K. J. INSTITUTE OF ENGINEERING AND TECHNOLOGY, SAVLI
CIVIL ENGINEERING DEPARTMENT
CONVENTIONAL POWER ENGINEERING (150906)
STEAM TURBINE
Q.1: Discuss advantages and disadvantages of steam turbine.
ANS: ADVANTAGES OF STEAM TURBINE:
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It is a rotary high speed machine.
It is compact and it has low weight to power ratio.
It has perfect balance and runs vibration free.
It needs less floor area.
It has low initial and maintenance cost.
It needs no internal lubrications.
Its condensate is not contaminated.
It is suitable as feed water.
It is suitable for electrical generators.
DISADVANTAGES OF STEAM TURBINE:
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Operation cost is high.
Maintenance cost is high.
Time needed for errection of plant is high before it is put to operation.
Large quantity of water is needed.
The part load efficiency is low.
Pollution causes health problems to workers and habitants.
Q.2: What are the general site selection criteria for steam power plant?
ANS: Followings factors must be considered for selection of site of thermal/steam power plant:
1. AVAILABILITY OF RAW MATERIAL:
 Coal and fuel should be available easily.
 Locate the plant as far as possible near the coal fields to reduce the cost of
transportation of fuel.
 Power plant should be located near the railway station.
 Atleast 15 days coal supply is needed which resulted into:
a) Increased space requirement
b) Increased investment
c) Additional staff requirement
d) Losses in storage.
2. NATURE OF LAND:
1.INTERNAL USE ONLY
KAVITA
K. J. INSTITUTE OF ENGINEERING AND TECHNOLOGY, SAVLI
CIVIL ENGINEERING DEPARTMENT
CONVENTIONAL POWER ENGINEERING (150906)
STEAM TURBINE
 Site should have high bearing capacity to withstand dead load of the plant.
 Reduce the cost of foundation.
 Should have sufficient space for future expansion.
 Land cost should be reasonable to reduce its capital cost.
 To reduce civil engineering cost, land should not need much leveling of the site.
 Site should not have any mineral deposits.
 Site should not require filling or blasting.
3. AVAILABILITY OF WATER:
 It uses water as working fluid.
 Necessary to locate the plant near a river, sea or lake.
4. LOAD CENTRE:
 Should be located near the load to which the power is supplied.
 Location of power plant at CG of loads.
 Reduces the cost of transmission line and the losses occurring on it.
 Also take into account the future developments while selecting the load centre.
5. TRANSPORT FACILITIES:
 Located where adequate transport facilities are available.
 For the transportation of fuel and machinery for installation.
6. AVAILABILITY OF LABOUR:
 Large men power is required.
 Labour should be available near the construction site.
 Should be available at cheap cost.
7. ASH DISPOSAL FACILITIES:
 Huge amount of hot ash comes out.
 It is hazardous to human and plant life.
 It is corrosive and polluting in nature.
 Sufficient space and facilities should be available for disposal.
8. FUTURE EXPANSION:
 It should allow future extensions of the plant with the estimated growth of load.
9. POLLUTION:
 Located away so as to avoid any nuisance from smoke, fly ash, noise and heat
discharged from plant.
10. AWAY FROM AIR FIELDS:
 Should be located away from the densely populated and industrial area.
 By taking into account the aerial warfare.
2.INTERNAL USE ONLY
KAVITA
K. J. INSTITUTE OF ENGINEERING AND TECHNOLOGY, SAVLI
CIVIL ENGINEERING DEPARTMENT
CONVENTIONAL POWER ENGINEERING (150906)
STEAM TURBINE
Q.3: What is the classification of steam turbines? Explain the working of Curtis type impulse
turbine with suitable velocity diagram.
ANS:
CLASSIFICATION OF STEAM TURBINES:
1. ACCORDING TO PRINCIPAL OF ACTION OF STEAM:
a) Impulse
b) Reaction
2. ACCORDING TO DIRECTION OF STEAM FLOW:
a) Axial
b) Radial
c) Tangential
3. ACCORDING TO NUMBER OF PRESSURE STAGES:
a) Single stage with one or more velocity stages
b) Multistage
4. ACCORDING TO METHOD OF GOVERNING:
a) Throttle b) Nozzle c) By-pass d) combination of throttle- bypass and nozzle
bypass.
