GB1579997A - Cryogenically cooled electrical machine - Google Patents

Description

(54) CRYOGENICALLY COOLED ELECTRICAL MACHINE (71) We, SPETSIALNOE KONSTRUK TORSKOE BJURO "ENERGOKHIMMASH", of prospekt Nauki, I, Novosibirsk, USSR, a USSR corporate body, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly -described in and by the following statement:- The present invention relates to electrical machines and, more specifically, to electrical machines with cryogenic cooling.

The invention is applicable to electrical machines, such as motors, generators and dynamotors, employed at atomic, steam and other types of power stations, as well as in transport and aviation. The invention may find extensive application in power units of spacecraft, as well as in all kinds of devices where it is necessary to cool a rotating wind ing to a superconducting state.

It is an object of the present invention to provide an electrical machine with cryogenic cooling, featuring a highly effective thermal protection of the superconducting exciting winding and a high efficiency.

The present invention essentially consists in providing an electrical machine with cryo genic cooling, wherein a superconducting exciting winding, whereto there are con nected busbars, is accommodated in a cavity of a rotor, which is filled with coolant and is secured to a shaft of the rotor, having an axial channel for the supply of coolant to the superconducting exciting winding provided at one end of the shaft and external channels for the removal of coolant, provided at both ends of the shaft, the shaft of the rotor being provided with grooves at the places where the superconducting winding is secured to the shaft, which grooves extend parallel with the axis of the shaft over the entire length of the superconducting exciting winding and com municate with the channel for the supply of coolant to the superconducting winding, the rotor shaft and with a further channel for the removal of coolant, said further channel extending along the axis of the shaft at the end opposite to said one end.

In order to reduce the influx of heat inside the rotor through the busbars, it is expedient that the busbars should be accommodated in the further channel for the removal of coolant.

The proposed design makes it possible to considerably improve the thermal protection of the superconducting exciting winding and maintain it at a temperature of 4.5 K by cooling it with a single-phase liquid coolant.

A better understanding of the present invention will be had from a consideration of the following detailed description of a preferred embodiment thereof, taken in conjunction with the accompanying drawings, wherein: Fig. I is an elevation view of an electrical machine with cryogenic cooling, in accordance with the invention; Fig. 2 is a magnified sectional view of the rotor of the electrical machine, taken on line 11-11 of Fig. 1; Fig. 3 is a magnified elevation view of a portion of the additional channel for the removal of coolant, illustrating the arrangement of the busbars.

According to the invention, the electrical machine with cryogenic cooling comprises a hollow rotor 1 (Fig. 1) whose shaft 2 rests on bearings 3 installed in end walls 4 of a sealed housing 5. Mounted on the internal surface of the housing 5 is a stator winding 6 (details of the stator winding 6 are not shown).

The rotor 1 is thermally insulated by vacuum in the spacing between the rotor 1 and the sealed housing 5. Vacuum is maintained with the aid of rotary vacuum seals 7 installed in the end walls 4. The hollow rotor 1 has a superconducting exciting winding 8 mounted on the shaft 2 of the rotor 1 and accommodated in a shell 9 which forms a cavity of the rotor I, filled with coolant 10.

The exciting winding 8 is manufactured from a material which becomes a superconductor at ultralow temperatures, for example, from niobium-titanium wire stabilized with a matrix of pure copper. The exciting winding 8 is cooled, until it reaches a superconducting state, by the coolant 10 which is liquid helium at a temperature of 4.2 K.

For cooling, the exciting winding 8 is provided with radially tapering radial grooves 11 whose number is only limited by the structural strength of the superconducting exciting winding 8. The superconducting exciting winding 8 is fastened to the shaft 2 in any known manner, for example, with the aid of bandages of glass laminate (the fastening of the winding 8 is shown conventionally). At the places where the exciting winding 8 is secured to the shaft 2 of the rotor 1, the shaft 2 is provided with grooves 12 which extend parallel to the axis of the rotor 1 and throughout the length of the exciting winding 8. The grooves 12 are covered with segments 13 of a heat-conducting material, for example, bronze. The segments 13 are provided with openings matched with the channels 11 of the superconducting exciting winding 8.

The ends of the shaft 2 of the rotor 1 are composed of two coaxial pipes 14 and 15 joined together by a screw thread whose gaps serve as channels 16 for the removal of coolant 10. The channels 16 communicate with the cavity of the rotor 1.

To supply coolant 10 to the exciting winding 8, the shaft 2 of the rotor 1 is provided with an axial channel 17 which is a vacuumtight pipe extending at one end of the shaft 2.

Extending at the opposite end and along the axis of the shaft 2 of the rotor 1 is a channel 18 for the removal of the coolant 10.

Like the channel 17, the channel 18 is a vacuum-tight pipe.

The channel 17 for the supply and the channel 18 for the removal of coolant 10 communicate the grooves 12. As coolant 10 leaves the channels 16 and 18, it is caught in gas collectors 19 arranged at the ends of the shaft 2. The exciting winding is energized through busbars 20 made of copper. The busbars 20 are accommodated in the channel 18 for the removal of coolant 10 and connected to collecting rings 21 mounted on the shaft 2 on the side of the channel 18 for the removal of coolant 10.

As shown in Fig. 2, the exciting winding 8 is a bipolar winding composed of two sections.

The number of grooves 12 corresponds to that of sections, so in the case under review there are two grooves 12.

