U.S. patent application number 10/885509 was filed with the patent office on 2005-04-14 for rotor assembly.
This patent application is currently assigned to American Superconductor Corporation. Invention is credited to Bushko, Dariusz Antoni, Kaveh, Mehdi, Madura, David D., Perez, Alexander, Voccio, John P..
Application Number | 20050077797 10/885509 |
Document ID | / |
Family ID | 32594986 |
Filed Date | 2005-04-14 |
United States Patent
Application |
20050077797 |
Kind Code |
A1 |
Bushko, Dariusz Antoni ; et
al. |
April 14, 2005 |
Rotor assembly
Abstract
A rotor assembly includes a substantially cylindrical support
structure having at least one first region, and at least one second
region. At least one rotor coil is positioned within each first
region of the substantially cylindrical support structure. Each
rotor coil includes a pair of distal end portions and a convex
center portion, and the average mechanical density of the convex
center portion is substantially equal to the average mechanical
density of the distal end portions. The average mechanical density
of the at least one first region is substantially equal to the
average mechanical density of the at least one second region.
Inventors: |
Bushko, Dariusz Antoni;
(Hopkinton, MA) ; Kaveh, Mehdi; (Westborough,
MA) ; Voccio, John P.; (West Newton, MA) ;
Madura, David D.; (Ashland, MA) ; Perez,
Alexander; (Framingham, MA) |
Correspondence
Address: |
FISH & RICHARDSON PC
225 FRANKLIN ST
BOSTON
MA
02110
US
|
Assignee: |
American Superconductor
Corporation
Westborough
MA
|
Family ID: |
32594986 |
Appl. No.: |
10/885509 |
Filed: |
July 6, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10885509 |
Jul 6, 2004 |
|
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10367125 |
Feb 14, 2003 |
|
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6759781 |
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Current U.S.
Class: |
310/208 ;
310/261.1 |
Current CPC
Class: |
Y02E 40/60 20130101;
H02K 3/47 20130101; H02K 55/04 20130101; Y02E 40/625 20130101 |
Class at
Publication: |
310/208 ;
310/261 |
International
Class: |
H02K 017/00; H02K
023/26; H02K 003/04 |
Claims
1. A coil comprising: a pair of distal end portions; and a center
portion positioned between the pair of distal portions, the average
mechanical density of the center portion being substantially equal
to the average mechanical density of the distal end portions.
2. The coil of claim 1 wherein the center portion has a convex
shape.
3. The coil of claim 1 further comprising a mandrel positioned
within an interior region of the coil.
4. The coil of claim 3 wherein the mandrel occupies a portion of
the interior region of the coil and is constructed of a material
having a mechanical density that is greater than the average
mechanical density of the first and second regions.
5. The coil of claim 4 wherein the mandrel includes removed
portions.
6. The coil of claim 3 wherein the mandrel occupies the interior
region of the coil and is constructed of a material having a
mechanical density that is substantially equal to the average
mechanical density of the first and second regions.
7. The coil of claim 6 wherein the mandrel includes removed
portions.
8. The coil of claim 3 wherein the mandrel is constructed of a
material chosen from the group consisting of stainless steel,
aluminum, phenolic, and copper.
9. The coil of claim 3 wherein the mandrel includes a pair of
distal end portions spaced by a pair of convex center portions.
10. The coil of claim 9 wherein the periphery of the distal end
portions of the mandrel are defined by a first radius, and the
periphery of the convex center portions of the mandrel are defined
by a second radius that is larger than the first radius.
11. The coil of claim 3 wherein the mandrel is an elliptical
mandrel.
12. The coil of claim 1 wherein the coil is a racetrack-type
coil.
13. The rotor of claim 1 wherein the coil is a saddle-type
coil.
14. The coil of claim 11 wherein the saddle-type coil is configured
such that the lines of magnetic flux produced by the saddle-type
coil are perpendicular with a surface of the substantially
cylindrical support structure and radially aligned toward an axial
centerline of the rotor assembly.
15. The coil of claim 1 wherein the coil is a superconducting
coil.
16. The coil of claim 15 wherein the superconducting coil includes
one or more high temperature superconducting windings.
