Field coil support structure and modular field coil design in superconducting machines

Abstract

The present invention relates to an electric machine, comprising an annular armature assembly and a non-rotating annular field winding assembly, the non-rotating annular field winding assembly being coaxial with the armature assembly and separated from the armature assembly by a gap. The field winding assembly comprises a field coil support structure having an annular array of recessed portions formed therein and extending around the field coil support structure. The field winding assembly further comprises a plurality of superconducting coils each disposed in a recessed portion of the annular array of recessed portions. A generator and a method for generating electric power are disclosed.

Description

Background Art

[0001] The present invention relates to electrical generators, and in particular to electrical machines including superconducting windings and maintaining and / or reducing magnetic gaps between field coils and armature winding coils during and following superconducting magnet cool down.

[0002] A typical electric machine (such as a motor and a generator) generally described includes a field coil and an armature winding coil. Once a voltage is applied, a magnetic field couples the field coil and the armature winding coil. The magnitude of the magnetic field depends on the amount of current passing through the field coil. The magnetic stress within the motor is converted into torque to cause the rotation of the rotor. The higher the magnetic field, the greater the torque per rotation for a given circumference of the armature winding coil. Due to the increased magnetic field strength caused by the superconducting material, the use of field coils made of superconducting materials makes the motor more compact, lightweight and efficient. Of particular interest in this article is a superconducting generator described as a field coil internal (FCI) construction.

[0003] In a typical superconducting generator, the field coils are formed on a large, main coil former structure, generally formed of aluminum. During the cooling of the field coils from room temperature to an operating temperature close to absolute zero, thermal contraction of the field coil former structure occurs in radial and axial directions. The radial contraction of the field coil former structure results in an increase in the magnetic gap between the field coils and the armature winding coils. This increase in the magnetic gap results in a degradation in the performance (and therefore efficiency) of the superconducting generator. Depending on the design, this can be up to 65 mm for a typical field coil former structure having a radius of 4 m or more, for example.

[0004] There has long been a felt need for a superconducting generator capable of generating multiple megawatts (MW) of electrical power (e.g., 10 to 35 MW) that incorporates means for maintaining a minimum magnetic gap between the field coils and the armature winding coils. The desired generator should be highly reliable and of a reasonable size and weight to allow economical shipping and placement. Summary of the invention

[0005] Aspects and advantages of the present disclosure are set forth below in the following description, or may be obvious from the description, or may be learned by practice of the disclosure.

[0006] According to one embodiment, an electric machine is disclosed. The electric machine includes an annular armature assembly and a non-rotating annular field winding assembly, which is coaxial with the armature assembly and separated from the armature assembly by a gap. The non-rotating annular field winding assembly includes a field coil support structure and a plurality of superconducting coils. The field coil support structure includes an annular array of recessed portions formed therein and extending around the field coil support structure. Each of the plurality of superconducting coils is disposed in a recessed portion in the annular array of recessed portions.

[0007] According to another embodiment, a generator is disclosed. The generator includes an annular armature assembly and a non-rotating annular field winding assembly, the non-rotating annular field winding assembly being coaxial with the armature assembly and separated from the armature assembly by a gap. The non-rotating annular field winding assembly includes a field coil support structure and a plurality of superconducting coils. The field coil support structure is formed of a non-contracting material having a negligible coefficient of thermal expansion. Each of the plurality of superconducting coils is disposed relative to the field coil support structure.

[0008] According to yet another embodiment, a method for generating electrical power is disclosed. The method includes: generating a magnetic field in a non-rotating toroidal field winding assembly in a generator; rotating an armature assembly of the generator; generating an electric current in the armature assembly by the rotation of the armature around the non-rotating toroidal field winding assembly; and cooling a plurality of superconducting coils to a superconducting condition using a cooling liquid, the cooling liquid at least partially evaporating as the cooling liquid cools the plurality of superconducting coils. The field winding assembly includes a field coil support structure and a plurality of superconducting coils. The field coil support structure includes an annular array of recessed portions formed therein and extending around the field coil support structure. Each of the plurality of superconducting coils is disposed in a recessed portion in the annular array of recessed portions. The armature assembly is coaxial with the non-rotating toroidal field winding assembly and electromagnetically coupled to the non-rotating toroidal field winding assembly, wherein the non-rotating toroidal field winding assembly is separated from the armature assembly by a gap. The field coil support structure is composed of a material having a low coefficient of thermal expansion to maintain the size of the gap between the non-rotating toroidal field winding assembly and the armature assembly during cooling of the plurality of superconducting coils to a superconducting condition.

