The answer is blowing in the wind.
Performing scientific experiments in the sort
of winds and weather conditions that blow off
the North Sea and across the Northumbrian hills,
calls for robust equipment and reliable researchers.
When scientists wanted a way of measuring the key parameters
for mapping the performance of vertical axis turbines sited in the
very North East of England, they turned to Sensor Technology’s
Torqsense rotary torque transducer to form the heart of their
monitoring system.
Vertical axis wind turbines are enjoying a revival of popularity,
as they are now understood to offer a number of advantages
over the more conventional propeller-type horizontal axis
generators. They tend to be quieter and safer as the leading
edges of the rotor cannot exceed the wind speed. Additionally
they do not need to be turned to face into the wind (this ‘yawing’
can be almost constant and absorbs a considerable amount of
power that would otherwise be converted into useful electricity),
and their design and construction is relatively simple because
there are few unbalanced or overhanging loads. Finally, they
are considered by many people to be less visually obtrusive
in sensitive landscapes.
Roy Wirachai, a researcher at the University of Northumbria’s
Mechanical Engineering Department is undertaking a programme
to analyse the performance of various types of vertical axis
turbines. He has just presented papers at international conferences
in Paris and Madrid detailing some of his finding based on last
winter’s weather conditions, as monitored by a Torqsense unit.
“We used an out of season Caravan Park as one of our local test
sites,” he told the assembly, “because we wanted a consistent
wind profile.”
Here he set up a Darrieus-type turbine and ran it for a week. This
proved able to self-start at wind speed about 4m/se and to rotate
at 50rpm in wind speed of 7 m/sec. Data was generated via
the RPM pick up of a Torqsense transducer and recorded using
the related Sensor Technology measurement devices. Torque
was also measured by the transducer, while other data such
as wind speed were logged by suitable instruments.
In a Torqsense transducer, surface waves are produced by
passing an alternating voltage across the terminals of two
interleaved comb-shaped arrays, laid onto one end of a
piezoelectric substrate. A receiving array at the other end
of the transducer converts the wave into an electric signal.
The frequency is dependant upon the spacing of the teeth
in the array and as the direction of wave propagation is at
right angles to the teeth, any change in its length alters the
spacing of the teeth and hence the operating frequency.
Tension in the transducer reduces the operating frequency
while compression increases it.
To measure the torque in a rotating shaft, two saw sensors
are bonded to a shaft at 45deg to the axis of rotation. When
the shaft is subjected to torque, a signal is produced which
is transmitted to a stationary pick up via a capacitive couple
comprising two discs, one of which rotates with the shaft,
the other being static.
Like horizontal axis wind turbines, vertical axis units can be
scaled to virtually whatever size is required.
Yachtsmen can mount a small one at the top of the mast or
on the coachroof; likewise householders are being offered
units about the size of a chimney, while development of a
3MW behemoth for mains supply is well underway.
“Ultimately we are trying to establish power coefficients and
optimised design,” says Roy. “Its painstaking work, so I am
delighted that the Torqsense has always performed perfectly,
taking accurate measurements and never failing – not even
after weeks on a caravan site in February.”
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For more information, please contact :-
Sensor Technology Ltd.
Tel: +44(0)1295 730746 Fax: +44(0)1295 738966
Email: info@sensors.co.uk
Website: www.sensors.co.uk
August 2003
