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Simple Turbine Construction

1. Modern high pressure turbine rotors are of the Rateau or pressure compounded design, with 8 to 10 stages to provide a shorter, lighter rotor with better vibration characteristics. The rotors are solid forged for homogeneity and thermal stability. 2. After forging and machining, the rotors undergo thermal and dynamic balancing tests. They use a "gashed disc" design for minimum shaft thickness and steam leakage. 3. Low pressure turbine rotors also have compact designs. The astern turbine uses velocity compounding and impulse blading. Separately machined astern wheels allow use of simpler forging and materials.

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ABHIRAM R
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122 views4 pages

Simple Turbine Construction

1. Modern high pressure turbine rotors are of the Rateau or pressure compounded design, with 8 to 10 stages to provide a shorter, lighter rotor with better vibration characteristics. The rotors are solid forged for homogeneity and thermal stability. 2. After forging and machining, the rotors undergo thermal and dynamic balancing tests. They use a "gashed disc" design for minimum shaft thickness and steam leakage. 3. Low pressure turbine rotors also have compact designs. The astern turbine uses velocity compounding and impulse blading. Separately machined astern wheels allow use of simpler forging and materials.

Uploaded by

ABHIRAM R
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as DOC, PDF, TXT or read online on Scribd
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Simple Turbine construction


HP rotor

Most modern HP turbine rotors are of the Rateau or


pressure compounded design.
Reduced number of stages ( 8 to 10 ) give a shorter
rotor and provides savings in weight and length. Also
provides for better critical vibration characteristics.
Rotors are solid forged providing
1. Homogenous rotor with even grain flow
2. Even expansion
3. Good thermal stability with less likelihood of distortion
under high temperatures
After forging the rotor is machined, wheels may be
parallel or slightly thickened at the base . The methods is
also used for the LP turbine which has 7 to 9 stages plus 2 to
3 astern.
After rough machining rotor is given a thermal stability test,
after further machining and fitting of blades the rotor is given
a static and dynamic balance.
This design is known as the Gashed disc rotor and gives a
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minimum shaft thickness and hence a minimum area for


gland sealing to prevent steam leakage.
Material ( up to 566oC )
o 0.27 - 0.37% Carbon
o 1.0% Manganese
o 0.04% Sulphur
o 0.2% Silicon
o 1.0% Chromium
o 0.5% Nickel
o 1.5% Molybdenum
o 0.3% Vanadium
LP Rotor

The loss of efficiency due to the two stage velocity


compounding of the astern turbine is more than made up by
the reduction in windage whilst running ahead ( the design
must still be able to supply 70% of the ahead revs which
approximates to 40% of the ahead power) The impulse
blading may have up to 20% reaction effect at the mean
blade height.
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The astern stage consists of one single wheel two


stage velocity compounded followed by a single stage wheel.
Material
o 0.45% Carbon
o 0.15% Silicon
o Trace amounts of phosphorus and sulphur
Blade material
o 11.5 - 13.5% Chromium
o 1% Nickel,manganese and silicon
o 0.12% Carbon
o Trace amounts of sulphur and Phosphorus
Stal-Laval LP Turbine design features
The Stal-Laval LP turbine is designed not to be flexible.This is
possible as the problems of gland leakage is not so great as
on the HP turbine, the HP turbine has reduced diameter rotor
so reducing the gland sealing area but allowing flexibility.
Having a stiff rotor allows the Astern turbine to be
built up and hence allows the bulk of the LP rotor to be
forged from a low grade steel whilst only the Astern parts are
made from the material necessary to withstand the
superheated steam.
If the rotor was flexible and a built up astern turbine
wheels fitted then a possibility of fretting exists.
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The use of separately machined astern wheels allows


the original forging to be more simplistic.
The forging of the higher grade steels required for use in
superheat conditions require an increased amount of energy,
and hence expense, in the original forging and subsequent
machining process.
Another big advantage is that the astern wheels
being of smaller mass and free to expand means that they
can take more rough treatment then if they formed part of a
single mass

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