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FIELD OF APPLICATION
The invention relates to the development of a multi stage low reaction high-speed axial
steam turbine which is used to generate power or as a prime mover through a gear box.
More particularly the invention relates to a low reaction stream turbine with drum type
rotor generating a power output of 8 MW operating at high speed with one uncontrolled
extraction, for generation of power or for use as a prime mover for driving compressors.
BACKGROUND OF THE INVENTION
WITH DIFFICULTIES OF PRIOR ARTS
Steam turbines are in existence for a long time now. The first turbine of which there is any
record was made by Hero of Alexandria, and it is probably obvious to most persons that
some power can be obtained from a jet of steam either by the reaction of the jet itself, like
a rocket or by its impact on some kind of paddle wheel.
In a steam turbine, steam is supplied to the turbine at high pressure and temperature and
is expanded in multiple rows of fixed and moving blades. The steam after expansion is
directed into a surface condenser mounted at the bottom of the exhaust flange of the
steam turbine in the case of a condensing turbine.

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Steam turbines have been classified as impulse and reaction type depending upon the
amount of heat drop taking place in the fixed and moving blades. Each has its own
advantage and the manufactures world over have been making these turbines. De Lavel
and Parsons made pioneering contributions to these two types of turbines. US patent No.
5308227 refers to the installation of blades in a drum rotor for an impulse turbine. US
patent No. 5125794 refers to the impulse turbine stage with reduced secondary losses.
Turbo-machinery stages having reduced secondary losses is also described in US patent
No. 5167486. Improved Blade profile design is described in the US patent No. 5035578.
US patent No. 6332754B1 describes the steam turbine with rated power output of 100MW
or more with main steam pressure and temperature of 100 kg / sq. cm 500 deg C
respectively.
US patent Nos. 6979178B2, 7179058B2, 7175393B2 describe the inventions with regard to
the blade profile employed in this turbine for the HP and LP stages.
The invention relates to one turbine where the hub and mean reaction are low (~ 0.30 and
0.37 respectively) and does not get classified either as impulse or as reaction turbine.

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DESCRIPTION OF THE INVENTION
The object of the present invention is the development of a low reaction turbine having
multiple numbers of stages with cylindrical blades in the high-pressure Stage and twisted
blades in the low-pressure stages.
The invention will be better understood from the following description with reference to the
accompanying drawings in which
Figure 1 shows blading plan of the turbine.
Figure 2 represents a solid model showing the sectional view of the tubine.
Figure 3 represents a sectional view of the turbine.
Figure 4 (a)
and 4 (b) represents graphs showing the performance parameters of the turbine.

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Referring to Figure 1, the total number of stages in the turbine are 12. The salient feature
of this development is that the rotor is drum type with low reaction (~ 0.30) at hub.
The first stage is a control stage where considerable heat drop takes place converting the
pressure energy into kinetic energy. The control stage is a partial admission stage with
four nozzle segments and each nozzle segment is governed by a separate governing valve.
The degree of partial admission is 0.41 with all the nozzle segments mounted in the upper
half of the casing.
The stage No. 2 to 9 constitutes the high-pressure (HP) part of the turbine. The guide and
moving blades in stage No. 2 to 9 of high-pressure part are cylindrical. The guide blades
and moving blades in HP part of the turbine are provided with T-root for fixing on the
casing and rotor respectively. Shroud is provided at the tip of the guide and moving blades
for all the HP stages. Sealing fins are fixed on the rotor and casing for minimizing the
leakage flow across the stage.
The last three stages form the low-pressure end of the turbine. All the moving blades of
low-pressure stages 1 to 3 (shown as LP1, LP2 and LP3) are twisted and tapered. The
guide blades of LP1 stage are straight and cylindrical. T- root is used for all the blade rows
except LP3 moving blade row. Forked root is employed for LP3 moving blade row. Taper

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pins are used for fixing the blade root to the rotor at two radial positions. Sealing fins are
fixed on the rotor for minimizing the leakage flow across the stage in LP part of the turbine
too. The LP guide blades are mounted in a LP guide blade carrier which is in two halves
and has a horizontal parting plane connected through bolts.
A diffuser is connected at the exit of the last stage before the flow enters the exhaust
hood.
Figure 2 shows the sectional view of the solid model without the upper casing in position.
The upper casing and lower casing are bolted at the horizontal parting plane. The exhaust
hood is connected to the casing through a vertical flanged joint. The exhaust hood is
provided with the necessary connections for supply of lubricating for supply of lubricating
oil and sealing steam.
Figure 3 shows the sectional view of the turbine in vertical plane. The turbine rotor is
mounted on a front bearing pedestal. The rear bearing pedestal is integral with the
exhaust hood. Provision is made for uncontrolled extraction after the 8th stage in the HP
part of the casing.

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Figure 4a shows the stage wise performance of the turbine. The parameters shown are
the reaction at hub, mean and tip; flow coefficient and the stage efficiency. The stage
wise efficiency of the turbine is seen to improve from 2nd stage till the penultimate stage.
The reaction at hub is nearly constant from stage 2 to stage 10 of the turbine. Figure 4b
shows the heat drop across the stages. The heat drop per stages increases uniformly from
stage 2 to 11.
Dated this 9th day of October 2007.

A low reaction high speed steam turbine comprising a plurality of pressure stages, a rotor (25) having a plurality of rotor blades (1-12), a turbine casing (22), exhaust hood (23) housing the rear bearing pedestal, rotor (25) being mounted on a front bearing pedestal (21) and, wherein the said pressure stages are divided into high pressure (HP) and low pressure (LP) stages, characterized in that the guide and moving blades (2-9) of the HP stage are cylindrical and moving blades (10-12) of the LP stage are twisted and tapered.