GB2037090A - Electrical machine with cryogenic cooling - Google Patents

Abstract

An electrical machine with cryogenic cooling has a hollow rotor (3) filled with a coolant, the rotor (3) comprising a superconducting winding (10) with at least two supply leads (11, 12), and hollow end shafts (4, 5) which incorporate ducts (14, 19) for the outflow of coolant. The positive lead (11) is disposed in the cooling duct (14). The cooling ducts (14, 19) are coupled, via respective outlets (20, 22) for withdrawing the coolant from the rotor (3), with respective coolant collecting chambers (23, 24) at each end. There is a coolant inflow passage (17) in the end shaft (5) for feeding the coolant to the superconducting winding (10), which passage is connected to an inlet (18). There is a further coolant outflow passage (16) inside the end shaft (4) which communicates with the cavity of the rotor (3) and with the coolant collecting chamber (23) via an outlet (21), and negative lead (12) is disposed in this passage (16). Current-collecting means (13, 15) are disposed in the coolant collecting chamber (23), and are of the sliding or liquid-metal type. The outlets (20, 22) may utilize a centrifugal pumping effect by incorporating vanes or spiral passages Figs. 4-6 (not shown). The conductor (12) has a proportion of superconducting material that increases from zero at its outer end to 100% at the other end; it may now be porous with a branched end, Figs. 8, 9 (not shown). <IMAGE>

Description

SPECIFICATION Electrical machine with cryogenic cooling The invention relates to electrical machines, and more particularly to electrical machines with cryogenic cooling, including electric motors, generators and convertors suitable for use at atomic, thermal and other power stations as well as for transport and aircraft uses.

The invention can also be applicable to space power stations and apparatus in which a rotatable object, for example, an electrical winding is to be maintained at cryogenic temperatures.

There is provided an electrical machine with cryogenic cooling having a hollow rotor filled with a coolant, the rotor comprising a superconducting winding with at least two supply leads, one of the supply leads being coupled to a plus sign current-collecting means and disposed in at least one cooling duct for cooling one end part of a hollow shaft of the rotor, the cooling ducts for cooling the both end parts of the hollow shaft of the rotor being connected, via respective means for withdrawing the coolant from the rotor, with respective coolant collecting chambers, the other supply lead being coupled to a minus sign current collecting means, the hollow shaft of the rotor being provided with a passage for feeding the coolant to the superconducting winding, the passage connecting with an inlet means for introducing the coolant into the rotor, the inlet means being disposed in the other end part of the hollow shaft which is supported in bearings each having a housing with a seal, the hollow shaft of the rotor having an additional passage made in the first one of the end parts of the hollow shaft and connected with the rotor cavity, an additional exhausting means for withdrawing the coolant from the rotor being provided by which the additional passage is connected with a respective coolant collecting chamber, the other supply lead coupled to the minus sign currentcollecting means being disposed in the additional passage, and the current-collecting means being disposed in a respective coolant collecting chamber.

Advantageously, an electrical machine should have two supply leads connected to two respective plus sign current-collecting means and disposed in two respective cooling ducts for cooling the both end parts of the hollow shaft of the rotor, a first one of the plus sign current-collecting means, connected to the supply lead which is disposed in the first end part of the hollow shaft of the rotor together with the supply lead coupled to the minus sign current-collecting means, being disposed, together with the latter, in a respective coolant collecting chamber.

Preferably, an electrical machine should have at least one of the exhausting means for withdrawing the coolant from the rotor arranged to provide for a communication between a cooling duct for cooling a respective end part of the hollow shaft of the rotor and a respective coolant collecting chamber and implemented in the form of a centrifugal wheel which is installed on the outlet end member of the cooling duct of a respective end part of the hollowshaft of the rotor and is disposed in a respective coolant collecting chamber in close proximity to the current-collecting means disposed in the latter.

Advantageously, an electrical machine should have the centrifugal wheel comprising two discs with a strip disposed therebetween to take a fixed helical arrangement so that the width of a passage formed by the strip increases as viewed from the periphery of the helix to its center in a direction coinciding with the direction of rotation of the rotor.

