Hydroreactor to Take Advantage of the Kinetic Energy From the Water in Places Where the Streams Are Meaningful for the Production Electric Power

The present invention refers to an hydraulic turbine of axial flow, designated from now on by hydroreactor, intended to take advantage of the kinetic energy from the water in places with relative depth in rivers, estuaries or inlets where the streams are meaningful for the production of electric power.

Within the known systems for taking advantage of hydraulic resources, using turbines are considered the closest prior art the ones disclosed in PCT patent application PCT/HU90/00072 (WO 91/07587) and PCT/CA91/00066 (WO 92/15782).

PCT/HU90/00072 (WO 91/07587) discloses a "Water current energy converter" designed for and capable of converting the flow energy of a moving body of water into electric power comprises, at least one water driven flow machine, especially a water driven turbine, an electric power generator and an energy transfer system arranged between the water turbine(s) and the power generator. According to the invention in at least one thoroughfare flow duct of a floating buoyant body at least one pumping unit comprising an hydraulic rotary pump coupled to a shaft of the water driven turbine is provided. The buoyant body is held by anchoring means in predetermined orientation and in substantially stationary position in a surface water. The hydraulic rotary pumps form component parts and serve hydraulic pressure sources in the hydraulic energy transfer system.

PCT/CA91/00066 (WO 92/15782) discloses an "Apparatus for recovering kinetic energy in a free flowing water stream" designed for converting the water stream into useful energy, it comprises a body immerged in a stream, the body defining a duct having an intake side and a discharge side. The discharge side is equipped with a deflector which flares outwardly for obstructing the flow of water around the duct to thereby create a negative pressure drag on the water being impelled as it is being discharged from the duct. The deflectors flare outwardly at an angle varying from 75.degree. to 160.degree. as measured from the longitudinal axis of the duct.

The object of the present invention is to provide an hydroreactor, which is designed to be used for production of electric power, not only in rivers but also in estuaries or inlets where the streams change their direction according to the sea tides action. It consists of a rotating system of sustained immersed conduit for taking advantage from the water streams.

The conduit having a special shape that will promote a suction effect, easing the flow of water through its interior in which is placed the turbine impeller through which the velocity is higher, with a specific relation, than the velocity of the stream at the outside before the conduit entrance. The object of the invention is designed to present an hydrodynamic shape allowing easier water ripping and minimising non wanted turbulence. The locals chosen for its implantation should be enough depth to assure the immersion of the structure.

The object of the invention differs from the mentioned patent application publication number WO 91/07587 in that:

i) is a well fitted sustained immersed conduit having a special shape (to be described later);

ii) the support allows robust attachment of the conduit to the depth bottom;

iii) it is an autonomous rotating system which can be used for taking advantage from water streams not only in rivers but also in estuaries and inlets, where the stream direction changes.

The object of the invention differs from the mentioned patent application publication number WO 92/15782 in that:

i) the conduit format is such that the flow inside it is axial from the entry to the exit sections, the velocity through the turbine impeller being higher, with a specific relation, than the stream velocity outside of the conduit;

ii) it is an autonomous rotating system which can be used for taking advantage from water streams not only in rivers but also in estuaries and inlets, where the stream direction changes.

The invention may be better understood by making reference to the following description taken together with the accompanying drawings, in which:

FIG. 1 gives a general overview of the hydroreactor structure through a longitudinal section A, symmetrical to a plane defined by the conduit axis and the bearing pedestal axis;

FIGS. 2 to 6 show several sectional elevation views of the conduit;

FIGS. 7 to 9 show several sectional elevation views of the main body of the support mobile part;

FIGS. 10 to 12 show several sectional elevation views of the rudder;

FIGS. 13 to 15 show several sectional elevation views of the balancing weight;

FIGS. 16 to 18 show several sectional elevation views of the support fixed part

FIGS. 19 to 21 show several sectional elevation views of metallic cylindrical jackets for protection and adjustment proposes of the hydraulic jack tubes;

FIGS. 22 to 24 show several elevation views of the turbine impeller 2;

FIG. 25 shows a graphic representing the ideally turbine propeller rotation against the stream velocity;

FIG. 26 shows a graphic representing the mechanic power ideally transmitted to the generator shaft against the stream velocity; and

FIG. 27 shows a graphic representing the electrical power ideally provided to the mains against the stream velocity.