17. The coil of claim 1 wherein the coil is a rotor coil.
Description
RELATED APPLICATIONS
[0001] This application is a continuation and claims the benefit of
priority under 35 USC 120 of U.S. application Ser. No. 10/367,125,
filed Mar. 10, 2003. The disclosure of the prior application is
considered part of (and is incorporated by reference in) the
disclosure of this application.
[0002] The following applications are hereby incorporated by
reference into the subject application as if set forth herein in
full: (1) U.S. Pat. No. 5,777,420, issued Jul. 7, 1998, entitled
"Superconducting Synchronous Motor Construction" (Atty. Docket No.
05770-044001/AMSC-169); (2) U.S. Pat. No. 6,489,701, issued Dec. 3,
2002, entitled "Superconducting Rotating Machine" (Atty. Docket No.
05770-099001/AMSC-438); (3) U.S. Pat. No. 6,420,842, issued Jul.
16, 2002, entitled "Exciter and Electronic Regulator for Rotating
Machinery" (Atty. Docket No. 05770-101001/AMSC-424); (4) U.S.
application Ser. No. 09/480,397, filed Jan. 11, 2000, entitled
"Stator Construction For Superconducting Rotating Machines" (Atty.
Docket No. 05770-102001/AMSC-445); (5) U.S. application Ser. No.
09/481,480, filed Jan. 11, 2000, entitled "Internal Support for
Superconducting Wires" (Atty. Docket No. 05770-105001/AMSC-448);
(6) U.S. application Ser. No. 60/266,319, filed Jan. 11, 2000,
entitled "HTS Superconducting Rotating Machine" (Atty. Docket No.
05770-106001/AMSC-450); (7) U.S. Pat. No. 6,347,522, issued Feb.
19, 2002, entitled "Cooling System for HTS Machines" (Atty. Docket
No. 05770-108001/AMSC-456); (8) U.S. Pat. No. 6,359,365, issued
Mar. 19, 2002, entitled "Superconducting Synchronous Machine Field
Winding Protection" (Atty. Docket No. 05770-112001/AMSC-458); (9)
U.S. application Ser. No. 09/632,600, filed Aug. 4, 2000, entitled
"Exciter For Superconducting Rotating Machinery" (Atty. Docket No.
05770-121001/AMSC-487); (10) U.S. application Ser. No. 09/632,602,
filed Aug. 4, 2000, entitled "Segmented Rotor Assembly For
Superconducting Rotating Machines" (Atty. Docket No.
05770-123001/AMSC-490); (11) U.S. application Ser. No. 09/632,601,
filed Aug. 4, 2000, entitled "Stator Support Assembly For
Superconducting Rotating Machines" (Atty. Docket No.
05770-124001/AMSC-491); (12) U.S. application Ser. No. 09/905,611,
filed Jul. 13, 2001, entitled "Enhancement of Stator Leakage
Inductance in Air-Core Machines" (Atty. Docket No.
05770-158001/AMSC-544); (13) U.S. application Ser. No. 09/956,328,
filed Sep. 19, 2001, entitled "Axially-Expandable EM Shield" (Atty.
Docket No. 05770-168001/AMSC-597); (14) U.S. application Ser. No.
10/083,025, filed Feb. 26, 2002, entitled "Tangential Torque
Support" (Atty. Docket No. 05770-150001/AMSC-528); (15) U.S.
application Ser. No. 09/909,412, filed Jul. 19, 2001, entitled
"Torque Transmission Assembly For Use In Superconducting Rotating
Machines" (Atty. Docket No. 05770-154001/AMSC-537); (16) U.S. Pat.
No. 6,376,943, issued Apr. 23, 2002, entitled "Superconductor Rotor
Cooling System" (Atty. Docket No. 05770-062001/AMSC-286); and (17)
U.S. application Ser. No. 10/128,535, filed Apr. 23, 2002, entitled
"Superconductor Rotor Cooling System" (Atty. Docket No.
05770-062002/AMSC-286).
TECHNICAL FIELD
[0003] This invention relates to rotating machines.
