AN ASSEMBLY FOR HIGH TEMPERATURE SUPERCONDUCTING (HTS) SYNCHRONOUS MACHINE
FIELD OF THE INVENTION
[001] The present invention in general relates to the high temperature
superconducting synchronous machines. More specifically, the present
invention relates to high temperature superconducting (HTS)
synchronous machines including an air core stator and air core rotor surrounded by a magnetic shield.
BACKGROUND OF THE INVENTION
[002] Background description includes information that may be useful in
understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior.
[003] In general High temperature superconducting wire is being actively
developed for a wide use of applications including circuit breakers,
transmission lines, and magnetic energy storage. Another important application
is found in the manufacture
of high temperature superconducting (HTS) synchronous machines, in
which high temperature superconducting wire replaces the typical field windings of a conventional synchronous machine.
[004] Conventional synchronous machines have been available for decades,
and include, but are not limited to, rotary generators, rotary motors, and linear motors. These synchronous machines include an armature and a field coil that produces a magnetic field. The armature consists of a series of current loops in
the form of a coil that interacts with the magnetic flux produced by the field coil. Relative rotational motion between the armature and the field coil produces a generated voltage due to the rate of change of flux linkage in the armature coils. The power of such a machine is equal to the product of the generated voltage times the current in the armature coils.
[005] An example synchronous machine is an AC motor in which, at steady
state, the rotation of the shaft is synchronized with the frequency of the supply current. Synchronous machines generally include a stator and rotor that are electromagnetically coupled, and commonly rely on copper field windings. The electrical resistance of copper windings, although low by conventional measures, is sufficient to contribute to substantial heating of the rotor in a synchronous machine. This in turn diminishes the efficiency of the machine.
[006] Recently, superconducting (SC) field coil windings made of high
temperature superconducting wire have been developed for rotors. SC windings have effectively no resistance and are highly advantageous rotor coil windings.
[007] Nowadays, the High Temperature Superconducting (HTS) synchronous
machines are in demand as they are highly efficient, compact, lighter, low noise, high output power to weight ratio and better dynamic response machines as compared to conventional copper conductor based machines. In addition, HTS synchronous machines are used worldwide for various strategic and critical industrial applications, because of the above mentioned advantages. The successful development of HTS synchronous machine requires HTS, electrical, mechanical, cryogenic and vacuum technologies.
[008] Hence, there is need to develop a high temperature superconducting
(HTS) synchronous machine in which core losses are lesser than the existing one at higher frequencies.

OBJECTS OF THE INVENTION
[009] Some of the objects of the present invention, which at least one
embodiment herein satisfy, are listed herein below.
[010] It is general or primary object of the present invention is to develop a
high temperature superconducting (HTS) synchronous machine with air core stator and air core rotor surrounded by a magnetic shield.
[011] It is another object of the present invention is to develop a high
temperature superconducting (HTS) synchronous machine with air core stator having multi-layer multi-phase stator winding supported by a non-magnetic core fastened on a magnetic shield placed in a frame wherein the stator winding is cooled by a separate liquid cooling arrangement attached to stator frame.
[012] It is yet another object of the present invention is to develop a high
temperature superconducting (HTS) synchronous machine with two or higher even multiple (equal to number of poles in the motor) HTS pole coils placed in a rotating cryostat encapsulated in a ultra-high vacuum chamber equipped with drive end and non-drive end torque tubes attached to drive end and non-drive end hollow shafts respectively at each end of rotor assembly.
[013] It is another object of the present invention is to develop HTS
synchronous machine in which the HTS pole coils of the rotor are cryogenically cooled with helium gas in closed loop configuration facilitated by rotary coupling connected to a stationary cryocooler and stator winding is cooled by water or ethylene glycol or ethylene glycol water mixture circulated in a separate liquid cooling arrangement.
[014] It is yet another object of the present invention is to develop HTS
synchronous machine in which all the rotor support structure is made of non-magnetic stainless steel alloys such as SS316 or SS316L or SS316LN etc.

