite ring being located outside said winding and adjacent to said additional axial end surface, wherein a projection of said ring, along said winding axis, onto said winding, covers at least a part of said additional axial end surface.

13. The transformer according to claim 1 , wherein said winding is a first winding and the transformer further comprises a second winding wound around said winding axis, said second winding terminating in an axial end surface of the second winding extending in a direction perpendicular to said winding axis.

14. The transformer according to claim 13 , wherein a projection of said ring, along said winding axis, onto said second winding, covers also at least a part of said axial end surface of the second winding.

15. The transformer according to claim 13 , wherein said ring is a first ring and the transformer comprises a second ring comprising magnetic material, said second ring being located outside said second winding and adjacent to said axial end surface of the second winding, wherein a projection of said second ring, along said winding axis, onto said second winding, covers at least a part of, preferably all of, said end surface of the second winding.

16. The transformer according to claim 13 , wherein a projection of said ring, along said winding axis, onto said second winding, covers also all of said axial end surface of the second winding.

17. The transformer according to claim 12 , wherein a projection of said ring, along said winding axis, onto said winding, covers all of said additional axial end surface.

18. The transformer according to claim 9 , wherein said conductive elements are arranged between said magnetic metal components or magnetic metal sheets.

19. The transformer according to claim 18 , wherein said conductive elements are copper elements or copper sheets.

20. The transformer according to claim 10 , wherein the electrically conductive layer comprise an aluminium or a copper layer.