DESCRIPTION
FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
& The Patent Rules, 2003
COMPLETE SPECIFICATION
1.TITLE OF THE INVENTION:
SELF-ORIENTING MARINE WIND TURBINE WITH TWO ALTERNATORS
2. APPLICANT:
Name: JEUMONT ELECTRIC
Nationality: France
Address: 367 rue de l'Industrie, 59460 JEUMONT, France.
3. PREAMBLE TO THE DESCRIPTION:
The following specification particularly describes the invention and the manner in which it is
to be performed:
2
DESCRIPTION
TECHNICAL FIELD OF THE INVENTION
5 The technical field of the invention is that of offshore wind turbines or marine
wind turbines and in particular those which are self-aligning.
TECHNOLOGICAL BACKGROUND OF THE INVENTION
Marine wind turbines are installed at sea or in an aquatic environment and
have to withstand the sometimes difficult marine conditions.
10 Although the first prototypes of offshore wind turbines were copies of
onshore wind turbines comprising blades connected to a rotating hub with a horizontal
axis, they are now adapted to the sea. With current technological developments, the
aim is to increase both size and power. These days, for example, they can have spans
of up to 126 m and powers of 5 MW (megawatts).
15 There are two types of offshore wind turbines: fixed wind turbines, which
are generally set up at depths of no more than 50 m, and floating wind turbines, which
are set up at depths greater than 50 m. Floating wind turbines are mounted to a floating
platform connected to the seabed by cables. Due to its construction, the floating wind
turbine is self-aligning or with passive orientation, that is, it orients itself according to
20 the direction of the wind.
On the other hand, wind turbines are always mounted in a configuration with
the rotor at the front, facing the wind, in order to minimise the shadow effect of the
tower, which is quite significant in traditional structures. This is why offshore solutions
have been developed that have a floating platform with 3 or 4 masts instead of a fixed
25 single-tower structure. The whole structure orients itself passively with the wind, thus
eliminating the need for a masthead orientation system on the nacelle.
The current trend is to further increase the span to 160m and even 200m,
with power from 8 MW to 12-15 MW. The International Energy Agency predicts the
need to multiply wind energy production by at least 7 by 2050. To reduce costs,
30 offshore wind farms with 10-20 MW machines are being contemplated. However, in
these power ranges, weight is a major restriction.
3
But these spans and powers imply an increase in the weight of the structure,
the cost of manufacture and assembly time, as well as difficulty of installation. On the
other hand, making alternators of such high power leads to complications because of
the size of the rotor and stator to be made.
5 SUMMARY OF THE INVENTION
The invention provides a solution to the problems discussed previously, by
making it possible to make a high-power marine wind turbine but with a nacelle of
reasonable dimensions and weight, similar to existing wind turbines.
The invention relates to a self-aligning marine wind turbine comprising a
10 floating platform, at least one mast to which is attached a nacelle comprising a hub
with a horizontal axis X and connected to blades, it is characterised in that the hub
cooperates with a rotor of two alternators and that the hub consists of a hollow axle or
a hollow axial cylinder adapted for maintenance by a man standing up. This
characteristic not only allows a complete overhaul of the nacelle structure with the
15 possibility of increasing the overall power of the wind turbine, but also provides easier
access to the apparatus and space to house the power electronics converters. The
alternators are thus of a size easier to be made with a stiffness of the structures
enabling dimensions of the air gap to be respected. The same power can therefore be
obtained with smaller alternators. In this way, for a total power of the wind turbine of
20 6 MW, each alternator will only be 3 MW, reducing the diameter from 7m to less than
5m. On the other hand, this has the advantage of being able to house the converters
close to the alternators, because as the blades become very large, if the converter is
on the base of the wind turbine, the length of cable can cause overvoltage in the
alternator windings (due to the capacitive effect of the cables), a risk that does not exist
25 if the connection is short.
Advantageously, the alternators are disposed on either side of the hub. By
disposing the alternators on either side of the hub, the balance of the nacelle is not
disturbed.
Advantageously, the wind turbine comprises at least three converging
30 masts. The nacelle with its blades is located between the masts and the alternators on
each side, so that the whole is better balanced.
4
Advantageously, the two alternators are symmetrical with respect to a plane
perpendicular to the axis of the hub. As the alternators are identical by symmetry, the
load balancing of the whole is respected.
Advantageously, the alternators are independent of each other and each is
5 connected to a converter. The wind turbine is thus still operational in degraded mode,
if one of the two alternators or its converter fails. If the wind is light, it is also possible
to operate only one alternator, so that at a low load of the wind turbine, the load of one
alternator will be doubled and the efficiency will be all the better, compared with an
alternator with twice the rated power.
10 Advantageously, at least one alternator comprises two independent
windings each connected to a converter. This makes it possible to adapt the power of
the alternator to the wind power. This adaptation is even finer since the two alternators
are independent of each other. Thus, if the electrical chain of a stator winding fails, the
electrical chains of the other windings will be operational and will allow the wind turbine
15 to be utilized until the fault is repaired.
