WO2015168810A1

WO2015168810A1 - Apparatus and system for hydroelectric power generation

Info

Publication number: WO2015168810A1
Application number: PCT/CH2014/000063
Authority: WO
Inventors: Jouni Jokela
Original assignee: Jouni Jokela
Priority date: 2014-05-06
Filing date: 2014-05-06
Publication date: 2015-11-12

Abstract

An apparatus for hydroelectric power generation comprising a turbine (12, 77, 102, 172, 173) with two bladed wheels (11, 12, 31, 32) successively arranged in a turbine tube section (10, 21) as a fore wheel (11,31) and an after wheel (12, 32) with respect to the water flow direction (23), the wheels (11, 12, 31, 32) being configured to rotate in opposite directions driven by the water flow, and a power generator (103, 176, 177) configured to generate electrical power from the rotational energy of at least one the wheels (11, 12, 31, 32). The apparatus further comprises a power controller (105) that is configured to regulate the electrical power generated by the power generator (103) in such a way that the rotational speed of the wheels (11, 12, 31, 32) and thus the water flow through the tube section (10, 21) is adjustable through said power regulation from the power controller (105).

Description

Apparatus and system for hydroelectric power generation

The invention relates to an apparatus for hydroelectric power generation comprising a turbine with two bladed wheels successively arranged in a turbine tube section as a fore wheel and an after wheel with respect to the water flow direction, the wheels being configured to rotate in opposite directions driven by the water flow, and a power generator configured to generate electrical power from the rotational energy of at least one the wheels. The invention also relates to a system for hydroelectric power generation comprising at least two of those apparatuses.

An apparatus comprising such a turbine for hydroelectric power generation is known from WO 2012/146768 Al to the same applicant. The turbine is constructed such that the wheels are adapted to be driven at a synchronized rotation speed by the water flow. The wheels are coupled to each other by a gearing that is connected to a power generator via a transmission shaft. This configuration allows the turbine to operate with a high efficiency. The turbine is preferably used in low head hydropower applications, in particular in a run- of- river hydroelectric power plant.

Run-of-river hydroelectric power plants known in the art comprise a reaction type turbine. such as a Kaplan turbine, including movable wicket gates and adjustable runner blades to allow a regulation of the water flow through the turbine and of the power output from the turbine. These moving components are typically located at a heavily loaded part of the turbine and are adjusted in dependence of the momentary river flow conditions in order to allow a desired or maximum power output from the turbine.

A proper adjustment of these components, however, is mostly dependent on external measurement data defining the water level of an upper canal, the wicket gate positions, the blade positions, etc. A thus required regulating system and control connection to the turbine is rather complex and expensive and needs a regular maintenance and calibrating if the production efficiency of the turbine is wanted to be kept at a high level. Due to the complexity of the system, a certain error-proneness cannot be avoided.

An example of a run-of-river hydroelectric turbine and control system is disclosed in US 2012/0146330 Al. The runner blades of the Kaplan turbine are adjustable by means of a runner angle servo and the wicket gates are adjustable by means of a wicket servo.

Independent control loops are required to regulate the wicket gate angle via a wicket gate controller and the runner blade angle via a runner blade controller in order to achieve an optimized generator power output. It would be desirable to reduce the complexity and thus the effort for maintenance and risk of failure of the control system in such a turbine.

It is therefore an object of the present invention to avoid at least one of the above mentioned disadvantages and to simplify the complicated regulating system of an apparatus for hydroelectric power generation. It is another object of the invention to improve the reliability and/or functionality and/or affordability of such an apparatus and/or of a power generation system comprising at least two of those apparatuses.

At least one of these objects is attained by the apparatus according to claim 1 and the system according to claim 17. The dependent claims define preferred embodiments.

Accordingly, the invention proposes a power controller that is configured to regulate the electrical power generated by the power generator in such a way that the rotational speed of the wheels and thus the water flow through the tube section is adjustable through said power regulation from the power controller. Thus, according to one aspect of the invention, the configuration of the initially addressed turbine having two successive wheels in the turbine tube section is preferably implemented in a regulation system of the turbine by which the rotational speed of the wheels can be changed by a proper setting of the power generator. Preferably, the rotational speed of the wheels and thus the water flow through the tube section is adjustable by the power generator through said power regulation from the power controller. The power generator is preferably coupled to at least one of the turbine wheels in such a way that a power regulation of the power generator effectuates that the turbine wheels are driven by the water flow with a variable rotation speed depending on the power regulation. Thus, the power controller is preferably configured to drive the turbine wheels via the power generator with a variable rotation speed. The rotational speed of the turbine wheels preferably corresponds to a power value of the power generator set by the power controller. This can be exploited to achieve a desired power output and/or turbine efficiency without the need of an adjustment of additional equipment to influence the water flow, in particular a wicket gate or a runner blade. In this way, a rather intricate determination of the proper settings of additional equipment influencing the water flow, such as the angle of a wicket gate or a runner blade, by means of a respective controller can be avoided. In consequence, a rather complex measurement of external parameters related to the water flow or a change of the water flow that would be required to determine those proper settings can also be omitted. According to a preferred configuration, the power generator comprises a permanent magnet generator. In this way, an excitation field required for mechanical power conversion is preferably provided by at least one permanent magnet. Such an arrangement may contribute to a low failure rate and can also allow an advantageous regulation of the power generator by which a corresponding adjustment of the rotational speed of the turbine wheels can be achieved. More generally, also other types of a power generator are conceivable which can be regulated and coupled to the turbine wheels in order to allow an adjustment of the rotational speed of the turbine wheels. For instance, a power generator comprising at least one electromagnet may be applied. In this case, the excitation field may be provided by means of a rotor winding connected to a current supply.

Preferably, the apparatus comprises a power information detector configured to detect information related to the electrical power generated by the power generator. The power information preferably represents an indicator of momentary operation conditions of the turbine, in particular at least one of the momentary water flow through the turbine, the momentary rotational speed of the wheels, and the momentary efficiency of the turbine.

In this way, the power information can be used to adjust the momentary operation conditions of the turbine in an advantageous way.

Generally, the power information preferably comprises at: least one of any information about a parameter related to the electrical power generated by the power generator.

Preferably, the power information comprises information about at least one of the current, voltage, and frequency of an alternating current generated by the power generator. More preferred, the power information comprises information about at least the voltage and the frequency. Preferably, the power information is used to deduce a different power value to regulate the power generator. Preferably, the different power value corresponds to different operation conditions of the turbine, in particular a different water flow through the turbine and/or a different rotational speed of the wheels. The power controller is preferably configured to set the power generator to a power value that is previously derived from said information detected by the power information detector. Preferably, the power controller is adapted to extract an amount of power from a power connection line with the power generator, thereby setting the output power of the power generator to a desired power value. Thus, a regulation feedback between the power controller and the power generator is preferably provided via a power connection line in between the power controller and the power generator.

Generally, the setting of the power value comprises the setting of at least one parameter influencing the electrical power generated by the power generator. Preferably, the setting of the power value comprises a setting of at least one of the current, voltage, and frequency of an alternating current generated by the power generator. Preferably, the setting of the power value results in different operation conditions of the turbine, in particular a different water flow through the turbine and/or a different rotational speed of the wheels.

The power controller preferably comprises a power setting algorithm to derive a desired setting of the power value of the generator from the power information deduced from the power information detector. For instance, the power setting algorithm may comprise a database containing different power setting values associated to different power information values. As a further example, the power setting algorithm may comprise a logical sequence for deriving a power setting value from a respective power information value.

The power controller preferably comprises a power converter for converting the voltage and/or frequency of the output power extracted from the power generated by the power generator to a value suitable for a power supply system or power distribution network. The power controller preferably comprises a transformer or rectifier converting the output power extracted from the power generator into a DC current. Advantageously, the apparatus according to the invention as presented above can react very rapidly to all changes of the water flow and head. Thus, it can be advantageously programmed such that a desired value of the water head can be kept at a substantially constant value and that practically no water overflow will occur. It is noted that such a regulation of the water flow and head may represent a key factor of an efficient power production, as any loss of water flow and head may largely exceed all the mechanical loss occurring in a hydroelectric power plant.

Preferably, the power controller is configured to regulate the electrical power generated by the power generator with respect to a maximum power value of momentary turbine operation conditions. The power controller preferably comprises an algorithm to deduce the maximum power value available at the momentary operation conditions. For instance, the power controller may comprise a maximum power point tracker (MPPT). In this way, the power controller is preferably adapted to deduce a maximum power point

corresponding to momentary turbine operation conditions. Preferably, the determination of the maximum power point comprises the measurement of at least one of the voltage, current, and frequency of the power generator. Preferably, the measurement is performed on a power line connected to the power generator. The power controller is preferably also configured to set the maximum power point on the power generator.

According to a preferred configuration of the apparatus, the rotational speed of the wheels and the water flow through the wheels is substantially only adjustable through the power regulation from the power controller. In particular, no wicket gates and/or no runner blades for regulating the water flow in the turbine tube section are preferably provided. More preferred, no other additional means for regulating the water flow in the turbine tube section are preferably implemented. In consequence, no sensors are preferably required in order to determine the proper settings of such additional regulating means. In this way, a comparatively simple construction of the apparatus having a high reliability and a low failure rate can be accomplished.

Preferably, the power controller is configured to regulate the electrical power generated by the power generator such that the head of the water flowing through the turbine tube section is substantially kept at a constant value. Thus, the head is preferably kept constant irrespective of a variation of the water flow through the turbine tube section. The power regulation of the power controller preferably provides an adjustment of the water flow through the turbine tube section in such a way, that the head substantially remains at a constant value. In this way, the water flow is preferably neither adjusted to a too large value, which would lead to a decrease of the head, nor to a too small value, which would lead to an increase of the head and finally to a loss of flow through spillway. The power output at the power generator is preferably optimized this way.

The fore wheel and the after wheel are preferably configured to be driven at a

substantially constant ratio of their rotational speed. Thus, a substantially synchronized rotation of the wheels can be achieved. Preferably, the geometry of the turbine tube section and/or the wheels is adapted such that the fore wheel and the after wheel are configured to be driven by the water flow at a constant ratio of their rotational speed, in particular at the same rotation speed. To this end, the turbine tube section is preferably provided with an inside diameter increasing in the water flow direction. Moreover, the wheels are preferably configured to rotate along a common rotation axis extending in the water flow direction.

The regulation of the power generator preferably allows an adjustment of the rotational speed of both wheels preserving the defined ratio of their rotational speed. For instance, the fore wheel and the after wheel are preferably configured to rotate at the same rotational speed, such that the ratio of their rotational speed equals one. Preferably, at least one of the wheels in the turbine tube section is coupled to the power generator such that the rotational speed of the fore wheel and the after wheel is adjustable by the power regulation through the power controller.

