US3705775A

US3705775A - Gas turbine power plants

Info

Publication number: US3705775A
Application number: US106380A
Authority: US
Inventors: Christian Paul Gilbert Rioux
Original assignee: SNECMA SAS
Current assignee: Safran Aircraft Engines SAS
Priority date: 1970-01-15
Filing date: 1971-01-14
Publication date: 1972-12-12
Anticipated expiration: 1989-12-12
Also published as: DE2101918B2; DE2101918C3; DE2101918A1; FR2076450A5; GB1340363A

Abstract

A gas turbine power plant comprising a compressor, a turbine and a system for transmitting the drive from the turbine to the compressor, wherein the transmission system comprises at least one homopolar electrical machine connected to the turbine and operating as generator, and at least one homopolar electrical machine connected to the compressor and operating as motor, wherein this motor is supplied with electrical current from the said generator.

Description

I Un1ted States Patent [151 3,705,775 Rioux 1 Dec. 12, 1972 [54] GAS TURBINE POWER PLANTS H I Re ferencesQitetl [72] Inventor: Christian Paul Gilbert Rioux, An- UNITED STATES PATENTS tony, France 2,914,688 11/1959 Matthews ..310/178 [7 Assigneer Swete Natwnale d Etude et 3,585,398 6/1971 Harvey ..310/178 x struction de Moteurs dAviation, Paris, France FOREIGN PATENTS OR APPLICATIONS 1221 Filed: Jan. 14, 1971 595,357 12/1947 Great Britain ..60/269 [2] 1 Appl' 10638.0 Primary ExaminerRobert M. Walker Attorney-William J. Daniel [30] Foreign Application Priority Data [57] ABSTRACT Jan. 15, 1970 France ..7001437 1 A gas turbine power plant comprising a compressor, a [52] U.S. Cl. ..417/411, 417/423, 60/269, in n a System for transmitting the drive from 310/178, 417/408 the turbine to the compressor, wherein the transmis- [51] I t, Cl ..F04b 17/00, F041 35/04, F02k 3/00, sion system comprises at least one homopolar electri- F16 35/00 cal machine connected to the turbine and operating as [58] Field of Search ..417/408, 411, 423; 310/178; g n rat r, and at least one homopolar electrical 318/253; 60/268, 269 machine connected to the compressor and operating as motor, wherein this motor is supplied with electrical current from the said generator.

ZQ QIaims, 15 Drawing Figures Mimi/111M 1 1 15 PATENTEU DEC 12 I972 SHEET 1 BF 8 PATENTEUnEc12 I972 SHEET l [1F 8 FIGS PATENTEDUEE 12 I972 3305. 775

SHEET 5 BF 8 FIG. 3

PATENTED DEC 12 I972 SHEEI 8 [IF 8 GAS TURBINE POWER PLANTS The invention relates generally to gas turbine power plants, and more particularly to power plants intended to be used as-jet propulsion power units in aircraft.

Gas turbine power plants used at present comprise at least one compressor supplying one or several combustion chambers, and at least one turbine in which the gases leaving the chamber or chambers are at least partially expanded. The turbine supplies the power required for driving the compressor and the auxiliary elements. Certain power plants have different gas or air paths which may be associated with at least one addi tional compressor or blower (multiple flow or by-pass installations). In the following the term compressor comprises also a blower of this kind.

Up to the present it has always been the case that at least one rotary transmission shaft has been used for connecting the turbine with the compressor (or blower) the shaft forms an element which is simple and light and the transmission performance of which may be very high.

However, the use of such a transmission means presents certain drawbacks which may be particularly undesirable, particularly in power, plants which are required to operate under widely varying operating conditions and from which high performances are required The speed and the direction of rotation of the compressor are obviously determined by those of the turbine, which makes it difficult to select the optimum speed of the different stages of the compressor for each running condition. The drawbacks of this condition have been limited to some extent by-using a compressor with several stages, each of which is driven separately by a turbine element; However, this method requires the use of several coaxial shafts which are very difficult to realize, since they present serious mechanical problems (great torsional stresses, different inherent frequencies), and necessitate particularly complicated bearing systems.

Since successive wheels of the compressor are mechanically interconnected with each other, it is necessary to provide between them fixed guide wheels which substantially increase the mass and the dimensions of the unit. It is known to eliminate this drawback by driving two successive wheels of the compressor by a center shaft and a tubular outer shaft respectively, which are connected to two contrarotating elements of the turbine. However, the construction of such a system brings about difficulties similar to thosealready mentioned above.

The invention has the object of removing at least the major part of the drawbacks of this transmission system, and even to remove them almost totally in certain preferred embodiments, although these are by no means exclusive. To this end, the invention proposes a gas turbine power plant of a kind comprising a compressor, a turbine and a system for driving this compressor from the turbine, wherein this driving system comprises atleast one homopolar electric generator connected to the turbine, and at least one homopolar motor connected to the compressor and supplied by this generator.

ln order to explain better the advantages resulting from these arrangements, it will be necessary first to discuss some of the features relating to homopolar machines, generators, or motors.

The most conventional example of a homopolar machineis the device known as Barlow s wheel.

Like the majority of reversable electrical machines, homopolar machines use the interaction between an electric current and a magnetic field, the so-called induction field. The current fiows in a rotary armature formed by an assembly of conductors'which may be separate from each other or not. This armature has no windings or pole pieces and may have about its axis of rotation a strictly revolutionary symmetrical shape, becoming thereby a very simple, very light and particularly robust element since the mechanical stresses may be uniformly distributed. The induction field necessary for the operation of such a machine has preferably a revolutional symmetry. Constructions of this kind can be obtained particularly simply in the known art.

The electrodynamic force relative to theaxis of rotation is greatest when at each point of the armature the vector density of the current and the magnetic field vector are perpendicular to each other and are located in one and the same axial plane. These conductions leave much choice for the construction of an efficient armature. l-lowever, amongst all the possible shapes it is possible to distinguish between two extreme types a. homopolar machines with radial field the current lines must be axial, and the armature may have the shape of a thin cylindrical ring, the two lateral ends of which form the electrical turbines b. homopolar machines with axial field in this case the current lines mustbe radial and the armature may be formed by a thin homogenous disc in which the two electrical terminals are formed by' the two concentric circles defining the same.

