Superconducting generator with conduction cooling of superconducting field winding modules

Abstract

A superconducting generator includes an armature assembly and a segmented field winding assembly having a plurality of interconnected field winding modules. Each field winding module includes a vacuum vessel and a plurality of superconducting field coils carried by a coil support structure within the vacuum vessel. The superconducting field coils are in direct thermal contact with a thermal bus network. At least one cryocooler is in direct thermal contact with the thermal bus network. The superconducting field coils are maintained at a cryogenic temperature via direct thermal conduction cooling by the cryocoolers and the thermal bus bar network.

Description

SUPERCONDUCTING GENERATOR WITH CONDUCTION COOLING OF SUPERCONDUCTING FIELD WINDING MODULESSTATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0001] This invention was made with U.S. Government support under Contract No. DE-EE0008787 awarded by the U.S. Department of Energy (DOE). The U.S. Government has certain rights in the invention.FIELD

[0002] The present disclosure relates generally to superconducting generators, and more particularly to a modular construction of the field winding assembly of a superconducting generator configured as a wind turbine generator.BACKGROUND

[0003] Superconducting generators are accepted as a viable means for power generation in wind turbines, particularly offshore wind turbine installations, because their high torque densities provide for a compact and lightweight generator design without loss of power production, which is important in terms of transportation, installation, and maintenance considerations at remote offshore locations. However, material cost and manufacturability of superconducting generators present obstacles to the widespread commercial use of these generators.

[0004] Consequent pole construction of the field winding assemblies has been considered in the industry to reduce the costs of superconducting generators. This structure makes use of physical poles and virtual poles, w herein the virtual poles are a consequence of magnet fields naturally seeking to close on themselves. As such, a consequent pole design requires one-half of the field coils of a conventional field winding assembly, which reduces material cost. In addition, consequent poles also create space for packaging the mechanical structure necessary to support the cryogenic system needed to cool the superconducting field winding assemblies. For a more detailed discussion of consequent pole constructions for a wind turbine superconducting generator, reference is made to the scholarly article: Song, X.. Mijatovic, N., Kellers, J., Btihrer, C., Rebsdorf, A. V., Hansen, J., Christensen, M.,Krause. J., Piltz, H., Wiezoreck, J., & Holboll, J. (2017). A Pole Pair Segment of a 2- MW High-Temperature Superconducting Wind Turbine Generator. IEEE Transactions on Applied Superconductivity. 27(4), [5201205], https: / / doi.org / 10.1109 / TASC.2017.2656778

[0005] As the advantages of consequent pole construction advance the commercial viability of superconducting generators, the industry continues to seek new and improved consequent pole constructions to further reduce the costs and increase the efficiency of such generators.

[0006] Within a superconducting machine, it is necessary to keep the superconductors at a sufficiently low temperature so that they retain their superconducting properties, specifically that of zero electrical resistance. The temperature at which superconductivity is achieved is a function of the conductor composition, the magnetic field seen by the conductor, and the current density within the conductor. For maximum benefit, it is preferable to operate the superconductors at a temperature well below the critical temperature where the conductor becomes superconducting with zero magnetic field and zero current.

[0007] Cryogenic equipment such as cryocoolers are used to extract heat from the superconductors and the supporting structure (collectively referred to as the “cold mass'’). The cooling of the cold mass is generally accomplished by liquids or gases known as cryogens. Different cryogens support different temperatures. For example, Helium is a cryogen used for low temperature superconductors and condenses at 4.2 K at atmospheric pressure.

[0008] Conventional cry ogenic systems for superconducting machines generally utilize plumbing, gas tanks, and liquid tanks. These systems, however, struggle to support the large physical size of generators for offshore wind turbines. In addition, these conventional cryogenic systems would prevent a modular approach to field winding assemblies that would be beneficial in bringing down assembly complexity, cost, and the component spacing necessary' to achieve acceptable electromagnetic performance of the generator.BRIEF DESCRIPTION

[0009] 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.

[0010] The present disclosure recognizes that a direct benefit of the consequent pole approach to field winding assemblies is the ability to modularize the field. Utilizing the tangential spaces between the physical poles (where the virtual poles are located), the present disclosure proposes to segment the field winding assembly into modules. Each module contains a number of physical poles and an equal number of virtual poles. The modules allow for generator assembly through integration of modules, rather than building a nested structure according to the temperature zones of the field winding assembly, as in the conventional process. There are distinct disadvantages with a nested structure design, including the requirement for substantial space and time on the manufacturing floor for a given throughput of assembled generators.

[0011] A modular field winding assembly in accordance with aspects of the present disclosure provides significant benefits. Each module is substantially more compact than the complete field, which simplifies supply chain and logistics considerations. Each module can be fully tested before it is assembled into a generator. The cryogenic cold mass within each module can be pre-cooled to near operating temperature before each module is assembled into the generator, saving valuable time in preparing the field to be operational for factory acceptance testing. Further, a modular field creates the possibility to replace a module in situ should an operational module fail in the deployed wind turbine.

[0012] The present invention also proposes an assembly for direct conduction cooling of the cold mass within each of the individual modules, which enables the construction, assembly, and practical use of the modular field winding assembly. The present disclosure proposes direct dedicated thermal conduction for removing heat from the cold mass of the individual module and eliminates or simplifies the plumbing, gas tanks, and liquid tanks typically associated with conventional cryogenic systems used in superconducting machines. This approach supports modularization of the superconducting field winding into segments that are moreeasily manufactured and assembled. This approach also provides the required effective thermal conduction path between the superconducting field coils and the cryogenic equipment responsible for removing heat, as well as creates a path of high thermal resistance between the structure holding the cold mass and the cryogenic equipment.

[0013] In accordance with aspects of the present disclosure, a superconducting generator includes an armature assembly, which may be of conventional construction, and a segmented field winding assembly formed from a plurality of interconnected field winding modules. Each field winding module includes a vacuum vessel and a plurality' of superconducting field coils carried by a coil support structure within the vacuum vessel. Each of the superconducting field coils is in direct thermal contact with a thermal bus network, and one or more cryocoolers are in direct thermal contact with the thermal bus network. With this configuration, the superconducting field coils are maintained at a cryogenic temperature via direct thermal conduction cooling by the thermal bus bar network and the cryocoolers.