According to a first preferred configuration, the fore wheel and the after wheel are preferably coupled to each other, in particular by at least one gearing. More preferred, the fore wheel and the after wheel are coupled to the power generator via the gearing. Thus, the rotational energy of the wheels is transmitted to the power generator via the gearing. According to a second configuration, at: least one of the fore wheel and the after wheel is preferably coupled to the power generator via a separate coupling. Thus, the rotational energy of the respective wheel is transmitted to the power generator via the separate coupling. According to a preferred configuration, at least one additional connection for the power output of the power generator is provided. The additional connection can advantageously be used to directly feed the produced output power to the power network or power supply system, in particular to avoid any losses induced by the power controller, if desired. More preferred, a switch at the power output of power generator is provided such that the power generator can be switched in between a connection with the power controller and the additional connection.

Preferably, the additional connection comprises a delta connection. The delta connection may also comprise a frequency converter arranged in between a delta circuit and the power network or power supply system, in order to allow a frequency adjustment.

Preferably, the additional connection comprises a star connection. The star connection preferably comprises a frequency converter arranged in between a star circuit and the power network or power supply system, in order to allow a frequency adjustment. Most preferred, a star connection and a delta connection with the power network or power supply system is provided, such that the power generator can be switched in between a connection with the power controller and the star connection and the delta connection. According to a preferred configuration, a frequency converter is only provided at the star connection and not at the delta connection.

Preferably, the apparatus comprises at least two turbines each comprising two bladed wheels successively arranged in a turbine tube section. Preferably, the turbines are arranged next to each other at substantially the same level of the water stream flow. More preferred, each turbine intake is arranged at a different height with respect to the water depth.

Preferably, each turbine is connected to a respective power generator. More preferred, a common power controller is provided to which each of the power generators can be connected by a switch. Preferably, each power generator is provided with a star connection and/or delta connection for the power output. Preferably, a switch at the power output of each power generator is provided, such that the power generator can be switched in between a connection with the power controller and the star connection and/or delta connection. The invention also relates to a system for hydroelectric power generation comprising at least one apparatus as described above with a turbine. The system further comprises at least a second apparatus of such a kind. The water source level of the second apparatus is preferably arranged downstream from the water outflow level of the first apparatus. In this way, a matrix of successively arranged turbines for hydroelectric power generation is preferably provided.

In such a matrix, control information is preferably simultaneously shared in between the apparatuses in the matrix. Preferably, several or all the turbines of the system are regulated by a regulation of the respective power generator with substantially the same control information. A respective power controller may be provided for each of several power generators and/or a common power controller may be provided for at least two power generators. Preferably, the control information comprises the power setting values for regulating the power generator of the respective apparatus via the power controller. Preferably, the power setting values comprise information about at least one of the current, voltage, and frequency of an alternating current generated by the power generator. In this way, at least two apparatuses within the matrix are preferably regulated to substantially the same power settings of the power generator by at least one power controller.

In a preferred application, such a matrix can be employed to provide a storage of the water of a river. A preferred method for providing such a storage comprises the step of taking the control information from an apparatus or turbine located downstream with respect to another apparatus or turbine within the matrix when filling the storage, and sharing the information with the other apparatus or turbine. The method preferably also comprises the step of taking the control information from an apparatus or turbine located upstream with respect to another apparatus or turbine within the matrix when emptying the storage, and sharing the inf ormation with the other apparatus or turbine. In this way, a lowering or raising of the water levels of the whole matrix is preferably achieved. It is noted that the lowering and raising of the water levels may be constrained within the limits offered by the respective weir structure.

In particular, such an application is preferably employed within a planned peak-demand production of the hydroelectric power to be generated. A corresponding method preferably comprises a programming of the emptying and/or filling parameters in the respective apparatuses or turbines of the matrix, in particular with respect to the desired velocities of the water flow and/or the rotational speed of the wheels. Preferably, the programmed emptying and/or filling parameters are chosen in accordance with prescribed low water levels and the usable storage volume of the river.

In another preferred application, such a matrix can be employed to effectively connect two reservoirs. In this application, the matrix can economically be used, in particular as a low head pumped-storage hydroelectric power plant.

Other preferred features of the apparatus according to the invention are described below:

Preferably, a first gear and a second gear are arranged along the rotation axis. The first gear is preferably connected to the fore wheel and the second gear is preferably connected to the after wheel such that each of the first and second gear is configured to rotate around the rotation axis driven by the respective wheel. The first gear and the second gear are preferably connected via an engagement gearing such that the fore wheel and the after wheel are coupled to each other with respect to their rotation speed. Preferably, the engagement gearing is connectable to a power generator.

Thus, due to the connection of the first gear and the second gear via the engagement gearing, a drivenly fixed connection between the fore wheel and the after wheel can be established, in which the relative rotation speed of the wheels is synchronized according to a predetermined ratio. In this way, a more reliable running performance of the turbine can be achieved, wherein an advantageous feedback between the wheels is preferably provided to a certain extent via the engagement gearing.

As a further advantage, the nominal rotation speed of the wheels can be effectively reduced for extracting a desired power output. Thus, a higher friendliness to living water organisms can be provided due to a more peacefully changing water pressure which may be combined with a more open inner tube structure.

Moreover, an advantageous power extraction from the turbine can be provided, in which both wheels can equally contribute to the power generation. Furthermore, the engagement gearing allows to feed the power extracted from both wheels to a single generator. In particular, small output powers delivered from a single wheel can thus be advantageously enhanced by the contribution of the second wheel to sufficiently supply the generator. It is to be noted that in the context of the present patent application, the term "water flow" can refer to the movement of flowing and of falling water.

For power extraction, the engagement gearing is preferably fixed to a transmission shaft for connecting the engagement gearing to the power generator, wherein the transmission shaft extends through an outer wall of the turbine tube section or of a tube section before or behind the turbine tube section. In this way, all kinds of power generators regardless the respective sizes can be disposed externally with an arbitrary lateral distance to the water flow. It is also conceivable, however, to provide the power generator before or behind the water flow tube comprising the turbine tube section. It is further conceivable to provide the power generator and its connection to the engagement gearing inside the turbine tube section or a tube section further upstream or downstream.

To drive the gear arrangement, the first gear is preferably connected to the fore wheel via a first shaft and the second gear is preferably connected to the after wheel via a second shaft, wherein one of the shafts is a hollow shaft and the other shaft extends

concentrically through the hollow shaft along the rotation axis. In this way, the gears can be advantageously provided at any position along the rotation axis and the wheel and gear design and location can be chosen to minimize the disturbance to the water flow. For this purpose, the first gear and the second gear are preferably disposed downstream with respect to the location of both wheels. A gear arrangement upstream with respect to the location of the wheels is also conceivable. A gear location in between the wheels is further conceivable, wherein both shafts can be arranged in a mutually opposed manner and no hollow shaft is needed. Preferably, the gears are successively arranged along the rotation axis. More preferred, the gears are arranged in a mutually opposing manner on the rotation axis.

According to a preferred embodiment, the engagement gearing is constituted by a single gear, in particular a conical gear, that is preferably disposed in between the first gear and the second gear. This allows a direct power extraction from the turbine and losses can be minimized. According to another preferred embodiment, the engagement gearing is constituted by a gearing assembly comprising several gears. This can be used, for instance, for a power extraction from a turbine in which the rotation speed of the wheels is synchronized to a value differing from each other, i.e. to a rotation speed ratio that is not equal to one. This can also be used to provide a desired transformation ratio of the rotation speed to a generator.

In order to allow a synchronized running of the wheels, the geometry of the turbine tube section and/or the wheels is preferably adapted to produce a desired ratio of the relative rotation speed of the wheels. In a preferred embodiment, the turbine tube section and/or the wheels are configured in such a way that the fore wheel and the after wheel can be driven by the water flow at substantially the same rotation speed. In this way, a stable running of the wheels and good power extraction can be accomplished. However, other ratios of the rotation speed are also conceivable. Moreover, various measures are conceivable to adapt the turbine tube section and/or the wheels accordingly. Some preferred measures are summarized below.

Preferably, the turbine tube section is provided with an inside diameter increasing in the water flow direction. In this way, the kinetic energy of the water can be lowered already inside the turbine tube section in which the bladed wheels are provided. In consequence, the dimensioning of a draft tube section that is needed to reduce the water flow speed behind the turbine tube section can be effectively reduced. Moreover, due to the increasing tube diameter, the flow area through the after wheel is preferably increased with respect to the flow area through the ore wheel. By an increase of the respective flow area, the rotation speed of the after wheel can be approached to a desired rotation speed of the fore wheel to avoid sacri tying of output power or turbine efficiency.

Preferably, the change of the inside diameter of the turbine tube section is chosen such that the water flow speed is reduced by at least 6%, more preferred by at least 20%, at the cross-sectional area at which the water flow exits the after wheel as compared to the cross-sectional area at which the water flow enters the ore wheel. In particular, an optimum turbine performance could be demonstrated in a preferred configuration which comprises a change of the inside diameter of the turbine tube section such that a decrease of the water flow speed of in between 40% to 60 % is achieved at the cross-sectional area at which the water flow exits the after wheel as compared to the cross-sectional area at which the water flow enters the fore wheel. The water flow speed is preferably defined as the average of the velocity profile of the water passing through the respective cross- sectional area.

A particularly efficient reduction of the water velocity inside the turbine tube section combined with a synchronization of the rotation speed of the wheels can be achieved when the inside diameter of the turbine tube section increases with a slope continuously increasing from the position at which the water flow enters the fore wheel to the position at which the water flow exits the after wheel. More preferred, the inner side wall of the turbine tube section exhibits a convex curvature along which the cross-sectional area widens in the water flow direction.

Preferably, the size and shape of the wheel blades is adapted to the inner wall geometry of the turbine tube section, such that the outer edges of the blades are substantially directly adjoining to the inner wall of the turbine tube section. Thus, the turbine efficiency can be maximized.

Preferably, the fore wheel or the after wheel or both have a diameter at a leading edge at which the water flow enters the wheel which is smaller as compared to the diameter at a leaving edge at which the water flow exits the respective wheel. This can further contribute to a synchronization of the rotation speed of the wheels. More preferred, the difference between the leaving edge diameter and the leading edge diameter of the after wheel is larger as compared to the di ference between the leaving edge diameter and the leading edge diameter of the fore wheel.

