The document summarizes key aspects of steam turbines. It begins by explaining that a steam turbine converts the heat energy of steam into kinetic energy and then rotational energy to generate power. It then describes the basic Rankine cycle used in steam turbine power plants. The main body explains the principles of operation for impulse and reaction turbines. In an impulse turbine, steam expands within nozzles and does not change pressure as it moves over blades, while in a reaction turbine steam pressure gradually drops as it expands over fixed and moving blades. Finally, it discusses methods to improve efficiency, such as compounding and reheat, where dividing the expansion process into multiple stages separated by reheaters increases overall efficiency compared to a single stage by

1. Prepared By :
Ravi Chhugani (121040119005)
Submit to :
Assistant Prof. Piyush Mistri..
(G.P.E.R.I. Mehsana)

2. Steam Turbine

3. Introduction
• A Turbine is a device which converts the heat energy of
steam into the kinetic energy & then to rotational energy.
• The Power in a steam turbine is obtained by the rate of
change in momentum of a high velocity jet of steam
impinging on a curved blade which is free to rotate.
• The basic cycle for the steam turbine power plant is the
Rankine cycle. The modern Power plant uses the rankine
cycle modified to include superheating, regenerative feed
water heating & reheating.

4. STEAM TURBINE is a prime mover in which pressure
energy of steam is converted into mechanical energy &
further electrical energy.

5. A steam turbine is a prime mover in which potential energy is
converted into kinetic energy and then to Mechanical energy.
Potential Energy
Kinetic energy
Mechanical Energy

6. Principle of operation
• The power in a steam turbine is obtained by the rate of
change in momentum of a high velocity jet of steam
impinging on a curved blade which is free to rotate.
• The steam from the boiler is expanded in a nozzle, resulting
in the emission of a high velocity jet. This jet of steam
impinges on the moving vanes or blades, mounted on a shaft.
Here it undergoes a change of direction of motion which gives
rise to a change in momentum and therefore a force.
• Steam turbines are mostly 'axial flow' types; the steam flows
over the blades in a direction Parallel to the axis of the
wheel. 'Radial flow' types are rarely used.

7. The steam energy is converted mechanical work by expansion
through the turbine.
Expansion takes place through a series of fixed blades(nozzles) and
moving blades.
In each row fixed blade and moving blade are called stage.

8. Classification of steam turbine
a) According to the method of steam expansion in
the turbine.
 Impulse turbine
 Reaction Turbine
 Combination of impulse and reaction turbine.
b) According to the direction of flow of steam in the turbine
 Axial flow turbine
 Radial flow Turbine
 Mixed flow Turbine

9. c) According to the final delivery pressure (or) Exhaust
condition of steam turbine.
 Condensing Turbine
 Back Pressure Turbine.
 Extraction Turbine.
d) According to the number of stages of turbines.
 Single stage turbine.
 Multi stage turbine.
e) According to the pressure of steam turbines.
 Low pressure turbine.
 Medium pressure turbine.
 High pressure turbine.

10. .
Compounding in Steam Turbine
The compounding is the way of reducing the wheel or
rotor speed of the turbine to optimum value.
Different methods of compounding are:
1.Velocity Compounding
2.Pressure Compounding
3.Pressure Velocity Compounding.
In a Reaction turbine compounding can be achieved only by
Pressure compounding.

11. Velocity Compounding :
There are number of moving blades separated by rings of
fixed blades as shown in the figure. All the moving blades
are keyed on a common shaft. When the steam passed
through the nozzles where it is expanded to condenser
pressure. It's Velocity becomes very high. This high
velocity steam then passes through a series of moving
and fixed blades. When the steam passes over the
moving blades it's velocity decreases. The function of the
fixed blades is to re-direct the steam flow without altering
it's velocity to the following next row moving blades
where a work is done on them and steam leaves the
turbine with allow velocity as shown in diagram.

13. Pressure Compounding :
These are the rings of moving blades which are keyed on a
same shaft in series, are separated by the rings of fixed
nozzles.
The steam at boiler pressure enters the first set of
nozzles and expanded partially. The kinetic energy of the
steam thus obtained is absorbed by moving blades. The
steam is then expanded partially in second set of nozzles
where it's pressure again falls and the velocity increase the
kinetic energy so obtained is absorbed by second ring of
moving blades.