Referring to FIGS. 1 to 21, the section B is defined according to a plane perpendicular to the section A, intercepting this section by the axis of the conduit 1, section C is defined according to a plane parallel to section B, intersecting half length the connecting rods 12 and 13, which connect the conduit 1 to the main body 16' of the support mobile part 16, section D intersecting the rudder 17 according to a line next to and following the contour of the main body 16' of the support mobile part 16, section E intersecting transversely the balancing weight 18 next to the rounded front edge of the main body 16' of the support mobile part 16 and section F following a plane perpendicular to the planes A, B and C extending through the centre between the two connecting rods 12 closer to the conduit entrance section and the rod 13 closer to the conduit exit section.

Referring particularly to FIG. 1 the hidroreactor is comprised by a conduit 1 inside which the water flows where is placed the turbine impeller 2, a support for the conduit 1 comprised by a fixed part 15 well fitted over the bearing pedestal 22, solidary with four or more equally spaced hydraulic jacks 20 to lift the structure, for maintenance proposes and depth control, and a mobile part 16, having a main body 16' which supports directly the conduit 1, a rudder 17 to drive the structure according to the stream direction, and a balancing weight 18, whose propose is to match the centre of mass of the structure mobile part 16 with the axis of the bearing pedestal 22.

Referring more particularly to FIGS. 2 to 6 the external surface of the conduit 1 is defined by circular transversal sections along it and the conduit external diameter varies slightly from its maximum diameter section, where the turbine impeller 2 is located, to its exit section, such as the angle .epsilon. defined between the axis of the conduit 1 and the line which approaches by linear regression to its external surface variation in this area, should not be higher than 10 degrees, in order to avoid as much as possible turbulence nearby this surface caused by the cavitation effect due to the water flow action. The internal shape of the conduit 1 is defined by an area corresponding to the entrance of the conduit 1, where its internal diameter decreases, from the entry section to the location point of the turbine impeller 2, called entrance chamber 10, an internal area of constant diameter in which are located the turbine impeller 2 and its support 3 and by an area corresponding to the exit of the conduit 1, from which the internal diameter increases until the exit section, called vacuum chamber 11. The vacuum chamber 11 is defined by an area of smaller diameter, just after the internal area of constant diameter, with a slighter internal diameter variation of the conduit 1, an intermediate area with a maximum variation and finally an area close to the exit section in which the variation is almost null.

The external diameter of the conduit 1, in the area of the entrance chamber 10, increases with a slope symmetrical to the decrease of the internal diameter to the location point of the turbine impeller 2, defining edges in this area that present in the sections A or B a symmetrical geometry according to a semi-elliptical shape, as to have a smoother and easier water ripping. The ratio between the entrance section diameter and the internal diameter of the conduit 1 at the location of the turbine impeller 2, is between 2 and 3, in order to be noticeable the difference between the stream velocity and the velocity of the water flowing through the turbine impeller 2 and on the other hand to avoid water from blocking the conduit entrance caused by an abrupt increase of pressure due to an exaggerate funnelling of the conduit entrance chamber 10. The external diameter decreases slightly from the turbine impeller 2 location point to the exit section, in order to avoid the build-up of turbulence close to the external surface in this area, by the cavitation effect due to the stream action. As it will be proved later in the description, the angle .epsilon. defined between the axis of the conduit 1 and the line which approaches by linear regression to its external surface variation in this area, is not higher than 10 degrees.

