FIELD OF THE INVENTION
The invention relates to high temperature superconducting synchronous motors. In particular, the invention relates to high temperature superconducting motor/generator/synchronous condenser.
BACKGROUND OF THE INVENTION
High Temperature superconducting (HTS) synchronous motors consist of HTS field windings in the rotor, wherein the stator consists of air gap copper windings. The HTSC motors are highly efficient, compact, lighter and noise free motors. The HTS motor field coils are cooled with low temperature Helium Gas (up to 30K). The helium gas is very light gas (atomic number is two) and leaks from even very minute cracks. The current is fed to the rotating HTS coils through a slip ring shaft arrangement. The slip ring shaft consists of vacuum port, current leads and slip rings with a provision of hollow bore for helium in and out pipes. This arrangement is fabricated with less joints and high rigidity for absolute vacuum. In this disclosure, a slip ring shaft arrangement is described which consists of vacuum tight current leads, vacuum port, slip ring with a provision of hollow bore for helium gas in and out pipes for use in HTS synchronous motor.
Patent No. EP2696443A3- The housing has a mounting wall by which the ring housing is attached at a first side of the housing. Three apertures are formed at a brush carrier space a connection space and a module space at second, third and fourth sides of the housing. Brush carriers are accessible through the carrier space. An electrical connection is accessible through the connection space. A slip ring module is arranged at the module space. A fastening unit fastens a brush carrier. One of the apertures is locked with a cover. An independent claim is also included for a slip ring assembly.

Patent No.P2696449A1- A slipring assembly comprises a slipring module having at least one slipring track which is in electrical contact with at least one slipring brush. The slipring module comprises an isolating body holding the at least one slipring track. Furthermore a heating element is embedded in the slipring module to generate heat within the slipring module and to increase the temperature of the at least one slipring track. This allows increasing the temperature of the slipring module to an optimum operation temperature and further to remove humidity from the surface of the slipring track.
Patent No. US20120020615A1 – The present invention is a limited rotation through-bore optical slip ring. This will enable one or more optical signals to pass across a rotational interface while leaving a center bore free. The present invention is passive, unlike many off axis or through bore optical slip rings and is low loss by nature.
Patent No. EP662736B1 – The electrical collector for a rotating machine includes a ring of conducting material formed about the rotating part, a multi-fibre brush comprises a bundle of two to five, and preferably three fibres in a group. These are supported in a ferrule at one end, whilst their free ends run in a groove in the conducting ring. The ferrule end is embedded in a support which allows a certain amount of bending of the assembly. The extent to which the assembly is bent determines the pressure applied by the brushes to the ring.
OBJECT OF THE INVENTION
It is therefore the object of the invention is to propose an improved slip-ring shaft for feeding DC current to the rotating field coils of HTS Synchronous motor, with following provisions :

1. Slip rings for feeding the current under rotational condition
2. Vacuum port for creation of vacuum upto 100-6mbar
3. Hallow bore for Helium gas in & out pipes
4. Vacuum tight current leads (2 Nos)
5. Helium leak tight in the order of 1 x 10-8 mbar lit/sec
6. Reduction of the number of joints for minimum leak & better vacuum.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure A is a sectional view of the slip ring shaft
1. Slip rings
2. Slip rings mounting sleeve
3. Vacuum creation port
4. Key way
5. Slip ring’s copper lead
6. Flange for assembly
7. Flange for Helium transfer coupling assembly
8. Hollow bore
9. Current lead
Figure B is Sectional and side view of Shaft with end flange of Slipring shaft
assembly. Figure C is a Sectional views of assembled slipring shaft arrangement in HTS
motor
1. Helium transfer coupling (HTC) flange
2. HTS rotor shaft flange
3. Vacuum tight current leads
4. Flexible copper rope
5. Slip ring shaft flange connected to HTC
6. Copper lead from HTS coils
7. Slip rings
8. Slip ring shaft flange connected to HTS rotor

9. Vacuum creation port
10. Helium gas in pipe
11. Hallow vacuum space
12. Helium gas out pipe
DETAILED DESCRIPTION OF THE INVENTION
High temperature superconducting coils are used as filed coils for HTS synchronous motors. These HTS field coils are placed in rotor of the motor. The HTS field coils are cooled to 30k using Helium gas for rated current operating. An arrangement is required to feed the DC current to the rotational field coils under vacuum conditions. The slip ring shaft arrangement is used for serving this requirement. It consists of two slip rings (figure A, Part 1). Vacuum creation port (Figure A, part 3). Current leads (Figure A, part 9), hollow shaft with flanges (Figure B). The Key way (Figure A, part 9) is used for assemble the slip ring shaft to the HTS rotor. One side of the slip ring shaft arrangement (Figure C, Part 8) is connected to the HTS rotor (Figure C, Part 2) and other side is connected to the Helium transfer coupling (Figure C, Part 1) through boils. The current leads (Figure C, Part 3) are connected to the HTS rotor copper leads (Figure C, Part 6). The sliprings (Figure C, Part 7) are connected to the current leads (Figure C, Part 3) by flexible copper rope (Figure C, Part 4). The vacuum port (Figure A, Part 3) is used for creating a vacuum up to 10-6 mbar in hollow space of the shaft. Helium in and out gas pipe lines (Figure C, part 10, 12) go through the hollow part of the shaft and surrounded by vacuum space (Figure C, Part 11). All weld joingts are vacuum tight joints and the leak rate is in the order of 10-8 mbar Lit/sec.
Advantages of the invention
1. Simple in assembly and dis-assembly
2. Ease of stand-alone testing before assembly

WE CLAIM :
1. An improved slipring shaft arrangement for feeding DC current to
rotating of high temperature superconducting synchronous motor, the
arrangement comprising :
a vacuum port, current leads, sliprings and hollow bore for helium gas in and out pipes; the vacuum level in the slipring shaft arrangement and leak rate of the arrangement is in the order of 1 x 10-6 mbar and 10-8 mbar 1/sec respectively, a plurality of flanges for connecting this arrangement to the rotor shaft of the motor and Helium transfer coupling.

2. A slip ring shaft arrangement as claimed in Claim 1, wherein the current lead arrangement from vacuum space to atmosphere is leak tight.
3. A slip ring shaft arrangement as claimed in claim 1, wherein the sliprings provide for feeding the current during rotational condition.
4. A slip ring shaft arrangement as claimed in Claim 1, wherein leaking of helium for cryogen in and out pipes is eliminated.
5. A slip ring shaft arrangement as claimed in claim 1, wherein a hollow bore is provided for creating vacuum and provision for Helium in and out pipes.