[0014] In a particular embodiment, each field winding module has a consequent pole configuration with a plurality of virtual poles interspaced betw een the physical poles defined by the superconducting field coils.

[0015] The cryocoolers may be mounted externally on the vacuum vessel, for example on a side wall of the vacuum vessel, and in direct thermal contact with the thermal bus bar network through a hermetic seal in the vacuum vessel wall. This embodiment may include a compressor associated with each cryocooler, wherein the compressors are also mounted externally on the vacuum vessel.

[0016] In an embodiment, each field winding modular may include a plurality of separately controlled temperature zones, wherein each temperature zone has at least one cryocooler associated therewith.

[0017] The thermal bus netw ork may be variously configured. For example, this network may include a thermally conductive ring (e g., a copper ring) surrounding each of the superconducting field coils, wherein each of the rings is in direct thermal contact with a header (e g., a copper bar) and the cryocoolers are in direct thermal contact with the header through the vacuum vessel. In this embodiment, a thermal shield within the vacuum vessel may surround the coil support structure, the thermalbus bar network, and the superconducting field coils. Each of the cryocoolers may include a first cooling stage in direct thermal contact with the thermal shield and a second cooling stage in direct thermal contact with the thermal bus network through the vacuum vessel.

[0018] The coil support structure may be variously configured. For example, the coil support structure may define a frame-like structure having arc-shaped side members and spanner members extending between the side members, wherein the superconducting field coils are arranged in alternate spaces defined by the spanner members. The virtual poles of the consequent pole configuration are defined in alternate open spaces defined by the spanner members between the physical field coils. In this embodiment, the spanner members may include a ledge (e.g., a rightangle member) extending from a main body, wherein the superconducting field coil and thermally conductive ring are mounted onto the ledge.

[0019] In a particular embodiment, the thermal bus network includes a frame that mimics and is attached to a face of the frame-like coil support structure, wherein the thermally conductive rings around the field coils are in direct thermal contact with the attached frame of the thermal bus network.

[0020] In still another embodiment, one or more sealed cryogen tanks is carried by the coil support structure within the vacuum vessel, the cry ogen tanks containing a liquid cryogen (e.g., helium) and in direct thermal contact with the coil support structure to provide a ride-through cooling capacity in a quench event. The cryogen tanks may be mounted on copper conductors that are, in turn, mounted to the coil support structure.

[0021] The present invention also encompasses a field winding module for use in a superconducting generator, wherein a plurality- of these field winding modules are interconnectable end-to-end in a circumferential direction to define a complete segmented field winding assembly for a superconducting generator. The individual field winding modules includes a vacuum vessel and a plurality of superconducting field coils carried by a coil support structure within the vacuum vessel. A thermal bus network is provided within the vacuum vessel, wherein each of the superconducting field coils is in direct thermal contact with the thermal bus network. One or more cryocoolers are in direct thermal contact with the thermal bus network. With thisconfiguration, the superconducting field coils are maintained at a cryogenic temperature via direct thermal conduction cooling by the cryocoolers and the thermal bus bar network.

[0022] The aspects of the field winding modules of the field winding assembly discussed above are pertinent to the individual field winding modules.

[0023] 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

[0024] 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:

[0025] Fig. 1 depicts a conventional wind turbine;

[0026] Fig. 2 depicts a conventional superconducting machine;

[0027] Fig. 3 is a cross-sectional view' of a conventional superconducting generator;

[0028] Fig. 4 is a cross-sectional view of a conventional field winding assembly of a superconducting generator;

[0029] Fig. 5 is a partial cross-sectional view of another conventional superconducting generator;

[0030] Fig. 6 is a partial cross-sectional view of a wind turbine superconducting generator in accordance with aspects of the present disclosure;

[0031] Fig. 7 is a perspective view of an armature and modular field winding assembly of a superconducting generator;

[0032] Fig. 8 is a perspective view of the field w inding modules and field winding assembly of the superconducting generator of Fig. 7;

[0033] Fig. 9 is partial cross-section view of a field winding module partially depicting a radial connector;

[0034] Fig. 10 is a perspective view of an embodiment of a connector;

[0035] Fig. 11 is a perspective view of an open field winding module;

[0036] Fig. 12 is a perspective view of the cold mass structure of the field winding module of Fig. 11;

[0037] Fig. 13 is a partial cross-sectional view of a field winding module;

[0038] Fig. 14 is a perspective view of an embodiment of a thermal shield;

[0039] Fig. 15 is a perspective view of an alternate embodiment of a thermal shield;

[0040] Fig. 16 is a perspective view of a thermal bus network and associated field coils;

[0041] Fig. 17 is an underside perspective view of the thermal bus netw ork and field coils of Fig. 16;

[0042] Fig. 18 is a perspective view of the cold mass structure of an alternate embodiment;

[0043] Fig. 19 is a cross-sectional view of the cold mass structure of Fig. 18 taken along the lines indicated;

[0044] Fig. 20 is a perspective view of still another embodiment of the cold mass structure for a field winding module; and

[0045] Fig. 21 is a perspective view of an embodiment of the cold mass structure with a quench ride- thro ugh capability.

[0046] Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements in the invention.DETAILED DESCRIPTION

[0047] 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.

[0048] 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.

[0049] Approximating language, as used herein throughout the specification and claims, is applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about”, “approximately”, and “substantially”, are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value, or the precision of the methods or machines for constructing or manufacturing the components and / or systems. For example, the approximating language may refer to being within a 10 percent margin.

[0050] While examples herein refer to the use of a superconducting generator for wind turbine applications, it should be appreciated that this is for illustrative purposes only. The present invention is not limited to wind turbines, or to a generator. The novel concepts disclosed herein can be employed in any type of superconducting machine, such as MRI machines.

