Steam Turbine - An Overview to Trainees

1. Gentech Design Center
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2. INTRODUCTIONINTRODUCTION
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3. Gentech Design Center 3
A STEAM TURBINE ESSENTIALLY CONSISTS
OF A FOLLOWING PARTS

4. Major Parts
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6. COMPONENTS OF STEAM TURBINES
 Casing (Cast Steel)Casing (Cast Steel)
 Nozzle Block (11% - 13% Cr. Steel for Nozzles)Nozzle Block (11% - 13% Cr. Steel for Nozzles)
 Rotor (Wheel with sets of rotating blades – 11% - 13%Rotor (Wheel with sets of rotating blades – 11% - 13%
Cr. Steel for blades)Cr. Steel for blades)
 Glands (carbon rings / labyrinths)Glands (carbon rings / labyrinths)
 Bearings (Journal / anti-frictionBearings (Journal / anti-friction
 Thrust Bearings (Tilting Pad / anti-friction)Thrust Bearings (Tilting Pad / anti-friction)
 Over Speed DeviceOver Speed Device
 GovernorGovernor
 Governor ValveGovernor Valve
 Emergency Steam Stop ValveEmergency Steam Stop Valve
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7. A) CASING
a)a) Generally Turbine casings are used for split horizontalGenerally Turbine casings are used for split horizontal
and vertical position.The casing houses the bladed rotorand vertical position.The casing houses the bladed rotor
Nozzles, Diaphrams.Nozzles, Diaphrams.
b)b) It also holds glands for steam sealing each end forIt also holds glands for steam sealing each end for
preventing leakage of steam.preventing leakage of steam.
c)c) Steam casing are generally of cast steel of BS 3100Steam casing are generally of cast steel of BS 3100
B2/A2.It can stand with temperature. 400oC.B2/A2.It can stand with temperature. 400oC.
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8. B) NOzzLES
 In the nozzle stam is expanded from ahigh pressure toIn the nozzle stam is expanded from ahigh pressure to
low pressure. Thus a certain amount of heat energy islow pressure. Thus a certain amount of heat energy is
converted into kinetic energy.converted into kinetic energy.
C) BLAdES
 The Steam with high velocity flows over curved bladesThe Steam with high velocity flows over curved blades
and its direction of motion changed. The Blades whichand its direction of motion changed. The Blades which
change the directiuo of steam issuing from nozzles.Thischange the directiuo of steam issuing from nozzles.This
causes a change of momentum and force thuscauses a change of momentum and force thus
developed devices the turbine shaft. Material Ofdeveloped devices the turbine shaft. Material Of
Construction : 21cr mov 57Construction : 21cr mov 57Gentech Design Center 8

9. TURBINE ROTOR
Design:
 The Turbine rotor consists of three principal portions: Front
Portion (1 to 6); Blading Portion (7 to 9) and Rear Portion (10 to 14)
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11. d) governor
 Governor is a device, Which senses the speed ofGovernor is a device, Which senses the speed of
turbine and controls the steam to the turbine to maintainturbine and controls the steam to the turbine to maintain
the speed at a desired level to meet changes in loadthe speed at a desired level to meet changes in load
(or) steam flow.(or) steam flow.
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12. Speed Setting
Mech.
Speed Governer. Transducer Control Valve
Actuator.
Speed
Sensor
T
Inlet
Steam
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13. governor
It regulates the speed of the Turbine
It operates a built in valve in the steam inlet line
It is either Mechanical or Hydraulic
In Mechanical type, the fly weights open out or close in,
which inturn opens or shuts the steam inlet vlave thereby
increasing or decreasing the speed respectively
In Hydraulic type, the oil pump pressure increases or
decreases raising or lowering the plunger or piston which
in turn actuates the steam valveGentech Design Center 13

14. e) Servo mechaniSm.
 This mechanism works and an amplifier of governorThis mechanism works and an amplifier of governor
signal for throttle valve activation.signal for throttle valve activation.
 This consists of a pressure balanced pilot valveThis consists of a pressure balanced pilot valve
controlling the supply of high pressure oil to the powercontrolling the supply of high pressure oil to the power
piston.piston.
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16. F) oiL pumpS
 Generally oil is containated in the reservoir which formsGenerally oil is containated in the reservoir which forms
the turbine and gear box base plate.the turbine and gear box base plate.
 Normally two oil pumps are available in turbines.Normally two oil pumps are available in turbines.
Main oil pumpMain oil pump
Auxiliary oil pumpAuxiliary oil pump
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17. main oiL pump
 The main oil pump is driven by the low spoeed gear box /The main oil pump is driven by the low spoeed gear box /
extension.extension.
 Main oil pump delivery pressure is approx.Main oil pump delivery pressure is approx.
5.0 to 6.0 kg/cm5.0 to 6.0 kg/cm22
..
auxiLiary oiL pump
 The auxiliary oil pump is driven by an electricalThe auxiliary oil pump is driven by an electrical
motor/steam and is provided for use when starting andmotor/steam and is provided for use when starting and
shutting down the turbine.shutting down the turbine.
 Auxiliary oil pump delivery pressure is approx.Auxiliary oil pump delivery pressure is approx.
1.5 to 3.0 kg/cm1.5 to 3.0 kg/cm22
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18. TypeS oF Turbine
A. Impulse Turbine
The steam pressure at the outlet side of the
blade is equal to inlet side such a turbine is
termed as impulse Turbine.
B. Reaction Turbine
The steam pressure at the outlet side of the
blade is less than at inlet side of the blade.
A. Impulse Turbine
The steam pressure at the outlet side of the
blade is equal to inlet side such a turbine is
termed as impulse Turbine.
B. Reaction Turbine
The steam pressure at the outlet side of the
blade is less than at inlet side of the blade.
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19. diFFerence
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20. (i) SimpLe impuLSe
Expansion of Steam takes place in one set of Nozzles.
Hence called Impulse Turbines.
Employed for Small PowerGentech Design Center 20

