FIELD

[0001] The present disclosure relates in general to superconducting machines, and more particularly to a cooling system for cooling a thermal shield of a superconducting machine.

BACKGROUND

[0002] Wind turbines have received increased attention as an environmentally safe and relatively inexpensive alternative energy source. With this growing interest, considerable efforts have been made to develop wind turbines that are reliable and efficient. Generally, a wind turbine includes a plurality of rotor blades coupled via the rotor hub to the main shaft of the turbine. The rotor hub is positioned on top of a tubular tower or base. Utility grade wind turbines (i.e., wind turbines designed to provide electrical power to a utility grid) can have large rotors (e.g., 100 or more meters in diameter). The rotor blades convert wind energy into a rotational torque or force that drives the generator, rotationally coupled to the rotor.

[0003] Low reactance machines (e.g., superconducting generators) are being explored for use in wind turbine installations, particularly in offshore installations. These machines use superconducting field windings and assemblies of armature coils, cooling systems, and nonmagnetic teeth disposed between coils in the armature. In a particular design, the superconducting generator includes an armature winding assembly that, unlike conventional machine (e.g., conventional, non-superconducting generator) configurations, rotates within a superconducting field assembly, which includes a cryostat with superconducting field coils inside the cryostat.

[0004] Superconducting machines also typically include a cryogenic cooling system for cooling various components thereof. Accordingly, the art is continuously seeking new and improved cooling systems for superconducting generators.

BRIEF DESCRIPTION

[0005] Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.

[0006] In an aspect, the present disclosure is directed to a generator that includes a non-rotatable component supporting a field winding assembly and a rotatable component oriented to rotate relative to the non-rotatable component during operation of the generator. Further, the generator includes an armature winding assembly fixedly coupled to the rotatable component so as to rotate therewith during the operation of the generator. The armature winding assembly includes a plurality of conducting coils. The generator further includes a thermal shield surrounding the field winding assembly fixedly coupled to the stationary component, a cryocooler in thermal contact with the thermal shield, and a gas tank adjacent to and in thermal contact with the thermal shield, the gas tank containing a cooling gas configured to circulate therein so as to provide uniform cooling to the thermal shield.

[0007] In another aspect, the present disclosure is directed to a cooling system for a superconducting generator. The cooling system includes a thermal shield for surrounding a field winding assembly fixedly coupled to a stationary component of the superconducting generator. The stationary component is oriented relative to a rotatable component during operation of the superconducting generator. The cooling system further includes a cryocooler in thermal contact with an outer surface of the thermal shield via a busbar. In addition, the cooling system includes a gas tank in thermal contact with the thermal shield, the gas tank comprising a toroidal shape and being positioned radially inward of the thermal shield on an inner surface thereof, the gas tank containing a cooling gas configured to circulate therein so as to provide uniform cooling to the thermal shield.

[0008] These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:

[0010] FIG. 1 illustrates a perspective view of one embodiment of a wind turbine having a generator according to the present disclosure;

[0011] FIG. 2 illustrates a perspective, internal view of one embodiment of a nacelle of a wind turbine having a superconducting generator according to the present disclosure;

[0012] FIG. 3 illustrates a side view of a generator in accordance with aspects of the present invention;

[0013] FIG. 4 illustrates a simplified, schematic diagram of a superconducting generator according to conventional construction, particularly illustrating a cooling system arranged with a thermal shield of the generator;

[0014] FIG. 5 illustrates a simplified, schematic diagram of an embodiment of a cooling system for a thermal shield of a superconducting generator according to the present disclosure, particularly illustrating a toroidal gas tank of the cooling system arranged with the thermal shield of the generator;

[0015] FIG. 6 illustrates a perspective view of an embodiment of a toroidal gas tank of a cooling system for a thermal shield of a superconducting generator according to the present disclosure;

[0016] FIG. 7 illustrates a perspective view of an embodiment of a toroidal gas tank of a cooling system for a thermal shield of a superconducting generator according to the present disclosure;

[0017] FIG. 8 illustrates a perspective view of an embodiment of a securement assembly for a toroidal gas tank of a cooling system for a thermal shield of a superconducting generator according to the present disclosure;

