TITLE: INTERMEDIATE PRESSURE (IP) INNER CASING SUITABLE FOR
TURBINE WITH REACTION BLADING
FIELD OF INVENTION
The present invention relates to an Intermediate Pressure (IP) inner casing
suitable for a single cylinder medium capacity reheat condensing steam turbine
with reaction blading.
BACKGROUND OF THE INVENTION
The existing medium capacity reheat condensing steam turbines are normally
available in two different designs. One is a double-cylinder-type having two
modules, namely HP and LP cylinders. The second type of steam turbine is a
single-cylinder medium capacity reheat condensing turbine which uses impulse
blading. Although, this type of turbines is comparatively compact, and less
expensive, however, its efficiency is lower due to adaptation of impulse blading.
The capacity of these prior art steam turbines ranges between 120-150 MW. In
order to improve the efficiency of the presently available steam turbines in this
medium capacity range, a single-cylinder medium capacity reheat conriensina

steam turbine with reaction is necessary. However, this requires a special inner
casing suitable for the admission of reheat steam turbine, and which can hold
the reaction blading for the expansion of the steam immediately after admission.
The available design of inner casing for the 2-cylinder reaction turbines is too big
to fit into the single cylinder design. Also, this big inner casing is a combination
of HP and IP inner casings, and is susceptible to thermal distortions due to the
large size and large temperature differences along its body.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an intermediate pressure
(IP) inner .casing suitable for an improved single cylinder medium capacity
reheat-condensing steam turbine which eliminates the disadvantages of prior art.
Another object of the invention is to propose an intermediate pressure (IP) inner
casing suitable for an improved single cylinder medium capacity reheat-
condensing steam turbine which can hold reaction blading for the immediate
expansion of the admitted reheat steam.
A still another object of the invention is to propose an intermediate pressure (IP)
inner casing suitable for an improved single cylinder medium capacity reheat-
condensing steam turbine which is separate from the HP inner casing, so that

the expansions of the HP and IP inner casings can take place independently, and
the temperature differences along its body are minimal.
Yet another object of the invention is to propose an intermediate pressure (IP)
inner casing suitable for an improved single cylinder medium capacity reheat-
condensing steam turbine which is provided with means for admission of reheat
of steam without allowing the reheat steam to come into contact with the outer
casing, which is at a lower temperature, to avoid undesirable thermal gradients
at the outer casing.
A still further object of the invention is to propose an intermediate pressure (IP)
inner casing suitable for an improved single cylinder medium capacity reheat-
condensing steam turbine which has a capacity between 120-150 MW.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Fig.l - shows a photo view of lower half of the casing as per invention

INVENTION
According to the invention, there is provided an intermediate pressure inner
casing for an improved single cylinder reheat condensing steam turbine with a
provision for reheat of steam, which uses reaction blading, and which is separate
and independent of the HP inner casing.
The intermediate pressure inner casing is a casting of alloy steel, and it splits
horizontally into two halves. It has two inlet connections (2,2) in the lower half
for admitting the reheat steam into the turbine, without coming into contact with
the outer casing. This helps in eliminating the undesirable thermal gradients in
outer casing, which is at a lower temperature. The two inlet pipes (2,2) of the
intermediate pressure inner casing (l)open into an annular chamber (3) for
proper mixing. Adjacent to this chamber, an extended conical volume is provided
for holding the reaction blading (4). The inner casing is axially located by a
circular web. The lower part of inner casing is supported vertically by two sets of
paws {5,5), one at the front end and one at the rear end. The inner casing is
also provided a central rib (6) on the upper part and lower part running along

the length of the casing to ensure uniform temperature distribution around the
periphery, and therefore to avoid distortion.
The intermediate pressure inner casing is an essential part of the improved
Single Cylinder Steam turbine, and helps in achieving the following comparative
advantages over the existing 2-cylinder Steam turbines:
1) More compact, thus saving on the material cost and manufacturing cost
and lesser manufacturing cycle time. Occupies less space, lesser weight,
therefore has less civil construction
2) Costs during installation

WE CLAIM
1. An intermediate pressure inner casing (1) suitable for a single
cylinder medium capacity reheat condensing turbine comprises:
- a casting assembly consisting of two halves (upper & lower) having
a horizontal parting line with two sets of paws (5,5), one at front
end and the other at rear end, for vertically supporting.the two
parts;
- lower half provided with reheat stream inlet pipes (2,2) disposed at
two opposite sides of the inner casing (1) for admitting the reheat
stream into turbine; and
- inlet pipes (2,2) of inner casing (1) which open into an annular
chamber (3) for proper mixing wherein an extended conical volume
is provided for holding reaction blading (4) which is adjacent to
the annular chamber (3); and
-. the inner casing is axially located by a circular web;
characterised in that reheat stream enters through the inlet pipes (2,2)
and flows into the reaction blading via said annular chamber (3) for
operating the turbine.

2. The intermediate inner casing as claimed in claim 1, wherein the
casting assembly is made of alloy steel.
3. The intermediate inner casing as claimed in claim 1, wherein inner
casing is provided a central rib on upper part and lower part along
the length of the casing to ensure uniform temperature distribution
around the periphery to avoid distortion.
4. The intermediate inner casing as claimed in claim 1, wherein the
reheat steam inlet pipes are cylindrical shaped having a round
opening.

An intermediate pressure inner casing (1) suitable for a single cylinder medium capacity reheat condensing turbine comprises a casting assembly consisting of two halves (upper & lower) having a horizontal parting line with two sets of paws (5,5), one at front end and the other at rear end, for vertically supporting the
two parts and; lower half provided with reheat stream inlet pipes (2,2) disposed at two opposite sides of the inner casing (1) for admitting the reheat stream into turbine; and inlet pipes (2,2) of inner casing (1) which open into an annular chamber (3) for proper mixing wherein an extended conical volume is provided
for holding reaction blading (4) which is adjacent to the annular chamber (3); and the inner casing is axially located by a circular web characterised in that reheat stream enters through the inlet pipes (2,2) and flows into the reaction blading via said annular chamber (3) for operating the turbine.