Preferably, an electrical machine should have each of the current collecting means comprising a respective disc rigidly mounted on the hollow shaft of the rotor and disposed in a space formed by a respective end face wall of a respective coolant collecting chamber and a respective partition wall made in the chamber, the spaces being filled with a liquidmetal alloy providing for electrical conduction and being connected with each other through the coolant.

Advantageously, an electrical machine should comprise at least one of the coolant collecting chambers made of an electrical/ thermal insulation material and rigidly attached, by virtue of its end face wall facing a respective bearing, to the housing of the bearing in order to provide for centering the disc of the current-collecting means disposed in a respective coolant collecting chamber with respect to the latter, that chamber, which is disposed on the end part of the hollow shaft of the rotor in the vicinity of the inlet means for introducing the coolant into the rotor, having its end face wall facing the inlet means in additional rigidly attached relation to the latter.

Preferably, in an electrical machine the supply lead connected to the minus sign currentcollecting means should be a porous one and made of a material composed of two components A and B, the component A possessing a normal conductivity and the component B possessing a superconductivity, said components A and B being distributed over the length of the supply lead in such a manner that the end of the supply lead connecting to the current-collecting means is made of a material composed of 100% the component A and the other end of the supply lead is made of a material composed of 100% the component B and that the contents of these components A and B gradually diminish as measured in opposite directions from respective ends of the supply lead, beginning at the maximum values of these contents at these ends.

The invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a partial longitudinal section showing an electrical machine with cryogenic cooling, according to the invention; Figure 2 is a partial longitudinal section showing an electrical machine with cryogenic cooling in which the supply leads connected to the plus sign current-collecting means are available to the both end parts of the hollow shaft, according to the invention; Figure 3 is a partial longitudinal section showing an electrical machine with cryogenic cooling with an exhausting means for withdrawing the coolant from the rotor made in the form of a centrifugal wheel, according to the invention; Figure 4 is a section on line IV-IV of Fig. 3, according to the invention;; Figure 5 is a partial longitudinal section showing an electrical machine with cryogenic cooling in which the exhausting means is made in them form of discs with a strip disposed therebetween and a liquid-metal alloy in the current-collecting means is provided, according to the invention; Figure 6 is a section on line VI-VI of Fig. 5, according to the invention; Figure 7 is a partial longitudinal section showing an electrical machine with cryogenic cooling in which the current-collecting means on the both end parts of the hollow shaft are provided with a liquid-metall alloy and the casings of the coolant collecting chambers are rigidly connected with the bearing housings disposed in the end shields of the stator casing, according to the invention;; Figure 8 is a partial longitudinal section of an electrical machine with cryogenic cooling in which the supply lead connected to the minus sign current-collecting means is a porous one and the current-collecting means are provided with a liquid-metal alloy, according to the invention; Figure 9 is a section on line IX-IX of Fig. 8, according to the invention.

The electrical machine with cryogenic cooling comprises, according to the invention, a casing 1 (Fig. 1) accommodating a stator winding 2 rigidly attached thereto (the stator winding 2 is shown diagrammatically in Fig.

1) and a hollow rotor 3 having end parts 4, 5 of its hollow shaft supported in bearings 6.

The latter are mounted in endshields 7 of the casing 1. The endshields 7 also mount vacuum-tight seals 8 and gas-tight seals 9 which are used to maintain a vacuum in the space between the stator winding 2 and the rotor 3.

A superconducting winding 10 (shown in Fig. 1 diagrammatically) is fixed within the cylindrical portion of the rotor 3 using, for example, an epoxy resin. The superconducting winding 10 has at least two supply leads 11, 12, according to the described embodiment, which are cooled. The supply lead 11 is coupled electrically to the superconducting winding 10 and to a plus sign current-collecting means 1 3 and is disposed in at least one cooling duct for cooling one of the end parts of the hollow shaft of the rotor 3. In the described embodiment there is a group of cooling ducts 1 4 arranged along a helix on the end part 4 of the hollow shaft of the rotor 3.The supply lead 1 2 is coupled electrically to the superconducting winding 10 and to a minus sign current-collecting means 1 5 and is disposed in an axial passage 1 6 which is made in the form of a tubing disposed in the end part 4 of the hollow shaft of the rotor 3 and connected with the cavity of the rotor 3.