[015] It is yet another object of the present invention is to develop HTS
synchronous machine in which torque tubes made of high mechanical strength and high thermal resistivity material such as Kevlar-49 or G10 etc.
[016] It is yet another object of the present invention is to develop HTS
synchronous machine in which the HTS pole coils are made of high temperature superconducting material not limited to BSCCO or YBCO or ReBCO etc.
[017] It is yet another object of the present invention is to develop HTS
synchronous machine which can be operated as generator or motor or synchronous condenser with higher operating magnetic field inside the machine with zero tooth saturation and higher current density in the stator to achieve higher power density, higher torque density along with overall compact size and lesser weight.
[018] It is yet another object of the present invention is to develop HTS
synchronous machine with rotary coupling having combination of labyrinth seals and graphite seals backed up by ferro-fluid seals.
[019] It is yet another object of the present invention is to develop HTS
synchronous machine having HTS pole coils in rotor excited by a slip ring based arrangement or shaft mounted brushless exciter.
[020] It is further object of the present invention is to develop HTS
synchronous machine with lesser acoustic noise signature and lesser mechanical vibration due to round rotor geometry and absence of magnetic teeth.
[021] It is another object of the present invention is to develop HTS
synchronous machine with higher overload capacity, lesser synchronous reactance, better control and maneuverability.
[022] These and other objects and advantages will become more apparent
when reference is made to the following description and accompanying drawings.

SUMMARY OF THE INVENTION
[023] This summary is provided to introduce concepts related to a structure of
a high temperature superconducting (HTS) synchronous machine. The concepts are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
[024] In accordance with an embodiment , the present disclosure defines an
assembly for high temperature superconducting (HTS) synchronous machine, the assembly comprising a stator assembly having an air core stator including a multi-layer multi-phase stator winding supported by a non-magnetic core fastened on a magnetic shield placed inside a frame wherein the stator winding is cooled by a separate liquid cooling arrangement attached to a stator frame; and a rotor assembly having an air core rotor including plurality of HTS pole coils ,wherein the HTS pole coils being placed inside a rotating cryostat encapsulated in an ultra-high vacuum chamber equipped with drive end and non-drive end torque tubes attached to drive end and non-drive end hollow shafts respectively at each end of rotor assembly.
[025] In accordance with an aspect, the inner space of the stator assembly is
taken by the HTS rotor assembly after maintaining a physical air gap.
[026] In accordance with an aspect, the stator frame covered the stator-rotor
assembly through DE side end cover and NDE side end cover.
[027] In accordance with an aspect, the air core stator and the air core rotor
are surrounded by a magnetic shield made of material having high electrical resistivity and high magnetic permeability.
[028] In accordance with an aspect, the liquid coolant based cooling system
is provided on the bottom of the stator assembly.

[029] In accordance with an aspect, the cooling inside the stator is enabled by
fixed coolant inlet and outlet pipes placed inside the stator assembly.
[030] In accordance with an aspect, a plurality of stator coil being placed
inside a stator slots of the stator assembly.
[031] In accordance with an aspect, the drive end shaft and a non-drive end
shaft of the air core rotor being mounted over the drive end bearing and non-drive end bearing.
[032] In accordance with an aspect, the air core rotor is connected to the load
in case of motor mode operation through a flange provided on the drive end shaft.
[033] In accordance with an aspect, the rotor pole coil excitation system being
attached to the NDE of the shaft of the air core stator.
[034] In accordance with an aspect, the extreme end of NDE shaft being
attached with rotary coupling.
[035] In accordance with an aspect, the rotary coupling being attached with a
cryocooler.
[036] Various objects, features, aspects and advantages of the inventive
subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[001] FIG.1 represents a stator assembly of HTS synchronous machine in
accordance with the present disclosure.
[002] Fig. 2 represents the diamond shaped stator coil which are assembled in
the stator slots of the stator assembly in accordance with the present disclosure.

[003] FIG.3 represents the longitudinal view of the high temperature
superconducting rotor assembly in accordance with the present disclosure
[004] Fig.4 represents the rotor HTS pole coil placed inside the rotor assembly
in accordance with the present disclosure.
[005] Fig.5 represents the radial view of the high temperature
superconducting synchronous machine in accordance with the present
disclosure.
[006] Fig.6 represents the longitudinal section details of High Temperature
Superconducting (HTS) synchronous machine.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS
[007] The following is a detailed description of embodiments of the invention
depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the invention. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.
[037] The present invention focusses on providing the HTS synchronous
machine with higher overload capacity, lesser synchronous reactance, better control and maneuverability.
[008] FIG.1 represents a stator assembly 100 of high temperature
superconducting synchronous machine in accordance with a present disclosure. The stator assembly 100 comprises a stator 101, a stator winding 102, a stator winding support structure 105 and a magnetic iron shielding 106 also known as

