Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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WINDMILL TRANSMISSION AND CONTROL SYSTEMS
Wind-power plants preferably include synchronous or
asynchronous generato~s whose des;gn requires t-he rotary
speed of the windmill blades to be substan-tially constant,
within very narrow ]imits. Since wind speeds are rarely
cons-tant, but vary as a result of gusts and squa]ls, very
high requirements are p]aced on the turbine and on the -trans-
mission and gearing between the turbine and the generator.
- To enable the p]ant to adapt to prevailing wind condi-
tions, the tur}ine blades of horizontal-shaft wind turbines
are preferably such as to enable them -to pivot or rotate
about their respective long axes, i.e. have automatic blade-
pitch change. In the case of large windmills, considerable
inertia forces must be overcome when changing the blade-
pitch, mainly due to the blade mass.
This change in blade-pitch by rotating said blades
; about their long axes is normally eEfected with the use of
mechanical or hydraulic machinery assisted by the force of
the wind against the blades, to which latter end the aero-
; dynamic centre of respective blades is offset from the
centre of rotation of -the blades.
Because, however, of -the high inertia forces which
must be overcome when changing the~blade-pitchj it has been
found impossible to prevent disturbances from propaga-ting
through the machinery and affecting the synchronous rotary
speed of the generator. Such distu~bances, can not be
tolerated, inter alia because they are reflected in the
electric network fed by the plant. Consequently, in addi-
tion to changes in the blade-pitch it has been necessary to
introduce technical solutions by which a soft coupling can
be had between the turbine and the generator. The plant
machinery can aIso be subjected to shock loads as a result,
for example, of the generator short circuiting. In con-
ventional constructions, the machinery as a whole is there-
fore suspended for rotation on a spring unit. When taking
into account the considerable dimensions of the machinery
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of a large wind-power plant, it will be realized that such
an arrangement is both complicated and expensive.
Those skilled in this art are agreed that a --
horizontal shaft, few-bladed turbine is one of the best
wind turbine designs-
Figure 1 is a diagram showing with a full line anexample of a characteristic curve of the aerodynamic
efficiency of a propeller as a function of the fast-speed
number ~ = Rw/v, where Rw = the trip speed of the propeller
and v = the wind velocity, and with a broken line a curve
representing an ideal wind turbine.
Figure 2 is a diagram showing one embodiment in
accordance with the present invention; and
Figure 3 is a diagram showing an efficiency curve
for a transmission discussed hereinafter.
It will be seen from the full-line curve in the
Figure 1 diagram that the ideal fast-speed number of the
propeller gives an efficiency of about 70~/O
For a wind turbine to produce the highest possible
energy output, it must operate with a fast-speed number that
is always close to the optimal ~. This means that the
- speed at which the turbine blades rotate must vary.
In order to enable a variable speed turbine to be
connected to, for example, a synchronous generator, which
~25 requires a constant rotary speed, means for regulating the
turbine speed hydrostatically, mechanically and electro-
magnetically have been tried. It has been found, however,
that the efficiency of these speed-regulating sys~ems is so
poor that practically the whole of the additional energy
gained through the use of a variable speed turbine is
utilized.
~ en synchronizing a synchronous generator
(alternator) with an electric network, there is required
a synchronous generator speed, a nominal open-circuit
voltage and a correct phase position. The rotary speed of
large wind-power pLants known hitherto is controlled or
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regulated solely by changing the blade-pitch. Because
of the unavoidable inertia of the system, this means
that the task of synchronizing a synchronous generator
with an electric network is both time consuming and
troublesome.
An object of the present invention is to provide
a wind-power plant in which the aforementioned problems
are substantially eliminated. By means of the invention,
the rotational speed of a generator can be kept synchronous
within narrow limits at the same time as the rotational
speed of the wind turbine is adapted to that fast-speed
number of the turbine in question which is the optimal in
every position. The efficiency of the plant is high,
because the major part of the power is transmitted via the
~` 15 mechanical part of the transmission. This is a considerable
improvement in efficiency compared with those solutions to
the problem of speed control previously proposed.
By means of the invention, the transmission
obtains an elasticity which can readily be given any desired
characteristic. Such additional arrangements as the sprung
suspension of the gear housing, etc., then become unnecessary.
Synchronization of the generator with an electric
network can be effected in a quick and easy fashion, since
the synchronous rotational speed of the generator is reached
earlier than the effect of a change in blade-pitch on the
generator speed.