15. Pressure velocity compounding :
This method of compounding is the combination of two
previously discussed methods. The total drop in steam
pressure is divided into stages and the velocity obtained in
each stage is also compounded. The rings of nozzles are fixed
at the beginning of each stage and pressure remains constant
during each stage as shown in figure. The turbine employing
this method of compounding may be said to combine many of
the advantages of both pressure and velocity staging By
allowing a bigger pressure drop in each stage, less number
stages are necessary and hence a shorter turbine will be
obtained for a given pressure drop.

17. Impulse turbine :
In the impulse turbine, the steam expands in the nozzles and
it's pressure does not alter as it moves over the blades.
In the impulse turbine, the steam expanded within the nozzle
and there is no any change in the steam pressure as it passes
over the blades.

18. In this type, the drop in pressure takes place in fixed nozzles
as well as moving blades. The pressure drops 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 (converging type).

19. Velocity diagram :
•V1 and V2 are the absolute velocities at the inlet
and outlet respectively.
•Vf1 and Vf2 are the flow velocities at the inlet
and outlet respectively.
•Vw1+U and Vw2 are the whirl velocities at the
inlet and outlet respectively.
• Vr1 and Vr2 are the relative velocities at the
inlet and outlet respectively.
•U1 and U2 are the velocities of the blade at
the inlet and outlet respectively.
•Alpha is the guide vane angle and Beta is
the blade angle.

21. Then by the law of moment of momentum, the torque on the fluid is given by :
For an impulse steam turbine :
Therefore, the tangential force on the blades is :
The work done per unit time or power developed :
When ω is the angular velocity of the turbine, then the blade speed is :
The power developed is then :

22. Blade efficiency :
Blade efficiency can be defined as the ratio of the work done on the blades to kinetic
energy supplied to the fluid, and is given by :
Stage efficiency :
A stage of an impulse turbine consists of a nozzle set and a moving wheel. The stage
efficiency defines a relationship between enthalpy drop in the nozzle and work done in
the stage.
Where, is the specific enthalpy drop of steam in the nozzle.

23. By the first law of thermodynamic :
Assuming that V1 is appreciably less than V2, we get ≈ Furthermore, stage
efficiency is the product of blade efficiency and nozzle efficiency, or
Nozzle efficiency is given by = where the enthalpy (in J/Kg) of
steam at the entrance of the nozzle is and the enthalpy of steam at the exit of the
nozzle is . .

24. The ratio of the cosines of the blade angles at the outlet and inlet can be taken
and denoted
The ratio of steam velocities relative to the rotor speed at the outlet to the
inlet of the blade is defined by the friction coefficient
K<1 and depicts the loss in the relative velocity due to friction as the steam
flows around the blades ( K=1for smooth blades)
The ratio of the blade speed to the absolute steam velocity at the inlet is
termed the blade speed ratio =
is maximum when or
That implies and therefore Now
(for a single stage impulse turbine)

25. Therefore, the maximum value of stage efficiency is obtained by putting the value
of in the expression of /
We get: .
For equiangular blades, therefore C=1 , and we get
If the friction due to the blade surface is neglected then
1. For a given steam velocity work done per kg of steam would be maximum when
or .
2. As increases, the work done on the blades reduces, but at the same time
surface area of the blade reduces, therefore there are less frictional losses.

26. Reaction turbine :
In the reaction turbine the steam expanded continuously as it
passes over the blades and thus there is gradually fall in the
pressure during expansion below the atmospheric pressure.

27. In the reaction turbine high pressure steam from the boiler,
passes through the nozzle. When the steam comes out
through these nozzles the velocity of steam increases & then
strike on fixed blade. In this type of turbine there is a
gradually pressure drop takes place over fixed & moving
blade.