5. ACCORDING TO HEAT DROP PROCESS:
a) Non-condensing b) Condensing
c) Regeneration
6. ACCORDING TO STEAM CONDIATIONS AT INLET:
a) Low pressure upto 2 bar
b) Medium pressure upto 50 bar
c) High pressure above 50 bar
d) Supercritical pressure above 225 bar.
7. ACCORDING TO THEIR USAGE:
a) Stationary with constant speed
b) Stationary with variable speed
c) Non-stationary used in steamers, ships, and railway locomotives etc.
Q.4: Differentiate between impulse turbine and reaction turbine.
ANS:
SR.NO
IMPULSE TURBINE
1.
It works on the principle of impulse
turbine.
2.
It follows the impulse momentum
equation.
3.
All the available head is first converted
into kinetic energy in nozzles.
4.
Water from nozzles comes out in the
form of jet impinges on the buckets of
3.INTERNAL USE ONLY
REACTION TURBINE
It works on the principle of impulse and
reaction.
It follows the law of angular momentum.
Only part of available head is converted
into kinetic energy in guide vanes.
Water is guided by the guide blades to flow
over the moving vanes.
KAVITA
K. J. INSTITUTE OF ENGINEERING AND TECHNOLOGY, SAVLI
CIVIL ENGINEERING DEPARTMENT
CONVENTIONAL POWER ENGINEERING (150906)
STEAM TURBINE
5.
6.
7.
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runner.
Flow of water over the runner is at
constant atmospheric pressure.
The runner of turbine need not run full.
The water may be admitted over the full
or part of periphery of runner.
Casing is not a must.
9.
The work is done due to change in
kinetic energy of jet.
10.
It is possible to regulate the flow of
water without loss.
Suitable for high heads.
Head loss due to installation of turbine
above tail race cannot be recovered.
11.
12.
Flow of water over the runner is under
pressure which gradually decreases from
inlet to outlet.
The runner needs to run full of water.
Water is admitted all over the
circumference of the runner.
Casing is essential since water flows from
inlet to outlet.
Most of the work is done due to change in
pressure head and very small of work is due
to change in kinetic energy.
It is not possible to regulate the flow of
water without loss.
Suitable for low and medium heads.
Head loss due to installation above tail race
can be recovered by using draft tube.
Q.4: What do you understand by compounding of steam turbine? State the different methods of
compounding of steam turbine and explain any one of them with neat sketch.
ANS: COMPOUNDING OF STEAM TURBINE:
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The method of reducing the rotor speed is known as compounding of impulse turbine.
With the advent of high pressure steam boilers the total pressure drop from boiler
pressure to condenser pressure in a ring of fixed blades.
Due to expansion of steam will cause a high velocity steam at its exit.
This is too high for practical reason that’s why compounding of steam is required.
1.
2.
3.
4.
DIFFERENT METHODS OF COMPOUNDING OF STEAM TURBINE:
Velocity compounded impulse turbine
Pressure compounded impulse turbine
Pressure – velocity compounded impulse turbine
Reaction turbine.
VELOCITY COMPOUNED IMPULSE TURBINE:
(REFER THE FIGURE FROM YOUR BOOK)
4.INTERNAL USE ONLY
KAVITA
K. J. INSTITUTE OF ENGINEERING AND TECHNOLOGY, SAVLI
CIVIL ENGINEERING DEPARTMENT
CONVENTIONAL POWER ENGINEERING (150906)
STEAM TURBINE
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In this type of turbine the steam expands in a set of nozzles, from the boiler pressure upto
the condenser pressure.
It converts its pressure energy into kinetic energy.
The high velocity steam is passed over the rings of moving blades.
A part of high velocity steam is absorbed in the first ring of moving blades.
The remainder is passed to the next ring of fixed blades.
The function of fixed blades is to change the direction of flow of steam.
So that it can glide over the second ring of moving blades.
The velocity of steam while passing over the fixed blades is constant except for the
energy lost for overcoming the friction losses.
Again a part of steam velocity is absorbed in the second ring of moving blades.
The process of absorbing the steam velocity continues till it is finally wasted to exhaust.
ADVANTAGES:
Due to relatively large heat drop, it requires comparatively small number of stages and
less space.