BACKGROUND
[0004] Rotating machines typically include a stationary stator
assembly and a rotor assembly that rotates within the stator
assembly. The rotor assembly, which is typically cylindrical in
shape, includes rotor coils that, during operation, are
magnetically linked with armature coils incorporated into the
stator assembly. During operation, the stator assembly generates a
rotating magnetic field, resulting in the rotation of the rotor
assembly. Or, if the rotor assembly is driven by an external
machine, the rotating field assembly generates voltages and
currents in the stationary stator assembly. As the rotor assembly
rotates, it is subjected to radial centrifugal forces that may
result in radial distortion of the rotor assembly.
SUMMARY
[0005] According to an aspect of this invention, a rotor assembly
includes a substantially cylindrical support structure having at
least one first region, and at least one second region. The rotor
assembly further includes at least one rotor coil positioned within
each first region of the substantially cylindrical support
structure, with each rotor coil including a pair of distal end
portions and a convex center portion, wherein the average
mechanical density of the convex center portion is substantially
equal to the average mechanical density of the distal end portions.
Further, the average mechanical density of the first region is
substantially equal to the average mechanical density of the second
region.
[0006] One or more of the following features may also be included.
One or more of the rotor coils includes a mandrel positioned within
an interior region of the rotor coil. The mandrel may occupy a
portion of the interior region of the rotor coil and is constructed
of a material (e.g., stainless steel, copper, aluminum, phenolic,
etc.) having a mechanical density that is greater than the average
mechanical density of the first and second regions. The mandrel may
occupy the interior region of the rotor coil and is constructed of
a material (e.g., stainless steel, copper, aluminum, phenolic,
etc.) having a mechanical density that is substantially equal to
the average mechanical density of the first and second regions.
[0007] The mandrel includes a pair of distal end portions spaced by
a pair of convex center portions. The periphery of the distal end
portions of the mandrel may be defined by a first radius and the
periphery of the convex center portions of the mandrel may be
defined by a second radius, such that the second radius is larger
than the first radius. Alternatively, the mandrel may be elliptical
in shape.
[0008] One or more of the second regions may include a member that
occupies a portion of the second region and has a mechanical
density that is greater than the average mechanical density of the
first and second regions. Alternatively, one or more of the second
regions may include a member that occupies the second region and
has a mechanical density that is substantially equal to the average
mechanical density of the first and second regions. These members
may be constructed of stainless steel, copper, aluminum, phenolic,
etc.
[0009] The rotor coils (e.g., racetrack-type or saddle-type coils)
may be superconducting coils and include one or more high
temperature superconducting windings. These rotor coils, which may
or may not be cryogenically cooled, generate a magnetic flux path
within the rotor assembly during operation. The substantially
cylindrical support structure may define an internal volume that
houses a magnetic material having high saturation flux density,
which is positioned within at least a portion of the flux path and
decreases the overall reluctance of the flux path generated by the
rotor coils. This magnetic material within the internal volume may
or may not be cryogenically cooled. The conductors within the rotor
coil may be wound such that the lines of magnetic flux produced by
the rotor coil proximate the convex center portions of the mandrel
are essentially radially aligned toward an axial center of the
rotor assembly.
[0010] The saddle-type coil may be configured such that the lines
of magnetic flux produced by the saddle-type coil are perpendicular
with a surface of the substantially cylindrical support structure
and radially aligned toward an axial centerline of the rotor
assembly.
[0011] One or more advantages can be provided from the above
aspects of the invention. The use of a convex or elliptical mandrel
results in rotor coils that have consistent mechanical densities.
Further, by matching the average mechanical density of the mandrel
to that of the rotor coil, rotor performance can be enhanced.
Additional enhancement can be obtained by matching the density of
the filler material to that of the rotor coil/mandrel combination.
By matching the density of the various components of the rotor
assembly, the high speed operation of the rotor can be enhanced, as
radial distortion due to centrifugal forces is reduced.
Additionally, the use of a magnetic core within the cylindrical
support structure of the rotor can enhance magnetic performance by
reducing reluctance.
[0012] The details of one or more embodiments of the invention are
set forth in the accompanying drawings and the description below.
Other features, objects, and advantages of the invention will be
apparent from the description and drawings, and from the
claims.
