Environmental Engineering Reference
In-Depth Information
Figure 7.2
At the redesigned Bogø windmill from 1953, the Danish
windmill concept was successfully determined (left); The 200
kW Gedser windmill from 1957 operated for 10 years with
high efficiency (right).
Another decisive innovation of the Bogø wind turbine was
the use of the AC machine as a generator. It was just an ordinary
45 kW AC induction motor, running under-synchronously when
functioning as a motor; but when connected to rotor and taken up
into over-synchronous working area, it delivers power to the grid
and maintains a constant speed. The more the wind blows, the
more it produces. When the same electrical machine is used as
motor, with increased load more power is drawn from the grid,
without, however, changing the speed of rotations by more than
a few percent. In this manner, Juul was able to keep the number
of rotations constant.
By adapting the rotor size, the number of rotations and the
capacity of the generator in an optimal way, Juul had solved a crucial
aspect of windmill technology with very simple means. When
the wind speed increases, more power is produced, until it reaches
its maximum capacity at a wind speed of 12-14 m/s. At higher
wind speeds the rotor will stall. The windmill is stopped only at
wind speeds over 25 m/s.
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