Whole Number 210

Thermal Power Plants

Applying our plant know-how for the stable supply of electricity

Air-cooled generator

Private-use power producing equipment

Non-reheating steam turbine

Since producing our first steam turbine in 1959, Fuji Electric has manufactured more than 464 turbines steam having a total combined output capacity that exceeds 23,619 MW, and has delivered turbines these to various countries throughout the world. In the industrial sector, Fuji Electric Japans shipped first supercritical, pure transformation plant in 1973, achieving higher operating than ever efficiency before. This has become the mainstream type of thermal power plant in Japan. medium Among capacity generators, Fuji has also produced and delivered the worlds largest class 162 single-cylinder steam turbines. In the geothermal power sector, Fuji delivered the first MW facility in Japan in 1960, and boasts a successful track record of producing generators that commercial 1,661 MW, such as the largest class of 110,000 kW generators. Fuji Electric is counted as one of exceed leading thermal power equipment manufacturers in the the world.

F u ji E le c tric s T h e rm a l P o w e r E q u ip m e n t

Thermal Power Plants

CONTENTSTrends and Future Outlook for Thermal Power Plants 70

Fuji Electrics Medium-capacity Steam Turbines FET Series

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Cover photo: Thermal power generation in Japan has been affected by the slowdown in demand for electric power and the decline in electric utility rates, and power companies have dramatically curtailed their investment in plants and equipment. IPP power generation has also fallen,1970s-like boom in power and a generation for private use is not expected. Overseas in countries such as China, India and Brazil, however, the potential for future growth is seen as large, and the construction of new power plants brisk. part of this trend toward supAs plying plants and equipment overseas, the co ver pho to sho ws Irelands West Offaly Power Station, which was delivered as a fullfledged coal-fired thermal power plant. The design has cleared the preliminary safety protocols common to both Europe and North America, and is a model of the power plant technology to be constructed overseas in the future. Also shown on the cover is a compact-size, nonreheating turbine, for which rapid growth is anticipated in the overseas markets.

Present Developmental Status of Fuji Electrics Turbine Generator

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Small Capacity Geothermal Binary Power Generation System

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Recent Technologies for Geothermal Steam Turbines

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Recent Technology for Reusing Aged Thermal Power Generating Units

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Head Office : No.11-2, Osaki 1-chome, Shinagawa-ku, Tokyo 141-0032, Japan

http://www.fujielectric.co.jp/eng/company/tech/index.htm l

T ren d s an d F u tu re O u tlo o k fo r T h erm al P o w er P lan tsHiroshi Nishigaki

1. IntroductionRecent events have caused modern society to appreciate anew the benefits it derives from electricity. A wide-ranging massive power outage extending from the northeastern United States to Canada and a power throughout all of Italy have occurred, and failure have had large impacts on the life of residents in those In Shanghai, rotating power outages have areas. been implemented for years and are a large impediment to normal business activities. In Japan, a stoppage of the operation of all nuclear power plants owned by The Electric Power Co., Inc. caused a great deal Tokyo of anxiety, but aided by the cool summer weather, did not result in a power outage. When ultimately a large-scale power outage occurs, trivial problems grad- increase and may potentially cause the ually collapse systems. of large Power plants are part of the infrastructure of modern society and it is essential that these power plant facilities by constructed so as to achieve a higher reliability. Moreover, it is the mandate level of of companies involved in this industry to contribute to society by realizing higher performance and lower cost.

of the BRICs (Brazil, Russia, India and China) wherehas been a significant increase in demand there for electrical power, for Libya which has recently returned to the international arena, and the Southeast Asian countries of Indonesia and Vietnam. In these coun- the supply of electrical power has not caught tries, up the speed of economic growth and with industrializa- demand for many new power tion, and this generating plants is expected to continue for several years. These plants will be mainly medium and small power capacity facilities, which is Fuji Electrics area of expertise. has a track record of many Fuji Electric successful including pure power generation applications and cogeneration plants based mainly on coal-fired power generation, and combined cycle power generation connecting an add-on to an existing achieved by gas turbine .

3. Technical TrendsFuji Electric was founded approximately 80 agoyears through a partnership between The Furukawa Ltd. and Siemens AG., to Electric Co., introduce technology to Japan at a time when European US technology was already widespread. Fuji Electric has involved in the production of thermal been power for approximately 40 years and has plants supplied many distinctive products by introducing technology from Siemens during construction of mainly Table 1 shows the history of utility power thermal plants. in Fuji Electrics main technologies and growth businesses. Recently, Fuji Electric has delivered a ultrasupercritical pressure steam turbine to the Isogo Thermal Power Station of The Electric Power Develop- (EPDC). This ultra supercritical ment Co. pressure steam turbine increases the efficiency of the power or in other words, reduces the plant, environmental load. Figure shows a view of the entire EPDC 1 Isogo Thermal Power Station Unit No. 1. Meanwhile, with the deregulation of the electric power industry, power plants are now being constructed by independent power producers (IPPs) and Fuji Electric is supplying various types of economically beneficial equipment to these plants.Vol. 51 No. 3 FUJI ELECTRIC REVIEW

2. Market TrendsThe climate surrounding Japans domestic electric utility industry is as severe as ever due to sluggish the demand for electrical power, the growth in ongoing in electrical power rates, the advancement decrease of electric utility deregulation, the establishment of new environmental taxes, and the rapid rise in prices of such fuels as oil and coal. Power generation by means of renewable energy has been favored following the enforcement of the Special Measures Law Concerning the Use of New Energy by Electric Utilities (RPS law) then the Kyoto Protocol, which came into effect and in February 2005. However this market sector will be stalled in a wait-and-see situation for the next 1 to 2ears, during which time, efforts to develop new y power are expected to sources idle.n overseas markets, there is strong demand I for electrical power in both the public and private sectors 70

Table 1 History of changes in Fuji Electrics main technologies and businessesEra Category 1970s TEPCO Ooi Thermal Power Station, Unit No. 3 (first pure sliding pressure operation in Japan) 1980s EPDC Ishikawa Coal Thermal Power Station, Unit Nos. 1 and 2 (high-temperature turbine) Okinawa Electric Power Makiminato, Unit No.9 (Fully automated oil thermal power) 1990s Tohoku Electric Power Noshiro Thermal Power Station, Unit No.1 (50 Hz, 600 MW largecapacity tandem machine) 2000s EPDC Isogo Thermal Power Station, new Unit No.1 (600 MW ultrasupercritical pressure plant)

Thermal power plants for utility in Japan

Kansai Electric Power Miyazu Energy Research Center, Unit No.2 (DSS operation) Fuji Electric Gas Turbine Research Center (69 MW gas turbine made by Siemens) UBE Power Center (60 Hz max. global vacuum pressure impregnated insulation air-cooled generator)

Thermal power plants for private use and IPP plants in Japan

UBE Industries, Ube plant (145 MW, largest privateuse power plant in Japan)

Kobe Steel, Kakogawa Works (axial flow exhaust turbine) Philippines: Battan, Unit No.2 Thailand: Mae Moh, (full-scale entry into overseas Unit Nos. 4 to 13 business of thermal power plant (largest thermal power plant in for utility) Southeast Asia) Australia: Gladstone Unit Nos. 1 to 4 (direct hydrogen-cooled generator) Taiwan: FPCC FP-1, Unit Nos. 1 to 4 (60 Hz, 600 MW large-capacity tandem machine) Bangladesh: Meghnaghat (combined-used turbine, largecapacity air-cooled generator) Indonesia: Wayang Windhu, Unit No. 1 (worlds largest singlecasing geothermal turbine) TEPCO, Hachijojima Geothermal Power Station

Overseas thermal power plants

Pakistan: Jamshoro Unit No.1 (largest indirect hydrogencooled generator)

Geothermal power plants

EPDC Onikobe Geothermal Power Plant (generator delivered)

El Salvador: USA: Coso Geothermal Ahuachapan, Unit No.3 Power Plant, Unit Nos. 2 to 9 (full-scale entry into (modular turbo-set) geothermal power plant business)

Technical development

Improved 12Cr rotor for Completion of new high temperature Shiraishi Factory 22 kV-class F resin/ F insulation Automated stator Direct hydrogen-cooling method winding machine F resin/ F II insulation Global vacuum pressure Experimental prototype of 126 impregnating facility for medium MVA air-cooled generator and small-size generator Global vacuum pressure 22 kV-class global impregnating facility for vacuum pressure large-size impregnated insulation system

High-temperature 12Cr rotor

Fig.1 EPDC Isogo Thermal Power Station new UnitPlant1 Fig.2 View of the entire UBE Power Center No.

Trends and Future Outlook for Thermal Power Plants

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The construction of utility thermal power plants in Japan has reached as standstill at present and is not expected to recover soon. Additionally, IPP Figure shows a view of planning become has also 2 saturated. UBE Power Center Plant that was the entire constructed as an IPP plant. Fuji Electric will continue to develop products while carefully monitoring these trends in the future. The technical trends market of medium and small capacity power plant equipment, which are Fuji Electrics main products at present, are described below.3.1 New small-capacity non-reheat steam turbines

Moreover, appropriate advice concerning preventative is also provided in order to avoid maintenance downtime due to mechanical failure.