[0018] FIG. 9 illustrates a simplified, schematic diagram of still another embodiment of a cooling system for a thermal shield of a superconducting generator according to the present disclosure, particularly illustrating a toroidal gas tank of the cooling system arranged with the thermal shield of the generator such that cooling gas circulates symmetrically in four quadrants of the gas tank;

[0019] FIG. 10 illustrates a simplified, schematic diagram of yet another embodiment of a cooling system for a thermal shield of a superconducting generator according to the present disclosure, particularly illustrating a toroidal gas tank of the cooling system arranged with the thermal shield of the generator such that cooling gas circulates in the gas tank in a single loop;

[0020] FIG. 11 illustrates a simplified, schematic diagram of another embodiment of a cooling system for a thermal shield of a superconducting generator according to the present disclosure, particularly illustrating a toroidal gas tank of the cooling system arranged with the thermal shield of the generator such that cooling gas circulates in the gas tank in a single loop;

[0021] FIG. 12 illustrates an internal, perspective view of another embodiment of a cooling system for a thermal shield of a superconducting generator according to the present disclosure, particularly illustrating a toroidal gas tank of the cooling system integrated with the thermal shield of the generator;

[0022] FIG. 13 illustrates a detailed, internal view of a toroidal gas tank of a cooling system for a thermal shield of a superconducting generator according to the present disclosure, particularly illustrating the toroidal gas tank of the cooling system integrated with the thermal shield of the generator;

[0023] FIG. 14 illustrates a partial, perspective view of an embodiment of a toroidal gas tank of a cooling system for a thermal shield of a superconducting generator according to the present disclosure;

[0024] FIG. 15 illustrates a partial, detailed view of the toroidal gas tank of FIG. 14;

[0025] FIGS. 16A-16D illustrate example cross-sectional shapes of a toroidal gas tank of a cooling system for a thermal shield of a superconducting generator according to the present disclosure;

[0026] FIG. 17 illustrates a cross-sectional view of an embodiment of a toroidal gas tank of a cooling system for a thermal shield of a superconducting generator according to the present disclosure, particularly illustrating the toroidal gas tank integrated at an edge of the thermal shield of the generator; and

[0027] FIG. 18 illustrates a cross-sectional view of another embodiment of a toroidal gas tank of a cooling system for a thermal shield of a superconducting generator according to the present disclosure, particularly illustrating the toroidal gas tank welded to an interior surface of the thermal shield. [0028] Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present invention.

DETAILED DESCRIPTION

[0029] Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. [0030] The terms “coupled,” “fixed,” “attached to,” and the like refer to both direct coupling, fixing, or attaching, as well as indirect coupling, fixing, or attaching through one or more intermediate components or features, unless otherwise specified herein.

[0031] Conventional thermal shields in superconducting generators have a large temperature difference around the circumference of the shield, which reduces the efficiency of blocking radiation heat to a cold mass the shield intends to protect. This is because cooling of the thermal shield takes place at the top of the thermal shield while thermal energy (radiative and conductive) is entering the thermal shield around the circumference.

[0032] Thus, the present disclosure is generally directed to a cooling system for a thermal shield of a generator, such as a superconducting generator, that moves heat more effectively thereby creating a more uniform temperature distribution. In particular embodiments, for example, the cooling system of the present disclosure includes a toroidally-shaped thermal shield for surrounding a field winding assembly fixedly coupled to a structural component of the superconducting generator, a cryocooler in thermal contact with an outer surface of the toroidally-shaped thermal shield via a busbar, and at least one gas tank in thermal contact with the thermal shield. Moreover, the gas tank may have a generally toroidal shape, such that circulation of the cooling gas in the gas tank reduces temperature differences around the circumference the thermal shield. Further, in an embodiment, the busbar that thermally connects the cryocooler to the thermal shield may be placed in an asymmetrical location relative to thermal shield to enhance gas circulation in the gas tank for maximizing heat transfer, thereby providing a more uniform thermal temperature distribution that reduces radiation heat transfer to the cold mass.

[0033] Referring to the drawings, FIG. 1 illustrates a perspective view of a wind turbine 10. As mentioned, the present disclosure is directed to a generator that, although not limited to such use, is particularly well-suited for use in a wind turbine 10. Although FIG. 1 depicts an “on-shore” (land-based) wind turbine 10 installation, it should be appreciated that the present invention is not limited to onshore wind turbines and is just as applicable to “off-shore” (water-based) wind turbine installations, with either fixed or floating foundations.

