BACKGROUND OF THE INVENTION
The present invention relates generally to a super-conducting coil in a synchronous
rotating machine. More particularly, the present invention relates to a cryogenic gas
coupling between a source of cryogenic fluid and the rotor of the machine.
Synchronous electrical machines having field coil windings include, but are not
limited to, rotary generators, rotary motors, and linear motors. These machines
generally comprise a slalor and rolor that are eleciromagneiically coupled The rotor
may include a multi-pole rotor core and coil windings mounted on the rotor core. The
rotor cores may include a magnetically-permeable solid material, such as an iron-core
rotor.
Conventional copper windings are commonly used in the rotors of synchronous
electrical machines. However, the electrical resistance of copper windings (although
low by conventional measures) is sufficient to contribute to substantial heating of the
rotor and to diminish the power efficiency of the machine. Recently, super-
conducting (SC) coil windings have been developed for rotors. SC windings have
effectively no resistance and are highly advantageous rotor coil windings.
Iron-core rotors saturate at an air-gap magnetic field strength of about 2 Tesla.
Known super-conductive rotors employ air-core designs, with no iron in the rotor, to
achieve air-gap magnetic fields of 3 Tesla or higher, which increase the power density
of the electrical machine and result in significant reduction in weight and size. Air-
core super-conductive rotors, however require large amounts of super-conducting
wire, which adds to the number of coils required, the complexity of the coil supports,
and the cost.
High temperature SC coil field windings are formed of super-conducting materials
that are brittle, and must be cooled to a temperature at or below a critical temperature,
e.g., 27°K, to achieve and maintain super-conductivity. The SC windings may be
formed of a high temperature super-conducting material, such as a BSCCO
(BixSrxCaxCuxOx) based conductor.
Super-conducting coils have been cooled by liquid helium. After passing through the
coil windings of the rotor, the hot helium is returned from the windings as room-
temperature gaseous helium. Using liquid helium for cryogenic cooling requires
continuous reliquefaction of the returned room-temperature gaseous helium. This
reliquefaction poses significant reliability problems and requires significant auxiliary
power for cryorefrigeration.
Prior cooling techniques include cooling an epoxy-impregnated SC coil through a
solid conduction path from a cryocooler. Alternatively, cooling tubes in the rotor may
convey a liquid and/or gaseous cryogen to a porous SC coil winding that is immersed
in the flow of the liquid and/or gaseous cryogen. Immersion cooling requires the
entire field winding and rotor structure to be at cryogenic temperature, as a result no
iron can be used in the rotor magnetic circuit because of the brittle nature of iron at
cryogenic temperatures.
A cooling fluid coupling is needed to connect the stationary cryorefrigeration unit to
the rotor and its SC coils. The coupling must transfer inlet and outlet cooling fluid
between a stationary source and the rotating end shaft of a rotor Contact seals are
commonly used in transfer couplings for cryogenic cooling systems connected to
rotors and other rotating components. Contact seals have increased rrictional losses
that degrade cryorefrigerator capacity, and limit the lite and reliability of the coupling
because of seal wear. Relative motion gap seals have also been used in transferring
cooling fluid to a rotor. However, relative motion gap seals have high heat transfer
losses. Extended thermal standoff lengths for the relative motion gaps have been used
to reduce heat transfer losses to the cryogenic gas and to improve cryorefrigerator
capacity. However, these long thermal standoff lengths result in long overhung tubes
that may vibrate excessively and come into rubbing contact with the rotor of the
generator. Accordingly, there is a long-felt need for better cryogenic gas couplings
with a rotor.
Heat transfer losses with respect to the cryogenic gas cooling system for the HTS
coils should preferably be minimized to conserve refrigeration power. The coupling
between the stationary cryogenic gas source and the rotor of the synchronous machine
is a potential source of cryogenic gas leakage. To minimize gas leakage at the
coupling, it is desirable that the leakage between the inlet and return gas streams be
minimized, and that adequate thermal insulation be provided between the cryogentic
gas and surrounding ambient temperature components. In addition, the operational
life and high reliability of the transfer coupling should be commensurate to the
expected life and reliability of the synchronous electrical machine.