4. Steam TurbinesVarious improvements to steam turbine technology have been previously requested in order to enhance the thermal efficiency and space efficiency of thermal power plant facilities. In the large-capacity generator Electric has advanced the development sector, Fuji of MW-class supercritical pressure steam 600 andturbines, with the improved thermal efficiency together due to higher temperature and pressure steam conditions and the development of large turbine blades, has reduced the number of low-pressure turbine casings to realize more compact turbines. In the medium and small-capacity generator sector, technology has been developed to increase the efficiency, compactness and serviceability of steam turbines, enabling smaller initial investment and higher reliability. Fuji Electric has continued to improve the space efficiency by migrating from the conventional three-casing structure to a two-casing structure and then to a singlecasing structure. With the increase in capacity, the ability to maintain stability of the shaft system as the distance bearings increases in a steam turbine between and measures to prevent erosion of the low-pressure blades presented technical challenges that have since been overcome due to greater analytical precision and structural improvements. A single casing turbine of MW maximum capacity has already been 165 brought to market and is achieving good operating results. In order to reduce the construction costs associated with aombined cycle steam turbine, axial flow steam c tur- are being widely used. Fuji Electric will bines continue to advance the development of technology to improve and lower the cost of medium and efficiency small capacity turbines.

Fuji Electric has newly developed a steam turbine (FET-N type) having a simple configuration suitable capacity (25 to 50 MW) applications. A for small first is already in operation in China, and a unit second already been shipped and is being unit has installed onsite.3.2 Large non-reheat steam turbines

Fuji Electrics expertise is greatest in the technical field that involves private-use power plants. These have multiple steam processes and plants require control. In a turbine, the process steam complex flow is controlled as required, and at the same time rate the electrical power output is adjusted. In the past, the output power was approximately several tens of MW in response to market needs, technology has but, been developed to achieve larger turbines capable of greater MW than 160 output.3.3 Single-casing reheat steam turbines

Fuji Electric has developed a reheat steam turbine configured with a single casing instead of the conventional two-casing construction, and a first unit has already been placed in service. Shortening the length turbine shaft has enabled a reduction of the in construction costs, including civil engineering work, realization of a more economical and the plant.3.4 New digital control system

5. GeneratorsAir-cooled generators, due to their low construction cost, short production time and ease of operation and maintenance, are gradually beginning to be used in applications traditionally associated with hydrogencooled generators. At present, Fuji Electrics aircooled generators are suitable for applications ranging up to MVA for 60 Hz generators and 300 MVA for 50 280 Hz generators. Because air, which has lower cooling performance than hydrogen, is used as a coolant with capacity generators, Fuji Electric implemented larger a technical verification test by fabricating a 126 MVA experimental generator and taking on-line measure- more than 1,000 on the stator and rotor. ments at The results of this test demonstrated that it was possible to manufacture a large-capacity air-cooled generator having sufficient reliability.Vol. 51 No. 3 FUJI ELECTRIC REVIEW

A new digital control system (TGR) that provides integrated control for a turbine and generator, and Fuji Electrics MICREX-SX, which is a uses highperformance PLC, has been placed into commercial it being applied to other operation and plants.3.5 Remote monitoring

A remote monitoring system has been developed that periodically gathers operating status data from generating equipment that has been delivered power toremote overseas location and transmits that data a via Internet to a maintenance department, where it the is received. Thus, even when a failure occurs in remote onsite equipment, the customer can be instructed to the appropriate measures, thereby quickly as mini- downtime and reducing the customers mizing loss. 72

For hydrogen-cooled generators, indirect cooling is also being used instead conventional direct cooling. cooling is the method of cooling used in Indirect aircooled generators, and technology acquired during the development of air-cooled generators is also being to hydrogen-cooled generators. At present, applied the applicable range for indirect hydrogen-cooled genera- an upper limit of 450 tors has MVA.

tions of equipment for removing this hydrosulfuric gas, which previously had been released into the atmosphere .

7. After-sales ServiceAfter-sales service has been implement thus far in a close working relationship with the user, mainly by providing periodic inspections of delivered equipment and replacing or repairing parts for preventative These activities include responding maintenance. to incidences of sporadic failure and also providing vari-suggestions for improvements. Periodic ous inspec- necessary to ensure the safety of a plant, tions are and in Japan, this is a characteristic of a regulated industry protected by laws. As the relaxation of regulations results in a shift from mandatory periodic inspections to voluntary inspections, technical sugges- manufacturers are being closely tions by scrutinized based on economic criteria to determine whether they are absolutely necessary for ensuring stable operation. backdrop, specialized maintenance Against this service companies have already begun operating in Europe US. The necessity for periodic inspections and the is also being recognized in Southeastern Asia, and these European and US maintenance companies are early participants in those markets. Fuji Electric intends to leverage its reliable and responsive after-sales service to insure the stable operation of power in order plants, compete as an equipment manufacturer and to against these specialized maintenance companies. After-sales service for an aged plant can encompass plans for major renovations or renovation of the entirein order to reuse the plants facilities. These plant types can be diverse and may involve conversion of plans of type of fuel that was used originally at the time of the construction, massive renovation of the entire plant such as changing the operating principle of the power and repairing or replacing worn out parts plant, to prolong the service life of the equipment or reducing maintenance cost and enhancing the efficiency of the plant. Technology has also made great advances since the time of the initial construction and a wide range of measures are available for problem solving.

6. Geothermal Power PlantsThere are presently no plans for the construction of geothermal power plants in Japan. The reason for this of plans is the high cost due to risks lack associated with underground resources, the large initial investment that is required, and the long lead time required to coordinate and reach a consensus concerning treat- of national parks and existing hot ment springs. small-scale binary power generation However, that utilizes previously unused steam and hot water from aot springs region is a promising model for h economical power plants because there are no geothermal drilling costs and the lead time is short. The RPS law has been enforced since 2003, obligating electrical power suppli-use renewable energy. Because ers to geothermal generation is also included in binary power this category, the construction of geothermal power plants is expected to gain momentum. due to the slowdown in the Overseas, global economy that began with the Asian currency crisis 1997 through 1998, developing countries from post- or froze almost all their geothermal poned development plans that required an initial investment or involved investment risk. However, in response to the increase for electrical power that accompanied in demand the subsequent economic recovery, plans that use public such as yen loans or financing from the funds Asian Development Bank for investigating geothermal resources and constructing geothermal power plants have been reinvigorated. geothermal power plants In the past, commonly adopted affordably-priced single-flash cycle. In order to achieve a more efficient use of resources, doubleflash cycle, combination with binary cycle using brine flash cycle and cogeneration of hot water from for house heating using exhaust or extracted steam are adopted . In order to improve plant efficiency and the utilization rate of geothermal turbines, the following technologies are recognized as important for geother- plants: technology for preventing the mal power adhe- and removing silica scale from sion of turbines, techniques and easy maintenance, monitoring and measures to prevent the adhesion of silica on reinjection piping or a re-injection well. Geothermal steam contains a minute amount of hydro-sulfuric gas as environmental quality standards become and, strict- increase is expected in the number of er, an installaTrends and Future Outlook for Thermal Power Plants

8. ConclusionThermal power plants are industrial goods that produce electricity. Moreover, these plants are impor- customers and are presumed to have a tant to service life of greater than twenty years. Accordingly, the reliability of a power plant is considered most important, followed by after-sales service and then economic As demand for electrical power efficiency. increases the world, Fuji Electric intends to throughout continue to supply power plants that provide to strive reliabili- performance and low price in accordance ty, high withneeds of the customers. 73

F u ji E lectrics M ed iu m -cap acity S team T u rb in es F E T S eriesKoyaYoshie Michio Hiroyuki Abe Kojima

1. IntroductionRecently, de-regulation of the electric power industry and rising needs for advanced solutions to environmental concerns, have caused a great change in the of thermal power generation. Further area improve- higher efficiency, a more compact ment for design, operating performance, and better optimal maintain- higher reliability is increasingly ability and requested of the steam turbine industry. For medium capacity steam turbines, there has been an increase in the use of combined cycle plants, in addition to their conventional use for private power generation. Accordingly, larger capacity single units, combined with advanced technology for higher efficien- been more in demand. Moreover, the cy, have axialexhaust type and the upward exhaust type flow steam configurations are more favorable and turbine popular, due to their lower construction costs. Features of Fuji Electrics FET Series of standard medium capacity steam turbines , which achieves high efficiency with low-cost, are introduced below.

function of extracting steam for various uses such as plant processes or utilities. The medium capacity steam turbine FET Series is a standardized model suitable for a wide range of steam and series output conditions. The types of steam turbines, applicable steam conditions, output range and the rotational speed of steam turbines are listedTable 1. the in2.2 Block design system

2. Concept of the FET Model Series2.1 Applicable range

The standard FET Series of steam turbines utilizes a modular block design system in which suitable selected from several standardized blocks are components (Fig. 1) corresponding to the various required specifications and steam conditions of each project. of modular system design enables the This type best selection of blocks over a wide application range. standard component has a proven Each track record of success, and a highly efficient turbine model realized by the proper selection of the can be optimum blocks. Standardization by means of this block design will shorten the production lead-time system and reduce the production cost. As a result, a steam that satisfies customer requirements can turbine be provided with a shortened delivery time.