[0051] Referring now to Fig. 1, a diagram of an exemplary wind turbine 100 is presented. The wind turbine 100 is configured to generate electrical power using wind energy and may be coupled to a power grid, for receiving electrical power therefrom to drive operation of wind turbine 100 and / or its associated components and / or for supplying electrical power generated by the wind turbine 100 thereto.

[0052] The ind turbine 100 includes a body 102 (“nacelle”) mounted atop a tower 108 and a rotor 104 coupled to the body 102. The rotor 104 is configured to rotate with respect to the body 102 about an axis of rotation 106.

[0053] The rotor 104 includes a hub 110 and a plurality of blades 112 extending radially outwardly from the hub 110 for converting wind energy into rotational energy. The rotor blades 112 may have any conventional shape or configuration.

[0054] The nacelle 102 may house a superconducting generator 114 and a shaft 116 that couples the superconducting generator 114 to the rotor 104, whereby rotations of the rotor 104 due to the wind energy' in turn cause a rotary' element (e.g.,an armature) of the superconducting generator 114 to rotate via the shaft 116. In some embodiments, the shaft 116 may also include a gear box (not shown) that increases the operating speed of the superconducting generator 114 and reduces the torque requirement for a given power level. The presence or absence of the gearbox is immaterial to the embodiments of the superconducting generator 114 described in the present specification.

[0055] The superconducting generator 114 generates electrical power based on the rotations of the armature relative to the stationary field. The superconducting generator 114 may be configured to produce increased magnitudes of electrical current in comparison to traditional generators. The superconducting generator 114 may be implemented in the form of a synchronous generator. Embodiments of the superconducting generator 114 incorporating aspects of the present disclosure will be described in greater detail below.

[0056] Fig. 2 is a schematic diagram of a superconducting machine 120 in general that may incorporate aspects of the present disclosure. As mentioned, the superconducting machine 120 may be used in any application other than wind turbines. By way of a non-limiting example, the superconducting machine 120 depicted in Fig. 2 may be implemented in superconducting gearbox, flywheel for energy storage, etc. Moreover, the electric machine 120 of Fig. 2 may also be a superconducting motor.

[0057] As depicted in Fig. 2, the superconducting machine 120 includes a stationary' field 122 and an armature 124 disposed in a housing 126. The armature 204 includes an armature winding, that may be a non-superconducting winding. By way of example, when the superconducting machine 120 is deployed as the superconducting generator 114 in the wind turbine 100 of Fig. 1, the armature 124 may be coupled to the rotor 104 of the wind turbine 100 via the shaft 116 or via both the shaft 116 and a gear box so as to be rotationally driven by the rotor. Due to the rotations of the armature 124, the superconducting machine 120 may generate electrical power by virtue of the voltage induced in armature windings as they move past the magnetic field established by the superconducting field winding 128.

[0058] The stationary field 122 is disposed concentric to and radially outward from the armature 124. The stationary field 122 is maintained at a temperature that isadequate for keeping the stationary field 122 in a superconducting state, generally much lower than the temperature of the armature 124. Typically, to enable the superconducting property, the stationary field 122 is maintained within a cryogenic range of about 4 degrees Kelvin if the superconducting field winding 128 is composed of low temperature superconducting material, which may include an alloy of niobium and tin, or an alloy of niobium and titanium.

[0059] A "magnetic gap’?is defined as the mean radial distance between the superconducting field winding 128 in the stationary field 122 and the armature winding disposed in the armature 124.

[0060] Fig. 3 is a schematic diagram showing in cross-section a conventional superconducting generator 22 having a stationary super-conducting field winding assembly 26 and a rotating armature 24 formed as an outer annular ring around the field winding assembly 26. The armature 24 is formed conventionally and may comprise conductive windings 27, e.g., coils or bars, arranged longitudinally along the length of the armature and on an inside cylindrical surface of the armature and connected at their opposite ends to one another by conductive end turns 28. The inside cylindrical surface of the armature windings is separated by a narrow magnetic air gap, e.g., about 10-25 mm, from the outer surface of the stationary’ field winding assembly 26.

[0061] The armature 24 includes a cylindrical yoke 30 that supports the coils and bars 27. The outer surface of the yoke 30 is fixed to a cylindrical housing 32 that rotates with the armature 24 and is fitted to a circular disc 34 that supports the housing and armature 24. The disc 34 has a circular aperture at its center that is mounted to an annular bracket 36 to which is attached the annular base 38 of the hub 20 (120 in Fig. 1) of the wind turbine. Thin and light weight gussets 52 extend from circular disc 34 to a support tube 40. The gussets structurally reinforce the disc 34.

[0062] The bracket 36 is mounted on an end of the rotating cylindrical support tube 40 that is radially inward of the armature winding. A reinforcing ring 37 is fixed to the inner comer between the bracket 36 and support tube 40. On an outside surface of the support tube 40, a slip ring assembly 41 is provided with contacts for each of the phases of AC power produced by the generator and a ground connection. The slip ring is electrically coupled to the w indings of the rotating armature 24 and rotateswith the support tube 40. A stationary connection, e.g. carbon brushes (not shown), conducts the electricity from the slip ring and armature to wire conductors that extend down the tower 12 and are coupled to a power utility grid, factory or other electrical power load.

[0063] A pair of annular bearings 42 arranged towards opposite ends of the support tube 40 rotatably support the support tube 40 on a stationary base tube 44 attached to a mount 47 that is supported by the floor of the nacelle. A ring bracket 46 may attach mount 47 to a bracket 45 for the base tube. Bolts secure the brackets 45, 46 together.

[0064] A disc brake grasps an annular lip 50 on an end of the housing 32. The brake can slow or stop the rotation of the blades, if the wind becomes excessive and the blades rotate too fast.

[0065] The base tube 44 supports a field winding support disc 54 on which is mounted the stationary field winding assembly 26. The assembly of the base tube 44 and support disc is an exemplary non-rotating support for the field winding assembly 26. The disc 54 may have cut-outs or holes 55 to reduce weight and is attached to an end of a cryostat housing 56 containing the superconducting coils of the field winding 26.