[0009] These and other features, aspects and advantages of the present disclosure 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 present disclosure and, together with the description, serve to explain the principles of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] A full and enabling disclosure of the present disclosure, including the best mode thereof for one skilled in the art, is more particularly set forth in the remainder of this specification, including reference to the accompanying drawings, in which:

[0011] Figure 1 is a schematic diagram of a superconducting generator illustrating an armature assembly separated from a non-rotating or stationary field winding according to one or more embodiments of the present disclosure;

[0012] Figure 2 is a schematic diagram illustrating a superconducting generator having an armature arranged around a field winding and including modular field coils according to one or more embodiments of the present disclosure;

[0013] Figure 3is a schematic diagram showing in cross section a superconducting generator having a toroidal rotating armature and a non-rotating superconducting field winding wrapped by the armature according to one or more embodiments presented herein;

[0014] Figure 4 is a perspective view of a bobbin structure including a plurality of modular field coils of superconducting field windings according to one or more embodiments presented herein; and

[0015] Figure 5 is a method of passing through a device according to one or more embodiments set forth herein. Figure 3 A cross-sectional view taken along line 5-5.

[0016] Corresponding reference characters indicate corresponding parts throughout the several views of the drawings. DETAILED DESCRIPTION

[0017] One or more specific embodiments of the present disclosure will be described below. In order to provide a concise description of these embodiments, all features of the 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, a large number of implementation-specific decisions must be made to achieve the developer's specific goals that may vary from implementation to implementation, such as complying with system-related constraints and business-related constraints. In addition, it should be appreciated that such development efforts may be complex and time consuming, but for ordinary technicians who benefit from this disclosure, such development efforts will be nothing more than a routine task of design, preparation, and manufacturing.

[0018] When introducing elements of various embodiments of the present invention, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the elements. The terms "comprising," "including," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements.

[0019] Superconducting alternating current (AC) generators have been developed that include an armature winding disposed around a field coil winding.

[0020] Figure 1 and Figure 2 Is in disassembly ( Figure 1 ) Construction and assembly ( Figure 2 ) is a schematic diagram of a superconducting generator 100 according to one embodiment of the present disclosure. The superconducting generator 100 may represent one embodiment of a superconducting generator used in a wind turbine, a motor or a generator (eg, in an application where the generator is driven by a gas turbine). Figure 1 and Figure 2The superconducting generator 100 depicted in FIG. 1 is a radial field generator configured with a field coil inside (FCI) design. Reference numerals 110 and 112 represent a radial direction and an axial direction of the superconducting generator 100, respectively.

[0021] like Figure 1 and Figure 2 As depicted in , the superconducting generator 100 includes a non-rotating (also referred to herein as a stationary) toroidal field winding assembly 102 and an toroidal rotating armature assembly 104 disposed in a housing 106. In particular, Figure 1 An exploded view of superconducting generator 100 is depicted to illustrate non-rotating field winding assembly 102 and annular rotating armature assembly 104 separately.

[0022] The non-rotating field winding assembly 102 is disposed adjacent to the toroidal rotating armature assembly 104. As used herein, in one embodiment, with respect to the positioning of the non-rotating field winding assembly 102 and the toroidal rotating armature assembly 104, the term “disposed adjacent to” refers to positioning the non-rotating field winding assembly 102 and the toroidal rotating armature assembly 104 relative to each other such that the non-rotating field winding assembly 102 is wrapped by the toroidal rotating armature assembly 104 (e.g., Figure 2 ).

