FIELD OF THE INVENTION
[001] The present invention in general relates to cryogenic cooling structures
for HTS synchronous machines having a rotor with a high temperature superconducting (HTS) coil and more particularly relates to reduce the convective heat load on the cryogenic structure, by maintaining the vacuum level as per requirement.
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] 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. The major components of a HTS rotor and copper winding stator topology synchronous machine are air gap copper winding stator, HTS rotor, excitation structure, cryogenic cooling and vacuum structures.
[004] Moreover, the High Temperature Superconducting (HTS) synchronous
machine is available in various topologies. Among them, the topology with high temperature superconducting pole coil based rotor and air gap winding based stator without magnetic teeth and both stator and rotor surrounded by a

magnetic iron shied (sometimes referred as back iron) is the most promising one. The high temperature superconducting pole coils of the rotor are need to be cooled and maintained at cryogenic temperature with the help of a cryocooler in a closed loop configuration. To eliminate the portion of convective heat load on cryocooler, it is essential to have high degree of vacuum in the cryogenically cooled HTS rotor. ‘
[005] The HTS rotor carries pressurized cryogen in the designated path to take
away the heat from HTS pole coils and maintain them at desired cryogenic temperatures. To reduce the convective heat load on the cryogenic structure, a good degree of vacuum is crucial. A combination of several vacuum pumps with different pumping capacity are used to achieve the desired level of vacuum.
[006] The distance of extreme point of the rotor is quite far away from the
vacuum pump, therefore the vacuum achieved at that point will be lesser. Hence, there is need to maintain good vacuum level across complete length of HTS rotor.
OBJECTS OF THE INVENTION
[007] Some of the objects of the present invention, which at least one
embodiment herein satisfy, are listed herein below.
[008] The object of the present invention is to develop a vacuum structure for
high temperature superconducting (HTS) pole coils in the rotor of high temperature superconducting (HTS) synchronous machine.
[009] Another object of the present invention is to develop the vacuum
structure in which even though the vacuum level decreases in any one or more sections of the rotor, the machine will continue to operate at higher thermal load and lesser output for a shorter period of time.

[010] Yet another object of the present invention is to develop the vacuum
structure for high temperature superconducting (HTS) synchronous machine that continue to work for some period of time even when the vacuum level inside the machine decreases.
[011] Another object of the present invention is to develop a vacuum structure
for high temperature superconducting (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.
[012] Yet, another object of the present invention is to develop a vacuum
structure for high temperature superconducting (HTS) rotor with HTS pole coils placed in 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.
[013] Yet, another object of the present invention is to develop a vacuum
structure bifurcated into three sections for better distribution and monitoring of vacuum in all sections of the rotor having enough strength at joints, better vacuum level and lesser leak rate.
[014] Yet, another object of the present invention is to develop a bifurcated
vacuum structure in the rotor having an increased conductance of vacuum path that helps in achieving better vacuum levels (upto 10-7 mbar) in the rotor.
[015] Yet, another object of the present invention is to develop a bifurcated
vacuum structure in the rotor having lower cryogenic heat load on the cryocooling structure along with easier assembly, maintenance and repair.
[016] Yet, another object of the present invention is to develop a vacuum
structure utilizing seal off valves at specific locations so as to maintain ultra-high vacuum levels in the rotor for longer time period during rotation.

[017] It is further object of the present invention is to develop a vacuum
structure for high temperature superconducting (HTS) rotor with optimized
vacuum pumping capacity.
[018] It is another object of the present invention is to develop a vacuum
structure through which the multi-layer insulation (MLI) provided on the
cryogenically cooled surfaces of the rotor works well, thereby reducing the
thermal radiation heat load on the cryogenic structure.
[019] 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
[001] This summary is provided to introduce concepts related to a structure
and a method that helps in accurately determining the average geometric profile of fusion zone of a weld bead. 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.
[002] In accordance with an embodiment, the present disclosure provides an
assembly for maintaining a vacuum level in HTS rotor, the assembly
comprising an HTS rotor section containing an HTS rotor having a drive end and a non–drive end, wherein the non-drive end of the HTS rotor includes a rotor vacuum termination flange, a rotor pole excitation section having a rotor pole coil excitation structure, wherein the rotor vacuum termination flange of the HTS rotor sector being connected with a rotor side flange of excitation structure; and a cryocooler section, wherein cryogen transfer coupling side

