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However, two over speeding situations where the mechanical
braking system failed brought the issue back to the fore. The
Herborg (later Vestas) turbine introduced by Karl Erik Jørgensen
and Henrik Stiesdal
18
in 1978 would also use the same basic
22 kW blade design from Økær, but only a few months after
installation, the prototype ran into an over speed situation and
the blade and hub system collapsed to the ground.
19
A second
failure occurring a few weeks later caused Økær to stop
production and focus on a braking solution that would be stable—
eventually this resulted in the creation of a tip braking system
similar to that of the Gedser turbine. The system on the Gedser
turbine was based on hydraulics but Økær used a spring loaded
system which would activate whenever the turbine lost power
connection from the grid and the mechanical brake failed.
Figure 5.21
Hütter-type flange of 5 m Økær blade made interfacing to
the hub uncomplicated (left); tip brake (right).
Another innovation of the Herborg turbine included the use
of two diferently sized asynchronous generators (at a lower and
higher
power
rating)
in
order
to
improve
overall
turbine
performance. This as well became part of the
Danish
wind turbine standard and the “Danish Concept” of the 1980s. In
1979, the Herborg design was licensed to Vestas which was at
that time a medium-sized enterprise that made former equipment
truck cranes and heat exchangers—the company that would later
become the largest wind turbine manufacturer in the world.
The stories of other Danish manufacturers are similar.
de facto
All
of the manufactures were originally focused on agricultural or
18
20
See chapter
From Herborg Blacksmith to Vestas
by Henrik Stiesdal.
19
See chapter
Økær Vind Energi—Standard Blades for the Early Wind Industry
by
Erik Grove-Nielsen.
20
NIVE and the extended wind industry network provided the basis on which
initial designs were selected by several companies (Maegaard, 2010).
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