Power house arrangements and hydraulic

Fig.17 Arrangement of the individual guide vane servomotor system. 
 
In addition, as mentioned earlier it is possible to arrange for opening one separate guide 
vane with sufficient controllable force by means of the individual servo system. The two 
technical descriptions have shown the main advantages for the individual servomotor 
system besides the fact that no sliding friction or breakage link system of the guide vane 
connections is necessary. This because the closing force on one guide vane is limited to 
the force from one of the individual servomotors which cannot destroy the guide vane.
The different parts of the servo system are described in fig.17 
The limitation of head for using Kaplan Bulb turbines will be the axial forces from runner 
blades, guide vanes and bulb which must be transferred to the surrounding concrete via the 
struts (7) shown in fig.14.
Another limitation is the safety of buckling for the generator bulb and the limitation of 
diameter which limits the available rotating inertia mass of the generator rotor which in turn 
increases the difficulty of obtaining stable speed control on isolated load. 
In order to explain the design further it will be convenient to study the erection procedure 
which gives a good description of the design requirements as illustrated in figs. 11a, b, c, d 
and e.

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The main structural part for embedment in concrete will be the outer cone connected to the 
inner down stream cone of the bulb by the struts (7) in fig.13 These parts are welded together 
and positioned as shown in fig. 11a, where the first stage concrete work has been finished 
before turbine erection starts. (See pos. 1, 2, 3, 4, in fig. 11b) 
For Kaplan Bulb turbines the axial forces are transferred via the main struts to the concrete 
which must be heavily reinforced in the area surrounding the struts. From experience this 
part of the foundation is the most critical place in a Kaplan Bulb turbine power plant. The 
dimension and strength of the concrete, limits the maximum head of operation of this type 
of turbines to approximately 15m (see fig.11).