DESCRIPTION OF DRAWINGS
[0013] FIG. 1 is an cross-sectional view of a rotating machine;
[0014] FIG. 2 is an isometric view of a portion of the rotor
assembly of the rotating machine of FIG. 1;
[0015] FIG. 3 is an isometric view of a rotor coil and mandrel of
the rotating machine of FIG. 1;
[0016] FIG. 4 is an plan view of the filler material of the
rotating machine of FIG. 1;
[0017] FIG. 5 is a diagrammatic representation illustrating the
flux paths in the rotating machine of FIG. 1;
[0018] FIG. 6 is a plot diagram showing the magnetic field
distribution within the rotor assembly of the rotating machine of
FIG. 1;
[0019] FIG. 7 is an alternative embodiment of the rotor coil of the
rotating machine of FIG. 1; and
[0020] FIG. 8 is a cross-sectional view of an alternative
embodiment of the rotor coil and mandrel of FIG. 3.
[0021] Like reference symbols in the various drawings indicate like
elements.
DETAILED DESCRIPTION
[0022] Referring to FIG. 1, a rotating machine 10 includes a stator
assembly 12 and a rotor assembly 14 having, in this embodiment, a
four pole topology. Rotor assembly 14 rotates within stator
assembly 12 and, in this four pole configuration, includes four
diametrically-opposed rotor coils 16, 17, 18, 19 (only two of which
are shown in this figure), which are mounted on a support structure
20, which is substantially cylindrical. The construction and
configuration of rotor coils 16, 18, which have substantially equal
average mechanical densities, will be discussed below in greater
detail. By setting these mechanical densities so that they are
substantially equal, non-uniform, radial distortion (or
ovalization) of the cylindrical support structure 20 can be
reduced.
[0023] Rotor assembly 14 includes a support member 22 attached to
an output shaft 24, which is supported by a pair of bearing plates
26, 28, one at each end of rotor assembly 14. Support member 22 is
typically fabricated from a high-strength, ductile, and
non-magnetic material (e.g., stainless steel, copper, aluminum,
phenolic, etc.). A torque tube 30 connects support member 22 to one
of the two end plates 32, 34 of rotor assembly 14, thus
establishing a torque path between support structure 20 and output
shaft 24. The details of one embodiment of torque tube 30 are
described in U.S. application Ser. No. 09/909,412, filed Jul. 19,
2001, entitled "Torque Transmission Assembly For Use In
Superconducting Rotating Machines" (Atty. Docket No.
05770-154001/AMSC-537).
[0024] A vacuum chamber sleeve 36 surrounds the rotor coils 16, 18
and support structure 20. The ends of vacuum chamber sleeve 36 are
connected to end plates 32, 34. Typically, vacuum chamber sleeve 36
is relatively thin (e.g., {fraction (3/16)}") and is constructed of
stainless steel. When vacuum chamber sleeve 36 is connected to the
end plates, an air-tight chamber is formed which encloses the rotor
coils 16, 18. This air-tight chamber may be evacuated, thus forming
a vacuum within the chamber. This helps to insulate the cooler
rotor coils 16, 18 from the warmer output shaft 24.
[0025] Stator assembly 12 includes an armature winding 38 (e.g., a
three phase stator winding) that is surrounded by an
electromagnetic shield 40. Electromagnetic shield 40 is typically
constructed of a non-magnetic material, such as copper, aluminum,
phenolic, or stainless steel.
[0026] In the case of a synchronous motor, during operation of
rotating machine 10, a voltage source (not shown, e.g., a
generator, a utility line, etc.) provides a supply voltage to
armature winding 38. Field energy is applied to rotor coils 16, 18.
The field energy is typically a DC current, as rotor coils 16, 18
require a DC current to generate the magnetic field (and the
magnetic flux) needed to link the rotor assembly 14 and the stator
assembly 12. However, if the field energy applied to rotor coils
16, 18 is an AC current, a rectifier/thyristor circuit (not shown)
is employed to convert the AC current into a DC current.
[0027] Rotor coils 16, 18 may be non-superconducting windings
(e.g., copper windings) or HTS (High Temperature Superconductor)
windings. Examples of HTS conductors are:
thallium-barium-calcium-copper-oxide;
bismuth-strontium-calcium-copper-oxide;
mercury-barium-calcium-copper-oxi- de; yttrium-barium-copper-oxide,
and magnesium diboride.