Specific demands for medium capacity steam turbines concern not only power generation, but also to industrial applications that provide relate theTable 1 Range of Fuji Electrics medium capacity steam turbine FET SeriesCondensing type Back pressure type Single / Double controlled

3. Scaling-up to Larger Capacity FET TurbinesMany steam turbines for private power usegeneration- the capability to provide process and having steam have been furnished. Due to the worldwide trend de-regulation of the supply of electric toward power, companies are increasingly joining IPPs private (Independent Power Producers), and the need to scaleup unit capacity of steam turbines has the increased. 101 MW FET turbine was put After the into operation in 1994, larger capacity units have been successively developed within the FET series, in accordance with market trends. The crosssectionalof a recent FET steam turbine is shown drawing Fig. in 2, and the specifications of these turbines are listed inTable 2.

Type

extraction condensing type Single / Double controlled extraction back pressure type Operable as a mixed pressure type or an extraction / mixed pressure type. 20 MW to 180 MW Main steam pressure : 130 bar or less C or Main steam temperature : 540 less-1 50 s (3,000 rpm) or -1 60 s (3,600 rpm)

Range of output Steam condition Rotational speed

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Vol. 51 No. 3 FUJI ELECTRIC REVIEW

Fig.1 Block design system of the FET SeriesFront bearing pedestal part High pressure part Extraction part Low pressure part

115 260 400 400-AX 120 125 130 135 FET Turbine Series Output range T Series (original type) 225 Exhaust direction 3-80 3-100 4-130 4-150 4-175 5-200 1.2/1.4/1. 6 2.3/2.2 3.2/2.8 4.0/3.5 5.0/4.4 6.3/5.6 8.0/6.9 10.0/8. 9

20 to 180 MW Upwards / Downwards

N Series (small capacity type) to 50 MW Upwards / Downwards 20 AX Series 50 to 180 MW Axial exhaust

Fig.2 161.99 MW steam turbine, assembled cross-sectional Steam turbine specifications drawingLP casing Reaction stage blades

Table 2Formosa Chemicals &Formosa Power Fibre Corporation (Ningbo) Ltd. Co. SK-G4 (Taiwan) NB-1 (China) Model Single-extraction condensing 147.88 MW C 123.6 bar / 538 / 7.7 bar 0.088 bar Single-extraction condensing 161.99 MW C 123.6 bar / 538 / 8.3 bar 0.088 bar-1 50 s (3,000 rpm)

Front bearing pedestal

LP blades

Output Steam condition extraction pressure Vacuum Operation start date

-1 Rotational speed 60 s (3,600 rpm)

May 2000

July 2004

Rotor Outer casing Inner casing

Rear bearing pedestal

Fig.3 Reaction type steam turbine rotor

3.1 Highest internal efficiency with throttle governing system

The FET steam turbine has adopted a design that features a throttle governing system and a double shell structure with outer and inner casings, casing similar of large capacity turbines for utility to that power generating use. This design achieves higher efficiency reaction blades in all stages, and does by utilizing not a nozzle governing impulse blades with use partialFuji Electrics Medium-capacity Steam Turbines FET Series

Reaction stage moving blades

LP moving blades

F admission loss (seeig. 3). Moreover, wear due to the 75

Fig.4 Advanced series low pressure blades Cr steel Fig.6 Creep rupture test result of 2 %L-0 LP moving blades 1,000

Fig.5 Erosion-resistant of the N Series casing Fig.8 Overview structureto condenser

Stress (MPa) 100 Drain slits Stationary blades 10 17 18 19 20 21 Moving blades Route of drain flow

Larson Mirror (time temperature) parameter LMP L-1 LP moving blades (20) = T LP moving blades L-2 [20+log( t )] / 1,000 LP rotor Lean radial stationary blades

Fig.9 Analysis of inlet part with temperature distribution

Fig.7 N Series steam turbine, assembled cross-sectional drawingRotor

LP stationary blades ring

impact of solid particles (particle erosion) or deteriora- blade surface can be reduced and tion of the deterioration of performance with aging will be minimal, due to lower steam velocity with reaction blades than the in impulse the stages.3.2 Adoption of advanced series low-pressure blades

Highly efficient low-pressure blades, designed ing uscompressible supersonic flow analysis (threedimensional time marching method), are utilized. A lean stationary blade, which curves toward radial the direction of the circumference is adopted in the Fig. 4). Moreover, final (L-0) (see lower half stage of enhanced performance is achieved by adopting a shroud the first stage (L-2) moving blade, ring in while continuing to maintain the wide range frequency of -5 to +3 %, which has been a allowance characteris- existing free standing blades (see tic feature of upper Fig. 4). half of3.3 Erosion prevention

Operated in wet steam, low pressure moving blades erode due to the impact of water droplets, and erosion increases in severity as the blade this length larger. To reduce this damage, the grows following have been implemented Fig. 5). measures (seeThe leading edges of the moving blades have (1) been hardened, and the surface hardness of flame the material has been blade improved. 76Fuji Electrics Medium-capacity Steam Turbines FET Series

(2) The final stationary blade (L-0) of larger models has a hollow structure with drain slits provided on surface in order to drain the water its droplets the condenser, thereby reducing the away to drain on latter-stage moving attack (3) blades. clearance after the trailing edge The axial of stationary blades has been enlarged sufficiently to decrease the size of water droplets that adhere steam flow onto the stationary from the blades, reducing the drain attack on thereby following moving blades. (4) The trailing edge of the stationary blades has been thinner, so as to minimize the size of made water droplets from the edge of the blades, thereby the drain attack on following reducing moving blades. efficiency by maintaining the same high steam condi- the medium class FET (up to 130 tions as bar/538C). the design 3.4 Adoption of 2 of Cr steel rotorwas confirmed by Reliability % simulating According to the increase in rotor diameter and the operating conditions, including the analysis LP of blade length corresponding to larger steam temperature and stress distributions or turbine the casing, on the basis ofthe rotor have proven deformations capacity, the centrifugal loads on plenty of well on Fig. under actual operating grown The strength 9). FET larger. turbines conditions (see was evaluated using finite element analysis and frac- 4.2 Adoptionprocedures. Accordingly, ture mechanics of high efficiency impulse stages differential 2 % adoption of a nozzleselected for heat-treated the Cr forged steel was governing system, With the Curtis stage a 60 -1 machine in which the order a shaft material of is applied as the top stage in Figure s the core part will be chamber pressureshows the to stress in reduce the wheel very and high.temperatureInresults of to reduce the secondary loss creep rupture test an effort this 6 effectively. material.Curtis stage, a three-dimensional blade of the profile is used in which Series) design 4. Compact FET Turbine (N the profile is curved in the The selectionthe small capacity FET turbines direction of of circumference in order to maintain has beenthe characteristic high efficiency of the FET N improved with the development of the turbine Fig. Series,was ). (see which 10 started and completed in Figure 2002. As a result, a 1.7 % improvement is expected shows cross-sectional drawing 7stage efficiency, compared in and typical specifications of the N to the existing blade Series. design.Vol. 51 No. 3 FUJI ELECTRIC REVIEW7 7

control valve

Extraction Steam control valve Main stop valve

Main steam inlet nozzle

HP part

Front bearing pedestal

Reaction stage blades

LP casing

Rear bearing pedestal

max.1

LP blades

max.2Rotor Outer casing

max. principal stress

Steam turbine for Shanghai Chung Loong Paper Co., Ltd. (China). Model Output Steam condition extraction pressure Vacuum Rotational speed Operation started since Single extraction condensing type 26 MW 123.6 bar/538 C/9.8 bar

0.079 bar 50 s (3,000 rpm) March 2005-1

4.1 Compact design by nozzle governing impulse stages for the small capacity model

The normal FET turbine has a throttle governing system and double shell casing structure as shown However, better flexibility for load change above. by and night is requested for small-capacity, day privategeneration turbines, and thus the nozzle power governing system will be more suitable for these conditions. N Series has adopted a nozzle The FET governing system and single shell casing as the most compact and suitable system for this application Fig. 8). (see The FET N Series has been developed for high

Fig.10 Three-dimensional impulse stage

Fig.12 AX Series steam turbine during assembly

Three dimensional impulse blades

Outer casing

Rotor

Central Geradora Termeletrica Fortaleza S.A. steam turbine (Brazil)

cations of an AX Series turbine.5.2 Utilization of fully electric protection devices

Model Output Steam condition Vacuum Rotational speed Operation start date

Mixed pressure condensing type 117.8 MW C 73.3 bar/517 0.065 bar 60 s (3,600 rpm) February 2004-1

With the axial flow exhaust type turbine, the Fig.11coupling fortype AX Series steam turbine motor and Axial exhaust the generator, turning shaft protection device are installed in the front pedestal because pedestal is located in the exhaust the rear hood. Therefore, to Front bearing pedestal simplify the front pedestal as much Steam control Exhaust nozzle as valve possible and to improve the maintenance, all Rear Main stop protection devices, such as the over-speed governor bearing valve and failure protection system have pedestal thrust adopted a fully electric configuration Fig. 13). (see

Fig.13 Concept of fully-electric protection deviceSpeed sensors for electric emergency governor

On load test

3500 /53 BENTLY NEVADADisplacement sensors for electric thrust protection device

3500 /42 3500 /32 BENTLY NEVADA Main steam inlet nozzleBearing oil pressure trip device

k y rac are rela Hardw SActuator for main stop valve Actuator for steam control valve