[0034] Referring still to FIG. 1, the wind turbine 10 includes a tower 12 extending from a support surface 14, a nacelle 16 mounted on the tower 12, and a rotor 18 coupled to the nacelle 16. The rotor 18 includes a rotatable hub 20 and at least one rotor blade 22 coupled to and extending outwardly from the hub 20. For example, in the illustrated embodiment, the rotor 18 includes three rotor blades 22. However, in an alternative embodiment, the rotor 18 may include more or less than three rotor blades 22. Each rotor blade 22 may be spaced about the hub 20 to facilitate rotating the rotor 18 to enable kinetic energy to be transferred from the wind into usable mechanical energy, and subsequently, electrical energy. For instance, the hub 20 may be rotatably coupled to an electric generator (not shown) positioned within the nacelle 16 to permit electrical energy to be produced.

[0035] Referring now to FIG. 2, a perspective, internal view of an embodiment of the nacelle 16 having a superconducting generator 23 housed therein according to the present disclosure is illustrated. Further, as shown, a support tube 41 is connected directly to the hub 20 and supports an armature winding assembly 24. Thus, the armature winding assembly 24 is considered as the rotating component of the generator 23 with a rotating first electromagnetic component configuration that rotate around a stationary field assembly 26 having a second electromagnetic component configuration, such as a superconducting field winding assembly 26.

[0036] The stationary field assembly 26 includes superconducting coils 52, which may be a group of wires formed in a racetrack shape. Thus, in certain embodiments, the superconducting coils 52 are constrained to retain the racetrack shape. Moreover, as shown, each superconducting coil 52 is supported in a recess/passage 50 in a casing 42 that may be conduction cooled by cryogenic cooling tubes filled with a cryogen (e.g., helium, hydrogen, or neon) for purposes of removing heat from the superconducting coils. As such, the casing 42 may be supported in a cryostat housing 36, also referred to herein as the vacuum vessel, which is fixed to a base tube 44.

[0037] Still referring to FIG. 2, the superconducting coils 52 may be arranged side by side in an annular array extending around the casing 42. For example, in an embodiment, thirty-six (36) coils may form an annular array of field windings that serve as the stator field winding for the generator 23. Furthermore, in an embodiment, the superconducting coils 52 may be each formed of (NbTi or other superconducting materials) wire wrapped in a helix around a racetrack form that may include cooling conduits for the cryogen. The stationary field assembly 26 includes superconducting coil magnets 54 created by passing current through the superconducting field coils 52, which are enclosed in the casing 42 and receive cryogen through cooling recesses/passages 50.

[0038] In additional embodiments, cryogen re-condensors 38, 40 may be housed in the field coil assembly 26, provided that the cryogen cooling liquid in the re- condensors 38, 40 is at least partially elevated above the superconducting field windings to provide for gravity feed of the cryogen to the windings. Alternatively, the re-condensors 38, 40 may be mounted on top of the field coil assembly.

[0039] Referring now to FIG. 3, a cross-section of an embodiment of the direct drive superconducting generator 23 with the annular rotating armature winding assembly 24 (“armature 24”) radially inward of the stationary field assembly 26 is illustrated. It should be understood that the present disclosure described herein can also function with the armature winding assembly 24 positioned radially outward of the stationary field assembly 26 as well. In particular, as shown, the armature 24 is essentially an inner annular ring configuration (FIG. 4) that rotates within the stationary field assembly 26. The armature 24 includes the conducting coils 52, e.g., coils or bars, arranged longitudinally along the length of the armature 24 and on an inside cylindrical surface of the armature 24. The conducting coils 52 may be connected at their opposite ends to one another by conductive end turns 28. The end turns 28 between the longitudinal conducting coils 52 are dependent on their number and arrangement, and the phases of electricity to be generated in the conducting coils 52. The outside cylindrical surface of the armature windings is separated by a narrow air gap, e.g., about 10-25 mm, from the inner surface of the stationary field assembly 26.

