thermal power plants - fuji electric global

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

Fuji Electric’s Thermal Power Equipment

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

Cover photo:Thermal power generation in

Japan has been affected by the slow-down in demand for electric powerand the decline in electric utilityrates, and power companies havedramatically curtailed their invest-ment in plants and equipment. IPPpower generation has also fallen,and a 1970s-like boom in power gen-eration for private use is not ex-pected.

Overseas in countries such asChina, India and Brazil, however,the potential for future growth isseen as large, and the constructionof new power plants brisk.

As part of this trend toward sup-plying plants and equipment over-seas, the cover photo showsIreland’s West Offaly Power Station,which was delivered as a full-fledged coal-fired thermal powerplant. The design has cleared thepreliminary safety protocols com-mon to both Europe and NorthAmerica, and is a model of the powerplant technology to be constructedoverseas in the future. Also shownon the cover is a compact-size, non-reheating turbine, for which rapidgrowth is anticipated in the over-seas markets.

Thermal Power Plants

CONTENTS

Trends and Future Outlook for Thermal Power Plants 70

Fuji Electric’s Medium-capacity Steam Turbines “FET Series” 74

Present Developmental Status of Fuji Electric’s Turbine Generator 80

Small Capacity Geothermal Binary Power Generation System 86

Recent Technologies for Geothermal Steam Turbines 90

Recent Technology for Reusing Aged Thermal Power Generating Units 96

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

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

Vol. 51 No. 3 FUJI ELECTRIC REVIEW70

Hiroshi Nishigaki

Trends and Future Outlook forThermal Power Plants

1. Introduction

Recent events have caused modern society toappreciate anew the benefits it derives from electricity.A wide-ranging massive power outage extending fromthe northeastern United States to Canada and a powerfailure throughout all of Italy have occurred, and havehad large impacts on the life of residents in thoseareas. In Shanghai, rotating power outages have beenimplemented for years and are a large impediment tonormal business activities. In Japan, a stoppage of theoperation of all nuclear power plants owned by TheTokyo Electric Power Co., Inc. caused a great deal ofanxiety, but aided by the cool summer weather,ultimately did not result in a power outage. When alarge-scale power outage occurs, trivial problems grad-ually increase and may potentially cause the collapseof large systems.

Power plants are part of the infrastructure ofmodern society and it is essential that these powerplant facilities by constructed so as to achieve a higherlevel of reliability. Moreover, it is the mandate ofcompanies involved in this industry to contribute tosociety by realizing higher performance and lower cost.

2. Market Trends

The climate surrounding Japan’s domestic electricutility industry is as severe as ever due to sluggishgrowth in the demand for electrical power, the ongoingdecrease in electrical power rates, the advancement ofelectric utility deregulation, the establishment of newenvironmental taxes, and the rapid rise in prices ofsuch fuels as oil and coal. Power generation by meansof renewable energy has been favored following theenforcement of the “Special Measures Law Concerningthe Use of New Energy by Electric Utilities” (RPS law)and then the Kyoto Protocol, which came into effect inFebruary 2005. However this market sector will bestalled in a wait-and-see situation for the next 1 to 2years, during which time, efforts to develop new powersources are expected to idle.

In overseas markets, there is strong demand forelectrical power in both the public and private sectors

of the BRICs (Brazil, Russia, India and China) wherethere has been a significant increase in demand forelectrical power, for Libya which has recently returnedto the international arena, and the Southeast Asiancountries of Indonesia and Vietnam. In these coun-tries, the supply of electrical power has not caught upwith the speed of economic growth and industrializa-tion, and this demand for many new power generatingplants is expected to continue for several years. Thesepower plants will be mainly medium and small capaci-ty facilities, which is Fuji Electric’s area of expertise.Fuji Electric has a track record of many successfulapplications including pure power generation andcogeneration plants based mainly on coal-fired powergeneration, and combined cycle power generationachieved by connecting an add-on to an existing gasturbine.

