WO2010082129A1

WO2010082129A1 - An archimedean screw apparatus for the production of hydroelectrical power

Info

Publication number: WO2010082129A1
Application number: PCT/IB2010/000080
Authority: WO
Inventors: Iuri Cantarini
Original assignee: WAM SpA
Current assignee: WAM SpA
Priority date: 2009-01-19
Filing date: 2010-01-19
Publication date: 2010-07-22
Anticipated expiration: 2011-07-19
Also published as: IT1392628B1; ITBO20090021A1

Abstract

An Archimedean screw apparatus (10; 10*; 10**; 10***) for the production of hydroelectrical power. The apparatus (10; 10*; 10**; 10***) comprising: a channel (12) located between an upper water surface (13A) and a lower water surface (14A); an Archimedean screw (11) housed in the channel (12); and an electric power generator (18) coupled to the Archimedean screw (11) The apparatus (10; 10*; 10**; 10***) being characterised in that the electric power generator (18) is a synchronous generator (18), provided with an inverter, connected electrically to an electricity distribution network.

Description

"AN ARCHIMEDEAN SCREW APPARATUS FOR THE PRODUCTION OF HYDROELECTRICAL POWER"

TECHNICAL FIELD The present invention relates to an Archimedean screw apparatus for the production of hydroelectrical power .

BACKGROUND ART

The use of Archimedean screw apparatus for the production of hydroelectrical power is known in the prior art.

Such apparatus have a number of advantages due to the fact that they can exploit even moderate hydraulic jumps and maintain high and constant efficiency levels compared with the efficiency of conventional hydraulic turbines (of the Francis, Pelton or Kaplan types) normally used in hydroelectrical power production plants .

Moreover, Archimedean screw apparatus have the additional advantage of not harming the environment and of allowing fish to travel through the waterway in which the Archimedean screw is installed.

An Archimedean screw apparatus for the production of hydroelectrical power normally comprises: - a channel located between an upper water surface and a lower water surface of a watercourse; - an Archimedean screw housed in the channel; and

- electric power generating means coupled to the Archimedean screw; the generating means being suitable to convert the water power produced by the liquid flowing between the upper water surface and the lower water surface into electric power.

For example, an apparatus of this type is described in European patent application EP-A2-1 930 597, in which the electric machine coupled mechanically to the Archimedean screw can be used as both a pump and a generator .

The Archimedean screw apparatus currently used for the production of hydroelectrical power use at least one asynchronous electric motor. As is known, said asynchronous electric motor is only used as a generator when power availability is limited and mainly when the electric machine is connected to a main electricity network (i.e. the national electricity network) . As is known, in order for an asynchronous motor to work as a generator it must be able to draw reactive energy from the grid to magnetize the rotor circuit (as "squirrel cage" rotor circuits have no excitation source) . The rotor is then activated by means of an external energy source (mechanical source) causing it to operate in hyper-synchronism (the magnetic field of the rotor rotates faster than that of the stator) , thus generating energy. in this condition, as the generator delivers active power to the grid, it also absorbs reactive power to continue to supply the rotating magnetic field.

According to a number of studies said asynchronous machines achieve efficiency levels of around 0.6 (60%), falling to 0.4 (40%) . This is far lower than the levels achieved by synchronous systems, but with the advantage of being robust and simple to control, in that an increase in the speed of the rotor does not generate over-frequency (higher frequency levels) , but generates braking of said rotor.

In other words, using an asynchronous generator when the Archimedean screw accelerates, for example due to an increase in the water flow rate, the asynchronous generator slows the Archimedean screw down; the opposite occurs when the Archimedean screw slows down.

However, the main disadvantage of using an asynchronous generator consists of the need for a mechanical multiplier, normally in the form of a cascade of gears, in order to bring the speed of the Archimedean screw (very low) to the speed required in order for said asynchronous generator to operate (1000/1500 rpxn) . Thus, by adding the loss of energy due to the necessary use of a mechanical multiplier to the low electrical efficiency typical of asynchronous motors, it is clear that a system for the production of hydroelectrical power that contemplates the use of an asynchronous generator is not particularly advantageous in terms of a correct energy balance.

On the basis of these observations the present invention proposes the use of a synchronous generator in place of the aforesaid asynchronous generator, already widely used in the prior art . This solution achieves improved efficiency also because it overcomes the need for a complex and low- efficiency mechanical multiplier.

As is known, a synchronous generator is an electric machine that consists of a fixed hollow part, called the stator, within which a cylindrical part called che rotor is keyed to the shaft and rotates .

The stator is provided with the electric windings on which the electromotive force is induced to sustain the electric current that is produced. The rotor generates a rotating magnetic field by means of electromagnets, one for each phase and pole pair; thus in the case of a three-phase two-pole generator (one pole pair) there are three electromagnets, in the case of a three-phase four-pole generator (two pole pairs) there are six electromagnets, which are in turn appropriately powered; alternatively permanent magnets can be used, which do not require a power supply and in the latter case there is only one pole pair (North and South) for each pair of stator poles . As is known, these synchronous generators achieve a very high level of efficiency, in the region of 0.97 (97%) falling to 0.85 (85%).

