Development of New
High Efficiency Steam Turbine
EIICHIRO WATANABE
TAKASHI NAKANOKEIZO TANAKAMASANORI TSUTSUMIYOSHINORI TANAKAHIROHARU OHYAMATOSHIHIRO MIYAWAKI
TANEHIRO SHINOHARA

Mitsubishi Heavy Industries, Ltd. (MHI) has developed new high performance turbine blades (reaction blades,
impulse blades, and LP end blades) and high performance seals, as new technologies that remarkably improve theperformance of steam turbines. Moreover, MHI has developed a new high efficiency steam turbine, adopting not only
these new technologies but also other latest technologies to improve performance and operability. The first unit of
new high efficiency steam turbine has started the operation at the “T-point” combined cycle verification power plantin Takasago Machinery Works of MHI, and performance and reliability were verified by special measurements. This
article describes the characteristics of the new technologies and the structures that were applied to the newly developed steam turbine and the results of the verification.

formance seal (Leaf seal) capable of significantly reducing steam leakage through the gland seals and blade tip/base clearance. Moreover, MHI has developed a new highefficiency steam turbine that not only adopts these newtechnologies but also other latest technologies to achieve
high performance and easy operability. The performanceand reliability of this new type steam turbine was verified by replacing the existing turbine at the “T-point”
combined cycle verification power plant at Takasago
Machinery Works of MHI.

1. Introduction
Steady efforts are actively being pursued throughout
the world to improve the efficiency of thermal power
plants in response to growing movements to conserve
energy resources and achieve greater environmental protection typically represented by the control of CO 2
emissions. One of these efforts is an attempt aimed at
improving thermal cycles by increasing the steam temperature and pressures handled in the steam turbines.
For this purpose, MHI has also realized a high efficiency
and large capacity commercial steam turbine that operates at a steam temperature of 600°C class (1) and has
developed materials capable of withstanding temperatures as high as 630°C (2) . In addition, MHI has also
positively strived to increase the efficiency of steam turbines by improving blade performance, reducing leaklosses and so forth. In particular, in order to improvethe blade performance, MHI has developed fully threedimensional design blades to increase their efficiency,
applying the latest computational fluid dynamics (CFD)
to the maximum extent possible (3), and has adopted suchblades for use in actual turbines. On the other hand, inorder to cope with growing levels of turbine capacity, MHI
has striven to elongate last stage rotating blades, andhas led the industry in commercial use of 40 inch steel
blades for 3 600 rpm machines and 48 inch steel bladesfor 3 000 rpm machines (4).
In order to improve turbine efficiency, MHI has now
developed new high performance reaction blades, impulse
blades, and low-pressure (LP) end blades with the intent of achieving further enhancements in efficiency,
utilizing the state of the art technologies of three-dimensional multi-stage viscous flow analysis and unsteadyflow analysis (5). MHI has also developed new high per-2. Outline of new high efficiency steam turbine
The new high performance blades and seals are applicable to all sorts of steam turbines ranging fromsmall sized machines to large scale units for use in combined cycle power plants and conventional thermal power
plants. Fig. 1 shows the first unit of new high efficiency
steam turbine that has been developed and manufactured
for the T-point verification power plant applying all the
new technologies mentioned above.
This turbine is a single-casing reheat type turbinewith a rated capacity of 105 MW. The upstream bladesof the high-pressure (HP) section are designed for impulse stages, while the downstream blades of the HP
section and all the blades of the intermediate-pressure(IP) section are designed for reaction stages. The newly
developed high performance blades are applied for boththe impulse and reaction stages, with the intent of improving the performance of both stages. The blades of
the LP section are composed of 36 inch LP end blades foruse in 3 600 rpm operation. These blades are designedby the profile and flow path designs that have been developed based on the latest CFD technology. In addition,leaf seals are applied to the sealing section between the
HP exhaust and the gland in order to reduce any steam
Mitsubishi Heavy Industries, Ltd.
Technical Review Vol.40 No.4 (Aug. 2003)

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New high performance
LP end blades
New high performance
impulse blades
and leaf seals