3. Technical Trends

Fuji Electric was founded approximately 80 yearsago through a partnership between The FurukawaElectric Co., Ltd. and Siemens AG., to introduceEuropean technology to Japan at a time when UStechnology was already widespread. Fuji Electric hasbeen involved in the production of thermal powerplants for approximately 40 years and has suppliedmany distinctive products by introducing technologyfrom Siemens during construction of mainly utilitythermal power plants. Table 1 shows the history ofgrowth in Fuji Electric’s main technologies and busi-nesses. Recently, Fuji Electric has delivered a ultra-supercritical pressure steam turbine to the IsogoThermal Power Station of The Electric Power Develop-ment Co. (EPDC). This ultra supercritical pressuresteam turbine increases the efficiency of the powerplant, or in other words, reduces the environmentalload. Figure 1 shows a view of the entire EPDC IsogoThermal Power Station Unit No. 1.

Meanwhile, with the deregulation of the electricpower industry, power plants are now being construct-ed by independent power producers (IPPs) and FujiElectric is supplying various types of economicallybeneficial equipment to these plants.


Fig.1 EPDC Isogo Thermal Power Station new Unit No. 1

Table 1 History of changes in Fuji Electric’s main technologies and businesses

Fig.2 View of the entire UBE Power Center Plant

Era 1970s 1980s 1990s 2000sCategory

Thermal power plants for utility in Japan

Thermal power plantsfor private use and IPP plants in Japan

Overseas thermal power plants

Geothermal power plants

Technical development

TEPCO Ooi Thermal Power Station, Unit No. 3(first pure sliding pressure operation in Japan)

EPDC Ishikawa Coal Thermal Power Station, Unit Nos. 1 and 2(high-temperature turbine)

UBE Industries, Ube plant(145 MW, largest private-use power plant in Japan)

Australia: GladstoneUnit Nos. 1 to 4(direct hydrogen-cooled generator)

Pakistan: Jamshoro Unit No.1(largest indirect hydrogen-cooled generator)

Bangladesh: Meghnaghat(combined-used turbine, large-capacity air-cooled generator)

Philippines: Battan, Unit No.2(full-scale entry into overseas business of thermal power plant for utility)

EPDCOnikobe Geothermal Power Plant (generator delivered)

High-temperature 12Cr rotor

Improved 12Cr rotor for high temperature

Completion of new Shiraishi Factory

22 kV-class F resin/ F insulation Automated stator winding machine

Direct hydrogen-cooling methodF resin/ F II insulation

Experimental prototype of 126 MVA air-cooled generator

Global vacuum pressure impregnating facility for medium and small-size generator

Global vacuum pressure impregnating facility for large-size

22 kV-class global vacuum pressure impregnated insulation system

El Salvador: Ahuachapan, Unit No.3(full-scale entry into geothermal power plant business)

USA: Coso Geothermal Power Plant, Unit Nos. 2 to 9(modular turbo-set)

Indonesia: Wayang Windhu, Unit No. 1(world’s largest single-casing geothermal turbine)TEPCO, Hachijojima Geothermal Power Station

Thailand: Mae Moh, Unit Nos. 4 to 13(largest thermal power plant in Southeast Asia)

Taiwan: FPCC FP-1, Unit Nos. 1 to 4 (60 Hz, 600 MW large-capacity tandem machine)

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)

Kobe Steel, Kakogawa Works(axial flow exhaust turbine)

Tohoku Electric PowerNoshiro Thermal Power Station, Unit No.1(50 Hz, 600 MW large-capacity tandem machine)

EPDC Isogo Thermal Power Station, new Unit No.1(600 MW ultra-supercritical pressure plant)

Okinawa Electric PowerMakiminato, Unit No.9(Fully automated oil thermal power)

Kansai Electric PowerMiyazu Energy Research Center, Unit No.2(DSS operation)


The construction of utility thermal power plants inJapan has reached as standstill at present and is notexpected to recover soon. Additionally, IPP planninghas also become saturated. Figure 2 shows a view ofthe entire UBE Power Center Plant that was con-structed as an IPP plant. Fuji Electric will continue todevelop products while carefully monitoring thesemarket trends in the future. The technical trends ofmedium and small capacity power plant equipment,which are Fuji Electric’s main products at present, aredescribed below.

3.1 New small-capacity non-reheat steam turbinesFuji Electric has newly developed a steam turbine

(FET-N type) having a simple configuration suitablefor small capacity (25 to 50 MW) applications. A firstunit is already in operation in China, and a secondunit has already been shipped and is being installedonsite.