[0066] Torque is applied by the hub 20 to turn the armature 24 around the field winding assembly 26.

[0067] The cryostat 56 and its cooling components form a vessel (“vacuum vessel”) that cools the superconducting coils of the field winding. The vessel for the cryostat 56 may be annular and rectangular in cross section. The dimensions of the cryostat housing 56 and other components of the generator and wind turbine are a matter of design choice and may vary depending on the design of the wind turbine.

[0068] As generally appreciated in the field, a “cryostat” is an annular vacuum vessel that encloses and cools the superconducting field winding to near absolute zero, e.g., to 10 Kelvin (K) and preferably to 4K, depending on the boiling point of the cryogen used in the system. A liquid cooled cryostat uses liquid cryogens, such as nitrogen or helium, circulated in a closed refrigeration loop to lower the temperature of a sample. These cryostats either hold the liquid within the unit (bath cryostats) orthe liquid is fed through the cryostat from an external transport vessel (flow cryostats).

[0069] Other known cryostats used in superconducting machines are conductively cooled by a cryocooler (such as a conventional Gifford-McMahon (GM) or pulse tube (PT) cryocooler) whose housing is hermetically connected to the vacuum vessel. In one configuration, the cry ocooler has a first stage that extends from the housing into the vacuum vessel to be in thermal contact with the thermal shield of the field winding, and a second stage that extends from the first stage to be in thermal contact with the superconducting coil or cold mass (which normally operates at about 4 Kelvin). Typical cryogenic cooling systems that use a GM type cryocooler, e g. a Cryomech® or Sumitomo® (SHI) cold head model RDK for MRIs, run with one or more cryocoolers installed to provide the required cooling capacity.

[0070] The cryostat 56 depicted in Fig. 3 is an example of a closed-loop, external, forced cooling system to cool the filed windings assembly 26. The vacuum vessel includes insulated conduits 58 to receive a liquid cry ogen (e.g., helium (He) or other similar cryogenic liquid) from a source external to the cryostat 56. In a wind turbine, for example, a conventional tw o-stage re-condenser 60 may7be mounted in an upper region of the nacelle, on top of the nacelle, or on top of the tow er, and above the field windings, and provides the cryogen using a gravity' feed. The cryogen flows around the superconducting coils of the field windings and cools the coils to achieve a superconducting condition. The coils are cooled, e.g., to about 4 K, as the He at least partially vaporizes. The He vapor flow s through one of the conduits 58 to the recondenser 60, where the He is cooled, liquified and returned via conduit 58 to the coils. The power leads for the superconducting coils also pass through the housing 56 with the insulated conduits 58 for the helium.

[0071] A second re-condenser 64 may7provide a second cooling liquid, e.g., liquid nitrogen or neon, to an inner thermal shield 70 of the housing 56 for the field winding. The second cooling liquid cools the thermal shield 70 for the superconducting magnets to about 30K to 80K. Cooling the thermal shield assists in cooling the superconducting winding by reducing the thermal radiation heat adsorbed by the cold mass. The second re-condenser 64 receives the vaporized liquid nitrogen or neon from the thermal shield 70, liquefies the nitrogen or neon, and provides liquid nitrogen orneon to the thermal shield via insulated conduits 66. The second re-condenser provides the liquid neon or nitrogen under a gravity feed and is mounted on the tower higher than the housing 56.

[0072] Fig. 4 is a schematic diagram showing the cryostat housing 56 for the superconducting coils 68 in cross-section. The interior of the housing is evacuated, which forms an insulating vacuum around the thermal shield 70. A first torque tube 72 suspends the thermal shield 70 in the evacuated interior of the cryostat housing 56. The torque tube 72 is mounted to an annular flange 74 inside the housing. The flange elevates the tube from the inside wall of the housing 56. Another annular flange 76, at the opposite end of the torque tube 72, elevates the thermal shield 70 from the tube and centers the thermal shield inside the housing 56. The torque tube 72 also transmits torque from the thermal shield 70 to the housing 56, and provides thermal insulation to the low temperature thermal shield from the ambient temperature housing 56.

[0073] A second torque tube 80, is supported on one end by a flange 76 on an inner wall of the thermal shield 70. The flange 76 may extend into the interior of the chamber 70 or may comprise two flanges (one inside the thermal shield and the other outside the thermal shield). The second torque tube 80 thermally insulates and suspends the annular casing 71 from the thermal shield. The second torque tube 80 transmits torque from the coils to the first torque tube 72. Both the first and second torque tubes may be formed of titanium alloys. The torque tubes arranged in opposite directions thermally and mechanically isolate the windings and their casings from ambient conditions.

[0074] Fig. 5 depicts an alternative superconducting generator 300 that includes a stationary field 302 with a superconducting field winding 308 and an armature 304 with an armature winding 320. In this embodiment, however, the stationary field 302 is disposed concentric to and radially outward from the armature 304 and includes the cryostat vacuum vessel 306 and the superconducting field winding 308. The cryostat system includes one or more cryogen tanks 310 and conduits 312, and a thermal shield 316 also enclosed within the vessel 306. A plurality of cryocoolers 314 are disposed partially within the vessel 306. Torque transfer tubes 318 are also within the vacuum vessel 306 and configured to support a reaction torque caused due to aninteraction between a magnetic fields produced by the armature and the field windings.

[0075] The thermal shield 316 is disposed inside the vacuum vessel 306 and encloses the superconducting field winding 308, thus aiding in maintaining the temperature of the superconducting field winding 308 at the cry ogenic temperatures.

[0076] The reference numerals 322 and 324 respectively represent an inner wall and an outer wall of the vacuum vessel 306. The stationary field 302 and the armature 304 are disposed such that the inner wall 322 of the vacuum vessel 306 is positioned radially opposite to an outer surface 326 of the armature 304.