[0040] Referring generally to FIG. 3, the armature 24 includes a cylindrical yoke or body 30 (referred to as “body” herein) that supports the conducting coils 52. In particular, the conducting coils 52 are contained in slots defined between adjacent teeth that extend radially from the body 30. The body 30 and teeth may be a layered, laminated construction. The inner surface of the body 30 is fixed to a cylindrical housing 32 that rotates with the armature 24. Moreover, as shown, stationary field winding assembly 26 may be supported by a field winding support disc 34. Further, the field winding support disc 34 is attached to an end of the cryostat housing 36 containing the superconducting coils 52 (FIG. 2) of the field winding assembly 26. The housing 36 and its cooling components form a cryostat that cools the superconducting coils of the field winding.

[0041] The cryostat housing 36 insulates the superconducting coils 52 so that they may be cooled to near absolute zero temperature, e.g., to about 20 Kelvin (K), and more preferably about 10 K, and still more preferably to about 4K. To cool the windings, the cryostat housing 36 may include one or more insulated conduits 46 to receive liquid helium (He) or other similar cryogenic liquid (referred to as cryogen). A conventional two-stage re-condensor 38 mounted in an upper region of the field coil assembly, on top of the field coil assembly, or on top of the tower 12, and above the field windings to provide cryogen, e.g., liquid He, using a gravity feed. The second re-condensor 40 possibly provides a second cooling liquid, e.g., liquid nitrogen or neon, to an inner thermal shield of the cryostat housing 36 via conduit 48. [0042] Referring now to FIG. 4, various components of a schematic diagram of a simplified cooling system 102 for a superconducting generator 100 according to conventional construction are illustrated. More specifically, as shown, the superconducting generator 100 generally includes a cooling system 102 arranged with athermal shield 104 of the generator 100, a vacuum vessel 106, a cold mass 108, and a cryocooler 110. In such embodiments, for example, the cold mass 108 may be a stationary component, such as the field winding assembly 26 within which the armature winding assembly 24 rotates. It should be understood that the annulus for the armature winding assembly is shown in FIG. 3, but is omitted from FIGS. 4-9 in an effort to simplify the figures and more clearly explain the details of the present disclosure. Furthermore, as an example, the vacuum vessel 106 may be a non-rotatable component supporting a field winding assembly, such as the stationary field assembly 26. Thus, in such embodiments, the rotatable component may be oriented to rotate relative to the non-rotatable component during operation of the generator 100 as shown in FIG. 3. In such conventional configurations, the thermal shield 104 intercepts and/or blocks radiation (as indicated by arrows 114) from the vacuum vessel 106. Further, as shown, heat is removed via a thermal bus/busbar 112 to the cryocooler 110, thereby blocking most radiation heat from the cold mass 108. Moreover, as shown, the thermal busZbusbar(s) 112 of such configurations are attached to the top of the thermal shield 104 for connection to the cryocooler 110. The thermal shield 104 also intercepts heat conducted in through structural components, such as those used to hold the stationary field assembly 26 in place. [0043] Thus, for conventional cooling systems, such as those illustrated in FIG. 4, the thermal shield 104 has a temperature (T) distribution around the circumference thereof. Cooling is providing by the cryocooler 110 through the thermal bus/busbar 112 that is positioned at the top of the thermal shield 104 for high efficiency heat transfer. As such, cooler temperatures are observed near the thermal bus/busbar 112 and warmer temperatures are observed farther away from thermal bus/busbar 112. Accordingly, a large difference in temperature is observed between the top and bottom of the thermal shield 104, thereby resulting in additional radiation heat from the thermal shield 104 to the cold mass 108. This large temperature difference is undesirable as it causes a high heat load to the cold mass 108 and therefore decreases the operating margins of the superconducting field windings. As mentioned, it should be understood that the configuration of FIG. 4 is simplified relative to the field winding assembly 26 of FIG. 3 to better illustrate the operating principles of the cooling system.

[0044] Thus, the present disclosure is directed to an improved cooling system 200 that addresses the aforementioned issues. In particular, the cooling system 200 of the present disclosure reduces the large temperature difference in the thermal shield 104 by reducing the temperature at the hottest spot on the thermal shield 104. For example, referring now to FIGS. 5-11, various components of embodiments of the improved cooling system 200 for the superconducting generator 100 according to the present disclosure are illustrated.

