Patent ID: 12212212

Unless otherwise indicated, the drawings provided herein are meant to illustrate features of embodiments of the disclosure. These features are believed to be applicable in a wide variety of systems comprising one or more embodiments of the disclosure. As such, the drawings are not meant to include all conventional features known by those of ordinary skill in the art to be required for the practice of the embodiments disclosed herein. Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

DETAILED DESCRIPTION

In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions may be made to achieve the developer's specific goals such as compliance with system-related and business-related constraints.

Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this specification belongs. The terms “first”, “second”, and the like, as used herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. Also, the terms “a” and “an” do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. The use of “including,” “comprising” or “having” and variations thereof herein are meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The terms “connected” and “coupled” are not restricted to physical or mechanical connections or couplings, and can include electrical or magnetic connections or couplings, whether direct or indirect. The term “paramagnetic” as used herein refers to a material that is weakly attracted by the poles of a magnet but does not retain any permanent magnetism. The term “mild carbon steel” and “mild or low carbon steel” as used herein refers to a material that contains a small percentage of carbon, typically on the order of 0.04% to 0.30% carbon, and more particularly, on the order of 0.06% to 0.30% carbon. Additional elements may be added or increased to achieve desired properties. The term “stationary field” as used herein refers to a field generating components that remains stationary during operation, such as the superconducting field winding, and the enclosure in which the field generating components are housed.

As used herein, the terms “may” and “may be” indicate a possibility of an occurrence within a set of circumstances; a possession of a specified property, characteristic or function; and/or qualify another verb by expressing one or more of an ability, capability, or possibility associated with the qualified verb. Accordingly, usage of “may” and “may be” indicates that a modified term is apparently appropriate, capable, or suitable for an indicated capacity, function, or usage, while taking into account that in some circumstances, the modified term may sometimes not be appropriate, capable, or suitable.

As will be described in detail hereinafter, various embodiments of a superconducting generator is presented. The superconducting generator includes an armature configured to be rotated via a shaft. The superconducting generator further includes a stationary field disposed concentric to and radially outward from the armature. The stationary field includes a plurality of superconducting field winding. To achieve thermal insulation of the superconducting field windings, the superconducting field windings are housed in a vacuum vessel, sometimes referred to as a field coil outer vacuum container (OVC). The vacuum vessel forms a portion of a cryostat and serves to thermally insulate the superconducting coils of the non-rotating superconducting field windings so that they may be cooled to near absolute zero, e.g., to 10 Kelvin (K) and preferably to4K. The superconducting generator is anticipated for use in a wind turbine.

The wind turbine includes a rotor having a plurality of blades. The wind turbine further includes a shaft coupled to the rotor. Moreover, the wind turbine includes the superconducting generator coupled to the rotor via the shaft. In alternate embodiments, the superconducting generator is anticipated for use propulsion systems, magnetic levitation devices for train transportation and nuclear fusion, or the like, and is not intended to be limiting to wind turbine implementations.

Referring now toFIG.1, a schematic diagram of an example wind turbine100is presented, in accordance with one embodiment of the present specification. The wind turbine100may be configured to generate electrical power using wind energy. The wind turbine100described and illustrated in the embodiment ofFIG.1includes a horizontal-axis configuration. However, in some embodiments, the wind turbine100may include, in addition or alternative to the horizontal-axis configuration, a vertical-axis configuration (not shown). The wind turbine100may be coupled to, such as, but not limited to, a power grid, for receiving electrical power therefrom to drive operation of wind turbine100and/or its associated components and/or for supplying electrical power generated by the wind turbine100thereto. The wind turbine100may be coupled to an electrical load (not shown) to supply electrical power generated by the wind turbine100thereto to the electrical load.

The wind turbine100may include a body102, sometimes referred to as a “nacelle,” and a rotor104coupled to the body102. The rotor104is configured to rotate with respect to the body102about an axis of rotation106. In the embodiment ofFIG.1, the nacelle102is shown as mounted on a tower108. However, in some other embodiments, the wind turbine100may include a nacelle that may be disposed adjacent to the ground and/or a surface of water.