Preferably, the diameter of the fore wheel comprises a value in between 60% to 97% of the diameter of the after wheel to achieve synchronization of the rotation speed of the wheels. According to a preferred configuration, the leading edge diameter of the fore wheel is at most 97%, more preferred at most 90% and most preferred at most 80%, of the leaving edge diameter of the after wheel. According to a specific example, an optimum turbine performance could be shown in a preferred configuration which comprises an increase in diameter of the leaving edge of the after wheel as compared to the leading edge of the fore wheel of in between 65% to 75%. Preferably, both wheels are arranged along the rotation axis before or after the gears with respect to the water flow direction. The fore wheel and the after wheel are preferably arranged in immediate proximity to each other, in particular such that the leaving edge of the fore wheel is substantially directly followed by the leading edge of the after wheel. In this way, the turbine efficiency can be further improved and misrouted currents or leakage currents at an intermediate volume or disruption between the wheels can be avoided. Preferably, the leaving edge diameter of the fore wheel substantially corresponds to the leading edge diameter of the after wheel.

According to a preferred configuration, an equal number of blades is provided on the fore wheel as compared to the number of blades on the after wheel. According to another preferred configuration, a different number of blades is provided on the fore wheel as compared to the after wheel. More preferred, the blade number on the fore wheel is larger as compared to the blade number on the after wheel. According to a specific example, one additional blade is preferably provided on the fore wheel. In particular, four blades in total are preferably provided on the fore wheel and three blades in total are preferably provided on the after wheel. Preferably, the length in the water flow direction of the after wheel is different than the length in the water flow direction of the fore wheel. In this way, the rotation speed of the after wheel can be approached to a desired rotation speed o the fore wheel according to a desired output power or turbine efficiency. Preferably, the length of the after wheel differs from the length of the fore wheel by at least 5%, more preferred at least 10%, of its length. Thereby, different wheel configurations are conceivable.

According to a preferred configuration, the fore wheel exhibits a larger length in the water flow direction as compared to the after wheel. Such a wheel configuration can be advantageous to balance the energy of the fore wheel and after wheel transmitted from the water flow to a desired value, in particular to an equal value. Such a wheel configuration is preferably employed when an equal number of blades is provided on the fore wheel as compared to the after wheel. According to another preferred configuration, the after wheel exhibits a larger length in the water flow direction as compared to the fore wheel. Such a wheel configuration can be advantageous to extend the length of the after wheel in order to provide a desired value of pitch of the wheel blades with respect to a line perpendicular to the rotation axis at the leaving edge of the after wheel. Such a wheel configuration is preferably employed when a larger number of blades is provided on the fore wheel as compared to the after wheel.

Preferably, the pitch of the wheel blades, in particular with respect to a defined flow line of the water flow, decreases in the water flow direction. Thereby, a continuously decreasing pitch angle with respect to the plane of rotation of the wheels is preferably provided in the water flow direction. Preferably, the radius corresponding to the pitch of the wheel blades, in particular with respect to a defined flow line of the water flow, increases in the water flow direction. Thereby, a shape of the wheel blades, in particular along a defined flow line of the water flow, is preferred which corresponds to a fractional revolution of a helix with a diameter increasing in the water flow direction and/or a pitch angle decreasing in the water flow direction. These measures can also be used for a synchronization of the rotation speed of the wheels.

Preferably, the course of the wheel blades around the hub of the fore wheel is continued correspondingly by the course of the wheel blades around the hub of the after wheel, in particular with respect to the pitch of the blades and/or the corresponding pitch radius.

An advantageous combination of two or more of the above described measures is preferably applied on the turbine tube section and/or the wheels inside to simultaneously allow synchronization of the rotation speed of the wheels, a stable running of the wheels and optimization of the power output and/or turbine efficiency.

The turbine in an apparatus according to the invention may be also described as an "axial turbine" comprising a rotation axis of the wheels extending in the water flow direction while nonetheless allowing to exploit a change of velocity of the water flow for energy generation. Up to now, a working principle based on a velocity change of the water jet is only known from impulse turbines in which, however, the rotation axis of the wheels must be arranged perpendicular to the water flow. On the other hand, a rotation axis of the wheels extending in the water flow direction is currently only used in reaction turbines which are based, however, on a differing working principle in which the velocity of the water flow remains unchanged.

The upstream end of the turbine tube section is preferably defined as a position at which the water flow enters the fore wheel or as a position further upstream. Before the upstream end, the turbine tube section is preferably adjoined by an entry tube section through which the water flow is delivered to the turbine tube section, wherein the entry tube section preferably exhibits a narrowing diameter in the water flow direction to increase the kinetic energy of the water flow.

The downstream end of the turbine tube section is preferably defined as a position at which the water flow exits the after wheel. At the downstream end, the turbine tube section is preferably adjoined by a draft tube section that is used to recover the kinetic energy. To this purpose, the draft tube section is preferably provided with an inside diameter increasing in the water flow direction and a length adapted to recover the water flow speed downstream of the turbine to a level of the water flow speed upstream of the turbine.

According to a preferred configuration, the length of the draft tube section corresponds to a value of at most four times the diameter of the fore wheel at a leading edge at which the water flow enters the wheel. Thus, above described technical features of the turbine according to the invention can be effectively exploited to reduce the si/.e that is necessary for the draft tube section to substantially achieve full recovery of the kinetic energy of the water flow.

A corresponding hydroelectric power plant comprises a flowing or falling water and at least one apparatus for hydroelectric power generation according to the foregoing description, wherein the flowing or falling water is channeled through the turbine tube section. Preferably, the hydroelectric power plant is installed in a flowing water, in particular a natural or artificial river environment.

In a preferred configuration of the power plant, the flowing or falling water exhibits a hydraulic head of at most 4 m. more preferred at most 2.5 m and most preferred 0.8 m, before entering the turbine tube section. More preferred, due to above described technical features of the turbine according to the invention allowing to employ a hydraulic head that can be substantially below 1 m, no separate fish-ladder constructions and no division of the main flow are necessary and provided in such a power plant. Moreover, such a power plant is preferably provided with a trashrack that is mainly cleaned by the residual water flow. Preferably, the trashrack is accordingly automatically adjusted by the turbine control system. Thus, the hydroelectric power plant can advantageously be constructed without a separate mechanical trashrack cleaning machine.

Further embodiments include a hydraulic machine having two plurality bladed wheels which rotate in opposite directions in the same rotation axis, placed on the water flow as a fore wheel and as an after wheel in a way where these wheels affect the flow of each other optimizing their functionality. Preferably, the fore wheel has more or an equal amount of blades as the after wheel. Preferably, the fore wheel has a smaller diameter than the after wheel. Preferably, the fore wheel has a different pitch and/or pitch diameter than the after wheel. Preferably, at least one or both of the wheels have a smaller leading edge diameter and a greater leaving edge diameter. Preferably, the leaving edge diameter of the fore wheel is equal to the leading edge diameter of the after wheel. Preferably, the two plurality bladed wheels have a driveable fixed connection between each other.

Preferably, the machine transfers the mechanical energy outside the water flow with a shaft. Preferably, the machine is installed into a tube in a way where the water flow speed is reduced also in the bladed wheel area together with the after tube area.

The invention is explained in more detail hereinafter by means of preferred embodiments with reference to the drawings which illustrate further properties and advantages of the invention. The figures, the description, and the claims comprise numerous features in combination that one skilled in the art may also contemplate separately and use in further appropriate combinations. In the drawings:

Fig. 1 is a longitudinal sectional view of a conventional hydraulic turbine

installation;

Fig. 2 is a schematic representation of a turbine in an apparatus according to the invention; is a perspective view of a turbine in an apparatus according to the invention; is a longitudinal sectional view of a turbine in an apparatus according to the invention; is a frontal view of a fore wheel of the turbine shown in Fig. 3 and Fig. 4; is a frontal view of an after wheel of the turbine shown in Fig. 3 and Fig. 4 is a side view of the fore wheel shown in Fig. 5; is a side view of the after wheel shown in Fig. 6; is a frontal view of a wheel hub illustrating a preferred wheel geometry according to the invention; is a side view of the wheel hub shown in Fig. 9; is a vector diagram illustrating the absolute velocity, the relative velocity and the blade speed at four different positions of the wheels in the turbine shown in Figg. 2-4; is a schematic illustration of an apparatus for hydroelectric power generation; is a schematic illustration of an apparatus for hydroelectric power generation according to a second embodiment; is a schematic illustration of an apparatus for hydroelectric power generation according to a third embodiment:

Fig. 15 is a schematic illustration of an apparatus for hydroelectric power

generation according to a fourth embodiment; and Fig. 16 is a schematic illustration of a system for hydroelectric power generation in a run-of river environment. Fig. 1 schematically shows a partial view of a conventional hydroelectric power plant. It comprises a water intake passage 2 having its inlet protected by a bar screen 5. A screen washing system, not shown, is also provided to avoid clogging-up of bar screen 5. Water intake passage 2 generally has a convergent shape which guides the water towards a wheel 3 of a turbine 4 of axis D. A distributor 6 is provided in water intake passage 2 upstream of turbine 4 to properly direct the water flow with respect to blades 7 of wheel 3 of turbine 4. Turbine 4 of hydroelectric power plant generally is a Kaplan turbine, which has the shape of a helix and which generally comprises adjustable blades 7. A draft tube 8 guides the water from the outlet of turbine 4 towards a tail race 9. Turbine 4 can be stopped by means of the closing of distributor 6 generally equipped with movable wicket gates.

In the example of Fig. 1 , axis D of turbine 4 is substantially horizontal, but it can also be a vertical. The electric generator (not shown) is arranged in a bulb-shaped carter 1 placed in the flow. It can also be placed outside the flow.

A Kaplan-type turbine generally has an optimal efficiency for a specific rotation speed of wheel 3. Water intake passage 2 aims at accelerating the water flow up to a velocity adapted to the optimal efficiency rotation speed of wheel 3. The velocity of the water coming out of wheel 3 is higher than the flow velocity upstream of hydroelectric power plant. Draft tube 8 aims at slowing down the flow coming out of wheel 3 and thus enables recovering as much of the kinetic energy remaining in the flow coming out of turbine 4 as possible. Normally the draft tube 8 length is greater than 4.6 times of the diameter of wheel 3. Generally, a ratio K characterizing turbine 4 of a given hydroelectric power plant type is defined, corresponding to the ratio between the kinetic energy of the flow coming out of wheel 3 and the potential energy of the head. Ratio K,

expressed in %, is given by the following relation: K = 100*V²/2gH where V is the average speed of the flow coming out of wheel 3, g is the gravitation constant and H the head height. Ratio K is representative of the energy still contained in the flow in kinetic form when coming out of wheel 3, divided by the energy available for the turbine, and is thus representative of the energy to be recovered by draft tube 8.

The higher the ratio K, the greater the slowing down is to be performed. For conventional low-head Kaplan turbines, Mr. Joachim Raabe. in its work entitled "Hydro Power", indicates that ratio K is 30%, 50%, and 80% for 70-meter, 15-meter, and 2-meter heads, respectively. The high kinetic energy to be recovered in very low head turbines at the outlet of wheel 3 leads to a construction of very large draft tubes since their divergence is limited by risks of separation of the liquid vein. The forming of water intake passage 2 and of draft tube 8 of a hydroelectric power plant thus requires the forming of large civil engineering constructions. The very high cost of such constructions considerably burdens the total cost of the plant and has strongly limited the construction of hydroelectric power plants on low heads and very low heads for which the coefficient K is particularly high.