High performanceaxial exhaust hood

New high performance
reaction blades
and leaf seals

Leaf seals

Hollow stationary blades andsuction slits for moisture removal

ACC seals
Welded rotor capable ofcoping with high temperature
operation and quick start

Scroll type main steam inlet andpaths for reducing pressure
losses in IP inlet and HP outlet

Fig. 1 New high efficiency steam turbine for the T-point (single-casing reheat type turbine)
The notes indicate the position where the new technologies are applied.

leakage. The same type of seals are also applied to the
HP and IP rotating blades for sealing the tip clearance
in order to improve the blade performance.
In addition to these key technologies, various othertechnologies have been applied to contribute to improving the performance and operability. For example, thenozzle box for the main steam inlet is designed as a scroll
type passage with the aim of homogenizing the steam
flow in the circumferential direction and reducing pressure losses, while the shapes of the flow paths at HP
exhaust and IP inlet parts have been designed utilizing
the CFD so as to reduce pressure losses. The Active
Clearance Control or ACC technology applied to the sealing area between the HP and IP sections improves thesealing performance using movable sealing segments.
This design results in larger clearance when the turbine
is starting or stopping, while a tighter clearance results
when the turbine operates under loaded conditions. A
welded rotor with large bore structure is employed inorder to reduce thermal stresses produced during startup of the turbine (hetero-material welded rotor) (6). As aresult, the operability of the turbine is improved for quick
start.

Stationary blades

Rotating bladesFig. 2 Example of unsteady flow analysis

Fig. 2of unsteady flow analysis (Fig.
2). Based on this knowledge, a new profile was developed to reduce unsteadylosses through optimum design. Results of tests at the
air turbine facility also confirmed that the performanceof the blade was remarkably improved by the new profile.
The structural design of the impulse stages was
modified (called high performance diaphragm structure). Conventional wide nozzles are separated into
profile sections and support columns. This method isbased on the idea that the strength of diaphragm isreinforced by support columns located upstream of thestationary blades and the width of stationary blades
can be reduced to increase the aspect ratio. Improvement of stationary blade performance is also achieved
by applying a three-dimensional design. The shape ofthe support columns and the profile of stationary blades
are optimized through the use of three-dimensional flow
analysis.

3. Characteristics of new technologies
3.1 New high performance impulse blades
A newly designed profile that reduces unsteady losses
has been applied for the rotating blades of impulse stage
adopted as the upstream stages of the HP section of the
new high efficiency steam turbine for the T-point. The
mechanism of unsteady losses that are produced due tothe interaction between the rotating blade and the stationary blade has been clarified through the effective use

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol.40 No.4 (Aug. 2003)

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Casing

Casing

1.0
0.8
Span

0.6
0.4
0.2
0.0

Hub

Hub
(b) Example of unsteady viscous analysis:
Result of prediction analysis of (a)(a) Measurement of loss distribution
using fast response aerodynamic probes

Fig. 3 Example of improvement of prediction accuracy using flow analysis
Stationary
bladesRotating
blades

Shrouds

Rotating
bladesStationary
bladesFig. 5 New high performance LP end blades (3 600 rpm - 36 inches)and stationary blade interact with secondary flow vortexes and increase the secondary flow losses.
Accordingly, MHI has attempted to optimize the shapeof the flow paths including those between the inside circumferences of the stationary blades and the rotor disks
and those around the rotating blade shrouds. Fig. 4
shows an analysis model of the flow fields including allof these flow paths.
As described above, new high performance reaction
blades have been developed through the latest analysis
technologies and the detailed verification of the internal flows, and applied to the downstream blades of the
HP section and to all the blades of the IP section of the
new type steam turbine at the T-point.
3.3 New high performance LP end blades
The performance of the LP end blades largely influences the performance of the turbine as a whole.
Consequently, MHI has striven to realize its various
improvements taking the progress of the flow analysis
technologies. The 3 600 rpm 36 inch blades shown in
Fig. 55, which have been developed this time as new highperformance LP end blades based on the latest unsteadymulti-stage viscous flow analysis, demonstrate further
advanced performance. This latest unsteady flow analysis can be used for evaluating the behavior of the wakesof stationary blades inside the downstream rotating
blades in multi-stage flow field, the behavior of wakes ofrotating blades inside the downstream stationary blades,
the interaction between wakes and secondary flows, andthe interaction between shock waves and boundary layers or secondary flows. The improvement in theperformance has been realized by taking these effects
into consideration, in addition to the optimization ofFig. 4 Example of computational mesh grids for analyzing
entire stream path (Downstream of HP section)