back iron. The stator winding support structure is made of high mechanical strength non-magnetic material to avoid any magnetic teeth saturation issue. This non-magnetic stator winding support structure has non-magnetic teeth 104 and slots 103. The slots contain the combination of solid and hollow conductors 109 so as to achieve proper ventilation in the machine.
[009] The combination of liquid coolant and forced air cooling method is used
for better thermal management of the stator. The central slot area has air ventilation duct 114 and inter layer insulation 110 and the slot opening is closed after winding with wedge 111. The stator winding support structure can be made from single solid or sectors depending on the size of the machine. The back iron supports the stator winding support structure using several key 107 arrangements. There are series of through holes 108 in back iron.
[010] Some of which act as back iron support holes through which back iron
is stacked and assembled. Whereas the rest of the holes act as axial cooling ducts. The stator assembly is guided inside the stator frame so that outer surface 113 of the back iron allows further heat transfer. The inner space 112 of the stator assembly is occupied by the high temperature superconducting rotor.
[011] FIG.2 represents the diamond shaped stator coil 201 which are
assembled in the stator slots of the stator assembly 100 and connected in overhang portion to realize the stator winding. The stator coil 201 has two straight portions 202 electrically shorted at each end portions 203 called as overhang. Each stator coil has end electrical terminals 204 and coolant inlet 205 and outlet ports 206.
[012] FIG.3 represents the longitudinal view of the high temperature
superconducting rotor assembly 300 in accordance with the present disclosure.
[013] The rotor assembly 300 contains multiple high temperature
superconducting pole coils 302 encapsulated in a cryostat 303 of rotor 301. The pole coils placed in cryostat that are cryogenically cooled and maintained at

desired temperature. The cryogen inlet line 304 carries the cold cryogen whereas the outlet cryogen line 305 takes away the warm cryogen. Both ends of the pole coil support structure are fastened to torque tubes 306. The torque tubes are made of high thermal resistivity and high mechanical strength based material. The torque tubes connect cold pole coil support structure side 308 to room temperature shafts side 307.
[014] It also has a central flange 309 for anchoring of the radiation shield 310.
The HTS pole coils 302 has a cylindrical sleeve on the outermost side to create vacuum inside the rotor. This sleeve is called vacuum sleeve 311. The vacuum sleeve 311 is welded on the DE (Drive End) 314 and NDE (Non-Drive End) 312 hollow shafts to eliminate the possibilities of any leak. During operation, inside hollow space of the cryostat other than the cryogen flow path is maintained under ultra-high vacuum to reduce convective heat load on the rotating cryostat.
[015] The rotor assembly is also provided with DE (Drive End) 315 and NDE
(Non-Drive end) 313 bearings for enabling it to spin along its longitudinal axis. The hollow space provided in the DE shaft is utilized for instrumentation and vacuum, whereas the hollow space 316 in the NDE shaft is used to route cryogen piping assembly. The DE flange is also provided with a flange 317 to connect it to load. On NDE side of rotor shaft, there is a rotor pole coil excitation system 318 based on either slip rings or brushless exciter. The rightmost flange 319 on NDE side is provided with connections so as to connect the rotor to a rotary coupling.
[016] FIG.4 represents the rotor HTS pole coil 302 placed inside the rotor
assembly 300. The rotor HTS pole coil 302 has two straight portions 402 electrically connected by two circular overhangs 403. The final electrical terminals 404 are provided on the top and bottom surfaces of the pole coil.

[017] FIG.5 represents the radial view of the high temperature
superconducting synchronous machine 500. The stator assembly 100 along with stator winding 102, non-magnetic support structure and back iron are placed inside the stator frame 502. The stator slot 103 shown in FIG.1 carries multi-layer multi-phase winding made of copper or copper alloy or silver or silver alloy or copper silver alloy. The end connections of the stator winding 102 are routed at a terminal box 503 attached to outer surface of the frame. The central area of the slot has air ventilation duct 114. The gap between outer surface of back iron and inner surface of frame creates one or more axial ventilation duct 114.
[018] The stator winding 102 and back iron are cooled by a combination of
liquid coolant based cooling system 515 and forced air ventilation system. The liquid coolant based cooling system 515 is provided on the bottom of the stator frame 502. The stator frame 502 is placed on a mounting platform with the help of mounting legs 514 and lifting hooks 507. The inner space of the stator assembly 100 is taken by the HTS rotor assembly 300 by maintaining a physical airgap 508. The outer surface 509 of the rotor 301 looks like a cylindrical structure. The rotor 301 contains multiple high temperature superconducting pole coils 302 placed in pole coil housings 511. The rotor pole coils 302 along with its housings are fastened onto the cylindrical pole coil support structure 510. The hollow space 513 in the rotor 301 is occupied by ultra-high vacuum.
[019] FIG.6 represents the longitudinal section details of High Temperature
Superconducting (HTS) synchronous machine 500. The stator assembly 100 contains the stator winding 102, non-magnetic support structure and back iron. The stator winding 102 and back iron are cooled by a combination of liquid coolant based cooling system and forced air ventilation system. The liquid coolant based cooling system 515 is provided on the bottom of the stator frame 502. The cooling is enabled by fixed coolant inlet 605 and outlet 606 pipes. The