3.2 Large non-reheat steam turbinesFuji Electric’s expertise is greatest in the technical

field that involves private-use power plants. Theseplants have multiple steam processes and requirecomplex control. In a turbine, the process steam flowrate is controlled as required, and at the same time theelectrical power output is adjusted. In the past, theoutput power was approximately several tens of MWbut, in response to market needs, technology has beendeveloped to achieve larger turbines capable of greaterthan 160 MW output.

3.3 Single-casing reheat steam turbinesFuji Electric has developed a reheat steam turbine

configured with a single casing instead of the conven-tional two-casing construction, and a first unit hasalready been placed in service. Shortening the lengthof the turbine shaft has enabled a reduction inconstruction costs, including civil engineering work,and the realization of a more economical plant.

3.4 New digital control systemA new digital control system (TGR) that provides

integrated control for a turbine and generator, anduses Fuji Electric’s MICREX-SX, which is a high-performance PLC, has been placed into commercialoperation and it being applied to other plants.

3.5 Remote monitoringA remote monitoring system has been developed

that periodically gathers operating status data frompower generating equipment that has been delivered toa remote overseas location and transmits that data viathe Internet to a maintenance department, where it isreceived. Thus, even when a failure occurs in remoteonsite equipment, the customer can be instructedquickly as to the appropriate measures, thereby mini-mizing downtime and reducing the customer’s loss.

Moreover, appropriate advice concerning preventativemaintenance is also provided in order to avoid down-time due to mechanical failure.

4. Steam Turbines

Various improvements to steam turbine technologyhave been previously requested in order to enhance thethermal efficiency and space efficiency of thermalpower plant facilities. In the large-capacity generatorsector, Fuji Electric has advanced the development of600 MW-class supercritical pressure steam turbines,and together with the improved thermal efficiency dueto higher temperature and pressure steam conditionsand the development of large turbine blades, hasreduced the number of low-pressure turbine casings torealize more compact turbines. In the medium andsmall-capacity generator sector, technology has beendeveloped to increase the efficiency, compactness andserviceability of steam turbines, enabling smallerinitial investment and higher reliability. Fuji Electrichas continued to improve the space efficiency bymigrating from the conventional three-casing structureto a two-casing structure and then to a single-casingstructure. With the increase in capacity, the ability tomaintain stability of the shaft system as the distancebetween bearings increases in a steam turbine andmeasures to prevent erosion of the low-pressure bladespresented technical challenges that have since beenovercome due to greater analytical precision andstructural improvements. A single casing turbine of165 MW maximum capacity has already been broughtto market and is achieving good operating results. Inorder to reduce the construction costs associated with acombined cycle steam turbine, axial flow steam tur-bines are being widely used. Fuji Electric will continueto advance the development of technology to improveefficiency and lower the cost of medium and smallcapacity turbines.

5. Generators

Air-cooled generators, due to their low constructioncost, short production time and ease of operation andmaintenance, are gradually beginning to be used inapplications traditionally associated with hydrogen-cooled generators. At present, Fuji Electric’s air-cooledgenerators are suitable for applications ranging up to280 MVA for 60 Hz generators and 300 MVA for 50 Hzgenerators. Because air, which has lower coolingperformance than hydrogen, is used as a coolant withlarger capacity generators, Fuji Electric implemented atechnical verification test by fabricating a 126 MVAexperimental generator and taking on-line measure-ments at more than 1,000 on the stator and rotor. Theresults of this test demonstrated that it was possible tomanufacture a large-capacity air-cooled generator hav-ing sufficient reliability.


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

6. Geothermal Power Plants

There are presently no plans for the construction ofgeothermal power plants in Japan. The reason for thislack of plans is the high cost due to risks associatedwith underground resources, the large initial invest-ment that is required, and the long lead time requiredto coordinate and reach a consensus concerning treat-ment of national parks and existing hot springs.However, small-scale binary power generation thatutilizes previously unused steam and hot water from ahot springs region is a promising model for economicalgeothermal power plants because there are no drillingcosts and the lead time is short. The RPS law has beenenforced since 2003, obligating electrical power suppli-ers to use renewable energy. Because geothermalbinary power generation is also included in thiscategory, the construction of geothermal power plantsis expected to gain momentum.

