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Types of Impulse Turbines Used in Large Scale Hydropower Plants

written by: Willie Scott • edited by: Lamar Stonecypher • updated: 7/23/2010

Large scale hydropower plants are operating in numerous countries all over the world using a water turbine to suit their particular properties. These are chiefly the water head between the penstock and turbine along with the velocity and quantity of the water supply, which governs the power output.

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    Introduction to the Different Types of Water Turbines within the Impulse Category

    Hydropower is a source of renewable energy and is the only power source to have a stored source of energy, i.e. the reservoir.

    The potential energy in the falling water is converted to kinetic energy by the water turbines which drive the generators to produce electricity.

    There are two different categories of water turbines used by hydropower plants today, namely impulse and reaction turbines, which depend on different properties of the water supply in order to operate. The water turbines are installed in a power house into which the water from the penstock is supplied to the turbines. The water turbines can be positioned in the horizontal or vertical positions, to suit the particular hydropower plant application and driving the power generators either alongside or above them, through couplings on the shafts.

    This is another article in my series on power from renewable energy, and a follow-up to my previous article on hydropower. In it we will look at the impulse turbine, examining the different types of turbines within this category which operate to give optimum efficiency to the hydroplant system.

    So we begin then with the types of impulse turbines.

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    Types of Impulse Turbines

    The types of turbines within this category of turbine are used in situations where a high head of water is available along with a low flow rate. There are three principle types and they all work on the principle of jets of water projecting onto blades or cups from nozzles. These nozzles convert the waters potential energy to high velocity kinetic energy, causing an impulse which rotates the turbine.

    Impulse turbines contain the following types,

    • Pelton Turbines

    The pelton turbine consists of a number of cup-shaped components arranged around the circumference of a circular runner and connected to a central hub. The pelton’s efficiency is enhanced by the cups being divided in the center to prevent a dead area in the middle area of the cup. The lips of the cups are slightly relieved by being cut back to promote a smoother transfer of water flow between the buckets.

    Water is injected onto the cups by nozzles which are arranged at positions around the runner. The nozzles convert the potential energy of the water to high velocity kinetic energy and as the water strikes the cups, cause an impulse which causes the turbine to rotate.

    A pelton turbine is installed horizontally and may contain numerous stages of runners and cups, each stage adding to the turbine's efficient kinetic energy to drive the power generator.

    • Turgo Water Turbine

    The turgo turbine is similar in operation to the pelton wheel. In fact, it resembles a pelton- only with half cups arranged around the runner. The water is once again injected through nozzles and because of the unique half cup design, the water from the jets can enter and exit from the cups, more easily and in greater quantities giving this turbine an efficiency of 90%. It is also installed in the horizontal position driving the power generator.

    • Crossflow Water Turbine

    This turbine has numerous trough-shaped blades arranged radially lengthwise around a cylindrical runner, tapered to a fine point at the water inlet and outlet edges to promote efficient flow. The ends of the blades are blanked off much like the old water wheels, earning this turbine the nickname “hamster cage.”

    The crossflow turbine has two independent nozzles which are set at an angle of 45ο projecting the water at the optimum angle to the blades, once again converting the potential energy of the water to kinetic energy.

    The flow of water is controlled by a regulating mechanism which revolves throttling or increasing the supply to the nozzles which also controls the power output.

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    Sketches of Impulse Turbines

    Crossflow TurbinePeltom Turbine
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    Internet Sites Visited

    Website: Segen - Introduction to Mini Hydro

    Google Docs (PowerPoint) - The Technology and Economics of Hydropower - Dr. Gareth Harrison