However, in Pelton turbine powerhouses the transformers
may be located between the
generators in the main powerhouse. The reason for this is that shock waves from possible
transformer explosions may be directed through weak "blow out" walls in the transformer
cell towards the free surface tail race tunnel outside a Pelton power house. Such free way
shock wave blasting tunnel is difficult to arrange in Francis turbine powerhouses due to the
submergence of the tail race tunnel and the turbines.
For low head plants it is often convenient to locate the power plant in the dam. In
that case
the Kaplan Bulb turbines are used for heads up to about 15 m instead of vertical Kaplan
turbines. The reason for this choice is illustrated in fig.15.3 and fig.15.4. It is clearly
illustrated that the deep excavation of the draft tube bend and the much
wider space needed
for Kaplan turbines will be a more expensive solution than if Bulb turbines are located inside
the dam.
Fig.3 Comparison of a vertical section of a Kaplan turbine and a Kaplan Bulb turbine
Fig.4 Comparison between a horizontal section of a Kaplan turbine and a Kaplan Bulb turbine.
However, the major differences in cost can be found in the
differences in width of the
vertical Kaplan alternative compared with the Bulb turbine, which is shown in fig.4a and
4b.
Because of the large axial forces from the turbine to the bulb supporting structure and
external hydraulics forces on the bulb, which will be
exposed to buckling, the limit of head
for this type of turbines will normally be approximately 15 m for economical reasons.
For Kaplan units the powerhouse is normally located in rock besides the dam on the river
bed for power houses with a small number of units. However, in large rivers as in China,
Russia and South America and other places with wide large
rivers also vertical Kaplan
turbines will be located in the dam as well as low head and medium head Francis turbines.
An example of a Kaplan turbine located besides the dam the turbine for Solbergfoss
delivered by KVAERNER in Sweden (see fig. 5) A typical example of a
Bulb turbine plant
is the turbines for Kongsvinger power plant in Norway also delivered by KVAERNER (see
fig.6).
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