SYSTEM AND METHOD FOR MAGNETIZATION OF RAREEARTH
PERMANENT MAGNETS
BACKGROUND OF THE INVENTION
[0001] The subject matter disclosed herein relates to the magnetization of
permanent magnets, and more specifically, to the magnetization of magnets disposed
within cylindrical structures using one or more superconducting materials.
[0002] Many electrical machines include one or more electric motors. Such
electric motors typically include a rotor having permanent magnets disposed within
the bulk of the rotor. During rotation, the rotor, having the permanent magnets,
produces a rotating magnetic field that interacts with a stator. This electromagnetic
interaction results in the conversion of electromagnetic energy into mechanical
motion that drives the machine.
[0003] Two approaches are typically used for the assembly of rotors having
permanent magnets. In one approach, shaped materials are magnetized to generate
the permanent magnets before they are disposed within the bulk of the rotor. This
approach may present several drawbacks. For instance, fully magnetized permanent
magnet pieces can be subject to electromagnetic interaction with any surrounding
objects, such as other adjacent or proximate magnets, which in turn adds to the
complexity of their handling procedures and insertion into the rotor. In a second
approach, the shaped materials are first disposed within the rotor and a magnetizer is
used to magnetize the permanent magnets. Such an approach is typically referred to
as an in-situ magnetization process.
[0004] The second approach can also present several drawbacks. To name a few,
the energy and fabrication costs for conventional resistive magnetizers capable of
generating a sufficient magnetic field flux for the magnetization process can be
prohibitive. For example, some in-situ magnetizers are able to produce small
magnetic fields sufficient only to magnetize small permanent magnets made of certain
materials or grades (e.g., alnico and ferrite) that have low intrinsic coercivity (i.e.,
materials that can be easily demagnetized). However, many emerging applications
1
for permanent magnet electric machines, such as wind turbine applications, or traction
(e.g., magnetic bearing and braking) applications, would benefit from the use of highcoercivity
rare-earth permanent magnet materials, which can often require strong
magnetic fields. Moreover, as the permanent magnets increase in size, their
magnetization becomes increasingly difficult due to inadequate field penetration
produced by typical magnetizers. It should therefore be appreciated that due to
physical constraints in addition to economic considerations, the in-situ magnetization
of such materials is typically very difficult to deliver with conventional restive
systems. Accordingly, it is now recognized that a need exists for a magnetizer
capable of magnetizing rare-earth, high-coercivity materials in an efficient manner.
BRIEF DESCRIPTION OF THE INVENTION
[0005] The present embodiments are generally directed towards such
magnetization. In one embodiment, a superconducting magnetizer assembly is
provided. The assembly includes a coil pack having an inner coil including a first
superconducting magnet material, the coil being configured to generate a first
magnetic field in response to an electric current supplied to the coil, and an outer coil
including a second superconducting magnet material, the outer coil being disposed
about the inner coil and being configured to generate a second magnetic field in
response to an electric current supplied to the outer coil. The coil pack also includes a
container configured to house the inner and the outer coils.
[0006] In another embodiment, a cryogenic container configured for use with a
magnetizer assembly is provided. The container includes a chamber configured to
house a superconducting magnet coil wound into a racetrack shape and to maintain
the coil at a set temperature, and a curved outer surface enclosing the chamber and
configured to radially interface with the surface of an annular member having one or
more materials susceptible to magnetization.