The impeller support 3 should present an inverted L shape, being as much thin as possible but large enough to enclose and allow the shielding of the shaft, associated bearings, pinions 5 and 6 and drive chain, with a limb (vertical portion of the inverted L) that ends in a rear sharp edge in order to minimise the turbulence and present a front edge surface in semi-elliptic shape for water ripping. The transmission ratio between the two first pinions, 5 and 6, is 1, in order to minimise the diameter of the drive pinion 5 and with that the thickness of the turbine impeller support 3 in its location area, the transmission conversion between the pinion 6 and the asynchronous generator 8 being made through the gearbox 7 and the centrifugal clutch. The distance, inside the constant diameter area, from the sharp edge of the impeller support 3 until the vacuum chamber 11, is approximately equal or slightly higher than the overall length of the turbine impeller 2 with its support 3, in order to attenuate completely the turbulence generated in the vacuum chamber 11, avoiding its extension to the edge of the impeller support 3 and on the other hand to generate a vacuum that compensates the charge losses inside the referenced area.

At the edge of the conduit 1 below the impeller support 3, is a room for housing an asynchronous generator 8, a centrifugal clutch and one gearbox 7, to which the access should be done by a masked door that guaranties reliable isolation from exterior when closed.

The conduit 1 is linked to the main body 16' of the mobile part 16, by three connecting rods, two of them 12 being closer to the entrance section, equally spaced from this section and from de plane of section A, and a connecting rod 13 closer to the exit section symmetric to section A, defined by a semi-elliptical frontal edge for water ripping and ending in a sharp edge in order to minimise the turbulence, of enough length to allow the free flow of water between these two parts. The option for three connecting rods and not for only one according to the pedestal axis or two according to the plane of section A, one closer to the entrance section and another closer to the exit section, will guarantee more stability.

The rudder 17, represented on FIGS. 10 to 12, is symmetrical to section A, and is linked to the main body 16' of the support mobile part 16, having enough area to easily transpose the inertia momentum of the mobile part of the structure, but not too large, and being placed sufficiently far away from the conduit 1 exit section in order to minimise the influence of the turbulence at the conduit 1 outlet in the stability of the mobile part of the structure.

The balancing weight 18, represented on FIGS. 13 to 15, is symmetrical to the plane of section A, being linked by a connecting rod to the main body 16' of the mobile part 16, forms a semi-arch defined by an elliptic section not to large in order to make it inert to the waving effects and of narrow thickness for relatively easier water ripping, and with a mass that makes the mobile structure centre of mass to match with the axis of the bearing pedestal 22.

According to FIGS. 7 to 9, the external surface of the main body 16' of the support mobile part 16, is symmetrical to the rudder 17 direction, defining a round edge in the opposite side to the rudder 17 for easier water ripping and ending in a sharp edge at the rudder 17 side in order to minimise the turbulence. It contains a cavity defined between two cylindrical surfaces of different diameter centered on the axis of the bearing pedestal 22, that fits in the support fixed part 15, and one internal cavity with a cylindrical format centered on the axis of the bearing pedestal 22, properly isolated from the outside, for avoiding any humidity from entering.

The support fixed part 15, represented on FIGS. 16 to 18, have a circular edge defined by the space between two cylindrical surfaces of different diameter both centered by the axis of the bearing pedestal 22, which fits adjusted in the external cavity of the support mobile part 16. On the top of the edge exists a giant ball bearing 14 in order minimise the friction between the support fixed part 15 and the mobile part 16. The top of the edge has external round shaped corners. At the area inside the edge there are on the floor a specific number of circular rails (according to the number electric phases), lined with an highly isolating material, where is established the contact between conducting metal brushes 24, constituting the ends of the cables (9) at the mobile part, and conducting metal rings 23, constituting the ends of the cables 9 at the fixed part. Several rotary rubber seals 26 should exist on the surface of contact between the support fixed and mobile parts to assure an isolation of extreme reliability that makes impossibly the entrance of any humidity to the area where the electric contacts are established. The lower surface of the support fixed part 15 which bears on the bearing pedestal 22, should present a bevel of conical shape that fits in an adjusted way in the cavity of the bearing pedestal 22. The support fixed part 15 is solidary with four or more equally spaced hydraulic jacks 21, whose function is to lift the structure emerging it for handling proposes or depth control. The internal face of the cavity edges of the bearing pedestal 22 defines an obtuse angle between 120.degree. and 135.degree., to present higher strength not being so prone for rupturing caused by the stream traction effect as in the case if it presents a rectangular internal corner. The cavity surface of the bearing pedestal 22 is lined with a metal film, in order to avoid the direct contact between the support fixed part 15 with the cement of the bearing pedestal 22. There are holes in the bearing pedestal 22 dressed with metallic cylindrical jackets 19 for protection and adjustment proposes where fit the hydraulic jacks pipe tubes 20.