Advantageously, one of the alternators comprises a parking brake
connecting the rotor to the stator. This brake enables the blades to be braked or
stopped if the wind is too strong.
Advantageously, one of the alternators includes an asynchronous
20 generator. This asynchronous generator is an auxiliary device which makes it possible
to supply electricity to the rotating part of the wind turbine without passing through a
sliding contact (rings and brushes), and therefore without wear.
Advantageously, the wind turbine comprises a wireless communication
system controlling the alternators. The communication system is thus simpler to set
25 up.
Advantageously, each alternator has a power of between 4 and 10 MW.
This gives, for example, multi-megawatt or deca-megawatt class power.
Advantageously, at least one alternator can be disconnected. It is thus
possible to disconnect one of the two alternators if need be.
30 Advantageously, the axial cylinder is hollow and comprises three gratings
placed on the side opposite to each of the blades and connecting the ends of the axial
5
cylinder. The gratings connecting the ends of the axial cylinder allow a man to pass
from one side to the other and thus access each alternator when the wind turbine is
stopped, the balance of the three blades means that there is always a grating in the
horizontal position.
5 Advantageously, a converter is placed in the hollow axle or in a nacelle
located at one end of the hollow axial cylinder. The converter is thus located close to
the alternators, which avoids overvoltage.
Advantageously, the converter is connected to the windings of an alternator
stator by a cable with a length I, the blades are of length L and I < L. As the converter
10 is no longer located at the foot of the wind turbine, but in proximity to the stator, there
are no more overvoltage in the windings of the alternator due to the capacitive effect
of the cables. Ideally, the length I should be less than 50 m.
The invention and its different applications will be better understood upon
reading the following description and upon examining the accompanying figures.
15 BRIEF DESCRIPTION OF THE FIGURES
The figures are set forth by way of indicating and in no way limiting purposes
of the invention.
[Fig. 1] is a wind turbine of the state of the art with a single mast,
Fig. 2] is a wind turbine of the state of the art with three masts.
20 [Fig. 3] is a perspective view of a nacelle according to the invention,
[Fig. 4] is a cross-section of the nacelle of Fig. 3 with its blades and masts,
[Fig. 5] is a front view of the nacelle of Fig. 4,
[Fig. 6] is a cross-section of an alternative nacelle according to the invention.
DETAILED DESCRIPTION
25 The figures are set forth by way of indicating and in no way limiting purposes
of the invention.
In the remainder of the description, "front" will be referred to as the side
facing the wind and "rear" as the opposite side.
Unless otherwise specified, a same element appearing in different figures
30 has a single reference.
6
The wind turbine 1 of the state of the art, illustrated in Fig. 1, is a land-based
wind turbine or a marine wind turbine attached to the seabed, it comprises a mast 2,
three blades 3 connected to a nacelle 4 by a hub 40 and a base 20 placed on the
ground. The blades 3 are placed facing the wind V, the nacelle 4 and the mast behind
5 the blades 3. An alternator 5 is placed in the nacelle 4.
The second wind turbine 1 of the state of the art in Fig. 2 is a floating wind
turbine, it comprises floats 22 connected to each other by beams 220, constituting a
floating platform and fastened to the ground by cables 23. It has three or four masts
21, each connected to a float 22. The nacelle 4 is attached to the masts 21. An
10 alternator 5 is disposed in the nacelle 4 at the rear thereof. Since the masts 21 are
thinner than the single mast in Fig. 1 and since these masts 21 are not oriented radially
to the hub 40 like the blades 3, the blades 3 can be disposed between the masts 21
without the latter casting a shadow and disturbing the path of the wind V and generating
significant vibrations in the wind turbine.
15 As the wind turbine 1 is connected to the seabed by cables 23, it can
orientate itself alone according to the direction of the wind V.
The nacelle 4 in Fig. 3 comprises an alternator 5 on each side and a hub 40
of axis X. This consists of a fixed axle 401 and a cage 402 rotationally movable about
the axle 401. The cage 402 has three openings 400 to place the blades 3 therein that
20 will rotationally drive said cage 402. Here, the axle is comprised of two half-axles each
having a flange 403 enabling them to be bolted together in the central part, which
facilitates assembly.
Each alternator 5 comprises a rotor 50 and a stator 51, the rotor 50 being
connected to the cage 402. The stator 51 is integral with the nacelle 4 and the axle
25 401. The alternators 5 are identical and arranged in mirror image on either side of the
plane of the blades perpendicular to the axis X.