[0023] Furthermore, the non-rotating field winding assembly 102 includes a superconducting field winding 108. The superconducting field winding may include one or more modular field coils (not shown) made using a conductive material that transforms into a superconducting state at a sufficiently low temperature. Such materials include any of niobium-tin alloys, niobium-titanium alloys, magnesium diboride alloys, and a large number of ceramic materials that have exhibited superconducting properties, or a combination thereof. Typically, conductive materials including, but not limited to, copper, aluminum, anodized aluminum, silver, gold, or a combination thereof are used in combination with superconducting alloys to achieve improved mechanical properties. In certain embodiments, lightweight conductive materials may be used to increase or at least maintain the power density of the superconducting generator 100. In some embodiments, the superconducting generator 100 may also include a suitable arrangement (not shown) for cooling the superconducting field winding to a freezing temperature. In an embodiment, the rotating armature assembly 104 may be superconducting.

[0024] By way of example, in some embodiments, when the superconducting generator 100 is deployed as a superconducting generator in a wind turbine, the annular rotating armature assembly 104 can be coupled to the rotor of the wind turbine. Therefore, the annular rotating armature assembly 104 may rotate due to the rotation of the rotor caused by wind energy. Due to the rotation of the annular rotating armature assembly 104, the superconducting generator 100 can generate electrical power by means of a voltage induced in the armature winding when the armature winding moves through the magnetic field established by the superconducting field winding 108.

[0025] Reference now Figure 3 , a superconducting generator 100 is illustrated in schematic cross-section having a non-rotating superconducting field winding assembly 102 surrounded by an annular rotating armature assembly 104. The rotating armature assembly 104 is configured as an outer annular ring surrounding the field winding assembly 102. The armature assembly 104 is conventionally formed and may include a conductive winding 114 (e.g., a coil or rod) disposed longitudinally along the length of the armature assembly 104 and disposed on an inner cylindrical surface of the armature assembly 104. By way of example, a longitudinal segment of the armature winding 114 may be 29 to 30 inches in length, with a thickness of 4 to 5 inches and an inner diameter between 135 and 136 inches. The coils or rods may be connected to each other at their opposite ends by conductive end turns 116. The end turn connections 116 between the longitudinal coils or rods depend on their number and arrangement and the phase of the power to be generated in the armature winding 114. The inner cylindrical surface of the armature winding 114 is separated from the outer surface of the non-rotating field winding assembly by a narrow air gap 120 (eg, approximately 1-2 inches).

[0026] The armature assembly 104 includes a cylindrical yoke 122 that supports the conductive winding 114. The outer surface of the yoke 122 is fixed to a cylindrical housing 106 that rotates with the armature assembly 104. The diameter of the housing 106 can be, for example, between 147 and 148 inches and has a length of 58 inches. The housing is fitted to a disk 124 that supports the housing 106 and the annular rotating armature assembly 104.

[0027] The rotating cylindrical support tube 126 is positioned radially inwardly of the armature winding 114. A pair of annular bearings 128 are arranged toward opposite ends of the non-rotating base tube 130, thereby enabling the armature assembly 104 to rotate about the non-rotating field winding assembly 102.

[0028] The non-rotating base tube 130 supports a field winding support disk 132 on which the non-rotating field winding assembly 102 is mounted. The field winding support disk 132 may have cut-outs or holes (not shown) to reduce weight. The field winding support disk 132 is attached to the end of a cryostat housing 134, which contains the superconducting coils of the superconducting field windings 108 (presently described). The cryostat housing 134 and its cooling components form a cryostat 136 that cools the superconducting coils of the superconducting field windings 108. The cryostat housing 134 may be annular, rectangular in cross-section, having an outer diameter of between 134 inches and 135 inches and a length of 49 inches. The size of the cryostat housing 134 and other components of the generator is a matter of design choice and may vary depending on the design of the generator.

[0029] The cryostat 136 insulates the superconducting coils of the non-rotating field winding 108 so that the superconducting coils can be cooled to near absolute zero, for example, to 10 Kelvin (K) and preferably to 4K. To cool the superconducting coils, the cryostat housing 134 includes insulating pipes 138 to receive liquid helium (He) or other similar refrigerated liquids (referred to as cryogen). A conventional two-stage recondenser 140 uses a gravity feed to provide cryogen (e.g., liquid He). The cryogen flows around the superconducting coils of the non-rotating field winding 102 and cools the coils to achieve superconducting conditions. When the He is at least partially evaporated, the coils are cooled to 4 degrees K, for example. The He vapor flows to the recondenser 140 through one of the pipes 138, where the He is cooled, liquefied, and returned to the coils via the pipes 138. The power conductors for the superconducting coils also pass through the cryostat housing 134 with insulating pipes 138 for helium.

