The present invention relates to a system of cooling shaft ends of rotor of high
temperature superconducting (HTS) machine.
BACKGROUND OF THE INVENTION
The shaft ends of a typical HTS machine rotor are usually at room temperature.
The torque tubes connected to these shafts and superconducting coils are subjected to
large temperature difference which lets a large amount of conduction heat in leak to
the superconducting system through these torque tubes, causing huge loss of efficiency
of the machine.
The conductive heat leak in through torque tubes to HTS machine rotor and also
heat leak in from atmosphere to HTS machine rotor is considerably high. Also the
cooldown time of the superconducting coils and HTS rotor is also very high. This causes
loss of efficiency of the machine.
This invention related to development of the liquid nitrogen jackets over shaft
ends (non-drive and drive ends) so as to reduce the temperature of shaft near torque
tube from room temperature to 77 K. The developed liquid nitrogen jacket over shaft
offers minimum temperature difference across the ends of torque tubes, reduce overall
heat in leak from atmosphere to HTS machine rotor and reduce conductive heat leak in

through torque tubes to HTS machine rotor. This system also reduce the cool down
time of the superconducting coils and HTS rotor. The utmost care shall be taken during
the design of liquid nitrogen jackets so that effect of liquid nitrogen cooling should not
reach the bearings and the lubricant preventing freezing of bearing. The invention aims
to improve the efficiency of the machine.
OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to propose a system of cooling shaft-
ends of rotor of high temperature superconducting machine, which is capable of
reducing heat leak in from atmosphere to HTS machine rotor.
Another object of the invention is to propose a system of cooling shaft-ends of
rotor of high temperature superconducting machine, which is able to reduce conductive
heat leak in through torque tubes to HTS machine rotor decreasing overall heat load of
system.
A still another object of the invention is to propose a system of cooling shaft-
ends of rotor of high temperature superconducting machine, which can achieve
minimum temperature difference at the ends of torque tubes fastened to end shafts at
one end and to rotor sleeve at other end.

A yet another object of the invention is to propose a system of cooling shaft-
ends of rotor of high temperature superconducting machine, which is able to reduce
cool down time of the superconducting coils and HTS rotor.
A further object of the invention is to propose a system of cooling shaft-ends of
rotor of high temperature superconducting machine, which can improve the vacuum
levels in the rotor by achieving cryo-pumping effect near shaft ends in HTS rotor.
A still further object of the invention is to propose a system of cooling shaft-ends
of rotor of high temperature superconducting machine, which is able to impede the flow
of frozen moisture over shaft ends to stator coils so as to maintain the high insulation
resistance throughout the life of HTS machine.
A further objection of the invention is to propose a system of cooling shaft-ends
of rotor of high temperature superconducting machine, which is able to prevent the
effect of liquid nitrogen reaching the bearings so that lubricant does not freeze.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 Liquid Nitrogen cooling on Non Drive end shaft of HTS machine.
Figure 2 Liquid Nitrogen cooling on Drive end shaft of HTS machine.
Figure 3 Liquid Nitrogen cooling at shaft ends of HTS machine.

Figure 4 Complete Assembly of Liquid Nitrogen cooling at shaft ends of HTS
Machine.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
The rotor of a typical HTS machine looks like a cylinder which forms the
innermost layer of a cryostat enhousing superconducting coils and associated pipings
and electrical and instrumentation connections. Outer most surface of HTS machine is
vacuum enclosure while the rear ends are shafts rested on bearing pedestals with the
help of bearings. The shaft ends are usually at room temperature. The torque tubes are
connected at one end to these shafts while to superconducting coils which are at
cryogenic temperatures to other end. This temperature difference lets a large amount
of conduction heat in leak to the superconducting system through the torque tubes.
Usually a cryocooler is used for achieving and sustaining desired cryogenic
temperatures in HTS machines to cool superconducting coils. The cryocooling operation
is carried out in a closed loop process. In this process, cold gas is transferred from
cryocooler to HTS application while warm gas is collected from HTS application and
given back to cryocooler.
The superconducting coils can be cooled to cryogenic temperatures by
conductive or convective type of heat transfer mechanisms. In convective type of heat
transfer process, superconducting coils are contained in a cryostat whose ends are

connected to torque tubes. These torque tube transfers the mechanical power from
machine rotor to the load through the shaft and mechanical coupling. This invention
related to develop a liquid nitrogen jacket over shaft ends so as to reduce the
temperature of shaft near torque tube and hence reduce the temperature across the
torque tubes.
The design of liquid nitrogen jacket should be such that in the event of
expansion of liquid nitrogen, from liquid phase to vapour phase, after warming up
inside the jacket, the structure should not explode. The vapours should be safely
vented through vent port, provided on the jacket itself, to atmosphere. There may be
freezing of atmospheric moisture over the shaft ends. But these traces of moisture
should not enter the stator portion of HTS machine or the bearings over which the rotor
is rested. Otherwise, over the period of time, this incoming moisture will reduce the
insulation resistance of the stator coils. And, at bearings, it may freeze the very
lubrication of bearing and hamper bearing performance.
Fig.1 represents the liquid nitrogen cooling arrangement on Non Drive End shaft
(101) of HTS machine. A jacket (105) made of SS 316 grade has been externally
welded (106) on the Non Drive End shaft surface as shown in drawing. There is an inlet
port (107) for allowing liquid nitrogen to enter into the Non Drive End shaft end and
also an exhaust port (108) to let vapours exit the jacket. On top of Non Drive End shaft,
vacuum sleeve (102) is welded to create an overall vacuum inside the machine rotor.