flange of excitation structure being connected with a cryogen transfer coupling
side flange of cryocooler.
[003] In an aspect, the HTS rotor includes plurality of HTS pole coils placed
inside a rotating cryostat.
[004] In an aspect, the rotating cryostat is encapsulated in cylindrical vacuum
enclosure equipped with drive end and non-drive end.
[005] In an aspect, a drive end shaft and a non- drive end shaft being provided
on both the sides of the HTS rotor.
[006] In an aspect, the drive end shaft and a non-drive end shaft being
mounted over the drive end bearing and non-drive end bearing.
[007] In an aspect, the HTS rotor is connected to the load in case of motor
mode operation through a flange provided on the drive end shaft.
[008] In an aspect, the HTS rotor is connected to the prime mover in case of
generator mode operation through a flange provided on the drive end shaft.
[009] In an aspect, atleast three vacuum pumps are connected to their
respective ports through braided bellows to create high degree vacuum in all
hollow spaces.
[010] In an aspect, a multi-layer insulated (MLI) cold cryogen inlet line feds
the cryogen to pole coils and a multi-layer insulated (MLI) warm cryogen outlet
line takes away the warm cryogen.
[011] In an aspect, the vacuum termination flange includes a vacuum sleeve
for both cold cryogen inlet line and warm cryogen outlet line enclosed inside
the rotor pole excitation section .
[012] 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
[013] FIG. 1 represents the complete assembly 100 for maintaining vacuum
in HTS rotor of HTS synchronous machine in accordance with the present
disclosure.
[014] FIG.2 represents an assembly 130 for maintaining the vacuum in HTS
rotor section in accordance with the present disclosure.
[015] FIG.3 represents an assembly 140 for maintaining the vacuum in rotor
pole coil excitation structure in accordance with the present disclosure.
[016] FIG.4 represents an assembly 150 for maintaining the vacuum in
cryocooler section in accordance with the present disclosure.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS
[020] 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.
[021] The present invention focusses on maintaining a good vacuum level
across complete length of HTS rotor. This vacuum structure is bifurcated into three sections. With this, even though the vacuum level deteriorates in any one or more sections of the rotor, the machine will continue to operate at higher thermal load and lesser output for a shorter period of time. Also, the multi-layer insulation (MLI) provided on the cryogenically cooled surfaces of the rotor

works well, thereby reducing the thermal radiation heat load on the cryogenic structure.
[022] In general, the High Temperature Superconducting (HTS) synchronous
machine comprises high temperature superconducting (HTS) pole coils in the rotor and multi-layer multi-phase forced air cooled winding in the stator.
[023] FIG. 1 represents the complete assembly 100 for maintaining vacuum
in HTS rotor of HTS synchronous machine. In order to maintain vacuum, the assembly is bifurcated into three sections viz. HTS rotor section assembly 130, rotor excitation section assembly 140, and cryocooler section assembly 150. The vacuum pumps 108, 113, 120 in all three sides are connected to their respective ports 110, 114, 122 through flexible SS (stainless steel) braided bellows 109, 123, 124 to create high degree vacuum in all hollow spaces.
[024] The HTS rotor vacuum section 130 containing HTS rotor 101 having
HTS pole coils with DE (Drive- end) and NDE (Non-Drive end) shafts at its ends. The rotor spins on its axis with the help of NDE (Non-Drive end) and DE (Drive- end) bearings 104, 105 provided on the NDE (Non-Drive end) and DE (Drive-end) shafts 102, 103 respectively. The rotor is connected to the load (in case of motor mode operation) or the prime mover (in case of generator mode operation) through a flange 106 provided for this purpose on DE shaft.
[025] The HTS pole coils of the rotor are cryogenically cooled and maintained
at desired temperature. The cold cryogen inlet line 205 feds the cryogen to pole coils and warm cryogen outlet lin e 206 takes away the warm cryogen. These cryogen lines are routed through rotor vacuum termination flange 107 to connect it to cryocooler 117 through rotor pole coil excitation structure 111 and cryogen transfer coupling 116. The cryogen transfer coupling 116 enables the flow of cryogen from stationary cryocooler 117 to rotating HTS pole coils and back to stationary cryocooler in a closed loop configuration.