[0007] In a further embodiment, a coil pack configured for use with a magnetizer
assembly is provided. The coil pack includes an inner coil having a first
superconducting magnet material, the coil being configured to generate a first
2
magnetic field in response to an electric current supplied to the coil. The pack also
includes an outer coil having a second superconducting magnet material, the outer
coil being disposed about the first coil and being configured to generate a second
magnetic field in response to an electric current supplied to the second coil. Further,
the pack includes a cryogenic container configured to house the inner and the outer
coils and maintain the inner and the outer coil at a set temperature.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] These and other features, aspects, and advantages of the present invention
will become better understood when the following detailed description is read with
reference to the accompanying drawings in which like characters represent like parts
throughout the drawings, wherein:
[0009] FIG. 1 is an embodiment of an assembly having a superconducting
magnetizer assembly and a rotor disposed within the magnetizer assembly, the
magnetizer assembly including a plurality of superconducting coils configured to
magnetize permanent magnet blocks within the rotor;
[0010] FIG. 2 is an embodiment of a coil configuration for the superconducting
coils of FIG. 1, the coil configuration including a non-conductive end spacer
configured to reduce the peak field at the coil;
[0011] FIG. 3 is a perspective illustration of an embodiment of a curved cryostat
configured to house superconducting coils, and the curved cryostat allows the coils to
interface with an annular rotor so as to facilitate magnetization of permanent magnets
within the rotor;
[0012] FIG. 4 is a schematic illustration of the cryostat of FIG. 3;
[0013] FIG. 5 is an end-on illustration of an assembly including a superconducting
magnetizer assembly and a rotor disposed within the assembly, the superconducting
magnetizer assembly utilizing the curved cryostat of FIGS. 3 and 4;
3
[0014] FIG. 6 is a perspective illustration of an embodiment of a dished cryostat
configured to house superconducting coils, and the dished cryostat allows the coils to
interface with an annular rotor so as to facilitate magnetization of permanent magnets
within the rotor;
[0015] FIG. 7 is a schematic illustration of the cryostat of FIG. 6;
[0016] FIG. 8 is an end-on illustration of an embodiment of an assembly including
a superconducting magnetizer assembly and a rotor disposed within the assembly, the
superconducting magnetizer assembly utilizing the dished cryostat of FIGS. 6 and 7;
[0017] FIG. 9 is an end-on illustration of an embodiment of an assembly including
a superconducting magnetizer assembly and a rotor disposed within the assembly, the
superconducting magnetizer assembly utilizing an external yoke configured to
enhance the field alignment within the permanent magnet material, and the
superconducting magnetizer assembly is arranged to allow the magnetization of 3
poles in one operation;
[0018] FIG. 10 is an end-on illustration of an embodiment of an assembly
including a superconducting magnetizer assembly and a rotor disposed within the
assembly, the superconducting magnetizer assembly utilizing a thin-profile external
yoke, widened coil packs, and yoke blocks interfacing with the coil packs;
[0019] FIG. 11 is an end-on illustration of an embodiment of an assembly
including a superconducting magnetizer assembly and a rotor disposed within the
assembly, the superconducting magnetizer assembly not having an external yoke but
having widened coil packs, and yoke blocks interfacing with the coil packs;
[0020] FIG. 12 is an end-on illustration of an embodiment of an assembly
including a superconducting magnetizer assembly and a rotor disposed within the
assembly, the superconducting magnetizer assembly not having an external yoke but
having widened coil packs and an internal yoke for interfacing with the coil packs;
4
[0021] FIG. 13 is an end-on illustration of an embodiment of an assembly
including a superconducting magnetizer assembly and a rotor disposed within the
assembly, the superconducting magnetizer assembly having a number of
superconducting magnets sufficient to magnetize all of the poles of a rotor in one
operation;
[0022] FIG. 14 is an end-on illustration of an embodiment of an assembly
including a superconducting magnetizer assembly and a rotor disposed within the
assembly, the superconducting magnetizer assembly having a number of
superconducting magnets interfacing with internal yokes, the superconducting
magnets being sufficient to magnetize all of the poles of a rotor in one operation, but
without the use of an external return yoke;
[0023] FIG. 15 is an end-on illustration of an embodiment of an assembly
including a superconducting magnetizer assembly and a rotor disposed within the
assembly, the superconducting magnetizer assembly having a number of
superconducting magnets interfacing with internal yokes and being enclosed by an
external yoke, the superconducting magnets being sufficient to magnetize all of the
poles of a rotor in one operation;
[0024] FIG. 16 is an end-on illustration of an embodiment of an assembly
including a superconducting magnetizer assembly and a rotor disposed within the
assembly, the superconducting magnetizer assembly having a combination of at least
two different superconducting materials in the form of interleaving coil packs capable
of magnetizing 3 poles in a single operation;
[0025] FIG. 17 is an end-on illustration of an embodiment of an assembly
including a superconducting magnetizer assembly and a rotor disposed within the
assembly, the superconducting magnetizer assembly having a combination of at least
two different superconducting materials, one of the superconducting materials being
configured to act as a main magnetization circuit to magnetize each pole in the rotor
individually;
5
[0026] FIG. 18 is an end-on illustration of an embodiment of an assembly
including a superconducting magnetizer assembly and a rotor disposed within the
assembly, the superconducting magnetizer assembly having hybrid coil packs forming
a main magnetization circuit and including one of the superconducting materials
being disposed on an inner, high field portion of the coil pack and the other
superconducting material being disposed on an outer, low field portion of the coil
pack.