[0030] The second recondenser 142 provides a second cooling liquid (e.g., liquid nitrogen or liquid neon) to an internal heat shield 144 of the cryostat housing 134 for the superconducting winding 108. The second cooling liquid cools the heat shield 144 for the superconducting coil to about 30 degrees K to 80 degrees K. Cooling the heat shield 144 helps to subcool the superconducting winding 108 by reducing the amount of thermal radiation heat absorbed by the helium. The second recondenser 142 receives evaporated liquid nitrogen or liquid neon from the heat shield 144, liquefies the nitrogen or neon, and provides the liquid nitrogen or liquid neon to the heat shield 144 via an insulating pipe 146.

[0031] Torque is applied to rotate the toroidal rotating armature assembly 104 around the non-rotating field winding assembly 102. Torque is applied to the non-rotating field winding assembly 102 through the toroidal rotating armature assembly 104 due to electromagnetic force (EMF) coupling.

[0032] Reference now Figure 4 and Figure 5 , in the simplified isometric view ( Figure 4 ) illustrates a portion of the non-rotating field winding assembly 102, and more particularly, illustrates the coil former or support structure 150 and the Figure 3 The line 5-5 is intercepted Figure 3 Schematic cross section of a portion of a superconductor generator ( Figure 5). A non-rotating field assembly 102 is shown including a field coil support structure 150 for a plurality of superconducting coils 152. In an embodiment, the plurality of superconducting coils 152 are generally racetrack shaped. More specifically, each superconducting coil 152 is comprised of a group of wires formed in the shape of a racetrack. The coils 152 are potted to retain the racetrack shape. For example, each racetrack may have a longitudinal section of two parallel sections that are 29 to 30 inches long and 10 inches wide. The field coil support structure 150 forms a support portion to hold the plurality of superconducting field coils 152.

[0033] Of particular interest in this context is the cooling of the superconducting field coils 152 and subsequently the cooling of the field coil support structure 150 in the radial direction 110 ( Figure 2 ) contraction. In order to minimize (if not eliminate) such contraction of the field coil support structure 150, the field coil support structure 150 disclosed herein is formed of a lightweight material that provides minimal (if not eliminated) contraction of the structure during cool down. In an embodiment, the field coil support structure 150 is formed of any material known for its relative lack of expansion or contraction with changes in temperature. In an embodiment, the field coil support structure 150 is formed of a nickel-cobalt-iron alloy (such as Kovar or Invar) and more particularly a controlled expansion alloy having a chemical composition maintained within a narrow range to provide precisely uniform thermal expansion properties. These nickel-cobalt-iron alloy materials are known for having uniquely low thermal expansion coefficients. In another embodiment, the field coil support structure 150 is formed of a composite material, such as a reinforced polymer, which is designed so that they do not contract or only expand minimally during or subsequent to cool down depending on the composite fiber winding angle.

[0034] The field coil support structure 150 includes an annular array of hollow recesses 154, each of which is configured to receive one of a plurality of racetrack-shaped superconducting coils 152. Each superconducting coil 152 is supported in a recess 154 in an annular array extending around the field coil support structure 150 and is cooled to cryogenic temperatures by a helium bath. For example, thirty-six (36) coils 152 may form an annular array of field windings that serve as stator field windings for a generator. The superconducting coils 152 may each be formed of (NbTi) wire wound in a helix around a racetrack form that may include cooling ducts for the helium.

[0035] More specifically, each of the plurality of racetrack-shaped superconducting coils 152 is seated in a corresponding recess 154 by a snap-fit ​​design (integral attachment) so that the coil 152 is secured in the recess 154. Thus, each of the plurality of racetrack-shaped superconducting coils 152 is positioned relative to the corresponding recess 154 to form an interlocking joint. The superconducting coils 152 tend to move magnetically radially toward the armature coils. By snap-fitting the superconducting coils 152 into the field coil support structure 150, the superconducting coils 152 are locked and retained in the recess 154 formed in the field coil support structure 150.