The axle 401 is hollow, thus constituting a service duct where a man
standing up can circulate to ensure maintenance, to be able, for example, to place
converters closer to the alternators and thus to connect each converter to an alternator
30 by virtue of cables 54 shorter than the dimension of the blades 3. It also houses the
converter(s) 52 and the cables 53 for discharging electrical energy. For example, one
converter can be provided for each independent stator winding, that is, one for each
7
alternator if there is only one winding per alternator, or two or three per alternator if
there are two or three windings per alternator, or n if there are n windings. The power
of the alternators can thus be adjusted as a function of the wind power, by utilizing or
not each alternator winding.
5 A parking brake 30 is provided in one of the two alternators 5 between the
rotor 50 and the stator 51. It enables rotation of the blades 3 to be blocked in the event
of strong wind or maintenance.
In the alternative in Fig. 6, the axle 401 is replaced by two half-nacelles 41.
Each half-nacelle 41 is connected to a float 22 by at least two masts 21, making a total
10 of at least 4 masts for the wind turbine.
The blades 3 are attached to the periphery of an axial cylinder 42 which is
connected to the two half-nacelles 41 by bearings 410 which ensure rigid cohesion of
the two half-nacelles. The rotors 50 are attached to each end of the axial cylinder 42.
Each stator 51 is integral with a half-nacelle 41.
15 An asynchronous generator 6 is placed in one of the alternators 5; it enables
electricity to be supplied to the rotating part of the wind turbine without passing through
a sliding contact (rings and brushes), and therefore without wear.
The axial cylinder 42 is hollow and comprises three gratings 420 placed on
the side opposite to each of the blades 3 and connecting the ends of the axial cylinder
20 42, it is then possible to access the inside for maintenance when the wind turbine is
stopped. There is always one of the gratings 420 being horizontal at a standstill, since
at this time one of the blades is vertical and the other two are below it for good balance.
An orientation system 31 for orienting the blades 3 is placed inside the axial
cylinder 42 for "feathering" the blades when the wind is too strong or when repairs or
25 maintenance are carried out. The orientation system 31 for orienting the blades 3
comprises a first toothed wheel 310 cooperating with a second toothed wheel 32
placed on the periphery of the base of the blade 3. The blade 3 is connected to the
axial cylinder by a bearing 33.
This alternative has the advantage of allowing a more conventional
30 connection of the blade orientation system via a set of rings (power without an
asynchronous generator and control signals). It also allows the use of conventional
nacelles, resulting in lower costs.
8
WE CLAIM:
[Claim 1] A self-aligning marine wind turbine (1) comprising a floating platform, at
least one mast (2, 21) to which is attached a nacelle (4) comprising a hub (40) of
horizontal axis X and connected to blades (3), characterised in that the hub (40)
5 cooperates with a rotor (50) of two alternators (5) and that the hub consists of a hollow
axle (401) or a hollow axial cylinder (42) adapted for maintenance by a man standing
up.
[Claim 2] The wind turbine (1) according to claim 1, characterised in that the
alternators (5) are disposed on either side of the hub (40).
10 [Claim 3] The wind turbine (1) according to one of the preceding claims,
characterised in that it comprises at least three converging masts (21).
[Claim 4] The wind turbine (1) according to one of the preceding claims,
characterised in that the two alternators (5) are symmetrical with respect to a plane
perpendicular to the axis X of the hub (40).
15 [Claim 5] The wind turbine (1) according to one of the preceding claims,
characterised in that the alternators (5) are independent of each other and each is
connected to a converter (52).
[Claim 6] The wind turbine (1) according to one of the preceding claims,
characterised in that at least one alternator (5) comprises two independent windings
20 each connected to a converter (52).
[Claim 7] The wind turbine (1) according to one of the preceding claims,
characterised in that one of the alternators (5) comprises a parking brake (30)
connecting the rotor (50) to the stator (51).
[Claim 8] The wind turbine (1) according to one of the preceding claims,
25 characterised in that it comprises a wireless communication system controlling the
alternators (5).
[Claim 9] The wind turbine (1) according to one of the preceding claims,
characterised in that each alternator (5) has a power of between 4 and 10 MW.
[Claim 10] The wind turbine (1) according to one of the preceding claims,
30 characterised in that at least one alternator (5) can be disconnected.
9
[Claim 11] The wind turbine (1) according to one of the preceding claims,
characterised in that one of the alternators includes an asynchronous generator (6).
[Claim 12] The wind turbine (1) according to one of the preceding claims,
characterised in that the axial cylinder (42) is hollow and comprises three gratings (420)
5 placed on the side opposite to each of the blades (3) and that they connect the ends
of the axial cylinder (42).
[Claim 13] The wind turbine (1) according to one of the preceding claims,
characterised in that a converter (52) is placed in the hollow axle (410) or in a nacelle
located at one end of the hollow axial cylinder (42).
10 [Claim 14] The wind turbine (1) according to the preceding claim, characterised in
that the converter (52) is connected to the windings of a stator (51) of an alternator (5)
by a cable with a length I, in that the blades (3) are of length L and in that I < L.