The rotor104may include a hub110and a plurality of blades112(sometimes referred to as “airfoils”) extending radially outwardly from the hub110for converting wind energy into rotational energy. Although the rotor104is described and illustrated herein having three blades112, the rotor104may have any number of blades112. The rotor104may have blades112of any shape and may have blades112of any type and/or any configuration, whether such shape, type, and/or configuration is described and/or illustrated herein.

In some embodiments, the nacelle102may house, fully or partially, one or more of a superconducting generator114, and a shaft116. The superconducting generator114may be coupled to the rotor104via the shaft116and configured to be operated via the rotor104. For example, rotations of the rotor104due to the wind energy in turn cause a rotary element (e.g., an armature) of the superconducting generator114to rotate via the shaft116. In some embodiments, the shaft116may also include a gear box (not shown). In certain embodiments, use of the gear box may increase the operating speed of the superconducting generator114and reduce the torque requirement for a given power level. The presence or absence of the gearbox is immaterial to the embodiments of the superconducting generator114described in the present specification.

The superconducting generator114is configured to generate electrical power based at least on the rotations of the armature (shown inFIGS.2and3) relative to the stationary field. In accordance with some embodiments described herein, the superconducting generator114may be configured to produce increased magnitudes of electrical power in comparison to traditional generators. The superconducting generator114may be implemented in the form of a synchronous generator. The superconducting generator114will be described in greater details in conjunction withFIGS.2-4.

InFIG.2, a schematic diagram of an electric machine, for example, a superconducting generator200is presented, in accordance with an embodiment of the present disclosure. The superconducting generator200may be representative of one embodiment of the superconducting generator114used in the wind turbine100ofFIG.1. Without limiting the scope of the present application, as previously asserted, the superconducting generator200may be used in any application other than wind turbines. By way of a non-limiting example, the superconducting generator200depicted inFIG.2is a radial field electric machine. Moreover, although the superconducting generator200is shown as the electric machine ofFIG.2, in some other embodiments, the electric machine ofFIG.2may also be a superconducting motor. Reference numerals210and212respectively represent an axial direction and a radial direction of the superconducting generator200.

As depicted inFIG.2, the superconducting generator200includes a stationary field202and an armature204disposed in a housing206. By way of example, in some embodiments, when the superconducting generator200is deployed as the superconducting generator114in the wind turbine100, the armature204may be coupled to the rotor104of the wind turbine100via the shaft116or via both the shaft116and a gear box. The armature204may be configured to be rotated via the shaft116. Due to the rotations of the armature204, the superconducting generator200may generate electrical power by virtue of the voltage induced in armature windings as they move past the magnetic field established by at least one superconducting field winding.

An exploded view of the superconducting generator200is depicted inFIG.2to separately show the stationary field202and an armature204. The stationary field202includes at least one longitudinally extending, race-track shaped superconducting field winding208(also identified by reference numeral308inFIG.3) that is configured to generate a magnetic field oriented in the radial direction212of the superconducting generator200. The superconducting field winding may be alternatively a saddle-shape or have some other shape that is suitable for a particular implementation. The armature204may include an armature winding (identified by reference numeral320inFIG.3). In some embodiments, the armature winding320is non-superconducting winding.

The stationary field202is disposed concentric to and radially outward from the armature204. The stationary field202is maintained at a temperature, adequate for keeping the stationary field202superconducting, generally much lower than the temperature of the armature204. Typically, to enable the superconducting property of the stationary field202, the stationary field202is maintained within a cryogenic range of about 4 Kelvin if the superconducting field winding208,308is composed of low temperature superconducting material; if the superconducting field winding208,308is composed of high temperature superconducting material, the stationary field202is maintained at a temperature of about 30 Kelvin. By way of non-limiting example, the low temperature superconducting material may include an alloy of niobium and tin, or an alloy of niobium and titanium. By way of non-limiting example, the high temperature superconducting material may include yttrium barium copper oxide (YBCO).