[0077] The cryocoolers 314 have a first cooling stage in thermal contact with the stationary’ superconducting field winding assembly 308 and / or thermal shield via a thermal connector or braid. The cryocoolers 314 include a second stage in fluid communication with the cryogenic fluid reservoir 310, which stores a cooling fluid, such as any ty pe of gaseous or condensed cooling fluids, for example, liquid helium. Flexible conduits (e.g.. high-pressure bearing braided flexible tubes) are used for thermal connection between the second-stage of the cryocoolers 314 and the cryogenic fluid reservoir.

[0078] The conduits 312 function as helium gas tanks that are thermally attached with the thermal shield. Circumferentially arranged cooling tubes (not shown) are attached on the outer surface of coil support structure (part of the cold mass and connected to the liquid tank 310. Liquid helium inside of the cooling tubes will cool and keep the superconducting field coils at about 4 K.

[0079] Fig. 6 depicts an embodiment of a superconducting machine 400 in accordance with aspects of the present invention. The superconducting machine 400 is shown and described herein as a superconducting generator for illustrative purposes only.

[0080] The superconducting generator 400 includes a segmented or modular field winding assembly 406 and an armature assembly 404. Similar to the embodiment of Fig. 5 above, the field winding assembly 406 is stationary and disposed concentric to and radially outward from the armature assembly 404, which is connected to the rotating hub 403. The field winding assembly 404 is connected to the stationary support tube 402 via frame members (discussed in greater detail below).

[0081] It should be appreciated that, in an alternative embodiment of the superconducting generator 400, the field winding assembly 404 may be connected to the rotating hub 403 and rotationally driven relative to the stationary armature assembly 404 that is connected to the stationary support tube 403, similar to the prior art embodiment depicted in Fig. 3.

[0082] Referring to Fig. 7, the segmented field winding assembly 406 includes a plurality of interconnected field winding modules 408 that are connected together in an end-to-end manner to form the ring-shaped field winding assembly 406. Each module 408 defines a self-contained vacuum vessel 416 having a radially outer wall 418, a radially inner wall 424, circumferentially extending arc-shaped sides 422, and end walls 420. In the depicted embodiment, each module 408 has a rectangular arcshaped profile.

[0083] Referring to Figs. 6 through 8, the field winding modules 408 are connected to each other along their adjacent end walls 420 using conventional means, such as mechanical connectors (e.g., bolts, interlocking structures, etc.). The assembly 400 also includes a continuous frame member 425 at an axial end face of the field winding assembly 400. This frame member 425 may include any configuration of static structural members connected or formed integral with the stationary support tube 402. In the depicted embodiment, the frame member 425 includes radially extending spokes 428 extending from an end face or flange 426 on the support tube 402. Arms 427 extend between the spokes 428 and the sides 422 of the individual modules 408. The arms 427 may be connected to the modules 408 by conventional means.

[0084] Referring to Fig. 8, each field winding module 408 is a consequent pole configuration having a plurality of superconducting field coils 414 defining physical poles and a plurality of interspaced virtual poles formed in circumferentially -arranged spaces 412 between the superconducting field coils 414. Each field coil 414 includes field windings on a racetrack-shaped member, as depicted in the various drawings. As explained above, the consequent pole construction of the field winding assemblies 408 is known in the field of superconducting generators. This structure makes use of physical poles and virtual poles, wherein the virtual poles are a consequence of magnet fields naturally seeking to close on themselves. As such, a consequent poledesign requires one-half of the field coils 414 of a conventional field winding construction.

[0085] Referring to Figs. 8 and 10-11. the field coils 414 are carried by a framelike coil support structure 430. In the depicted embodiment, the coil support structure 430 includes opposite arc-shaped side members 434, wherein the racetrack-shaped field coils 414 extend between these side members 434. End members 432 extend between the side members 434 at opposite ends of the coil support structure 430. Spaced-apart spanner members 438 also extend between the side members 434 and define the spaces 412 for the virtual poles described above. The physical poles defined by the field coils 414 are located within alternating spaces defined by the spacer members 438.

[0086] The coil support structure 430 may include brace members 436 that extend between the spanner members 438 in the spaces 412.

[0087] The coil support structure 430 is enclosed within a thermal shield 423 within the vacuum vessel 416. For example, the coil support structure 430 may be completely encased within the thermal shield 423. as depicted for example in Figs. 13-15, which aids in maintaining the temperature of the superconducting field coils 414 at cryogenic temperatures. The thermal shield 423 may have a conventional construction and be formed from, for example, aluminum plates. As described in greater detail below, the thermal shield 423 may be in thermal contact with a thermal bus bar network that, in turn, delivers heat to the cryocoolers 468.

[0088] Managing the mechanical loads imposed on the superconducting field coils 414 is an important consideration in superconducting electric machines. In general, minimizing mechanical loads minimizes the cryogenic cooling requirements of the overall system. In this regard, the thermal shield 423 needs to be a good thermal conductor. Generally, good thermal conductors are also good electrical conductors. However, if the thermal shield 423 is a good electrical conductor, it can be subject to substantial mechanical loads caused by induced eddy currents should a field coil quench when the superconductor machine spontaneously reverts from its superconducting state to its normally conducting state.

[0089] Referring to Figs. 14 and 15 in particular, in a unique embodiment of the present invention, the thermal shield 423 may be a good thermal conductor but a poorelectrical conductor, thereby minimizing quench-induced loads on the thermal shield 423 that would otherwise require offsetting structure that increases the thermal load on the cryogenic system. In this embodiment, the thermal shield 23 is formed from an aluminum skin 488 that encases a fiberglass mat. The aluminum skin (wall) is slit or sliced through without slitting the underlying fiberglass mat to allow thermal conduction toward the cryocoolers while inhibiting the flow of eddy currents that would create mechanical loads on the thermal shield 423 during a field quench. The slits 486 are strategically placed in the thermal shield 423 so as not to inhibit the flow of heat to the cryocoolers where the heat is removed, but to inhibit the flow of eddy currents that can create large quench-induced forces on the thermal shield. In Fig. 14, the slits 486 are arranged in a fan pattern from the location of the cryocoolers 468. In the embodiment of Fig. 15, the slits 486 are generally parallel and extend across the face of the thermal shield 430.