The turbine impeller 2 shown in FIGS. 22 to 24, in which there are only represented two of all the blades 25 in order to simplify the figures and with this to ease their understanding. The impeller blades 25 should not overlap, being defined by a small interval of free space between the projections of adjacent blades delimitation lines over a plane perpendicular to the propeller axis, to ease the water flow through it, being a non exaggerated interval in order not to imply a significant lose of power. The turbine impeller 2 should have between 6 and 8 blades 25, in order not to have very broad blades 25 offering a great resistance to the water flow and not to have very narrow blades 25 implying a significant lose of power. According to this, the angle .theta. between the projections of the extremities of each blade 25 over a plane perpendicular to the impeller axis should be slightly lower than the ratio between 360.degree. and the number of blades. The projections of the impeller blade 25 over their bisecting plane on .theta., should be defined by a constant length L independently to the considered distance r from the axis of the turbine impeller 2. Once the linear velocity of a specific point on a blade, depends to its distance r from the axis, decreasing with r, the incidence angle of the blades into water, is a function of r that should be done by the following expression: ##EQU1##

The incidence angle of the blades 25 into water on the periphery points .alpha.(R), where R is the turbine impeller 2 radius, is not lower than 45.degree. in order to guarantee a specific impeller rotation frequency F.sub.HT not offering a great resistance to the water flow through it. The blade incidence edge into water is defined by an half-round 24 of round format, in order to ease the incidence and with this its reaction to the flow. The impeller hub 23, has a round format frontal part in order to ease water ripping. The blades 25 are linked to the hub 23 only by a thin rod in the contiguity of the half-round 24 incidence edge, resulting in an aperture around the impeller hub 23, close to which the blades 25 present an higher incidence angle, easing the turbine impeller 2 reaction to the water flow. The lower edge of the blades 25, where they present an higher incidence angle, is almost all rectilinear in order to optimise the drag on and the turbine impeller 2 reaction to water flow rate, and terminates according to a curve line format in the liberation area and in the periphery area (farthest area from the turbine impeller 2 axis) in order to minimise turbulence and to ease the reaction to water flow. The hub 23 diameter is equal to the diameter of the horizontal limb of the impeller support 3, having two elements with contiguous surfaces in order to minimise water flow irregularities.

On practice the stream velocity V.sub.c and so the turbine impeller 2 rotation frequency F.sub.HT vary. For this reason it is proposed for electric power production the use of an asynchronous generator 8 with the rotor coils short-circuited (it may be adopted a squirrel cage type rotor), operating on an auto-excited generator operating state (this is, with compensation of the active and reactive components of the generated electrical current). This generating state is attained when the shaft rotation frequency is higher than the frequency of the stator electrical rotating field resulting from the phase shifting of individual stator coil electrical fields (which corresponds to the oscillation frequency of electric fields on electricity mains F.sub.E =50 Hz or 60 Hz), this in the case of one pole per coil machines, and higher than F.sub.E /N.sub.P in the generic case of machines with N.sub.P poles per coil. It is usual to find asynchronous machines with 2, 3 or even 4 poles per coil.

From graphic of FIG. 25, it can be verified that the turbine impeller 2 rotation frequency F.sub.HT will be much lower than the relation F.sub.E /N.sub.P. It will then be necessary a gearbox 7, which imposes a specific transmission relation between the shaft of the turbine impeller 2 and the shaft of the asynchronous generator 8. There is an electromechanical system that connects the stator coils to the electricity mains only when the product F.sub.HT,N.sub.CV (where N.sub.CV represents the gearbox 7 multiplication factor) be higher than the ratio F.sub.E,N.sub.P, disconnecting them when F.sub.HT.N.sub.CV .ltoreq.F.sub.E IN.sub.P (operating state as a motor). The connection of the shaft of the turbine impeller 2 to the shaft of the asynchronous generator 8 by means of a centrifugal clutch, should be performed just after the shaft of the asynchronous generator 8 reach the angular velocity of synchronism .OMEGA..sub.S =F.sub.E IN.sub.P, allowing so a soft drag on traction effect with the help of the electrical power from the electricity mains, becoming the turbine impeller 2 free whenever the stream velocity will not be enough to provide electric power to the electricity mains. For this propose, the connection of the stator coils to the electricity mains is performed in such a way that the rotor direction of rotation matches with the direction of rotation of the turbine impeller 2.