A counter rotating double turbine according to the invention, as further described below, can especially be used efficiently as an extreme low head turbine. The main problem in known Kaplan turbines is that with low heads the turbine diameter grows rapidly. For example -35 kW Turbine power can been reached with a flow of Q = 1 m³/s and a head of H = 4 m, or Q = 4 m³/s and H = 1 m, but at the same time the regular Kaplan turbine diameter grows from -47 cm to -133 cm. Or with a turbine power of just -9 kW with Q = 1 m³/s and H = l m it grows to a diameter of -67 cm. The reason for increasing the turbine diameter is to reduce the water speed and thus cavitations on turbine. With the counter rotating double turbine according to the invention it is possible to reduce the diameter to 2/3 - 3/4 from the original size.

As the turbine diameter is the main factor which regulates also all the surrounding structures it is the key dimension which determines if the waterpower-project is even feasible. Normally civil work cost is found out to be 5 times higher under 1,5 m head as compared to under 3 m head. In very low heads the turbine diameter easily exceeds the head height and leads to a situation where the whole turbine must be rearranged as shown in Patent CA Pat. No. 2,546,508, or the problem is solved with a matrix of turbines as shown in Patent U.S. Pat No. 6,281 ,597.

Another known problem in existing Kaplan- and Francis-type water turbines is that their efficiency curve drops relatively rapidly when the flow is not in the planned optimum. This phenomenon can be reduced with variable pitch propellers and wicket gates, but it also increases the investing costs and such a system needs also constant process surveillance. As the invention described here is not based on an optimally developed vortex like water flow, i.e. the water flow as in a conventional Kaplan turbine, but instead an axially symmetric water flow, its efficiency-curve is less reliant to the optimum water flow. This gives the invention a benefit where great flow-variances occur. Fig. 2 schematically indicates a turbine 77 that is provided in an apparatus for hydroelectric power generation according to the invention. Turbine 77 comprises the following components: two propeller-type turbine wheels 11, 12 rotating in counter directions in a flow tube 10. The shape of flow tube 10 comprises an increasing diameter in the water flow direction which allows a synchronized movement of the wheels 11, 12 with respect to their rotation speed. The mechanical energy provided by the wheels 11, 12 is turned into electric energy by a power generator outside the water flow tube.

Fig. 3 is a perspective view of a turbine 17 that is provided in an apparatus for hydroelectric power generation according to the invention. The turbine 20 comprises a water flow tube 18 with a substantially cylindrical outer wall 19. A flowing water with a flow direction 23 is fed into flow tube 21 at an upstream tube end 24. Flow tube 18 is composed of an entry tube section 20 beginning at upstream tube end 24, an intermediate turbine tube section 21 , and a subsequent draft tube section 22 leading to an downstream tube end 25.

Entry tube section 20 is provided with an inner wall 26 with an inner diameter decreasing in the flow direction 23 in order to increase the kinetic energy of the flowing water. Turbine tube section 21 is provided with an inner wall 27 with an inner diameter increasing in the flow direction 23, for the reasons further explained below. Thus, the kinetic energy of the flowing water is already decreased in the turbine tube section 21. Draft tube section 22 is provided with an inner wall 28 with an inner diameter further increasing in the flow direction 23 in order to further decrease the kinetic energy of the flowing water to an upstream energy level before it enters into flow tube 18.

With respect to water flow direction 23, first a fore wheel 31 and subsequently an after wheel 32 are arranged inside turbine tube section 21 in immediate proximity to each other such that wheels 31, 32 can rotate along a common rotation axis 30 extending in water flow direction 23. Wheels 31, 32 are from the type of the wheels of a propeller turbine. It is also conceivable, however, that wheels 31 , 32 are from the type of the wheels of a Kaplan turbine.

Wheels 31, 32 are each composed of a hub 33, 34 and several blades 35, 36. Blades 35, 36 are formed such that wheels 31, 32 rotate counterwise, i.e. in a mutually opposite rotation direction, driven by the water flow in direction 23. Fore wheel 31 has four blades 35 and after wheel 32 has three blades 36. The shape of the outer edge 37, 38 of blades 35, 36 is adapted to the geometry of inner wall 27 of turbine tube section 21 , such that blades 35, 36 can rotate in immediate proximity to inner wall 27 of turbine tube section 21.

The position at which the water flow enters wheels 31, 32 is subsequently denoted as the respective leading edge 39, 40 of wheels 31, 32. The position at which the water flow exits wheels 1 , 32 is subsequently denoted as the respective leaving edge 41 , 42 of wheels 31, 32. The diameter of leaving edge 41 of fore wheel 31 corresponds to the diameter of leading edge 40 of after wheel 32. Turbine tube section 21 ends at leaving edge 42 of after wheel 32, at which draft tube section 22 follows. At leading edge 39 of fore wheel 31. a hydrodynamic nose structure 29 is provided as an upstream extension of hub 33 to improve the fluid dynamics. The length of draft tube section 22 corresponds to approximately three times of the leading edge diameter 39 of fore wheel 31.

Inside draft tube section 22, i.e. further downstream with respect to leaving edge 42 of after wheel 32. a gear arrangement 45 is provided. Gear arrangement 45 comprises a first gear 46 and a second gear 47 subsequently arranged around rotation axis 30 in a mutually opposing manner such that gears 46, 47 are facing each other. Gears 46, 47 are conical gears. An engagement gearing 48 facing rotation axis 30 is provided above rotation axis

30 in such a manner, that it engages with both other gears 46, 47. For this purpose, first gear 46 and second gear 47 are arranged on the downstream and upstream end of engagement gearing 48, respectively. Engagement gearing 48 is constituted by a conical gear. Wheels 31, 32 are connected to gears 46, 47 each via a respective shaft 56, 57, as further explained below.

At its outer surface, engagement gearing 48 is fixed to a transmission shaft 51.

Transmission shaft 51 extends from engagement gearing 48 orthogonally to outer wall 19 to a region outside of flow tube 18. For this purpose, a through hole 52 is provided in outer wall 19 of flow tube 18. Around the position of through hole 52, a mounting block 53 is provided by which an outer cylinder 54 is fixed on outer wall 19. Transmission shaft 51 extends along the central axis of outer cylinder 54 to its upper end, where transmission shaft 51 is provided with a driving crank 55. Driving crank 55 or transmission shaft 5 1 is connected to a power generator to produce electrical energy. The generator can be installed, for instance, inside or above or in place of outer cylinder 54.

From Fig. 4 depicting a detailed sectional view of turbine 17 it is apparent that fore wheel

31 is connected to first gear 46 via first shaft 56 and after wheel 32 is connected to second gear 47 via second shaft 57. The respective gears 46, 47 are arranged inversely with respect to water flow direction 23 as compared to fore wheel 31 and after wheel 32, i.e. first gear 46 is arranged after second gear 47 along rotational axis 30.

Shafts 56, 57 extend along rotation axis 30. Second shaft 57 is a hollow shaft through which first shaft 56 concentrically extends. Via shafts 56, 57, gears 46, 47 are driven to rotate in the same direction as respective wheels 3 1 , 32 driven by the water flow. Thus, a counterwise rotation of gears 46, 47 is achieved through the water flow, such that gears 46, 47 rotate in a mutually opposite direction, which is necessary to drive engagement gearing 48. Moreover, an equivalent rotation speed of gears 46. 47 is intrinsic for the drive of engagement gearing 48. In this way, the rotation speeds of wheels 31, 32 are mutually coupled by means of engagement gearing 48. To provide the rotation speeds of wheels 31. 32 at the desired equivalent value, the geometry o turbine tube section 21 and wheels 31, 32 is adjusted accordingly. It becomes further apparent from Fig. 4, that inner wall 27 of turbine tube section 21 exhibits a convex curvature along which the cross-sectional area of turbine tube section 21 widens in water flow direction 23. Thus, the inner diameter of turbine tube section 21 increases with an increasing slope and a flow profile of inner wall 27 is provided along which the mean fluid velocity decelerates. The convex curvature of inner wall 27 extends from a position with a forward distance to leading edge 39 of fore wheel 31 to the position of leaving edge 42 of after wheel 32. This geometry is used to synchronize the rotation speed of wheels 31, 32. Draft tube section 22 following turbine tube section 21 after the position of leaving edge 42 of after wheel 32 has a diameter further increasing in water flow direction 23. The shape of inner wall 28 of draft tube section 22 exhibits a slightly concave curvature or a substantially constant slope. The geometry and length of inner wall 28 of draft tube section 22 is designed for recovery of the kinetic energy of the water flow. Nonetheless, also the geometry of inner wall 27 of turbine tube section 21 - together with the inner arrangement of wheels 31 , 32 - largely contributes to the recovery of kinetic energy. This leads to an effective reduction of the length required for draft tube section 28.

Fig. 5 shows a frontal view of fore wheel 31. Fore wheel 31 comprises four blades 35a- 35 d with an identical shape and equidistantly arranged around hub 33.

Fig. 6 shows a frontal view of after wheel 32. After wheel 32 comprises three blades 36 a- 36c with an identical shape and equidistantly arranged around hub 34. Blades 36a-36c have a larger surface as compared to blades 35a-35d. The diameter of fore wheel 31 at its leaving edge 41 substantially corresponds to the diameter of after wheel 32 it its leading edge 40. The diameter of fore wheel 31 at its leading edge 39 deviates from the diameter of after wheel 32 it its leaving edge 42 by approximately 25% to 30%.

Fig. 7 shows a side view of fore wheel 31. In the figure, a blade angle a in between outer edge 37 of blades 35 and a plane 61 orthogonal to rotation axis 30 is indicated. Blade angle a varies with the longitudinal position of orthogonal plane 61 along rotation axis 30. This longitudinal variation of blade angle a is affected by the course 58 of blades 35 along which blades 35 extend around hub 33, by the desired rotation direction of fore wheel 31 driven by water flow 23 and by the shape of inner wall 27 of turbine tube section 21 such that outer edges 37 of blades 35 seamlessly border onto inner wall 27. Course 58 of blades 35 along hub 33 can be described as a partial helix winding around hub 33, as further described below.