[0036] More specifically refer to Figure 5 In an embodiment, an inner heat shield 158 and an outer heat shield 160 are arranged around the field coil support structure 150. The heat shields 158, 160 are each configured as a tubular, cylindrical structure. It is of interest that during and following the cooling of the superconducting field coil 152, the outer heat shield 160 is disposed in the radial direction 110 ( Figure 2 Due to the lack of contraction of the field coil support structure 150 as disclosed herein, contraction of the outer heat shield 160 in the radial direction 110 will result in the outer heat shield 160 touching the field coil support structure 150, resulting in an inability to operate the field coils 152 due to high heat loads.

[0037] In order to minimize (if not eliminate) such shrinkage of the outer heat shield 160, the outer heat shield is composed of a plurality of radially segmented aluminum shields 162. In an embodiment, the inner heat shield 158 may additionally be composed of a plurality of radially segmented aluminum shields 162, thereby enabling the vacuum envelope to be kept as small and tight as possible. By forming the outer heat shield 160 as a radially segmented structure 162, any shrinkage (or diameter shrinkage) in the radial direction 110 will be "broken", and each segment 162 of the outer heat shield 160 will only be susceptible to shrinkage relative to the thickness of each segment 162. In an embodiment, each heat shield segment 162 of the outer heat shield 160 is approximately 5 to 10 mm. For this minimum size of shield thickness, the shrinkage after temperature reduction will be 4.3 thousandths, which means that for a 5 mm wall thickness, it will shrink by 0.0215 mm.

[0038] As best illustrated in FIG. 5 , in an embodiment, a plurality of short, low thermal conductivity support struts 156 are provided to support and stabilize the segmented heat shield structure 162 of the outer heat shield 160 relative to the field coil support structure 150. Each of the plurality of support struts 156 acts as a thermal support column that carries the weight of the corresponding segmented heat shield structure 162. Depending on the cryostat design, each of the support struts 156 may be designed to expand rather than contract. In an embodiment, support struts capable of providing such support are generally referred to as Heim columns.

[0039] During the process of generating electrical power, a magnetic field is generated in the non-rotating toroidal field winding assembly. The armature assembly is rotating about the non-rotating toroidal field winding assembly to generate an electric current in the armature assembly. The plurality of superconducting coils of the non-rotating toroidal field winding assembly are cooled to a superconducting condition using a cooling liquid that at least partially evaporates as the cooling liquid cools the plurality of superconducting coils. The field coil support structure of the non-rotating toroidal field winding assembly is composed of a material having a low coefficient of thermal expansion to maintain the size of a magnetic gap between the non-rotating toroidal field winding assembly and the armature assembly during cooling of the plurality of superconducting coils to a superconducting condition.

[0040] A generator and operating method having a superconducting field winding assembly including a plurality of modular semiconductor field coils, a field coil support structure, and an external armature (as described above) will have a high torque density and be relatively lightweight. The generator can reach a power output of 10 MW or more and is lightweight. In an embodiment, the superconducting generator is capable of generating multiple megawatts (MW) (e.g., 10-35 MW) of electrical power, such as in wind power applications. In another embodiment, the superconducting generator is capable of generating multiple MW (e.g., 100 MW or more) of electrical power, such as in a superconducting ship propulsion system.

[0041] The superconducting field winding assembly minimizes (if not eliminates) the shrinkage of the magnetic gap formed between the semiconductor assembly and the armature assembly during (and following) the cooling of the superconducting magnet. By maintaining the magnetic gap so that the gap does not widen, the benefit of extending the superconducting field winding magnetic field into the magnetic gap is maintained, and a higher flux density is obtained, resulting in a cost benefit. In addition, as an additional cost benefit, a certain percentage of the cost of superconducting wire can be saved in the superconducting system. If the magnetic gap is not maintained and the gap size is increased, the performance and efficiency of the superconducting generator may be severely degraded.

