Coil layout for a generator having tape conductors

Field of invention

The present invention relates to a coil layout for a electric generator having tape conductors, in particular a high- temperature superconducting (HTS) generator. The present in vention further relates to a method of providing a coil lay out in an electric generator having tape conductors, in par ticular in a high-temperature superconducting (HTS) genera tor. Particularly, but not exclusively, the present invention may be applied to a HTS generator in a wind turbine.

Art Background

In the above described technical field, it is known to use superconducting electric generators for wind turbines. The use of superconductors in wind turbines is attractive because it permits to reduce weight or to generate a larger amount of power. High-temperature superconducting (HTS) generators may be conveniently used in wind turbine applications, as they are characterized by a higher critical temperature for super conductivity (77K or lower) .

In electrical generators a coil layout having overlapping coils at the end-windings may be required. Contact interfer ences between the coil conductors at the end-windings have to be avoided.

In normal conducting electric generators this can be achieved easily by bending the coil conductors, which have a circular section, at the end-windings. In superconducting electric generators the bending is however made problematic by the section shape of typical superconducting conductors (in par ticular superconducting conductors used in HTS applications) , which are typically shaped as a tape, i.e. with a flat rec tangular section. This may produce a bending stress within the superconducting conductor, which could damage or even break the coil.

There may be therefore still a need for providing a supercon ducting electric generator including a coil layout, which al lows overlapping of the coils at the end-windings without generating a dangerous level of bending stress.

A further need is that of allowing the above described over lapping, at the same time avoiding complex coil geometries.

Summary of the Invention

This need is met by the subject matter according to the inde pendent claims. Advantageous embodiments of the present in vention are described by the dependent claims.

According to a first aspect of the invention there is provid ed an electric generator. The electric generator has a sta tor, a rotor and a plurality of superconducting coils, the stator extending axially along a longitudinal axis between a first axial end and a second axial end, the stator including a plurality of slots, the plurality of slots being circumfer entially distributed around a longitudinal axis of the sta tor, each of the superconducting coils respectively compris ing :

- two slot portions respectively housed in two slots of the stator,

- two end-windings axially protruding from stator at the first axial end and a second axial end,

wherein the slot portions are shaped and positioned in the respective slots so that the end-windings of two circumferen tially adjacent coils overlap and are distanced in a radial direction orthogonal to the longitudinal axis.

Advantageously, the arrangement of the coil in two adjacent slots provides radial clearance for the end-windings while avoiding complex coil geometries.

The present invention may be applied to both integral-slot and fractional-slot electric generators. This invention can be efficiently adapted to a superconduct ing electric generator of a wind turbine.

According to a second aspect of the invention there is pro vided a method of providing a coil layout in an electric gen erator. The electric generator has a stator and a rotor, the stator extending axially along a longitudinal axis between a first axial end and a second axial end, the stator including a plurality of slots, the plurality of slots being circumfer entially distributed around a longitudinal axis of the sta tor, the coil layout including a plurality of superconducting coils each respectively comprising:

- two slot portions respectively housed in two slots of the stator,

- two end-windings axially protruding from stator at the first axial end and a second axial end.

According to the method the slot portions are inserted in the respective slots so that the end-windings of two circumferen tially adjacent coils overlap and are distanced in a radial direction orthogonal to the longitudinal axis.

According to the invention a slot portion of a first super conducting coil is housed in a respective first slot and a slot portion of a second superconducting coil is housed in a respective second slot circumferentially adjacent to the first slot.

According to a possible embodiment of the present invention, the slot portions of the first and the second superconducting coils have respective different curvatures in a longitudinal section including the longitudinal axis.

According to another embodiment of the present invention, the slot portions of the first and the second superconducting coils are inclined with respect to each other in a longitudi nal section including the longitudinal axis.

According to a further embodiment of the present invention, the slot portions of the first and the second superconducting coils are parallel and radially distanced in a longitudinal section including the longitudinal axis. All the above described embodiments apply to both the appa ratus and the method of the present invention.

The aspects defined above and further aspects of the present invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to the examples of embodiment. The invention will be described in more detail hereinafter with reference to examples of embodi ment but to which the invention is not limited.

Brief Description of the Drawing

Figure 1 shows a schematic section of a wind turbine in cluding an electric generator and a cooling sys tem according to the present invention,

Figure 2 shows a schematic partial cross section view of the stator of the electric generator of Fig. 1, taken according to the section line II-II of Fig ures 3, 4 and 5.

Figure 3 shows a schematic longitudinal section view of the stator of a first embodiment of the electric generator of Figs. 1 and 2.

Figure 4 shows a schematic longitudinal section view of the stator of a second embodiment of the electric generator of Figs. 1 and 2.

Figure 5 shows a schematic longitudinal section view of the stator of a third embodiment of the electric generator of Figs. 1 and 2.

Detailed Description

The illustrations in the drawings are schematic. It is noted that in different figures, similar or identical elements are provided with the same reference signs.

Figure 1 shows a wind turbine 1 according to the invention. The wind turbine 1 comprises a tower 2, which is mounted on a non-depicted fundament. A nacelle 3 is arranged on top of the tower 2.

The wind turbine 1 further comprises a wind rotor 5 having two, three or more blades 4 (in the perspective of Figure 1 only two blades 4 are visible) . The wind rotor 5 is rotatable around a rotational longitudinal axis Y. When not differently specified, the terms axial, radial and circumferential in the following are made with reference to the rotational axis Y. The blades 4 extend radially with respect to the rotational axis Y.