Overseas, due to the slowdown in the globaleconomy that began with the Asian currency crisisfrom 1997 through 1998, developing countries post-poned or froze almost all their geothermal developmentplans that required an initial investment or involvedinvestment risk. However, in response to the increasein demand for electrical power that accompanied thesubsequent economic recovery, plans that use publicfunds such as yen loans or financing from the AsianDevelopment Bank for investigating geothermal re-sources and constructing geothermal power plantshave been reinvigorated.

In the past, geothermal power plants commonlyadopted affordably-priced single-flash cycle. In orderto achieve a more efficient use of resources, double-flash cycle, combination with binary cycle using brinefrom flash cycle and cogeneration of hot water forhouse heating using exhaust or extracted steam areadopted.

In order to improve plant efficiency and theutilization rate of geothermal turbines, the followingtechnologies are recognized as important for geother-mal power plants: technology for preventing the adhe-sion of and removing silica scale from turbines,monitoring techniques and easy maintenance, andmeasures to prevent the adhesion of silica on re-injection piping or a re-injection well. Geothermalsteam contains a minute amount of hydro-sulfuric gasand, as environmental quality standards become strict-er, an increase is expected in the number of installa-

tions of equipment for removing this hydro-sulfuricgas, which previously had been released into theatmosphere.

7. After-sales Service

After-sales service has been implement thus far ina close working relationship with the user, mainly byproviding periodic inspections of delivered equipmentand replacing or repairing parts for preventativemaintenance. These activities include responding toincidences of sporadic failure and also providing vari-ous suggestions for improvements. Periodic inspec-tions are necessary to ensure the safety of a plant, andin Japan, this is a characteristic of a regulatedindustry protected by laws. As the relaxation ofregulations results in a shift from mandatory periodicinspections to voluntary inspections, technical sugges-tions by manufacturers are being closely scrutinizedbased on economic criteria to determine whether theyare absolutely necessary for ensuring stable operation.Against this backdrop, specialized maintenance servicecompanies have already begun operating in Europeand the US. The necessity for periodic inspections isalso being recognized in Southeastern Asia, and theseEuropean and US maintenance companies are earlyparticipants in those markets. Fuji Electric intends toleverage its reliable and responsive after-sales servicein order to insure the stable operation of power plants,and to compete as an equipment manufacturer againstthese specialized maintenance companies.

After-sales service for an aged plant can encompassplans for major renovations or renovation of the entireplant in order to reuse the plant’s facilities. These typesof plans can be diverse and may involve conversion ofthe type of fuel that was used originally at the time ofconstruction, massive renovation of the entire plant—such as changing the operating principle of the powerplant, and repairing or replacing worn out parts toprolong the service life of the equipment or reducingmaintenance cost and enhancing the efficiency of theplant. Technology has also made great advances sincethe time of the initial construction and a wide range ofmeasures are available for problem solving.

8. Conclusion

Thermal power plants are industrial goods thatproduce electricity. Moreover, these plants are impor-tant to customers and are presumed to have a servicelife of greater than twenty years. Accordingly, thereliability of a power plant is considered most impor-tant, followed by after-sales service and then economicefficiency. As demand for electrical power increasesthroughout the world, Fuji Electric intends to continueto strive to supply power plants that provide reliabili-ty, high performance and low price in accordance withthe needs of customers.


Koya YoshieMichio AbeHiroyuki Kojima

Fuji Electric’s Medium-capacitySteam Turbines “FET Series”

1. Introduction

Recently, de-regulation of the electric power indus-try and rising needs for advanced solutions to environ-mental concerns, have caused a great change in thearea of thermal power generation. Further improve-ment for higher efficiency, a more compact design,optimal operating performance, and better maintain-ability and higher reliability is increasingly requestedof the steam turbine industry.

For medium capacity steam turbines, there hasbeen an increase in the use of combined cycle plants, inaddition to their conventional use for private powergeneration. Accordingly, larger capacity single units,combined with advanced technology for higher efficien-cy, have been more in demand. Moreover, the axialflow exhaust type and the upward exhaust type steamturbine configurations are more favorable and popular,due to their lower construction costs.

