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 geometry having superposed turns of one or more conductors in the shape of a tape may be required. In superconducting electrical machines, higher flux density on the high-temperature superconductors in the direc tion orthogonal to major side of the tape section (c-axis di rection) results in lower critical current and then lower torque. To reduce the c-axis flux density on the superconduc tors, flux diverters may be installed next to the supercon ductors to attract flux from the superconductors. There may be therefore still a need for providing a supercon ducting electric generator including a coil geometry, which allows significantly reducing the flux density perpendicular to the superconductors tape sections, without any other addi tional construction of the electrical machine.

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 coil on said stator or on said rotor. The coil includes a plurality of turns of one or more high- temperature superconducting conductors shaped as a tape, each tape conductor including a substrate having a flat sec tion and a high-temperature superconducting layer, the high- temperature superconducting layer being laid over one of the two major sides of the substrate, the high-temperature super conducting layer having a width in a direction parallel to the major side of the substrate. The turns of the coil are stacked in such a way that the major sides of the substrate are superposed to one another to form a coil section having a first dimension parallel to the width of the high-temperature superconducting layer and a second dimension orthogonal to the first dimension, the ratio between the first dimension and the second dimension being comprised between 2 and 5.

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 in a stator or a rotor of an electric generator. The method includes the step of providing a plurality of turns on said stator or said rotor of one or more high-temperature superconducting conductors shaped as a tape, each tape conductor including a substrate having a flat section and a high-temperature superconducting layer, the high-temperature superconducting layer being laid over one of the two major sides of the substrate, the high- temperature superconducting layer having a width in a direc tion parallel to the major side of the substrate, the turns of the coil being stacked in such a way that the major sides of the substrate are superposed to one another to form a coil section having a first dimension parallel to the width of the high-temperature superconducting layer and a second dimension orthogonal to the first dimension, the ratio between the first dimension and the second dimension being comprised be tween 2 and 5.

The coil geometry provided by the present invention allows significantly reducing the flux density perpendicular to the superconductors tape sections, without any other additional construction of the electrical machine

According to possible embodiments of the present invention, the turns of the coil are stacked along the direction axis of the flux density of the current flowing in high-temperature superconducting conductors.

According to other possible embodiments of the present inven tion, the width of the high-temperature superconducting layer is comprised between 4.3 mm and 13 mm.

According to further possible embodiments of the present in vention, the coil includes a plurality of N turns of one or more high-temperature superconducting conductors shaped as a tape, N being comprised between 20 and 60.

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.

Figure 2 shows a schematic partial cross section view of a coil geometry provided on the stator or the rotor of figure 1, the coil including a plurality of turns configured according to the present inven tion.

Figure 3 shows a schematic cross section view of a coil geometry provided on the stator or the rotor of figure 1, the coil including a plurality of turns configured according to the present invention,

Figure 4 shows a schematic representation of the critical current and the critical torque T in the section of figure 3.

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 circumfer ential in the following are made with reference to the rota tional axis Y. The blades 4 extend radially with respect to the rotational axis Y. The wind turbine 1 comprises a perma nent magnet electric generator 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 rota tional axis Y. The permanent magnet electric generator 10 in cludes a stator 20 and a rotor 30. The rotor 30 is rotatable with respect to the stator 20 about the rotational axis Y.

The stator 20 and/or the rotor 30 may have a toothed struc ture. On the stator 20 and/or on the rotor 30 a coil includ ing one or more high-temperature superconducting (HTS) con ductors is provided according to the present invention and configured as described in the following.

Figure 2 shows a geometry of a coil 100 including one or more high-temperature superconducting (HTS) tapes 101. The tape 101 includes a substrate 102 having a flat rectangular sec tion and a high-temperature superconducting layer 110, which is laid over one of the two major sides of the substrate 102. The high-temperature superconducting layer 110 has a width W, in a direction parallel to the major side of the substrate 102. According to embodiments of the present invention, W may be comprised between 4.3 and 13 mm. The tape 101 further in cludes a copper coating 103 surrounding the assembly made of the substrate 102 and the high-temperature superconducting layer 110. The critical current of the HTS tape is determined by the flux density on the perpendicular direction of the high-temperature superconducting layer 110, which is also the direction perpendicular to the two major sides of the sub strate 102. This direction is defined as the c-axis 120 of the HTS tape 101. In the coil 100 geometry the HTS tape(s)

101 is(are) usually stacked alongside the c-axis 120. In oth er words, the turns in the coil 100 geometry (five turns are shown in the coil geometry 100 of figure 2) are stacked in such a way that the major sides of the substrate(s) 102 are superposed to one another. In the section view of figure 2, the high-temperature superconducting layers 110 are arranged in alternating disposition with the substrates 102.

According to other embodiments of the present invention (not shown), the width W of the coil may be made up of a plurality of tapes 101 connected in parallel or series, each of the tape being narrower than W, so that the coil width ratio is not limited to the maximum dimensions of the tapes. If the tapes are connected in parallel, then they can be preferably arranged to minimize current imbalance between parallel strands in a stator slot, according to well-known techniques for a person skilled in the art of electrical machine design.

Figure 3 shows an embodiment of the coil 100 having a section S obtained by stacking a plurality of N turns of one or more high-temperature superconducting (HTS) tapes 101, as de scribed in figure 2. According to embodiments of the present invention, N may be comprised between 20 and 60. The section S is rectangular is shape, having a first dimension LI per pendicular to the c-axis 120 and a second dimension L2 paral lel to the c-axis 120. The first dimension LI is greater than the second dimension L2. The ratio R=L1\L2 between the first dimension LI and the second dimension L2 is comprised between 2 and 5.

Figure 4 shows the critical current J in the section S and the critical torque T generated by the critical current J.

The critical current J is schematically represented by a plu rality of closed current paths 201 (three closed paths 201 are shown in figure 4) distributed along the direction or thogonal to the c-axis 120, i.e. along the first dimension LI of the section S. The critical torque T is schematically rep resented by a closed torque path 301, being the envelope of the plurality of current paths 201. As shown in figure 4, at areas of the section S where two current paths 201 are adja cent a flux cancellation is achieved, because in such areas the fluxes deriving from the two adjacent current paths 201 are of equal magnitude and opposite direction. This permits to achieve higher critical currents with respect to coil sec tions having other aspect ratio, in particular with respect to coil sections where the second dimension L2 parallel to the c-axis 120 is greater than the first dimension LI orthog onal to the c-axis 120. Critical current and torque can be significantly improved with a section S having an aspect ra tio which is wider along the tape width W.