The superconducting winding 10 is also connected hydraulically, for the purpose of cooling, with an axial passage 1 7 implement in the end part 5 of the hollow shaft of the rotor 3 as a tubing provided with thermal/vacuum insulation means and connected with an inlet means 1 8 for introducing the coolant into the rotor 3. To cool the end part 5 of the hollow shaft of the rotor 3, that end part is provided with cooling ducts 1 9 which are similar to the cooling ducts 14.

Exhausting means 20, 21, 22 for withdrawing the coolant from the rotor 3 are provided at the outlets of the cooling ducts 1 4, 1 9 as well at the outlet of the axial passage 16, in the end parts 4, 5 respectively of the hollow shaft of the rotor 3, said exhausting means 20, 21, 22 provide for a communication between the cooling ducts 1 4, 1 9 and the passage 1 6 and coolant collecting chambers 23, 24 mounted respectively on the end parts 4, 5 of the hollow shaft of the rotor 3. In the described embodiment, the exhausting means 20, 21, 22 are radial passages made in the wall of the hollow shaft of the rotor 3.

Mounted in the end face walls of the coolant collecting chambers 23, 24 are rotatable gastight seals 25 which are analogous to the rotatable gas-tight seals 9 (the seals 9, 25 are shown diagrammatically in Fig. 1).

In the described embodiment the currentcollecting means 1 3, 1 5 are disposed in the coolant collecting chamber 23, each being comprised of a metallic slip ring rigidly attached to the end part 4 of the hollow shaft of the rotor 3, and of a current-collecting brush.

To reduce the total inflow of heat to the superconducting winding 10 along the end parts 4, 5 of the hollow shaft of the rotor 3 and along the supply leads 11, 12, other embodiments dealing with their mutual arrangement are possible.

There is an embodiment which deals, in addition to the supply lead 11 connected to the plus sign current-collecting means 12, with another supply lead 26 (Fig. 2) disposed in the cooling ducts 1 9 for cooling the end part 5 of the hollow shaft of the rotor 3 and analogous to the supply lead 11. The supply lead 26 is electrically coupled to the superconducting winding 10 and to a plus sign current-collecting means 27 and is disposed within the coolant collecting chamber 24.

To reduce the pressure of the gaseous coolant in the rotor 3 and to increase the effectiveness of the exhausting means, which in turn results in greater effectiveness of the cooling ducts 14, 1 9 and the passage 16, one of the exhausting means, namely, that labelled at 20, is made in the form of a centrifugal wheel 28 (Figs. 3, 4) which is rigidly attached to the end part 4 of the hollow shaft of the rotor 3 at the location where the outlet of the cooling ducts 14 (Fig.

3) is positioned. The inlet of the centrifugal wheel 28 is located at the same radius as the outlet of the cooling ducts 1 4. The passages of the centrifugal wheel 28 and those of the outlet branch of the coolant collecting chamber 23 as well as the latter proper are so implemented that the coolant is delivered from the cooling ducts 14 to the centrifugal wheel 28 in a shockless manner and does so when it leaves the centrifugal wheel 28 and is introduced into the inlet branch of the coolant collecting chamber 23.

In the described embodiment the centrifugal wheel 28 is located in the coolant coliecting chamber 23 in close proximity to the plus sign (1 3) and minus sign (15) current-collecting means. The exhausting means 21, implemented in the form of radial passages providing a communication between the passage 1 6 accommodating the supply lead 1 2 and the coolant collecting chamber 23, is located between the centrifugal wheel 28 and the minus sign current-collecting means 15.'As stated above, each of the current-collecting means 13, 1 5 is comprised of a rotatable metallic slip ring and a graphite brush immovably mounted with respect to the rotor 3.

To eliminate the effect of the increased pressure of the gaseous coolant on the exhausting properties of the cooling ducts 1 4 within the coolant collecting chamber 23, it is good practice to implement the centrifugal wheel 28, which provides for a communication between the cooling ducts 14 and the coolant collecting chamber 23, in the form of discs 29 (Fig. 5) and 30 with a strip 31 helically wound therebetween as a helix. The strip 31 is so arranged that the width of a passage 32 formed by it and by the end faces of the discs 29, 30 increases a viewed from the periphery of the helix to its center and a direction, in which the width of the passages 32 (Fig. 6) increases, coincides with the direction of rotation of the rotor 3.In this embodiment it is good practice to have the plus sign (13, Fig. 5) and the minus sign (1 5) current- collecting means in the form of discs 33, 34 respectively which are made of a high electric conductivity material, for example, copper.