The wind turbine 1 comprises a permanent magnet electric gen erator 11.

According to other possible embodiments of the present inven tion (not represented in the attached figures) , the present invention may be applied to any other type of permanent mag net machine with either internal or external rotor.

The wind rotor 5 is rotationally coupled with the permanent magnet generator 11 either directly, e.g. direct drive or by means of a rotatable main shaft 9 and through a gear box (not shown in Figure 1) . A schematically depicted bearing assembly 8 is provided in order to hold in place the main shaft 9 and the rotor 5. The rotatable main shaft 9 extends along the ro tational axis Y.

The permanent magnet electric generator 10 includes a stator 20 and a rotor 30. The rotor 30 is rotatable with respect to the stator 20 about the rotational axis Y.

Figure 2 schematically shows a partial and schematic section al view of the rotor 20, orthogonal to the longitudinal axis

Y.

The stator 20 extending axially along the longitudinal axis Y between a first axial end 22 and a second axial end 23 and includes a plurality of slots (six slots 51a, 52a, 53a, 51b, 52b, 53b in the non-limiting embodiment of Figure 2) circum ferentially distributed around the longitudinal axis Y and alternating with a plurality of teeth 60 along circumferen tial direction X, orthogonal to the longitudinal axis Y.

Along the circumferential direction X, the six slots 51a, 52a, 53a, 51b, 52b, 53b are ordered in series as a first slot 51a, a second slot 52a, a third slot 53a, a fourth slot 51b, a fifth slot 52b and a sixth slot 53b.

A plurality of superconducting coils (three coils 41, 42, 43 in the non-limiting embodiment of Figure 2) is arranged in the slots 51a, 52a, 53a, 51b, 52b, 53b.

The superconducting coils comprise superconducting conductors shaped as a tape, i.e. having a flat rectangular section where one dimension is significantly greater than the other. According to the different embodiments of the present inven tion, the greater dimension of the conductor section may be oriented parallel or orthogonal to the circumferential direc tion X.

A first superconducting coil 41 comprises:

- two slot portions 41a, 41b respectively housed in two re spective slots (the first slot 51a and the fourth slot 51b in the non-limiting embodiment of Figure 2),

- two end-windings 41c axially protruding from stator 20 at the first axial end 22 and a second axial end 23.

A second superconducting coil 42 comprises:

- two slot portions 42a, 42b respectively housed in two re spective slots (the second slot 52a and the fifth slot 52b in the non-limiting embodiment of Figure 2),

- two end-windings 42c axially protruding from stator 20 at the first axial end 22 and a second axial end 23.

A third superconducting coil 43 comprises:

- two slot portions 43a, 43b respectively housed in two re spective slots (the third slot 53a and the sixth slot 53b in the non-limiting embodiment of Figure 2),

- two end-windings 43c axially protruding from stator 20 at the first axial end 22 and a second axial end 23.

The above described winding layout of the superconducting coils 41, 42, 43 may be repeated along the circumferential axis X beyond the first slot 51a and the sixth slot 53b.

The above described winding layout determines an overlapping of the end-windings 41c, 42c, 43c.

According to different embodiment of the present invention (not shown) a different number of superconducting coils may be provided. According to different embodiment of the present invention (not shown) the superconducting coils are housed in the stator 20 according to any other winding layout which causes an overlapping of the end-windings

To avoid interference between the end-windings 41c, 42c, 43c the slot portions 41a, 41b, 42a, 42b, 43a, 43b are shaped and positioned in the respective slots 51a, 51b, 52a, 52b, 53a, 53b so that the end-windings 41c, 42c, 43c of two circumfer entially adjacent coils 41, 42, 43 overlap and are distanced in a radial direction R orthogonal to the longitudinal axis Y and to the circumferential direction X.

Three different embodiments are respectively shown in Figures 3, 4 and 5, where the slot portions 41a, 42a, 43a of the su perconducting coil 41, 42 43 and the first, second and third slots 51a, 52a, 53a are shown superposed to one another in a longitudinal section including the longitudinal axis Y.

In the first embodiment of Figure 3, the slot portions 41a, 42a, 43a have respective different curvatures. Particularly, the slot portion 41a of the first superconductive coil 41 is curved with a convex shape pointing towards the longitudinal axis Y, the slot portion 42a of the second superconductive coil 42 is straight and the slot portion 43a of the third su perconductive coil 43 is curved with a convex shape pointing away from the longitudinal axis Y.

In the second embodiment of Figure 4, the slot portions 41a, 42a, 43a are inclined with respect to each other. Particular ly, the slot portion 41a of the first superconductive coil 41 is inclined towards the first axial end 22, the slot portion 42a of the second superconductive coil 42 is straight and the slot portion 43a of the third superconductive coil 43 is in clined towards the second axial end 23.

In the third embodiment of Figure 5, the slot portions 41a, 42a, 43a are parallel and radially distanced with respect to each other. Particularly, the slot portion 41a of the first superconductive coil 41 is closer to the longitudinal axis Y, the slot portion 42a of the second superconductive coil 42 is intermediate and the slot portion 43a of the third supercon ductive coil 43 is more remote from the longitudinal axis Y.

Other embodiments (not shown) may be provided according to the present invention, provided that it is assured that, at the first axial end 22 and the second axial end 23 or at a longitudinal distance from the first axial end 22 and the second axial end 23, the end-windings are distanced along the radial direction R.

The present invention applies also more in general to non superconducting coils comprising non-superconducting conduc- tors shaped as a tape.