Fig. 8 depicts a corresponding side view of after wheel 32, in which blade angle β in between outer edge 38 of blades 36 with respect to plane 61 orthogonal to rotation axis 30 is indicated. Blade angle β also exhibits a longitudinal variation, the amount of which being affected by the course 59 of blades 36 along hub 34, by the desired rotation direction of after wheel 32 driven by water flow 23 and by the shape of inner wall 27 of turbine tube section 21 such that outer edges 38 of blades 36 seamlessly border onto inner wall 27. Course 59 of blades 36 can be described as a continuation of the partial helix winding along course 58 around hub 33. The helical course 58, 59 of blades 35, 36 around hubs 33, 34 of wheels 31, 32 is subsequently described in greater detail on the basis of a schematic illustration shown in Figg. 9 and 10.

The length of after wheel 32 in water flow direction 23 along which blades 36 extend exceeds the corresponding length of fore wheel 31 along which blades 35 extend. In this way, a desired pitch of the helical course 59 of blades 36 can be reached at leaving edge 42 of after wheel 32. The blade geometry allows to compensate for the chosen lower number of blades 36 on after wheel 32 as compared to the number of blades 35 on fore wheel 31 in order to synchronize the rotation speed of the wheels.

Fig. 9 schematically shows a frontal view through a cross-sectional area 63 inside turbine tube section 21 with a cylindrical body 66 at its center. Cylinder 66 extends along rotation axis 30. A helix 64 with a diameter increasing in water flow direction 23 winds around cylinder 66.

Fig. 10 shows a corresponding side view of cylinder 66 and helix 64. Cross-sectional areas 61 further upstream with respect to cross-sectional area 63 are also indicated. In addition, various flow lines 67, 68 of the water flow inside inner wall 27 of turbine tube section 21 are indicated. The distance between flow lines 67, 68 widens in water flow direction 23 with an increasing slope. Helix 64 winds around the most outer flow lines 68. Cylinder 66 serves as a schematic illustration of hub 33 of fore wheel 31 or of hub 34 of after wheel 32 or of a combination of both hubs 33, 34 in which fore wheel 31 and after wheel 32 are directly arranged one after the other along water flow direction 23. Helix 64 serves to illustrate the corresponding shape of blades 35, 36 at the position of outer flow lines 68.

More precisely, helix 64 defines a pitch line, i.e. a line that passes through the leading edge 39, 40 and leaving edge 41, 42 of blades 35, 36 at the position of outer flow lines 68. The shape of blades 35, 36 changes accordingly at inner flow lines 67. As already noted, the length of courses 58, 59 of blades 35, 36 along hub 33, 34 of fore wheel 31 and after wheel 32 corresponds to a partial helical revolution around cylinder 66.

Three subsequent longitudinal distances PI, P2, P3 in flow direction 23 are indicated in Fig. 10, each corresponding to one revolution of helix 64. Longitudinal distances PI, P2, P3 of the helix revolutions decrease in flow direction 23. The corresponding radiuses Rl, R2, R3, R4 of the respective helix revolutions increase in flow direction 23.

Corresponding angles γΐ, γ2. γ3 between helix 64 and cross-sectional areas 61

continuously decrease in flow direction 23.

Longitudinal distances PL P2, P3 define the pitch of blades 35, 36 at outer flow lines 68. Pitch PL P2, P3 is a measure of the axial fluctuation in motion of a given radial position Rl, R2, R3, R4 that has been covered after one complete revolution of blades 35, 36. Radiuses R l , R2. R3. R4 are subsequently denoted as pitch radius. Angles γΐ . γ2, γ3 define the pitch angle of blades 35, 36 at outer flow lines 68. Pitch angles γΐ , γ2, γ3 are a measure of the pressure face of blades 35, 36 along pitch line 64 with respect to plane of rotation 61.

Accordingly, pitch PI, P2. P3 of blades 35, 36 of wheels 31, 32 shown in Figg. 7 and 8 continuously decreases in water flow direction 23. Pitch radius R L R2. R3, R4 of blades

35. 36 of wheels 31. 32 continuously increases in water flow direction 23. Pitch angle γΐ, γ2, γ3 of blades 35, 36 of wheels 31 , 32 continuously decreases in water flow direction 23. In the vector diagram shown in Fig. 11, a specific example of the absolute velocity, relative velocity and blade speed at two different positions of fore wheel 11, 31 and at two different positions of after wheel 12. 32 is illustrated.

The absolute velocity CI at leading edge 39 of fore wheel 31 is given by the sum of the relative velocity Wl and the blade speed Ul at leading edge 39 of fore wheel 31. The absolute velocity C2 at leaving edge 41 of fore wheel 31 is given by the sum of the relative velocity W2 and the blade speed U2 at leaving edge 41 of fore wheel 31. The absolute velocity C3 at leading edge 40 of after wheel 32 is given by the sum of relative velocity W3 and blade speed U3 at leading edge 40 of after wheel 32. The absolute velocity C4 at leaving edge 42 of after wheel 32 is given by the sum of the relative velocity W4 and the blade speed U4 at leaving edge 42 of after wheel 32. The vectors are designated in a Cartesian coordinate system with an axial vector component X in water flow direction 23 and a tangential vector component Y in an orthogonal direction.

Absolute velocities CI, C2, C3, C4 are a measure of the speed of the incoming water flow in an absolute frame of reference. Clm denotes the meridian velocity at leading edge 39 of fore wheel 31 averaged over the cross sectional area of the water flow. Blade speeds Ul, U2, U3, U4 are a measure of the tangential velocity ω · r of blades 35. 36 at: a radial distance r, when wheels 1 1, 12, 31, 32 rotate with rotation speed ω. Relative velocities Wl, W2, W3, W4 are a measure of the speed of water flow in a frame of motion relative to blade speeds U l , U2, U3, U4. Thus, relative velocities Wl, W2, W3, W4 are influenced by the respective angle of blades 35, 36 of wheels 1 1. 12, 31. 32 with respect to line 61 orthogonal to rotation axis 30.

In common axial turbines, such as in Kaplan, Francis or propeller turbines, the velocity of the passing water jet substantially remains unchanged and only the water pressure is changed as the water jet acts on the turbine blades. Such a type of turbine is also referred to as reaction turbine.

As depicted in Fig. 11 , however, the velocity CI, C2, C3, C4 of a water jet changes during its passage of turbine tube section 21 of axial turbine 17. Turbine 17 according to the invention may therefore be regarded as an "axial impulse turbine" in which also a change of velocity of the water flow can be exploited for energy generation. This means that not only the Eulers Turbine equation can be used, but also the common Impulse equation is needed to get the correct energy output calculated. Ie. Cl^A2/2 - C4^A2/2.

Moreover, the axial turbine loss during the water passage of the wheels and therefore the efficiency of axial turbines, in particular of current Kaplan, Francis or propeller type turbines, generally depends on approximately the square of the relative velocity W of the water flow relative to the blade speed. However, since relative velocity Wl, W2, W3, W4 of a water jet passing through turbine tube section 21 according to the invention is strongly reduced due to the decrease of absolute velocity CI, C2, C3, C4, the efficiency of an axial turbine 17 according to the invention can be optimized.

Subsequently, several features of turbine 17 depicted in Figg. 3-8 and other embodiments and advantages are summarized:

The turbine drive depicted in Fig. 3 is designated to be directly mounted to the input shaft of a generator (not shown). The drive contains a reversing mechanism 45 which has a driving shaft 51 having a conical gear 48 in constant engagement with two conical gears 46 and 47. The gear 46 is driven by a propeller shaft 56 and the gear 47 is driven by a propeller shaft 57 in the form of a hollow shaft mounted concentrically to the shaft 56. The shaft 56 carries a propeller 31 and the shaft 57 a propeller 32. With the arrangement described, the propeller shafts will rotate in opposite directions. The shown arrangement can been placed after the propellers 3 1 and 32 as shown in Fig. 3 or it can been placed before the propellers 31, 32.

The after propeller 32 has a greater diameter than the fore propeller 31 , and the flow tube 10. 1 8 must be formed, as schematically illustrated in Figg. 2 and 4, so that both propellers can function efficiently and an axially symmetric water flow can been maintained with a maximum water velocity and pressure reduction on the propellers 31 ,

32.

As water speed can be efficiently lowered already in the turbine 17 itself, it means also that the optimal draft tube 22 relative length is smaller than it is with regular turbines. The flow tube 10, 18 can been build up tube as in the embodiment shown in Figg. 2-4, or it can been a virtual tube in free water just describing the flow.

In the embodiment shown in Figg. 2-8, the diameter of the fore propeller 31 is 93% of the diameter of the after propeller 32, but depending on various factors such as head height and flow for example, the diameter of the fore propeller 31 can be also 80-97% or 60- 97% or beyond of the diameter of the after propeller 32. The fore propeller 31 can have the same or greater pitch than the after propeller 32. The fore propeller has more blades 35 (i.e. 4 pes), while the after propeller has less blades 36 (i.e. 3 pes), as shown in the embodiment in Figg. 2-8.

As shown in the embodiment in Figg. 2-8, the propellers leading edge has a smaller diameter than the leaving edge. This helps the turbine to reach the optimum flow tube form 10 shown in Figg. 2-4.

The propellers 31, 32 pitch PI, P2, P3 may also vary in the blade area if there is also a difference on blade edge diameters. Fig. 12 schematically depicts an apparatus 101 for hydroelectric power generation according to a first embodiment. Apparatus 101 comprises a turbine 102 con-esponding to turbine 77 shown in Fig. 2 or to turbine 17 shown in Figs. 3 and 4. By means of a mechanical coupling 104, turbine 102 is coupled to a power generator 103. Thus, power generator 103 is arranged to generate electrical power from the rotational energy of the wheels 11, 12, 31 , 32 of turbine 102. Power generator 103 provides an alternative current (AC) power output having a voltage and frequency that is proportional to the rotational speed of wheels 1 1 , 12, 31 . 32 of turbine 102. In the preferred embodiment, power generator 103 is provided by a permanent magnet generator (PMG). It will be appreciated that also other types of an electric generator can be employed.

Mechanical coupling 104 comprises a rotor that connects at least one of the wheels 1 1 , 12. 31 , 32 of turbine 102 to power generator 103 in such a way that the rotational speed of this wheel is variable in dependence of the electrical power produced by power generator 103. Since turbine 102 is configured such that its wheels 1 1. 12, 31. 32 are driven at a substantially fixed ratio of their rotational speed, as described above, the rotational speed of both the fore wheel 11 , 31 and the after wheel 12, 32 is variable in dependence of the electrical power produced by power generator 103. For instance, the rotor of coupling 104 may be provided by transmission shaft 51 of turbine 17 shown in Figs. 3 and 4. Thus, the rotational energy of fore wheel 31 and after wheel 32, which are mutually connected via gearing 48 that is connected to transmission shaft 51, can be transmitted to power generator 103 and converted into electrical energy. A regulation of the power output of power generator 103 then limits the rotational speed of the rotor of coupling 104 and thus also limits the rotational speed of wheels 31 , 32 within their substantially fixed ratio of their rotational speed.