The discs 33, 34 are rigidly fixed, via thermal/electrical insulation gaskets 35, to the end part 4 of the hollow shaft of the rotor 3 at the outgoing points of the supply leads 11, 1 2. The discs 33, 34 are preferably disposed in individual spaces 36, 37 respectively formed by the end face walls of the coolant collecting chamber 23 and internal annular wall partitions 38, 39 and are coupled electrically via respective contacts 40, 41 to the terminals of the current-collecting means 13, 15, the contacts 40, 41 being made of a galliumindium eutectic alloy providing for electrical conduction. The casing of the coolant collecting chamber 23 and the partition walls 38, 39 are preferably made of a therma I/electrical insulation material which may be a conventional glass plastic or ceramic composition.

In the described embodiment the discs 29, 30 are disposed in a central space 42 formed by the partition walls 38, 39 and having a communication with the spaces 36, 37 through the agency of the coolant, while the exhausting means 21 providing a communication between the passage 1 6 and the coolant collecting chamber 23 is located between the discs 30, 34. The space 42 communicates with a coolant discharge branch 43 which connects the space 42 with a refrigerator (not shown in the drawings). The branch 43 has a widening cross-section, is mounted on a tangent line to the space 42 and has its outlet directed to the side opposite to the direction of rotation of the rotor 3.

In order to provide for centering the discs 33, 34 relative to the spaces 36, 37 respectively and to reduce the number of the gastight seals 25 (Fig. 7), the coolant collecting chambers 23, 24 are rigidly connected to the housings of the bearings 6, mounted in the endshields 7 of the casing 1, while the coolant collecting chamber 24 is additionally fixed to the inlet means 1 8. In the described embodiment the plug sign current-collecting means 27 disposed in the chamber 24 is analogous to the plus sign current-collective means 1 3 located in the chamber 23. The current-collecting means 27 comprises a disc 44, installed in a space formed by a partition wall 45 and the end face wall of the chamber 24, and a liquid-metal contact 46 analogous to the contacts 40, 41.

To provide for stable operation of the electrical machine of the invention during the start mode and under transient conditions, for better control of the flow rate of the gaseous coolant in the cooling ducts 14, 1 9 and in the passage 1 6 as well and for greater effectiveness of the three latter elements, it is good practice to make the supply lead 1 2 (Fig. 8), connected to the minus sign current-collecting means 15, a porous one and composed of a material incorporating two components A and B, the component A possessing a normal conductivity property and the component B possessing a superconductivity property.The components A and B are distributed over the length of the supply lead 1 2 in such a manner that the end of the supply lead 1 2 connecting to the current-collecting means 1 5 is made of a material composed of 100% the component A and the other end of the supply lead (12) connecting to the superconducting winding 10 (Fig. 1) is made of a material composed of 100% the material B. It is necessary that the contents of the components A and B be gradually diminished as measured in opposite directions from respective ends of the supply lead 12, beginning from their maximum values at these ends.In this embodiment there exists a portion in the middle section of the supply lead 12, amounting in length to 10 through 20 diameters of the lead 12, said portion comprising identical amounts of the components A and B.

In the described embodiment the supply lead 1 2 is fabricated using a conventional method (for example, sintering or molding) and offers a porous structure through the overall length from the superconducting winding 10 to the disc 34 (Fig. 8) of the currentcollecting means 1 5. Such a construction of the supply lead 1 2 makes it possible to combine it with a respective exhausting means. To this end, passages 47 are provided in the disc 34 while the supply lead 1 2 has a branched end whose branches are disposed in the passages 47. In the described embodiment there are eight passages 47 (Fig. 9) and eight branches of the branched end.

