Fig. 15 Rotating parts for a Kaplan Bulb turbine
The runner hub is the most complicated part for a Kaplan or a Kaplan Bulb turbine and in
fig. 16 a drawing of a modern design of a runner hub is shown.
The main body of the hub
(1) is normally casted, as shown in fig.16, but this complicated part has also been
fabricated from slabs (thick plates) in order to avoid casting defects.
The stresses and
deformations in such hubs must be carefully analysed by Finite Element Method (FEM)
especially for high head Kaplan turbines where the number of blades may be as high as 8.
Fig.16 Runner hub for a Kaplan Bulb turbine or a Kaplan turbine (courtesy KVÆRNER)
In Kaplan Bulb turbines the maximum head is normally below 15 m and the number of
blades are normally limited to 4 due to the high specific speed.
Besides the main body of the hub (1) the blades pivots (2) with its support, the blades (4)
with blade pivot connections and water seal for the blades are the most critical components.
Also the runner blade levers with hubs (3) and connecting links (5) to the servomotor (6)
are parts which are vital for the reliability of the turbine. Note that the
servomotor cylinder
is the movable part of the servomotor and the piston attached to the piston rod, is the
stationary part in this case.
In fig.17 the arrangement of a servomotor system with individual servomotor is shown.
Because of the guide vanes location on a cone the individual servomotors will transmit the
forces in a plane normal to the rotating axis of each guide vane. This is not possible with a
regulating
ring and link lever connection, because the regulating ring is rotating around the
axis of the turbine shaft.