[0042] While the invention has been described in conjunction with what are presently considered to be the most practical and preferred embodiments, it will be understood that the invention will not be limited to the disclosed embodiments, but on the contrary is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A motor, comprising: Ring armature assembly; and a non-rotating annular field winding assembly coaxial with the armature assembly and separated from the armature assembly by a gap, wherein the field winding assembly comprises: a field coil support structure having an annular array of recesses formed therein and extending around the field coil support structure; a plurality of superconducting coils, each of the plurality of superconducting coils being disposed in a recessed portion of the annular array of recessed portions; and At least one segmented heat shield is disposed about the plurality of superconducting coils and one or more support struts are disposed to support the at least one segmented heat shield relative to the plurality of superconducting coils.

2. The motor according to claim 1, wherein: The armature assembly is formed around the non-rotating toroidal field winding assembly to define a field coil interior (FCI) configuration.

3. The motor according to claim 1, wherein: Each of the plurality of superconducting coils is a racetrack-shaped superconducting coil.

4. The motor according to claim 1, wherein: Each of the plurality of superconducting coils forms a snap-fit ​​joint within a corresponding one of the annular array of recesses.

5. The motor according to claim 1, wherein: The field coil support structure is formed from a material having a low coefficient of thermal expansion.

6. The motor according to claim 5, wherein: The field coil support structure is formed from Invar alloy.

7. The motor according to claim 5, wherein: The field coil support structure is formed from Kovar.

8. A generator, comprising: Ring armature assembly; and a non-rotating annular field winding assembly coaxial with the armature assembly and separated from the armature assembly by a gap, wherein the field winding assembly comprises: a field coil support structure formed of a non-shrinking material having a negligible coefficient of thermal expansion; and a plurality of superconducting coils, each of the plurality of superconducting coils being disposed relative to the field coil support structure; and At least one segmented heat shield is disposed about the plurality of superconducting coils and one or more support struts are disposed to support each of the at least one segmented heat shield relative to the plurality of superconducting coils.

9. The generator according to claim 8, wherein: The armature assembly is formed around the non-rotating toroidal field winding assembly to define a field coil interior (FCI) configuration.

10. The generator according to claim 8, wherein: Each of the plurality of superconducting coils is a racetrack-shaped superconducting coil.

11. The generator according to claim 8, wherein: Each of the plurality of superconducting coils is coupled to the field coil support structure.

12. The generator according to claim 8, wherein: The field coil support structure comprises an annular array of recesses formed therein and extending around the field coil support structure.

13. The generator according to claim 12, wherein: Each of the plurality of superconducting coils is disposed in a recessed portion of the annular array of recessed portions.

14. The generator according to claim 13, wherein: Each of the plurality of superconducting coils forms a snap-fit ​​joint within a corresponding one of the annular array of recesses.

15. The generator according to claim 8, wherein: The field coil support structure is formed from Invar alloy.

16. The generator according to claim 8, wherein: The field coil support structure is formed from Kovar.

17. The generator according to claim 8, wherein: The generator achieves a power output of 10 MW or more.

18. A method for generating electrical power, comprising: A magnetic field is generated in a non-rotating toroidal field winding assembly in a generator, wherein the non-rotating toroidal field winding assembly comprises: a field coil support structure having an annular array of recesses formed therein and extending around the field coil support structure; a plurality of superconducting coils, each of the plurality of superconducting coils being disposed in a recessed portion of the annular array of recessed portions; and at least one segmented thermal shield disposed about the plurality of superconducting coils and one or more support struts disposed to support each of the at least one segmented thermal shield relative to the plurality of superconducting coils; rotating an armature assembly of the generator, wherein the armature assembly is coaxial with and electromagnetically coupled to the non-rotating toroidal field winding assembly, wherein the non-rotating toroidal field winding assembly is separated from the armature assembly by a gap; generating an electric current in the armature assembly by rotating the armature assembly about the non-rotating toroidal field winding assembly; and cooling the plurality of superconducting coils to a superconducting condition using a cooling liquid, the cooling liquid at least partially evaporating as the cooling liquid cools the plurality of superconducting coils, wherein the field coil support structure is composed of a material having a low coefficient of thermal expansion to maintain a size of a gap between the non-rotating toroidal field winding assembly and the armature assembly during cooling of the plurality of superconducting coils to the superconducting condition.

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