[0028] As superconducting conductors only achieve their
superconducting characteristics when operating at low temperatures
(e.g., <100 Kelvin.), if such superconducting conductors are
employed, rotating machine 10 includes a cryogenic cooler (not
shown), which maintains the operating temperature of rotor coils
16, 18 at an operating temperature sufficiently low to enable the
conductors to exhibit their superconducting characteristics. The
details of embodiments of the cryogenic cooler (not shown) are
described in: U.S. Pat. No. 6,347,522, issued Feb. 19, 2002,
entitled "Cooling System for HTS Machines" (Atty. Docket No.
05770-108001/AMSC-456); U.S. Pat. No. 6,376,943, issued Apr. 23,
2002, entitled "Superconductor Rotor Cooling System" (Atty. Docket
No. 05770-062001/AMSC-286); and U.S. application Ser. No.
10/128,535, filed Apr. 23, 2002, entitled "Superconductor Rotor
Cooling System" (Atty. Docket No. 05770-062002/AMSC-286).
[0029] Referring also to FIG. 2; a rotor support structure 20,
which is typically constructed of stainless steel is included, upon
which are disposed rotor coils and filler material that define two
regions. The first of the regions 42 receives rotor coils (i.e.,
"coil" regions), and the second of the regions 44 do not receive
rotor coils (i.e., "filler" regions). The rotor coils and filler
material are conformed to the shape of the rotor support structure.
For this particular four pole embodiment, four rotor coils are
included in rotor assembly 14. Therefore, rotor support structure
20 is divided into eight regions, four "coil" regions (one for each
rotor coil), and four "filler" regions positioned between the four
coil regions. Typically the material from which the "filler"
regions are fabricated is referred to as filler material, as it
fills the space or gap between the rotor coils.
[0030] Referring also to FIG. 3, two rotor coils 16, 18 (of the
four rotor coils included in rotor assembly 14) each include a pair
of distal end portions 46, 48 and a convex center portion 50. When
rotor coils 16, 18 (which are typically saddle-type coils) are
constructed, a conductor 52 (either superconducting or
non-superconducting) is repeatedly wound around a mandrel (e.g.,
mandrel 54). Accordingly, mandrel 54 (which is typically
constructed of stainless steel, copper, aluminum, phenolic, etc.)
determines the final shape of the rotor coil, e.g., rotor coil
16.
[0031] Mandrel 54 includes a pair of distal end portions 56, 58
(one defining the top and one defining the bottom of mandrel 54)
and a pair of convex center portions 60, 61 (one defining each side
of mandrel 54). Accordingly, when the conductor 52 is wound around
mandrel 54, the final shape of the rotor coils is determined by the
mandrel 54 around which the conductor 52 is wound. The convex
center portions 60, 61 of mandrel 54 has curved edges 62, 64 that
are not parallel with each other and actually bulge out in the
middle, such that the width of the middle of the pair of convex
center portions is wider than the pair of convex center portions at
either the top or bottom (i.e., where the pair of convex center
portions 60, 61 abuts distal end portions 56, 58). The pair of
convex center portions 60, 61 have a large radius of curvature
(e.g., 50-100 inches), which is selected based on the stiffness of
the conductor, the size of the coil, and/or the mechanical
properties of the insulation system. The dimensions of the mandrel
vary depending on the particular application and design on the
machine. For a particular embodiment of machine 10, the mandrel is
twelve inches long and eight inches wide, and the variation in
width along the convex center portions of the mandrel is
approximately one inch.
[0032] When conductor 52 is repeatedly wound around mandrel 54, the
rotor coil 16, 18 is formed, such that the cross-section of any
portion of this rotor coil includes numerous cross sections of
conductor 52, due to the conductor being repeatedly looped around
the mandrel. When forming rotor coils 16, 18, the number of times
that conductor 52 is wound around mandrel 54 varies depending on
the design and application of machine 10. For a particular
embodiment of machine 10, conductor 52 is wound around mandrel 54
one-hundred-eighty times.