In the case of a three phase system, the compensation of the reactive component of the generated electrical current, can be done with an arrangement of capacitors in a star configuration with a capacity given by: ##EQU2## where L.sub.EE represents the auto-induction coefficient of the stator coils. The compensation of the active component from the generated electrical current can be done with an arrangement of varying resistors (potentiometers) in a star configuration, whose value varies in accordance to the effective value of active component of the generated electrical current [I.sub.E ].sub.eff. according to: ##EQU3## where [U.sub.E ].sub.eff. represents the effective value of the voltage tensions between adjacent phases on the electricity distribution network. As the [I.sub.E ].sub.eff. values depend from the sliding factor S and hence from angular velocity .OMEGA. of the asynchronous generator 8 shaft, the resistor values are controlled as a function of .OMEGA..

The monitoring of the equipment conditions (rotary rubber seals, etc.) and the obtaining of data relative to its operation can be performed remotely on the land field with the help of a telesurveillance system.

All cables 9 should pass through the interior of under grounded pipes below the river, estuary or inlet bedstead.

Water presents very low kinetic viscosity v characteristic values (of the order of 10.sup.-6 m.sup.2 .multidot.s.sup.-1), resulting so in a very high number of Reynolds (relation between the kinetic strength associated to the water motion and the viscous strength associated with the inter-molecular links of the water), which means an almost non existent surface boundary layer (film by definition formed close to a plan surface, in a real fluid sliding over it, where there is a non uniform distribution of water velocities due to the molecular diffusion caused by friction tensions on the surface) on a flow over a polished plan surface, and by this reason may be considered as an almost perfect fluid.

Considering the conduit edges and turbine impeller 2 characterised by having polished surfaces (for example with plastic fibre coating) and the flow rate through the turbine impeller 2 substantially equal to the flow rate at the conduit entrance, the ratio between the velocity V.sub.HT by which water transverses the turbine impeller 2 and the stream velocity V.sub.C is inversely proportional to the relation between the conduit entrance section S.sub.E and the conduit internal section at the turbine impeller 2 location S.sub.HT. ##EQU4##

Where d.sub.HT is the diameter of the conduit 1 internal section at the turbine impeller 2 location and d.sub.E the conduit 1 entrance section diameter. According to claim 10, the conduit 1 edge is symmetrical at the entrance chamber area, the maximum diameter of the conduit exterior surface d.sub.Max can be expressed as a function of d.sub.E and d.sub.HT by the following equation:

The inertia strength F.sub.A associated with the area A of a fluid in motion with a constant velocity V.sub.C (considering the plane of area A perpendicular to the fluid motion direction), is given by the following expression:

where .rho. represents the fluid density (about 1000 kg.multidot.m.sup.-3 for the water).

According to this, the exercised pressure or linear tension T is given by:

Being this one applied on the maximum diameter conduit 1 exterior section, it is decomposed in two components, one consisting on its projection over the exterior surface of the conduit 1 between the maximum diameter exterior section and the exit section, with an amplitude given by T.cos(.epsilon.) (representing .epsilon. the angle between the conduit 1 axis and the line that approximates by linear regression the conduit 1 exterior surface variation in the considered area) and with the same orientation as the stream and an other component with an amplitude given by T.sin(.epsilon.) with a direction perpendicular to the considered surface and oriented from the interior to the exterior of the conduit. In order to not generate a cavitation effect nearby the upper part of the conduit 1 exterior surface, the projection of the second component on the vertical direction should be lower than the relative pressure P.sub.Rel of the water at the depth by which is the upper part of the conduit 1 exterior surface (the relative pressure of the water at a N.times.1 m depth is about N.times.1000 kgf.multidot.m.sup.-2). The absolute pressure P.sub.Abs at a specific depth, is given by the sum of the atmospheric pressure P.sub.Atm at the water surface with the relative pressure of the water at that specific depth. If the projection of the second component on the vertical direction be higher than the relative pressure of the water, the pressure nearby the upper part of the conduit 1 exterior surface becomes approximately equal to the atmospheric pressure (1 atm=10330 kgf.multidot.m.sup.-2), which is usually designed by cavitation effect. Thus, in order to avoid this effect the following relation must be verified: ##EQU5##