PSVacuum trip device

Relay circuit Relay circuit

PS

S

5. Use in Combined Cycle PlantsDue to the growing global environmental awareness in recent years, the major application of thermal power generation equipment has shifted to combined (CCPPs), which use gas and steam cycle plants tur- in combination to achieve higher thermal bines efficiency. According to this market trend, variations that combine use with a 100 to 200 MW class gas turbine have also been added. For CCPPs, there is great demand for axial flow exhaust type turbines since the and period for construction can be reduced cost greatly structure. Accordingly, the axial flow by this exhaust Series FET was developed, based on type AX existing downward exhaust type FET turbine technology Fig. (see11). CCPPs tend to be constructed in the vicinity of the consumers in order to reduce the power transmission loss. An air-cooled condenser is a suitable choice then, it allows for the unrestricted selection of site since 78Fuji Electrics Medium-capacity Steam Turbines FET Series

Master trip push button Other protection relays

Power supply system

AC

DC battery

locations for the power plant, compared to a water- condenser which requires access to a cooled large amount of river or sea water. In order to operate compatibly with the higher exhaust pressure limita- an air-cooled system, a low vacuum type tion of steam series was turbine added.5.1 Axial flow exhaust type FET steam turbine

Development of the axial exhaust type AX wasSeries completed and the first unit was put into opera- 1999. The AX Series has been utilized in tion in many CCPPs. Figure shows a photograph and lists the 12 specifiVol. 51 No. 3 FUJI ELECTRIC REVIEW9 7

Fig.14 Strengthened low pressure bladesStrengthened low pressure blades

These electric protection devices are also used Fuji in Electrics larger capacity steam turbines, in common with the FET turbines.5.3 Correspondence to air-cooled condenser

The vacuum obtained by an air-cooled condenser lessis than that of a water-cooled condenser. This higher exhaust pressure severely stresses the low-pressure blades in the steam turbine exhaust part.development of strengthened low pressure The Fig. blades has solved this issue (see 14).

6. ConclusionThe medium-capacity steam turbine FET has Series expanded so as to be applicable to a been wide- market. Due to continuous requests ranging for advanced solutions in response to global environmen- de-regulation of the electric tal needs and power industry, the demand for equipment supply with efficiency and lower-cost will increase more higher and in the future. Fuji Electric intends to continue more to advance technical development in order to accommo- growing needs. date these

Table 1 Factory test results of 280 MVA air-cooled turbine generatorOutput 280 MVA 14.7 kV 0.9

Fig.3 Cross-sectional view of 450 MVA indirectly hydrogencooled turbine generator

P resen t D evelo p m en tal S tatu s o f F u ji E lectrics T u rb in e G en erato rVoltage Current Specification Power factor Frequency Thermal class Coolant temperature Excitation system Standard Stator winding Factory test results temperature rise Rotor winding temperature rise 10,997 A Rotating speed 3,000 r/min 50 Hz 155 (F class) 40C Thyristor excitation IEC60034-3 81 K 80 K

12000

HiromichiHiwasa ToruHase KohjiHaga

4500

1. Introduction

Fig.1 280 MVA air-cooled turbine generator

The capacities of air-cooled, two-pole turbine Short circuit ratio 0.52 generators have increased dramatically. About 10 Transient reactance 26.7 % unsaturated value GeneratorGenerator Table 2 Specifications of the 450 MVA indirectly hydrogenyears ago, hydrogen-cooled generator was used in 150 Sub-transient reactance 20.1 % unsaturated value cooled turbine generator MVA- turbine generators, but nowadays, airclass ExciterExciter 98.82 % conventional cooled generatorEfficiency being used in 200 MVA-class efficiency is even and above turbine generators. Meanwhile, at combined cycle power plants, 400MVA-class generators are being coupled to singleshaft or multi-shaft type steam turbines, and the with epoxy resin throughout the entire stator directly hydrogen-cooled stator winding type or the after winding insertionwinding type are directly water-cooled stator into the stator stator appliedgenerators. Based on customer needs for the The following analysis and evaluation core. for were used to advance theoperability, the techniques economy, maintainability and increase in capacity of Fig.2 Cross-sectional view of 280 MVA air-cooled turbine generator generaairtor having the indirectly hydrogen-cooled stator cooled windgenerators. ing (hereafter referred stator indirectly hydrogen(1) Evaluation of to as and rotor winding cooled tempera- three-dimensional flow and generators) isusing suitable. Fuji Electric has ture most 11600 devel- series analytical techniques utilizing the and oped a tempera- MVA air-cooled generators ture of 300 Bearing Bearing Exciter upto-450 MVA indirectly hydrogen-cooled generators finite element method Stator that a global vacuumstray load impregnated use (2) (FEM) Analysis of pressure loss using 4700 insulation resin/GII), (hereafter referred to as electromagnetic system (F field analytical techniques utilizing 3. Technology Rotor for Enlargement in the Capacity the (3) FEM Global VPI insulation system). strength of the rotor Evaluation of fatigue of Indirectly Hydrogen-cooled Turbine Generusing An overview of the technical development strength analytical techniques utilizing ators in involved FEM creation of this product series, in the impor- Shop test results of the 280 MVA air-cooled turbine tant developments of the Global VPI insulation 2.2 A 400 MVA-class indirectly hydrogen-cooled system generatorlarge-capacity generators, and for high voltage turbine generator in which Global VPI insulation auto- manufacturing technology50 Hz, 280 MVA airsystem matic In the abovementioned are described is applied to the stator winding has been below. cooled Fig. 3 shows a crossdeveloped. turbine generator, the type rating was tested with As a representative Figures 1 and no- characteristic test, short circuit Airexample, view and Table 2 lists the ratings2 cooled generator into practical 2. Practical Application of Large-capacity load sectional use. specifications of athe external appearance and characteristic show a photograph of 450 MVA and cooled Generators rise test, and by measurement of test, temperature arawing In consideration of the this the Type rating specifications and the shop d generator.cross-section of economic reasons and of the loss. Air-cooled generators havearesimpler test a listed Table 1. All the generator. Fuji proprietary technology and results for this generator Electrics structure 2.1 Technical features manufacturing than in hydrogen-cooled generators and because results are satisfactory and demonstrate that facilities, the following guidelines were adopted they theno auxiliary systems such as achieved. As regards the cooling methods, the indirect to require a hydrogen required performance has been during gas Additionally, ashop test, the rotor winding development. supply system the sealing oil supply system, or ing cool- The maximum output of the generator to is applied for the stator winding and the as part of (1) the temperature the statormaintenance of airdirect (radial flow) shall be limited by the capability installation, operation and winding temperature cooling be distribution, developed is applied for the rotor cooled and the stator vibration were measured. winding. of generators is quick and easy. Furthermore, airdistribuAnd air coolers are installed in the side of the tion Global VPI facility. cooled stator The rotor is supportedof the generator to generators are results were then compared to the These frame. The rotor and stator by two bearing measured advantageous because their (2) production and toand initial investmentfrom is pedestals on a bed shall adopt the exciterstructure or design positioned be lead-time is short data measurements cost values developed plate, and the same or the low. previously collector the are mounted on the as an indirect airrings Based on the results of verification testing of manufactured generators, and then evaluated. same production method anti-turbine side a26MVAthe comparisons and evaluation, the Based cooled 1 shaft. on prototype generator built in 1999, turbine Fuji Electric has worked and high reliability of this excellent For the stator winding, Global VPI characteristics to develop larger capacity (3) generator. Newly installed manufacturing facilities such air- generator insulation cooled generators and has shiped 50 Hz, 280 MVA system is applied. The stator winding is the rotor as have been automatic brazing equipment for air- verified. impregnated wind80Present Developmental Status of Fuji Electrics Turbine Generator Vol. 51 No. 3 FUJI ELECTRIC REVIEW1 8

Bearing

Stator

Rotor

Ventilation fan plate Cushion

Stator frame Main terminal

Output Voltage Current Power factor Rotating speed Frequency Thermal class Coolant temperature Coolant pressure Excitation system Standard

450 MVA 21 kV 12,372 A 0.85 3,600 r/min 60 Hz 155 (F class) 40C 400 kPa (g) Thyristor excitation IEC60034-3

ing (to be described later) shall be used to the maximum extent possible.3.1 Construction

Fig.4 Impulse-force hammer testRotor

The 400 MVA-class indirectly hydrogen-cooled turbine generator differs from an air-cooled generator in the stator frame functions as a pressure that vessel and bracket type bearings are used, since hydrogen is used as the coolant. The stator and rotor both basically adopt the same construction and manufactur-as the air-cooled generator, ing method however. Moreover, similar to the air-cooled generator, the stator winding also utilizes a Global VPI insulation system, which is one of Fuji Electrics principal technol- order to realize this configuration, it ogies. In was necessary to make the Global VPI insulation system compatible with high voltages. The relevant chapter 4. technical development is described in detail in After Global VPI processing, the completed stator is inserted into the cylindrical stator frame, which is aressure vessel, and secured via a spring plate to p the stator frame. The spring plate, stator and stator frame are welded in the same manner as a large aircooled generator . The rotor winding utilizes the same radial flow direct cooling as the air-cooled generator, but has a thicker conductor due to the larger field current. In case of the air-cooled generator, the the ventilation conductor is formed with a punchhole for the process to enhance the economic efficiency of in order the processing. In the case of the indirectly hydrogencooled turbine generator, that same punch processingused due to the deformation of the punchcannot be out of the conductor, capacity of part manufacturing facilities, and other such factors. However, after investigation of many factors, including careful the clearance of the punching die and the sectional profile conductor, a punch process was realized for of the this fabrication step.3.2 Ventilation and cooling In a large capacity air-cooled turbine