DETAILED DESCRIPTION OF THE INVENTION
[0027] The present disclosure is generally directed towards improved systems and
methods for the magnetization of materials disposed within a bulk material, such as
the magnetization of as-formed permanent magnets disposed within an electric motor
rotor. In accordance with the disclosed embodiments, one or more superconducting
materials may be utilized to perform the in-situ magnetization of the as-formed
permanent magnets. Moreover, the superconducting materials may be disposed in
specially configured packs so as to facilitate the magnetization of the as-formed
permanent magnets in a non-cubic shaped matrix, such as within the cylindrical rotor
described above. Moreover, embodiments of magnetizer assemblies having features
for controlling the magnetic fields generated by the superconducting materials are
disclosed. Accordingly, to facilitate discussion of the present approaches towards
such improved embodiments, FIG. 1 illustrates an assembly 10 including a rotor 12
having as-formed permanent magnets 14 (e.g., rare-earth magnets such as neodymium
magnets) disposed within a bulk 16 (e.g., laminations) of the rotor 12. In one
embodiment, the permanent magnets 14 may be NdFeB magnets. The rotor 12 is
disposed inside of a superconducting magnetizer assembly 18 having an annular
opening 20 configured to receive the rotor 12. In some embodiments, the
superconducting magnetizer assembly 18 may support at least a portion of the weight
of the rotor 12 as the magnetization process is performed.
[0028] In a general sense, the superconducting magnetizer assembly 18 includes a
set of superconducting coils 22 wound in a racetrack-like manner. Such a
configuration, as referred to herein, may be racetrack coils 22. The racetrack coils 22,
6
as noted above, may incorporate a number of superconducting materials, for example
niobium-3 tin (NbsSn), niobium-titanium (NbTi), MgB2 magnesium diboride,
vanadium gallium (VsGa), YBCo, or combinations thereof in one or more coils such
as an inner coil and an outer coil, as will be discussed in further detail below. In the
illustrated embodiment, and in the embodiments described below with respect to
FIGS. 2-15, the coils 22 are NbTi coils. However, it should be noted that the
superconductor material or materials chosen may be application specific and may
contain a High Temperature Superconducting or Low Temperature Superconducting
material, or both. Generally, the racetrack coils 22 produce a magnetic field when a
current is passed through the coils. In some embodiments, the materials mentioned
above that form the racetrack coils 22 exhibit decreased resistance when cooled.
Accordingly, in such embodiments the racetrack coils 22 may be cooled so as to
produce maximum magnetic flux.
[0029] Using cooling agents such as liquid helium, it may be possible to approach
absolute zero in temperature (i.e., 0 Kelvin (K)), for example, below about 40 K. In
one embodiment, liquid helium, which has a temperature of approximately 4 K, may
be used as the active coolant to maintain the temperature of the racetrack coils 22 at
the temperature of the liquid helium. It will therefore be appreciated that each of the
racetrack coils 22 may be disposed in a cryostat 24, which may include other features
such as thermal transfer agents (e.g., thermally conductive rods, heat pipes, thermal
buses). Together, the racetrack coils 22 and the cryostats 24 each form coil packs 26.
[0030] Because the racetrack coils 22 are formed from superconducting materials,
such as NbTi and/or NbsSn, which are capable of handling very high current
densities, thermal dissipation may be reduced compared to conventional resistive
magnetizers. That is, in conventional resistive magnetizers, the system must be
pulsed to attain the required field levels for short periods of time. For instance,
magnetizers incorporating superconducting coils may be energized and de-energized
at much slower speeds, such as at ramp rates of ~1 Tesla per minute, compared to
conventional magnetizers incorporating conventional resistive coils, which need to be
energized and de-energized at ramp rates of ~1 Tesla per second. It should be noted
7
that such ramp rates may be achieved with power supplies much smaller than those
required for conventional magnetizers.