Features of Fuji Electric’s “FET Series” of standardmedium capacity steam turbines , which achieves highefficiency with low-cost, are introduced below.

2. Concept of the FET Model Series

2.1 Applicable rangeSpecific demands for medium capacity steam tur-

bines concern not only power generation, but alsorelate to industrial applications that provide the

function of extracting steam for various uses such asplant processes or utilities. The medium capacitysteam turbine FET Series is a standardized modelseries suitable for a wide range of steam and outputconditions.

The types of steam turbines, applicable steamconditions, output range and the rotational speed ofthe steam turbines are listed in Table 1.

2.2 Block design systemThe standard FET Series of steam turbines utilizes

a modular “block design system” in which suitableblocks are selected from several standardized compo-nents (Fig. 1) corresponding to the various requiredspecifications and steam conditions of each project.This type of modular system design enables the bestselection of blocks over a wide application range.

Each standard component has a proven trackrecord of success, and a highly efficient turbine modelcan be realized by the proper selection of the optimumblocks. Standardization by means of this block designsystem will shorten the production lead-time andreduce the production cost. As a result, a steamturbine that satisfies customer requirements can beprovided with a shortened delivery time.

3. Scaling-up to Larger Capacity FET Turbines

Many steam turbines for private power generation-use and having the capability to provide process steamhave been furnished. Due to the worldwide trendtoward de-regulation of the supply of electric power,private companies are increasingly joining IPPs (Inde-pendent Power Producers), and the need to scale-upthe unit capacity of steam turbines has increased.

After the 101 MW FET turbine was put intooperation in 1994, larger capacity units have beensuccessively developed within the FET series, inaccordance with market trends. The cross-sectionaldrawing of a recent FET steam turbine is shown inFig. 2, and the specifications of these turbines arelisted in Table 2.

Table 1 Range of Fuji Electric’s medium capacity steamturbine “FET Series”

Type

20 MW to 180 MW

Main steam pressure : 130 bar or lessMain steam temperature : 540°C or less

Range of output

Steam condition

Rotational speed 50 s-1 (3,000 rpm) or60 s-1 (3,600 rpm)

™Condensing type™Back pressure type™Single / Double controlled extraction condensing type™Single / Double controlled extraction back

pressure typeOperable as a mixed pressure type or an extraction / mixed pressure type.


Fig.2 161.99 MW steam turbine, assembled cross-sectionaldrawing

Fig.3 Reaction type steam turbine rotor

Fig.1 Block design system of the FET Series

Table 2 Steam turbine specifications

Front bearingpedestal part

High pressure part Extraction part Low pressure part

260

400

400-AX

115

3-80

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

3-100

4-130

4-150

4-175

5-200

120

125

130

135

225FET Turbine Series

T Series (original type) 20 to 180 MW Upwards / Downwards

N Series (small capacity type) 20 to 50 MW Upwards / Downwards

AX Series 50 to 180 MW Axial exhaust

Output range Exhaust direction

LP casing

LP blades

Reaction stage bladesFront bearing

pedestal

Rotor

Inner casing

Outer casingRear bearing pedestal

Single-extraction condensing

Single-extraction condensing

147.88 MW 161.99 MW

123.6 bar / 538°C/ 7.7 bar

123.6 bar / 538°C/ 8.3 bar

0.088 bar 0.088 bar

60 s-1 (3,600 rpm) 50 s-1 (3,000 rpm)

Model

Output

Steam conditionextraction pressure

Vacuum

Rotational speed

Operation start date May 2000 July 2004

Formosa Chemicals & Fibre CorporationSK-G4 (Taiwan)

Formosa Power (Ningbo) Ltd. Co.NB-1 (China)

3.1 Highest internal efficiency with throttle governingsystemThe FET steam turbine has adopted a design that

features a throttle governing system and a double shellcasing structure with outer and inner casings, similarto that of large capacity turbines for utility powergenerating use. This design achieves higher efficiencyby utilizing reaction blades in all stages, and does notuse a nozzle governing impulse blades with partial admission loss (see Fig. 3). Moreover, wear due to the

Reaction stage moving blades LP moving blades


impact of solid particles (particle erosion) or deteriora-tion of the blade surface can be reduced and deteriora-tion of performance with aging will be minimal, due tothe lower steam velocity with reaction blades than inthe impulse stages.