Optimum blade speed ratio decreases with increase in number of stages.
Cost of turbine is low
Casing is not required.
DISADVANTAGES:
Friction losses are large.
Its efficiency is low.
Its efficiency keeps on decreasing with number of stages.
Power developed in later stages keeps on decreasing.
These stages require same material space and cost of fabrication.
PRESSURE COMPOUNDED IMPULSE TURBINE:
(REFER FIGURE FROM YOUR TEXT BOOK)
In this type of turbine the total pressure drop does not take place in a single ring of
nozzles.
But it is divided up in between the set of nozzles rings.
Steam from boiler is partially expanded in the first ring of nozzles.
Then it is passed over the ring of moving blades till its velocity is absorbed.
Exhaust from the moving blade ring is passed over the second rings of nozzles for further
expansion partially.
Its velocity is absorbed in the second ring of moving blades.
5.INTERNAL USE ONLY
KAVITA
K. J. INSTITUTE OF ENGINEERING AND TECHNOLOGY, SAVLI
CIVIL ENGINEERING DEPARTMENT
CONVENTIONAL POWER ENGINEERING (150906)
STEAM TURBINE
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Process is repeated till the steam is expanded upto the condenser pressure.
The steam is partially expanded in each ring of nozzles, the velocity of steam would not
be very high, hence turbine velocity would be low.
PRESSURE-VELOCITY COMPOUNDED IMPULSE TURBINE:
(REFER THE FIGURE AS SHOWN IN YOUR TEXT BOOK)
In this method both the method of velocity and pressure compounding are utilized.
The total pressure drop of steam is divided into stages. (explain here process taking place
in pressure compounded impulse turbine)
Velocity of steam obtained due to expansion in each stage is also compounded. ( explain
here velocity compounded impulse turbine)
Since the numbers of stages are less we get a more compact turbine.
REACTION TURBINE:
(REFER THE FIGURE AS SHOWN IN YOUR TEXT BOOK)
Unlike impulse turbines nozzles are not provided in this turbine.
There is a continuous pressure drop in the rings of fixed and moving blades.
The function of fixed blades, which also act as nozzles, is to change the direction of
steam.
So that it can enter into the next ring of moving blades without shock.
The term reaction is used because the steam expands over the ring of moving blades
giving reaction on moving blades also.
The steam velocity and the turbine velocity is not high because the steam is continuously
expanding.
The diameter of the turbine must increase after each set of blade rings.
Q.5: Explain in brief principle and operation of steam turbine?
ANS: (REFER THE FIGURE FROM YOUR RESPECTIVE BOOK)
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A steam turbine is rotary machine which is designed to convert the energy of high
pressure and high temperature steam into mechanical power.
The operation of steam turbine wholly depends upon the dynamic action of the steam.
In this the steam is first expanded in a set of nozzles or passages upto exit pressure.
In which pressure energy is converted into kinetic energy.
Nozzles are provided just to change the direction of steam.
6.INTERNAL USE ONLY
KAVITA
K. J. INSTITUTE OF ENGINEERING AND TECHNOLOGY, SAVLI
CIVIL ENGINEERING DEPARTMENT
CONVENTIONAL POWER ENGINEERING (150906)
STEAM TURBINE
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Due to this there is a change in momentum and it will exert a resultant force on blades.
Q.6: Define blade efficiency and hence drive an expression for maximum blade efficiency for a
single stage impulse turbine.
ANS: BLADE EFFICIENCY: It is defined as the ratio of workdone on the blades to the kinetic
energy supplied to the blade.