[0031] In the illustrated embodiment of FIG. 1, the superconducting magnetizer
assembly also includes a yoke 28, which may be made from iron, permendur, or
similar materials, or any combination thereof. The yoke 28 is generally configured to
improve efficiency of the magnetization process by reducing fringe magnetic fields
and balancing radial forces produced by the coils 22. In the illustrated embodiment,
the yoke 28 includes a plurality of openings 30 configured to house each of the coil
packs 26. In this embodiment the rotor 12 includes six pairs of permanent magnets 14
or "poles," and the superconducting magnetizer assembly includes three coil packs 26
each configured to magnetize a pair of permanent magnets 14. Therefore, in the
depicted embodiment, at least two operations must be performed so as to magnetize
the rotor 12. For example, an embodiment of such a process may include energizing
the racetrack coils 22 so as to magnetize the permanent magnets 14 adjacent to their
respective coil packs 26, followed by a clockwise or counter-clockwise rotation of the
rotor 12 so as to bring non-magnetized permanent magnet pairs in proximity to the
coil packs 26, which allows magnetization of the remaining permanent magnets 14.
[0032] While the racetrack coils 22 in accordance with FIG. 1 may be generally
applicable to the magnetization of rotors, it should be noted that as the size of the
rotor 12 increases, the required volume of the magnetic field produced by each of the
racetrack coils 22 must also increase so as to provide sufficient magnetization of the
permanent magnets 14. However, as noted above, it can be very difficult for
conventional resistive magnetizers to produce such fields.
[0033] For example, in embodiments where the diameter of the rotor 12 is on the
order of 0.1 m and above, the racetrack coils 22, in a simple wound configuration,
may not be sufficient to provide sufficient magnetic field saturation of the permanent
magnets 14. Accordingly, it may be desirable to manipulate the magnetic field
produced by the coils 22 to as to provide more efficient magnetization. In accordance
with the present disclosure, one approach, which is illustrated in FIG. 2, is to increase
saturation by the racetrack coils 22 to reduce and move the peak magnetic field
8
produced by the racetrack coils 22 from an end winding section 32 of the coils 22 to a
long section 34 of the coils 22, the sections being more clearly illustrated in the inset
of FIG. 1. Other approaches may include shaping the cryostat 24 so as to bring the
racetrack coils 22 in closer proximity with the rotor 12, modifying the placement of or
removing the yoke 28 to improve the magnetic field circuit, using multiple
superconducting materials for the coils 22, or any combination thereof Such
embodiments are described in further detail with respect to FIGS. 3-18 below.
[0034] Therefore, keeping in mind the general characteristics of the assembly 10
of FIG. 1, an embodiment of the approach of moving the peak field produced by the
coils 22 is illustrated in FIG. 2. Specifically, FIG. 2 is a diagrammatic illustration of
one of the racetrack coils 22 having a non-conductive end spacer 40 disposed between
an outer coil 42 and an inner coil 44 of the windings of the coils 22. Generally, the
outer coil 42 is disposed about the inner coil 44, and the superconducting magnet
materials that form each of the coils may be the same, or may be different, as will be
discussed in detail below. In the illustrated embodiment, the outer coil 42 and the
inner coil 44 include the same superconducting magnet material. When a current is
passed through the inner coil 44 and/or the outer coil 42, respective first and second
magnetic fields may be produced. In some embodiments, one of the coils may have a
higher critical current than the other. In such embodiments, the coil having the higher
critical current may produce a stronger magnetic field. Such embodiments are
discussed below. It should be noted that the peak magnetic field produced by such a
racetrack coil 22 may be approximately 90%, 88%, or 85% lower than the peak
magnetic field of the racetrack coils of FIG. 1 with no end spacer. For example, in an
embodiment, the peak field may be reduced from approximately 8.8 Tesla (T) to
approximately 7.7 T. Moreover, because the peak field is now moved to the long
portion 34 of the coils 22, magnetic flux is produced by a greater area of the coils 22,
which may provide a greater area of saturation to magnetize the permanent magnets
14.
[0035] Another approach to increasing magnetic efficiency, as noted above, is to
shape the cryostat 24 so as to allow the coils 22 to be in closer proximity to the rotor
12. Embodiments of such approaches are illustrated with respect to FIGS. 3-8, and
9
may be used in lieu of, or in combination with, the embodiment illustrated in FIG. 2.