28. Velocity diagram :

29. Difference between impulse and reaction turbine :

31. Degree of reaction :
Degree of reaction or reaction ratio (R) is defined as the ratio
of static pressure drop in the rotor to the static pressure drop
in the stage or as the ratio of static enthalpy drop in the rotor
to the static enthalpy drop in the stage.
It is given as;

32. Parson’s turbine :
 Parson’s turbine is a particular case of reaction turbine in
which the degree of reaction is half.
 The section of blades of this turbine is the same in both
fixed and moving rows of blades.
 In the parson’s turbine, the blade section and the mean
diameter of fixed as well as the moving blades are the same.
 The blade height is progressively so increased such that the
velocity of steam at exit from each row of blades is uniform
throughout the stage.

33. Thus, the velocity triangle at the inlet and outlet of moving
blades will be similar.
The parson’s turbine is designed for 50% reaction, then the
equation of degree of reaction can be written as
R=1/2=Vf(cot -cot )/2Vb
therefore, Vb=Vf(cot -- cot )
Also , Vb can be written as
Vb=Vf(cot -cot α)
Vb=Vf(cot α -cot β)
Comparing the equations, α= and = β

34. Velocity diagram for Parson’s reaction turbine :

35. Condition for maximum efficiency of parson’s
reaction turbine :
Work done per kg of steam is given by
W=Vb(Vw1+Vw2)=Vb[V1cosα+(Vr2cos -Vb)
For parson’s turbine ,
=α and Vr2=V1
Therefore, W=Vb[2V1 cosα- Vb]
=V1
2[2VbV1 cosα/v1
2-Vb
2/V1
2]
= V1
2 [2 cosα-2]
Where, =Vb/V1

36. The kinetic energy supplied to the fixed blade=V1
2/2g
The kinetic energy supplied to the
moving blade= Vr2
2-Vr1
2/2
Therefore, Total energy supplied to the stage,
h=(V1
2/2)+(Vr2
2-Vr1
2/2)
For symmetrical tri-angels Vr2=V1
h= (V1
2/2)+(V1
2- Vr1
2/2 )= V1
2- Vr1
2/2

37. Considering the ABD from velocity diagram :
Vr1
2= V1
2+ Vb
2-2VbV1 cosα
h= V1
2-(V1
2+ Vb
2-2VbV1 cosα)/2
=(V1
2 +2VbV1 cosα-Vb
2)/2
= V1
2 /2[1+2Vbcosα/V1-(Vb/V1) 2 ]
h=V1
2 /2[1+2 cosα- 2 ]

38. The blade efficiency of the reaction turbine is given by :
ƞ=Work done(W)/Total energy supplied( h)
=V1
2(2 cosα- 2 )/V1
2/2(1+2 cosα- 2)
=2(2 cosα- 2)/(1+2 cosα- 2)
=2 (2cosα- )/(1+2 cosα- 2)
=2(1+2 cosα- 2)-2/(1+2 cosα- 2)
=2-2/ 1+2 cosα- 2

39. The ƞb becomes maximum when factor 1+2 cosα- 2
becomes maximum :
Therefore ,the required condition is
d/d (1+2 cosα- 2 )=0
therefore,2cosα-2 = 0
=cosα
i.e. The condition for maximum efficiency, =Vb/V1
=cosα

40. Substituting the value of in the equation, we get
(ƞb)max=2-2/1+2cosαcosα-cos2α
therefore,
Maximum efficiency=
(ƞb)max=2cos2α/1+cos2α

41. Reheat factor :
The Thermodynamic effect on the turbine efficiency can be
best understood by considering a number of stages between
two stages 1 and 2 as shown in Figure
The total expansion is divided into four stages of the same
efficiency and pressure ratio.
22
1
P
P
P
P
P
P
P
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y
x
x


43. The overall efficiency ( )of expansion is . The actual work
during the expansion from 1 to 2 is
Reheat factor (R.F.)=
( R.F is 1.03 to 1.04 )
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44. If remains same for all the stages or is the mean stage
efficiency.
We can say;
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45. This makes the overall efficiency of the turbine greater than
the individual stage efficiency.
The effect depicted by eq (B) is due to the
thermodynamic effect called “reheat”. This does not imply
any heat transfer to the stages from outside. It is merely the
reappearance of stage losses an increased enthalpy during
the constant pressure heating (or reheating) processes AX, BY,
CZ and D2.

46. Thank you..