[0045] In particular, as shown in FIGS. 5 and 9-11, the cooling system 200 includes a thermal shield 204 configured to surround a stationary component 208, such as the field winding assembly 26. As mentioned, the thermal shield 204 is arranged between a cold mass, which may be the stationary component 208, such as the field winding assembly 26, and the vacuum vessel 106, which may be a non-rotatable component supporting a field winding assembly, such as the stationary field assembly 26. Thus, in such embodiments, the rotatable component may be oriented to rotate relative to the non-rotatable component during operation of the generator. It should be further understood that the vacuum vessel 106 may also be separate and apart from the stationary field assembly 26 except for the structural components that are used to support the thermal shield and the cold mass within the vacuum vessel 106.

[0046] Still referring to FIGS. 5 and 9-11, the cooling system 200 also includes a cryocooler 210 in thermal contact with the thermal shield 204. In particular, as shown in FIGS. 5 and 9-11, the cryocooler 210 is in thermal contact with the thermal shield 204 via a busbar 212. Further, in an embodiment, as shown in FIGS. 5-7 and 9-11, the cooling system 200 includes a gas tank 206 adjacent to and in thermal contact with the thermal shield 204. Thus, in such embodiments, the gas tank 206 contains a cooling gas 213 configured to circulate therein so as to provide uniform cooling to the thermal shield 204. For example, in an embodiment, the cooling gas 213 may be helium gas at a certain pressure, such as about one (1) bar pressure, though pressures higher and lower than 1 bar can also be utilized.

[0047] More specifically, as shown in FIGS. 6 and 7, in an embodiment, the gas tank 206 may have a generally toroidal shape 211, i.e., similar to a donut shape. As described herein, a toroidal shape may include any three-dimensional shape having a surface of revolution with a hole in the middle. Thus, the toroidal shape may have a circular or oval cross-section (as shown in FIG. 6) as well as a square or rectangular cross-section (as shown in FIG. 7). In addition, the gas tank 206 may be a single gas tank or may be segmented to include a plurality of gas tanks 206. It will be appreciated that segmentation into multiple tanks is possible without deviating from the spirit of the invention if the multiple gas tanks 206 are each toroidal and connected to the thermal shield.

[0048] Moreover, in an embodiment, the gas tank 206 may be constructed of any suitable material, such as steel, aluminum, and/or another other suitable metal or metal alloy. Further, as shown in the illustrated embodiment, the gas tank 206 may be positioned radially inward of the thermal shield 204, e.g., against an inner surface 214 of the thermal shield 204. In alternative embodiments, the gas tank 206 may be positioned radially outward of the thermal shield 204, e.g., against an outer surface of the thermal shield 204. Accordingly, as shown, in an embodiment, the gas tank 206 may extend around an entire internal circumference of the thermal shield 204. It will be appreciated that physical contact between the gas tank 206 and the thermal shield 204 couple the two components thermally, thereby allowing the gas tank 206 to participate in determining the temperature distribution around the circumference of the thermal shield 204.

[0049] In additional embodiments, as shown in FIG. 8, for example, the gas tank 206 may be secured to the thermal shield 204 using any suitable means, such as via securement assembly 226. In particular, as shown, the securement assembly 226 may include one or more brackets 228 that can be secured around and/or to the gas tank 206 and/or the thermal shield 204. Such brackets, 228, in an embodiment, may be metal brackets, such as aluminum brackets, or any other suitable material in addition to aluminum.

[0050] Referring particularly to FIGS. 5 and 9, in an embodiment, the busbar 212 may be positioned at a substantially 12 o’clock position of the thermal shield 204 such that the cooling gas 213 circulates symmetrically in four quadrants (e.g., labeled as I, II, III, and IV) of the gas tank 206, as indicated by arrows 216. Thus, in such embodiments, the symmetrical gas circulation in all four quadrants reduces a temperature difference between upper and lower locations 220, 222 of the thermal shield 204.