It must be noted that due the pressure increase with the increase of the depth and to the friction on the bedstead, the verified stream intensity decreases with the depth and consequently the tracking tensions. Due to this fact, the upper part of the exterior of the surface conduit 1 (at a lower depth) is maintained at depths close to the water surface (about 0.5 m to 1.5 m depth from the water surface), and so the structure high should be regulated by an automatic system that controls the hydraulic jacks high according to the evolution of the water surface levels.

Basing on expressions 7 and 8 and considering the conduit upper surface at 1 m depth, maximum admissible values for angle .epsilon. of about 6.degree. and 9.degree. result, above whom the cavitation effect can be verified, considering as maximum values for the stream velocity respectively 3 m.multidot.s.sup.-1 and 2.5 m.multidot.s.sup.-1. It must be noted that as the depth increases, the maximum admissible value for .epsilon. increases, considering as reference the same value of maximum stream velocity limit above which would occur the cavitation effect. According to these results and pretending, the carry of a maximum stream velocity limit of about 2.5 m.multidot.s.sup.-1 at 1 m depth without the occurrence of the cavitation effect nearby the upper part of the conduit 1 exterior surface, it is established a maximum limit for .epsilon. of 10.degree. on the 3.sup.rd claim.

The linear velocity of rotation V.sub.Rot (r) of a specific point on a blade 25, is a function of the distance r to the turbine impeller 2 symmetry axis. As previously mentioned, the projection of each blade 25 over a longitudinal plane bisecting the angle .theta., must be defined by a constant length L independently of the distance r to the turbine impeller 2 symmetry axis. The intersection points of each impeller blade 25 with a cylindrical surface of ray r centered on its symmetry axis, are projected on a transversal plane according to an arch of length .theta..r. Thus, the following relation is verified between V.sub.Rot (r) and V.sub.HT : ##EQU6##

The linear velocity of rotation V.sub.Rot (r) of the turbine impeller 2 at a distance r from its axis, can be defined as a function of the turbine impeller 2 rotation frequency F.sub.HT by:

According to the preceding two expressions, the turbine impeller 2 rotation frequency F.sub.HT may be obtained as a function of the velocity V.sub.HT by which the water transverses the impeller 2 and implicitly according to expression 4 as a function of the stream velocity V.sub.C by the following expression: ##EQU7##

As it may be verified the rotation frequency of the turbine impeller 2 is ideally directly proportional to the velocity V.sub.HT by which the water flows through the turbine impeller 2 (and so implicitly to the stream velocity V.sub.C), decreasing with the number of blades and with their length L. Thus, the values of L and .theta. should be such that would allow an ease drag of turbine impeller 2 in and a specific rotation frequency F.sub.HT of the turbine impeller 2 without offering great resistance to the water flow through it.

A impeller 7 with blades, .theta.=40.degree., R=0.5 m and L=0.35 m, from which results according to expression 1, .alpha.(R)=45.66.degree., satisfies perfectly to all the requirements imposed on claims for the characteristics of the turbine impeller 2. Such values are going to be taken as reference values in the following calculations. The graphic on FIG. 25, shows the ideal characteristic curbs of F.sub.HT (V.sub.C) for values of K.sub.D equal to 2, 2.5 and 3.