BRIEF SUMMARY OF THE INVENTION
A cooling gas coupling has been developed to connect a supply of cryogenic gas (or
cooling fluid) to the shaft of a rotor in a synchronous electrical machine. Cooled
cryogenic gas (orother fluid) is transferred from a stationary cryorefrigerator through
a stationary bayonet to a tube rotating with the rotor having a HTS coil winding. The
"cooling gas transfer occurs using a cryogenic gas transfer joint attached to the
collector end of the rotor. A relative motion gap created with a clearance seal about a
bayonet coupling limits leakage of the inlet cooling gas to the lower pressure return
gas, and a relative motion gap over a length of the rotating return tube provides
thermal insulation to the return cryogenic gas.
In a first embodiment, the invention is a cooling fluid coupling for providing cooling
fluid to a rotor having a super-conducting winding of a synchronous machine and a
source of cryogenic cooling fluid. The fluid coupling comprises an inlet cooling tube
and an outlet cooling tube in the rotor and coaxial with an axis of the rotor. The inlet
cooling tube has an input port coupled to receive inlet-cooling fluid from the source of
cryogenic cooling fluid. The outlet cooling tube has an output port coupled to return
cooling fluid from the rotor to source. A rotating, motion gap seal separates the input
port and output port of the coupling.
In another embodiment, the invention is a cooling fluid coupling between a rotor for a
synchronous machine and a source of cryogenic cooling fluid. The coupling
comprises: (i) a rotating inlet cooling tube and a rotating outlet cooling tube in the
rotor and coaxial with an axis of the rotor; (ii) the inlet cooling tube is coupled to
receive inlet cooling fluid from the source of cryogenic cooling fluid; (iii) the outlet
cooling tube is coupled to return cooling fluid from the rotor to source, and (iv) a
rotating motion gap seal supports the inlet cooling tube in the outlet cooling tube.
In a further embodiment, the invention is a cooling fluid coupling between a rotor for
a synchronous machine and a source of cryogenic cooling fluid. This coupling
comprises: (i) a rotating inlet cooling tube and a rotating outlet cooling tube in the
rotor and coaxial with an axis of the rotor; (ii) the inlet cooling tube is coupled to
receive inlet cooling fluid from the source of cryogenic cooling fluid; (iii) the outlet
cooling tube is coupled to return cooling fluid from the rotor to source; (iv) a rotating
non-contact motion gap seal supporting the inlet cooling tube in the outlet cooling
tube; (v) a stationary third tube encircling the outlet cooling tube and said third tube
supported by a bearing, and (vi) a magnetic field seal supporting the outlet cooling
tube in the stationary third tube.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings in conjunction with the text of this specification describe
an embodiment of the invention.
FIGURE 1 is a schematic side elevational view of a synchronous electrical machine
having a super-conductive rotor and a stator.
FIGURE 2 is a schematic diagram of a racetrack SC coil having cooling gas passages.
FIGURE 3 is a schematic diagram with a partially cut-away view of a rotor having a
racetrack SC coil winding;
FIGURES 4 and 5 are cross-sectional diagrams of a rotor having a racetrack SC coil
winding and end shafts;
FIGURE 6, 7 and 8 show cross-sectional diagrams of the collector end shaft of the
rotor.
FIGURE 9 is a schematic cross-sectional view of a cryogenic gas transfer coupling
assembly.
DETAILED DESCRIPTION OF THE INVENTION
FIGURE 1 shows an exemplary synchronous generator machine 10 having a stator 12
and a rotor 14. The rotor includes field winding coils 34 that fit inside a cylindrical
vacuum cavity 16 of the stator. The rotor fits inside the vacuum cylindrical cavity of
the stator. As the rotor turns within the stator, a magnetic field 18 (shown by dotted
lines) generated by the rotor and rotor coils moves through the stator and creates an
electrical current in the windings of the stator coils 19. This current is output by the
generator as electrical power.
The rotor 14 has a generally longitudinally-extending axis 20 and a generally solid
rotor core 22. The solid core 22 has high magnetic permeability and is usually made
of a ferromagnetic material, such as iron. In a low power density super-conducting
machine, the iron core of the rotor is used to reduce the magnetomotive force (MMF),
and, thus, minimize the coil winding usage. For example, the iron of the rotor can be
magnetically saturated at an air-gap magnetic field strength of about 2 Tesla.