3.2 Adoption of advanced series low-pressure bladesHighly efficient low-pressure blades, designed us-

ing compressible supersonic flow analysis (three-di-mensional time marching method), are utilized. A leanradial stationary blade, which curves toward thedirection of the circumference is adopted in the finalstage (L-0) (see lower half of Fig. 4). Moreover, en-hanced performance is achieved by adopting a shroudring in the first stage (L-2) moving blade, whilecontinuing to maintain the wide range frequencyallowance of -5 to +3 %, which has been a characteris-tic feature of existing free standing blades (see upperhalf of Fig. 4).

3.3 Erosion preventionOperated in wet steam, low pressure moving

blades erode due to the impact of water droplets, andthis erosion increases in severity as the blade lengthgrows larger. To reduce this damage, the followingmeasures have been implemented (see Fig. 5).(1) The leading edges of the moving blades have been

flame hardened, and the surface hardness of theblade material has been improved.

(2) The final stationary blade (L-0) of larger modelshas a hollow structure with drain slits provided onits surface in order to drain the water dropletsaway to the condenser, thereby reducing the drainattack on latter-stage moving blades.

(3) The axial clearance after the trailing edge ofstationary blades has been enlarged sufficiently todecrease the size of water droplets that adherefrom the steam flow onto the stationary blades,thereby reducing the drain attack on followingmoving blades.

(4) The trailing edge of the stationary blades has beenmade thinner, so as to minimize the size of waterdroplets from the edge of the blades, therebyreducing the drain attack on following movingblades.

3.4 Adoption of 2 % Cr steel rotorAccording to the increase in rotor diameter and LP

blade length corresponding to larger steam turbinecapacity, the centrifugal loads on the rotor have grownlarger. The strength under actual operating conditionswas evaluated using finite element analysis and frac-ture mechanics procedures. Accordingly, differentialheat-treated 2 % Cr forged steel was selected for theshaft material of a 60 s-1 machine in which the stressin the core part will be very high. Figure 6 shows thecreep rupture test results of this material.

4. Compact FET Turbine (N Series)The selection of small capacity FET turbines has

been improved with the development of the N Series,which was started and completed in 2002.

Figure 7 shows a cross-sectional drawing andtypical specifications of the N Series.

Fig.4 Advanced series low pressure blades Fig.5 Erosion-resistant structure

LP stationary blades ring

Lean radial stationary blades

L-1 LP moving blades L-2 LP moving bladesLP rotor

L-0 LP moving blades to condenser

Route of drain flow

Stationary blades

Moving blades

Rotor

Drain slits


efficiency by maintaining the same high steam condi-tions as the medium class FET (up to 130 bar/538°C).Reliability of the design was confirmed by simulatingthe operating conditions, including the analysis oftemperature and stress distributions or deformationson the casing, on the basis of plenty of well proven FETturbines (see Fig. 9).

4.2 Adoption of high efficiency impulse stagesWith the adoption of a nozzle governing system, a

Curtis stage is applied as the top stage in order toreduce the wheel chamber pressure and temperatureeffectively. In an effort to reduce the secondary loss ofthe Curtis stage, a three-dimensional blade profiledesign is used in which the profile is curved in thedirection of the circumference in order to maintain thecharacteristic high efficiency of the FET turbine (seeFig. 10).

As a result, a 1.7 % improvement is expected instage efficiency, compared to the existing blade design.

Fig.7 N Series steam turbine, assembled cross-sectionaldrawing

Fig.9 Analysis of inlet part with temperature distribution

Fig.8 Overview of the N Series casingFig.6 Creep rupture test result of 2 % Cr steel

17 18 19 20 21

1,000

100

10

Larson Mirror (time temperature) parameterLMP (20) = T × [20+log(t)] / 1,000

Str

ess

(MP

a)

HP part

RotorOuter casing

Rear bearing pedestalReaction

stage blades

LP blades

LP casing

Front bearing pedestal

Steam turbine for Shanghai Chung Loong Paper Co., Ltd. (China).