[026] The rotor pole coil excitation structure 111 is used to feed DC current
to HTS pole coils during operation of the machine. The rotor vacuum termination flange 107 is connected to rotor side flange 112 of excitation structure 111. The cryogen transfer coupling side flange 115 of excitation structure 111 connects the excitation structure 111 to cryocooler 117 though cryogen transfer coupling side flange 118 of cryocooler 117. The cryogen transfer coupling side flange 118 of cryocooler enables the connection of cryocooler 117 to rotor pole coil excitation structure 111 which in turn connected with HTS rotor. The cryocooler also comprises of an extension pipe 121 containing cryogen inlet and outlet lines. The extension pipe 121 enables the connection of outlet (cold cryogen) of cryocooler to inlet of cryogen transfer coupling and connection of outlet of cryogen transfer coupling (warm cryogen) to inlet of cryocooler in an auxiliary vacuum chamber 119.
[027] FIG.2 represents a vacuum structure 130 for HTS rotor side having high
temperature superconducting (HTS) pole coils in the rotor of high temperature superconducting (HTS) synchronous machine. Precisely, this figure describes the longitudinal section of HTS rotor 101 with its vacuum structure.
[028] The HTS rotor section having HTS rotor 101 with a rotating cryostat
202 containing more than one HTS pole coil. There are two torque transferring media (TTM) 203, 204 provided at each drive end (DE) and non-drive end (NDE) to transfer the generated electromagnetic forces as well as to reduce the conduction heat load on cryogenic structure. The rotor spins on its axis with the help of DE and NDE bearings 105,104 provided on the DE and NDE shafts 103,102 respectively.
[029] The rotor is connected to the load (in case of motor mode operation) or
the prime mover (in case of generator mode operation) through a flange 106 provided for this purpose on DE shaft.

[030] The HTS pole coils 202 of the HTS rotor 101 are cryogenically cooled
and maintained at desired temperature. The multi-layer insulated (MLI) cold cryogen inlet line 205 feds the cryogen to pole coils and multi-layer insulated (MLI) warm cryogen outlet line 206 takes away the warm cryogen. The complete rotor is encapsulated in a cylindrical vacuum enclosure 207 so as to create high degree vacuum in all the hollow spaces 208 inside the rotor. There is a vacuum port 110 on DE shaft to enable the connection of vacuum pump to the HTS rotor. The port 210 provided on NDE shaft enables the routing of all sensors placed inside the rotor for instrumentation.
[031] The extreme non-drive end of the HTS rotor has a vacuum termination
flange 107. This flange bifurcates the vacuum structure of HTS rotor 130 from rotor excitation section 140. This vacuum termination flange 107 has vacuum sleeve 218 for both cold cryogen inlet line 219 and warm cryogen outlet line 220 fitted inside the rotor excitation section 140. It also has few electrical and instrumentation ports 217. The electrical port enables the excitation of rotor HTS pole coils with direct current, whereas the instrumentation port enables the routing of sensor placed inside the rotor. All the cryogen piping’s and most of cryogenically cooled surfaces of the rotor are covered in multi-layer insulation (MLI) to reduce the thermal radiation heat load on the cryogenic structure.
[032] FIG.3 represents a vacuum rotor pole excitation section 140
comprising the rotor pole coil excitation structure 111. The rotor pole coil excitation structure 111 is used to feed DC current to HTS pole coils during operation of the machine. The rotor vacuum termination flange 107 as shown in FIG.1 is connected to rotor side flange 112 of excitation structure 111. The cryogen transfer coupling side flange 115 of excitation structure 111 connects the excitation structure 111 to cryocooler 117 though cryogen transfer coupling side flange 118 of cryocooler.

[033] The cryogen transfer coupling 116 enables the flow of cryogen from
stationary cryocooler 117 to rotating HTS pole coils and back to stationary cryocooler 117 in a closed loop configuration. There is a vacuum port 114 provided on excitation structure which enables the connection of vacuum pump 113 to excitation structure 111 using a flexible SS braided bellow 123 to create high degree vacuum in all hollow spaces.
[034] FIG.4 represents the vacuum structure 400 provided at cryocooler side.
The cryogen transfer coupling 116 enables the flow of cryogen from stationary cryocooler 117 to rotating HTS pole coils and back to stationary cryocooler 117 in a closed loop configuration. For this, the cryocooler has an extension pipe 121 containing multi-layer insulated (MLI) flexible cryogen inlet and outlet lines. The extension pipe 121 enables the connection of outlet (cold cryogen) of cryocooler to inlet of cryogen transfer coupling and connection of outlet of cryogen transfer coupling (warm cryogen) to inlet of cryocooler in an auxiliary vacuum chamber 119. There is a vacuum port 122 provided on auxiliary vacuum chamber which enables the connection of vacuum pump to auxiliary vacuum chamber using a flexible SS braided bellow 124 to create high degree vacuum in all hollow spaces.
TECHNICAL ADVANTAGES
[035] The present invention develops a vacuum structure for high temperature
superconducting (HTS) pole coils in the rotor of high temperature superconducting (HTS) synchronous machine.
[036] The present invention develops the vacuum structure in which even
though the vacuum level decreases in any one or more sections of the rotor, the machine will continue to operate at higher thermal load and lesser output for a shorter period of time.