The rotor 14 supports a generally a longitudinally-extending, racetrack-shaped high
temperature super-conducting (HTS) coil winding 34. HTS coil winding may be
alternatively a saddle-shape coil or have some other coil winding shape that is suitable
for a particular HTS rotor design. The cooling coupling disclosed here may be
adapted for coil winding and rotor configurations other than a racetrack coil mounted
on a solid core rotor.
The rotor includes a pair of end shafts 24, 30 that bracket the core 22 and are
supported by bearings 25. The collector end shaft 24 includes a collector rings 35 for
electrically connecting to the rotating SC coil winding. The collector end shaft has a
eryogen transfer coupling 26 to a source of cryogenic cooling fluid used to cool the
SC coil windings in the rotor. The cryogen transfer coupling 26 includes a stationary
segment coupled to a source of cryogen cooling fluid and a rotating segment which
provides cooling fluid to the HTS coil. The drive end shaft 30 may be driven by a
power turbine via drive coupling 32.
FIGURE 2 shows an exemplary HTS racetrack SC field winding 34. The SC field
winding 34 of the rotor includes a high temperature super-conducting coil 36. Each
HTS coil includes a high temperature super-conducting conductor, such as a BSCCO
(BixSrxCaxCuxOx) conductor wires laminated in a solid epoxy impregnated winding
composite tape. For example, a series of BSCCO 2223 wires may be laminated,
bonded together and wound into a solid epoxy impregnated coil.
The SC coil is typically layer wound SC tape that is epoxy impregnated. The SC tape
is wrapped in a precision coil form to attain close dimensional tolerances. The tape is
wound around in a helix to form the racetrack SC coil 36.
The dimensions of the racetrack coil are dependent on the dimensions of the rotor
core. Generally, each racetrack SC coil encircles the magnetic poles of the rotor core,
and is parallel to the rotor axis. The coil windings are continuous around the
racetrack. The SC coils form a resistance free electrical current path around the rotor
core and between the magnetic poles of the core. The coil has electrical contacts 37
that electrically connect the coil to the collector 35.
Fluid passages 38 for cryogenic cooling fluid are included in the coil winding 34.
These passages may extend around an outside edge of the SC coil 36. The
passageways provide cryogenic cooling fluid to the coil and remove heat from the
coil. The cooling fluid, e.g., helium, maintains the low temperatures, e.g., 27°K, in
the SC coil winding needed to promote super-conductive conditions, including the
absence of electrical resistance in the coil. The cooling passages have an input port
39 and an output port 41 at one end of the rotor core. These ports connect to the
cooling passages 38 on the SC coil and to the cryogen transfer coupling 26 at an
opposite end of the end shaft 24.
the coil winding 34 in the rotor. While one tension rod and channel housing is shown,
the coil support system will generally include a series of tension rods that each have
coil support housings at both ends of the rod. The tension rods and channel housings
prevent damage to the coil winding during rotor operation, support the coil winding
with respect to centrifugal and other forces, and provide a protective shield for the
coil winding.
The HTS coil winding and structural support components are at cryogenic
temperature. In contrast, the rotor core is at ambient "hot" temperature. The coil
supports are potential sources of thermal conduction that would allow heat to reach
the IITS coils from the rotor core. The rotor becomes hot during operation. As the
coils are to be held in super-cooled conditions, heat conduction into the coils is to be
avoided. The rods extend through conduits 46 in the rotor but are not in contact with
the rotor. This lack of contact reduces the conduction of heat from the rotor to the
tension rods and coils.
To reduce the heat transfer to the coil, the coil support is minimized to reduce the
thermal conduction through support from heat sources such as the rotor core. There
are generally two categories of support for super-conducting winding: (i) "warm"
supports and (ii) "cold" supports. In a warm support, the supporting structures are
thermally isolated from the cooled SC windings. With warm supports, most of the
mechanical load of a super-conducting (SC) coil is supported by structural members
spanning from cold to warm members.
In a cold support system, the support system is at or near the cold cryogenic
temperature of the SC coils. In cold supports, most of the mechanical load of a SC
coil is supported by structural members which are at or near a cryogenic temperature.