[0090] Referring particularly to Figs. 8 through 13, the coil support structure 430 is suspended within the vacuum vessel 416 by a plurality of extended connectors 440. Each of the connectors 440 is a generally rigid, lightweight member having a first end connected to the coil support structure 430 and an opposite end connected to an inner wall or surface of the vacuum vessel 416. An embodiment of the connector 440 is shown in Fig. 10 and includes a body 456 between opposite heads 452. The body 456 may be formed by rigid strap members (e.g., carbon fiber straps) and the heads 452 may include conventional mechanical devices, such as threaded bolts and nuts.

[0091] Referring to Fig. 12, the connectors 440 may include comer connectors 450 that attach to each comer of the coil support structure 430, extend through the thermal shield 423. and connect to the inner opposite comers of the vacuum vessel 416. In the depicted embodiment, two comer connectors 450 are provided at each comer of the coil support structure 430, with one connector 450 attached to the outer wall 418 and one connector 450 attached to the inner wall 419 (Fig. 13) of the vacuum vessel 416.

[0092] The connectors 440 may also include one or more radial connectors that extend from the side members 434 of the coil support structure 430 through the thermal shield 423 and outer wall 418 of the vacuum vessel 446, as particularly depicted in Fig. 9. In Fig. 9, one head 452 of the radial connector 446 connects to abracket 458 on the side member 434 of the coil support structure 430, and the opposite head 452 extends through and is bolted against the outer wall 418 of the vacuum vessel 416. In the depicted embodiment, each module 408 includes four of the radial connectors 440 (two along each side member 434 of the coil support structure 430).

[0093] As particularly seen in Figs. 8, 11, and 12, the connectors 440 may include a plurality of tangential connectors 448. For example, a pair of the tangential connectors 448 may be connected generally at or near the midpoint of each side member 434 of the coil support structure 430, extend in a tangential direction, and connect to an inside of the outer wall 418 via brackets provided inside the vacuum vessel 416.

[0094] Referring to Figs. 16 through 21, as discussed above, the field coils 414 must be maintained at a cryogenic temperature to achieve the superconducting state of zero resistance. Cry ostats used in superconducting machines may be conductively cooled by a cryocooler 468 (such as a conventional Gifford-McMahon (GM) or pulse tube (PT) cryocooler) having a housing that is hermetically connected to the vacuum vessel 416. In one configuration, the cryocooler 468 may have a first stage that extends from the housing into the vacuum vessel 416 to be in thermal contact with the thermal shield 423. and a second stage that extends from the first stage to be in thermal contact with the superconducting field coil 414. An example of a GM type cryocooler is the Cryomech® or Sumitomo® (SHI) cold head model RDK. GM cryocoolers may be preferred in that they are not sensitive to orientation, whereas the PT cryocoolers need to be vertically oriented in all operating states.

[0095] Still referring to Figs. 16 through 21. each of the superconducting field coils 414 within the vacuum vessel 416 is in direct thermal contact with a thermal bus network 460 formed from a highly thermally conductive material, such as copper. The “direct” thermal contact may be achieved by physical communication between the components, for example by abutting contact of the field coils with a member of the thermal bus network 460 (as described below) or via an intermediate thermally conductive member, such as a braided copper or aluminum strap.

[0096] One or more cryocoolers 468 are in direct thermal contact with the thermal bus network 460. In the depicted embodiments, the cryocoolers 468 extend throughthe vacuum vessel side wall 422 at defined cold head locations 484 and include a first or second stage cooling member that directly abuts against the thermal bus network 460. A separate cooling stage may be in direct thermal contact with the thermal shield 423. With this configuration, the superconducting field coils 414 are maintained at a cry ogenic temperature via direct thermal conduction cooling by the cryocoolers 468 and the thermal bus bar network 460 without the use of a cryogenic fluid for moving heat.

[0097] In the embodiment depicted in the figures, the cryocoolers 468 are mounted externally on the vacuum vessel 416, for example on the side wall 422 of the vacuum vessel 416. A compressor 470 associated with each cryocooler 468 may also be mounted externally on the vacuum vessel 416, for example on the same side wall 422. The function and operation of the compressors 470 with a cryocooler are understood by those skilled in the art.

[0098] Each field winding modular 408 may include a plurality of separately controlled temperature zones, wherein each temperature zone has at least one cryocooler 468 associated therewith. Not all of the cryocoolers 468 need to be operated at the same time depending on the heat profile of the field coils 414 and thermal shield 423.

[0099] The thenwal bus network 460 may be variously configured with the field coils 414 and the coil support structure 430. For example, as depicted in Figs. 16-17, this network 460 may include a thermally conductive ring 462 (e.g., a copper ring) surrounding and in abutting contact with each of the superconducting field coils 414. Each ring 462 is, in turn, in direct abutting thermal contact with a header 464 (e.g., a copper bar or a set of copper braids). The rings 462 and header 462 may be formed as a unitary piece. This header 464 may abut directly against one of the arc-shaped side members 434 of the coil support structure 430. The cryocoolers 468 extend thorough the vacuum vessel 416 (and the coil support structure 430) and are in direct thermal contact with the header 464.

[0100] The coil support structure 430 may be integrated with the thermal bus network 460 in various ways. For example, in the embodiment of Figs. 16-19, wherein the field coils 414 are arranged in alternate spaces between the spanners 438 of the coil support structure 430, each spanner 438 may include a body 472, such as arectangular bar. A ledge 474 may extend from a side of the body 472. A right-angle member 476 may be attached to the body 472 and define the ledge 474. The thermally conductive ring 462 and field winding coil 414 are mounted on the ledge 474. As particularly seen in Fig. 19, the ring 462 may have an L-shaped profile and include a section 475 between the ledge 474 and the field winding coil 475.

