FIELD OF THE INVENTION
The present invention generally relates to cooling the major portion of the outer
casing of a high-temperature steam turbine, so that conventional material can be
used for the portion of the casing other than the inlet portion. More particularly,
the invention relates to a device for cooling an outer casing of a steam turbine
below a valve chest with cooler steam from balance piston gland.
BACKGROUND OF THE INVENTION
It is generally known that the efficiency of a steam turbine is dependent on the
inlet and reheat parameters of the steam turbine. The higher the parameters,
the higher the efficiency. However, turbines with conventional materials are
unable to sustain an inlet/reheat temperature higher than 565 deg. C. Beyond
this temperature, costly materials (high-chromium steels or other materials which
can withstand high temperatures) are used. Moreover, it becomes prohibitively
expensive to use the costly materials for the entire casing. Further, in some
embodiments, it becomes necessary to have a cooling mechanism for the
components of the casing which although disposed away from the high
temperature inlet components, but connected to the casing and therefore
subjected to heating by conduction. In such a configuration, the inlet
components alone can be made of high temperature materials, while the other
components of the casing being made of conventional materials.

OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a method of cooling an outer
casing such that high temperature material is required only at the inlet portion
and major portion of the casing is made of conventional materials.
Another object of the invention is to propose a method of cooling an outer casing
of high temperature turbines with the major components of the casing made of
conventional materials, in which the casing is cooled to allow the steam turbines
to handle inlet steam at a much higher temperature thereby the efficiency of the
turbine.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1 shows a typical partial-section of a turbine with outer casing, and inner
casings and rotor provided with blades. It also represents the casing cooling
features described in the detailed description.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
According to the invention, there is provided a cooling connection from the
balance-piston leak-off to the chamber below the inlet valve chest.
As shown in figure 1, the turbine has an outer casing (1), an inner casing (2).
The other components of the turbine are not shown in the partial section, as
they are not particularly relevant in context of the present invention. The outer
casing (1) has a valve chest (4) made of high chromium steel or a material which
can withstand very high temperature. The valve chest (4) is separately cast and
welded to an upper part of the outer casing (1) which is made up of conventional
material. The valve chest (4) is supported on thin walls (5a, 5b) from the upper
part of the outer casing (1). These walls (5a, 5b) are partly made integral with
the valve chest (4), and' partly made integral with the upper part of the outer
casing (1). The two parts of the thin walls (5a. 5b) are joined by the welding (6)
around the vertical walls of said thin walls (5a, 5b), as shown. A chamber (3) is
thus created by the vertical walls, the valve chest (4) on top and outer casing (1)
at the bottom.
In order to balance the thrust of the turbine, a balance piston gland (7) is
provided at front end of the turbine. The high temperature steam, after
expansion through the HP blading, encounters this balance piston gland (7). The
other side of the balance piston gland (7) is normally connected to a lower
pressure zone in the outer casing (1), so that the different pressure across the
balance piston (7) plurality compensates the thrust. The leak-off steam from this

gland (7) enters the lower pressure portion (10) of the outer casing (1) for
further expansion.
In the proposed method, the balance piston leak-off steam connection is not
given directly to the lower pressure portion (10) of the outer casing (1), but is
connected to the chamber (3) below the valve chest (4). This chamber (3) is
then connected on the other side to the lower pressure portion (10) of the outer
casing (1). The balance piston leak-off steam from the exit of the HP-stages,
which is at a much lower temperature than the inlet steam, therefore cools the
chamber (3) between the valve chest (4) and the outer casing (1). Because of
this, the vertical walls of the chamber (3) which conduct the heat from the high
temperature inlet steam are cooled. The location of the weld (6) is so selected
that the portion of the wall at very high temperature is above the weld (6), and
the portion of the wall compatible with the conventional material is below the
weld (6). This way, the major portion of the outer casing (2) can be made of
conventional material. Also the heat taken away from the valve chest by cooling
is not lost, but is utilized in the turbine.

WE CLAIM :
1. A device for cooling an outer casing of a steam turbine below a valve
chest with cooler steam from balance piston gland,
wherein a chamber (3) is provided by welding at a location (6) two parts
(5a, 5b) of thin walls supporting the valve chest (4). So, that the outer
casing (1) remains below the chamber (3), and the valve chest (4)
positioned above the chamber (3), and wherein the leak-off steam from a
balance piston gland (7) is connected to the chamber (3) instead of a
lower pressure portion (10) of the outer casing (1) enabling cooling off
the chamber by the leak-off steam which is at a lower temperature being
exited from HP-Stages of the steam turbine.
2. The device as claimed in claim 1, wherein the vertical portions of said
then walls (5a, 5b) above said welded location (6) is formed of high-
chromium steel, and the balance portion of the chamber (3) and the
remaining part of outer casing constituting a substantially large portion is
formed of conventional material of low-cost.
3. A device for cooling an outer casing of a steam turbine below a valve
chest with cooler steam from balance piston gland, as substantially
described and illustrated herein with reference to the accompanying
drawings.

The invention relates to a device for cooling an outer casing of a steam turbine
below a valve chest with cooler steam from balance piston gland, wherein a
chamber (3) is provided by welding at a location (6) two parts (5a, 5b) of thin
walls supporting the valve chest (4). So, that the outer casing (1) remains
below the chamber (3), and the valve chest (4) positioned above the chamber
(3), and wherein the leak-off steam from a balance piston gland (7) is
connected to the chamber (3) instead of a lower pressure portion (10) of the
outer casing (1) enabling cooling off the chamber by the leak-off steam which
is at a lower temperature being exited from HP-Stages of the steam turbine.