Water has been used for the production of power force since ancient times: initially for handling of millstones and knitting machines up to the generation of electrical energy, originating from hydraulic engineering works that have given a start to hydroelectric power plants.
The operating principle of a hydroelectric power plant exploits the movement of large masses of water through the leap that is generated by a difference in height: a certain amount is collected at a determined altitude to be returned, without any chemical-physical alteration, to a lower one.
The potential energy of water is thus transformed into kinetic energy which, in making its leap, rotates the turbine connected to an electrical current generator, also called alternator, which in turn produces electricity.
This happens in two steps: first through a distributor and then through an impeller. If both are adjustable, the turbine is said to be a double-regulator, but if only one part is regulating and the other is fixed, it is defined mono-regulator or helical.
The hydraulic turbines are divided into three large types, which vary depending on the amount of water, flow, and the available difference in height or “hydraulic jump”. The main types of turbine are Kaplan, Francis and Pelton, the names of which derive from their inventors.
In the presence of a low hydraulic jump, less than 20 m and of high water flow, indicatively higher than 20 m3/s, the Kaplan turbine is used.
In the presence of a medium jump, between 20 m and 100/150 m approximately and of an average water flow, the Francis turbine is generally used. This type of machine has only one adjustment: the distributor blades move to better manage the flow of water and direct it to the impeller which consists of fixed hydraulic sections.
In the presence of large jumps, over 100/150 m and with limited flows, normally less than 10 m3/s, the Pelton turbine is used. The principle of operation of this turbine reflects that of the classic paddle wheel of the old mills. In this case the blades are shaped like a double spoon: the water passes through one or more adjustable nozzles which direct the jet to the centre of the double spoon, thus rotating the turbine.