Specifically, FIG. 3 depicts a cryostat 50 having a flat surface 52 that is configured to
be placed against the yoke 28 or other supporting structure. The cryostat 50 also
includes a curved surface 54, which may be configured to allow the coils 22 inside the
cryostat 50 to be disposed radially around the circumference of the rotor 12.
[0036] FIG. 4 depicts the arrangement of the coils 22, which may have constant
perimeter end windings, or other winding configurations which fit closely on a
cylindrical surface, so as to allow more penetration of the magnetic field into the
permanent magnets 14. An assembly 60 having the superconducting magnetizer
assembly 18, the rotor 12, and the curved cryostat 50 is depicted in FIG. 5. As may
be appreciated, the cryostat 50 is placed against the circumferential bounds of the
rotor 12 so as to allow the coils 22 to be disposed in a close-spaced relationship. It
should be noted that in the embodiment depicted in FIGS. 3-5, the cryostat 50 allows
the yoke 28 to be constructed from a single piece having the annular opening 20
configured to receive the rotor 12.
[0037] An embodiment of a similar approach is depicted in FIG. 6, which
illustrates a dished cryostat 70 having flat surfaces 72 bounding either side of a recess
74 within the cryostat 70. The recess 74 may be considered a dish that is formed so as
to receive a portion of the rotor 12 therein. The placement of the coils 22 in the
dished cryostat 70 is illustrated in FIG. 7, which shows the long section of the coil 22
as being at least as long as the length of the recess 74. Moreover, the width of the end
section 32 of the coil 22 is at least as large as the width of the recess 74. Such spatial
relationships may allow effective magnetic field penetration into the permanent
magnets 14 by the coils 22 in combination with the approach described with respect to
FIG. 2.
[0038] FIG. 8 depicts an embodiment of an assembly 80 using the dished cryostat
70. As illustrated, when placed over the rotor 12, each of the cryostats 70 has the flat
surfaces 72 extending over the rotor 12, which is disposed within the respective
recesses 74 of each of the cryostats 70. In the illustrated embodiment, the assembly
80 includes a yoke 82 formed from a plurality of sections 84. Each section 84 is
10
configured to receive one cryostat 70 each, although in other embodiments each
section 84 may include more than one cryostat 70. The yoke 82 of the assembly 80
may require such sections 84 due to the manner in which each of the cryostats 70
interface with the rotor 12. For example, each of the sections 84 may be removed and
replaced in the directions depicted by arrows 86.
[0039] As noted above, another approach to improving the efficiency of the
magnetization of the permanent magnets 14 is to vary the magnetic circuit by
changing geometries, arrangements, and/or magnetic materials. Such embodiments
are illustrated with respect to FIGS. 9-12. FIGS. 9 and 10 depict embodiments where
the yoke is retained, and FIGS. 11 and 12 depict embodiments where the yoke is not
present. Again, in some embodiments, certain magnetic materials may be replaced
with others.
[0040] One such embodiment of an assembly 90 is depicted in FIG. 9, which has
the same geometric configuration as the assembly 10 of FIG. 1. In the embodiment of
FIG. 9, the assembly 10 has a yoke 92 that is constructed from permendur, which is
an alloy of cobalt and iron. By replacing the iron yoke with the permedur yoke 92,
the magnetizing field normal to the surface of the coil packs 26, the peak magnetic
fields produced by the racetrack coils 22, and the operating margin is varied. As an
example, the minimum magnetizing fields produced by the racetrack coils 22 may be
increased, but the maximum magnetizing fields may be decreased. Peak magnetic
field on the superconducting element may also be decreased, along with improving
the operating margin of the superconductor.
[0041] In the embodiment illustrated in FIG. 10, an assembly 110 includes a
permendur yoke 112 having a thinner profile than the yokes of the embodiments
described above. Additionally, the yoke 112 includes a series of block protrusions
114 that are disposed proximate the center of each of a set of widened coil packs
116116. In the assembly 110, the magnetizing field normal to the surface of the coil
packs 116 and the peak magnetic fields produced by the racetrack coils 22 decrease
compared to assembly 100, but the operating margin increases, for example by over
11
25% (e.g., from an operating margin of about 15% to an operating margin of about
19%), compared to assembly 100.