Generally, the electromotive force (or counter elec- 'tromotive force) E of a homopolar machine is given by the relation in which is the flux of the magnetic induction passing through the armature and m is the angular velocity of the armature.

The utilization of homopolar machines for the transmission of energy between the turbine and the compressor of a gas .turbine power plant is of great interest in view of their extremely high mass power, their great simplicity, and their symmetry of revolution which makes them easily integrated into the structure of the power plant, to which they impart a great operational flexibility, as will be shown further below.

Amongst the characteristics of homopolar machines there are certain features which make the use of nonconventional means highly preferable, although not absolu tely essential for carrying out the invention, which means particularly facilitate the use of highintensities and induction fields for obtaining motors or generators which combine great power withan excellant electric power yield, whilst the dimensions, either axial or radial, are of the same order as rotating elements in conventional gas turbine power plants.

Thus, for example, the intensity of the current flowing through the armature of a homopolar motor driving a bladed rotor of the compressor of a gas turbine jet must be of the order of 10 to 10 amperes. At the rotationalspecds which are currently used and which are comparatively high, the problem of making electrical contact between the rotating armature and the supply leads has not been satisfactorily solved by the use of a conventional ring type commutator, which gives rise to comparatively high losses caused by friction and by the Joule effect. A preferred solution consists in using a ring of liquid metal retained between two conducting walls, one of which forms the fixed part, and the other the revolving part of the electric contact zone. To this end, it is possible to use, for example, mercury, a mercury-indium alloy, a eutectic of potassium and sodium, or generally any metal or alloy which combines good electric conductivity with a melting point which is lower than the temperature under which this metal or this alloy operate during the running of the machine, or preferably to the minimum ambient temperature under service conditions.

The requirements relating to the electric power yield and to the power to be transmitted lead, at the given rotational speed, to the use of high flux values dz. In order to concentrate the latter within a small region and to reduce thereby the dimensions of the armature as far as possible, it is necessary to utilize high intensity induction fields, of the order of several Teslas, which may be supplied by the coils of superconducting fields.

By means of induction windings formed, for example, form an alloy of niobium and titanium and held in a state of superconductivity by a bath of liquid helium, fields of 8 to 9 Teslas may be obtained. Alloys of niobium and tin which are studied at present make it possible to reach values in excess of Teslas.

The superconducting field coils may be formed by a thin ring formed by tight turns centered on the axis of rotation of the homopolar machine. In a machine with radial field, the field may be produced by two of such coils located on either side of the cylindrical armature, and carrying current in opposite directions. In a machine with axial field, thearrangement of the coils may be the same, but the currents must flow through the coils in the same direction.

The electrical consumption of superconducting field coilsin negligible in fact, it is reduced to the dissipation under the Joule effect in the parts of the induction circuit which are not in the superconducting state, that is to say in the connections.

Tl-le control of the speed to of a homopolar motor may be effected by acting on the intensity of the current which flows through the field coil in order to modify the flux dz: if several homopolar motors are used of which each drives an element or a stage of the compressor, it is possible to adapt the speed of each motor for any running condition of the power plant in such a manner that the aerodynamic yield of the unit is at optimum value. Since the current intensities flowing through the field coils may have comparatively low values, the construction of the means for adjusting or controlling. these values do not present any major technical problem. I

The particular properties of the means hereinbefore described make it also possible to solve by simple means the problems of compensation aerodynamic stresses, and of eliminating conventional bearings hitherto used for this purpose.

. from these stresses. It follows therefrom that it is possible to calculate the armature of a homopolar machine in such a manner that the inclination of the current lines (which plays here a role rather similar to that of the blades of a wheel) gives rise to-an exact compensation of the resultant of the axial aerodynamic stresses affecting a wheel or a group of combined wheels of this armature in consequence of the resultant of the corresponding axial electrodynamic stresses for any permanent running condition. Complementary means using this principle will be described further below and are adapted to maintain this balance during transitional running conditions, if necessary. By way of example, an embodiment of the invention uses for this purpose oblique slots in the armature of machines with radial fields. I e

In so far as the radial stresses are concerned, which affect the wheels, their rotating contact of liquid metal may combine the function of electric conduction with that of centering bearings, using techniques known I from fluid hydrostatic or hydrodynamic bearings.

By way of example, we may mention the following numerical data which correspond substantially to the characteristics to be looked for in a drive motor for an axial compressor with several stages in a turboreactor with fairly high thrust Total power input 1 MW Overal yield 98,9 Electromotive force 20 volt Rotational speed 1,000 r.p.s. Mean induction field: l0 Teslas The armature is of copper alloy and liquid contacts of mercury are used. The overall output takes into account the losses under the Joule effect in the armature and in the contacts, and the losses incurred by viscous friction at the level of the contacts,

For the two particular types of homopolar machines referred to above, the following features are arrived at which give an idea of the factors according to which a choice may be made between these two types, or a type of intermediate construction at different levels where its use may seem desirable a. for a radial induction machine The working part of the armature is a cylinder of mm radium, 1 mm thickness, and 50 mm length. Its mass is 280 grammes and its mass power is 4.10 W/kg.

b. For an axial induction machine The armature comprises a disc with 100 mm inner radius, l20 mm outer radius, and 3 mm thickness. its mass is 370 grammes and its mass power 2.7 X 10 W/kg.

Thus, in addition to their extremely high mass power, their great simplicity and their symmetry of revolution, which make it particularly easy to construct compact assemblies in a simple manner in which a homopolar machine is perfectly integrated with an element for a stage of a compressor or turbine without substantially increasing the mass or the bulk of these parts, the homopolar machines of an electrical transmission in accordance with the invention may form with the current leads which interconnect them, and the means for producing magnetic induction fields, an assembly which has generally an almost perfect rotational symmetry, which coincides very advantageously, especially both in the functional plane and in the morphological plane, .with the axial rotational symmetry which is so important to the conception and operation of turbine power plants.

Another property of the assembly of great interest is that the most advantageous aerodynamic configuration in which all the stages of the compressor and all the stages of the turbine are relatively contra-rotating, may correspond to the simplest and most efficient electrical layout, in which the generators and motors are in series, thereby increasing to a maximum simultaneously the mechanical, electrical and aerodynamic efiiciency, whilst maintaining the capability of controlling the speed of each stage in a practically independent manner by acting independently on the current flowing through the field coils, co-operating with each wheel or group of wheels.