To provide for free and uniform passage of the coolant from the disc 34, which in turn provides for even distribution of heat over the latter, the outlets of the passages 47 (Figs. 8, 9) leaving the disck 34 of the current-collecting means 1 5 must (Fig. 8) be directed to the side of the space 42 of the coolant collecting chamber 23 and be located on a radius less than the radius of a free surface of the liquidmetal contact 41 (Fig. 9) generated during rotation of the rotor 3.

Arrows are used in Figs. 1, 2, 3, 4, 5, 6, 7, 8, 9 to indicate the direction of movement of the coolant.

To maintain the superconducting winding 10 (Fig. 1) in a superconducting state, it is submerged into a bath with a liquid coolant such as liquid helium. Due to the action of centrifugal forces on the liquid helium passing from the axis of the rotor 3 to its periphery, a pressure gradient is developed in the helium with the result that the temperature of the latter, as well as the temperature of the superconducting winding 10 to which the helium is supplied, are increased. To maintain the temperature of the coolant and, therefore, that of the superconducting winding 10 in preset limits, it is common practice to reduce the pressure of the gaseous phase of the coolant above its liquid phase. In the embodiment of Fig. 1 this is done in the following manner.

The liquid helium delivered under a small gauge pressure from a refrigerator (not shown in the drawing) via the inlet means 1 8 passes through the passage 1 7 into the cavity of the rotor 3 and into the passages (not shown in the drawing) of the superconducting winding 1 0. When passing from the axis of the rotor 3 to its periphery, the coolant tends to cool the superconducting winding 10 and is divided into liquid and gaseous phases. The liquid helium is accumulated on the inner wall of the cylindrical portion of the hollow rotor 3, while the gaseous helium tends to occupy the space in the vicinity of the axis of the rotor 3. In close proximity to the axis of the rotor 3 the gaseous helium is divided into three flows.

Two of the latter are supplied to the cooling ducts 14, 1 9 for cooling the end parts 4, 5 of the hollow shaft of the rotor 3 whereas a third flow passes into the passage 1 6 accommodating the supply lead 1 2 and providing for a communication between the superconducting winding 10 and the minus sign current-collecting means 1 5. Since the liquid helium provides for a higher heat transfer to the superconducting winding 10 as compared to the gaseous helium, the temperature of the superconducting winding 10 is determined by the temperature of the liquid helium distributed over the inner wall of the cylindrical portion of the hollow rotor 3.The superconducting winding 10 receives more cooling in the case of higher exhausting properties of the cooling ducts 14, 1 9 and respective exhausting means 20, 22 which provide for a communication between the cooling ducts 14, 1 9 and respective coolant collecting chambers 23, 24.

The reduction of the temperature of the liquid helium and, therefore, that of the superconducting winding 10 will depend on the amount of heat conducted to the superconducting winding 10 and to the liquid helium from the end parts 4, 5, from the supply leads 11, 1 2 and from the current-collecting means 13, 1 5. For this purpose, the gaseous helium supplied to the cooling ducts 14 passes to the end part 4 of the hollow shaft of the rotor 3 with the supply lead 11 and to the plus sign current-collecting means 1 3 to flow inwardly of them, whereas the gaseous helium supplied to the cooling ducts 1 9 conducts inwardly of the end part 5 of the hollow shaft of the rotor 3. To provide for intense removal of heat from the supply leads and currentcollecting means, the supply leads connected to the minus and plus sign current-collecting means are made independent of each other, whereas the current-collecting means are located in the coolant collecting chambers which also accommodate the exhausting means for withdrawing the coolant from the rotor, said latter means being used to connect the chambers with the cooling ducts. In the described embodiment the supply lead 1 2 connected to the minus sign current-collecting means 1 5 is disposed in the passage 16, while the exhausting means 21 as well as the minus sign current-collecting means 1 5 are located in the coolant collecting means 23.As a consequence, the gaseous helium applied to cool the supply lead 12, as well as the gaseous helium applied to cool the supply lead 11 disposed in the cooling ducts 1 4 of the end part 4 of the hollow shaft of the rotor 3, pass the cooling ducts 14 and the passage 1 6 and enter, via respective exhausting means 20, 21, the coolant collecting chamber 23.In the latter the two flows of gaseous helium are joined together and used to cool concurrently the plus sign current-collecting means 1 3 and the minus sign current-collecting means 1 5. The gaseous helium leaving the coolant collecting chamber 23 is delivered to a refrigerator (not shown in the drawing) which also receives the flow of the gaseous helium passing through the cooling ducts 1 9 and the exhausting means 22 to the coolant collecting chamber 24.

