in an impulse turbine entire pressure energy is converted in
to kinetic energy as in case of a pelton turbine where the
nozzle does this..
In a reaction turbine only a part of the pressure energy is
converted to kinetic energy as in case of Francis and kaplan
in case u want to know more pls refer Hydraulic Machines by
Modi And Seth...
Impulse turbine works on the principle of Newton's second
law of motion.
Reaction turbine works on the principle of Neewton's third
law of motion"For every action there is an equal and
The main difference between reaction and impulse turbine is
that reaction turbine operates on newtons third law of
motion that is when steam leaves the rotor blades at an
angle the turbine is pushed towards opposite direction and
to a certain extent static pressure impulse is also
utilised for the movement.
Where as in impulse turbine only kinetic head of steam is
responsible for movemement of turbine.that is movement of
turbine takes place in direction of impact and not opposite
to the impact as was the case with reaction turbines.
In impulse turbine, the drop in pressure of steam takes
place only in nozzles and not in moving blades. This is
obtained by making the blade passage of constant cross-
- In this type, the drop in pressure takes place in fixed
nozzles as well as moving blades.
- The pressure drop suffered by steam while passing through
the moving blades causes a further generation of kinetic
energy within these blades, giving rise to reaction and add
to the propelling force, which is applied through the rotor
to the turbine shaft.
- The blade passage cross-sectional area is varied
An impulse turbine has fixed nozzles that orient the steam
flow into high speed jets. These jets contain significant
kinetic energy, which the rotor blades, shaped like
buckets, convert into shaft rotation as the steam jet
changes direction. A pressure drop occurs across only the
stationary blades, with a net increase in steam velocity
across the stage.
As the steam flows through the nozzle its pressure falls
from inlet pressure to the exit pressure (atmospheric
pressure, or more usually, the condenser vacuum). Due to
this higher ratio of expansion of steam in the nozzle the
steam leaves the nozzle with a very high velocity. The
steam leaving the moving blades is a large portion of the
maximum velocity of the steam when leaving the nozzle. The
loss of energy due to this higher exit velocity is commonly
called the "carry over velocity" or "leaving loss".
In the reaction turbine, the rotor blades themselves are
arranged to form convergent nozzles. This type of turbine
makes use of the reaction force produced as the steam
accelerates through the nozzles formed by the rotor. Steam
is directed onto the rotor by the fixed vanes of the
stator. It leaves the stator as a jet that fills the entire
circumference of the rotor. The steam then changes
direction and increases its speed relative to the speed of
the blades. A pressure drop occurs across both the stator
and the rotor, with steam accelerating through the stator
and decelerating through the rotor, with no net change in
steam velocity across the stage but with a decrease in both
pressure and temperature, reflecting the work performed in
the driving of the rotor.