Impulse hammer

ness and arrangement of the stator core block and the arrangement of the rotor winding ventilation axial hole determined using analytical techniques that were had verified with the abovementioned 126 MVA been prototype generator.3.3 Suppressing the vibration of a long rotor

generator, ventilation is implemented using a double flow design. In this design, in order to achieve a uniform distribution of the stator winding temperature, the middle portion of the stator core is provided with atructure that flows a coolant gas from the s outer diameter to the inner diameter of the stator core. On other hand, since hydrogen gas has a lower the density and larger thermal capacity, when the coolant gas passes through the ventilation fan and generator gap, the gas temperature rise is less than in the case of air. Accordingly, ventilation of the 450 MVA indirect hydrogen-cooled turbine generator is implemented with asingle flow design in which a coolant gas flows only the inner diameter to the outer diameter of from the stator core. In order to optimize the gas flow volume distribution in the axial direction, the optimum thick82

As generator capacities increase, rotors are designed to be longer in the axial direction. Consequently however, mass unbalance and asymmetry in the stiffness of the rotor readily cause the shaft to vibrate. issue of vibration must be given Thus, the due consideration . In order to verify double frequency vibration caused by asymmetry in the stiffness of the rotor, a factor which cannot be reduced by balancing the rotor, an impulse-force hammer test was performed as shown 4 to compute the natural frequency in in Fig. the principal axis direction of moment of inertia of area, and the asymmetry was compared with the calculation results of this analysis and results. The comparison were reflected in the design of the compensation slit for rotor pole, which compensates asymmetry in the the stiffness of the shaft.

4. Insulation Technology for the Stator WindingUsing its Global VPI insulation technology, has which acquired over many years, and its been world- Global VPI manufacturing equipment, leading Fuji Electric has been appling Global VPI insulation tech- to turbine generators since 1993, and nology has subsequently delivered approximately 100 units. As capacities of the abovementioned indirectly the hydrogen-cooled turbine generators increase, the capability to withstand high voltages and provide stable insulation quality are required of Global VPI insulation technology. Accordingly, Fuji Electric has developed a lobal VPI insulation system for 22 kV-class G rated turbine generators.Vol. 51 No. 3 FUJI ELECTRIC REVIEW

4.1 Features of Global VPI insulation for turbine generators

4.2 Development of 22 kV-class Global VPI insulation for turbine generators

Global VPI insulation system is advantageous because the stator windings and the stator core are impregnated and hardened together, thereby improv-cooling performance of the stator windings ing the and reliability against loosening of the windings, Figure shows the and realizing less maintenance 5 work. appearance of a Global VPI insulated stator Fig. 6 and shows the cross-section of the stator winding. This VPI insulation for turbine generators Global utilizes the following insulation technologies in order to ensure the reliability of the insulation. heat-resistant epoxy (1) Highly (2) resin pregnable mica paper Highly (3) tape Internal electric field relaxation layer providing high voltage endurance and a long service (4) life Thermal stress relaxation layer providing high cycle resistance heat

Fig.5 Appearance of stator after Global VPI (280 MVA aircooled generator)

Core

Coil

Fig.6 Cross-sectional view of stator winding

Internal electric field relaxation layer

Strand Core

Thermal Main insulation stress relaxation layer

The 22 kV-class Global VPI insulation for tionapplica-MVA-class hydrogen-cooled generators, to 400 the are longer, the insulation is thicker and coils the withstand voltage is higher than in previous stator coil. Thus, Fuji Electric developed this technology by focusing on the taping characteristics and impregnation characteristics of the main insulation layer and reliability of the end corona shield, and the by evaluating the reliability of the Global VPI insulation. 4.2.1 Analysis of the main insulation taping The stator coil is insulated by winding a main insulation tape of mica paper several times around the The insulation characteristics of this stator coil. coil influenced by the taping method and the are thickness of the tape. For an example, and width overlapping main insulation tape affects the state of the break voltage (BDV) value, so that it is required down to study the taping method in order to achieve the maximum BVD value with the same layer numbers. obtain the optimum condition for taping, In order to an analytical software program had been developed and applied. In the operating voltage and withstand electric field was observed to voltage, the concentrate of the cross-section of the stator at the corners coil insulation. While taping, the number of Figure overlapping not decrease at these layers must 7 locations. analysis results of taping with 22 kVshows the class insulation. The number of overlapped tape layers increases at the coil corners, and it was verified thattaping is regular. This result is reflected in the the taping process of the 22 kV coil. 4.2.2 Temperature distribution of end corona shields End corona shield zones are provided at the end the of stator to relieve the potential gradient from the of the coil. The temperature distribution of end the corona shield zones was quantified with end this 22kV-class insulation. Figure shows the temperature distribution of the 8 end corona shield zone while the nominal operating voltage is applied. The maxi- temperature occurs near the edge of the mum slot corona shield, and this is in agreement with the results of surface potential measurements. The maximum temperature rise of 1.6 K was a small value, however. Even in withstand voltage tests, (2 E +1, where E is the voltage [kV]), no abnormalities such as rated flashover discharge were observed. Thus, it has or surface been verified that the end corona shield zones with 22 kV- insulation provide sufficient class functionality. 4.2.3 Evaluation of insulation reliability A straight bar model and full-scale model were manufactured for the evaluation of insulation reliability. A heat cycle test and V - t test were performed withstraight bar model, verifying that that the insulationstable performance in response to heat provided stress sufficient voltage endurance lifetime. and a Moreover, 83

Present Developmental Status of Fuji Electrics Turbine Generator

Fig.7 Fig.11 Automatic brazing equipment in 22 kV model Isolayer distribution over coil surface with taping in both directions

Fig.9 Fig.13 Automatic bending machine Appearance of 22 kV full-scale modelStator core (segment core) ring

Rotating

View from above Stator coil Side view Main insulation layer

Length (mm)

Fig.10 Tan - V characteristics of full-scale model during thermal cycle testing Fig.8 Surface temperature distribution on end corona shield in 22 kV model Fig.12 Automatic transposing equipment

Dummy core

End of slot corona shield Maximum temp. : 1.6 K

Coil end portion

Previously, the end portion of the stator coil has 1 been formed by manually bending the coil, placing it With guard electrode in shape, and then hardening it. An automatic a 0 bending has been newly developed, however, and machine5 0 10 15 20 25 30 is shown inFig. 13. The automatic bending machine Voltage (kV) uses robotic technology to automate all processes from bending the coil end portion into an involute shape and forming, to cutting the conductor at the coil heat Fig. end.of this automatic bending machine achieves the full-scale model shown in 9 was also manufacUse unitured in order to verify reliability of the formity of the involute shape of the coil 5. Manufacturing Automation Technology end insulation, method of manufacture. were fulland including its the brazing filler metal The computed, inserting shorter leadscaleand times. model assumes a 450 MVA indirectly hydrogenconditional settings for the automated machinery The market place demands turbine generators cooled generator. The on such relationships as the were toshort delivery times, low for the Global VPI turbine determined based model core is 4.5 m in have5.4 Automatic process controlprice and stablesystem length strength and cross-sectional analysis of the materiquality. Moreover, in the Global VPI process, which is and has 5 slots. The full-scale model is built with al In order to meet with these demands, Fuji Electric the brazed Moreover, inactual generator, i.e. with has most important manufacturingfor the the same configuration as an the case of a rotor coil copper portion. developed and applied technology technique, the an bar stator coil, a fastened coilto manufacturing automation resin used manufacturing processes. impreginserted of different dimensions, prior end and Global and mechanization of is controlled strictly and the nating VPI an A impregprocessing, generator, a brazed sample is fabricated and ortion of this technology is introduced below. are actual and therefore a coil end support p nation and rotational hardening processes and atrengthare attached to theverify whether the Previ- generator manufacturing technology regulatsupport ring test performed to stator core of the s ously, automatically. Also, during the ed full- condi- settings are appropriate and to ensure depended impregnation scaletional so that after the vacuum pressure model largely upon the impregnation monitoring system is process, an skill of the manufacturing impreggood workers, utilized nation procedure, the stator coils and core can be quality. but the ensure that the automated and to introduction of resin has impregnated the cured rotating. mechanized of the coil. has made if possible process insulawhile manufacturing processes Thus, the Global VPI tion layer to is stable 5.2 the initial withstand voltage (2 E +1) test, AfterAuto-transposing machine achieve implemented under strict manufacturing process 25 In order to cycle test are the stator coil, quality. aiming to realize automation and good stability coniterations of a heat reduce loss in then carried out trol, withfull-scale model. other vs. voltage transposition, 5.1 Automatic brazing equipment for the rotor coil Roebel of quality. the transposition, in The words, strand the tan during the heat cyclethe characteris- Fig. 10. is tics utilized. Previously, testing are shown tasks of strand Until now, the process of manufacturing a in cutting, characteristicswere performed manually Since the forming, and transposing do not exhibit coil rotorConclusion involved the manual brazing of a copper 6. tan for from their initial value to their value at much change work process. An auto-transposing machine bar. each Automatic brazing equipment has been newly Fig. the has newly the thermalhowever, and isstability devel- however, and is shown Fuji Electrics development 25th been iteration of developed, cycle test, the shown oped, The present status of 11. This Fig. of insulation performance was verified. of the in 12. This auto-transposing machine automates in turbine generators has beenbrazes copper brazing equipment continuously automatic Moreover, thework processesinsulation bars described. afterseries of heat cycle, an from strand cutting, the 25th with a high-frequency brazing machine, and Fuji Electric intends to continue to develop breakdown of the full-scale model was performed in stripping then nology to produce high quality and highly techvoltageinsulation from the strand ends, strand of test finishes the copper bars to form spiral-shaped an forming, air, and the breakdown voltage atmosphere of transposing, and inserting of insulation material, rotorreliable generators the brazing work from coils.turbine In changing over in response to market was to to be at least three times greater than a anual to an automated operation, the verified strand bundling. When strand wire and m needs. the insulating temperature rated voltage (in during high-frequency heating and the timing air). forEnd corona shield