[037] The present invention develops the vacuum structure for high
temperature superconducting (HTS) synchronous machine that continue to work for some period of time even when the vacuum level inside the machine decreases.
[038] The present invention develops a vacuum structure for high temperature
superconducting (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.
[039] The present invention develops a vacuum structure for high temperature
superconducting (HTS) rotor with HTS pole coils placed in 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.
[040] The present invention develops a vacuum structure bifurcated into three
sections for better distribution and monitoring of vacuum in all sections of the rotor having enough strength at joints, better vacuum level and lesser leak rate.
[041] The present invention develops a bifurcated vacuum structure in the
rotor having an increased conductance of vacuum path that helps in achieving better vacuum levels (upto 10-7 mbar) in the rotor.
[042] The present invention develops a bifurcated vacuum structure in the
rotor having lower cryogenic heat load on the cryocooling structure along with easier assembly, maintenance and repair.
[043] The present invention develops a vacuum structure utilizing seal off
valves at specific locations so as to maintain ultra-high vacuum levels in the rotor for longer time period during rotation.
[044] The present invention develops a vacuum structure for high
temperature superconducting (HTS) rotor with optimized vacuum pumping capacity.

[045] The present invention develops a vacuum structure through which the
multi-layer insulation (MLI) provided on the cryogenically cooled surfaces of the rotor works well, thereby reducing the thermal radiation heat load on the cryogenic structure.
[046] 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.
[047] 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.”
[017] 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.
[018] 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 (100) for maintaining vacuum level in HTS rotor of HTS
synchronous machine, the assembly comprising
an HTS rotor section (130) containing an HTS rotor (101) having a drive end and a non–drive end, wherein the non-drive end of the HTS rotor (101) includes a rotor vacuum termination flange (107);
a rotor pole excitation section (140) having a rotor pole coil excitation structure (111), wherein the rotor vacuum termination flange (107) of the HTS rotor (101) being connected with a rotor side flange (112) of excitation structure (111); and
a cryocooler section (150), wherein cryogen transfer coupling side flange (115) of excitation structure (111) being connected with a cryogen transfer coupling side flange (118) of the cryocooler (117).
2. The assembly (100) as claimed in claim 1, wherein the HTS rotor (101)
includes plurality of HTS pole coils placed inside a rotating cryostat (202).
3. The assembly (100) as claimed in claim 2, wherein the rotating cryostat (202) is encapsulated in cylindrical vacuum enclosure (207) equipped with drive end and non-drive end.
4. The assembly (100) as claimed in claim 3, wherein a drive end shaft (103) and a non- drive end shaft (102) being provided on both the sides of the HTS rotor.
5. The assembly (100) as claimed in claim 4, wherein the drive end shaft (103) and a non-drive end shaft (102) being mounted over the drive end bearing (105) and non-drive end bearing (104).
6. The assembly (100) as claimed in claim 1, wherein the HTS rotor (101) is connected to the load in case of motor mode operation through a flange (106) provided on the drive end shaft (103).

7. The assembly (100) as claimed in claim 6, wherein the HTS rotor (101) is
connected to the prime mover in case of generator mode operation through
a flange (106) provided on the drive end shaft (103).
8. The assembly (100) as claimed in claim 1-7, wherein atleast three vacuum pumps (108, 113, 120) are connected to their respective ports (110, 114, 122) through braided bellows (109, 123, 124) to create high degree vacuum in all hollow spaces.
9. The assembly (100) as claimed in claim 1-7, wherein a multi-layer insulated (MLI) cold cryogen inlet line (205) fe eds the cryogen to pole coils and a multi-layer insulated (MLI) warm cryogen outlet line (206) takes away the warm cryogen.
10. The assembly (100) as claimed in claim 1, wherein the vacuum termination flange (107) includes a vacuum sleeve (218) for both cold cryogen inlet line (219) and warm cryogen outlet line (220) enclosed inside the rotor pole excitation section (140).