In the course of its movement the coolant tends to absorb some amount of heat produced by the above-described elements, thereby resulting in the transfer of heat from them. As a result, the inflow of heat to the superconducting winding 10 is restricted.

In the embodiment having two supply leads 11, 26 (Fig. 2) connected to the plus sign current-collecting means 13, 27, the transfer of heat from the end parts 4, 5 of the hollow shaft of the rotor 3, from the supply leads 11, 1 2 and from respective current-collecting means 1 3, 1 5 of plus and minus sign, as well as the cooling of the superconducting winding 10, are accomplished in a manner similar to that described above.The only difference is that the heat is also removed from the supply lead 26 disposed in the cooling ducts 1 9 and from the plus sign current-collecting means 27 so that the inflow of heat to the superconducting winding 10 is effected more adequately in the start mode and in the case of transient conditions where the current values exceed their rating by a factor of 3 to 5. The actuator for the supply lead 26 (not shown in the drawing) may be located both outside or inside the electrical machine.When the supply lead 26 is turned on or off, it is necessary to control the flow rate of the coolant passing through the cooling ducts 14, 1 9 and passage 1 6 in order to attain their optimum operation in relation to the total inflow of heat conducted to the superconducting winding 10 along the end parts 4, 5 of the hollow shaft of the rotor 3 and along the supply leads 11, 12, 26 disposed respectively in the cooling ducts 14, 19 and the passage 16.In principle, this kind of control can be effected with the help of controls (not shown in the drawing) which could be installed only at the outlets of the cooling ducts 14, 1 9 and passage 1 6 in a "heat-transmitting'' zone; if this is not so, the construction of the machine becomes much more complex and its reliability is reduced. The above-mentioned controls may be automatic throttling devices mounted at the outlets of the cooling ducts 14, 1 9 and passage 1 6 respectively. However, the use of such devices in conjunction with the rotatable ducts makes the machine construction more complex and causes irrecoverable loss due to the throttling of the coolant passing through the devices.For this reason, at least one of the exhausting means which provides for communication between the cooling ducts 14 and the coolant collecting chamber 23 takes the form of the centrifugal wheel 28 (Figs. 3, 4).

Controlling the pressure in the coolant collecting chamber 23 makes it possible to redistribute the flow rate of the coolant relative the cooling ducts 14 and passage 1 6.

To provide for more effective control of the flow rate of the coolant in small electrical machines or machines with a low flow rate of the coolant, a preferable embodiment includes at least one of the exhausting means comprising two discs 29 (Fig. 5), 30 with a helical strip 31 disposed therebetween. In this embodiment an increase in the pressure of the gaseous helium in the coolant collecting chamber 23 tends to deteriorate the exhausting properties of the cooling ducts 1 4 to much less extend, whereas the flow rate related to the passage 1 6 can be increased or decreased depending on the operating mode of the machine.

To cool the current-collecting means 13, 1 5 more effectively, they comprise the discs 33, 34 with the liquid-metal contacts 40, 41.

Additional cooling for the means 13, 1 5 is provided by the gaseous helium passing in the coolant collecting chamber 23. In operation, the discs 33, 34 cause the contacts 40, 41 to rotate with the result that the latter are distributed evenly over the spaces 36, 37 and better cooling is therefore attained. Liquidmetal contacts possess as a ruie high chemical activity and their normal operation is thus achieved only under vacuum conditions or in the inert atmosphere provided, for example, by argon or helium. The gaseous helium passing into the chamber 23 therefore prevents the contacts 40, 41 from being oxidated.At the same time, the coolant itself is protected by the discs 33, 34 and contacts 40, 41 from foreign matter resulted from a wear of the gas-tight seals 25 of the coolant collecting chamber 23; the coolant is also prevented from being contaminated by foreign matter produced during a wear of the current-collecting means 13, 1 5.

