Transformer with shielding rings in windings

1. A coil and electric shielding arrangement for a dry-type transformer, the electric shielding arrangement comprising:

a winding wound around a longitudinal axis of the transformer forming the coil;

an electric shielding device arranged at a distance from the winding at an axial end of the winding perpendicular to the longitudinal axis and parallel to a to surface of the coil such that the electric shielding device covers a cross-sectional area of the winding perpendicular to the longitudinal axis, the electric shielding device having first rounded edges not facing the winding, and second rounded edges facing the winding, wherein a radius of the first rounded edges and a radius of the second rounded edges are adapted such that an electric shielding of the winding is provided by the electric shielding device; and

an insulation material attached to the winding and to the electric shielding device, the insulation material establishing a first distance between the winding and the electric shielding device along the longitudinal axis such that the winding is shielded against another electric field,

wherein the winding and the electric shielding device are casted in a block which insulates the electric shielding device from the electric field of the winding by providing a second distance between the winding and the electric shielding device,

wherein the casted block includes third rounded edges near the electric shielding device with radii corresponding to the radii of the first rounded edges of the electric shielding device, and

wherein the electric field generated by the windings is smoothed by a combination of the electric shielding device with the first rounded edges and the third rounded edges of the cast block near the first rounded edges.

2. The arrangement of claim 1 , wherein the first rounded edges have a radius of 5 to 20 mm and the second rounded edges have a radius of 2 to 5 mm.

3. The arrangement of claim 2 , wherein the first round edges have a radius of 10 mm and the second rounded edges have a radius of 3 mm.

4. The arrangement of claim 1 , wherein the electric shielding device is electrically connected to the winding.

5. The arrangement of claim 1 , wherein the distance between the winding and the electric shielding device is between 5 to 40 mm.

6. The arrangement of claim 1 , wherein the electric shielding device has an open ring shape or an annular shape.

7. The arrangement of claim 1 , wherein the radii of the third rounded edges is between 5 to 15 mm.

8. The arrangement of claim 1 , wherein a cross-section of the shielding device is selected from a group of polygonal cross-sections with rounded edges, semi-elliptical cross-sections, or a circular cross-section.

9. The arrangement of claim 1 , wherein the winding includes at least one of a high voltage winding and a low voltage winding, and the electric shielding device covers a cross-sectional area of at least one of the high voltage winding and the low voltage winding perpendicular to the longitudinal axis.

10. The arrangement of claim 1 , wherein a cross-section of the attached insulation material comprises rounded edges.

11. The arrangement of claim 9 , comprising:

a low voltage winding with a second shielding device; and

an insulating barrier,

wherein the insulating barrier is provided between the high voltage winding and the low voltage winding and prevents charge avalanche between the high voltage winding and the low voltage winding.

12. The arrangement of claim 1 , wherein the shielding device comprises a non-conductive material frame covered by a layer of conductive material.

13. A method of manufacturing a coil and electric shielding arrangement for a transformer, the method comprising the steps:

winding a winding of the transformer around a longitudinal axis of the transformer forming the coil;

arranging an electric shielding device at a first distance from the winding, on an axial end of the winding perpendicular to the longitudinal axis, and parallel to a top surface of the coil such that the electric shielding device covers a cross-sectional area of the winding perpendicular to the longitudinal axis, the electric shielding device being formed with first rounded edges not facing the winding, and second rounded edges facing the winding, wherein a radius of the first rounded edges and a radius of the second rounded edges are adapted such that an electric shielding of the winding is provided by the electric shielding device;

attaching an insulation material to the winding and to the electric shielding device establishing a second distance between the winding and the electric shielding device along the longitudinal axis; and

casting the winding and the electric shielding in a block which insulates the electric shielding device from the electric field of the winding by providing a distance between the winding and the electric shielding device, the casted block including third rounded edges near the electric shielding device with radii corresponding to the radii of the first rounded edges of the electric shielding device,

wherein combination of the electric shielding device with the first rounded edges and the third rounded edges of the cast block near the first rounded edges is configured to smooth the electric field generated by the windings.