In addition to these advantages, the machinery,
without additional arrangements, can be rotated slowly,
which is of great value when inspecting and test-running
said machinery. The invention can be applied with both
horizontal-shaft and vertical-shaft wind-power plants. In
the case of vertical-shaft wind turbines with fixed
turbine blades, the invention provides for a considerable
increase in the yearly power output.
In one aspect of the present invention, there is
L provided a wind-power plant comprising a substantially
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mechanically functioning transmission for converting a
variable turbine input speed to a substantially constant
output speed, whereat the turbine speed is constantly
adapted to that fast-speed n~ber which provides maximum
efficiency under the influence of a speed variator which
when the turbine speed is lower than a nominal speed
refeeds part of the power back to the transmission, the
part increasing with a decrease in speed, and at a speed
which is higher than a nominal speed transfers an increas-
ing part of the power through the variator, characterizedby at least one speed variator having connected thereto
to a shaft, a gear in mesh with a gear fixedly connected
to a gear ring.
An exemplary embodiment of the invention is
illustrated schematically in Figure 2. In the Figure
i there is shown a propeller 1 comprising, in the illustrated
embodiment, blades which can be pivoted or rotated about
their respective long axes by known control means not
shown. The propeller 1 is connected to a shaft 2 which
is ~ournalled for rotation in a bearing 3. Fixedly
connected to the shaft 2 is a yoke 4 having at respective --
ends thereof bearings 6 and 7 for planet gears 9 and 8
respectively. ~he planet gears 8 and 9 mesh with a sun
gear 10 and a gear ring 11-
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The gear ring 11 is mounted for rotation in a bearing 12 and
is connected on the other side of the bearing with a gear
13. The sun gear 10 is fixedly connected to a transmission
shaft 14 which is carried by bearings 15 and 16. Connected
to the end of -the shaft 14 remote frorn the bearing 16 is a
gear 17 which meshes with a gear 18. The gear 18 is fixedly
connec-ted to the ;nput shaf-t 19 of a speed var;a-tor 20.
The speed variator is of a kind known per se and may comprise
a hydrostatic transmission which incluces a variable-
displacement hydraulic purnp and a hydraulic motor, which byway of an alternative may conversely be driven as a motor
or a pump, or said varia-tor may be a mechanically or elec-
trically operating speed variator. The output shaft 21 of
the speed variator 20 is fixedly connected to a gear 22
which meshes with the gear 13. A transducer 23 indicates
-the rotational speed of the turbine, while a transducer 24
~;~ indicates the rotational speed of a generator 26. Signals
from the transducers are processed in a known rnanner in a
control means 25, which is arranged to send command signals
to the speed variator 20.
The described gear box is of a known planet-gear design.
It is characterized in that the rotational speed of the gear
ring of said planet-gear system is controlled by the output
` speed of -the transmission via a speed variator. By suitable
dimensioning of the transmission, the major part of the
power transmitted is transfered over the mechanical part of
the transmission, resulting in a high efficiency.
The described transmission enables the speed of the
turbine to vary within well defined limits while still ob-
taining a constant transmission output speed so as to enablea synchronous generator -to be used.
Figure 3 illustrates an efficiency curve which is
normal for the kind of transmission described. It will be
seen from the Figure that the transmission has a maximum
~35 efficiency at the rotational speed nO of the propeller or
turbine. At nO the whole of the power is transmitted as
mechanical power. At speeds beneath nO a part of the power
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which increases with decreasing ro-ta-tional speed is fed back
to the gear box.
At speeds above nO part of the powe~ which increases
with increasing speed passes -through the speed variator.
By setting the rated speed nO of the -transmission so that it
- .coincides with maximum effic;.ency, it is possib].e t-o obtain
a 10% increase in the yearly energy.
The described embodimen-t is not restr;c'ive of the
inventi.on, but can be modified with;.n the scope of the
claims.
~: Conveniently, the speed var;.ator is dr;.ven from the
secondary side of the transmission and that -the speed can be
: :; converted in the variator and caused to influence the total
transmission ratio, so~that sai.d ratio becomes,greater or
lS smaller than a nominal transmiss;.on ratio. Further, the
variator 20 may be an electric motor which is supplied from
~: an external source, e.g. from the network fed by the gene-
rator 26.
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