The exemplary coil support system disclosed here is a cold support in that the tension
rods and associated housings that couple the tension rods to the SC coil windings are
maintained at or near a cryogenic temperature. Because the supporting members are
cold, these members are thermally isolated, e.g., by the non-contact conduits through
the rotor core, from other "hot" components of the rotor. Insulating tubes 52 separate
the tension rods 42 from the conduit walls in the rotor core. These tubes are inserted
into the ends of each conduit 42. The tension rods extend through the center of the
tube. The insulating tubes 52 center the tension rods in the conduits and prevent heat
from the hot rotor core from transferring to the cold tension rods.
An individual support member consists of a tension rod 42 (which may be a bar and a
pair of bolts at either end of the bar), a channel housing 44, and a dowel pin 80 that
connects the housing to the end of the tension rod. Each channel housing 44 is a U-
shaped bracket having legs that connect to a tension rod and a channel to receive the
coil winding 34. The U-shaped channel housing allows for the precise and convenient
assembly of the support system for the coil. A series of channel housings may be
positioned end-to-end along the side of the coil winding. The channel housings
collectively distribute the forces that act on the coil, e.g., centrifugal forces, over
substantially the entire side sections 40 of each coil.
The dowel pin 80 extends through apertures in the channel housing and tension rod.
The dowel may be hollow for low weight. Locking nuts 84 are threaded or attached
at the ends of the dowel pin to secure the housing 44 and prevent the sides of the
housing from spreading apart under load. The dowel pin can be made of high strength
Inconel or titanium alloys. The tension rods are made with larger diameter ends 82
that are machined with two flats 86 at their ends to fit the coil housing and coil width.
The flat ends 86 of the tension rods abut the inside surface of the HTS coils, when the
rod, coil and housing are assembled together. This coil support assembly reduces the
stress concentration at the hole in the tension rod that receives the dowel.
The rotor core 22 is typically made of magnetic material such as iron, while the rotor
end shafts are typically made of non-magnetic material such as stainless steel. The
end shafts 24, 30 may be formed of stainless steel. The rotor core and end shafts are
typically discrete components that are assembled and securely joined together by
either bolting or welding.
The iron rotor core 22 has a generally cylindrical shape suitable for rotation within the
rotor cavity 16 of the stator 12. To receive the coil winding 34, the rotor core has
recessed surfaces 48, such as flat or triangular regions or slots. These surfaces 48 are
formed in the curved surface of the cylindrical core and extending longitudinally
across the rotor core. The coil winding 34 is mounted on the rotor adjacent the
recessed areas 48. The coils generally extend longitudinally along an outer surface of
the recessed area and around the ends of the rotor core. The recessed surfaces 48 of
the rotor core receive the coil winding. The shape of the recessed area conforms to
the coil winding. For example, if the coil winding has a saddle-shape or some other
shape, the recess(es) in the rotor core would be configured to receive the shape of the
winding.
The end sections 54 of the coil winding 34 are adjacent opposite ends 56 of the rotor
core. A split-clamp 58 holds each of the end sections of the coil windings in the rotor.
The split clamp at each coil end 54 includes a pair of opposite plates 60 between
which is sandwiched the coil winding 34. The surface of the clamp plates includes
channels to receive the coil winding and connections 112, 114 to the winding.
The split clamp 58 may be formed of a non-magnetic material, such as aluminum or
lnconel alloys. The same or similar non-magnetic materials may be used to form the
tension rods, channel housings and other portions of the coil support system. The coil
support system is preferably non-magnetic so as to preserve ductility at cryogenic
temperatures, since ferromagnetic materials become brittle at temperatures below the
Curie transition temperature and cannot be used as load carrying structures.
The split clamp 58 is surrounded by, but is not in contact with a collar 62 of each end
shaft. There is a collar 62 attached to both ends of the rotor core 22, although only-
one collar is shown in FIGURE 3. The collar is a thick disk of non-magnetic material,
such as stainless steel, the same as or similar to the material, that forms the rotor
shafts.
The collar has a slot 64 orthogonal to the rotor axis and sufficiently wide to receive
and clear the split clamp 58. The hot side-walls 66 of the slot collar are spaced apart
from the cold split clamp so they do not come in contact with each other.