stator frame 502 is placed on a mounting platform 621 with the help of mounting legs 514 and lifting hooks 507. The stator frame 502 has two end covers viz. DE side end cover 609 and NDE side end cover 610 to close the complete stator-rotor assembly. The rotor is placed in the bore of the stator.
[020] The gap between stator 100 and rotor 300 is termed as physical air gap
508. The high temperature superconducting (HTS) rotor 301 looks like a rotating cryostat encapsulating all the HTS pole coils. The rotor pole coil support structure is fastened to DE (Drive-End) and NDE (Non-Drive End) shafts through torque tubes.
[021] Over DE (Drive-end) 314 and NDE (Non Drive-end) shafts 312, a
cylindrical vacuum sleeve 311 is welded. On each DE (Drive-end) and NDE (Non Drive-end) shafts, high surface finish steps are provided to place the DE (Drive-end) 315 and NDE (Non Drive-end) 313 bearings. The DE (Drive-End) and NDE (Non Drive-end) bearings 315,313 are each placed on DE and NDE bearing pedestals 615, 616. The DE shaft has a flange 317 for connecting it to the mechanical load. At NDE shaft, there is a rotor pole coil excitation system
318 (either slip-ring connection or brushless exciter) for feeding the current to HTS coils. The extreme end of NDE shaft 312 is provided with rotary coupling
319 which enables the flow of cryogen from cryocooler 620 to HTS coil and back to cryocooler 620.
TECHNICAL ADVANTAGES
[022] The present invention provides a high temperature superconducting
(HTS) synchronous machine with air core stator and air core rotor surrounded by a magnetic shield.
[023] The present invention provides a high temperature superconducting
(HTS) synchronous machine with air core stator having multi-layer multi-phase stator winding supported by a non-magnetic core fastened on a magnetic shield

placed in a frame wherein the stator winding is cooled by a separate liquid cooling arrangement attached to stator frame.
[024] The present invention provides a high temperature superconducting
(HTS) synchronous machine with two or higher even multiple (equal to number of poles in the motor) HTS pole coils placed in a rotating cryostat encapsulated in a ultra-high vacuum chamber equipped with drive end and non-drive end torque tubes attached to drive end and non-drive end hollow shafts respectively at each end of rotor assembly.
[025] The present invention provides HTS synchronous machine in which the
HTS pole coils of the rotor are cryogenically cooled with helium gas in closed loop configuration facilitated by rotary coupling connected to a stationary cryocooler and stator winding is cooled by water or ethylene glycol or ethylene glycol water mixture circulated in a separate liquid cooling arrangement.
[026] The present invention provides HTS synchronous machine in which all
the rotor support structure is made of non-magnetic stainless steel alloys such as SS316 or SS316L or SS316LN etc.
[027] The present invention provides HTS synchronous machine in which
torque tubes made of high mechanical strength and high thermal resistivity material such as Kevlar-49 or G10 etc.
[028] The present invention provides HTS synchronous machine in which the
HTS pole coils are made of high temperature superconducting material not limited to BSCCO or YBCO or ReBCO etc.
[029] The present invention provides HTS synchronous machine which can
be operated as generator or motor or synchronous condenser with higher operating magnetic field inside the machine with zero tooth saturation and higher current density in the stator to achieve higher power density, higher torque density along with overall compact size and lesser weight.

[030] The present invention provides HTS synchronous machine with rotary
coupling having combination of labyrinth seals and graphite seals backed up by
ferro-fluid seals.
[031] The present invention provides HTS synchronous machine having HTS
pole coils in rotor excited by a slip ring based arrangement or shaft mounted
brushless exciter.
[032] The present invention provides HTS synchronous machine with lesser
acoustic noise signature and lesser mechanical vibration due to round rotor
geometry and absence of magnetic teeth.
[033] The present invention provides HTS synchronous machine with higher
overload capacity, lesser synchronous reactance, better control and
maneuverability.
WORKING OF INVENTION
[034] The High Temperature Superconducting (HTS) synchronous machines
proposed by the present invention are highly efficient, compact, lighter, low
noise, high output power to weight ratio and better dynamic response machines
compared to conventional copper conductor based machines. The HTS
synchronous machines are used worldwide for various strategic and critical
industrial applications, because of the above mentioned advantages. Successful
development of HTS synchronous machine requires HTS, electrical,
mechanical, cryogenic and vacuum technologies. The major components of a
HTS rotor and copper winding stator topology synchronous machine are air gap
copper winding stator, HTS rotor, excitation system, cryogenic cooling and
vacuum systems. One of the promising topologies available for High
Temperature Superconducting (HTS) synchronous machine is HTS pole coils in rotor and air gap copper coils in stator. HTS coils are used in a rotor of the HTS synchronous machines, in place of the conventional copper coils.

