Moving water, such as a river or a waterfall, has mechanical energy.
‘Mechanical energy is the energy that is possessed by an object due to its motion or
stored energy of position.’ This means that an object has mechanical energy if it’s in
motion or has the potential to do work (the movement of matter from one location to
another,) based on its position. The energy of motion is called kinetic energy and the
stored energy of position is called potential energy.
Water has both the ability and the potential to do work. Therefore, water contains
mechanical energy (the ability to do work), kinetic energy (in moving water, the
energy based on movement), and potential energy (the potential to do work.)
The potential and kinetic/mechanical energy in water is harnessed by
creating a system to efficiently process the water and create electricity
A hydroelectric power plant harnesses the energy found in moving or still
water and converts it into electricity.
Hydropower to Electric Power
How Hydropower Works
Water from the reservoir
flows due to gravity to
drive the turbine.
Turbine is connected to a
Power generated is
transmitted over power
How Hydropower Works (2)
A water turbine that cover the energy of flowing
or falling water into mechanical energy that
drives a generator, which generates electrical
power. This is a heart of hydropower power
A control mechanism to provide stable electrical
power. It is called governor.
Electrical transmission line to deliver the power
to its destination.
Components of hydroelectric power
Dam and Reservoir
Understanding the components
The rain water falls on a large area called catchment area, gets collected in the form of streams and
flows as runoff to plant site.
DAM AND RESERVOIR
The dam is usually built on a large river that has a drop in elevation, so as to use the forces
of gravity to aid in the process of creating electricity. A dam is built to trap water,
usually in a valley where there is an existing lake. An artificial storage reservoir is
formed by constructing a dam across a river.
The area behind the dam where water is stored is called the reservoir. The
water there is called gravitational potential energy. The water is in a stored
position above the rest of the dam facility so as to allow gravity to carry the
water down to the turbines. Because this higher altitude is different than
where the water would naturally be, the water is considered to be at an
altered equilibrium. This results in gravitational potential energy, or, “the
stored energy of position possessed by an object.” The water has the
potential to do work because of the position it is in (above the turbines, in
It carries water from reservoir to the hydraulic turbine
The penstock is a long shaft that carries the water towards the turbines where the
kinetic energy becomes mechanical energy. The force of the water is used to turn
the turbines that turn the generator shaft.
Trash rack, Gates and anchorages
Trash rack prevent the entry of debris into the
These debris would otherwise damage the gates,
nozzles and turbine blades by erosion.
Gates control and regulate the flow of water into
Anchorages prevent the movement of penstock
due to dynamic forces at vertical and horizontal
bends and on slopes.
Draft tube and tail race.
Draft tube is a kind of a
Because of this shape, the
water flows through this
tube is decelerated and it
comes out of tube with
minimum kinetic energy.
The exit of draft tube is
submerged in tail race.
CONTROL GATES AND
Control gates arrangement is provided with
Spillway is constructed to act as a safety valve. It
discharge the overflow water to the down stream
side when the reservoir is full. These are
generally constructed of concrete and provided
with water discharge opening, shut off by metal
control gates. By changing the degree to which
the gates are opened, the discharge of the head
water to the tail race can be regulated inorder to
maintain water level in reservoir.
It is a safety device.
Whenever the electrical load on the generator drops down
suddenly, the governor partially closes the gates which admits
water flow to the turbine. Due to this sudden decrease in the rate
of water flow to the turbine, there will be sudden increase of
pressure in the penstock. This phenomenon results in hammering
action called water hammer in the penstock.
When turbine gates are suddenly opened to produce more power,
there is a sudden rush of water through penstock and it might
cause a vacuum in water flow system which might collapse
penstock. Penstock withstands positive hammer and vacuum
SURGE TANK acts as a temporary reservoir. It helps in stabilizing
the velocity and pressure in penstock and thereby saves penstock
from getting damaged.
Uses the velocity of the water to move the
runner and discharges to atmospheric
The water stream hits each bucket on the
High head, low flow applications.
Types : Pelton turbine, Turgo turbine
Combined action of pressure and moving
Runner placed directly in the water stream
flowing over the blades rather than striking
Lower head and higher flows than
compared with the impulse turbines.
Parts of Francis turbine
- Guide vane cascade
- Turbine covers
- Shaft seal
- Regulating mechanism
- Draft tube
The water from the penstock is conducted
through the scroll casing and distributed
around the stay ring and the complete
circumference of the guide vane cascade.
Guide vanes are adjustable.
The vanes are shaped according to
hydraulic design specifications and given
a smooth surface finish. The bearings of
the guide vane shafts are lubricated with
oil or grease.
It is attached to shaft which in turn is
attached to generator shaft.
Due to action of water, it rotates and
Difference between Impulse and
The difference between impulse and reaction turbines is impulse
turbines convert the kinetic energy of a jet of water in air into movement
by striking turbine buckets or blades - there is no pressure reduction as the
water pressure is atmospheric on both sides of the impeller. The blades of a
reaction turbine, on the other hand, are totally immersed in the
flow of water, and the angular as well as linear momentum of the water
is converted into shaft power - the pressure of water leaving the runner is
reduced to atmospheric or lower