The invention also comprises other arrangements which may be used advantageously in with those mentioned above in a general manner, but may also be applied independently.

The following description given by way of example,

with reference to the accompanying drawings, explains how the invention may be carried into practice.

In the drawings FIG. 1 shows diagrammatically a single flow gas turbine power plant, using an electrical transmission in accordance with the invention, and shown in axial crosssection FIGS. 2 and 3 are axial cross-sections showing in greater detail respectively a part of the compressor and of the turbine, forming part of the power plant shown in FIG. I

FIG. 4 is a cross-section along the line IV-IV in FIG. 2 or in FIG. 3 of the center structure of the power plant shown in FIG. 1

FIGS. 5 and 6 are diagrams showing in development the preferred means for compensating aerodynamic axial stresses FIG. 7 shows diagrammatically in elevation a modification of the arrangements in accordance with FIGS. 5 and 6 FIGS. 8 and 9 represent, in axial cross-section and in development, respectively, other arrangements for compensating axial stresses, and comprising means for controlling this compensation;

FIGS. 10 and II represent, respectively, in elevation and in axial cross-section, a modification of the arrangements in accordance with FIGS. 8 and 9 FIG. 12 is an axial half-section of another modification of a compressor and the means for driving the same FIG. 13 is an axial half-section of yet another modification of a compressor and the means for driving the same FIG. 14 shows diagrammatically in axial cross-section a double flow gas turbine power plant, comprising a blower driven by an electrical transmission according to the invention FIG. 15 is a more detailed axial cross-section of the transmission elements driving the blower shown in FIG. 14.

The gas turbine power plant shown in FIG. 1 is of the single flow type and is formed by a gas turbine jet engine mounted, as known per se, in a housing 8 provided with an air inlet 9 and terminating in a jet pipe 10. Viewed in the direction of flow, this engine comprises a compressor A, for example with ten stages, a combustion chamber C, and a two-stage turbine D. The direction of the gas flow is indicated by the arrow F. Contrary to conventional arrangements, the center structure of the engine, shown generally at S, is formed by coaxial elements which are all stationary. These elements serve as supports for the rotating parts of the compressor and of the turbine, ensure the mechanical rigidity of the assembly, and the transmission of the electrical current produced by the generators to the motors the path of the electrical current is indicated diagrammatically by arrows I. The center structure S is rigidly connected with the housing 8 by radial arms, such as 13 and 15. The compressor wheels A which are all contra-rotating, are driven independently from each other by homopolar electrical motors supplied by equally independent homopolar generators, coupled with the wheels of the turbine D which are also contrarotating. The center structure S (FIGS. 2, 3 and 4) is constituted by three fixed coaxial parts a solid shaft 11, and intermediate staged cylinder 16, and an outer cylinder 44. The center shaft 11 forms a first electrical conductor which connects the generators with the motors. The intermediate cylinder 16 is keyed coaxially to the center shaft 11 by an annular spacer 12, and a ferrule 14 (FIGS. 2 and 3) which locate the shaft 11 at its ends. It forms by means of bearings the support for the rotor wheels of the compressor and of the turbine. The cylinder 44 is adjacent to the preceding to which it is connected. It forms a second electrical conductor between the generators and the motors.

The intermediate cylinder 16 which makes mechanical contact with various elements which it supports and which have different electrical potentials, is coated along its periphery with a coating of alumina 89 (FIG. 4) which provides the necessary electrical insulation. Since the voltage differences are always less than a few hundred volts at the most, this layer may be sufficiently thin to present no mechanical problem, and no impairment of the evacuation of heat. As will be seen further below, the center structure may be cooled by a system of channels in which the fuel circulates.

The compressor A, whose upstream and downstream parts are shown in FIG. 2, comprises ten contra-rotating stages which are each associated with an homopolar motor.

The wheel 122 which forms the first stage of the compressor comprises a ring of vanes mounted on a support consisting of a rim 124 adapted to receive the vanes, connected by fittings 126 to the armature 128 in the form of the drum of the corresponding homopolar motor. The electric current flows through the armature 12% in the axial direction. It is supplied by two

rotating contacts

130 and 131 of liquid metal, located substantially at the lateral ends of the armature 128. These rotating contacts also form fluid bearings for centering the wheel. Each of them consists of a ring of liquid metal wetting two co-operating surfaces, one of which forms one end of the rotating armature with which the wheel 122 is firmly connected, and the other is a stationary shoulder which simultaneously ensures the flow of the 'cur rent and the correct position of the wheel during rotation. r

The fixedpart of the contact 130 is a shoulder 16a of the front 'end of the intermediate cylinder'l6, which is in electrical contact with the conducting center'shaft 11, through theannular spacing element 12. The fixed part of the contact 131 is a shoulder 1340 of the ring 134, which is electrically insulated from its support 16 by the alumina film 89 mentioned above.

The armature 128 may be, for example, of alloyed copper having at the same time an excellent electrically conductivity and a satisfactory mechanical stability.

The induction field is provided by two super-com ducting fields coils 36 aNd 136 comprising a certain number of turns and wound along the axis of the wheel. They are located substantially to the right of either end of the armature .128, and are supplied by current passing through each of them in opposite directions, so

as to provide an induction indicated schematically by the force lines (arrows B), the direction of which is substantially radial in the vicinity of the armature 128.

The following stages of the compressor have a construction identical to the first stage, and for this reason FIG. 2 shows only the three first and the two last stages. The

rotating contacts

230 and 231 of the wheel 222 of the second stage have, respectively, as fixed parts, a second shoulder 134b of the ring 134 and a first shoulder 234a of the ring 234 which, as above, is integral with the intermediate cylinder 16 and electrically insulated against the same. The ring 134 therefore, makes electrical contact between the downstream end of the armature 128 of the first stage and the upstream end'of the armature 228 of the second stage. Similarly, in so far as the

armature

228 and 328 of the second and third stages are concerned, and so on up to the tenth stagewhich rests through the liquid contact 1031 on the shoulder 44a of the outer cylinder 44, forming as outlined above, .the second element of the assembly of two conductors transmits to the compressor the electric energy produced by the generators coupled to the turbine.

The induction field of the'homopolar motor of the second stage of the compressor is formed by the field coil 136 and a field coil 236. The latter coil carries the current in the same direction as the coil 36, and the field lines, represented by the arrows B, are substan-, tially radial in the vicinity of the armature 228.

