SVREC DEPARTMENT OF M.E
FM & HM Lab Manual 2020-21 39
Theory:
Hydraulic (or Water) turbines are the machines which use the energy of water (Hydro –
Power) and convert it into mechanical energy. Thus the turbine becomes the prime-mover to run
the electrical generators to produce the electricity, Viz., Hydro-Electric Power.
The turbines are classified as Impulse & Reaction types. In impulse turbine, the head of
water is completely converted into a jet, which impulses the forces on the turbine. In reaction
turbine, it is the pressure of the flowing water, which rotates the runner of the turbine. Of many
types of turbine, the Pelton wheel, most commonly used, falls into the category of turbines.
While Francis & Kaplan falls in category of impulse reactionturbines.
The Kaplan turbine is an inward flow reaction turbine, which means that the working
fluid changes pressure as it moves through the turbine and gives up its energy. The design
combines radial and axialfeatures.
The inlet is a scroll-shaped tube that wraps around the turbine's wicket gate. Water is
directed tangentially, through the wicket gate, and spirals on to a propeller shaped runner,
causing it to spin. Between the scroll casing and the runner, the water turns through right angle
into the axial direction and passes through the runner and thus rotating the runner shaft. The
runner has four blades which can be turned about their own axis so that the angle of inclination
may be adjusted while the turbine is in motion. When runner blade angles are varied, high
efficiency can be maintained over wide range of operating conditions. In other words even at
part loads, when a low discharge is flowing through the runner, a high efficiency can be attained
in case of Kaplan turbine, whereas this provision does not exist in Francis & Propeller turbines
where, the runner blade angles are fixed and integral withhub.
The outlet is a specially shaped draft tube that helps decelerate the water and recover
kineticenergy. The turbine does not need to be at the lowest point of water flow, as long as the
draft tube remains full of water. A higher turbine location, however, increases the suction that is
imparted on the turbine blades by the draft tube. The resulting pressure drop may lead to
cavitation.
Normally, Pelton wheel (impulse turbine) requires high heads and low discharge, while
the Francis & Kaplan (reaction turbines) require relatively low heads and high discharge. These
corresponding he1ds and discharge are difficult to create in laboratory size turbine from the
limitation of the pumps availability in the market. Nevertheless, at least the performance
characteristics could be obtained within the limited facility available in the laboratories. Further,
understanding various elements associated with any particular turbine is possible with this kind
offacility.