[0042] As noted above, FIGS. 11 and 12 illustrate embodiments wherein the yoke
is not included in the assembly. It should be noted that when no external yoke is
used, other features, such as a support stand or similar structure may be included so as
to balance the radial forces produced by the superconducting magnets. Specifically,
FIG. 11 illustrates an assembly 120 having a similar configuration to that of the
assembly 110 illustrated in FIG. 10, but not having the thin profile yoke 112.
However, it will be appreciated that the permendur blocks 114 are maintained within
the assembly 120, for example using other support structures. In the assembly 120,
the magnetizing field normal to the surface of the coil packs 116 and the peak
magnetic fields produced by the racetrack coils 22 decrease compared to assembly
110, and the operating margin increases, for example by about 5% (e.g., from an
operating margin of about 19% to an operating margin of about 20%), compared to
assembly 110.
[0043] FIG. 12 depicts an embodiment of an assembly 130 wherein the permendur
blocks 114 of assembly 120 are removed, and a set of permendur blocks 132 are
placed towards the end windings of the coil packs 116. Placing the permendur blocks
132 in such a location may reduce the peak magnetic field at the racetrack coils 22.
Indeed, in the assembly 130, the magnetizing field normal to the surface of the coil
packs 116 and the peak magnetic fields produced by the racetrack coils 22 decrease
compared to assembly 120, with the operating margin remaining about the same as
the assembly 120.
[0044] While varying the geometry and/or magnetic materials present within the
superconducting magnetizer assembly may have certain advantages, it may be
desirable to increase the number of magnetizing poles within the magnetic circuit.
For example, by increasing the number of magnetizing poles (i.e., increasing the
number of coil packs), it may be possible to decrease the total number of operations
required to magnetize a rotor. Further, in having a larger number of magnetizing
12
features, the magnetization efficiency may increase. Such embodiments are
illustrated diagrammatically in FIGS. 13-15.
[0045] Specifically, FIG. 13 illustrates an assembly 140 having six coil packs 26,
each having racetrack coils 22 (with end spacers 40) so as to generate six sets of
magnetic fields, one for each of the six pairs of permanent magnets 14. It will be
appreciated that when magnetization is performed using the assembly 140 illustrated
in FIG. 13, that only one operation may be required to fully magnetize the rotor 12.
Additionally, as illustrated, the assembly 140 includes the iron yoke 28 to improve
magnetization efficiency, reduce stray magnetic fields, and balance radial forces. In
the assembly 140, the magnetizing field normal to the surface of the coil packs 26 and
the peak magnetic fields produced by the racetrack coils 22 may be much higher
compared to the assemblies described with respect to FIGS. 1 and 9-12. However,
operating margin decreases greatly, for example by over 400% (e.g., from an
operating margin of about 13% to an operating margin of about 3%), compared to
assembly 10.
[0046] FIG. 14 illustrates an assembly 150 having a series of six coil packs 152
including the coils 22 and end spacers 40 for magnetizing each pole in one operation.
The assembly 150 does not have an external yoke, but includes internal iron yokes
154 that are internal to the coil packs 152 so as to improve magnetization efficiency
and reduce the peak fields at each coil 22. For the assembly 150, both the
magnetizing field and the peak field decrease as compared to assembly 140, with
operating margin increasing when compared to the same.
[0047] FIG. 15 illustrates an embodiment of an assembly 160 having features
similar to those of assemblies 140 and 150 of FIGS. 13 and 14, respectively.
Specifically, assembly 160 includes the coil packs 152 having the internal iron yoke
154 so as to control peak field and improve magnetization efficiency. Additionally,
the assembly 160 includes the external iron yoke 28, which may balance radial forces
as well as further reduce peak fields and improve magnetization efficiency. Indeed,
when compared to assembly 150, assembly 160 has increased magnetization
efficiency, reduced peak field, and increased operating margin.
13
[0048] It should be noted that the utilization of a high field wind and react (or react
and wind) superconductor, for example NbsSn, in all of the coil packs may be
prohibitive from a logistical and cost standpoint. For example, NbaSn coils require
features to offset the forces resulting from the large electromagnetic interactions.
