In hydropower plants, the potential energy of the water [with a density (rho) of 1000 kg/cubic metre] is converted into kinetic energy with the help of gravity ( g; 9.81 metres per second squared) as it flows at a flow rate ( Q cubic metres per second) from a higher level to a lower level ( through a net head of H metres). This kinetic energy turns a turbine runner ( a stainless steel wheel) at an efficiency of about 93% for most modern hydro turbines which is connected to a shaft that is connected to a generator. The generator has a rotor that rotates in a stationary electrical housing with conductors called a stator. The functioning of the generator is generally the same for all forms of power generation ( hydro, geo-thermal, thermal, wind, diesel, etc). The water in hydropower is just a prime mover that turns the rotor inside the stator.!!!
There are currently three types of hydro turbines in world namely Kaplan, Francis and Pelton.
In KenGen the turbines are used as follows:
1. Kaplan turbines are used at Masinga, Kindaruma and Gogo.
2. Francis Turbines are used at Kiambere, Gitaru, Kamburu, Turkwel, Sondu, Tana, Wanjii, Mesco, Ndula and Sagana
(my colleagues to confirm these).
3. The Turgo Wheel which is a modified Pelton turbine is used at Sosiani power station about 25km from Eldoret town in the direction of Uganda.
To automatically control the flow of water at different power out puts from the hydropower plant, a governor is usually installed.
Thus to calculate the power P (KW) from a river with a flow of Q (M^3/s) and a fall of H metres is as follows:
P = H x Q x g x n x (rho) ;
From the above formula, the case of Masinga power Station machines gives the unit rating of power as P = 49 x 45.9 x 9.81x1000 x 0.93 = 20,519,214 Kilowatts (KW) or [ 20.52 Megawatts (MW) ].
The design figure from the manufacturers for Masinga machines ESCHER WYSS of Germany is 20.6 MW which is quite close to the one from the formula.