Turning now toFIGS.3and4, a perspective cross-sectional view300of a portion of the superconducting generator200ofFIG.2is presented (FIG.3) and an enlargement of a portion ofFIG.3is presented (FIG.4), in accordance with an embodiment of the present disclosure. The superconducting generator200includes a stationary field302(similar to the stationary field202ofFIG.2) and an armature304(similar to the armature204ofFIG.2). The stationary field302is disposed concentric to and radially outward from the armature304and includes a vacuum vessel306and at least one superconducting field winding308. The vacuum vessel306forms an outer vacuum container (OVC) and is described more particularly with regard toFIG.4.

In some embodiments, the superconducting generator200may also include one or more tanks310, one or more conduits312, a cooling apparatus314, an optional thermal shield316, one or more torque transfer structures318such as torque tubes, or combinations thereof. Moreover, the armature304includes an armature winding320. In some embodiments, the armature winding320is non-superconducting winding. In the embodiment shown inFIG.3, torque tubes are used as the torque transfer structures318. Other types of torque transfer structures or torque transfer mechanisms may also be used in place of or in addition to the torque tubes, without limiting the scope of the present disclosure. In the description hereinafter, the terms “torque transfer structures” and “torque tubes” are interchangeably used.

As depicted in the perspective cross-sectional views300ofFIGS.3and4, the vacuum vessel306(sometimes referred to as a cryostat) is an annular, cylindrical shaped vessel that houses, either fully or partially, the superconducting field winding308, the tank310, the one or more conduits312, the cooling apparatus314, the optional thermal shield316, and the one or more torque tubes318. The reference numerals322and324, respectively, represent an inner wall and an outer wall of the vacuum vessel306. In some embodiments, the inner wall322faces the armature304. More particularly, the stationary field302and the armature304are disposed such that the inner wall322of the vacuum vessel306is positioned radially opposite to an outer surface330of the armature304. As illustrated, a portion of the outer wall324defines a cold box326in which the one or more tanks310, the one or more conduits312, and the cooling apparatus314are housed. A plurality of radially extending sidewalls328couple the inner wall322of the vacuum vessel306to the outer walls324of the vacuum vessel306.

As illustrated inFIG.4by shading, in this particular embodiment, the vacuum vessel306is at least partially constructed of a ferromagnetic material. As illustrated, the inner wall322is comprised of one of a non-magnetic material or a paramagnetic material having a low magnetic permeability, typically μ/μ0of <7, and more particularly μ/μ0on the order of 1.0 to 2.0, such as a stainless steel where μ/μ0=1.005, where to symbolizes the permeability of free space, μ symbolizes the absolute permeability of the medium, and μ/μ0symbolizes the relative permeability. The outer wall324and sidewalls328are formed of ferromagnetic material, having a magnetic permeability of approximately μ/μ0˜100-10,000. Suitable ferromagnetic materials for use in forming the wall324and sidewalls328of the vacuum vessel306include cobalt, nickel and steel, in particular, steel containing from 0.04% to 0.30% carbon, more particularly from 0.06% to 0.30% carbon. Examples of suitable steel materials include, but are not limited to, SAE-AISI 1010, SAE-AISI 1020, and ASTM A36. In yet another embodiment, in combination with the inner wall322, only the outer wall324is formed of ferromagnetic material. In this embodiment, the sidewalls328, similar to the inner wall322, may be formed of one of a non-magnetic or a paramagnetic material, such as stainless steel.

Complete, or at least partial, construction of the vacuum vessel306of a mild or low carbon steel, not only provides for a more cost effective vacuum vessel306, but additionally provides enhancement of the magnetic field near the ends309of the superconducting field winding208and provides some level of passive magnetic shielding, in combination greatly reducing overall cost of the vacuum vessel306.