However, the use of said synchronous generator requires an inverter to convert the voltage and the frequency of the electric energy generated by said synchronous motor to values accepted by the grid or by the utilities in general.

As we shall see from the following description, another consequence of the use of a synchronous motor with the relative inverter is the need to use a particular braking system for the Archimedean screw, as, in this type of system, the use of traditional braking systems (which can be used with asynchronous generators) is not convenient. DISCLOSURE OF INVENTION

Therefore, according to the present invention there is provided an Archimedean screw apparatus for the production of hydroelectrical power according to that claimed in the appended independent claim, and preferably, in any one of the claims depending directly or indirectly on said independent claim. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to the accompanying drawings, which illustrate some non-limiting embodiments thereof, in which: - figure 1 illustrates a first embodiment of the Archimedean screw apparatus for the production of hydroelectrical power according to the present invention;

- figure 2 illustrates a second embodiment of the Archimedean screw apparatus for the production of hydroelectrical power according to the present invention;

- figure 3 illustrates a third embodiment of the Archimedean screw apparatus for the production of hydroelectrical power according to the present invention;

- figure 4 is a front view of a braking system of an Archimedean screw belonging to any one of the apparatus illustrated in figures 1, 2, 3; and - figure 5 is a side view of the braking system illustrated in figure 4.

BEST MODE FOR CARRYING OUT THE INVENTION In figure 1, designated as a whole by number 10 is a first embodiment of an Archimedean screw apparatus for the production of hydroelectrical power according to the present invention. The apparatus 10 comprises, in turn, an Archimedean screw 11 contained in a respective channel 12 for conveying water from a first upper watercourse 13 , having an upper water surface 13A, to a second lower watercourse 14 having a water surface 14A. The hydraulic jump (H) between the two water surfaces 13A and 14A clearly represents the water power that can be used in the apparatus 10.

Moreover, in the first watercourse 13 there is a dam (DG) adjacent to a channel 15 through which the water from the first watercourse 13 flows towards the channel 12.

More in particular, the Archimedean screw 11 is wound about a cylinder 16, which, in turn, in use, rotates about a pin 17 that is fixed with respect to the ground (GR) .

As illustrated in figure 1, the cylinder 16 is coupled to a synchronous generator 18 which is also fixed with respect to the ground (GR) . The synchronous generator 18, in turn, is electrically connected to an electric line (not illustrated) via an inverter (which is also not illustrated in figure 1) for the purposes described previously. To summarize, in the first embodiment illustrated in figure 1 the rotor (not illustrated) of the 3

synchronous generator 18 is directly coupled to the cylinder 16 about which the Archimedean screw 11 is wound.

The method of operation of the apparatus 10 is easily deducible from the above description.

A flow of water (in the direction of an arrow (Fl) ) from the first watercourse 13 is conveyed first into the channel 15 and then into the channel 12.

The water flowing out of the channel 12 induces the rotation of the Archimedean screw Il and of the cylinder 16, which, in turn, causes the rotor of the synchronous generator 18 to rotate. The water is thus discharged into the second watercourse 14 where it flows in the direction of an arrow (F2) . Thus a certain amount of electric energy is produced that, after being reprocessed by an inverter

(not illustrated) connected electrically to the synchronous generator 18, is introduced into the grid

(not illustrated) , or sent to a utility (not illustrated) . The amount of electric energy that is produced is clearly given by the value of the hydraulic jump (H) after deducting the efficiency of the Archimedean screw 11, the synchronous generator 18 and the inverter. According to an alternative embodiment of the present invention illustrated in figure 2, in which the same parts are indicated by the same reference numbers and letters as those used in figure 1, a coupling device 20 is arranged between the cylinder 16 and the synchronous generator 18 in an Archimedean screw apparatus 10*.

Said coupling device 20 may be a simple mechanical joint, or a magnetic gear that multiplies the revolutions of the Archimedean screw 11 in relation to the synchronous generator 18. According to another embodiment of the invention the magnetic gear 20 is integrated in the rotor of the synchronous generator 18.

According to a third embodiment of the present invention illustrated in figure 3, in which the same parts are indicated by the same reference numbers and letters as those used in figures 1 and 2, a chain drive 30 is arranged between the cylinder 16 and the synchronous generator 18 in an Archimedean screw apparatus 10** for the production of hydroelectrical power .

The solutions illustrated in figures 2 and 3 are proposed for the purpose of reducing the cost of the synchronous generator 18.

If said generator 18 were to be coupled directly to the Archimedean screw 11 and, thus_/ were to rotate at its same angular velocity (very slowly) , it would have to be very big due to the large number of poles. Therefore, with a magnetic gear, or with a high- efficiency chain drive, the negative impact of the problem would be limited given the more economical nature of slow multi-pole synchronous generators.