[0101] Referring to Fig. 20, in a particular embodiment the thermal bus network 460 may include a copper frame 478 that essentially mimics and is attached to a face of the frame-like coil support structure 430. Each of the conductive rings 462 is in direct thermal contact or formed integrally with the frame 478.

[0102] It may be desirable to provide a ride-through cooling capability to each of the modules 408 in the event of a cooling interruption in the superconducting generator caused by power outage or other electncal / mechanical failure of the cryogenic cooling system. The temperature rise of superconducting coils during the cooling outage could result in a quench of the coils if their temperature rises above critical temperature (normally 5-7 K for NbTi coils). As understood by those in the art. a quench refers to the sudden loss of superconductivity in the field coils 414 due to a temperature rise. In the superconducting state, the resistance of the field coil windings is zero and hence no energy is required to maintain current flow. If the coil temperature rises above the superconductivity threshold, the windings suddenly revert to a normal conducting state with a finite resistance and the circulating current passing through this elevated coil resistance creates heat. A quench will interrupt the power generation of the generator. A ride-through capability provides a means to maintain the field coils 414 at a cry ogenic temperature below the superconductivity threshold (critical temperature) until the cooling outage passes (e.g., until the power recovers). Referring to Fig. 21, this nde-through capability may be provided by one or more sealed cryogen tanks 480 carried by the coil support structure 430 within the vacuum vessel 416. The cryogen tanks 480 contain a liquid cryogen (e.g., liquid helium) and are in direct thermal contact with the coil support structure 430, for example by being mounted on copper conductors 482 that are, in turn, mounted to the coil support structure 430. Liquid helium boils at 4.2 degrees Kelvin and the tanks 480 will maintain the coil support structure 430 (and field coils 414) at thistemperature until all of the liquid helium in the tanks 480 boils off (becomes helium gas), which provides time for the cooling outage to pass.

[0103] 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.

[0104] Further aspects of the invention are provided by the subject matter of the following clauses:Clause 1: A superconducting generator, comprising: an armature assembly; a segmented field winding assembly, the segmented field winding assembly further comprising: a plurality of interconnected field winding modules; each field winding module comprising: a vacuum vessel; a plurality of superconducting field coils carried by a coil support structure within the vacuum vessel; each of the superconducting field coils in direct thermal contact with a thermal bus network; one or more cryocoolers in direct thermal contact with the thermal bus network; and wherein the superconducting field coils are maintained at a cryogenic temperature via direct thermal conduction cooling by the cryocoolers and the thermal bus bar network.Clause 2: The superconducting generator of clause 1, wherein each field winding module comprises a consequent pole configuration having plurality of virtual poles interspaced between the superconducting field coils.Clause 3: The superconducting generator of clause 1 or 2, wherein the cryocoolers are mounted externally on the vacuum vessel and in direct thermal contact with the thermal bus bar network through the vacuum vessel.Clause 4: The superconducting generator of any preceding clause, further comprising a compressor associated with each of the cryocoolers, the compressors mounted externally to the vacuum vessel.Clause 5: The superconducting generator of any preceding clause, wherein each field winding modular comprises a plurality of separately controlled temperature zones, each temperature zone having at least one of the cryocoolers associated therewith.Clause 6: The superconducting generator of any preceding clause, wherein the thermal bus network comprises a thermally conductive ring surrounding each of the superconducting field coils, each of the rings in direct thermal contact with a header, the cryocoolers in direct thermal contact with the header.Clause 7: The superconducting generator of any preceding clause, further comprising a thermal shield within the vacuum vessel surrounding the coil support structure, the thermal bus bar network, and the superconducting field coils, each of the cryocoolers comprising a first cooling stage in direct thermal contact with the thermal shield and a second cooling stage in direct thermal contact with the thermal bus network.Clause 8: The superconducting generator of any preceding clause, wherein the coil support structure defines a frame-like structure comprising side members and spanner members extending between the side members, the superconducting field coils arranged in alternate spaces defined by the spanner members.Clause 9: The superconducting generator of any preceding clause, wherein each field winding module comprises a consequent pole configuration having a plurality of virtual poles interspaced between the superconducting field coils in spaces defined between the spanner members.Clause 10: The superconducting generator of any preceding clause, wherein the spanner members comprise a ledge extending from a main body, the superconducting field coil and thermally conductive ring mounted onto the ledge.Clause 11: The superconducting generator of any preceding clause, wherein the thermal bus netw ork comprises a frame that mimics and is attached to a face of the frame-like structure of the coil support structure, the thermally conductive rings in direct thermal contact with the frame of the thermal bus network.Clause 12: The superconducting generator of any preceding clause, further comprising a sealed cryogen tank carried by the coil support structure within the vacuum vessel, the cryogen tank containing a liquid cryogen and in direct thermalcontact with the coil support structure to provide a ride-through cooling capacity in a quench event.Clause 13: A field winding module for use in a superconducting generator, wherein a plurality of the field winding modules interconnect end-to-end in a circumferential direction to define a segmented field winding assembly, the field winding module comprising: a vacuum vessel; a plurality of superconducting field coils carried by a coil support structure with the vacuum vessel; a thermal bus network within the vacuum vessel, each of the superconducting field coils in direct thermal contact wi th the thermal bus network; one or more cryocoolers in direct thermal contact with the thermal bus network; and wherein the superconducting field coils are maintained at a cryogenic temperature via direct thermal conduction cooling by the cryocoolers and the thermal bus bar network.Clause 14: The field winding module of clause 13, w herein the field winding module comprises a consequent pole configuration having plurality of virtual poles interspaced between the superconducting field coils.Clause 15: The field winding module of clause 13 or 14. wherein the cryocoolers are mounted externally on the vacuum vessel and in direct thermal contact with the thermal bus bar network through the vacuum vessel, and further comprising a compressor associated with each of the cryocoolers, the compressors mounted externally to the vacuum vessel.Clause 16: The field winding module of any one of clauses 13-15, wherein the thermal bus netw ork comprises a thermally conductive ring surrounding each of the superconducting field coils, each of the rings in direct thermal contact with a header, the cryocoolers in direct thermal contact with the header.Clause 17: The field winding module of any one of clauses 13-16. further comprising a thermal shield within the vacuum vessel surrounding the coil support structure, the thermal bus bar netw ork, and the superconducting field coils, each of the cryocoolers comprising a first cooling stage in the direct thermal contact with the shield and a second cooling stage in direct thermal contact with the thermal header.Clausel8: The field winding module of any one of clauses 13-17, wherein the coil support structure defines a frame-like structure comprising side members andspanner members extending between the side members, the superconducting field coils arranged in alternate spaces defined by the spanner members.Clause 19: The field winding module of any one of clauses 13-18. wherein the spanner members comprise a ledge extending from a main body, the superconducting field coil and thermally conductive ring mounted onto the ledge.Clause 20: The field winding module of any one of clauses 13-19, wherein the thermal bus network comprises a frame that mimics and is attached to a face of the frame-like structure of coil support structure, the thermally conductive rings in direct thermal contact with the frame of the thermal bus network.