3.2 New high performance reaction blades
MHI has always made steady efforts to improve theaccuracy of the predictions of efficiency and internal turbine flows. Three-dimensional multi-stage flow analysis
taking viscosity into consideration was used for this purpose and the results of this analysis were confirmed at
air turbine verification test. Recently, in addition to conventional steady state analysis, MHI has established anunsteady flow analysis method capable of predicting lossproducing mechanisms even more precisely, as shown in
Fig. 3
3. As a result, MHI has developed new high performance reaction blades using these methods.
The degree of reaction and the three-dimensional
stacking of profile are further optimized, compared withthe flow patterns of conventional blades. As a result,production of the secondary flow vortexes are controlled
and the vortex zones are shifted toward the inside andoutside endwall of each blade, so that losses due to thesecondary flows in the rotating blades are reduced. In
addition, a new profile to reduce unsteady losses produced by the interaction between the rotating blades andstationary blades is applied to the middle zone of theblade height where profile losses are dominant.
Unsteady flow analysis has also quantitatively clarified that vortexes produced in the vicinities of the insideand outside endwall of each blade due to leakage fromand inflow into the spaces between each rotating blade

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol.40 No.4 (Aug. 2003)

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stage loading, loading distribution along the blade height
and the blade profile for high Mach number flow, whichhave been implemented so far. Since these effects in
unsteady flow field are evaluated at every moment, thedesign was made to achieve maximum efficiency by timeaveraging.
The advance of the flow analysis technology has remarkably increased the prediction accuracy of exciting
forces acting on a blade and enabled to improve vibratory strength of the blades largely. This increases thedegrees of freedom related to the flow path design andstacking of the blade profiles, enabling MHI to thoroughly
review the design to improve performance. As a result,the base diameters and heights of the upstream rotating blades as well as the lengths of the last stage blade
could be increased, and the flow fields of the LP end
blades as a whole including the blade endwall contours
has been further optimized. Further, the skewed profile
inclined in the axial direction, in addition to the conventional bowed profile, was adopted for the stacking of thestationary blades.
On the other hand, it has also become possible to predict drain trajectories precisely using the flow analysis
described above, so that the positioning of the drain slits
can be optimized in order to reduce losses caused by drain(moisture losses) peculiar to the LP end blades.
3.4 Seal technology
In developing a new high efficiency steam turbine,
MHI has striven to develop and apply new sealing andclearance-controlling technologies that contribute toimproving turbine performance, as well as the technologies to improve the performance of blades. The new
sealing technologies also make it possible to reduce theaxial span needed to seal each section of a turbine, compared with conventional labyrinth seals, by improving
sealing performance. This also allows the design of the
shaft system and blades to have some margin.
3.4.1 Leaf seals
The structure of leaf seal is shown in Fig. 66, and themechanism of its operation is shown in Fig. 7
7. The leaf
seal is a seal based on a new design concept that differsfrom non-contact type seals represented by conventional
labyrinth seals and from contact type seals such as brushPushing force due topre-pressure of the setting

Leaf
Lifting force due to sealdifferential pressure

Rotor surface
Direction ofrotation

Lifting force due tohydrodynamic pressure

Fig. 7 Mechanism of leaf seal operation
The tip of the leaf is lifted-up by a balance of the pushing force due topre-pressure of the setting, lifting force due to hydrodynamic pressure
generated during rotation of the rotor, and lifting force due to thedifferential pressure of the seal.