[0033] When conductor 52 is wound around the distal end portions of
mandrel 54, the conductor loop is compressed such that the
individual loops of the conductor within the rotor coil are
compressed together. The amount of compression is inversely
proportional to the radius of curvature of the mandrel. As the
periphery of the distal end portions 56, 58 of mandrel 54 are
defined by a smaller radius than the periphery of the convex center
portions 60, 61, the level of compression experienced by the
conductor proximate the distal end portions 56, 58 of mandrel 54 is
greater than the level of compression experienced by the conductors
proximate the convex center portions 60, 61. In one particular
embodiment of the rotor coil, the compression level of the
conductors proximate the distal end portions 56, 58 may be as high
as 2.0 lb/in.sup.2 (for a mandrel with distal end portions having a
5" radius), while the compression level of the conductors proximate
the convex center portions 60, 61 may be 0.20 lb/in.sup.2.
[0034] This type of coil/mandrel configuration will provide an
essentially uniform average turn thickness around the coils and,
hence, improve the mechanical properties of the rotor coils.
Additionally, this coil/mandrel configuration minimizes variations
in tilt of the conductor, thus improving the repeatability of the
coil thickness. Further, this configuration reduces the requirement
for vertical clamping during coil fabrication and provides for
lower cost mold equipment. Also, this configuration increases the
area enclosed by the coil for a given external coil envelope, thus
increasing coil dipole moment (and the torque produced). In short,
this configuration allows for faster and less expensive coil
fabrication, while improving coil performance.
[0035] By using convex center portions 60, 61, as opposed to center
portions having parallel sides, the level of compression
experienced by the conductors proximate the convex center portions
60, 61 is enhanced, as the tension of the conductor that is wound
around the mandrel is converted to a compressive force in which the
conductors are compressed radially toward the center of the mandrel
54. Accordingly, due to the use of convex center portions 60, 61,
the variation in compression of the conductors looped around the
mandrel is reduced, resulting in the distal end portions 46, 48 and
convex center portion 50 of the rotor coil having substantially
equal mechanical densities. For a particular embodiment of the
rotor coil, the average mechanical density is 0.20 pounds per cubic
inch (for glass conductor insulation) and 0.22 pounds per cubic
inch (for paper conductor insulation).
[0036] By substantially equalizing the mechanical density of the
various portions of the rotor coils 16, 18, the rotation of rotor
assembly 14 will have an equal effect on all portions of the rotor
coils. For example, in a high-revolution, four-pole, 60-hertz
application (such as a generator), the rotor assembly spins at
3,600 rpm. As this rotor assembly 14 spins, the various components
of the rotor assembly are subjected to centrifugal forces that vary
based on the density of these rotor assembly components. Therefore,
by equalizing the density of the portions 46, 48, 50 of the rotor
coils 16, 18, the centrifugal forces acting on these portions are
also equalized, resulting in these components (i.e., rotor coils
16, 18) of the rotor assembly 14 being balanced, and the
non-uniform radial distortion of the rotor assembly 14 being
reduced.
[0037] By matching the mechanical density of the rotor coil 16, 18
to the mechanical density of the mandrel 54, the rotor assembly can
be further balanced and its performance further enhanced.
Specifically, if the mandrel has a higher density than the rotor
coil surrounding it, during operation, the mandrel is subjected to
greater centrifugal forces than the lower density rotor coil.
Accordingly, non-uniform, radial distortion (or ovalization)
occurs, as the mandrel is radially pulled away from the axis of
rotation of the rotor assembly at a greater rate than the rotor
coil surrounding it.
[0038] There are several ways to match the mandrel density to that
of the average density of the rotor coil. The mandrel 54 may be
constructed of a material that has a density substantially equal to
the average density of the rotor coil. For example, if the average
mechanical density of the rotor coil is 0.20 pounds per cubic inch,
the mandrel can be constructed from a material having a
substantially equal mechanical density.
[0039] If such a material is not available, a higher density
material (e.g., stainless steel, copper, aluminum, phenolic, etc.)
may be used, provided the material is processed to lower its
average mechanical density. For example, if the mandrel is going to
be constructed of stainless steel having a mechanical density of
0.30 pounds per cubic inch, the mandrel can be machined so that, on
average, one third of the material of the mandrel is removed. This
can be accomplished by machining holes 66, 68, 70 and/or slots 72,
74 into the mandrel, such that the surface area of mandrel 54 is
reduced by the appropriate percentage. For example, if the desired
mandrel density is 0.20 lbs./inch.sup.3 and the actual mandrel
density is 0.30 lbs./inch.sup.3, the actual density of the mandrel
is 50% greater than required. Therefore, when machining in the
holes and/or slots into the mandrel, the holes and/or slots should
occupy one-third of the mandrel's surface area. When machining
these holes and/or slots, their size should be kept to a minimum
and spatial frequency kept to a maximum to homogenize the density
distribution throughout the mandrel. A typical example of the size
and spatial frequency of these holes is one-half inch diameter
holes on two inch centers.