Theinterrnediate coils, such as for example the coil 136, are common to two consecutive compressor stages by means of the formation of the induction field. They are supplied in such a manner that anytwo consecutive coils carry current in opposite directions. The feed circuit for these coils has not been shown, but the means for its construction will be outlined further below.

During operation the armatures carry electric current in series and in the same direction and have a magnetic induction flux, the sign of which changes from one stage to the next. It follows therefrom that any two consecutive stages revolve in opposite directions. It may be noted that this effect is obtained by the simplest possible arrangement, both of the armatures and of the field coils.

The field coils 36, 136T". 103 a... formed by assembly of coils is mounted in a thermal insulating casing 45 equipped with

channels

46 and 48 forming an inlet and an outlet for liquid helium; this casing is fitted between the center'shaft and the intermediate cylinder The field coils of each homopolar motor of the compressor are preferably connected to a general programming system, not shown, which, by manual or preferably automatic control of the current intensity passing through each coil, makes it possible to vary the corresponding induction field and to adjust the rotational speed of each stage of the compressor in such a manner that its aerodynamic output has an optimum value under all flying conditions. Althoughthe means for obtaining the induction field forjeach stage are not completely independent from one stage to the following, such an adjustment is practically possible within much wider limits than thosewhich' are necessary to permit the aerodynamic adaptation mentioned above.

In the same wayas with the compressor, the stages of the turbine shown in FIG. 3 are contrarotating and each associated with the armature ofa homopolar machine. They also comprise turning contacts of liquid metal forming at the same time fluid centering bearings.

The first wheel of the turbine 1 comprises a ring of vanes mounted in a rim 152 which forms part of the armature 154 of the homopolar generator with which it is associated. The armature.154 comprises a drum-shaped zone 154a which extends radially towards the periphery to form a disc-shaped section 154b. The arrangement of the armature 254 of the second stage is symmetrical to that of the armature 154, and its construction is identical thereto.

The axial end of the zone 1540 makes electrical contact with a shoulder 44b of the outer cylinder 44 by means of a rotating contact 161- of liquid metal. The radial end on the periphery'of the zone 1541; makes I electrical contact with the corresponding part of the armature 254 by means of

rotating contacts

162 and 262 of liquid metal through a fixed ring 56 forming part of a disc 54 which is mounted on the intermediate cylinder 16. 1 Finally, a rotating contact 261 of liquid metal makes electrical contact between the axial end of the zone 254a, having the form of the armature drum 254 and the center shaft 11 through a ferrule 14. The two generators are, therefore, connected in series and electrically connected to the motors of the compressor by the said

conductors

11 and 44. The direction of the induction fields, explained further below, is such that the electromotive forces of the generators are additive.

The field coils of the generators, indicated by

reference numerals

60, 160, 260, 154, 254 are mounted substantially symmetrically relative to the median plane of two turbine stages. The

coils

60, and 260 are supplied with current flowing in the same direction, and form a substantially axial and comparatively uniform field in the disc-shaped part of the

armatures

154 and 254 of the generators. The two

coils

164 and 264 carry current in the same direction and opposite to the current flow in the

coils

60, 160 and 260. In view of the presence of the preceding, these coils form a substantially radial field near the drum-shaped zone of the armatures. The arrows B show diagrammatically the configuration of the field. Since the two turbine stages are counter rotating, it is clear that the electrical association of the armatures just described, which is the simplest possible, corresponds to the additivity of the electromotive force.

As in the case of the compressor, the field coils, 60, 160,260, 164, 264 are formed from a material which is maintained in the superconducting state by liquid helium in shells 70 surrounding the coils. In the same way as the armatures of the motors, the armatures of the generators are made from a metal having good electrical conductivity and a strength adequate to withstand mechanical stresses. As may be seen from FIG. 3, the disc-shaped part of the armatures of the generators acts mechanically after the manner of turbine discs of conventional turbojet engines and must withstand particula'rly considerable centrifugal stresses. For this reason, this zone may consist according to one modification of a composite material formed from two parts which are bonded together, of which one is an alloy of conventional composition and of high mechanical strength, and the other is thinner, consists of a high conductivity metal or alloy and acts as actual armature.

The circulation of the current between the armatures of the generators and the armatures of the motors is indicated by arrows I (FIGS. 2 and 3).

It should be noted that the liquid-solid interfaces at the level of the rotating contacts are so orientated that the magnetic field lines are substantially tangential thereto this arrangement makes it possible to eliminate losses caused by Foucault's currents inthe liquid metal during rotation.

FIGS. 2 and 3 do not show the electric circuit feeding the field windings of the homopolar machines. This circuit must supply at weak power a current of comparatively high intensity (several thousand amperes) and may comprise, for example, a static electrical convertor controlled by semiconducting elements of the type known as thyristors, which make possible a very flexible control of the intensity of the current flowing through them which makes them particularly suitable as control elements for the speed of the revolving bladed wheels of the kind the application of which has been mentioned above.

The cooling of the central structure S which is particularly subject to heating by the Joule effect is accomplished by circulating the fuel of the turbojet engine through

channels

72 and 74 provided in the intermediate cylinder 16, and in the center shaft 11. The fuel is admitted into the channels 72 arranged as a ring (FIG. 4) in the intermediate cylinder 16, and flows back through U-shaped connections 76 into channels '75 in the center shaft 11. The field circuit leads then to the injectors not shown in the drawing.

The axial stresses imposed on the compressor and turbine stages are compensated by generating an electrodynamic force in the sense opposite to the axial resultant of the aerodynamic stresses affecting the blading of each stage. To this end a tangential component may be given to the density of the current in the armatures of the corresponding homopolar machines, for example by providing slots such as shown in FIGS. 5 and 6 or, more generally, by making the electric conductivity of at least part of the armature anisotropic. It

is also possible to use field coils which are so arranged that that induction field has an appreciable tangential component near the armatures, but such an arrangement is not easy to realize.

FIG. 5 shows in development the configuration of the armatures of the compressor shown in FIG. 2. Each armature comprises a set of narrow slots 68 which are regularly spaced apart, possibly filled with an insulating or little conducting substance. These slots have the effect of inclining the current lines passing through the armatures 128 1028.