FIGURES 4 and 5 are cross-sectional diagrams of the rotor, where FIGURE 5 shows
in plan view ihe coil winding around the rotor core, and Figure 4 shows a view
orthogonal to FIGURE 5. FIGURES 6, 7 and 8 are cross-sectional close-up diagrams
of the collector end shaft 24. In particular, these figures show a conduit tube 76
extending through the collector end shaft 24 of the rotor. This conduit 76 provides a
passageway for the cooling tubes and electrical contacts that connect to the SC
winding. The conduit 76 extends through the end shaft 24 from the collar 62 to the
opposite end of the shaft at the cooling coupling 26. FIGURES 6 and 7 show the
conduit 76 near the rotor core 22 and the end shaft 24. FIGURE 8 shows an enlarged
view of the cooling inlet and outlet ports 39, 41 that connect to the coil winding 38.
The electrical connections 37 from the coil winding 34 are connected to electrical
lines that extend the length of the end shaft 24 towards the collector ring 35. The
electrical lines extend through the conduit 76 in the shaft and are supported inside a
thin-walled tube 174.
The cooling inlet and outlet ports 39, 41 from the coil connect to the inlet and outlet
cooling tubes 156, 166 that extend the length of the end shaft. The inlet tube 156
extends to an inlet port 39 that is coaxial with the rotor axis. The cooling gas outlet
port 41 is offset from the rotor axis and couples through a gas transfer housing to an
annular outlet tube 166. The outlet tube 166 is coaxial with the inlet tube and external
to the inlet tube.
FIGURE 9 shows an exemplary transfer coupling 26 having rotating shaft
components 150 and stationary components 152 that surround the shaft components.
The transfer coupling connects the rotor end shaft 24 to a stationary source of
cryogenic cooling fluid used to cool the SC coil windings in the rotor.
Cold cryogenic gas is transferred from a stationary cryorefrigrator 190 (shown
schematically) through a stationary bayonet 154 to an inlet tube 156 rotating with the
rotor shaft 24. Right facing arrows 157 show the inlet cooling gas passing through the
coupling and flowing along the axis 20 of the rotor towards the UTS coils. The
bayonet is coaxial with the rotor axis 20. The end 158 of the bayonet provides a non-
contact seal with the inlet tube 156. The opposite end of the bayonet is connected to a
flexible tube 160 connected to cryorefrigrator and provides a source of the inlet
cooling Helium gas. A rotating relative motion gap seal 162 with a clearance seal
about the bayonet limits leakage of the inlet cooling gas to the lower pressure return
gas.
Hot cooling gas (shown by left facing arrows 164) flows in an annulus formed
between the cooling inlet tube 156 and a cooling outlet tube 166, which is coaxial
with the inlet tube. The hot cooling gas passes through the HTS coil windings and
removes heat from those windings.
The hot cooling gas exits the rotating outlet tube 166 and passes between the gap seal
162 and a stationary cylindrical casing 168 surrounding the gap seal An end disk 169
of the casing has an outlet port offset from the rotor axis that connects to the return
flexible tube 170 for transferring hot cryogenic gas from the rotor to the
cryorefrigerator 190. The hot cooling gas enters a flexible tube 170 that is connected
to the cryorefrigerator. The flexible tube is offset from the axis 20 of the rotor.
All cryogenic gas transfer tubes 156, 166 are vacuum jacketed 172 to minimize heat
transfer to the gas. The return gas stream 164 is thermally insulated from ambient
temperature by a length of thin wall tube 174 with a small relative motion gap
(between the thin wall tube 174 and the rotating vacuum jacketed tube 166) to
minimize convection heat transfer. Further thermal insulation is provided by a
vacuum applied to the gap between the thin wall tube 174 and cylindrical housing
186.
A magnetic fluid seal 176 at the end of the shaft 174 provides a non-contacting
positive sealing of the pressurized gas system. Air flow 177 is provided from an
external source to serve as a buffer that separates the oil of bearings 178 from the
magnetic fluid of the magnetic seal, so that the bearing oil cannot contact the
magnetic fluid.
The cryogenic gas transfer coupling 26 is supported on the rotor shaft by precision
bearings 178 that limit the overhung tube vibration and run out in order to prevent
rubbing of the seals and at the relative motion gaps. Oil jet nozzles 180 provide
lubricant for the bearings. An oil drain 182 allows for removal of old and excess
bearing oil. Labyrinth seals 184 prevent leakage of oil from the bearings.
