STEAM TURBINES AND ITS GOVERNINGS
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Transcript of STEAM TURBINES AND ITS GOVERNINGS
STEAM TURBINES AND ITS GOVERNING
MOHAMMED FARIS A K42
INTRODUCTION
The steam turbine is a prime mover in which the potential energy of steam is transformed into kinetic energy , and latter in its turn is transformed to mechanical energy of rotation of the turbine shaft.
Utilised in most diverse fields of industry, for power generation and for transport
CLASSIFICATION
Based on action of steam Impulse Reaction Combination of impulse and reaction Based on number of pressure stages Single stage Multi stage Impulse and Reaction turbines Based on Direction of steam flow Axial turbines Radial turbines Based on no of cylinders Single Double Three cylinder Four cylinder
Based on method of governing Throttle governing Nozzle governing According to heat drop process Condensing turbines with generators Back pressure turbines Topping turbines Low pressure turbines Mixed pressure turbines According to steam conditions at inlet Low pressure (1.2-2 atm) Medium pressure ( upto 40 atm ) High pressure (above 40 atm ) Very high pressure ( 170 atm and above and temp of 550 C
and above ) Super critical (above 225 atm ) Based on usage in industry Stationary ( variable and constant speed ) Non stationary
Advantages of Steam Turbine over the Steam Engines• Thermal efficiency higher for steam
turbine• Power generation at uniform rate • Higher speeds and higher outputs• No internal lubrication and minimised
balancing problem• No loss due to initial condensation of
steam• Utilise high vaccum very advantageously
COMMON TYPES OF TURBINES• Simple impulse turbine
Steam expands in the nozzles and its pressure does not alter as it moves over the blades.Eg: De laval turbine Expansion takes place in one set of nozzles.
• Reaction turbine Steam expands continuously as it passes over the blades and thus there is gradual fall in the pressure during expansion. No of stages required is more.
Difference between Impulse and Reaction Turbines
Sl no
Particulars Impulse Turbine Reaction Turbine
1.
2.
3.4.
5.
6.
7.
8.9.
10.
Pressure drop
Area of blade channelsBladesAdmission of steamNozzles
Power
Space
EfficiencySuitability
Blade manufacture
Only in nozzles and not in moving blades.Constant.
Profile type.Not all round.
Diaphragm contains the nozzles.Small power capacities.
Less space for same power.
LowSmall power requirements.
Easy
In fixed blades(nozzles) as well as in moving blades.Varying.
Aerofoil type.All round.
Fixed blades attached to the casing.Much power can be developed.More space required.
HighFor medium and high power requirements.Difficult
Methods for reducing rotor speed• Velocity compounding
• Pressure compounding
• Pressure velocity compounding
Steam turbine governing and control
Objective is to keep turbine speed fairly constant irrespective of load . Different methods are• Throttle governing
• Nozzle governing
• By pass governing
Comparison of Throttle and Nozzle control Governing
Sl no.
Particulars Throttle control Nozzle control
1.2.
3.
4.
5.
Throttling lossesPartial admission lossesHeat drop availableUse
Suitability
SevereLow
Lesser
In both Impulse and Reaction turbines.Small turbines
Little lossesHigh
Larger
Mostly in Impulse turbine.Medium and Large turbines.