[0040] An alternative way of reducing the density of the mandrel is
to reduce the thickness of the mandrel by the requisite amount.
Accordingly, if the mandrel was reduced in thickness by one third,
the same net result would be achieved, as the average density of
the mandrel would be reduced by one-third.
[0041] As stated above, rotor support structure 20 is divided into
two types of regions, "coil" regions 42 and "filler" regions 44,
such that the "coil" regions 42 receive one or more rotor coils and
the "filler" regions 44 receive a filler material (e.g., stainless
steel, copper, aluminum, phenolic, etc.) that fills the space or
gap between the rotor coils (i.e., the "coil" regions 42).
Referring also to FIG. 4, filler material 76 is typically a
substantially hour-glass shaped piece of stainless steel that is
rolled to the appropriate radius of rotor support structure 20, so
as to accommodate the shape of the rotor coils and the support
structure.
[0042] Rotor assembly 14 may be further balanced and performance
further enhanced by matching the mechanical density of the filler
material 76 (i.e., the "filler" region) to that of the rotor coil
16, 18 and mandrel 54. As explained above, if the filler material
76 has a higher mechanical density than the rotor coil/mandrel
combination, during operation, the filler material 76 is subjected
to greater centrifugal forces than the lower density rotor
coil/mandrel combination. Accordingly, non-uniform, radial
distortion (or ovalization) occurs, as the filler material 76 is
radially pulled away from the axis of rotation of rotor assembly 14
at a greater rate than the rotor coil/mandrel combination. As with
the mandrel 54, there are several ways to match the filler material
mechanical density to that of the average mechanical density of the
rotor coil/mandrel combination.
[0043] The filler material 76 may be constructed of a material that
has a density substantially equal to the average density of the
rotor coil/mandrel combination. Alternatively, a higher density
material, such as stainless steel, copper, aluminum, or phenolic,
may be used, provided the material is machined to lower its average
mechanical density. As explained above, this may be accomplished
by, for example, machining holes 78, 80, 82 and/or slots 84, 86 in
filler material 76, such that the surface area of the filler
material is reduced by the appropriate percentage. When machining
these holes and/or slots, their size should be kept to a minimum
and spatial frequency kept to a maximum to homogenize the density
distribution throughout the filler material. A typical example of
the size and spatial frequency of these holes is one-half inch
diameter holes on two inch centers.
[0044] An alternative way of reducing the density of the filler
material 76 is to reduce its thickness by the requisite amount.
Accordingly, if the density of the filler material needs to be
reduced by one-third, the thickness of the filler material 76 could
be reduced by one-third and the required mechanical density
reduction would be achieved.
[0045] While armature winding 38 is described above as a
three-phase armature winding, other configurations are possible.
For example, armature winding 38 may be a single-phase armature
winding.
[0046] While the mandrel 54 is described above as having a pair of
distal end portion 56, 58 having a first radius and a pair of
convex center portions 60, 61 having a second radius, other
configuration are possible. For example, mandrel 54 may be
elliptical in shape and, therefore, have a continually varying
radius.
[0047] While support member 22 is described above as being
fabricated of a non-magnetic material (e.g., aluminum), support
member 22 may be constructed of a magnetic material (e.g., iron).
Referring also to FIG. 5, in an alternative embodiment, support
member is an iron core 22' formed from a series of stacked
laminations. The stacked laminations, which may or may not be
cooled by the cryogenic cooler, are placed within the inner volume
of the cylindrical support structure 20. The torque tube 30 is then
allowed to cool so that the tube shrinks around the laminations,
capturing the laminations in a compressed state within the tube.
Torque tube 30 may also be "shrink welded" to preload the torque
tube around the iron core.