If C and F are, respectively, the moment and the axial resultant of the electrodynamic forces generated by the flow of the current, it follows, independently of the current intensity passing through the armature, that wherein a is the mean inclination of the slopes relative to the axis of rotation, and R is the radius of the armature. In the case of a compressor wheel, an inclination of the order of a few degrees makes it possible to obtain the necessary axial balance which is maintained under all continuous running conditions, as already indicated above.

The current lines passing through the armatures are indicated by the dotted line I. Their inclination corresponds substantially with that of the slots. In view of the directional change of the induction field in successive armatures, the slots are directed alternately in one direction and in the other.

FIG. 6 shows in development the configuration of the drum-shaped parts 154a and 254a of the turbine armatures shown in FIG. 3, comprising an identical system of regularly spaced slots 69. In view of the fact that the charge of each turbine rotor is much larger than that of each compressor rotor, and that the slots 69 occupy only a small part of the working surface of the armatures 154i and 254, their inclination is substantially greater than that of the slots 69 of the armatures of the compressor. It is sufficient to adjust once and for all the ratio between the intensities flowing through the coils I64 and 264 and those flowing through the peripheral coils such as 160 for the compensation of the axial stresses to be ensured for any running condition. However, while acting separately on the fonner, it is possible to achieve during operation a fine adjustment of the compensation without changing substantially the torques of the generators.

FIG. 7 shows a modification of the embodiment which makes it possible to produce an axial electrodynamic component in a disc-shaped armature. To this end, the armature 81 has a set of slots 82 which are regularly spaced apart and inclined at an angle a relative to the planes passing through its axis of rotation. These slots take up a radially more or less extended zone in which the induction field B has an appreciable radial component B,.

If one assumes in the armature 81 a substantially circular ring with a radius r located in the zone of the slots 82, and if B, is the axial component of the field B, the

106010 Ol2l since the means for producing the field B comprise only a single winding,the ratio K is also independent of the intensity of the current flowing through this winding, and, in the case of several windings, it depends only on the ratio of the intensities flowing through each wind- As above, a suitable value of the angle 11 makes it possible to ensure for any continuous running condition the required axial compensation.

In order to be able to carry out comfortably a fine adjustment of the electrical compensation of axial stresses, the arrangements shown in FIGS. 8, 9, l and 11 may be used.

FIG. 8 shows diagrammatically two consecutive compressor rotors 22a and 22b, each of which is rotatively driven by a homopolar machine comprising an armature in the shape of a drum.

The armature 28a, forming part of the rotor 22a, is subjected to a substantially radial magnetic field of the machine. An auxiliary coil 37a is added to the coils 36a and 36b and is located substantially'in the transverse median plane of the armature 28a.

v FIG. 9 shows the construction of the armature 28a of FIG. 8. This armature comprises slots 80 in regular spacing, the mean inclination ofwhich is substantially unequal on either side of the median plane of the coil 37a. Preferably, this inclination is so chosen that when the coil 37a does not carry current, the resulting axial electrodynamic force substantially balances the axial aerodynamic stresses to which the rotor 22a is exposed under continuous running conditions. The field generated by the How of a current in the coil 37a has the effect of modifying the distribution of the magnetic flux on either side of its plane which causes a variation of the resultant of the axial electrodynamic forces without giving rise to any appreciable variation of the overall magnetic flux of the armature, owing to the substantially median position of the coil 37a relative to the armature 38a. Such an arrangement makes possible the fine adjustment of the axial force, achieving the compensation without changing the torque of the homopolar machine. This application is particularly suitable for producing a strict axial compensation, particularly during the transitional running conditions of a turbo machine in accordance with the invention.

The homopolar machine driving the rotor 22b shown in FIG. 8 has similar arrangements. Obviously, taking into account the respective directions of the field and of the current flow, the orientation of the slots in the armature 38b must be symmetrical to that of the slots of the armature 28a.

The arrangement shown in FIGS. 10 and 11 relates to a homopolar machine with axial field, and has the same object as that shown in FIGS. 8 and 9.

The armature 83 in the shape of a disc has slots 84 inclined relative to its axial planes, and the shape of which depends only on the most desirable radial distribution of the axial electrodynamic forces which they generate. Two

identical coils

85 and 86, the diameters of which are preferably similar to the outer diameter of the armature 83, are mounted coaxially in two planes symmetrical relative thereto. They carry currents in the same direction which create a magnetic field, the direction of which is substantially axial in the zone of the armature 83, and the control of which makes it possible to vary the moment taken up or supplied by the machine. The auxiliary coils 87 and 88, arrangedin the same manner as described above and having a diameter preferably near the inner diameter of the armature 83, carry currents in the opposite direction. The axial and radial components of the magnetic field formed by each of them in the zone of the armature 83 are, respectively, subtractive and additive, with the result that if the coils carry currents of the same intensities, the magnetic flux of the armature is independent therefrom and the control of this intensity modifies only the radial component of the field, that is tosay the electrodynamic compensating force of the axial stresses.

FIG. 12 shows in axial cross-section an embodiment of the invention suitable for driving the rotor ofa compressor element with rotor and stator. This element comprises, as known in the art, a row of fixed bladed rings, such as 11 18 forming part of a housing 1000, and alternating with a row of rotating vane rings, such as 1 119, mounted on a drum 1 which turns in

bearings

1121 and 1122. V

The drum 1120 is rotatively driven by a homopolar electric motor formed by a set of alternatively fixed and rotating discs, such as 1123 and 1124, respectively, and a field coil 1125 retained by a ringv 1126 forming part of the ring 1131 of a fixed vane ring 1118.

a The set of rotating discs 1124 forms the actual armature of the homopolar motor these discs are fixed with their outer edges on the drum 1120, but are electrically insulated against the same. The fixed 'discs .1123, located between the rotating discs 1124, make electrical contact between the outer edges of such fixed rotating discs and the inner edges of the adjacent rotating discs, by means of revolving contacts such as l127' which are preferably formed by a'ring of liquid metal. Finally, the outermost discs 1123a and 1124a make electrical contact with conducting

cylinders

1128 and 1129 respectively, between which is mounted an insulating cylindricalsleeve 1130, on which are fixed the stationary discs other than 1123a. 7 I

The field coil shown diagrammatically at 1125 is formed by a superconducting winding surrounded by a cryogenic element. This winding has turns coaxial with the armature. The arrow B shows the lines of the magnetic field generated by the coil 1125. In the zone occupied by the discs 1124, the field B is substantially homogenous and axial. The arrows I shown the current path across thearmature it may be seen that it passes each disc 1124 in the same direction. It follows therefrom that the Laplace forces caused by the field B and by the current I generate in each disc 1124 electrodynamic moments in the same direction.