Due to ambient pressure outside, and vacuum inside, the vacuum vessel306is subjected to differential pressure loading. Accordingly, in some embodiments, the inner wall322of the vacuum vessel306is thinner than the outer wall324of the vacuum vessel306. Radially outward forces are applied on the inner wall322of the vacuum vessel306which may load the inner wall322in tension. The forces on the outer wall324of the vacuum vessel306are directed in a radially inward direction, thereby loading the outer wall324in compression. The compressive forces may cause buckling if the outer wall324is not sufficiently thick. Due to the difference in direction of the radial forces between the inner wall322and the outer wall324, the outer wall324may be designed to be thicker than the inner wall322. In an embodiment, the inner wall322has a thickness of approximately 6-12 mm, the sidewalls328have a thickness of approximately 12-20 mm thick and the outer wall324has a thickness of approximately 20-25 mm thick. In an embodiment, a portion of the outer wall324forming the coldbox326has a thickness of approximately 10 mm.

Further, in some embodiments, the stationary field302may also include suitable arrangement for cooling and maintaining the superconducting field winding308at cryogenic temperatures. By way of example, such arrangement for cooling the superconducting field winding308may include one or more of the tanks310, the conduits312, and the cooling apparatus314. The tank310is disposed in fluid communication with the cooling apparatus314and stores a cooling fluid. Although the stationary field302is shown as including a single tank310, use of two or more such tanks for holding the cooling fluid is also envisioned within the scope of the present specification. Non-limiting examples of the cooling fluid may include any type of gaseous or condensed cooling fluids, for example, helium.

Furthermore, the cooling apparatus314may be disposed inside or outside vacuum vessel306and configured to cool the cooling fluid so as to maintain the superconducting field winding308at a temperature that is below a cryogenic temperature. At the cryogenic temperature, the material of the superconducting field winding308is superconducting. The appropriate temperature range for operation of the superconducting field winding308depends on the superconducting material selected for the superconducting field winding308. In particular, the cooling apparatus314may be configured to cool the cooling fluid so as to maintain the superconducting field winding308at the cryogenic temperatures, for example, at about 4 Kelvin that may be appropriate for the low temperature superconducting material such as an alloy of niobium and titanium. In another non-limiting example, the cooling apparatus314may be configured to cool the cooling fluid so as to maintain the temperature of the superconducting field winding308in a range of about 4 Kelvin to about 10 Kelvin that may be appropriate for the low temperature superconducting material such as an alloy of niobium and tin. In yet another non-limiting example, the cooling apparatus314may be configured to cool the cooling fluid so as to maintain the temperature of the superconducting field winding308in a range of about 20 Kelvin to about 26 Kelvin that may be appropriate for a high temperature superconducting material such as yttrium barium copper oxide (YBCO). Moreover, in a non-limiting example, liquid helium may be used as the cooling fluid for low temperature superconductors because it has a temperature of about 5.19 Kelvin. In another non-limiting example, for the high temperature superconducting materials, hydrogen or neon may be used as the cooling fluid.

The conduits312may be disposed inside the vacuum vessel306and fluidly coupled to the tank310. The conduits312may be disposed annularly inside the vacuum vessel306. The conduits312are configured to facilitate flow of the cooling fluid within the stationary field302. In particular, the cooling fluid passively circulates annularly inside the stationary field302through the conduits312, driven by density gradients and phase change. While being circulated, the cooling fluid removes any heat (such as from radiation or conduction heat transfer or from eddy current heating created by generator operation) deposited onto or into a low-temperature structure of the stationary field302and superconducting field winding308, thereby maintaining the superconducting field winding308at cryogenic temperatures.