To reduce hydraulic loss at the outlet of the chamber 23, the latter has a widening branch 43 (Fig. 6) which is affixed to the chamber 23 on a tangent line thereto and is directed to the side opposite to the direction of rotation of the rotor 3. The coolant leaves the passage 32 in which it is subject to twisting, enters the branch 43 without considerable hydraulic loss and then passes to the inlet of a refrigerator (not shown in the drawing).

In the embodiments shown in Figs. 7, 8, 9 the electrical machine of the invention operates in a manner similar to that described in the case of Figs. 1, 2, 3, 4, 5, 6. The only difference is that the coolant leaving the cooling ducts 1 9 (Fig. 7) for cooling the end part 5 of the hollow shaft of the rotor 3 provides for an additional protection of the liquid-metal contact 46; in addition, the coolant itself is prevented from being contaminated by foreign matter, namely, the particles resulted from a wear of the gas-tight seal 9 by the disc 44 of the plus sign current-collecting means 27 disposed in the coolant collecting chamber 24.

After teaving the latter, the coolant enters the refrigerator through the branch 43.

To provide for troublefree operation of the electrical machine of the invention during the start mode and under transient conditions and to improve its reglation response, the flow rate of the coolant as related to the supply lead 1 2 and passages 47 (Figs. 8, 9) is preferably so selected that the component B of the supply lead 1 2 becomes superconducting at that point where the percent contents of the components A and B are equal to each other. In this case, the supply lead 1 2 operates adequately which means that the amount of heat conducted through it to the superconducting winding 10 is kept at a minimum and is not dependent upon abrupt changes of the current.

To provide for due thermal insulation between the stator winding 2 (Fig. 7) and the rotor 3, the space between them is evacuated and a vacuum condition therein is maintained by virtue of the gas-tight seals 9 of the hollow shaft of the rotor 3 and continuously operated vacuum pumps (not shown in the drawing). A vacuum-tight insulation must be also provided between the end parts 4, 5 of the hollow shaft of the rotor 3 and the passages 16, 1 7 used respectively to introduce the coolant in and withdraw it from the cavity of the rotor 3.

The construction of the electrical machine of the invention makes it possible to withdraw the gaseous helium from the cavity of the rotor on a more effective basis. Since the removal of the gaseous helium results in a decrease in the pressure of the latter present above the liquid helium within the rotor, then the pressure and temperature of the coolant itself and, therefore, the temperature of the superconducting winding are reduced. A decrease in the temperature of the superconducting winding results in its greater reliability and in an increase in the density of the current flowing through the superconductor; as a result, the efficiency of the whole machine is increased.As the machine runs at a greater number of revolutions, the helium is withdrawn at higher rate and favorable tem perature conditions for the superconducting winding are created; on the other hand, more efficient use of the "heat-absorbing" property of the helium vapor in cooling the end parts of the shaft, supply leads and current-collecting means provides for a decreased overall consumption of the helium necessary for maintaining the superconducting state of the superconducting winding.

The arrangement of the supply leads connected to the current-collecting means of plus and minus sign in independent passages ensures simpler insulation methods for the leads and makes them more reliable since the shaft possesses higher heat capacity as compared to that of a supply lead; as a result, the supply leads connected to the plus sign current-collecting means are not affected considerably by heat surges occurred in the machine during the start mode and under transient conditions. On the other hand, the supply leads connected to the minus sign currentcollecting means are made of a porous material composed of the components A and B possessing respectively normal conductivity and superconductivity properties.This allows for an extension of the zone in which these supply leads become superconducting; as a result, the current flowing through the supply leads and the amount of gaseous helium required for their adequate operation can be adjusted in a wide range.

The supply leads connected to the currentcollecting means of plus and minus sign can be cooled in a better way due to the Peltier effect as follows. In a supply lead connected to a plus sign current-collecting means a certain amount of heat is absorbed at the soldered joint between a conventional conductor and a superconductor incorporated in the lead. On the other hand, in a supply lead connected to a minus sign current-collecting means the same amount of heat is evolved in an identical condition. Since the "minus sign" supply lead has a greater contact area for helium, the above-mentioned heat can be removed with ease. The joint arrangement of the exhausting means and the current-collecting means makes it possible to operate them in a better way. The outgoing gaseous helium provides for intense cooling of the rotatable liquid-metal contacts and prevents the latter from being oxidated. At the same time, the liquid-metal contacts tend to resist a contamination of the outgoing gaseous helium with foreign matter produced due to a wear of the rotatable gas-tight seals. The above-mentioned advantages provide for an increase of the reliability and efficiency of the machine of the invention and for a decrease of the operational cost.