21. (II) PRESSURE COMPOUNDED IMPULSE TURBINE
Number of Impulse Machines in series on the same shaft, allowing
the exhaust of one turbine to enter the Nozzles of the succeeding
turbine. Each simple Impulse Machine would be teamed as a
‘STAGE’. Gentech Design Center 21

22. (III) VELOCITY COMPOUNDED IMPULSE TURBINE (CURTIS TYPE)
This type comprises of a Nozzle of a wheel with two or more rows of moving
blades. There are also guide blades, suitably arranged between the moving
blades and set in reverse manner.
Features: More efficient, better control of speed than simple impulse
turbines. (Coppus Turbines) Gentech Design Center 22

23. STEaM TURBINES MaY BE CLaSSIfIED
INTO ThE fOLLOwINg TYPES:
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 Turbin
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24. STEaM TURBINES MaY BE CLaSSIfIED
INTO ThE fOLLOwINg TYPES:
c) According to the final delivery pressure (or)
Exhaust condition of steam turbine.
 Condensing Turbine
 Back Pressure Turbine.
 Extraction Turbine.
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25. STEaM TURBINES MaY BE CLaSSIfIED
INTO ThE fOLLOwINg TYPES:
d) According to the number of stages of turbines.
 Single stage turbine.
 Multi stage turbine.
d) According to the pressure of steam turbines.
 Low pressure turbine.
 Medium pressure turbine.
 High pressure turbine.
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26. SafETY DEVICES
(MEChaNICaL DEVICES)
1. Over speed Trip
2. Master trip
3. LP Trip
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30. DaNgER SIgNaLS
UNUSUaL VIBRaTION
NOISY BEaRINgS
aBNORMaLLY hOT BEaRINgS
OIL RINgS NOT TURNINg
DISCOLOURED OIL
LOw OIL PRESSURE
ExCESSIVE gLaND LEakagE
BROkEN LUBRICaTORS
gOVERNOR hUNTINgGentech Design Center 30

31. Starting the turbine
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32. Protection SyStem
Special Purpose Turbines
Low Lub. Oil Pressure Trip
High Brg. Temp. Trip
High Vibn. Trip
High Axial Disp. Trip
Const. Speed Governor
Relief Valve in Exhaust
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33. What to check for in running turbineS
Noise Levels
Leakage from Glands
Vibration at Bearing Housings
Bearing Temperatures
Movement of Oil Rings of Sleeve Bearings
Governor Oil Level (for Oil Relay Governors)
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34. StandardS
API 611
General purpose steam turbines for refinery service (non-
critical)
API 612
Special purpose steam turbine for refinery service (critical)
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35. Parameter range
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Inlet Pressure : ~ 4 ATA to 140 ATA
Inlet Temperature : ~ 1400
C to 5400
C
Extraction Pressure : ~ 3 ATA to 64 ATA
Exhaust Pressure : ~ Condensing to 45 ATA
Speeds : 3000 rpm to 25000 rpm
Power : ~ 1 MW to ~ 100 MW
Driven Machines : Generator
Compressor
Axial Turbo Blower
Boiler Feed Pump
Inlet Temperature upto 5700
C for Special Application

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trouble Shooting
• - Progressively increasing Vibration.
- Steam Leakage
- Seal Damage
Causes
* Journal/ Thrust Bearing failure
* Rotor Shaft Bent
* Heavy fluctuations in inlet steam temperature Remedy
* Check and replace Journal/ Thrust Bearing
* Check & record readings of rotor
* Proper operation of Boiler.
Labyrinth Rubbing

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trouble Shooting
- Damage to Bearing
- Vibration Causes
* Oil Contamination.
* Inlet temp of Oil is high.
* Less oil supply .
Remedy
* Rectify Laby Glands.
* Check oil cooler supply.
* Check oil supply line is not chocked.
Bearing Failure

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trouble Shooting
Governor - Hunting
- Cycle variations in speed above and below the normal
set speed.
Causes
* Worn out thrust carrier
* worn out needle roller bearing of rocker arm
* worn out Gov. weights.
- Remedy
* Check & replace the bearings
* Check & replace needle roller bearing of rocker arm
* Check & replace Gov. weights.

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