The power derived from the kinetic energy of the mass of water flowing through the turbine impeller 2 per unit of time, may on a punctual case for which it is considered the water flowing through the turbine impeller 2 with a constant velocity (V.sub.HT =C.sup.te), be expressed by: ##EQU8## where .mu. represents the quantity of water mass that flows through the turbine impeller 2 in average per unit of time. Having in consideration that the water density is approximately .rho.=1 kg/dm.sup.3 =1 kg/l, it comes: ##EQU9## where Q.sub.HT represents the flow of water that transverses the turbine impeller 2, given by: ##EQU10## It results then from expressions 4, 13 and 14 that: ##EQU11## having in attention that:

This on an ideal case for which the energy loses due to friction at the conduit entrance chamber edges are not considered. Representing .gamma..sub.m the resultant of mechanic loses: by energy dispersion due to friction at the conduit entrance chamber edges, at the turbine impeller 2 and due to friction on transmission devices; the mechanic power P.sub.m transmitted to the generator shaft is given by:

The graphic of FIG. 26 shows the characteristic curves of P.sub.HT (V.sub.C) for values of K.sub.D equal to 2, 2.5 and 3.

The internal power P.sub.i of an asynchronous generator in the operating state as a generator (power transmitted from the rotor to the stator discounting the electrical loses from the Joule effect on the rotor coils) is given as a function of the mechanical power P.sub.m applied to the generator shaft by: ##EQU12## defines the sliding factor of the rotor angular velocity .OMEGA.=2.pi.N.sub.CV F.sub.HT (being N.sub.CV the gearbox multiplication factor) with respect to the angular frequency of the stator electrical rotating field .omega..sub.E =2.pi.F.sub.E (which corresponds to the frequency of the electrical field in the electricity distribution network). The operating state as a generator happens for negative sliding factor values. ##EQU13##

From expressions 4, 11 and 17 comes: ##EQU14##

The electric power provided to the electricity mains can be estimated discounting from P.sub.i the electrical loses by the Joule effect at the stator conductors. The graphic of FIG. 27 shows the characteristic curves of P.sub.i (V.sub.C) for values of K.sub.D equal to 2, 2.5 and 3; considering as an example the product between the multiplication factor of the gearbox and the number poles per coil N.sub.CV .multidot.N.sub.P =30.

As it may be verified that electrical power provided to the electricity mains, depends for a specific stream velocity: from the turbine impeller 2 format and dimensions (not forgetting the requirements imposed on the claims with relation to its characteristics), from the conduit dimensions relatively to the turbine impeller 2 and from the product between the multiplication factor of the gearbox 7 and the number of poles per coil. Whatever higher will be the multiplication factor of the gearbox 7 and the number of poles per coil, lower will be the generated power but on the other hand higher will be the time percentage during which there is electricity production. Higher will also be the difficulty to overcome the inertia momentum of the rotor. As higher will be the number of poles per coil, lower has to be the multiplication factor of the gearbox 7 for the same effect in terms of quantity of electrical power produced decreasing by this the difficulty in overcoming the rotor inertia momentum.

For a more precise interpretation of the graphics from FIGS. 25, 26 and 27, bellow is presented a table with the numeric values calculated for F.sub.HT, P.sub.HT and P.sub.i as functions of V.sub.C.

As it can be verified from the obtained results for stream velocities lower than a certain value, the electric power is higher than the mechanic power which means that there is a consume of electric power from the electricity mains (operating state as a motor) and for stream velocities higher than that value, the electric power is lower than the mechanical power which means the provision of electric power to the electricity mains (operating state as a generator). The stream velocity threshold under which there is consume of electric power (motor) and above which there is provision of electric power (generator), can be estimated from expression 11, making F.sub.HT =F.sub.E I(N.sub.CV .multidot.N.sub.P). Thus, the obtained stream velocity V.sub.C threshold value, considering K.sub.D equal to 2, 2.5 and 3, was respectively 1.3125 ms.sup.-1, 0.84 ms.sup.-1 and 0.583(3) ms.sup.-1, what is in conformity with the evolution of the mechanical and electrical power values presented in Table 1.

As it was above mentioned, the centrifugal clutch and stator coils should remain disconnected for stream velocities below this threshold. The graphic of FIG. 27 relative to the production electrical power, is then comprised by an inactivity area "OFF" for stream velocities below the mentioned threshold and an activity area "ON" for stream velocities above that threshold.