In a medium-pressure steam turbine of single-flow chamber type design, for use as a ship's turbine, cooling steam is conveyed via holes in the wall of the inflow part for cooling the rotor surface and the first few rows of rotor blades. The cooling steam is guided by a baffle at the wall of the inflow part to annular spaces between the shaft seal of the guide vanes and the rotor surface and via axial cooling ducts in the rotor to the bases of the rotor blades. At each rotor blade of the rows connected by the axial cooling ducts, radial connecting canals are provided in the blade bases for guiding the cooling steam into axial canals which connect the annular spaces under the shaft seals of the adjacent guide vanes.

BACKGROUND OF THE INVENTION 
This invention relates to a medium-pressure steam turbine, particularly of 
the single-flow type for use in a high-temperature steam turbine system 
having a reheater. 
Such medium-pressure steam turbines are known, in which cooling steam is 
fed via holes in the steam chest to an annular spaced located above the 
rotor surface and defined by a baffle which extends axially (as defined by 
the axis of rotation of the rotor) from the stuffing gland on one side to 
an axial extension of the first guide vanes on the other side, this 
extension forming the shaft seal at the input end of the turbine. The 
rotor blades of at least the first few rows are provided with canals 
extending parallel to the rotor rotation axis which are located above the 
rotor surface and interconnect annular spaces bounded in a radial 
direction by the shaft seals of the adjacent guide vanes and the rotor 
surface and in the axial direction by successive turbine blade rows. 
A medium-pressure steam turbine which receives cooling steam from the 
reheater prior to reheating of the steam is described by W. Traupel in 
"Thermal Turbo-Machines," Vol. II, 2d Edition, 1968, pages 341 to 342. The 
relatively low-temperature steam for cooling the rotor is fed into an 
annular space adjacent to the stuffing gland and formed by recesses in the 
housing of the inlet part and the rotor, this cooling steam in part also 
serving a sealing function. The baffle, closely juxtaposed to the rotor 
surface, separates a region from the free steam chest for the working 
steam in the inlet part and conducts therein part of the cooling steam 
along the rotor surface up to an extension of the first guide vane, this 
extension forming the shaft seal and the inner termination point of the 
baffle. In this manner the cooling steam reaches the vicinity of the first 
rows of blades. However, heat is transferred to the cooling steam from the 
in-flowing driving steam, which with its 580.degree. C. temperature is 
approximately 150.degree. C. hotter than the cooling steam, through the 
thin wall of the baffle, whereby the cooling steam is already heated up 
before it reaches the blades. The blade bases of the first two rows of 
rotor blades are formed with axial canals located above the rotor surface 
so that the cooling steam provides a cooler under-current at least as far 
as the third guide vane for reducing the temperatures of the rotor surface 
at these highly stressed points. With such a turbine design the rotor in 
high-temperature steam turbines can be fabricated from a ferritic material 
instead of austenitic steel which has unfavorable thermal expansion 
characteristics and production requirements. 
An object of the invention is to provide an improved medium-pressure steam 
turbine of the above-described type, in which the thermally induced stress 
of the rotor in the region of the first rows of blades is further reduced 
by the additional cooling steam, in order to retain the advantage of using 
ferritic or martensitic materials at still higher live-steam temperatures. 
SUMMARY OF THE INVENTION 
In a medium-pressure steam turbine according to the invention the inner 
wall of the driving-steam inlet extends to the shaft seal of the first 
guide vane and carries the baffle on its surface facing the rotor. The 
rotor body contains eccentrically disposed axially extending cooling ducts 
which, at least in the first rows of the rotor blades, establish 
communicating channels between the blade bases of adjacent rotor blades. 
Radial connecting canals which open into the axial canals of the rotor 
blades are provided in the blade bases of the rotor blades of the first 
rows. 
The driving steam is fed or transported from the system's reheater to the 
inlet canal of the medium-pressure steam turbine, while the 
low-temperature steam flows at a relatively high velocity in the narrow 
annular space between the baffle and the rotor surface. Heat transfer to 
the cooling steam is reduced owing to the thickness of the wall of the 
steam chest which wall is located between the rotor surface and the inlet 
canal of the reheated working steam. Heating of the cooling steam by the 
driving steam is further reduced owing to spaces remaining between the 
baffle and the wall, these spaces being filled with air or steam. The 
cooling steam acts on the entire rotor surface between the stuffing gland 
and the shaft seal of the first row of guide vanes as if by a veil. The 
cooling steam in the thin annular space under the baffle is set in 
rotation owing to the small distance of the baffle from the rotor surface. 
