Coolant connecting head for an electric machine with a superconducting rotor winding

#This invention relates to electric machines with superconducting rotor windings in general and more particularly to a coolant conducting head for such a machine.

#A coolant connecting head for an electric machine which comprises a rotor supported rotatably about an axis with a superconducting winding which can be deep cooled by a coolant, with a device for feeding the coolant from a non-rotating coolant line part into a rotating coolant line part connected to the rotor, which contains at least one sealing device which serves for sealing off a space formed between said line parts and which allows, in the operating condition of the machine, a predetermined leakage rate which depends on the pressure difference prevailing therein is described in the literature reference "Advances in Cryogenic Engineering," vol. 23, New York, 1978, pages 125 to 131.

#For cooling a superconducting winding in the rotor of an electric machine, especially of a turbo-generator, devices must be provided for conducting a coolant between the rotor and stationary connecting lines. The coolant, for instance, liquid or gaseous helium, is fed to the winding in the rotor or is discharged again therefrom through such a device. The machine is therefore provided with a connecting head which contains a suitable transfer device. The design of this device, also called a coupler, is difficult, especially with respect to low thermal losses of the coolant loop for the superconducting winding and with respect to low leakage rates. For, the coupler must have rotary seals with relatively little friction, which seal the coolant, particularly the liquid helium, on the one hand, from the outside and which, on the other hand, separate the inlet side from the outlet side within the rotating system. The sealing devices required therefor must, in addition, permit radial and axial shaft clearance and operate without trouble for extended periods of time, e.g., several years.

#The single FIGURE is a schematic longitudinal cross section of an embodiment of a coolant connecting head according to the present invention .

#In the FIGURE, only the upper half of a coolant connecting head for a machine is illustrated as a longitudinal section. This machine, not further detailed in the FIGURE, may in particular be a turbo-generator which contains a rotor with a superconducting field winding that can be cooled to a low temperature and is surrounded by at least one co-rotating damper shield which generally can also be cooled, to reduce heat inflow into the deep-cooled winding, the latter is furthermore surrounded by vacuum spaces. To this end, the entire rotor can be enclosed by a co-rotating vacuum housing (see U.S. Pat. No. 3,942,053 and "Siemens Forschungs- und Entwicklungsberichte," vol. 5, 1976, No. 1, pages 10 to 16). However, the rotor can also rotate in a vacuum space.

#The coolant connecting head, detailed only in part in the FIGURE, of the machine contains a stationary head part 2, into which the lateral end section 3 of a shaft supported rotatably about an axis of rotation 4 is inserted. This shaft end section is connected to the rotor, not shown in the FIGURE, and is usually located on that side of the machine which is opposite the drive side. The shaft end section 3 contains a hollow outer cylinder 6 at room temperature which is arranged concentrically about an inner hollow cylinder 7, the end section 8 of which protrudes a predetermined length from the open end face 9 of the outer hollow cylinder 6. Between the outer hollow cylinder 6 and the inner hollow cylinder 7, two double tubes 11 and 12 are arranged concentrically in such a manner that an outer annular canal 13 is formed between the outer double tube 11 and the outer hollow cylinder 6, and an inner annular canal 14 between the inner double tube 12 and the inner hollow cylinder 7. The double tubes 11 and 12 define radially outward an annular space 16. Each tube consists of two concentrically arranged hollow cylinders which are closed off in a vacuum tight manner from each other at their end face. The interiors 17 and 18 thus formed between the two hollow cylinders of each double tube are evacuated for reasons of thermal insulation.

#The connecting head part 2 also contains a substantially hollow cylindrical non-rotating outer housing 20 which encloses the end of the rotating outer hollow cylinder 6 of the shaft end section 3 for a distance in the axial direction and is supported at this hollow cylinder 6 via a main bearing 22. In addition, the connecting head part 2 contains an inner, substantially hollow cylindrical housing part 23 which concentrically encloses the end section 8 of the inner rotating hollow cylinder 7 of the shaft end section 3 and which is supported at the end section 8 via a secondary bearing 25. This housing part 23 is rigidly connected via an end part 26, of essentially annular disc shape, to the outer housing 20. The parts 20, 23 and 26 define essentially an inner space located ahead of the end face 9 of the outer hollow cylinder 6 of the shaft end section 3 inside the connecting head part 2. For sealing this inner space, a sealing system 29 is provided parallel to the bearing 22 between the non-rotating outer housing 20 and the rotating hollow cylinder 6. Similarly, the inner housing part 23 is also sealed from the end section 8 of the inner hollow cylinder 7 by means of a sealing system 30. These sealing systems may be, for instance, ferro-fluidic seals, such as are known from British Pat. No. 1,312,698.