How is a plant made

A hydroelectric plant usually includes five elements: a water collection system, a penstock a turbine transforming potential energy into mechanic energy, a generator converting mechanic energy into electric energy and a control system regulating the water flow. After being used, water is returned to its natural flow without undergoing any transformation from the viewpoint of its chemical and physical properties.
The collection system is mainly a barrage or a dam. It has to comply with very rigorous building and operating principles regulated by the law and, in the case of larger plants, monitored by the National Dam Service. The surface levelling hoses and the bottom outlet ensure a controlled management of the water in the basin.
According to the characteristics of the area where the barrage is built, different types of batters (small size barrages) or dams apply.
After it has been collected, the water is conveyed into a turbine through pipes. These pipes start from the place where the water is collected and take the water to the plant where electric energy is produced. They are inclined and consist of round steel tubes (they also have valves on the head and foot that allow them to block the water passage).
The variables determining its capacity are the available head and the rate of flow. The first is the difference between the level at which the water is before entering the collection system and the outlet level. The rate of flow is the volume (measured in cubic metres) of water passing through a section in one second’s time.
In order to calculate the hydroelectric potential of a site, it is necessary to know the flow variation during the year and the available gross head. Sometimes the hydrographic services install a measurement unit and collect the data about the previous flowing rates. Should the hydro-geological data be unknown, it will be necessary to measure the flow rate for one year.
Each turbine contains a water intake and distribution device leading it to an impeller where the potential energy is transformed into mechanic energy. Moreover, turbines can be divided into impulse turbines and reaction turbines. In the former the whole transformation takes place inside the water distribution device and therefore they are preferred when the available head is higher (up to 1,000 metres) and the rate of flow is limited.
If the available head is lower (up to 200 metres) and the rate of flow greater, a reaction turbine is preferable to exploit the action of the impeller as well.
Solidly fixed to the turbine shaft, a generator transforms mechanic energy into electric energy.
Each generator includes a moving rotor, upon which a magnet is installed, and stator, a fixed component. The magnetic field generated by the rotor transmits a electromagnetic power – electricity – to the copper coils in the stator.
Through suitably dimensioned copper cables, the electric energy, which is originally characterised by a 5,000 volts voltage, goes from the generator to the transformer. Here the voltage is increased up to 150,000 volts before the electricity is conveyed into the distribution network.
The whole hydroelectric system is governed, controlled and protected by electronic devices monitoring the production process and intervening in case of failure and/or anomalous operation, stopping the plant immediately. Over the last years, thanks to I.T. and telecommunications, almost all plants are remotely operated from a limited number of control centres supervising all the necessary operations to allow the plants to work correctly.

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