The imparted angular momentum facilitates the entry of the cooling steam 
into the axial cooling ducts in the rotor body which ducts connect the 
blade bases of the first rows of rotor blades to each other. In the region 
of the blade bases the cooling steam is again distributed in ring-fashion 
along the rotor blade mounting recesses or slots over the entire 
circumference of the rotor. Owing to the radial connecting canals in each 
rotor blade of the first rows, each such individual rotor blade and the 
adjacent rotor region is effectively cooled. The cooling of these 
components and in particular of the outer rotor surface is enhanced by the 
transport of the cooling steam into the axial canals from the radial 
canals of the rotor blades and by the mixing there of this cooling steam 
with the cooling steam portion coming from the first shaft seal. The 
cooling steam is gradually mixed with the active steam flow via the axial 
canals under the shaft seals, without the danger that an interfering 
secondary flow can develop which would have an adverse effect on 
efficiency. 
In this manner, in spite of the high temperature of the working steam in 
the steam chest, the temperatures of the rotor surface and the rotor blade 
bases of the highly stressed rows of rotor blades are reduced so much that 
the use of highly heat resistant austenitic steel for the rotor is 
obviated. 
In a medium-pressure steam turbine according to the present invention, 
difficulties arising from the different thermal expansion rates of the 
different materials in the housing are avoided. In the prior art 
medium-pressure turbines, these difficulties can be substantial because of 
the heat cycles. 
Another advantage inherent in the present invention is the improvement in 
the stiffness of the rotor due to the low temperature which prevails over 
a relatively wide region of the rotor (from the third row of rotor blades 
to the exit of the stuffing gland). This improved rotor stiffness results 
in a more advantageous location of the flexure-critical speed in the case 
of a thicker rotor body than would be possible if austenitic steel were 
used. Because of the improved rotor stability (gap excitation and oil film 
excitation), the efficiency of blade plan also in a chamber-type turbine 
can be increased. 
The cooling of the medium-pressure steam turbine component of a 
high-pressure system, in accordance with the present invention, can be 
used in stationary installations as well as ships' turbines in order to 
improve process efficiency by enabling utilization of higher live-steam 
temperatures. Especially in the case of ships' turbines, as well as all 
small high-speed machines having relatively high load change rates and 
speed changes, the improvements in cooling owing to the present invention 
are particularly advantageous because of enhanced safety and because the 
rotor may be made of ferritic or martensitic steel instead of austenitic 
steel, thereby enabling turbine operation in the region of permissible 
thermal stresses. 
The axial canals and the radial connecting canals in the blade bases of the 
rotor blades may take the form of holes or ducts. However, it is 
preferable to design these canals as laterally open elongate recesses or 
grooves because they can then be produced by a simple milling process. 
Furthermore, the holes or ducts for feeding the cooling steam to the 
annular space between the baffle and the rotor surface are preferably 
located in the lower parting gap flanges of the housing and the steam 
chest, since in this case the lines need not be separated when the upper 
housing part is uncovered.

DETAILED DESCRIPTION 
The drawing illustrates a medium-pressure steam turbine of the single-flow 
chamber type for use in a high-temperature steam turbine installation 
having a reheater, which installation is utilizable as a ship's turbine. A 
housing 1 with a driving steam inlet part 2 surrounds a drum-type rotor 3 
carrying six rows of rotor blades 4. In front of each row of rotor blades 
4 is disposed a guide vane bottom 5 fastened to housing 1. Each guide vane 
bottom 5 is provided on a side facing an outer rotor surface 6 with a 
shaft seal 7 in the form of an axial extension which extends forwardly up 
to the adjacent rotor blade 4 and thereby defines an annular space 8 above 
rotor surface 6. Rotor blades 4 have base portions 9 inserted into annular 
slots or recesses 10 of rotor 3. 
Inlet part 2 has an inner wall 11 extending to the shaft seal 7 of the 
guide vane bottom 5 of the first row. On a side of wall 11 opposite the 
driving steam intake port is located a stuffing gland 12. 
