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September 30, 2020
Turbines division according to the working principle
Whether hydro turbines are Pico, Micro, Mini, Small, Large or Very system they could be further divided according to the energy conversion into impulse, reaction or driven by medium properties.
According to the energy conversion
In case of impulse turbines represented by commonly used standard Pelton, Ossberger-BankiCrossflow types or Pico and Micro installations represented by Turgo and various water jet types the technological configuration applies mostly high heads and low flow volumes.
Although these are ideal conditions for impulse turbines, sometimes the natural conditions and economics requires various adjustments like multi jet Pelton or dual Pelton runner due to lower head, but higher flow volumes, better performance or simply larger generator to be turned. Technologically speaking impulse turbines using water impulses, water jet that is constantly interrupted by individual blades of the runner which causes vibrations that are usually eliminated by flywheel or mentioned multi jet, especially in large installations.
Reaction turbines like Francis, Kaplan or micro Propeller types on the other hand are much slower with higher torque and are placed directly into the moving water mass which presses on turbine blades(action) and causing runner to turn(reaction). Since they are literary working inside the medium, they require higher flow volumes hence they are many times used in previously mentioned current or tidal power plants. Reaction turbines are more versatile, better regulated via guide vanes, flaps or adjustable blades, they are sophisticated and therefore more expensive. On the other hand, since they are mixed pressure systems they are also subject for cavitations risk. These types of turbines can perfectly react to the fluctuations of the grid or unstable river conditions hence their installation in reversible form within PS hydro complexes.
The medium properties turbines are mostly research types and represent development sphere.
Largely they are reaction bladeless types that using physical properties of the water e.g.viscosity, non compressibility, boundary layer, cohesion, centrifugal force etc. Good examples are MUMT Micro Urban Multipurpose Turbine Mark I from 2012 which is still in research, or already commercially available SETUR turbine from 1991. If it comes to bladeless impulse turbines one of the old examples is Nicola Tesla´s centripetal flow TESLA turbine patented in 1913.
According to the head
According to the head water turbines could be divided into three categories namely High,
Low and Ultra Low Head (ULH). ULH could be found in micro applications usually with low water discharge e.g. small irrigation canal or local village stream, but in larger scales the discharge could rise, e.g.: larger canal if available or simply wider river bed. Canal applications are literary direct stream applications without changing the original course of the river hence their name Run-of-the-river(ROR) systems. Good examples are Japan, Philippine, Vietnam, Cambodia and Laos irrigation canal power plants or Italian adjustable hydroelectric wheel from Ener.Cat.Italia, Bonciani placed on Canavese Canal in Torino or in Marano sul panaro in Modena further Canadian Instream hydrokinetic turbine or smaller Japanese Ibasei Kappa generator. Many SHP are also called ROR due to low head with mostly high discharge e.g.: previously mentioned wide riverbed. Nowadays ROR SHPs implement rubber dam due to possible flood risk and bio corridor for natural fish bypass hence their environmental impact is mostly considered as positive rather than negative