[0051] In alternative embodiments, as shown in FIG. 10, the busbar 212 may be offset from a 12 o’clock position of the thermal shield 204 such that the cooling gas 213 circulates in the gas tank 206 in a single loop 218. In such embodiments, as shown, by offsetting the busbar 212, the gas circulation pattern is broken, thereby forcing gas circulation throughout the entire gas tank 206. Therefore, in an embodiment, the one loop circulation increases the heat transfer within the gas tank 206 and reduces the temperature difference between upper and lower locations 220, 222, as well as the overall temperature at hot spot 224 on the thermal shield 204 relative to the symmetrical configuration of FIG. 9.

[0052] In particular, as shown, the busbar 212 may be positioned in a first quadrant (e.g., labeled as I in FIG. 10) of the thermal shield 204 such that the cooling gas 213 circulates in the gas tank 206 in a clockwise direction that is driven by gravity. Thus, as shown, the first quadrant I generally refers to the quadrant between the 12 o’clock position and a 3 o’clock position of the thermal shield 204.

Accordingly, as an example, the busbar 212 is positioned from about a one (1) o’clock position to about two (2) o’clock position.

[0053] Alternatively, in an embodiment, as shown in FIG. 11, the busbar 212 may be positioned in a fourth quadrant (e.g., labeled as IV in FIG. 11) of the thermal shield 204 such that the cooling gas 213 circulates in the gas tank 206 in the clockwise direction that is driven by gravity. Thus, as shown, the fourth quadrant generally refers to the quadrant between the 9 o’clock position and a 12 o’clock position of the thermal shield 204. Accordingly, as an example, the busbar 212 is positioned from about a ten (10) o’clock position to about an eleven (11) o’clock position.

[0054] Referring now to FIGS. 12-18, further embodiments of the gas tank 206 described herein are further illustrated. Rather than being secured to the thermal shield 204 via the securement assembly 226, the gas tank 206 of FIGS. 12-18 is integrated with the thermal shield 204. In particular, as shown in FIGS. 12 and 13, the gas tank 206 is integrally formed with (or welded to) the thermal shield 204, such as at one or more edges of the thermal shield 204.

[0055] The integrated gas tank 206 may have a variety of configurations or shapes. For example, as shown in FIGS. 12-16A, the gas tank 206 may have a circular opening 228 defining the tank portion to receive the cooling gas 213 with tangential flanges 230 configured to align with walls 232 (FIG. 13) of the thermal shield 204. In further embodiments, as shown in FIG. 16B, the gas tank 206 may include the circular opening 228 with opposing thickened edges 234 for connecting with the walls (FIG. 13) of the thermal shield 204. Similarly, as shown in FIG. 16C, the gas tank 206 may include the circular opening 228 with opposing thickened edges 234 for connecting with the walls (FIG. 13) of the thermal shield 204, but also include a cutout 236 for reducing overall material of the gas tank 206.

[0056] In still further embodiments, as shown in FIG. 16D, the gas tank 206 may include the circular opening 228 embedded in a square or rectangular wall 238 for connecting with the walls (FIG. 13) of the thermal shield 204. In such embodiments, as shown in FIGS. 17 and 18, the wall 238 of the gas tank 206 can be secured at an edge of the thermal shield 204 (FIG. 17) or to an inner surface 242 of the thermal shield 204 (FIG. 18). In each of FIGS. 17 and 18, as an example, the wall 238 of the gas tank 206 can be secured to the thermal shield 204 using e.g., welding, as indicated via weld joints 244.

[0057] Moreover, as shown in FIG. 14, the gas tank 206 may be a monolithic tank formed of a single, curved part, e.g., via extrusion. In contrast, as shown in FIG. 15, the gas tank 206 may be formed of multiple segments 240 arranged circumferentially together. In such embodiments, as shown the segments 240 may be linear rather than curved.

[0058] Various advantages can be recognized using the gas tanks described herein, such as improved thermal contact and mechanical stability.