seals whose application has been expanding recently.
This seal consists of a number of thin metal plate (leaf)
inclined in the circumferential direction so that the tipof the seal is kept in a non-contact state with negligibly
small clearance when the rotor is rotating. This is done
by a lifting force produced due to a hydrodynamic pressure effect acting between the tip of the leaf and the rotor.
The result is that both the seal and rotor are prevented
from wear and the durability of the seal is increased when
the turbine is running, different from contact type seals
such as brush seals. In addition, since the seal itself isin the shape of plate with axial width, it has a higher
rigidity in the direction of the pressure difference andthe sealing function can be kept up to a higher differential pressure compared with brush seals.
Fig. 8 shows the results of the verification test of seal
performance and lifting characteristics (test to verify theelectricity discontinuity between the seal and rotor) carried out in the shop. The results confirm that the flowrate through the seal can be reduced to about one-thirdthat of conventional labyrinth seals. The result of theelectricity discontinuity test also indicates that the lifting-up of the seal is performs well even if the seal iseccentrically positioned against the rotor. The leaf seal
has already installed and tested at the existing steam
turbine of the T-point power plant and soundness was
confirmed during inspections carried out one year after
the verification operation was begun. The further improved seals are applied to the new type steam turbine
for the T-point.
3.4.2 ACC (Active Clearance Control)
The structure of the ACC is shown in Fig. 9
9. The ACC
seal is a seal with a structure in which segments of labyrinth seal rings are made to be movable in the radial
direction. When the turbine is starting, stopping or during turning operation after stopping, the segments areraised by a spring force to keep the clearance between
the rotor and the seal fins large. On the other hand,when the turbine load is increasing, the seal segments
are shifted until the proper clearance is maintained radially toward the center by utilizing the pressure

Direction of rotation
Fig. 6 Structure of leaf seal

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol.40 No.4 (Aug. 2003)

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Measurement ofpotential difference: Labyrinth (Clearance: 0.5 mm, 4 stages): Leaf seal (Predicted): Measurements in test

1 000

Test rotor

Amount ofleakage
1/3

500
0

1
2
3
4
Differential pressure (kg/cm2)

1.2: Electricity continuity: Rotating speed

1.0

Leaf

Slip ring5

Concept for electricity
continuity measurement: Electricity continuity: Rotating speed

6 000
5 000

0.8

4 000

0.6

3 000

0.4

2 000

0.2

1 000

0.0
0

50 100 150 200 250 300 350 400
Time (sec)
At time of starting0

Rotating speed (rpm)

1 500

Electricity continuity
measurement between
the leaf and rotor (V)Flow rate (kg/h)

2 000

0
50 100 150 200 250 300 350 400
Time (sec)
At time of stopping

Fig. 8 Results of verification tests of leaf seal performance and lifting characteristics of the leaf

seal. Based on these results, these seals have been
adopted to nine turbines including a 700 MW unit andhave started actual operations.
In the new type steam turbine developed for the Tpoint, four stages of the ACC seal are installed in theline at the HP dummy ring. In this case, wear of theseal fins due to deformation of the casing during starting and stopping of the turbine is avoided by controlling
the pressure distribution and spring force of each segment. During the rated load operation, the clearance iskept small in order to reduce any leak losses and to improve the performance of the turbine.

Stationary side
P1

SpringPressure(radial direction)

Clearance
duringoperatingHP side
P1

P1

Pushing
force

Sealing surface
Seal ringLP sideP2
Leak steam

Rotation side
Pushing
force
Pressure drop
through sealing fins
Axial direction

P2
Differences inpressure before
and after seal

4. Verification tests on the actual turbine
The new high efficiency steam turbine provided withvarious new advanced technologies and installed at the
T-point verification power plant replacing the existingturbine began operations in May 2003. In this turbine,pressure and temperature sensors have been installedat the necessary points inside the turbine casing in order to confirm the improvement in the performance ofeach component, that achieved through the applicationof new technologies, as well as the improvement in theperformance of the turbine as a whole. The measurement of the internal flows in the IP blades, LP blades,
and the exhaust hood is also carried out using Pitot-traversing devices. In addition, confirmation of theperformance of the seals was carried out by measuring
the differential pressure through each seal and the gap
Fig. 10
between the rotating parts and stationary parts (Fig.
10).
The test results show that improvements in the performance of entire turbine were as expected. The results
also confirmed that the performances of the new highFig. 9 Construction of ACC
Seal ring moves in the radial direction as a result of the difference inforce between the spring force and the force due to the differences inpressure between the inner and outer circumference of each seal ring.