Accordingly, it may be desirable to incorporate features into the embodiments
described above so as to mitigate such concerns. One such approach is to incorporate
other superconducting materials, such as niobium-titanium (NbsTi), vanadium gallium
(VaGa), and so forth, into the assemblies described herein. Accordingly, FIGS. 16-18
illustrate embodiments wherein at least two different types of superconducting
materials are incorporated into the magnetizing assembly.
[0049] FIG. 16 illustrates an embodiment of an assembly 170 having NbsSn coil
packs 172 having NbsSn racetrack coils 174 and end spacers 40 interleaved with
NbsTi coil packs 176 having NbTi racetrack coils 178. It should be noted that in
order to facilitate discussion, each coil pack is illustrated as a cross-section. While the
NbTi coils 178 do not perform any substantial magnetization of the permanent
magnets 14 as the NbsSn coils 174 do, this efficiently minimizes the use of high field
wind and react superconductors in the overall assembly, so that magnetic efficiencies
and peak field reductions may be achieved similar to those exhibited by the
embodiments illustrated in FIGS. 13-15. However, rather than being able to
magnetize all of the magnetic poles in one operation as with assemblies 140, 150, and
160, two operations must be performed for the assembly 170, wherein three of the
pairs of permanent magnets 14 are magnetized, followed by rotation and
magnetization (i.e., re-energizing the coils).
[0050] In another embodiment, which is illustrated as assembly 180 of FIG. 17,
rather than interleaving the coils, two of the sets of NbsSn coils 174 may be disposed
proximate one another, with the other four sets of coils being the NbsTi coils 178.
The assembly 180 therefore has one main magnetizing circuit, which is formed by
combining the two sets of NbsSn coils 174 in a single cryostat 182. Because the
NbsSn coils 174 are disposed proximate one another, the main magnetizing circuit
magnetizes two pairs of the permanent magnets 14 at once. Accordingly, three
operations are required to magnetize all of the permanent magnets 14 in the
14
embodiment depicted in FIG. 17. In a similar manner to the NbsSn coils 174, the
NbTi coils 178 may be combined into a single cryostat 184. Such an arrangement is
generally configured to increase the inter coil pack distance to help offset inter coil
pack forces.
[0051] To further reduce the amount of NbsSn that is utilized, it may be possible to
hybridize the coils, wherein a single coil pack includes both NbTi coils and NbsSn
coils. Such an embodiment is illustrated with respect to FIG. 18. Specifically, FIG.
18 illustrates an assembly 190 having a main magnetization cryostat 192, and four
separate NbTi coil packs 176 each having NbTi coils 178. The main magnetization
cryostat 192 houses two hybrid coil sets 194 having both NbsSn coils and NbTi coils.
Specifically, as shown in the expansion, the NbsSn coils are employed in the inner,
high field section 198 and the NbTi are employed in the outer, lower field section
200. Such an arrangement allows the NbsSn coils to have maximum proximity to the
permanent magnets that are being magnetized, which allows for complete local
magnetic saturation of two pairs of the permanent magnets 14. In the illustrated
embodiment, the NbsSn coils are stepped in to allow more volume for force
containment resulting from coil interactions. Optionally, the non-conductive end
spacer 40 may be used to further reduce peak fields.
[0052] Technical effects of the invention include lower running costs of the
superconducting system, a smaller footprint than conventional magnetizers, and the
ability to be deployed without the requirement of special facilities for operation (due
to the lower power requirements). Moreover, the present embodiments lead to higher
magnetization throughput than a conventional system. The embodiments describe
herein may be modular, such as by using the separate coil packs described above,
which allows components to be replaced as needed. Additionally, a greater
percentage of magnetization of permanent magnets may allow more robust and longer
lifetime magnetically-driven equipment, such as turbines, brakes, bearings, and so
forth.
15
[0053] 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. It should also be understood that the various examples
disclosed herein may have features that can be combined with those of other examples
or embodiments disclosed herein. That is, the present examples are presented in such
as way as to simplify explanation but may also be combined one with another. 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.