Model Single extraction condensing type

Output 26 MW

Steam condition extraction pressure

123.6 bar/538°C/9.8 bar

Vacuum 0.079 bar

Rotational speed 50 s-1 (3,000 rpm)

Operation started since March 2005

4.1 Compact design by nozzle governing impulse stagesfor the small capacity modelThe normal FET turbine has a throttle governing

system and double shell casing structure as shownabove. However, better flexibility for load change byday and night is requested for small-capacity, privatepower generation turbines, and thus the nozzle govern-ing system will be more suitable for these conditions.

The FET N Series has adopted a nozzle governingsystem and single shell casing as the most compactand suitable system for this application (see Fig. 8).

The FET N Series has been developed for high

Main steam inlet nozzle

Main stop valve

Steam control valve

Extraction control valve

max. principal stress

max.1

max.2


Fig.10 Three-dimensional impulse stage

5. Use in Combined Cycle Plants

Due to the growing global environmental aware-ness in recent years, the major application of thermalpower generation equipment has shifted to combinedcycle plants (CCPPs), which use gas and steam tur-bines in combination to achieve higher thermal effi-ciency. According to this market trend, variations thatcombine use with a 100 to 200 MW class gas turbinehave also been added. For CCPPs, there is greatdemand for axial flow exhaust type turbines since thecost and period for construction can be reduced greatlyby this structure. Accordingly, the axial flow exhausttype AX Series FET was developed, based on existingdownward exhaust type FET turbine technology (seeFig. 11).

CCPPs tend to be constructed in the vicinity of theconsumers in order to reduce the power transmissionloss. An air-cooled condenser is a suitable choice then,since it allows for the unrestricted selection of site

Three dimensional impulse blades

Fig.11 Axial exhaust type AX Series steam turbine

Fig.12 AX Series steam turbine during assembly

Exhaust nozzle

Rear bearing pedestal

Steam control valve


Main stop valve

Main steam inlet nozzle

RotorOuter casing

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

Model Mixed pressure condensing type

Output 117.8 MW

Steam condition 73.3 bar/517°C

Vacuum 0.065 bar

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

Operation start date February 2004

´

locations for the power plant, compared to a water-cooled condenser which requires access to a largeamount of river or sea water. In order to operatecompatibly with the higher exhaust pressure limita-tion of an air-cooled system, a low vacuum type steamturbine series was added.

5.1 Axial flow exhaust type FET steam turbineDevelopment of the axial exhaust type AX Series

was completed and the first unit was put into opera-tion in 1999. The AX Series has been utilized in manyCCPPs.

Figure 12 shows a photograph and lists the specifi-

Fig.13 Concept of fully-electric protection device

S

S

3500/53BENTLYNEVADA

3500/423500/32BENTLYNEVADA

Displacement sensors for electric thrust protection device

Bearing oil pressure trip device

Speed sensors forelectric emergency

governor

Actuator for main

stop valve

Actuator for steam

control valve

On loadtest

Power supply system

Relay circuit

PS

Vacuum trip device

Relay circuit

PS

AC DC battery

Master trip push button

Other protection

relays

Har

dwar

e re

lay

rack


cations of an AX Series turbine.

5.2 Utilization of fully electric protection devicesWith the axial flow exhaust type turbine, the shaft

coupling for the generator, turning motor and protec-tion device are installed in the front pedestal becausethe rear pedestal is located in the exhaust hood.Therefore, to simplify the front pedestal as much aspossible and to improve the maintenance, all protec-tion devices, such as the over-speed governor andthrust failure protection system have adopted a fullyelectric configuration (see Fig. 13).

Fig.14 Strengthened low pressure blades These electric protection devices are also used inFuji Electric’s larger capacity steam turbines, incommon with the FET turbines.

5.3 Correspondence to air-cooled condenserThe vacuum obtained by an air-cooled condenser is

less than that of a water-cooled condenser.This higher exhaust pressure severely stresses the

low-pressure blades in the steam turbine exhaust part.The development of strengthened low pressure bladeshas solved this issue (see Fig. 14).

