Hydro-Power Stations

Since water resources are abundant around the globe, generation of electricity by means of hydro-turbines is not a novel method.

There are mainly 2 types in the utilisation of hydro energy for power generation:
1. Reservoir type (see the above figure)
2. Run-of-River type (for a good illustration see this)
3. Pumped storage (see this picture)


Reservoir type plants store river water in natural/ artificial Dam structures. At the same time, Run-of-River type does not employ any permanent storage but depends on a diversion of an existing river.

In Sri Lanka, Victoria and Randenigala are few examples of big water reservoirs used for hydro-power, coming under the Mahaweli irrigation scheme.

Due to the nature of not having a permanent storage, Run-of-River type power stations suffer in drought seasons.

A big hydro power station will normally consist of the following elements after the dam.

1. Water Tunnel: to draw water from the reservoir
2. Penstock:       to deliver water to the hydro turbines
3. Valves:           before and after the Penstock for operation and safety

Hydro turbine is a mechanical device which is rotated by the energy imparted by the massive flow of water. Those are classified depending on their Head-charactersitics.
1. Kaplan Turbine
2. Francis Turbine
3. Turgo Turbine
4. Pelton Turbine

Impulse turbines Vs. Reaction turbines

It is notable that the rotational speed of Hydro-turbines is considerably lesser than that of Gas-Turbines found in Thermal power stations.

Hydro turbines are coupled with the alternators (AC Generators) either horizontally or vertically.

Useful Power (in MW) developed by the alternator is controllable by adjusting the control gates called ‘Guide Vanes’, which determine the amount of water flow into the turbine.

Potential Energy of flowing Water = m*g* h ………. in usual notations]

=> Power output of Turbine         = (m*g*h) / t
                                                 = (m/t)*g*h
                                                 = (water flow rate)*g*h ………..g, h are constants

=> Power output of Turbine IS PROPORTIONAL TO water flow rate, for a given head (h)

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