In this way, referring to the vector diagram shown in Fig. 11, the blade speeds Ul, U2, U3, U4 and thus also the absolute velocities CI, C2, C3, C4 of the water flow can be influenced and thus advantageously regulated by the regulation of the power output of power generator 103. In particular, the regulation of the velocity CI of the incoming water flow at the leading edge 39 of fore wheel 31 and the according synchronization of the after wheel blade speeds U3, U4 further downstream with respect to the fore wheel blade speeds Ul, U2 allows to avoid to exert any other external influence on the water flow, in particular the use of movable wicket gates and adjustable runner blades, in order to optimize the turbine efficiency.

A very simple example can be given with real values of variables of Euler's pump equation:

Flowl/1 : CI = 5.7, Ul = 4.55, C2 = C3 = 4.7, Cu2 = Cu3 = 0.66, U2 = 5, C4 = 3.6, U4 = 5.6. Y'impulse' = 9.72. Y'Euler' = 6.6. Y'Total' = 16.3:

Flowl/2: CI = 2.85, U1 = 3.41, C2 = C3 = 3, Cu2 = Cu3 = 1.88, U2 = 3.75, C4 = 1.8, U4 = 4.2, Y'impulse^* = 2.4, Y'Euler" =14.1 , Y'Total' = 16.5; Power generator 1 3 is connected to a power line 108, 109. Power line 1 8. 109 comprises a power connection cable 108 connecting power generator 103 to a power controller 105 and a power output cable 109 constituting a power output of apparatus 101, in particular to feed the generated electrical power into an electrical network. Power output cable 109 is connected to the output of power controller 105. Power controller 1 5 comprises a power converter system to convert the AC output power of power generator 103, in particular by changing at least one of the voltage and frequency of the AC output power. The converted AC power of power generator 103 is then delivered via power output cable 109 to a power supply system or a power network. For instance, power controller 105 may comprise a power inverter.

On the one hand, power controller 105 is adapted to provide the output power in power output cable 109 at a voltage and frequency value that is inherently required for the feeding into the power supply system or power network. On the other hand, power controller 105 is adapted to extract power from power connection cable 108 in such a way, that the current voltage and frequency in power connection cable 108 produced by power generator 103 yields a desired value corresponding to a desired value of the blade speeds Ul, U2, U3. 114 of turbine 102 and thus also of the absolute velocities CI, C2, C3, C4 of the water flow.

Thus, power controller 105 fulfills the first function of controlling the voltage and frequency produced by power generator 103 via a feedback provided through power connection cable 108 and thereby controlling the water flow through turbine 102 via mechanical coupling 104 of power generator 103 with wheels 1 1, 12, 31, 32 of turbine 102. And power controller 105 fulfills the second function of converting the voltage and frequency produced by power generator 103 to a suitable value of a power supply system or a power network connected with power output cable 109. An exemplary embodiment of power controller 105 fulfilling those functions is described below: Power controller 105 comprises a power regulator 107 configured to regulate the frequency and/or voltage of the AC output power of power generator 103 in a power feedback loop with power generator 103 that is provided by power connection cable 108. In particular, the frequency and/or voltage of the AC output power of power generator 103 may be regulated by extracting a respective amount of power from power feedback loop 108 between power generator 1 3 and power controller 105. By regulating the power extracted by power controller 105 from power connection cable 108. the frequency and/or voltage of the AC output power generated by power generator 103 can be set. By changing the frequency and/or voltage of the AC output power of power generator 103, the rotational speed of the rotor inside power generator 103 is ad justed. As a result, also the rotational speed of wheels 11, 12, 31, 32 of turbine 102 is adjusted via mechanical coupling 104.

Power regulator 107 further comprises a power converter in order to convert the voltage and frequency of the amount of power extracted from power feedback loop 108 to a value suitable for the power supply system or power network. For instance, an output power of power generator 103 with a voltage in between 0 and 1000 V may be extracted by power regulator 107 from power feedback loop 108 which is then converted to a value of 220 V or 400 V corresponding to a standard value of a power network. Correspondingly, the frequency of the extracted output power may be converted to value of 50 Hz or 60 Hz. The converted power is then fed into power output cable 109.

Power regulator 107 may further comprise a transformer or rectifier converting the AC output power of power generator 103 to be extracted from power feedback loop 108 into a DC current. The extracted DC current is then converted into an AC current with the suitable voltage and frequency value for the power supply system or power network by the power converter in power regulator 107.

Power controller 105 further comprises a power information detector 106. Power information detector 106 is configured to measure information about the output power provided from power generator 103, in particular at least one of the voltage and frequency of the AC output power. For this purpose, power controller 105 is connected via a measuring line 110 to a measuring point of the AC output power of power generator 103. For instance, power connection cable 108 may be connected to power connection cable 108 via measuring line 1 10 and/or to a power output of power generator 103 and/or to a power input of power controller 105 via measuring line 110.

Thus, the above described power feedback loop 108 in between power generator 103 and power controller 105 allows to extract a desired amount of output power from power generator 103 which is to be delivered to the power supply system or power network via power output cable 109. By extracting the respective amount of its output power, power generator 103 is set to an according power value of power production by which the rotational speed of the turbine wheels is set via mechanical coupling 104. In this way, the water flow through the turbine tube section is set according to the rotational speed of the turbine wheels determined by the power value generated by power generator 103 which is set by extracting and delivering a specific amount of the output power of power generator 103 to power output cable 109. Correspondingly, the power information derived from power information detector 106 allows to draw conclusions about the momentary operation conditions of turbine 102, such as at least one of the rotational speed of wheels 11, 12, 31, 32 of turbine 102, the water flow through turbine tube section 10, 21, and the turbine efficiency.

The power information obtained from power information detector 106 is transmitted to power regulator 107 via a power information line 111. Power regulator 107 is configured to regulate the AC output power of power generator 103 in dependence of the obtained power information by changing the frequency and/or voltage of the AC output power, in particular by extracting a respective amount of power from power feedback loop 108. The AC output power of power generator 103 is regulated to a value that results in an optimization of the momentary operation conditions of turbine 102, in particular at least one of the rotational speed of wheels 11, 12, 31, 32 of turbine 102, the water flow through turbine tube section 10, 21, and the turbine efficiency. hi order to provide an optimized power value for power generator 103 from the power information derived from power information detector 106, power information detector

106 comprises a maximum power point tracker (MPPT). The MPPT comprises an algorithm that is configured to determine a maximum power point (MPP) of momentary operation conditions of turbine 102 from the power information obtained from power information detector 106. This results in a power value, in which the rotational speed of wheels 1 1 . 12. 3 1. 32 of turbine 102 and the water flow through turbine tube section 10, 21 is adjusted in such a way, that the head of the water of turbine 102 is substantially kept at a constant value and the efficiency of turbine 102 is optimized.

In this way, an adjustment of the water flow and an optimization of the turbine efficiency can be achieved without additional regulation means of the water flow, such as wicket gates and runner blades and any other regulating systems of those additional components, as used in prior art. This results in a largely reduced complexity of the apparatus for hydroelectric power generation according to the invention. Instead, the apparatus exploits an intrinsic regulating mechanism of the water flow by exploiting the advantageous correlation of fore wheel 11, 31 and the after wheel 12, 32 with respect to their rotational speed inside turbine 102, which can be adjusted by a proper regulation of power generator 103. Thus, according to the invention, the whole regulation of hydroelectric power plant 101 can be achieved by a combination of a turbine 17, 77, 102 with two bladed wheels 11, 12, 31 , 32 that are correlated with respect to their rotational speed, as described in

WO2012146768 Al, and power generator 103 connected to a power controller 105 comprising a MPPT regulating its rotational movement (rpm). As MPPT 105 measures the current and/or voltage and/or frequency of power generator 103 through power line 108, , and these can be calibrated depending on the present situation of turbine operation conditions including all losses, it means finally, that hydro-power plant 101 can fully control the water level or head (H) and water flow (Q) without any sensors or regulating mechanisms placed in difficult environmental conditions. Stated differently, the turbine- generator-combination according to the invention works as such a sensor itself.

In this context it is to be noted that the voltage value of the AC output power of power generator 103 is correlated with the water flow Q through turbine 102 and the current value of the AC output power is correlated with the head H. Thus, the water flow Q through turbine 102 can be advantageously adjusted by regulating the voltage of the AC output power of power generator 103 to a respective value, by keeping the head H at a substantially constant value.

The ease of such a regulation takes also advantage of an individual speed constant of power generator 103, in particular in the case of a permanent magnet generator (PMG). In this way, a fixed connection between an electric potential difference U (Volt V) and a rotation speed ω (rpm) does exist. Therefore, the rotation speed ω (rpm) and power P (Watt W) of such a machine can be easily regulated by a regulation of electric current I (Ampere A), wherein the power P equals the voltage U (Volts V) times the current I (P = U'l). The basic principle of the MPPT is to seek such a combination of U and I which leads to a maximum P. i.e. the maximum power point (MPP). It is to be noted that the connection of the rotation speed ω and voltage U is constant only if the current I is constant. But as the current I must be varied to allow the power P and thus the voltage U and thus the rotation speed ω to change, the control of the rotation speed ω should be measured through frequency, which always gives an accurate value.

Subsequently, a regulation of apparatus 101 for hydroelectric power generation is illustrated on a specific example:

In hydroelectric power generation, the power of a power plant is given as P = H-Q'g, where the flow Q (m³/s) is variable, the head H (m) is wanted to be kept at maximum and g is constant (g=9.81 m/s²). In a run-of-the-river hydroelectric power plant, where little or no water storage is provided, the flow Q must be regulated to follow exactly the maximum Q that is momentary available. In the present example, a hydro-power plant is assumed to have a constant head H = 2 m and the turbine flow Q can vary between 0 to 2 m³/s. The efficiency η is considered as a constant value of 80%. Thus, the maximum power available is given as P_max = H*Q*g- η = 2 m · 2 nrVs · 9.81 m/s² · 0.8 = 31.4 kW. The turbine 102 is considered to have a maximum rotational speed <¾ = 300 1/min at the maximum flow Q.

The turbine 102 is further assumed to be connected to the permanent magnet generator 103 via coupling 104 through a gearing comprising a gear ratio of 1 :2.5. This yields a maximum rotational speed co_g = 750 1/min of power generator 103. The maximum voltage V from the system is considered to be 400 Volts. PMG 103 has 4 pole pairs per phase and therefore the rotational speed ω„ of 750 1/min translates to 50 Hz. The speed constant of PMG 103 is then calculated as 400 V / 750 1/min = 0.53 V / rpm. The overflow Yc width is 5 m. (Detailed overflow Yc calculations are based on this, but are not presented here) Now it is assumed that turbine 102 runs stable with a flow of Q = 1.0 ni3/s and power controller 105 has regulated the power P and thus the rotational speed ω of turbine 102 and power generator 103 to the following balanced values: power P = 1 m³/s · 2 m · 9.81 m/s^2■ 0.8 = 15.7 kW;

rotation speed of turbine: ω, = 150 1/min;

rotation speed of generator: co_g = 150 l/min-2.5 = 375 1/min;

frequency of the generator: f = 25 Hz;

voltage of the generator: V ~ 200 V;

current regulated by MPPT: I ~ 78.5 A

These values are programmed to a match or approximately match the maximum-power- point (MPP) of the momentary operation conditions.