Slot corona shield

24. C (Maximum temp.) 1

material are input into the auto-transposing 5 Initial machine, the machine transposes the strands time outputs a C 1 and Heat-cycle : 160 Heat-cycle : 160 designed coil. auto-transposing machine isC 10 times with The 4 C 25 times Heat-cycle : 160 aroprietary transposing mechanism to realize p tanhomoge3 (%) neity of the Without guard electrode transposing.2 5.3 Automatic bending machine

84

Present Developmental Status of Fuji Electrics Turbine Generator

Vol. 51 No. 3 FUJI ELECTRIC REVIEW5 8

Spiral-shaped rotor winding

)FBUGPSNJOHQPSUJPO 4UBUPSDPJMFOEQPSUJPO

*OWPMVUFTIBQF CFOEJOHQPSUJPO Copper bar

Brazing machine

Roebel transposition forming portion Cutting portion

Transposing portion

S m all C ap acity G eo th erm al B in ary P o w er G en eratio n S ystemShigetoYamada HiroshiOyama

1. Introduction

Japan is a volcanic country having abundant geothermal resources. To date, Japan has 20 geother- generation facilities, with a total mal power installed of 550 MW. Most of these facilities are capacity large capacity geothermal power plants constructed by utility power companies, but due to various circumstances, there are no further plans to build large capacity the near future. The New Energy plants in and Industrial Technology Development Organization (NEDO) is continuing its program of Geothermal Promotion Surveys, which since Development 2003 targeted the development of small and have medium resources. There are many high capacity temperature wells and steam discharge sites in Japan which are not utilized. Various studies are being carried out to expand the usage of such geothermal energy sources not currently utilized for domestic that are energy generation. Efforts are underway to promote the use of natural resource-based energy systems, including geothermal energy, and this initiative is known as EIMY (energy in my yard). addition, RPS (renewable portfolio In standard) legislation mandating the utilization of electricity from renewable energy has been enacted generated in many countries. In Japan, the RPS became effective in April 2003. The renewable energy required for use in accordance with the RPS includes geothermal energy. Consequently, utilization of low temperature geothermal resources for electricity Fig.1 Schematic diagram of binary power generation system generation, which was not considered previously, is now being planned. For small scale or low temperature Evaporator geothermal resources, it is sometimes more economical to use Geothermal ainary power generation system having a lower b steam boiling or hot Turbine point medium than that of conventional water geothermal steam turbines. In consideration of these circumstances, Fuji tric Elecis developing a small capacity geothermal binary generation power Production Re-injection well well system.

lize a geothermal resource (steam or hot water) as aeating source to evaporate a low boiling point h fluid, drives a turbine. Such a system is called which abinary power generation system because it uses two different kinds of fluids, geothermal fluid and Figure low boiling point fluid. shows a conceptual schematic diagram of1a geothermal binary power generation system. In Japan, binary systems were experimentally operated for 5 years beginning in 1993 by NEDO (new energy and industrial technology organization). During that development experimental operation, hydrochlorofluorocarbon (HCFC) was used low boiling point fluid, however, HCFC use as the must be abolished by 2020. There is a manufacturer abroad commercialized a binary power who has generation uses hydrocarbons such as butane system that or pentane. Another system is the so-called Kalinawhich uses a mixture of ammonia and cycle water.countries such as the USA, Philippines, In New Zealand and Iceland, binary power generation systems utilized for geothermal power generation are widely at facilities ranging in capacity from several hundreds of to tens of thousands of kW. The binary kW power generation system by Ormat Industry, Inc. that uses pentane is especially well known and has been deliv-to many geothermal countries. One of ered those systems has been delivered to Japan at the Hachobaru Power Station of Kyushu Electric Geothermal Power as a pilot machine. Several published Co., Inc. papers

Generator

Condenser

2. Binary Power Generation SystemFluid circulation pump

Geothermal binary power generation systems uti86Vol. 51 No. 3 FUJI ELECTRIC REVIEW

describe small capacity geothermal binary power generation systems of other manufacturers that are being operated in Europe. In Japan, there are no manufacturers supplying geothermal binary power generating commercial products, although there systems as have instances of experimental operation. been When importing a power generation system from overseas, of the small capacity geothermal the owners binary generation system may require technical power sup- from Japanese engineers to comply with port Japans requirements such as documentation various and inspections in accordance with the Electricity Utilities Law. There might also be some Industry concerns the after sales service of the regarding importedIn this regard, we consider it quite system. important scale geothermal binary power that small generation supplied by Japanese systems be manufacturers. The first geothermal power generation (1) wasexperiment carried out in Italy in successfully , and 1904 the experimental system reportedly used a steam engine by steam obtained from pure water driven evaporated by the geothermal steam. This system is one type of ainary power generation b system. A binary power generation system is driven by the vapor of fluid different from the heat source, and such source is not necessarily a geothermal heat resource. In Minakami, Gunma, a binary power generation been constructed and operated system has utilizing steam generated by an RDF (refuse derived fuel) boiler. A binary power generation system can be used to generate electricity from various heat sources such as industrial waste heat.

Fuji Electric plans the experimental operation of a prototype binary power generation system and intends to develop a product series based on the results of study and evaluation of the experimental operation.

4. Prototype System4.1 Overview of prototype system

3. Development Through Experimental OperationFuji Electric is proceeding with the development of a geothermal binary power generation system, aimingJapanese market of small scale low at the temperatureresources as well as geothermal geothermal resources the world which may be suitable for throughout ainary system. b Binary power generation systems use the Rankine cycle and basically apply the technologies associated power generation systems. One of with thermal the important issues is the selection of the most most appropriate and economical low boiling fluid, which effectively functions between the high heat source (geothermal resource) and the low heat source (atmo- Once a fluid is selected, the heat cycle can sphere). be planned with a simpler heat balance calculation than conventional thermal power for a plant. other important issue is the selection The of optimum design conditions so that the design is both efficient and economical. It is also important to apply appropriate measures to prevent leakage of the fluid. Economical design is quite important for a small capacity system.Small Capacity Geothermal Binary Power Generation System

In consideration of the targeted heat source (low temperature geothermal resources) Fuji Electric decid-use iso-pentane which effectively evaporates ed to with heat sources and condenses at such atmosphericAlthough iso-pentane is a flammable conditions. gas, be safely used with proper design and it can handling. since the similar hydrocarbon of butane Moreover, is recently being used as a cooling medium for homeuse refrigerators, it is likely that the usage of hydrocarbon accepted by future will be easily owners. In order to facilitate proper evaluation of the results from the experimental operation, the prototype been designed in consideration of system has the geothermal resource temperature at the actual well It is expected that a mixture of geothermal site. steam water will be used, and that the separated and hot hot water will be used for pre-heating and the separated be used for evaporating at the presteam will heater evaporator respectively. Also, an airand the cooled type condenser is used because large amounts of cooling water will not always be available at sites where the binary power generation system will be installed. The prototype system is designed with aimple cycle, that is, the pentane vapor s evaporated pre-heater and the evaporator drives through the the turbine, pentane vapor exhausted from the turbine is condensed at the condenser, and the condensed pen- is pumped back to the pretane Figure heater. shows the main flow diagram of 2 the prototype system, Fig. 3 shows an overview of the and prototype system. In order to realize an economical system, the prototype system is designed with general products and technologies, and does not require the develop-any new equipment or ment of materials.4.2 Pre-heater and evaporator

Both the pre-heater and evaporator use the geothermal fluid as their heat source. In general, the geothermal fluid contains calcium carbonate or silica causes scaling, and therefore, the pre-heater which and evaporator should be designed with a the construction easy periodic cleaning of the that enables internal For the prototype system, shell-and-tube works. type exchangers are utilized, and the geothermal heat Table 1 lists major features of fluid on the tube flows side. the pre-heater and the evaporator.4.3 Turbine and generator

Iso-pentane is non-corrosive to metals, and there87

Fig.2 Main flow diagram of prototype system

Separator

Evaporator

Air-cooled condenser

Level header tank

Turbine

Induction generator

Pre-heater

Fluid measuring tank

Flash tank

Fluid circulating pump

Fig.3 OverviewFeatures of pre-heater and evaporator of prototype systemAir-cooled condenser

Table 1Item Type Pre-heater Capacity Major features Horizontal shell-and-tube type 720 kW Iso-pentane : 36 / C 84

Temperature Inlet / outlet Geothermal hot water : 130 / C 100 Type Horizontal shell-and-tube type 1,990 kW Capacity

Pre-heater Evaporator

Evaporator

C Iso-pentane : 84 / 105 Temperature Inlet / outlet Geothermal hot water : 130 / C 130

Table 2 Features of turbine and generatorItemInduction generator Oil cooling unit Turbine

Major features Horizontal, single stage, impulse type 220 kW (maximum)-1 1,800 min

Type Turbine Output Speed Type of shaft seal Type Generator Output Speed

fore, a standard single-stage steam turbine is utilized. a dual mechanical seal system is applied However, at shaft seals to eliminate any leakage of isothe pentane shaft from the ends. Because a standard induction generator is utilized, a speed governor is not provided for the turbine. Therefore, the use of a standard turbine stop valve and governing valve is unnecessary, and instead, a stan88

Dual mechanical seal Three phase induction type 250 kW-1 1,800 min

dard process stop valve and control valve which have no fluid leakage can be used. The control valve is usedVol. 51 No. 3 FUJI ELECTRIC REVIEW

Fig.4 Section of turbine1st blades 2nd blades

Main bearing

Main bearing Shaft

considered as the primary option, and the prototype employs air-cooling with fin-tubes. system also The air-cooled condenser is the largest component in the system and determines the dimensions of the system. When large amounts of water can be used for the purpose of cooling, a water-cooled condenser may be to achieve a smaller sized used system.