The motor is connected to the associated homopolar generator, not shown, by means of a cylindrical conductor 1 129 and a center conductor 1 1 1 1.

FIG. 13 shows a modification of the counter rotating compressor illustrated in FIG. 2, in which, however, the arrnatures are not cylindrical but disc-shaped.

This compressor may comprise, for example, eight contra-rotating blade rings 1219 which rest during rotation, through means described further below, on a hollow cylinder 1211 which is fixed and serves simultaneously as electrical conductor and as frame for the compressor assembly. The cylinder 1211 may be fixed, for example, by means of radial arms (not shown) to a housing (not shown) which defines in a conventional manner the flow of gas at the periphery of the blading.

Each stage of the compressor comprises a ring of vanes 1219 fixed to a rim 1231 forming part of a disc 1224 which forms the armature of the associated homopolar motor. On either side of each armature 1224 and coaxially relative thereto are mounted superconducting windings 1125 surrounded by a cryogenic shell 1125a, containing circulatingliquid helium and mounted on fixed elements, such as discs, indicated at 1223, 1223a, 1223b, which are'mechanically integral with the cylindrical support 1221 and electrically insulated against the same by a layer of alumina (not shown).

The windings 1225 carry current in the same direction and generate an axial magnetic field whose lines of force are diagrammatically indicated by arrows B.

With the exception of the first upstream blade ring, the inner edge of the armatures 1224 forms a first electrical terminal which rests on one of the lateral ends of a cylindrical foot 1228 of the fixed discs 1223a by means of a rotating contact 1227a of liquid metal. The armatures 1224' have at their periphery a circular shoulder 1224a forming a second electrical terminal which rests through another rotating electrical contact 1227b of liquid metal on a conducting bush forming part of the fixed discs 1223b which alternate in the axial direction with the fixed discs 1223a.

In the upper part of the zonelocated between two consecutive windings 1225, the field B has an appreciable radial component. The orientation of the armatures 1224 therefore evolves and has an inclined portion 1224b in the corresponding zone. It may also be noted that the meridian contour of the surfaces defining the

rotating contacts

1227a and 1227b :is substantially parallel to the lines of the field B in their vicinity. In this manner, it may be avoided that during the rotation parasitic currents appear in the liquid metal which might lead to substantial losses.

It may also be seen from FIG. 13 that the general arrangement of the armatures is such that the assembly formed by two consecutive contacts is generally symmetrical in relation to the median plane of the fixed disc 1223a or 1223b (as the case may be) mounted between these armatures. It may be noted that the arrangement of the first and of the last stage of the com pressor differs from that of the intermediate stages, in that the rotating contact 1227a of the first stage is in direct contact with the center cylinder 1211, and the cylindrical foot 1228' of the last fixed disc 1223a is formed by an extension of the annular conductor 1212 which surrounds the conductor 1211. As in the preceding cases, the

conductors

1211 and 1212 are connected to the homopolar generator, not shown.

The arrows I in FIG. 13 indicate diagrammatically the path of the feed current of the armatures 1224. It may be seen that the

elements

1228 and 1229 mount the'assembly of armatures electrically in series, and that two consecutive armatures carry currents flowing in opposite directions and generally axial magnetic fields in the same direction. It follows therefrom that the Laplace forces moments acting on each of them have opposite signs, as also the directions of the rotation of consecutive blade rings 1219a and 1219b driven by them, as described hereinbefore.

The radial and axial stresses of each stage of the compressor during rotation are contained according to two separate systems. The radial stresses are absorbed by the rotating contacts of liquid metal, which fulfil the function of liquid centering bearings. With a view to carrying out the compensation of axial stresses, the armatures 1224 shown in FIG. 13 have, as indicated above with reference to FIG. 7, inclined slots 12240 which are uniformly distributed. over their circumference in a zone in which the field B has a noticeable radial component. The inclination of these slots makes it possible to give the density vector of the current a tangential component which is porportional to the generated electrodynamic force. The direction of the inclination of the slots 1224c corresponds to the compensation of the axial aerodynamic stresses, the direction of the current I flowing through the armature, and the direction of the magnetic field being assumed to be as shown in FIG. 13.

For an observer located on the same side of the compressor blades shown in FIG. 13, the direction of the slope of the the slots 1224c is the same for the armatures of rotating blade rings 12190 which rotate in one direction, and 1219b rotating in the other direction.

The driving installation of a double flow gas turbine shown diagrammatically in FIG. 14 comprises, as

' known in the art, a front fan 10 of high dilution rate which forces air on the one hand into an annular peripheral conduit formed between an outer casing 2c and a shell 3c, and on the other hand into a center conduit comprising, in-the direction of flow, two compressor elements 40 and 50 respectively of low and high pressure, a combustion chamber 6c and a high pressure and low pressure turbine element 7c and 8c respectively.

According to the embodiment of the invention, the transmission of energy supplied by the expanding members to the compression members is effected by mixed means in that it comprises the use of an electrical transmission according to the invention with conventional means. The elements 4c and 5c of the compressor are connected in a conventional manner by coaxial rotating shafts 9c and 10: to the corresponding

turbine elements

8c and 70, whilst the fan 1c is driven by an electrical transmission shown diagrammatically at 110, which as will be seen further below in greater detail, comprises a homopolar generator connected to the low pressure turbine 8c through the shaft 9c and supplying a homopolar motor which supplied the fan with the torque necessary for its actuation.

This arrangement makes it possible to eliminate the necessity for driving the fan by an additional low pressure turbine which, particularly if the required dilution rate is high, must turn at very low speed, and must therefore comprise a large number of stages which work under particularly unfavorable conditions. The electrical homopolar transmission machines 11c may be constructed in such a way that the optimum rotation of the fan 1c is obtained with a rotational speed of the shaft corresponding only to the conditions of good adaptation of the compressor 4c and the turbine 80 of which it forms a part.

FIG. shows in greater detail an embodiment of the electric transmission 11c connecting the blower to the low'pressure turbine of the turboreactor in accordance with FIG. 14.