Change 1:

In the above example, it is now assumed that the flow Q changes to 1.05 m s and therefore becomes an overflow of 0.05 m Vs. which also increases the head H to approx. 2.02 m. Therefore the power P and generator current I increase by approximately 1%, which is noted by the program of power controller 105. Thus, power controller 105 starts to regulate the values according to an algorithm comprising a programmed curve of desired power values. The Q is increased until the power controller 105 finds a new programmed match corresponding to a maximum-power-point (MPP). The corresponding values are: P = 16.5 kW, o¾ = 157.5 1/min, c¾ = 394 1/min, V ~ 210 V, and 1 ~ 78.5 A.

Change 2:

In the above example, it is now further assumed that the flow Q changes to 1.8 m³/s and therefore becomes an overflow of 0.75 m³/s. This also increases the head H to approximately 2.13 m. Therefore the power P, and generator current I increases by 6%. This is is noted by the program of the power controller 105. The power controller 105 starts to regulate the values back to the programmed curve. The flow Q is increased until the power controller 105 finds the new programmed match or MPP. The corresponding values are: P = 28.25 kW, o¾ = 270 1/min. c¾ = 675 1/min. V ~ 360 V. and I ~ 78.5 A

Change 3: In the above example, it is now further assumed that the flow Q changes to 0.5 nr /s and therefore the head H drops. Therefore the power P, and generator current I drops by 6%, which is noted by the program of the power controller 105. The power controller 105 starts to regulate the values back to the curve. The flow Q is decreased until the power controller 105 finds the new programmed match or MPP. The corresponding values are: P =7.85 kW, co, = 75 1/min, c% = 187.5 1/min, V ~ 100 V , and I ~ 78.5 A.

As seen from the above examples the generator current I remains practically constant. This allows an easy optimization of generator 103 and helps to keep up high efficiency.

In summary, a similar linear behaviour of turbine 102 and power generator 103 defining the output power P can be expressed by the equation:

P = H (constant) · Q (variable) · g

= U (Variable) · I (constant)

Thus, the output power P can be essentially regulated by means of a variable water flow Q in turbine 102 and a variable voltage U of generator 103, wherein the head H in turbine 102 and the electric current I of generator 103 are substantially kept at a constant value. The variable values of turbine 102 and power generator 103 are adjustable by a change of their respective rotational speed (¾, c% defining the output power P. This similar linear behaviour in the regulation of turbine 102 and power generator 103 makes the

combination of the two techniques very suitable to use in a run-of-the-river hydroelectric power plant.

It is noted that such a regulation by power controller 103 can particularly notice a drop of the head H, and therefore it is very easy to correct the resulting decreasing water flow Q to an optimized value. In the case of an increasing water flow Q, a regulation by power controller 103 is not so obvious, as a resulting overflow of water may limit an increase of head H. For this case, an appropriate functionality of power controller 103 is subsequently described more precisely: It is well known that the overflow of a weir has an exponential curve expressed in very simple form as q = c · Yc^A1.5, where q is the flow Q per unit width B (q = Q/B), and Yc is the height of the head H of water over the crest, and c is constant. The exponential growth of the value of Yc (having an exponent of 1.5) may indicate a situation where the loss of energy in a turbine with a low head due to a loss of the flow Q appears to be smaller than the increase of energy due to a corresponding increase of head H. But with a precise calculation it can be shown that such a loss of Q is finally very minimal, and it can even be used to feed sufficient steady water flow to a fish pass in a river environment.

As the presented invention can react very rapidly to all changes on the flow Q and head H, it can easily be programmed to work with such a head H in which practically now overflow loss will occur. Further, as is well known, the main losses of pumped-storage hydroelectricity stem from a friction loss of the water transportation lines. A key factor to prevent this loss is to lower the flow-velocity on pipes and to increase the pipe diameter. As seen on the Darcy-Weisbach equation, the increase in velocity increases the loss exponentially and the increase in pipe diameter decreases the losses linearily. And as the pipeline costs increase exponentially together with the diameter, it results in a situation where low-head pumped-storage is seen as an unrealistic option, as this means that the flow Q will be equally greater as the Head H is lowered, and the increase of Q increases the Costs of such a power plant to the fourth exponent. And these costs are mainly caused from the pipe-lines to be installed.

Yet. the turbine 17, 77, 102, and the apparatus for hydroelectric power generation 101 according the present invention can be applied in a matrix of hydropower, where the source level of one power plant, is simultaneously the outflow level of another power plant, as shown in Fig. 13. Fig. 13 schematically depicts an apparatus 151 for hydroelectric power generation according to a second embodiment. Corresponding features with respect to apparatus 101 shown in Fig. 12 are denoted with the same reference numerals. In between power generator 103 and power controller 105 of apparatus 151 a power line 152 is arranged. Power line 152 comprises a switch 153. Switch 153 has two switching states. In a first switching state, power generator 103 and power controller 105 are electrically interconnected via power line 152. Thus, the above described adjustment of the water flow by a regulation of the power output of power generator 103 can be achieved in the first switching state of switch 153. In the first switching state, power line 152 represents a power feedback loop between power generator 103 and power controller 105 which can be regulated based on the power information derived via measuring line 1 10 according to the above description. In a second switching state of switch 153, the output of power generator 103 is connected to a circuit 154 comprising a delta circuit 155. Delta circuit 155 by itself is well known in the art, in particular in the context of electrical network arrangements. Commonly, in such a delta circuit 155 three wires are connected in such a way that they form a triangular closed loop. Circuit 154 is further connected to power output cable 109. In this way, a direct connection of power generator 103 via delta circuit 155 to a power supply system or a power network can be achieved in the second switching state of switch 153. Circuit 154 is subsequently referred to as a delta connection of power generator 103.

Circuit 154 may further comprise a frequency converter in order to adjust the frequency of the current generated by power generator 103 to a required frequency value of the power supply system or power network connected to power output cable 109. Such a frequency converter may also reduce the efficiency of the output power production but may have the advantage of a longer lifetime as compared to power controller 105 and it may also allow to adjust the output current to any desired frequency value.

Preferably, power generator 103 is switched to the first switching state of switch 153 when variations of the water flow at the upstream tube end of the turbine 1 2 are to be expected or when the water flow is lower than a predetermined level. This allows an advantageous power regulation of turbine 1 2 in the above described manner. Accordingly, power generator 103 is preferably switched to the second switching state of switch 153 when no variations of the water flow at the upstream tube end of the turbine 102 are to be expected or when the water flow has exceeded a predetermined level. In this way, an advantageous direct coupling of power generator 103 to a power supply system or a power network through delta connection 154 in which power losses which may be caused by the interaction of power controller 105 in the first switching state of switch 153 can be effectively reduced. For instance, power controller 105 may comprise an inverter having a typical power efficiency of 94% such that 6% of the generated electrical power would be lost. Such a loss can be circumvented in the second switching state of switch 153.

Fig. 14 schematically depicts an apparatus 161 for hydroelectric power generation according to a third embodiment. Corresponding features with respect to apparatus 151 shown in Fig. 13 are denoted with the same reference numerals.

Power line 152 in between power generator 103 and power controller 105 of apparatus 161 has a switch 163 comprising four switching states, wherein two of these switching states correspond to the switching states of apparatus 151 described above.

In a third switching state of switch 163, the output of power generator 103 is connected to a circuit 164 comprising a star circuit 165. Star circuit 165 by itself is well known in the art. in particular in the context of electrical network arrangements. Commonly, in such a star circuit 165 three wires are connected to a common point to form a Y-like pattern. Circuit 164 is further connected to power output cable 109. In this way, a direct connection of power generator 103 via star circuit 165 to a power supply system or a power network can be achieved in the third switching state of switch 163. Preferably, circuit 154 further comprises a frequency converter in order to adjust the frequency of the current generated by power generator 103 to a required frequency value, as described above. Circuit 164 is subsequently referred to as a star connection of power generator

103.

The power output via star connection 164 in the third switching state of power generator 103 is reduced by approx 1 /Squareroot 3 with respect to the power output via delta connection 154 in the second switching state of power generator 103. Thus, in the third switching state via star connection 164 the voltage is reduced by factor Squareroot 3 and the current adjusted accordingly as power provided from power generator 103 is significantly reduced. By connecting power generator 103 during lower water flow levels through turbine 102 via star connection 164 and during higher water flow levels 102 via delta connection 154 with power output cable 109 occurring losses can be further reduced.

In a fourth switching state of switch 163, the output of power generator 103 is connected to ground 169. In this way, in the fourth switching state an undesired coupling of the output power of power generator 103 to power output line 109 can be avoided. For instance, power generator 103 may be switched to the fourth switching state of switch 163 when substantially no water flow is occurring through turbine 102 or when the water flow is below a predermined level. The connection of the output of power generator 103 to ground 169 is subsequently referred to as zero connection.

Fig. 15 schematically depicts an apparatus 171 for hydroelectric power generation according to a fourth embodiment. Corresponding features with respect to apparatus 161 shown in Fig. 14 are denoted with the same reference numerals.

Two more turbines 172, 173 are provided in addition to turbine 102. Each additional turbine 172, 173 also comprises a mechanical coupling 174. 175 to a respective power generator 176, 177. A power line 182, 183 comprising a switch 184, 185 having four switching states is arranged at the power output of each power generator 176, 177. The function of these switching states corresponds to the switching states of switch 163 of apparatus 161 described above 152.

In the first switching state of switches 184, 185, power generators 176, 177 are connectable to the power entry of power controller 105 via a respective connection cable 178, 179. In the second and third switching state of switches 184, 185. power generators 176, 177 are connectable to power line 109 via a respective delta connection 186, 187 comprising a respective delta circuit 188, 189 or via a respective star connection 191, 192 comprising a respective star circuit 193, 194. In the fourth switching state of switches 184, 185, power generators 176, 177 connectable to ground via a respective zero connection 195, 196.

Apparatus 171 allows an advantageous power generation by a simultaneous operation of up to three turbines 102, 172, 173, wherein only one power controller 105 is required. In particular, this can contribute to significant cost savings.