In a high-temperature steam turbine installation, the working steam fed to 
the medium-pressure steam turbine from the reheater has a very high 
temperature, e.g., 600.degree. C. For this reason the components of the 
medium-pressure turbine which first come into contact with the working 
steam, such as wall 11 or inlet part 2, the first guide vane bottoms 5, 
the first row of rotor blades 4 and the rotor region at the input end of 
the turbine, are very highly stressed. So that the temperature increases 
occurring at the steam input of the turbine can be absorbed even with 
ferritic or martensitic materials, separate cooling is provided by feeding 
to the turbine relatively low-temperature steam which is tapped after 
leaving the high-pressure turbine and before entering the reheater. This 
cooling steam is transported to the medium pressure turbine via a 
controlled reducing valve (not illustrated) and via holes or ducts 13 
located in lower parting gap flanges 14 of a lower housing section 15 of 
inflow part 2, as shown in FIG. 4. Holes 13 communicate with a ring canal 
16 (FIGS. 1, 2 and 4) which is open toward rotor 3. Lower housing 15 and 
wall 11 of inflow part 2 support, on an inner surface 17 facing the outer 
surface 6 of rotor 3, a baffle 18 formed with openings 19 for the passage 
of cooling steam in the region of ring canal 16. This baffle 18 extends 
from the stuffing gland 12, on one side, to the shaft seal 7 of the first 
guide vane bottom 5, on the other side. It defines an annular space 20 
located above rotor surface 6. 
The relatively low-temperature steam flowing into annular space 20 via the 
ring canal 16 is divided there into a cooling steam stream proper for 
cooling the active rotor portion, and into sealing steam for stuffing 
gland 12. The cooling steam is distributed by ring canal 16 over the 
entire housing or rotor circumference and forms in annular space 20 a cold 
steam veil which flows over rotor surface 6. Because baffle 18 is closely 
juxtaposed to rotor surface 6, the cooling steam is accelerated in the 
circumferential direction in the annular space 20 and thereby set in 
rotation. 
Rotor 3 of the medium-pressure steam turbine contains axial cooling holes 
or ducts 21 distributed about the periphery of rotor 3. Ducts 21 are 
located at the height of bases 9 of rotor blades 4 and interconnect the 
slots 10 in which the bases of the first two rows of blades are inserted. 
In both of these rows, the blade base 9 of each rotor blade 4 is provided 
with a laterally open radially extending elongate recess 22 which 
communicates with a respective axial canal 23 located above rotor surface 
6 and extending parallel to an axis of rotation of rotor 3, the axial 
canal 23 serving to interconnect consecutive annular spaces 8 defined by 
the shaft seals 7 of adjacent guide vein bottoms 5 and by rotor surface 6. 
These axial canals 23 perform the further function of the equalization 
holes customary in a chamber-type turbine. For this reason, rotor blades 4 
in other rows also have corresponding axial canals 23. 
A portion of the cooling steam contained in annular space 20 in front of 
the first guide vane bottom 5 enters annular spaces 8 below the shaft 
seals 7 of the guide vane bottoms 5 and flows along rotor surface 6. 
Another portion of the cooling steam, aided by the rotation thereof, 
enters axial cooling ducts 21 and is fed to the annular slots 10 
corresponding to the two first rows of rotor blades 4. In each of these 
first two rows, the cooling steam is distributed along rotor slots 10 over 
the entire circumference of rotor 3 and flows through radial connecting 
canals 22 and axial canals 23 to rejoin the other portion of the cooling 
steam. In addition to cooling rotor surface 6, the low-temperature steam 
effects a cooling of bases 9 of rotor blades 4 and of the adjacent part of 
the rotor. 
The division of the cooling steam streams depends on the cross-section 
dimensions of axial cooling ducts 21 and of annular spaces 8, as well as 
on their manufacturing tolerances. The cross sections and pressure 
conditions are chosen so that the cooling effect is still only small after 
the second row of rotor blades 4 and so that thorough mixing of the 
cooling steam with the active working steam occurs without the transition 
of the cooling steam into the working steam which takes place in the 
annular spaces 8, and without generating a secondary flow which could have 
an adverse effect on efficiency. By a cooling of the highly stressed 
active parts of rotor 3 in accordance with this invention, a sufficiently 
great cooling effect is obtained with small quantities of cooling steam at 
the points of highest stress, so that the high temperature strength limits 
of ferritic or martensitic steel used for rotor 3 are not exceeded.