This transmission comprises in a profiled casing 12c, coaxial to the housing 3c (FIG. 14) and fixed thereto by means not shown, a homopolar generator 14c and a homopolar motor 15c whose respective armatures 16c and 170 are discs with radially decreasing thickness towards the periphery, so that the density of the current flowing therethrough is substantially uniform.

The armature 160 is fixed through a link 18c to a tubular shaft 19c which fonns an extension of the rotor 200 of the low pressure compressor 4c (FIG. 14) ,upstream of a ballbearing 210 in which it is mounted.

The ring of rotating vanes 1c of the blower is mounted on a. conical element 220 forming an extension of a tubular shaft 230 which is coaxial 'with the shaft 190, comprising a flange 240 which carries the armature l'7c of the homopolar motor 15c. The shaft 23c revolves in a ball bearing 25c and in a roller bearing 26c, the outer race of which is mounted on the shaft 190 at the point of the bearing 21c.

The

bearings

21c and 25c are mounted with their outer races, respectively, to an inner extension 260 of the casing 120 and to a stay 27c forming therewith a rigid structure.

A fixed annular conductor 28c integral with the stay 27c interconnects the radial peripheral ends of the armatures 16c and 170 by means of rotating contacts 29c and'30c, respectively, of liquid metal. An annular conductor 31c mounted on the base of the armature 17c connects this armature to the base of the armature 16c by means of a third revolving contact 320 of liquid metal. This constitutes a closed electric circuit which comprises the armature 16c, the fixed conductor 28c, the armature 17c, and its extension 31c. The circuit is immersed in its entirety into the substantially axial magnetic field generated by a superconducting winding shown diagrammatically at 33c, and mounted on the stay 27c. In view of the configuration of the circuit, the armatures 16c and 17a revolve in the same direction and their respective speeds are in the same ratio as the magnetic fluxes flowing through them. This ratio is determined by the radial heigh of the conductor 280 which acts as reaction element.

In order to make possible the use in the rotating contacts of an alloy such as sodium-potassium eutectic, which is highly oxidizable, a tight chamber 340 comprising means (not shown) for introducing an inner gas under pressure, such as nitrogen or argon, is formed around the electric circuit by means of enclosures 35c and 360 fixed to the conductor 28c and provided with fittings 37c and 380 which make tight contact with the

shafts

19c and 230, and a third sealing element 39c arranged between the shafts.

The wall 360 is electrically insulated against the conductor 28c and supports the fixed element 40c of a rotating contact 2 lc, the moving part of which consists of a flange 42c forming part of the armature 17c and electrically connected the-reto. Thus, when the installation is under running conditions, it is possible to obtain between the wall 36c and its support 28c, an electric voltage capable of supplying, through conductors not I shown, the different electrical installations provided on board of the aircraft. Moreover, the starting of the installation may be achieved by connecting at a given moment the said conductors to an external source of electrical energy.

The

bearings

21c, 25c and 260 are located on either side of the field winding 33c and at a certain distance therefrom. This measure has the object of eliminating the generation of induced currents in the rolling elements, such as balls or rollers. Moreover, andwith the same object in view, windings 43c and 44c are located in the vicinity of these bearings and have the object of generating a magnetic field, which opposes locally the magnetic field generated by the winding 33c. These arrangements are completed by shielding elements 450 and 46c, formed by a ring of high magnetic permeability which make it possible to suppress the'effects of the residual field in the

bearings

21c and 25c.

As already explained further above,the.speed ratio between the fan 1c and the rotor 200 is defined by the ratio between the magnetic fluxes passing through the armatures 16c and 170. In the arrangement of FIG. 15 and in view of the uniqueness of the field windings 33c, this ratio depends only on the geometrical layout of the armatures. However, with a view to making this ratio variable, it is possible to replace the said winding 33c by two distinct field windings provided with means for varying the ratio between the current intensities passing through them.

Obviously, the embodiments hereinbefore described are given merely by way of example, and may be modified, particularly by substituting technical equivalents, without thereby departing from the principle of the invention.

I claim: I

1. A turboelectrical unit comprising: an axial flow turbomachine having at least one bladed rotor, and a homopolar electrical machine including (a) an armature connected to said bladed rotor for rotation therewith, said armature being traversed by an electrical current and including means defining for the flowof current in said armature a path having a component extendingin a plane passing perpendicular to the axis of the rotor, and (b) magnetic field generating means for producing at least o ne induction field through said armature, said induction field having a component extending in the same plane as and normal to said first mentioned component, whereby there is imparted to the rotor an electrodynamic force having a component parallel to said rotor axis.

2. A turboelectrical unit according to claim 1 wherein at least a portion of the armature of the homopolar machine has, with respect to its electrical conductivity, an anisotropic structure adapted to impart to the lines of electrical current in said armature a component directed tangentially with respect to the axis of said rotor. I

3. A turboelectrical unit according to claim 2 wherein said portion of the armature of the homopolar machine is formed with slots inclined away from a radial plane passing through the axis of said rotor, said slots comprising said current path defining means.

4. A turboelectrical unit according to claim 3 wherein said slots are constituted by plural axial sections of different inclinations.

5. A turboelectrical unit according to claim 4 wherein said magnetic field generating means is adapted to produce separate induction fields through the portions of the armature carrying the respective slot sections and comprises means for varying the ratio between said separate induction fields.

6. A turboelectrical unit according to claim 5 wherein said magnetic field generating means include at least one main field winding, and said varying means include at least one auxiliary field winding.

7. A turboelectrical unit comprising: an axial flow turbomachine including at least one bladed rotor; and at least one homopolar electrical machine including (a) an armature rotating with said rotor and comprising a disc-like section and (b) magnetic field generating means adapted to produce an induction field through said armature and comprising two windings mounted on either side of said disc-like section in coaxial relation therewith, said winding being traversed by equidirectional currents. v a

8. A turboelectrical unit according to claim 7 comprising at least two consecutive independent bladed rotors each having a disc-like armature section rotating therewith, each of said disc-like sections including two annular electrical terminals with different diameters coaxial with said rotors, said unit further comprising a fixed support carrying a fixed element between and coaxial with said rotors, said fixed element including an electrically conductive ring coaxial with said rotors and connecting electrically through sliding contacts with the corresponding annular terminals on the rotors adjacent thereto.

9. A turboelectrical unit according to claim 8 wherein at least one of the electrical terminals on each rotor is of frustoconical shape and, through a sliding electrical contact, bears on a correspondingly shaped frustoconical portion on said fixed element.