5. ConclusionThe prototype system will be constructed the within year of 2005, and experimental operation fiscal willcommenced thereafter. Fuji Electric intends be to expand the utilization of low temperature geothermal energy in Japan and throughout the world by providing economical and easy-to-operate binary power generation systems, and anticipates that all forms of renewable energy and natural energy will be recog-as important energy sources. Furthermore, nized Fuji Electric hopes that the expanded utilization of renew- clean geothermal energy will contribute able and to preservation of the global environment and will enable to leave natural resources for our society future generations .Reference (1) Geothermal Resources Council: Stories from a Heated Earth. 1999.

Nozzles

to regulate the inlet pressure so as to maintain the evaporator outlet vapor pressure. The stop valve immediately at the occurrence of an closes emergency and stops the turbine and the Table 2 generator. lists major features of the turbine and the generator Figure shows a cross-sectional view of the 4 . turbine .4.4 Air-cooled condenser

As described above, the air-cooled condenser is

Small Capacity Geothermal Binary Power Generation System

89

Table 3 Chemical composition of blade and rotor material that has been developed and selected

R ecen t T ech n o lo g ies fo r G eo th erm al S team T u rb in esC Si Mn Existing material (1 % Cr steel) Rotor Selected material material (2 % Cr steel) Selected material (3.5 % Ni steel)

Material

Chemical composition (%) C r Cu Ni P S Nb Mo V W Al

Existing material 0.17 to 0.10 to 0.30 to 13.0 to 0.30 to (13 % Cr steel) 0.22 0.50 0.80 0.030 0.020 14.0 0.80 Blade material Developed material 0.05 0.10 to 0.30 to 0.025 0.005 15.0 to 4.2 to 3.0 to 0.20 to (16 % Cr 4 % Ni steel) 0.35 0.60 16.0 5.0 3.7 0.35 0.24 to 0.10 0.30 to 1.10 to 0.50 to 0.34 1.00 0.007 0.007 1.40 1.00 2.05 to 0.70 to 0.21 to 0.10 0.65 to 0.23 0.75 0.007 0.007 2.15 0.80 0.26 to 0.07 0.32 0.04 0.007 0.007 1.40 to 3.40 to 1.70 3.60

Yoshihiro0.20 to 1.00 to 0.008 1.50 0.35 KenjiNakamura Sakai 0.80 Kunio to 0.25 to 0.60 to 0.90 Shiokawa 0.35 0.700.30 to 0.15 0.45 0.010

1. IntroductionFig.1 Corrosion cracking and corrosion fatigue testmaterials Fatigue limit diagram of existing and new equipment

Table 1 Standard environment for corrosion tests Fig.2 2Cl 10,000 ppm1

Geothermal energy differs from fossil fuels such Stress clean oil, as Plane bending testgas in that it is a corrosion test machine coal and natural machine (Schenk plane (SCC) energy,little impact bending) environment and having on the Rotating motor Spring emits no carbon dioxideload) ), nitrogen oxides load) almost 2 (fluctuating (CO (static x (NO ) or sulfur oxides (SO ). Fuji Electric delivered x Japans first practical geothermal power plant to the Fujita Enterprises Co. at Hakone Kowaki-en, Tourist sincehas gone on to deliver more than 50 then geothermal plants in Japan and around the world. Fuji Electric is counted as one of the leading manufacturers of geo- Test power plants in the thermal portion Test portion world. Because geothermal steam is highly corrosive, when designing steam turbines for geothermal power generation, it is extremely important to realize and due consideration to the corrosion of give materials. For this reason, Fuji Electric has carried out continuous corrosion testing onsite at the location of geother- generation, and materials testing in mal power a laboratory. The valuable data thus 2acquired Na SO ) Corrosive solution circulation tank (H S, N , NaCl, 2 4 2 was reflected in the turbine design in order to realize high reliability. Moreover, Fuji Electric has also actively to enhance the efficiency of geothermal worked blade and rotor materials. New materials have steam by applying recent blade row turbines higher chromium content than the existing materials, technology. This paper introduces Fuji Electrics recent to and contributes to their better resistance this tech- new blade materials are also heat treated nologies for geothermal steam corrosion. The turbines. appro- in order to lower their susceptibility priately to 2. Recent Materials Technology for Geothermal corrosion and section 2.1 was cracking. Steam Turbines The corrosion test described in implemented for the existing blade material and 2.1 Corrosion testing in a modeled geothermal environfor new blade material, and the fatigue limit the ment diagram from the result of this testing is shown obtained Fig. in 2. to increase the reliability of In order The results verified that under the geothermal operational steam turbines, it is important to assess the life stress conditions of the turbine, the new blade of materimaterials under thehigher stress amplitude, and als tolerated a conditions of the geothermal corrosion resistance the corrosiveness environment. Fuji Electric tests and reliability. This exhibited higher of imgeothermal steam believedmaterials andthe provement is turbine to be due to evaluates their increased additive, which has the effect of applicability to even more severe chromium environmental suppressing of corrosion pitting that has a conditions. the formation large on corrosion resistance and Assuming harsh conditions as the environment impact to Figure reliability. shows the environmental which a turbine is exposed, results of a stress 3 conditions werecracking propagation test (K1SCC test) that was established corrosion for a concentrated corrosion test so the long-term usage condition of a turbine areas that used to evaluate the propagation of cracking at could of 90Recent Technologies for Geothermal Steam Turbines

H2 S S 300 ppm

O

4

pH

Temp.

50 ppm

3.5 to 4.0 60C

(1.8 %, (H2S gas sealed (Mixed as as NaCl) 0.8at of stress Na2SO ) 4 Amplitude 0.2 L/min)(relative value) 0.6 0.4

Table 2 Contents of the corrosion testTest0.2 0

Description Immersed in a corrosive solution. Weight reduction is measured and 0.2 0.4 0.6 corrosiveness is assessed. 0.8Mean stress a static stress, While applying (relative value) immersed in a corrosive solution and the time to failure is evaluated.

Corrosion test 0

1

Stress corrosion cracking (SCC) test

Fig.3 K1SCC test Repeatedly applied bending load while results Corrosion fatigue test immersed in a corrosive solution, and number of ruptures are evaluated.Static mean stress and dynamic cyclic Corrosion fatigue test load are applied simultaneously, and (mean stress loading) the fatigue limit is obtained. Static stress is loaded, and the amount Blunt notched compact of generated SCC cracking tension (BNCT) test propagation is evaluated. Pre-cracking is formed, and the Double cantilever beam susceptibility of propagation due to the (DCB) test and concentration of stress at the tip of the Stress corrosion crack cracking is evaluated (2 types of test propagation (K1SCC) are performed with different shaped test test specimens)

Table 1 lists the standard be modeled Table 2 lists the various quickly. corrosion test environment, sion tests performed in ordercorroto assess various Fig. 1 shows the external appearance stress conditions, and corrosion test of the equipment.2.2 Use of new turbine materials

In existing geothermal steamthe existing material concentrated stress in both turbines, 13 % Cris used blade blade material and steeland new as the material. The crack1 % Cr steel the is usedpropagation the stress intensity factor (in units of as the rotor threshold of material. These materials are usedMPa was 10a successful track value of 0.17) for widely m) have and m (relative record. However, we had developed and selected materials(relative value MPa the m for both existing blade material and 60 the MPa rotortheorder material, thus demonstrating blade and for in new to obtain even higher of 1.0) Table 3 lists the corrosion resistance and the superiority of this new material. On the other reliability.compositions of the of corrosionand Fig. chemical4 shows the results developed fatigue hand, selected testingVol. 51 No. 3 FUJI ELECTRIC REVIEW1 9

Fig.4 Results of rotor corrosion test1.0 Amplitude of stress (relative value)

Fig.5 SCC test results (with and without shot peening)1.0

3.5 %Ni steel 1 % Cr steel 2 % Cr steel 2 % Cr steel

Stress (relative value)

3.5 % Ni steel % Cr steel 1 0.5 0.5

0 0.001

0.01 0.1 1.0 Number of cycles to failure (relative value)

0 0.001

0.01 0.1 Time to failure (relative value)

1.0

performed on the rotor material. As in the case of the material, it can be seen that the application blade of selected material (2 % Cr steel) resulted in the higher resistance to corrosion.2.3 Shot peening technology