𝑤𝑜𝑟𝑘𝑑𝑜𝑛𝑒 𝑜𝑛 𝑡ℎ𝑒 𝑏𝑙𝑎𝑑𝑒𝑠
Ƞb= 𝐾𝐸 𝑠𝑢𝑝𝑝𝑙𝑖𝑒𝑑 𝑡𝑜 𝑡ℎ𝑒 𝑏𝑙𝑎𝑑𝑒
OR
Ƞb =
𝐶ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝐾𝐸 𝑜𝑓 𝑠𝑡𝑒𝑎𝑚
𝐾𝐸 𝑠𝑢𝑝𝑝𝑙𝑖𝑒𝑑
CONDIATION FOR MAXIMUM DIAGRAM EFFICIENCY FOR IMPULSE TURBINES:
(REFER FIGURE FROM YOUR RESPECTIVE BOOK)
Workdone per kg of steam,
W = (Cwi + Cwo).Cb
= Cb [(Cricosɵ + Cb) + (Cro.cosɸ - Cb)]
= Cb . Cricosɵ (1+ (Crocosɸ)/(Cricosɵ)
= Cb (Cicosα – Cb) (1 + KC)
Where, K = Friction factor = Cro/Cri
C = cosɸ/cosɵ
………….(i)
………….(ii)
………….(iii)
………….(iv)
Blade speed ratio, s = Cb/Ci
𝑤𝑜𝑟𝑘𝑑𝑜𝑛𝑒 𝑝𝑒𝑟 𝑘𝑔 𝑜𝑓 𝑠𝑡𝑒𝑎𝑚
Blade efficiency, ƞb = 𝑒𝑛𝑒𝑟𝑔𝑦 𝑠𝑢𝑝𝑝𝑙𝑖𝑒𝑑 𝑡𝑜 𝑏𝑙𝑎𝑑𝑒 𝑝𝑒𝑟 𝑘𝑔 𝑜𝑓 𝑠𝑡𝑒𝑎𝑚
=
𝐶𝑏 (𝐶𝑖𝑐𝑜𝑠𝛼 – 𝐶𝑏)(1 + 𝐾𝐶)
𝐶 /2
= 2 ( scosα – s2) (1 + KC)
…………(v)
From equation (i),
Work would be maximum if cosα = 1,
7.INTERNAL USE ONLY
KAVITA
K. J. INSTITUTE OF ENGINEERING AND TECHNOLOGY, SAVLI
CIVIL ENGINEERING DEPARTMENT
CONVENTIONAL POWER ENGINEERING (150906)
STEAM TURBINE
i.e. α = 0, if Cb, Ci, K, ɵ & ɸ are fixed.
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In such case, the axial component of velocity Cfi = 0
It will not be possible to carry the steam to next ring of blades.
For a given mass flow rate of steam, the annulus area will decrease with the increase in
nozzle angle α.
Since the axial component of velocity Cfi = Ci.sinα increases and the work developed by
the turbine decreases.
Reduction in area will also increases the friction losses in the blade passages.
If α, K and C are kept constant, the diagram efficiency will depend upon the blade speed
ratio.
Optimum blade speed ratio,
(s)optimum = cosα/2 = Cb/Ci
Substituting this value in equation (v), we get
𝑐𝑜𝑠𝛼
(ƞb)max = 2 [ 2 . cosα – (cosα/2)2] (1 + KC)
= cos2α/2 (1 + KC)
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For a De-laval turbine neglecting friction i.e. K = 1.
For symmetrical blades i.e. ɵ = ɸ hence, C =1.
(Ƞb)max = cos2α
Expression for maximum work becomes,
Wmax =
𝐶𝑖𝑐𝑜𝑠𝛼
=
( Cicosα –
2
𝐶2𝑖𝑐𝑜𝑠𝛼
2
𝐶𝑖𝑐𝑜𝑠𝛼
2
) (1 + KC)
( 1 + KC)
In case K = 1, C = 1 (blades symmetrical) & Ci = 2Cb/cosα. Then,
Wmax = 2. Cb2
Q.7: Define governing. State the various methods of governing of steam turbine and explain any
one of them in detail.
ANS: GOVERNOR: The function of a governor is to control the fluctuation of speed of a
prime mover within the prescribed limits with the variations of loads on it.
METHODS USED FOR GOVERNING OF STEAM TURBINES ARE:
1. Throttle governing
2. Nozzles governing
8.INTERNAL USE ONLY
KAVITA
K. J. INSTITUTE OF ENGINEERING AND TECHNOLOGY, SAVLI
CIVIL ENGINEERING DEPARTMENT
CONVENTIONAL POWER ENGINEERING (150906)
STEAM TURBINE
3. By-pass governing
4. Combined throttle and nozzle governing
5. Combined throttle and by-pass governing.
THROTTLE GOVERNING (REFER FIG FROM YOUR BOOK)
 In this type of governing the steam is throttled down to a lower pressure according to the
load on the turbine before it is supplied to the turbine.
 It reduces the enthalpy drop.
