Hydroelectric Power Generation - Renewable Energy: Technology, Economics and Environment - page 361

Because of the different heads and flow rates and the resulting varying water
pressure and speed conditions, various turbine types are built. They can be catego-
rised, according to the energetic conversion, into impulse turbines and reaction
turbines.
− Reaction turbines. Reaction turbines convert the potential water energy mainly
into pressure energy that is transferred to the turbine blades, where it is con-
verted into rotation. Reaction turbines are i.e. Francis, propeller, Kaplan and
Straflo turbines. Currently, the maximum power produced by Kaplan turbines
is 500 MW per unit, and for Francis turbines, approximately 1,000 MW per
unit.
− Impulse turbines. In impulse turbines the potential and the pressure energy of
water is converted completely into velocity energy. This energy is then trans-
ferred to the turbine which converts it into mechanical energy. The pressure be-
fore and after the turbine is the same; it is roughly the same as the atmospheric
pressure. Impulse turbines are Pelton turbines and cross-flow turbines. Cur-
rently, the maximum power output for Pelton turbines is approximately
500 MW per unit.
Nowadays, heads from 1 to almost 2,000 m are exploited /8-8/. The common ar-
eas of use for medium-size and larger capacities are (Fig. 8.8):
• Pelton turbines

approximately 600 to 2,000 m

• Cross-flow turbines approximately 1 to 200 m

• Francis turbines approximately 30 to 700 m

• Kaplan turbines, vertical axis approximately 10 to 60 m

• Kaplan turbines, horizontal axis approximately 2 to 20 m

2,000

1,400

Pelton turbine

1,000

700

500

300

200
140
100

Francis turbine

Diagonal turbine

50

Vertical
Kaplan turbine

Cross flow
turbine

20

Bulb turbine

10

5

20

0.5 1 2 5 10 50 100 200 500 1,000

Flow rate in m³/s

Fig. 8.8 Application of different turbine types (see /8-6/)