10. A turboelectrical unit according to claim 8 wherein said fixed element carries a field winding.

11. A turboelectrical unit comprising: an axial flow turbomachine having at least one bladed rotor; and at least one homopolar electrical machine including (a) an armature rotating with said rotor comprising a substantially axially extending drum-like section and (b) magnetic field generating means adapted to produce an induction field through said armature and comprising two windings mounted in coaxial relation with said drum-like section and traversed by currents flowing in opposite directions.

12. A turboelectrical unit according to claim 11 comprising at least two consecutive independent bladed rotors having a drum-like armature section rotating therewith, each such section including two annular electrical terminals coaxial with said rotors, said unit further including a fixed support carrying a fixed element between and coaxial with said rotors, said fixed element including an electrically conductive ring coaxial with said rotors and connecting electrically through sliding contacts the corresponding annular terminals on the rotors adjacent thereto.

13. A turboelectrical unit according to claim 12 wherein at least one of the electrical terminals on each rotor is of frustoconical shape and, through a sliding electrical contact, bears on a correspondingly shaped frustoconical portion on said fixed element.

14. A turboelectrical unit comprising: an axial flow turbomachine having at least one bladed rotor; and at least one homopolar electrical machine including (a) an armature rotating with said rotor and comprising a first disc-like section and a second substantially axially extending drum-like section, (b) first magnetic field generating means adapted to produce a substantially axial induction field through said disc-like section and including two windings mounted on either side of said disc-like section and coaxial therewith, said windings being traversed by equidirectional currents, and (c) second magnetic field generating means adapted to produce a substantially radial induction field through said drum-like section and including at least one winding mounted coaxial to said drum-like section for traversal by an electrical current flowing in a direction opposite to the direction of said equidirectional currents.

15. A turboelectrical unit comprising: a fixed support; an axial flow turbomachine including at least one bladed rotor rotating on said support; at least one homopolar machine including an armature being traversed by an electrical current and including at least one rotary annular electrical terminal coaxial with said rotor; a fixed annular electrical terminal mounted on said fixed support in coaxial relation with said rotary annular terminal; and bearing means for rotatably supporting said rotor on said fixed support, said bearing means including means for maintaining said rotary annular electrical terminal in sliding electrical contact with said fixed electrical terminal.

16. A turboelectrical unit according to claim 15 wherein said bearing means include liquid metal bearing means adapted to provide said electrical sliding contact.

17. A turboelectrical unit comprising: a fixed support; an axial flow turbomachine having at least one bladed rotor; bearing means for mounting said rotor for rotation on said fixed support; at least one homopolar electrical machine including (a) an armature rotating with said rotor, (b) main magnetic field generating means adapted to produce an induction field through said armature, and (c) auxiliary magnetic field generating means adapted to produce in the region of said bearing means a magnetic field opposed to that produced by said main magnetic field generating means.

18. A turboelectrical unit comprising: an axial flow turbomachine having at least one bladed rotor; at least one homopolar electrical machine including an armature rotating with said bladed rotor for traversal by an electrical current; an auxiliary electrical circuit, and means electrically connecting said armature with said auxiliary circuit.

19. A gas turbine power plant comprising:

a. an axial support,

b. a compressor rotor mounted on said support,

0. a turbine rotor mounted on the same support in axially spaced relation to said compressor,

(1. at least one homopolar electrical machine including an armature rotating with said turbine rotor and fixed field means cooperating with said armature to generate an electrical current therein upon rotation thereof,

at least one additional homopolar electrical machine including an armature rotating with said compressor rotor and including fixed field means cooperating with said armature to rotate the same upon the passage of an electrical current therethrough, and

conductor means establishing an electrical circuit between the armature rotating with the turbine rotor and the armature rotating with the compressor rotor, said conductor means comprising:

1. outside fixed conductor means provided adjacent the exterior of said axial support in the region extending between said armatures and in the regions adjacent the remote sides of said armatures,

2. sliding contact means connecting opposite sides of the respective armatures with the adjacent terminations of said outside fixed conductor means, and

3. inside fixed conductor means extending within the interior of said axial support and connected at its opposite ends to the outside fixed conductor means in the regions adjacent the remote sides of said armatures.

20. The power plant according to claim 19 wherein said outside fixed conductor means comprises an intermediate generally annular casing section extending between the armatures, a forward generally annular casing section upstream of the armature rotating with said compressor rotor and a rearward generally annular casing section downstream of the armature rotating with said turbine rotor, all of said casing sections comprising conductive material.

Claims

1. A turboelectrical unit comprising: an axial flow turbomachine having at least one bladed rotor, and a homopolar electrical machine including (a) an armature connected to said bladed rotor for rotation therewith, said armature being traversed by an electrical current and including means defining for the flow of current in said armature a path having a component extending in a plane passing perpendicular to the axis of the rotor, and (b) magnetic field generating means for producing at least one induction field through said armature, said induction field having a component extending in the same plane as and normal to said first mentioned component, whereby there is imparted to the rotor an electrodynamic force having a component parallel to said rotor axis.

2. A turboelectrical unit according to claim 1 wherein at least a portion of the armature of the homopolar machine has, with respect to its electrical conductivity, an anisotropic structure adapted to impart to the lines of electrical current in said armature a component directed tangentially with respect to the axis of said rotor.

7. A turboelectrical unit comprising: an axial flow turbomachine including at least one bladed rotor; and at least one homopolar electrical machine including (a) an armature rotating with said rotor and comprising a disc-like section and (b) magnetic field generating means adapted to produce an induction field through said armature and comprising two windings mounted on either side of said disc-like section in coaxial relation therewith, said winding being traversed by equidirectional currents.

19. A gas turbine power plant comprising: a. an axial support, b. a compressor rotor mounted on said support, c. a turbine rotor mounted on the same support in axially spaced relation to said compressor, d. at least one homopolar electrical machine including an armature rotating with said turbine rotor and fixed field means cooperating with said armature to generate an electrical current therein upon rotation thereof, e. at least one additional homopolar electrical machine including an armature rotating with said compressor rotor and including fixed field means cooperating with said armature to rotate the same upon the passage of an electrical current therethrough, and f. conductor means establishing an electrical circuit between the armature rotating with the turbine rotor and the armature rotating with the compressor rotor, said conductor means comprising: