Technical overview of turbines

Summarised representation of turbines in terms of head and flow rate

Kaplan turbines are mainly used in run-of-river power plants with high flow rates and low heads (and therefore low pressure). It is equipped with an impeller that looks like a ship's propeller. The blades of the water wheel can be adjusted. The water flows onto the turbine wheels to drive the generator. The tail unit directs the incoming water so that it hits the blades of the impeller at an optimum angle. This makes it possible to react optimally to fluctuations in the water supply.
This turbine is used in our "Zompitta", "Casotto", "Cigliè", "Brzeg", "Erbognone I" and "Erbognone II" hydropower plants.

Very Low Head turbines, also known as VLH turbines, are characterized by large runner diameters with low flow rates and low speeds (40 - 50 revolutions per minute). It is used in run-of-river power plants with low heads. The turbine is equipped with a Kaplan runner with 8 rotating runner blades. The runner is preceded by a guide vane with 18 fixed guide vanes and followed by a direct-coupled, variable-speed generator. The inlet screen is integrated into the guide vane with a screen cleaner. Thanks to the use of hydraulics, the turbine can be lifted completely out of the water for maintenance or to protect it from floating debris. The low speed and large dimensions of the turbine mean that it is classified as very fish-friendly.
This type of turbine is used in our "Ospedaletto" power plant in the municipality of Gemona del Friuli on the Tagliamento river.

A hydropower screw, also known as a screw turbine, is a screw with several turns. Driven by the outflowing water, it rotates slowly (around 15 to 30 rotations per minute) around its own axis. This rotary motion is converted into electrical energy. It is used in run-of-river power plants with low flow rates and low heads. Because "water cushions" are created in the large chambers between the windings, fish can migrate safely downstream through the turbine. Stones and pieces of wood can also pass through the screw without any problems. This makes this turbine relatively low-maintenance.
Our hydropower plants "Fornovo" in the Emilia-Romagna region on the River Taro and "Cividale" approx. 15 kilometers north-east of the city of Udine on the River Natisone are equipped with turbines of this type.

Francis turbines are installed at medium to high water volumes and medium heads (20 m - 700 m) and achieve an efficiency of up to 90 %. The turbine is equipped with a runner to which the water is fed through the spiral housing (the spiral-shaped feed pipe) via the fixed guide wheel and the movable guide vanes. The moving guide vanes allow the water volume to be regulated. In pumped storage power plants, this turbine can also be used as a pump.

The operation of a Pelton turbine is particularly economical at high heads (from 50 to 1,500 m) and small water volumes. The runner of the turbine is equipped with cup-shaped blades. The water is directed through nozzles under high pressure onto the blades of the runner. The amount of water can be regulated by adjusting the nozzle needle. The Pelton turbine is used particularly in storage power stations.

Through-flow turbines, also known as Ossberger turbines, are used for a head range of 2 to 200 m and for medium and fluctuating flow rates. It is equipped with a cylindrical impeller with radially arranged partially cylindrical blades. The guide vane controls the motive water so that it first flows through the impeller from the outside to the inside. After passing through the inside of the impeller, the water exits again on the opposite side. This process allows the impeller to clean itself automatically.