A cylindrical housing 186 surrounds the bayonet end of the cooling transfer coupling
26 and the flexible tubes 160, 170. The housing is attached to a flexible cylindrical
bellows 188 connected to the cryorefrigerator 190. A vacuum is maintained within
the housing 186 to provide thermal insulation between ambient temperature and the
flexible tubes and gas transfer coupling.
The magnetic fluid seal 176 is encased in a cylindrical housing 196 and is sealed with
O-rings 198 with respect to the non-rotating components of the coupling 26 to prevent
leakage of the return gas.
The rotating tubes 156, 166 are thermally insulated from each other by a vacuum
jacket 172. The cooling gas inflow tube 156 is maintained separate from the gas
outflow by a stationary motion gap seal 162 (as well as the double walls of the inflow
gas tube 156 which are vacuum jacketed). Similarly, the double-walled outer rotating
tube (cooling outlet tube 166) is vacuum jacketed 172 and is further housed in a thin
wall stationary' tube 174. These inlet and outlet tubes 156, 166 extend from the
coupling to the inlet and outlet ports 39,41 of the HTS coil winding.
To provide gas flow sealing between the rotating and stationary components of the
coupling 26, non-contact clearance seals and magnetic fluid seals are used in
conjunction with precision bearings and short overhang tubes with narrow relative
motion gaps. These features of the gas transfer coupling 26 prevent frictional heating.
Such frictional heating occurs in contact sealing systems due to rubbing or vibration.
Other advantages of a non-contact scaling system arc long coupling life, high
reliability gas seals, and low thermal losses in the gas coupling.
In operation, the bayonet tube 154 of the transfer coupling 26 is coupled to a source of
cryogen cooling fluid via flexible tube 160. Similarly, the outlet tube 166 and casing
for gas seal 168 are coupled to the outlet flexible tube 170 The cryogenic seal
housing 186 is connected to the cylindrical housing of the transfer coupling 26.
Vacuums are established in the housing 186 and in the vacuum jackets 172 of the
rotating tubes.
The cooling gas is usually an inert gas, such as helium, neon or hydrogen.
Temperatures that are suitable for HTS super-conductors are generally below 30°K
and preferably around 27°K. Cryogen fluid exits the cryorefrigerator at a temperature
around 27°K. Cooling fluid (arrow 157) flows from the inlet flexible tube 160,
through the bayonet tube 154 and inlet tube 156 to the rotor and HTS coil winding 34.
The cooled cryogenic fluid passes through the conduits in the rotor and into the
cooling passages 38 of the HTS coil 36. The cooling gas removes heat from the HTS
coil and maintains the coil at a sufficiently low temperature to achieve super-
conducting characteristics of the coil. The cooling conduits have input and output
ports 39,41 at one end of the rotor core that connect to the cooling fluid coupling 26.
Heat transfer losses to the cryogenic gas are minimized to conserve refrigeration
power and maintain the low operating temperatures needed for the SC coil. Heat
losses are minimized by minimizing cooling fluid leakage and by minimizing heat
transfer to the cryogenic cooling fluid.
A relative motion gap seal 162 is created with a clearance seal about the bayonet tube
154 that limits the leakage of the inlet cryogenic gas (arrow 157) to the lower pressure
of the out-flowing return gas (arrow 164). Cooling fluid leakage has the effect of
transferring unwanted thermal energy into the cooling system. Thus, cooling fluid
leakage is reduced to increase the thermal insulation and total cooling efficiency of
the cryogenic cooling system 26.
In addition to cooling fluid leakage, a second source of thermal inefficiency is
conduction of heat from the surrounding components in the rotor. Adequate thermal
insulation is provided between the cryogenic cooling gas and the surrounding ambient
temperature components to minimize heat transfer to the cryogenic gas. For example,
the cryogenic gas transfer tubes 156, 166 are vacuum jacketed 172 to ensure high
thermal insulation.