[0048] Although a solid iron core may be used, a stacked set of
laminations is preferable so that if one of the laminations cracks,
the crack is isolated to that lamination and will not propagate to
neighboring laminations. Cracking in the iron core can be a serious
concern if the non-ductile iron core is cryogenically cooled along
with the rotor coils 16, 17, 18, 19. At cryogenically-low
temperatures, the brittleness characteristic of the iron is
increased. In order to increase the ductile strength of the
laminated structure in the radial direction, reinforcing layers
(e.g., fiberglass or stainless steel) may be placed between the
laminations. The laminations and reinforcing layers can then be
impregnated with, for example, epoxy.
[0049] The positioning the iron core 22' within the torque tube
provides significant advantages in the operation of the rotating
machine 10. When positioning iron core 22', the rotor coils should
be positioned in close radial proximity to iron core 22'. In order
to appreciate these advantages, a simplistic representation of the
flux paths generated by each of the rotor coils superconducting
windings is shown. One of the four flux paths corresponding to the
upper left-hand quadrant, starts at a point 88 in the iron core
22', extends in a path 90 running generally parallel with axis 92
until it encounters the back iron member 94 which provides a low
impedance path. At this point, the flux path extends
counterclockwise through the back iron member and, then back along
a path 96 parallel to axis 98 toward point 88 to close the loop.
The flux paths for the remaining quadrants extend away from the
iron core, through the back iron member and back to the iron core
in similar fashion.
[0050] It is apparent from FIG. 5 that a significant portion of the
flux path passes through the iron core 22' positioned within the
inner volume of the support structure 20. Because iron is a high
saturation flux density material (i.e., approximately 2.0 Tesla),
it acts, in a sense, as a magnetic short circuit so as to reduce
the overall reluctance of the flux path and increase the amount of
flux generated for a given number of ampere-turns of the windings.
Thus, a lower-loss magnetic circuit is provided resulting in a more
efficient motor.
[0051] Referring also to FIG. 6, a plot showing the magnetic field
distribution within the rotor assembly 14 shows the increased flux
flowing through the iron core 22'.
[0052] While rotor coils 16, 18 are described above as including a
convex center portion 50, other configurations are possible. For
example, the center portion may have parallel sides and, therefore,
the center portion would be rectangular in shape, as opposed to
convex.
[0053] While rotor coils 16, 18 are described above as being
saddle-type coils, other configurations are possible, such as the
racetrack-type rotor coil configuration 100 shown in FIG. 7.
Racetrack-type coil 100 is typically constructed of several coil
windings (e.g., windings 102, 104, 106) that are stacked on top of
each other.
[0054] Referring also to FIG. 8, there is shown a cross-sectional
view of an alternative embodiment of the rotor coil 16' in which
the conductor 52 used to wind the rotor coil is wound around a
mandrel 54', such that the periphery of the convex center portions
60', 61' of the mandrel 54' is perpendicular to the surface 108 of
the rotor support structure 20. Accordingly, the individual
conductors positioned proximate the convex center portions 60', 61'
of the mandrel 54' are perpendicular to the surface 108 of the
rotor support structure 20. As conductors 52 have a rectangular
cross-sectional shape, the broad face of the conductor 52 is also
positioned perpendicular to the surface 108 of the rotor support
structure 20. Accordingly, this rotor coil configuration radially
aligns (i.e., toward the axial centerline of the rotor assembly)
the lines of magnetic flux (e.g., flux lines 110, 112, 114)
produced by the individual conductors wound around the mandrel 54',
as the lines of magnetic flux are parallel with the broad face of
conductor 52. By radially aligning the line of magnetic flux so
that the flux lines perpendicularly strike iron core 22, magnetic
efficiency is enhanced. Additionally, as this coil configuration
produces a rotor coil having a convex exterior surface 116, the
rotor coil can be positioned tightly against the rotor support
structure. Further, the concave interior surface 118 of this
configuration of the rotor coil allows it to be positioned in close
proximately with iron core 22.
[0055] A number of embodiments of the invention have been
described. Nevertheless, it will be understood that various
modifications may be made without departing from the spirit and
scope of the invention. Accordingly, other embodiments are within
the scope of the following claims.
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