With the Archimedean screw apparatus 10 according to the present invention the use of a braking system is necessary to prevent anomalous accelerations in the event of a sudden interruption in the electric load. The system is already known in conventional machines in the form of an electromagnetic brake coupled to the fast shaft of the speed multiplier. However, said system is not convenient in apparatus that use a synchronous generator due to the excessively low speed and relative excessively high transmission torques .

Two different methods are proposed to overcome this drawback:

(1) when the system detects, via specific devices, the interruption in the load, the reduction in the load, or in the case of anomalous accelerations, the electric current that is produced, instead of being sent to the grid as happens during normal operation, is diverted towards an electric ballast (not illustrated) to achieve dynamic braking of the Archimedean screw 11 and of the cylinder 16; and

(2) in case of a sudden interruption in the electric load, if only the flow of water from the channel 15 is blocked, the channel 12 would continue to be full of water; the natural emptying of the channel 12 towards the second watercourse 14 would produce an acceleration o£ the Archimedean screw 11; to prevent this the cylindrical wall of the channel 12 of an apparatus 10*** may be provided with one or more ports 40 (preferably with a cylindrical section) , each operated by a respective actuator 41, as illustrated in figures 4 and 5; the water is thus discharged rapidly via a drainage channel 42 (in the direction shown by the arrow (F3)) which extends parallel to the channel 12.

An electronic control unit (not illustrated) connected to the grid opens the ports 40 as necessary. The main advantages of the apparatus described above are as follows :

- elimination of the need for large, expensive speed multipliers between the Archimedean screw and the electric generator; - improved overall efficiency due to the elimination of multipliers; use of electric generators (synchronous generators) which achieve far higher efficiency than those normally used in the prior art (asynchronous generators) ;

- less reactive power drawn from the grid; - perfect control of anomalous accelerations of the Archimedean screw without the use of expensive electromagnetic friction brakes;

- possibility of use for the production of energy for local utilities,-

- possibility of using the ballast electric load to produce heat (co-generation) ,-

- maintenance of the upstream water level thanks to the use of a machine with a synchronous generator; the electric generator reduces speed when the water flow decreases ;

- the system is more reliable and requires less maintenance compared with conventional systems; reduced noise levels (slow machine without multiplier) ;

- the machine is more compact and robust; better strategy for the use of the hydroelectrical power produced, with better control, including from remote stations; - the most suitable system for supporting conventional power stations to restore voltage levels in the event of faults,-

- the use of a magnetic gear or chain drive means that smaller permanent magnet synchronous generators can be used.

Claims

1. An Archimedean screw apparatus (10; 10*; 10**; 10***) for the production of hydroelectrical power,- said apparatus (10; 10*; 10**; 10***) being placed between an upper water surface (13A) of an upper watercourse (13) and a lower water surface (14A) of a lower watercourse (14); said apparatus (10; 10*; 10**; 10***) comprising:

- a channel (12) located between the upper water surface (13A) and the lower water surface (14A) ,-

- an Archimedean screw (11) housed in the channel (12); and

- electric power generating means (18) coupled to the Archimedean screw (11); the generating means (18) being adapted to convert the water power produced by the water flow between the upper water surface (13A) and the lower water surface (14A) into electric power; the apparatus (10; 10*; 10**; io***) being characterised in that said electric power generating means (18) comprise a synchronous generator (18) .

2. Apparatus () according to Claim 1, characterised in that it further comprises an inverter placed between said electric power generating means (18) and the electric network.

3. Apparatus (10) according to any of the preceding Claims, characterised in that it provides a direct coupling between the rotor of said electric power generating means (18) and the Archimedean screw (11) .

4. Apparatus (10*) according to any of Claims 1, 2, characterised in that it provides a coupling device (20) between the rotor of said electric power generating means (18) and the Archimedean screw (11) .

5. Apparatus (10*) according to Claim 4, characterised in that the coupling device (20) is a mechanical coupling.

6. Apparatus (10*) according to Claim 4, characterised in that the coupling device (20) is a magnetic gear (20) that multiplies the revolutions of the Archimedean screw (11) .

7. Apparatus (10*) according to Claim 6, characterised in that the magnetic gear (20) is integrated with the rotor of said electric power generating means (18) .

8. Apparatus (10**) according to any of Claims 1, 2, characterised in that it provides a chain drive (30) between the rotor of said electric power generating means (18) and the Archimedean screw (11) .

9. Apparatus (10; 10*; 10**; 10***) according to any of the preceding Claims, characterised in that, when anomalous accelerations of the Archimedean screw (11) are detected, the produced electric current is deviated towards an electric ballast for achieving a dynamic braking of the Archimedean screw (11) .

10. Apparatus (10***) according to any of the preceding Claims, characterised in that_/ when anomalous accelerations of the Archimedean screw (11) are detected, at least one • port (40) is opened on the cylindrical wall of the channel (12), the port (40) being driven by a respective actuator (41) for achieving a rapid discharge of the water contained in the channel

(12) through a discharge channel (42) .