16
10 magnetizing assembly
12 rotor
14 as-formed permanent magnets
16 bulk
18 superconducting magnetizer assembly
20 annular opening
22 superconducting coils
24 cryostat
26 form coil packs
28 yoke
30 openings
32 end winding section
34 long section
40 non-conductive end spacer
42 outer coil
44 inner coil
50 cryostat
52 flat surface
54 curved surface
60 assembly
70 dished cryostat
72 flat surfaces
74 recess
80 assembly
82 yoke
84 sections
86 arrows
90 assembly
92 yoke
110 assembly
9o
112 permendur yoke
114 block protrusions
116 coil packs
100 Magnetizing assembly
120 Magnetizing assembly
130 Magnetizing assembly
132 permendur blocks
140 Magnetizing assembly
150 Magnetizing assembly
152 six coil packs
154 internal iron yokes
160 Magnetizing assembly
170 Magnetizing assembly
172 Nb3Sn coil packs
174 Nb3Sn racetrack coils
176 Nb3Ti coil packs
178 NbTi racetrack coils
180 Magnetizing assembly
182 single cryostat
184 single cryostat
190 Magnetizing assembly
192 main magnetization cryostat
194 hybrid coil sets
198 high field section
200 lower field section

CLAIMS:
1. A superconducting magnetizer assembly (18), comprising:
a coil pack, comprising:
an inner coil (44) comprising a first superconducting magnet material, the
coil being configured to generate a first magnetic field in response to an electric
current supplied to the coil;
an outer coil (42) comprising a second superconducting magnet material,
the outer coil (42) being disposed about the inner coil (44) and being configured to
generate a second magnetic field in response to an electric current supplied to the
outer coil (42); and
a container configured to house the inner and the outer coils (42, 44).
2. The assembly of claim 1, comprising a yoke (28) disposed proximate the
coil pack being configured to constrain the first and second magnetic fields to reduce
the strength of the first field at an end winding (32) of the inner coil (44).
3. The assembly of claim 2, wherein the yoke (28) is disposed within the coil
pack.
4. The assembly of claim 2, wherein the yoke (28) comprises iron or
permendur.
5. The assembly of claim 2, wherein the yoke (28) comprises an annular ring
configured to at least partially envelop the coil pack.
6. The assembly of claim 1, wherein the first superconducting magnet
material and the second superconducting magnet material are the same.
7. The assembly of claim 1, wherein the first superconducting magnet
material is different fi-om the second superconducting magnet material, and the first
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superconducting magnet material has a higher critical current where the magnetic
field is stronger than the second superconducting magnet material.
8. The assembly of claim 1, wherein the container is a cryogenic container
configured to maintain the inner and the outer coils (42, 44) at a set temperature, and
the container is curved so as to radially interface with the surface of an annular rotor
(12), wherein the curved surface (54) runs at least partially along the length of the
container.
9. The assembly of claim 1, comprising addifional coil packs (26) having
respective coils with superconducting magnet materials, the coils being configured to
generate respective magnetic fields in response to an electrical current applied to the
additional coils.
10. The assembly of claim 9, comprising an annular shaped yoke (28)
configured to receive the coil pack and the additional coil packs (26), the coil packs
(26) being disposed radially about an inner circumference of the yoke (28) and
forming an annular opening (20) configured to receive a cylindrical rotor (12) having
one or more permanent magnets (14), and the coils of the coil packs (26) are
configured to provide approximately 100% saturation of the permanent magnets (14)
with a magnetization field formed by the first and second magnetic fields generated
by each of the coils.
11. The assembly of claim 9, wherein the respective superconducting
magnet materials of at least one of the additional coil packs (26) is different than the
first or the second superconducting magnet material.
12. The assembly of claim 1, wherein the coil pack comprises a nonconductive
end spacer (40) disposed between an end winding (32) of the inner coil
(44) and an end winding (32) of the outer coil (42).
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13. A cryogenic container configured for use with a magnetizer assembly
(18), comprising:
a chamber configured to house a superconducting magnet coil wound into a
racetrack shape and to maintain the coil at a set temperature; and
a curved outer surface enclosing the chamber and configured to radially
interface with the surface of an annular member having one or more materials
susceptible to magnetization.
14. The cryogenic container of claim 13, wherein the curved outer surface
is bounded by flat surfaces (52) to form a dished surface configured to partially
enclose the annular member.
15. The cryogenic container of claim 13, wherein the curved outer surface
runs the entire length of the container.
16. A superconducting magnetizer assembly, substantially as herein
described with reference to accompanying drawings and example.
17. The cryogenic container, substantially as herein described with
reference to accompanying drawings and example.