A Pelton rotor has 20 to 40 rotor buckets depending on the size. The water leaves one or many adjustable nozzles with high pressure on the blade between the half shells. The water jet is diverted almost 180° into the hollows of the blades. In this way the energy can be almost completely released over the turbines. The advantage of this type of turbine construction method lies in the drop-height. Pelton turbines are suitable for drop-heights of 50 to 1500 m. With a drop-height of 1000 m, the water jet can reach a speed of 500 km/h. The efficiency of this turbine is between 85% and 90%. As the drop-height plays an important role in Pelton turbines, such turbines are typically used in power plants situated in the mountains. Moreover, relatively small quantities of water are used. An important advantage of the Pelton turbine is that every single nozzle can be independently regulated, allowing fluctuations in the water quantity to be managed without problem. The Pelton turbine is classified in the category of constant-pressure turbine because the pressure before and after the power output at the turbine wheel is the same.
With the Francis turbine, water spins through a spiral-shaped tube. After this, the water is aimed over the guide blades and manoeuvred onto the moving wheel inside. Through the pressure of the water, the rotor wheel is placed in motion. With the help of the guide blade, the rotational speed and the output of the turbine can be controlled. When the water has passed the turbine rotor, it flows downwards and away. The Francis turbine is suitable for medium drop heights from 50m to 700m and medium flow rates. It is therefore implemented in run-of-river power plants and in storage power plants.
The construction principle is simple and yet cleverly conceived. A rigid propeller turbine coupled directly with a generator saves space and reduces the technical complexity – and therewith minimises sources of error and maintenance costs as well. The modular construction facilitates the installation in the existing plant and the optimised planning of new hydropower plants. In addition to cost reduction, the focus in the development of StreamDiver© was also on ecological improvements. The bearings are smeared with river water and the operation of the compact turbine is thus carried out entirely without oil. High-maintenance sealing systems are dispensed with, since the turbine generator strand is completely filled with water.
Directly above the turbine is the generator. The generated kinetic energy is transferred from the turbine to the generator with the help of a vertical shaft. The Kaplan turbine is characterised by its adjustable turbine rotor blade and propeller. With this, the Kaplan turbine can be adjusted optimally to fit the amount of water and the drop height. Thus 80-90% efficiency can be attained. The Kaplan turbine's field of use is in hydraulic power stations, because these types of turbines also work well at low drop heights and fluctuating rates of flow. The water pressure constantly decreases from the moment it enters the rotors till when it leaves them, therefore, this turbine falls into the reaction turbine category.
From the mill wheel to the turbine
Water power has been used for thousands of years already. What the water wheel was to the miller, the turbine is for us.
The Egyptians, Greeks and Romans used water to operate mills, sawmills and irrigation systems. Up until 1900, water power was used solely for mechanical purposes. Not until the generator was developed and turbines were refined did it become possible to generate electricity through hydropower. Here we'd like to introduce the different kinds of turbines that are employed in our hydropower plants.