[0059] Furthermore, the skilled artisan will recognize the interchangeability of various features from different embodiments. Similarly, the various method steps and features described, as well as other known equivalents for each such methods and feature, can be mixed and matched by one of ordinary skill in this art to construct additional systems and techniques in accordance with principles of this disclosure. Of course, it is to be understood that not necessarily all such objects or advantages described above may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the systems and techniques described herein may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

[0060] Further aspects of the invention are provided by the subject matter of the following clauses:

Clause 1. A generator, comprising: a non-rotatable component supporting a field winding assembly; a rotatable component oriented to rotate relative to the non-rotatable component during operation of the generator; an armature winding assembly fixedly coupled to the rotatable component so as to rotate therewith during the operation of the generator, the armature winding assembly comprising a plurality of conducting coils; a thermal shield surrounding the field winding assembly fixedly coupled to the stationary component; a cryocooler in thermal contact with the thermal shield; and a gas tank adjacent to and in thermal contact with the thermal shield, the gas tank containing a cooling gas configured to circulate therein so as to provide uniform cooling to the thermal shield.

Clause 2. The generator of clause 1, wherein the gas tank has a toroidal shape.

Clause 3. The generator of any of the preceding clauses, wherein the gas tank is positioned radially inward of the thermal shield.

Clause 4. The generator of any of the preceding clauses, wherein the gas tank extends around an entire internal circumference of the thermal shield.

Clause 5. The generator of any of the preceding clauses, wherein the stationary component comprises a vacuum vessel.

Clause 6. The generator of any of the preceding clauses, wherein the cooling gas comprises cryogen gas.

Clause 7. The generator of any of the preceding clauses, wherein the cryocooler is in thermal contact with the thermal shield via a busbar.

Clause 8. The generator of clause 7, wherein the busbar is positioned at a substantially 12 o’clock position of the thermal shield such that the cooling gas circulates symmetrically in four quadrants of the gas tank.

Clause 9. The generator of clauses 7-8, wherein the busbar is offset from a 12 o’clock position of the thermal shield such that the cooling gas circulates in the gas tank in a single loop.

Clause 10. The generator of clause 9, wherein the busbar is positioned in a first quadrant of the thermal shield such that the cooling gas circulates in the gas tank in a clockwise direction that is driven by gravity, the first quadrant being between the 12 o’clock position and a 3 o’clock position of the thermal shield.

Clause 11. The generator of clauses 9-10, wherein the busbar is positioned in a fourth quadrant of the thermal shield such that the cooling gas circulates in the gas tank in a counterclockwise direction that is driven by gravity, the fourth quadrant being between the 12 o’clock position and a 9 o’clock position of the thermal shield.

Clause 12. The generator of any of the preceding clauses, wherein the generator is a superconducting generator and the plurality of conducting coils are superconducting coils.

Clause 13. A cooling system for a superconducting generator, the cooling system comprising: a thermal shield for surrounding a field winding assembly fixedly coupled to a stationary component of the superconducting generator, the stationary component oriented relative to a rotatable component during operation of the superconducting generator; a cryocooler in thermal contact with an outer surface of the thermal shield via a busbar; and a gas tank in thermal contact with the thermal shield, the gas tank comprising a toroidal shape and being positioned radially inward of the thermal shield on an inner surface thereof, the gas tank containing a cooling gas configured to circulate therein so as to provide uniform cooling to the thermal shield.

Clause 14. The cooling system of clause 13, wherein the gas tank extends around an entire internal circumference of the thermal shield.

Clause 15. The cooling system of clauses 13-14, wherein the stationary component comprises a vacuum vessel. Clause 16. The cooling system of clauses 13-15, wherein the cooling gas comprises cryogen gas.

Clause 17. The cooling system of clauses 13-16, wherein the busbar is positioned at a substantially 12 o’clock position of the thermal shield such that the cooling gas circulates symmetrically in four quadrants of the gas tank.

Clause 18. The cooling system of clauses 13-17, wherein the busbar is offset from a 12 o’clock position of the thermal shield such that the cooling gas circulates in the gas tank in a single loop.

Clause 19. The cooling system of clause 18, wherein the busbar is positioned in a first quadrant of the thermal shield such that the cooling gas circulates in the gas tank in a clockwise direction that is driven by gravity, the first quadrant being between the 12 o’clock position and a 3 o’clock position of the thermal shield.

Clause 20. The cooling system of clauses 18-19, wherein the busbar is positioned in a fourth quadrant of the thermal shield such that the cooling gas circulates in the gas tank in a counterclockwise direction that is driven by gravity, the fourth quadrant being between the 12 o’clock position and a 9 o’clock position of the thermal shield.

[0061] This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.