Claims

WHAT IS CLAIMED IS:

1. A superconducting generator, comprising: an armature assembly; a segmented field winding assembly, the segmented field winding assembly further comprising: a plurality of interconnected field winding modules; each field winding module comprising: a vacuum vessel; a plurality of superconducting field coils carried by a coil support structure within the vacuum vessel; each of the superconducting field coils in direct thermal contact with a thermal bus network; one or more cryocoolers in direct thermal contact with the thermal bus network; and wherein the superconducting field coils are maintained at a cryogenic temperature via direct thermal conduction cooling by the cryocoolers and the thermal bus bar network.

2. The superconducting generator of claim 1, wherein each field winding module comprises a consequent pole configuration having plurality of virtual poles interspaced between the superconducting field coils.

3. The superconducting generator of claim 1, wherein the cryocoolers are mounted externally on the vacuum vessel and in direct thermal contact with the thermal bus bar network through the vacuum vessel.

4. The superconducting generator of claim 3, further comprising a compressor associated with each of the cryocoolers, the compressors mounted externally to the vacuum vessel.

5. The superconducting generator of claim 3, wherein each field winding module comprises a plurality of separately controlled temperature zones, each temperature zone having at least one of the cryocoolers associated therewith.

6. The superconducting generator of claim 3, wherein the thermal bus network comprises a thermally conductive ring surrounding each of the superconducting field coils, each of the rings in direct thermal contact with a header, the cryocoolers in direct thermal contact with the header.

7. The superconducting generator of claim 6, further comprising a thermal shield within the vacuum vessel surrounding the coil support structure, the thermal bus bar network, and the superconducting field coils, each of the cryocoolers comprising a first cooling stage in direct thermal contact with the thermal shield and a second cooling stage in direct thermal contact with the thermal bus network.

8. The superconducting generator of claim 6, wherein the coil support structure defines a frame-like structure comprising side members and spanner members extending between the side members, the superconducting field coils arranged in alternate spaces defined by the spanner members.

9. The superconducting generator of claim 8, wherein each field winding module comprises a consequent pole configuration having a plurality of virtual poles interspaced between the superconducting field coils in spaces defined between the spanner members.

10. The superconducting generator of claim 8, wherein the spanner members comprise a ledge extending from a main body, the superconducting field coil and thermally conductive ring mounted onto the ledge.

11. The superconducting generator of claim 8, wherein the thermal bus network comprises a frame that mimics and is attached to a face of the frame-likestructure of the coil support structure, the thermally conductive rings in direct thermal contact with the frame of the thermal bus network.

12. The superconducting generator of claim 1, further comprising a sealed cryogen tank carried by the coil support structure within the vacuum vessel, the cryogen tank containing a liquid cryogen and in direct thermal contact with the coil support structure to provide a ride-through cooling capacity in a quench event.

13. A field winding module for use in a superconducting generator, wherein a plurality' of the field winding modules interconnect end-to-end in a circumferential direction to define a segmented field winding assembly, the field winding module comprising: a vacuum vessel; a plurality' of superconducting field coils carried by a coil support structure with the vacuum vessel; a thermal bus network within the vacuum vessel, each of the superconducting field coils in direct thermal contact with the thermal bus network; one or more cryocoolers in direct thermal contact with the thermal bus network; and wherein the superconducting field coils are maintained at a cryogenic temperature via direct thermal conduction cooling by the cryocoolers and the thermal bus bar network.

14. The field winding module of claim 13, wherein the field winding module comprises a consequent pole configuration having plurality of virtual poles interspaced between the superconducting field coils.

15. The field winding module of claim 13, wherein the cryocoolers are mounted externally on the vacuum vessel and in direct thermal contact with the thermal bus bar network through the vacuum vessel, and further comprising a compressor associated with each of the cryocoolers, the compressors mounted externally to the vacuum vessel.

16. The field winding module of claim 13, wherein the thermal bus network comprises a thermally conductive ring surrounding each of the superconducting field coils, each of the rings in direct thermal contact with a header, the cryocoolers in direct thermal contact with the header.

17. The field winding module of claim 16, further comprising a thermal shield within the vacuum vessel surrounding the coil support structure, the thermal bus bar network, and the superconducting field coils, each of the cryocoolers comprising a first cooling stage in the direct thermal contact with the thermal shield and a second cooling stage in direct thermal contact with the thermal header.

18. The field winding module of claim 13, wherein the coil support structure defines a frame-like structure comprising side members and spanner members extending between the side members, the superconducting field coils arranged in alternate spaces defined by the spanner members.

19. The field winding module of claim 18, wherein the spanner members comprise a ledge extending from a main body, the superconducting field coil and thermally conductive ring mounted onto the ledge.

20. The field winding module of claim 18, wherein the thermal bus network comprises a frame that mimics and is attached to a face of the frame-like structure of coil support structure, the thermally conductive rings in direct thermal contact with the frame of the thermal bus network.

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