Table 4 Results of coating test

Fatigue limit line from 16 % Cr 4 % Ni steel test

As described above, the application of newly developed materials was confirmed to achieve higher resis- to corrosion, but in order to support operation tance in even more severe corrosive environment and an under stress, shot peening technology is also higher being and utilized. Shot peening generates studied compressive residual stress by impacting a blade or rotor area in which the generated stress is severe with a steel ball having a certain amount of energy. corrosion cracking tests were performed Stress the on shot-peened blade and rotor material, Fig. 5 and shows results that verify their longer life. It can be that the time to failure is at least twice as long seen for shot-peened material compared to material that is not shot-peened. Based on these results, Fuji Electric began using shot peening as an effective measure to increase the corrosion life of steam turbines.2.4 Coating technology

Fatigue limit line from 13 % Cr steel test

1.0 13 % Cr steel (relative value) 16 % Cr 4 % Ni steel

application method were verified to be at a level suitable dt practical application to steam for 0.1 turbines. / da2.5 Welding repair technology for the rotor k propagation speed

Blade material is required to be resistant to both corrosion and to erosion. Increasing the corrosion generally requires that the materials resistance hard-be increased. However, when the hardness ness is increased, the stress corrosion cracking characteristics Flame spray coating is considered become poorer. to a method potentially capable of realizing be resistance to both corrosion and erosion simultaneously. Sevenof materials were selected as candidates for types the flame spray coating, their hardnesses were measured, and the corrosion test described section 2.1 and a in blast erosion test were performed for each. The results are listed inTable 4. These results show that the CoCr material has WCexcellent corrosion resistance and erosion resistance as a flame spray coating material. spray coating conditions were optimized The flame for material and the flame spray coating material this and 92

As described above, various technologies have been developed and selected in order to increase 0.01 corrosion However, products that have already resistance. been delivered contain existing materials and their corrosion resistance is insufficient compared to the Crac new products. In some geothermal steam turbines that been in operation for a long time, corrosion have 0.001 0 1.0 has caused pitting and stress corrosion is causing cracks Stress intensity factor (relative value) to appear. Accordingly, a repair technology was needed already-delivered for these products. case of a rotor, stress corrosion In the cracking occurs at the bottom of the blade groove where the concentration of stress is highest. If cracks occur in area, the propagation can be suppressed this by shaving the area of occurrence so as to eliminate the crack. However, if the crack grows larger, it will be necessary to shave the entire blade groove. At such a time, technologies for overlay welding and for reusing groove are the blade required.Vol. 51 No. 3 FUJI ELECTRIC REVIEW

After welding conditions were selected for the plate material, welding was performed according to the dimensions of the turbine and then a mechanical and a corrosion test were property test implemented.is used as the overlay material and 13% Cr steel the welding was implemented as multi-layer tungsten (TIG) inert gas welding. specimen was sampled at the weld A test andlocation, the results of its corrosion fatigue testing are shown in Fig. 6 and the samples overlay microstructure iswelding Fig. 7. The shown in zero defects. Excellent mechanical properties microstructure has and corrosion resistance were verified for the rotor host material, and this welding repair technology was established for steam turbines. As described above, a method has been established for assessing corrosion, which largely impacts the reliability of geothermal steam turbines, and new materials, shot peening technology, coating technologytechnology have been developed and and repair estab- By using these materials and lished. technologies according to the geothermal appropriately conditions and the generated stress, it is thought that higher reliability can be achieved. future, Fuji Electric plans to advance In the the assessment and research of corrosion under geothermal conditions and intends to evaluate techniques forFig.6 Results of corrosion fatigue test of repair welded area1.0 Amplitude of stress (relative value) Repair welded area

achieving even higher reliability and for assessing the residual life.Shot With shot No shot 3. New technologies of Improving the Efficiency peening peening peening effect of Geothermal Steam Turbines

As a measure to improve the efficiency of ruptured malgeothersteam turbines, recent technologies based on expertise acquired from the development of 13 % Cr steel steam 13 % Cr conventional thermal power turbines for steel (shot generation Crmainly to blade rows in order to realize are applied 4 % Ni steel 16 peening) % 16 % Cr 4 % Ni steel aignificant improvement in efficiency. s (shot peening)3.1 Advanced reaction blades (high load and high efficiency reaction blades)

Un-

Utilizing recent blade row design technology, highefficiency reaction blades capable of maintaining high efficiency while increasing the load per stage are Blast used Stress with the exception of low-pressure in blade rows, Corrosion erosion Coating corrosion Hardness blade cracking Fatigue weight (amount rows, material in geothermal steam turbines. For the Hv reduction of average same (SCC) number of stages, the use of these reaction wear) blades increases the efficiency by at least 1 % compared to CoNiCrAlY+ Poor Poor Excellent Good 790 conventional reaction blades Fig. 8). Al 2O 3the 2 TiO (see Excellent x c e lle n t E x ce lle nExcellent 1,100 WC-10Co4Cr E tCoCrMo Al-Zn

3.2 Improving the performance of low-pressure bladesPoor Fair Excellent Good 650

1 % Cr steel

13 % Cr steel 13 % Cr steel 1 % Cr steel Repair welded area 0 0.001 0.01 0.1 1.0

Number of cycles to failure (relative value)

Because low-pressure blades in a Poor geothermal steam turbine account for a larger proportion of Stellite the turbine load thanPoor conventional total in a No. 6B Good 540 spraying steam improving the performance of these turbine, 50 % low- Cr C pressure blades will have a greater effect on 3 2 Excellent Fair Fair Good 770 50 % improving NiCr the performance of the total turbine than in the case 75 % ofconventional steam turbine. Originally developed Cr 2 a3 C Fair Good 810 25 % NiCr for with conventional steam turbines, a new series use : Not tested of low-pressure blades having much higher performance are being adjusted for use in an environment of highly corrosive geothermal steam and are being applied to actual turbines. features of this new series of lowBelow, pressure blades will be described from the perspective of their efficiency and the status of the compact-size highefficiency low-pressure blades currently being developed will also be discussed.Fig.8 Efficiency of conventional and advanced reaction blades1.02 1.00

Fig.7 Microstructure of the overlay weldingConfirm health of microstructure

Relative efficiency 0.98 0.96 0.94 0.92 0.90 0.88 0 1.0 2.0 3.0 4.0 Loading factor 5.0 6.0

Welding

1st layer 25 m

Final layer

25 m

Recent Technologies for Geothermal Steam Turbines

93

(1) Transonic profiles Recent advances in computational fluid dynamics have made it possible to simulate accurately the flow a blade row, and by optimizing the within velocity distribution within that blade row, a low-loss Fig. 9 ). The new profile shape profile realized can be (see is characterized by a convergent-divergent profile (a profile designed so that the flow path widens towards that is adapted for transonic flow. The the end) results wind-tunnel testing confirmed that when of steam the outlet Mach number is large, use of the new profile reduces profile loss to less than 1/2 of the shape prior value. (2) Lean-radial stationary blades Using a 3-dimensional time-marching method, various profile shapes were compared while varying the pattern, and from the results of this comparison flow it could be understood that a banana-shaped stationary leans toward the circumferential blade which direction and toward the radial direction at its tip, at its root as shown inFig. 10, was the optimal shape. By using this type of lean-radial stationary blade, flow in the vicinity of the root, where separation is likely to occur, has improved dramatically. The results of a been model test confirmed that stage efficiency was turbine imFig.9 Advanced low-pressure blade analysis example and steam wind-tunnel test results

proved by at least 2 % compared to the conventional stationary blades. (3) Development of high efficiency, compact-size lowpressure blades The technologies used to design the new series of low-pressure blades for conventional large steam tur- were also applied to the design of 500 mmbines andshorter low-pressure blades, and a highefficiency compact-size low-pressure blade series that achieves dramatically higher performance is presently Table 5). being developed (see This series is designed originally under consideration with use in geothermal steam turbines, and will be provided the following features as well as also the adopted to enhance efficiency by using this items new of low-pressure series blades. (1) Highly reliable, rugged design for operation in aorrosive c (2) environment mounting area in all stages uses The blade root aimple inverted Ts (3) shape Redusing leakage loss from the blade tip with shroud is in all Figure stages shows the blading plan for the largest size11 blades (490 mm) in this series.

4. Example Applications of the Recent TechnologiesIntroduced below are examples of actual malgeothersteam turbines to which the abovedescribed recent technologies have been applied.Table 5 Development of high efficiency compact-size lowpressure blades

0.8

5 Conventional profile Relative profile loss 40.9

3 2 1 0 1.2 Advanced profile Operating range 1.4 1.6 1.8 Mach number of blade row outlet

1.1 1.2 1.5 1.3 1.4 1.5 1.6 1.7 1.8

1.3 1.5 1.6

Fig.11 Blading plan for 490 mm low-pressure blades Fig.10 Results of efficiency test of lean-radial stationary blades in a model turbineDrain slits 1.1 Relative stage efficiency 1.0 0.9 0.8 0.7 0.6 0.6 Lean-radial stationary blade Advanced reaction blades

Trailing edge

Leading edge

Conventional reaction blades

0.8 1.0 1.2 1.4 1.6 Relative volumetric flow

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Vol. 51 No. 3 FUJI ELECTRIC REVIEW

50 Hz-use (nominal exhaust area) 490 mm blade (2.5 m ) 350 mm blade (1.6 m ) 290 mm blade (1.3 m )2 2 2 2

60 Hz-use (nominal exhaust area) 410 mm blade (1.7 m ) 290 mm blade (1.1 m ) 240 mm blade (0.9 m )2 2

Lean-radial stationary blade

Conventional stationary blade

Fig.12 Cross-section of 64.7 M