On rear side of Non Drive End shaft, Non Drive End torque tube (103) is fastened (104)
as shown in drawing.
Fig.2 represents the liquid nitrogen cooling on Drive End Shaft (201) of HTS
machine. A jacket (205) made of SS 316 grade steel has been externally welded (206)
on the Drive End shaft surface as shown in drawing. There is an inlet port (207) for
allowing liquid nitrogen to enter into the Drive End shaft end and also an exhaust port
(208) to let vapours exit the jacket. On top of Drive End shaft, vacuum sleeve (102) is
welded to create an overall vacuum inside the machine rotor. On rear side of Drive End
shaft, Drive End torque tube (203) is fastened (204) as shown in drawing.
Fig.3 represents liquid nitrogen cooling at shaft ends of HTS machine. Both the
shaft ends along with liquid nitrogen cooling arrangements are shown in the drawing.
The rotor (301) of high temperature superconducting machine is shown along with
Drive End and Non Drive End shaft (201, 101), Drive End and Non Drive End-torque
tubes (203, 103), Drive End and Non Drive End side liquid nitrogen jacket (205, 105),
vacuum sleeve (102), Non Drive End shaft extension to rotary coupling (312), Drive End
and Non Drive End side bearing pedestals (305, 306), and base frame (307) on which
motor is assembled. The superconducting pole coils and associated pipings (302) are
shown as a box in the drawing. The drive end is connected to load applied on the
machine while the Non Drive End is extended and connected to rotary coupling which
allows the transfer of cryogen into the superconducting rotor from a stationary to rotary
frame.

Fig.4 represents the complete assembly of liquid nitrogen cooling at shaft ends
of HTS machine. Both the shaft ends along with liquid nitrogen cooling arrangements
are shown along with Drive End and Non Drive End side extension pipes (416, 417) to
allow the transfer of liquid nitrogen from both sides of liquid nitrogen tank (414, 415).
Two separate liquid nitrogen tanks are provided at each end of shaft for continuous
supply of liquid nitrogen during machine operation. The extension pipes are braided SS
bellow based pipes which allow flexibility and ease of operation. The rotor (301) of high
temperature superconducting machine has Drive End and Non drive End shaft (201,
101) on which Drive End and Non Drive End torque tubes (203, 103) are fastened while
vacuum sleeve (102) is welded. The shaft ends are provided with welded Drive End and
Non Drive End side liquid nitrogen jackets (205, 105). The assembly part is also shown
to comprehend the position of superconducting rotor vis-à-vis Drive End and Non Drive
End side bearing pedestals (305, 306) and base frame (307).The superconducting pole
coils and associated pipings (302) are shown as a box in the drawing.

WE CLAIM
1. A system of cooling shaft-ends of rotor of high temperature superconducting
(HTS) machine comprising;
two liquid nitrogen jackets (105, 205) one being welded on the non drive end
shaft (101) surface and other on drive end shaft (201) surface of the rotor (301)
fastened with non drive end and drive end torque tubes (103, 203);
two inlet ports (107, 207) at non drive and drive end shaft disposed for allowing
liquid nitrogen to enter into the non drive end shaft end and drive end shaft end jackets
(105, 205);
two exhaust ports (108, 208) at non drive and drive end shaft disposed for
allowing vapours of nitrogen to exit the Jacket (105) from each side of non drive end
(101) shaft and drive end (201) shaft;
characterized in that,
two liquid nitrogen jackets (105, 205) are disposed over non drive and drive
shaft ends for reducing the temperatures of shafts near torque tubes from room
temperature to 77K offering minimum temperature difference across the ends of torque
tubes and for reducing overall heat in leak from atmosphere to HTS machine rotor and
also for reducing conductive heat leak in through torque tubes to HTS machine rotor
resulting improved efficiency of the machine,

wherein two tanks (415, 414) are disposed at non-drive end and drive end of
shaft for continuous supply of liquid nitrogen to jackets (105, 205) during machine
operation through extension pipes (416, 417) attached to the respective tanks (415,
414) at one end and connected to the Jacket at other end wherein the base frame
(307) holds the entire unit including bearing pedestals (305, 306).
2. The system as claimed in claim 1, wherein the jackets (105, 205) are made of SS
grade steel.