 In case of small turbines the throttle valve can be actuated directly with the help of
governor.
 In case of medium and large power plants the effort of governor may not be sufficient to
actuate.
 Due to this an oil operated relay is incorporated in the circuit.
WORKING MECHANISM OF THROTTLE GOVERNING:
 Consider the case when load on turbine shaft is equal to the power developed by the
turbine, the speed is constant and the system is in equilibrium.
 Let us assume that the load on the turbine is reduced suddenly.
 At this stage since the power developed is more than the load.
 The turbine and governor speeds will increase due to the excess energy developed by the
turbine.
 The governor balls will fly out.
 It will raise the sleave of the governor, the differential level will cause pilot piston to be
raised.
 The oil which is supplied under a pressure of 3-4 bar will flow through the pipe A to the
cylinder of relay piston.
 It would force the relay piston to move downwards, while the oil from relay piston
cylinder is drained out through the pipe B.
 The downward movement of relay piston operates the throttle valve which in turn closes
the steam ports partially.
 It throttles the steam pressure at inlet to the turbine is reduced.
 When the power developed by the turbine equals to the load on the turbine, the oil ports
C – D are covered and relay piston is locked.
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NOZZLES GOVERNING: (REFER FIG FROM YOUR RESPECTIVE BOOK)
This method of governing is more efficient than the throttle governing.
In this method only the mass flow rate of steam supplied to the turbine is controlled.
9.INTERNAL USE ONLY
KAVITA
K. J. INSTITUTE OF ENGINEERING AND TECHNOLOGY, SAVLI
CIVIL ENGINEERING DEPARTMENT
CONVENTIONAL POWER ENGINEERING (150906)
STEAM TURBINE
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Total number of nozzles required is divided into number of sets like N1, N2, N3.
Each set consists of the number of nozzles required to affect the required control on the
mass flow rate corresponding to the required power control.
Due to this, different sets of nozzles will have different number of nozzles.
The supply of steam to the nozzles is controlled by opening and closing of valves
V1,V2,V3.
At full load all the valves will supply the steam to all the nozzle and a part loads one or
more number of valves are closed.
In nozzle governing the total enthalpy drop is available.
Due to this the efficiency at part loads remain unaffected in case of nozzle governing.
Q.8: Define “degree of reaction” of steam turbine. Derive an expression for calculating degree of
reaction in terms of velocities.
ANS: DEGREE OF REACTION:
𝑒𝑛𝑡ℎ𝑎𝑙𝑝𝑦 𝑑𝑟𝑜𝑝 𝑖𝑛 𝑚𝑜𝑣𝑖𝑛𝑔 𝑏𝑙𝑎𝑑𝑒𝑠
RD =𝑒𝑛𝑡ℎ𝑎𝑙𝑝𝑦 𝑑𝑟𝑜𝑝 𝑖𝑛 𝑚𝑜𝑣𝑖𝑛𝑔 𝑏𝑙𝑎𝑑𝑒𝑠 + 𝑒𝑛𝑡ℎ𝑎𝑙𝑝𝑦 𝑑𝑟𝑜𝑝 𝑖𝑛 𝑓𝑖𝑥𝑒𝑑 𝑏𝑙𝑎𝑑𝑒𝑠
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Enthalpy drop in moving blades is equal to increase in KE of the steam.
(∆h)m =( C2ro – C2ri)/2
Enthalpy drop in fixed blade is given by
(∆h)f = (Ci2 – Co2)/2
Total heat drop for the stage (∆hm + ∆hf) is equal to work done by the steam and it is
equal to
(∆h)m + (∆h)f = Cb ( Cwi + Cwo)
Hence, degree of reaction, RD = C2ro – C2ri/ 2.Cb (Cwi + Cwo)
VELOCITY DIGRAM: (REFER FIG.FROM YOUR BOOK)
From fig.
Cro = Cfocosecɸ
and
Cri = Cficosecɵ
(
10.INTERNAL USE ONLY
KAVITA
K. J. INSTITUTE OF ENGINEERING AND TECHNOLOGY, SAVLI
CIVIL ENGINEERING DEPARTMENT
CONVENTIONAL POWER ENGINEERING (150906)
STEAM TURBINE
11.INTERNAL USE ONLY
KAVITA