Claims (8)

1. An electrical machine with cryogenic cooling having a hollow rotor filled with a coolant, said rotor comprising a superconducting winding with at least two supply leads being cooled, a first one of said two supply leads being coupled to a plus sign currentcollecting means and disposed in at least one cooling duct for cooling one end part of a hollow shaft of the rotor, the cooling ducts for cooling the both end parts of the hollow shaft of the rotor being connectevia respective exhausting means for withdrawing the coolant from the rotor, with respective coolant collecting chambers, a second one of said two supply leads being coupled to a minus sign current-collecting means.74the hollow shaft of the rotor being supported in bearings, each having a housing with a seal, and being provided with a passage for feeding the coolant to the superconducting winding, said passage being coni, nected with an inlet means for introducing the coolant into the rotor, the inlet means being disposed in the second end part of the hollow shaft of the rotor, a second passage being implemented in the first end part of the hollow shaft of the rotor and being connected with the cavity of the rotor and with a first one of said coolant collecting chambers via a third exhausting means for withdrawing the coolant from the rotor, the second supply lead being disposed in the second passage, and the current-collecting means being disposed in the first coolant collecting chamber.

2. An electrical machine as claimed in claim 1 having two supply leads connected to plus sign current-collecting means and disposed in cooling ducts for cooling end parts of the hollow shaft of the rotor, one of the current-collecting means, connected to the supply lead which is disposed in the first end part of the hollow shaft of the rotor together with that supply lead which is coupled to the minus sign current-collecting means, being disposed, together with the latter, in the first coolant collecting chamber.

3. An electrical machine as claimed in claim 1 or 2 having at least one of the exhausting means for withdrawing the coolant from the rotor arranged to provide communication between a respective cooling duct for cooling a respective end part of the hollow shaft of the rotor and a respective coolant collecting chamber and implemented as a centrifugal fan which is installed on the outlet end member of a respective cooling duct for cooling the first end part of the hollow shaft of the rotor and is disposed in the first coolant collecting chamber in close proximity to one of or both current-collecting means available in the first coolant collecting chamber.

4. An electrical machine as claimed in claim 3 in which the centrifugal fan comprises two discs with a strip fixedly wound therebetween to take the form of a helix so that the width of a passage formed by the strip increases as viewed from the periphery of the helix to its center in a direction coinciding with the direction of rotation of the rotor.

5. An electrical machine as claimed in any one of the preceding claims in which each of the current-collecting means comprises a respective disc rigidly mounted on the hollow shaft of the rotor and located in a respective space each formed by a respective end face wall of the first coolant collecting chamber and a respective partition wall made in that chamber, the spaces being filled with a liquidmetal alloy providing for electrical conduction and being connected with each other through the coolant.

6. An electrical machine as claimed in claim 5 in which at least one of the coolant collecting chambers is made of an electrical/thermal insulation material and is rigidly attached, by virtue of its end face wall facing a respective bearing, to the housing of that bearing in order to provide for centering a respective disc of a respective current-collecting means disposed in a respective coolant collecting chamber with respect to the latter, the coolant collecting chamber, disposed on the second end part of the hollow shaft of the rotor in the vicinity of the inlet means for introducing the coolant into the rotor, having its end face wall facing the inlet means in additional fixed relation to the latter.

7. An electrical machine as claimed in any one of the preceding claims in which the supply lead connected to the minus sign current-collecting means is a porous one and is made of a material composed of two components A and B, the component A possessing a normal conductivity property and the component B possessing a superconductivity property, the components A and B being distributed over the length of the supply lead in such a manner that the end of the supply lead connecting to the current-collecting means is made of a material composed 100% the component A and the other end of the supply lead is made of a material composed of 100% the component B and that the contents of these components A and B gradually diminish as measured in opposite directions from respective ends of the supply lead, beginning from their maximum values at these ends.

8. An electrical machine substantially as herein described with reference to any of the Figures of the accompanying drawings.