In an exciting winding 8 with a different number of poles, grooves are provided under each section of the winding. The width and depth of the grooves 12 depend upon the strength characteristics of the shaft 2.

Interposed between the poles of the exciting winding 8 are inserts 22 (Fig. 2) of an electric- and heat-insulating material, for example, micarta.

Provided in the exciting winding 8 (Fig. 1), between the radial channels 11 and in the interpolar inserts 22 (Fig. 2), are longitudinal channels 23 which communicate with the gap between the shell 9 and the exciting winding 8 through radial openings spaced over the entire length of the channel 23.

The channel 18 (Fig. 1) for the removal of coolant 10 is composed of two coaxial pipes 24 and 25 (Fig. 3). Each of the busbars 20 is composed of two copper conductors of different polarities, accommodated in the internal pipe 24. The pipe 24 is arranged in the pipe 25 and rests on arched supports 26 made of an electric- and heat-insulating material.

The external pipe 25 is arranged in the axial bore of the shaft 2 and rests on ball supports 27 made of an electric- and heat-insulating material, for example, Awl203.

In Figs. 1, 2 and 3, the direction of circulation of coolant 10 is indicated by arrows.

In the proposed electrical machine with cryogenic cooling, the exciting winding 8 (Fig. 1) is cooled as follows.

The coolant 10 (Fig. 1) is liquid helium which is forced under pressure from a refrigerating machine (not shown) through the channel 17 to the cavity of the rotor 1. First, the coolant 10 reaches the grooves 12 of the shaft 2, where the centrifugal forces drive its liquid phase towards the internal surface of the segments 13, whereas the gaseous phase, produced by the centrifugal compression and friction, is driven towards the axis of the shaft 2. The centrifugal forces and pressure drive liquid phase of the coolant 10 through the openings provided in the segments 13 and through the channel 11 of the exciting winding 8 into the internal cavity of the rotor 1. On the internal surface of the shell 9, the coolant 10 is once again divided into a liquid phase and a gaseous phase; the liquid phase remains on the surface of the shell 9, while the gaseous phase proceeds through the radial openings and the longitudinal gas channels 23 (Fig. 2) to the annular gaps formed by the end face of the shell 9 and the exciting winding 8, wherefrom it goes to the channels 16 for the removal of coolant at both ends of the shaft 2, and is collected in the gas collector 19. As this takes place, the gaseous phase of the coolant 10 in the grooves 12 enters the channel 18 for the removal of coolant, cools the busbars 20 and is forced into the gas collectors 19. From these, the coolant is forced to the refrigerating machine (not shown).

The proposed design of an electrical machine provides for an effective cooling of the superconducting winding of the rotor, whereby its temperature is never higher than that of the coolant, keeping in mind that the centrifugal compression in the grooves has no significant effect upon the temperature.

The winding cooling system in accordance with the invention makes it possible to use liquid helium under pressure and at a reduced temperature, thus making the thermal protection of the superconducting winding more effective and raising the efficiency of the electrical machine. As a result, the output of an electrical machine according to the invention is 50 per cent higher than that of a conventional machine of the same size.

WHAT WE CLAIM IS: 1. An electrical machine with cryogenic cooling, wherein a superconducting exciting winding, whereto there are connected busbars, is accommodated in a cavity of a rotor, which is filled with coolant and is secured to a shaft of the rotor, having an axial channel for the supply of coolant to the superconducting exciting winding provided at one end of the shaft and external channels for the removal of coolant provided at both ends of the shaft, the shaft of the rotor being provided with grooves at the places where the superconducting exciting winding is secured to the shaft, which grooves extend parallel with the axis of shaft over the entire length of the superconducting exciting winding and communicate with the channel for the supply of coolant to the superconducting exciting winding and with a further channel for the removal of coolant, said further channel extending along the axis of the rotor shaft at the end thereof opposite to said one end.

2. An electrical machine with cryogenic cooling as claimed in claim 1, wherein the busbars are accommodated in the further axial channel for the removal of coolant.

3. An electrical machine with cryogenic cooling, substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. no significant effect upon the temperature. The winding cooling system in accordance with the invention makes it possible to use liquid helium under pressure and at a reduced temperature, thus making the thermal protection of the superconducting winding more effective and raising the efficiency of the electrical machine. As a result, the output of an electrical machine according to the invention is 50 per cent higher than that of a conventional machine of the same size. WHAT WE CLAIM IS:

1. An electrical machine with cryogenic cooling, wherein a superconducting exciting winding, whereto there are connected busbars, is accommodated in a cavity of a rotor, which is filled with coolant and is secured to a shaft of the rotor, having an axial channel for the supply of coolant to the superconducting exciting winding provided at one end of the shaft and external channels for the removal of coolant provided at both ends of the shaft, the shaft of the rotor being provided with grooves at the places where the superconducting exciting winding is secured to the shaft, which grooves extend parallel with the axis of shaft over the entire length of the superconducting exciting winding and communicate with the channel for the supply of coolant to the superconducting exciting winding and with a further channel for the removal of coolant, said further channel extending along the axis of the rotor shaft at the end thereof opposite to said one end.

2. An electrical machine with cryogenic cooling as claimed in claim 1, wherein the busbars are accommodated in the further axial channel for the removal of coolant.

3. An electrical machine with cryogenic cooling, substantially as hereinbefore described with reference to the accompanying drawings.