difference for sealing. Then, the narrowest clearance iskept during the loaded operation.
The verification test of the ACC seal in the actualmachine has already been carried out at the existing
steam turbine of the T-point power plant. The movement of the ACC seal segments was measured using gap
sensors. As a result, it was confirmed that the clearance enlarged and narrowed together with the start andstop of the turbine, thereby ensuring that clearance control is performed precisely. Inspections carried out one
year after the operation of the turbine confirmed thatthe seal fins on the ACC seal segments remained sound,while traces of wear were found in the seal fins of theconventional segments installed adjacent to the ACC

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol.40 No.4 (Aug. 2003)

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: Pressure and temperature measurements

Amount of removed drain
Performanceof leaf seal

: Measurements by Pitot-traversing device
Clearance
Performanceof diffuser

Performanceof leaf seal

Clearance
Pressure
distribution
at HP inlet

Pressure
distribution
at IP inlet

Clearance

Performanceof leaf seal
Performance of
new HP reaction
bladesPerformanceof ACC
Performance of
new impulse
bladesPerformanceof leaf seal
Performance of
new IP reaction
bladesPerformance andblade vibration of
36 inch LP end
bladesPerformance of
exhaust hoodFig. 10 Special measurement points in the new steam turbine for the T-point

Symposium on Power and Energy Systems (SPES 2002), Tokyo, (2002.6), p.141(5) V.S.P.Chaluvadi et al., Blade Row Interaction in a High Pressure Steam Turbine, Transaction of the ASME, Journal of
Turbomachinery Vol.125 No.1 (2003) p.14
(6) Shige et al., Development of Large-Capacity Highly Efficient
Welded Rotor for Steam Turbines, Mitsubishi Heavy Industries Technical Review Vol.38 No.1 (2001) p.6

performance blades applied to the HP section, the IP
section and the LP end blades as well as the advanced
components such as the leaf seals, ACC seals, and passage for reducing inlet and outlet losses were achieved
as planned.

5. Conclusion
MHI has successfully developed a new high efficiency
steam turbine by integrating a range of techniques to realize the latest advanced technologies. Results ofverification tests carried out with the new steam turbine
for the T-point power plant confirmed that improvementsin performance could be achieved as intended, and verified the reliability of the turbine and its each component.
The new technologies adopted in this new type steam turbine can contribute to the improvement of the efficiencies
of a wide range of turbines from small and medium sized
turbines to large scale turbines. Hence, it is planned thatthese technologies will be successively applied to both
newly installed turbines and existing units.
MHI will continue to develop advanced technologies
aimed at achieving ever higher levels of efficiency inpower plants and higher performance in steam turbines
through the application of these technologies.

POWER SYSTEMS HEADQUARTERS

Eiichiro Watanabe

Yoshinori Tanaka

Takashi Nakano

TAKASAGO MACHINERY WORKS

Hiroharu
OhyamaKeizo
TanakaNAGASAKI RESEARCH & DEVELOPMENT CENTER,TECHNICAL HEADQUARTERS

References(1) Tanaka et al., Feature and Operating Experience of 1000 MW
Class Steam Turbine with Highest Efficiency in the World,
Mitsubishi Juko Giho Vol.39 No.3 (2002) p.132(2) Yoshikuni KADOYA et al., "Alloy Design and Production of
an Advanced 12Cr Steel Rotor Applicable to Elevated Steam
Temperatures", Fifth International Conference on CLEANSTEEL (1997)(3) Sugitani et al., Development of Advanced High Performance
Blades and Their Operating Experience, Mitsubishi Heavy
Industries Technical Review Vol.31 No.3 (1994) p.125(4) Hiroharu OHYAMA et al., Development of High Efficiency
and Reliability Low Pressure End Blade, The 8th National

Masanori
Tsutsumi

TAKASAGO RESEARCH & DEVELOPMENT CENTER,TECHNICAL HEADQUARTERS

Toshihiro
Miyawaki

Tanehiro
Shinohara

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol.40 No.4 (Aug. 2003)

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