Moreover, the return gas stream (arrows 164) is thermally insulated from ambient
temperature by thin wall tubes 174 and vacuum jacketed tube 166 with a small
relative motion gap (between the stationary tube 174 and rotating vacuum jacketed
tube 166} to minimize convection heat transfer. These thermal standoff lengths, e.g.,
vacuum jacketed gaps between tubes, of relative motion gaps reduce the heat transfer
to the cryogenic fluid and improve the capacity of the cryorefrigerator (by reducing
thermal losses). Long thermal standoff lengths can result in long overhung tubing that
vibrates excessively and may come into rubbing contact.
The cryogenic gas transfer coupling 26 support system is designed to reduce problems
associated with tube vibration. The coupling 26 is supported on the rotor shaft by
precision bearings 178 that limit overhung tube vibration and ran out.
While the invention has been described in connection with what is presently
considered to be the most practical and preferred embodiment, it is to be understood
that the invention is not to be limited to the disclosed embodiment, but on the
contrary, is intended to cover all embodiments within the spirit of the appended
claims.
WE CLAIM
1. A cooling fluid coupling (26) between a rotor (14) for a synchronous
machine (10) and a source of cryogenic cooling fluid (190) comprising:
a rotating inlet cooling tube (156) and a rotating outlet cooling tube (166)
in the rotor and coaxial with an axis (20) of the rotor.;
said inlet cooling tube (156) having an input port coupled to receive inlet
cooling fluid from the source of cryogenic cooling fluid (190).
Said outlet cooling tube having an output port coupled to return cooling
fluid from the rotor to source, and
a stationary motion gap sea (132) separating the input port and output
port.
2. A cooling fluid coupling as claimed in claim 1 comprising a magnetic fluid
seal (176).
3. A cooling fluid coupling as claimed in claim 1 comprising a vacuum jacket
(172) between the inlet cooling tube and the outlet cooling tube.
4. A cooling fluid coupling as claimed in claim 1 comprising a bayonet tube
(154) extending into the inlet cooling tube and said bayonet tube
connected to the source of cryogenic cooling fluid (190).
5. A cooling fluid coupling as claimed in claim 1 wherein the cryogenic
cooling fluid is helium gas.
6. A cooling fluid coupling as claimed in claim 1 comprising a flexible tube
(170) offset from an axis of the rotor coupled to outlet cooling tube and a
second flexible tube (160) adjacent to the first tube and connected to the
inlet cooling tube, wherein the second flexible tube is coaxial with the
rotor axis.
7. A cooling fluid coupling as claimed in claim 1 comprising a stationary tube
(152) surrounding and coaxial with the outlet cooling tube.
8. A cooling fluid coupling as claimed in claim 7 comprising vacuum jacket
(172) between the outlet cooling tube and the stationary tube.
9. A cooling fluid coupling as claimed in claim 7 comprising a bearing (178)
supporting the stationary tube.
10. A cooling fluid coupling as claimed in claim 7 comprising a bearing
supporting the stationary tube (152); a magnetic field seal (176)
supporting the outlet cooling tube in the stationary tube, and a rotating
motion gap seal supporting the inlet cooling tube in the outlet cooling
tube.
11.A cooling fluid coupling (26) between a rotor (14) for a synchronous
machine (10) and a source of cryogenic cooling fluid (190) comprising:
a rotating inlet cooling tube (156) and a rotating outlet cooling tube (166)
in the rotor and coaxial with an axis of the rotor;
said inlet cooling tube coupled to receive inlet cooling fluid from the
source of cryogenic cooling fluid;
said outlet cooling tube coupled to return cooling fluid from the rotor to
source;
a rotating non-contact motion gap seal supporting the inlet cooling tube in
the outlet cooling tube;
a third tube encircling the outlet cooling tube and said third tube
supported by a bearing (178); and
a magnetic field sea supporting the outlet cooling tube in the stationary
tube.
12. A cooling fluid coupling as claimed in claim 11 comprising a vacuum jacket
between the inlet cooling tube and the outlet cooling tube.
13. A cooling fluid coupling as claimed in claim 11 comprising a bayonet tube
extending into the inlet cooling tube, and said bayonet tube connected to
the source of cryogenic cooling fluid.
14.A cooling fluid coupling as claimed in claim 11 wherein the cryogenic
cooling fluid is helium gas.