Moreover, in some embodiments, the optional thermal shield316may be disposed inside the vacuum vessel306. In some embodiments, the optional thermal shield316may be disposed inside the vacuum vessel306such that the thermal shield316encloses the superconducting field winding308and further aids in maintaining the temperature of the superconducting field winding308at the cryogenic temperatures.

Additionally, in some embodiments, the stationary field302may include one or more torque tubes318disposed inside the vacuum vessel306. In some embodiments, the torque tubes318may be annularly disposed inside the vacuum vessel306. By way of example, in an embodiment whereby a thermal shield316is included, the torque tubes318may be disposed adjacent to one or more walls of the thermal shield316. In particular, while some torque tubes318may be disposed inside the thermal shield316, some other torque tubes318may be disposed outside the thermal shield. In an embodiment, whereby the thermal shield316is not included, the torque tubes318may be disposed adjacent to one or more of the sidewalls328and outer walls324of the vacuum vessel306.

The torque tubes318are configured to support a reaction torque caused due to an interaction between a magnetic field produced by the armature304and a magnetic field produced by the superconducting field winding308.

Referring now toFIG.5, a flow diagram400of a method for operating the wind turbine100ofFIG.1, in accordance with one embodiment of the present disclosure.FIG.5will be described in conjunction withFIGS.1-4. The method ofFIG.5includes, operating, at step402, the wind turbine100having the superconducting generator114,200including the armature204,304having the armature winding320and the stationary field202,302having the superconducting field winding208,308. As previously noted, the superconducting field winding208,308is disposed in a vacuum vessel306constructed having an inner wall322comprised of one of a non-magnetic material or a paramagnetic material and an outer wall324formed of a low or mild carbon steel. The superconducting field winding208,308is disposed concentric to and radially outward from the armature204,304.

In particular, the inclusion of the vacuum vessel306at least partially constructed from a mild or low carbon steel provides for a more cost effective vacuum vessel, thus reducing the overall cost of the superconducting generator. The vacuum vessel306further provides increased magnetic flux near the superconducting field winding ends309and provides partial magnetic shielding, as described previously.

The step402of operating the wind turbine100includes imparting rotations to the armature204,304of the superconducting generator114,200via the rotor104of the wind turbine100, as indicated by step404. The rotor104of the wind turbine100is mechanically coupled to the armature204,304of the superconducting generator114,200so that rotations of the rotor104due to the wind energy results in rotations of the armature204,304of the superconducting generator114,200.

Further, the step402of operating the wind turbine100includes cooling the superconducting field winding208,308to a cryogenic temperature via the cooling apparatus314, as indicated by step406. The cooling fluid such as liquid helium, hydrogen, neon, or combinations thereof, may be cooled and circulated via the cooling apparatus314inside the stationary field202,302through one or more conduits312so as to maintain the superconducting field winding208,308at the cryogenic temperature so that the material of the superconducting field winding308is superconducting.

In accordance with the embodiments described herein, an improved superconducting generator such as the superconducting generator114,200and wind turbine such as the wind turbine100including the improved superconducting generator are provided. The improvements in the superconducting generator114,200and the wind turbine100may be achieved, at least partially, due to the inclusion of a vacuum vessel306constructed as least partially of a mild or low carbon steel as disclosed herein in accordance with embodiments of the present disclosure. The inclusion of the vacuum vessel306as described herein provides a more cost effective vacuum about the superconducting field winding, a means for enhancing the magnet field near the ends of the field winding and passively providing some level of magnetic shielding. By forming the vacuum vessel306of cost effective materials, the overall cost of the superconducting generator is reduced.

In addition, due to the vacuum vessel306being constructed with the thinner inner wall322in comparison to the outer wall324thereof, structural loads/forces acting inside and outside the superconducting generator114,200may be compensated.

This written description uses examples to disclose the invention, including the preferred embodiments, 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 have 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. Aspects from the various embodiments described, as well as other known equivalents for each such aspects, can be mixed and matched by one of ordinary skill in the art to construct additional embodiments and techniques in accordance with principles of this application.