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Spherical Variator
Wind Turbines
Stepless Gear Ratio Variator
The
advantage of using this variator is that it can make the electric
generator work at a constant speed, therefore in areas where it can be
more productive, eliminating the need for an inverter. Even in the presence of very little ventilation, the spherical variator provides a highly efficient wind plant. This product offers excellent reliability at a low cost thanks to the minimal quantity of pieces needed to create the variator.
For a minimal additional cost, the spherical variator wind turbine provides significantly more
energy, thereby justifying the slightly higher sales price presented to the customer.
Information:
Cesare Mengoli cesare.mengoli@alice.it
Stefano Manara Mail: s.manara1@tin.it
INTRODUCTION
The
new stepless gear ratio variator project emanates from the desire to
create a simple solution that is rational and operational for an
industry which is full of wonderful ideas and patents, yet lacks valid,
successful realizations that are usually expensive with low mechanical
performance.
I have dedicated over ten years to the development of
this variator, and thanks to the important collaboration of my friend
and colleague, Cesare, engineer Bucci and engineer Calboli of Procomec
Engineering and the Micali studio, I am finally able to create a
detailed and accurate study of wind machines, which is one of the more
promising markets at this time, thanks to the trend of clear and
continuous growth tied to the needs and incentives of the renewable
energy market.
PRESENTATION
The product consists of a speed converter, whose operation is easily described by referring to
common
motor scooters circulating our streets. No motor scooter can function
without a speed converter, due to the fact that the power supplied by
the motor is not constant, rather, it is supplied according to the
number of revolutions made. This type of operation is similar to that
of a wind generator in which the energy produced is not constant, as it
is based on wind presence, which, like an internal combustion engine,
does not provide constant energy.
Stefano Manara
ANALYSIS FOR APPLICATIONS IN WIND GENERATOR
ENVIRONMENTS
The
wind generator market is a mechanical sector that has expanded
considerably in recent years. It has never experienced an economic
crisis and has a promising future with continued expansion predicted.
There are many wind turbine manufacturers today that construct these
products with different power levels ranging from hundreds of watts to
several megawatts.
Generally speaking, these devices are moved by wind using aerodynamic blades with variable
input
rotation speeds depending on the rate of wind flow. Speeds are quite
low going from 10 rpm on the larger air-generators to 300-400 rpm on
the smaller generators.
This implies the generator is frequently connected to the blades using planetary gear set to
increase
the number of rotations input into the generator. Then, an
Inverter/Transformer electronic system must stabilize the voltage
current and frequency to be able to feed it to the electrical grid.
This electronic system is necessary because the generator does not
rotate at a constant rate. The advantage that comes with the variator
is that it will make the electric generator work at a constant speed
and, therefore, in areas where it can be more productive, eliminating
the need for an inverter.
After an in-depth examination of the
documentation and the market, no mature applications using mechanical
variators as a replacement for electronic systems exist, even though
there are projects in progress.
“Voith Turbo Wind” Project:
This
company has reached the advanced phase of testing a hydrodynamic
converter that would replace electronic systems for applications that
generate a significant amount of power. A diagram and operating
principles are shown below:
The red input drive shaft is connected to the blades of the wind generator. A planetary gear
set (red and blue section) makes the output drive shaft (blue) move. A hydraulic turbine and
pump system operated with oil (yellow) activates a gear (light blue) that moves the planetary
gearing
system for the external crown in order to supply a self-adjusting
system. A variable choke system (green) allows other adjustments to be
made.
“Sky Stream Energy” Project:
Other applications studied include “micro-wind” applications characterized by much more
contained power generation. These applications are expanding quickly in the market.
A
2.6 kW model has been selected amongst the many models available. This
wind turbine can be used in residential micro-generation environments.
An
electronic device is present in this application, as always occurs in
applications connected to an electrical grid, which provides constant
voltage current and frequency even though the rotor speed varies
according to the wind speed (50-330 rpm).
Regarding costs, installation of this device is priced at about 10,000 euro.
The application has been analyzed theorizing the use of a spherical variator to check its feasibility:
n generator 1500 rpm
Power 2,4 kW
Ø 5 m
n min 50 rpm
n max 330 rpm
Vp min 13 m/s
Vp max 86 m/s
gear ratio 10
n' min 500 rpm
n' max 3300 rpm
Variator ratio max 3,0
variator ratio min 0,5
Variator Ø 220 mm
C max 15 Nm
By
examining this 2.4 kW power application, we can see why a single-stage
gear unit (10 ratio) and a variator must guarantee a larger control
range. Torque is compatible with variators that have sphere (in steel)
dimensions lower than 250 mm. The layout demonstrates that horizontal
axes can be easily integrated with the turbines. The obstacle lies in
reaching a cost lower than 800 euro (approximately) for gear set +
variator, which could be used as a reference for the industrial cost of
the electronic control part for this level of power.
CONCLUSIONS
A summary of the feasibility study for the system, object of the patent, and potential applications follows:
1. The spherical variator takes advantage of the rotation of one or more roller bearing
contacts. The solution that seems to provide the best compromise between simplicity and
efficiency is a 2 sphere solution.
2. Steel is one of the best materials for obtaining good performance levels on the roller
bearing contacts for its modulus of elasticity and resistance ratio.
3. The sphere pre-loading system eliminates the need for a power control, requiring only a
power adjuster.
4. The use of special lubricants called ”traction fluids” is essential for high efficiency and a low
rate of wear.
5. The wind generator market sector, which is experiencing much growth, has been analyzed
for fixed applications. The conclusion reached for this potential application follows.
As a result of the studies made, the most promising application for the device seems to be
horizontal axis wind generators with power levels up to about 5 kW. The torque, power and
dimensions are compatible for these applications. In this case, the layout and features of the
device that operates at variable rates due to variable wind speeds can propose the following use:
It
may be used as a support with a 90° bevel gearbox that integrates the
gear transmission box with a planetary gear stage connected to the slow
shaft with blades and to the fast shaft with spherical variator, which
is connected to the generator output. All this could integrate auxiliary
mechanical systems, such as centrifugal brakes and couplings.
The advantages of this application are:
· The 90° gearbox is required for this type of wind generator in any case
· A variator system is also necessary. An inverter is presently used to adjust the current
frequency.
· A gear set between blades and generator provide less torque to the variator and generator,
thereby allowing the electric generator to be more efficient, as it compensates for gear set
losses.
· There is the possibility of integrating the bearings that hold up the blades and the rotating
center plate into the body.
· There is the possibility of integrating a clutch system and centrifugal brakes into the gear
set-variator unit to allow free blade rotation for low breeze winds, and to allow the blades to
brake for storm-type winds.
· There is the possibility to implement a “centrifugal” control on the variator actuator in order
to maintain the generator speed constant
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