In a preferred configuration, the two additional turbines 172, 173 are arranged next to turbine 102 at substantially the same level of the water stream flow. More preferred, each turbine 102, 172, 173 is arranged at a different level with respect to the water depth. For instance, turbine 102 may be arranged such that its upstream tube end is arranged at a lower water level, turbine 172 may be arranged such that its upstream tube end is arranged at a medium water level, and turbine 173 may be arranged such that its upstream tube end is arranged at a higher water level.

The respective position of switches 163, 184, and 185 is then preferably determined based on the momentary water height of the river environment. Subsequently, a method for a preferred operation of apparatus 171 is described: If the water height of the river is below the lower water level corresponding to the upstream tube end of turbine 102. all power generators 103, 176, 177 are switched to zero connection 169. 195, 196. If the water height of the river rises to the lower water level, power generator 103 is preferably connected to power controller 105 by changing switch 163 to the first switching position. If the water height rises to the medium water level corresponding to the upstream tube end of turbine 172, power generator 103 of turbine 102 is switched to star connection 164 and power generator 176 of turbine 172 is connected to power controller 105 by changing switch 184 to the first switching position. If the water height rises to the higher water level corresponding to the upstream tube end of turbine 173, power generator 176 of turbine 172 is also switched to its star connection 191 and power generator 177 of turbine 173 is connected to power controller 105 by changing switch 1 85 to the first switching position.

If the water flow of the river further increases, indicated with respective hight variations described before, power generator 103 of turbine 102 is switched to delta connection 154. If the water flow still further increases, power generator 176 of turbine 172 is also switched to its delta connection 186. If the water height still further rises, power generator 177 of turbine 173 is switched to its star connection 192. If the water height still further rises, power generator 177 of turbine 173 is switched to its delta connection 189.

Fig. 16 schematically depicts a system 122 for hydroelectric power generation in a river environment 122. System 122 comprises multiple apparatuses for hydroelectric power generation 123, 124, 125, 126, in particular corresponding to apparatus 101 shown in Fig. 12 and/or apparatus 151 shown in Fig. 13 and /or apparatus 161 shown in Fig. 14 and/or apparatus 171 shown in Fig. 17. Apparatuses 123-125 are arranged successively one after another downstream the river 122. Thus, the water source level of a second apparatus 124 is arranged downstream from the water outflow level of a first apparatus 123. The water source level of a third turbine apparatus is arranged downstream from the water outflow level of second apparatus 124. The water source level of a forth apparatus 126 is arranged downstream from the water outflow level of third apparatus 125. Each apparatus 123, 124, 125, 126 is arranged at a respective water-retaining structure 133, 134, 135, 136. Alternatively, apparatuses 123, 124, 125, 126 may also be installed at a natural river flows without any particular water barrier but rather just simple drop structures. The system of apparatuses 123, 124, 125, 126 thus forms a matrix 122 of hydropower.

These power plants 123, 124, 125, 126 are connected via river 121 , which is dimensioned to be able to transfer the flooding flows, which are normally many times greater than the flow Q that is economically usable for hydroelectricity. Therefore the flow velocity is by nature really slow between power plants 123, 124, 125, 126 of matrix 122. Furthermore, the energy loss is minimal. Moreover, it doesn't need any separate actions to construct such a water canal, except the requirement to build the hydroelectric arrangement of such a connected matrix with common water levels.

Therefore, as it would be unrealistic to realize a single pumped-storage hydroelectricity because the stored energy amount would be minimal, it is technically interesting to build such a matrix 122 between to reservoirs, or to build such a matrix 122 between a reservoir and an existing high-head power plant. An example of such a situation would be the water system of Grimsel-Aare-Brienzersee in Switzerland. There is an existing reservoir of the lake Grimselsee on the level +1900 m AA with a storage capacity of 0.095 km³. There is an existing hydroelectric powerplant with a capacity of 65 m /s and an ouflow at a level of + 624 m AA. There is the river Aare with an average width of 26 m and a flooding flow capacity of 450 m /s. And there is the lake Brienzersee on the level + 564 m AA, with a volume of 5.17 km³, at a horizontal distance of 15 km from the power plant outflow.

It could be economically really interesting to use such an existing hydroelectric power plant in terms of a pumped-storage hydroelectric power plant with a capacity of approximately 25 m³/s. As 1276m/1336 m, also 95.5% of the total head H, and therefore the total energy would be already realised and could be used in a pump-storage hydroelectric power plant with good efficiency if only a lower reservoir would be present. But actually, the turbine-efficiency between the outflow and the Brienzersee doesn't even matter in the case of a conventional pumped-storage hydroelectric power plant, since in this case a pipeline with a diameter in between 5-6 m would be necessary in order to be economical. Therefore, it would involve high construction costs and it would also meet other difficulties, in particular to find an acceptable place for such a construction other than underground.

Yet, such an economical capacity would be easily organized within the existing river by applying the present invention. It would be incorrect to assume that such a system could be easily applied with an existing technology. If realised with ca. 1 m phases, this would need a synchronization of ca. 50 water levels, wherein only one wrongly regulated single unit would immediately affect two other units, which would rapidly lead to an overflow or high efficiency losses.

As the invention described here can be effectively controlled from only one turbine, working as a master unit and defining the parameters of other units, all the turbines 123, 124. 125, 126 within the matrix 122 can independently synchronise each other. If all the turbine pump-units are regulated in the above described way, leading to an unified theoretical head H of the water 121 in between the units 123- 126. then, i one should have some kind of blockage which would reduce the effective head H of one unit, this would lead to a reduced flow Q with current head H, and therefore this unit would pump less than the units before and after it.

This in turn would slowly lead to a rise of an intake level, and a drop on an outflow level. This further, would give more load to the units before and after the overloaded unit which would ease the troubled unit. Moreover, this correction, which would be needed because of e.g. snow or ice, would be rapidly and fully automatically transferred throughout the whole matrix 122 and thus the system 122 would balance the rotational speeds of the turbines 123-126 and waterlevels automatically to the most optimum conditions.

Such a balancing between different units 123-126 would theoretically also be possible to be realized with existing hydroelectric generation technologies. But it would be extreme fragile to any sensor failures or interference, and would need a highly complicated control program to balance the whole system 122.

From the foregoing description, numerous modifications of the invention are apparent to one skilled in the art without leaving the scope of protection of the invention that is solely defined by the claims.

Claims

1. An apparatus for hydroelectric power generation comprising a turbine (12, 77, 102, 172, 173) with two bladed wheels ( 1 1 , 12. 31 , 32) successively arranged in a turbine tube section (10, 21) as a fore wheel (11, 31) and an after wheel (12, 32) with respect to the water flow direction (23), the wheels (11 , 12, 31, 32) being configured to rotate in opposite directions driven by the water flow, and a power generator (103, 176, 177) configured to generate electrical power from the rotational energy of at least one the wheels (11, 12, 31, 32), characterized by a power controller (105) that is configured to regulate the electrical power generated by the power generator (103) in such a way that the rotational speed of the wheels (11, 12, 31, 32) and thus the water flow through the tube section (10, 21) is adjustable through said power regulation from the power controller (105).

2. The apparatus according to claim 1 , characterized in that the power generator (103, 176, 177) comprises a permanent magnet generator.

3. The apparatus according to claim 1 or 2, characterized by a power information detector (106) configured to detect information related to the electrical power generated by the power generator (103, 176, 177).

4. The apparatus according to claim 3. characterized in that the power controller (105) is configured to set the power generator (103, 176, 177) to a power value that is previously derived from said information detected by the power information detector (106).

5. The apparatus according to claim 3 or 4, characterized in that said setting of the power value comprises a setting of at least one of the current, voltage, and frequency of an alternating current generated by the power generator ( 103. 176. 177).

6. The apparatus according to one of the claims 3 to 5, characterized in that said information detected by the power information detector ( 106) comprises information about at least one of the current, voltage, and frequency of an alternating current generated by the power generator (103, 176, 177).

7. The apparatus according to one of the claims 1 to 6, characterized in that the power controller (105) is configured to regulate the electrical power generated by the power generator (103, 176, 177) with respect to a maximum power value of momentary turbine operation conditions.

8. The apparatus according to one of the claims 1 to 7, characterized in that the rotational speed of the wheels (11, 12, 31, 32) and the water flow through the tube section (10, 21) is substantially only adjustable through said power regulation from the power controller (105).

9. The apparatus according to one of the claims 1 to 8, characterized in that the power controller (105) is configured to regulate the electrical power generated by the power generator (103, 176, 177) such that the head of the water flowing through the turbine tube section (10, 21) is substantially kept at a constant value irrespective of a variation of said water flow.

10. The apparatus according to one of the claims 1 to 9, characterized in that the fore wheel (1 1, 31) and the after wheel (12, 32) are coupled to each other by at least one gearing (48).

1 1 . The apparatus according to claim 10. characterized in that the gearing (48) is coupled to the power generator (103, 176, 177).

12. The apparatus according to one of the claims 1 to 1 1 , characterized in that the turbine tube section (10, 21) is provided with an inside diameter increasing in the water flow direction (23).

13. The apparatus according to one of the claims 1 to 12. characterized in that the geometry of the turbine tube section (10, 21) and/or the wheels (11, 12, 31 , 32) is adapted such that the fore wheel (1 1, 31) and the after wheel (12, 32) are configured to be driven by the water flow at a constant ratio of their rotation speed.

14. The apparatus according to one of the claims 1 to 13, characterized in that a star connection (164, 191, 192) and/or delta connection (164, 191, 192) for the power output of the power generator (103) and a switch (153, 163, 184, 185) at the power output of the power generator (103, 176, 177) is provided, such that the power generator (103, 176, 177) can be switched in between a connection with the power controller (105) and the star connection (164, 191, 192) and/or delta connection (164, 191 , 192).

15. The apparatus according to one of the claims 1 to 14, characterized in that it comprises at least two turbines (12, 77, 102, 172, 173) each comprising two bladed wheels (11, 12, 31, 32) successively arranged in a turbine tube section (10, 21), wherein the upstream tube end (24) of the turbines (102, 172, 173) is arranged at a different height with respect to the water depth.

16. The apparatus according to one of the claims 1 to 15, characterized in that it comprises at least two turbines (12, 77, 102, 172, 173) each comprising two bladed wheels (11, 12, 31, 32) successively arranged in a turbine tube section (10, 21) and each connected to a respective power generator (103, 176, 177), wherein a common power controller (105) is provided to which each of the power generators (103, 176, 177) can be connected by a switch (153, 163, 184, 185).

17. A system for hydroelectric power generation comprising at least two apparatuses ( 101 , 123, 124. 125, 126, 151. 161. 171 ) according to one of the claims 1 to 16. wherein the water source level of the second apparatus (101, 123, 124, 125, 126, 151 , 161 , 171) is arranged downstream from the water outflow level of the first apparatus (101, 123, 124, 125, 126, 151, 161, 171).