15. A cooling fluid coupling as claimed in claim 11 comprising a flexible tube
offset from an axis of the rotor coupled to outlet cooling tube and a
second flexible tube adjacent to the first tube and connected to the inlet
cooling tube, wherein the second flexible tube is coaxial with the rotcr
axis.
16. A cooling fluid coupling as claimed in claim 11 comprising a vacuum jacket
between the third tube and the outlet cooling tube.
17.A cooling fluid coupling as claimed in claim 11 wherein the third tube is
stationary.
18. A cooling fluid coupling between a rotor for a synchronous machine and a
source of cryogenic cooling fluid comprising:
a rotating inlet cooling tube and a rotating outlet cooling tube in the rotor
and coaxial with an axis of the rotor;
said inlet cooling tube coupled to receive inlet cooling fluid from the
source of cryogenic cooling fluid;
said outlet cooling tube coupled to return cooling fluid from the rotor to
source;
a rotating non-contact stationary motion gap seal supporting the inlet
cooling tube in the outlet cooling tube;
a third tube encircling the outlet cooling tube and said third tube
supported by a bearing;
a magnetic fluid sea supporting the outlet cooling tube in the stationary
tube, and a flexible tube offset from an axis of the rotor coupled to outlet
cooling tube and a second flexible tube adjacent to the first tube and
connected to the inlet cooling tube, wherein the second flexible tube is
coaxial with the rotor axis.
19. A rotor (14) in a synchronous machine (10), the rotor comprising:
a rotor core (22) having at least one conduit (46) extending through the
core (21);
a superconductive coil winding (36) extending around at least a portion of
the rotor core (22), said coil winding (34) having a pair of side sections
(40) on opposite sides (56) of said rotor core (22);
at least one tension rod (42) extending between the pair of side sections
(40) of the coil winding (34) and through said at least one conduit (46) of
the rotor (14); and
an insulating tube (52) in the conduit (46) thermally separating the
tension rod (42) from the rotor (14).
20. A rotor as claimed in claim 19, wherein said insulating tube (52) has an
outside surface in contact with said conduit (46).
21. A rotor as claimed in claim 19, wherein said insulating tube (52) has an
inside surface in contact with an attachment on an end of said rod (42).
22. A rotor as claimed in claim 19, wherein the rotor core (22) is a solid core
and said conduit (46) extends through the solid core (22).
23.A rotor as claimed in claim 19, comprising an outside ring at one end of
the tube (52) in contact with the conduit (46), and an inside ring at an
opposite end of the tube (52) in contact with a lock-nut (84) at the end of
the rod (42).
24.A rotor as claimed in claim 19, wherein the insulating tube (52) is in the
conduit (46) and is adjacent an outside surface of the core (22).
25.A rotor as claimed in claim 19, comprising a locking-nut securing the
insulating tube (52) to the conduit (46) in the core (22).
26. A rotor as claimed in claim 19, wherein said tension rod (42) is formed of
a high-strength and non-metallic metal alloy.
27. A rotor as claimed in claim 19, wherein said tension rod (42) is formed of
an Inconel metal alloy.
28.A rotor as claimed in claim 19, wherein said tension rod (42) extends
through a longitudinal axis (20) of the rotor (22).
29. A rotor as claimed in claim 19, wherein each of said at least one tension
rod (42) extends through a separate conduit in said core (22), and said at
least one insulating tube (52) is mounted in each end of said conduit (46).
30. A rotor as claimed in claim 19, wherein said tension rod (42) is spaced
from rotor walls of the conduits (46) by said insulating tube (52).
31. A rotor as claimed in claim 19, comprising a coil housing at an end of said
tension rod (42), and wherein said housing is attached to said coil winding
(34) and is attached to said tension rod (42).

The invention relates to a cooling fluid coupling (26) between a rotor (14) for a synchronous machine (10) and a source of cryogenic cooling fluid (190) comprising a rotating inlet cooling tube (156) and a rotating outlet cooling tube (166) in the rotor and coaxial with an axis (20) of the rotor, said inlet cooling tube (156) having an input port coupled to receive inlet cooling fluid from the source of cryogenic cooling fluid (190). The outlet cooling tube having an output port coupled to return cooling fluid from the rotor to source, and a stationary motion gap sea (132) separating the input port and output port.