Compact, less weight, highly efficient, greater overloading capacity and less noise machines can be developed using this technology. These machines can be used for strategic applications as well as industrial applications, i.e. ship propulsion, compact wind generators etc.
TEST RESULTS
[035] The developed High Temperature Superconducting (HTS) synchronous
model machine using this topology is scaled down having rating of 100 kW.
[038] These and other advantages of the present subject matter would be
described in greater detail with reference to the following figures. It should be noted that the description merely illustrates the principles of the present subject matter. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present subject matter and are included within its scope.
[039] It will be understood by those within the art that, in general, terms used
herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply

that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.”
[001] It will be further appreciated that functions or structures of a plurality
of components or steps may be combined into a single component or step, or the functions or structures of one-step or component may be split among plural steps or components. The present invention contemplates all of these combinations. Unless stated otherwise, dimensions and geometries of the various structures depicted herein are not intended to be restrictive of the invention, and other dimensions or geometries are possible. In addition, while a feature of the present invention may have been described in the context of only one of the illustrated embodiments, such feature may be combined with one or more other features of other embodiments, for any given application. It will also be appreciated from the above that the fabrication of the unique

structures herein and the operation thereof also constitute methods in
accordance with the present invention. The present invention also encompasses
intermediate and end products resulting from the practice of the methods herein.
The use of “comprising” or “including” also contemplates embodiments that
“consist essentially of” or “consist of” the recited feature.
[002] Although embodiments for the present subject matter have been
described in language specific to structural features, it is to be understood that the present subject matter is not necessarily limited to the specific features described. Rather, the specific features and methods are disclosed as embodiments for the present subject matter. Numerous modifications and adaptations of the structure/component of the present invention will be apparent to those skilled in the art, and thus it is intended by the appended claims to cover all such modifications and adaptations, which fall within the scope of the present subject matter.

WE CLAIM
1. An assembly (500) for high temperature superconducting (HTS)
synchronous machine, the assembly (500) comprising
a stator assembly (100) having an air core stator (101) including a multi¬layer multi-phase stator winding (102) supported by a non-magnetic core fastened on a magnetic shield (106) placed inside a frame (607) wherein the stator winding (102) is cooled by a liquid cooling arrangement attached to a stator frame (502); and
a rotor assembly (300) having an air core rotor (301) including plurality of HTS pole coils (302), wherein the HTS pole coils (302) being placed inside a rotating cryostat (303) encapsulated in an ultra-high vacuum chamber equipped with drive end and non-drive end torque tubes (306) attached to drive end (314) and non-drive end (312) hollow shafts respectively at each end of rotor assembly.
2. The assembly (500) as claimed in claim 1, wherein the inner space (112) of the stator assembly (100) is occupied by the HTS rotor assembly (300) maintaining a physical air gap (508).
3. The assembly (500) as claimed in claim 1-2, wherein the stator frame (502) covers the stator-rotor assembly through drive end (DE) side end cover (609) and Non-drive end (NDE) side end cover (610).

4. The assembly (500) as claimed in claim 1-3, wherein the air core stator (101) and the air core rotor (301) are surrounded y a magnetic shield made of material having high electrical resistivity and high magnetic permeability.
5. The assembly (500) as claimed in claim 1-4, wherein the liquid coolant based cooling system (515) is provided on the bottom of the stator frame (502).

6. The assembly (500) as claimed in claim 1-5, wherein the cooling inside the
stator is enabled by fixed coolant inlet (605) and outlet (606) pipes placed
inside the stator assembly (100).
7. The assembly (500) as claimed in claim 1-6, wherein a plurality of stator
coils (201) being placed inside a stator slot of the stator assembly (100).
8. The assembly (500) as claimed in claim 1, wherein the drive end shaft (314) and a non-drive end shaft (312) of the air core rotor (301) being mounted over the drive end bearing (315) and non-drive end bearing (313).
9. The assembly (500) as claimed in claim 1 and 8, wherein the air core rotor (301) is connected to the load in case of motor mode operation through a flange (317) provided on the drive end shaft (314).
10. The assembly (500) as claimed in claim 8-9, wherein rotor pole coil
excitation system (318) being attached to the Non-Drive end (NDE) of the
shaft (316) of the air core stator (301) which is attached with a rotary
coupling (319) and then with a cryocooler (620).