6. Conclusion

The medium-capacity steam turbine FET Serieshas been expanded so as to be applicable to a wide-ranging market. Due to continuous requests foradvanced solutions in response to global environmen-tal needs and de-regulation of the electric powersupply industry, the demand for equipment withhigher efficiency and lower-cost will increase more andmore in the future. Fuji Electric intends to continue toadvance technical development in order to accommo-date these growing needs.

Strengthened low pressure blades


Hiromichi HiwasaToru HaseKohji Haga

Present Developmental Status ofFuji Electric’s Turbine Generator

1. Introduction

The capacities of air-cooled, two-pole turbine gen-erators have increased dramatically. About 10 yearsago, hydrogen-cooled generator was used in 150 MVA-class turbine generators, but nowadays, air-cooledgenerator is even being used in 200 MVA-class andabove turbine generators.

Meanwhile, at combined cycle power plants,400 MVA-class generators are being coupled to single-shaft or multi-shaft type steam turbines, and thedirectly hydrogen-cooled stator winding type or thedirectly water-cooled stator winding type are appliedfor the generators. Based on customer needs foreconomy, maintainability and operability, the genera-tor having the indirectly hydrogen-cooled stator wind-ing (hereafter referred to as indirectly hydrogen-cooledgenerators) is most suitable. Fuji Electric has devel-oped a series of 300 MVA air-cooled generators and up-to-450 MVA indirectly hydrogen-cooled generators thatuse a global vacuum pressure impregnated insulationsystem (F resin/GII), (hereafter referred to as theGlobal VPI insulation system).

An overview of the technical development ininvolved in the creation of this product series, impor-tant developments of the Global VPI insulation systemfor high voltage large-capacity generators, and auto-matic manufacturing technology are described below.

2. Practical Application of Large-capacity Air-cooled Generators

Air-cooled generators have a simpler structurethan hydrogen-cooled generators and because theyrequire no auxiliary systems such as a hydrogen gassupply system or a sealing oil supply system, theinstallation, operation and maintenance of air-cooledgenerators is quick and easy. Furthermore, air-cooledgenerators are advantageous because their productionlead-time is short and initial investment cost is low.Based on the results of verification testing of a126 MVA prototype generator built in 1999, FujiElectric has worked to develop larger capacity air-cooled generators and has shiped 50 Hz, 280 MVA air-

cooled generator into practical use. Figures 1 and 2show a photograph of the external appearance and adrawing of the cross-section of this generator.

2.1 Technical featuresAs regards the cooling methods, the indirect cool-

ing is applied for the stator winding and the directcooling (radial flow) is applied for the rotor winding.And air coolers are installed in the side of the statorframe. The rotor is supported by two bearing pedestalspositioned on a bed plate, and the exciter or thecollector rings are mounted on the anti-turbine sideshaft.

For the stator winding, Global VPI insulationsystem is applied. The stator winding is impregnated

Fig.1 280 MVA air-cooled turbine generator

Fig.2 Cross-sectional view of 280 MVA air-cooled turbinegenerator

GeneratorGenerator

ExciterExciter

4700

11600

Bea

rin

g

Bea

rin

g

Stator

RotorE

xcit

er


with epoxy resin throughout the entire stator afterstator winding insertion into the stator core.

The following analysis and evaluation techniqueswere used to advance the increase in capacity of air-cooled generators.(1) Evaluation of stator and rotor winding tempera-

ture using three-dimensional flow and tempera-ture analytical techniques utilizing the finiteelement method (FEM)

(2) Analysis of stray load loss using electromagneticfield analytical techniques utilizing FEM

(3) Evaluation of fatigue strength of the rotor usingstrength analytical techniques utilizing FEM

2.2 Shop test results of the 280 MVA air-cooled turbinegeneratorIn the abovementioned 50 Hz, 280 MVA air-cooled

turbine generator, the type rating was tested with no-load characteristic test, short circuit characteristictest, temperature rise test, and by measurement of theloss. Type rating specifications and the shop testresults for this generator are listed in Table 1. All theresults are satisfactory and demonstrate that therequired performance has been achieved. Additionally,as part of the shop test, the rotor winding temperaturedistribution, the stator winding temperature distribu-tion and the stator vibration were measured. Thesemeasured results were then compared to the designvalues and to data measurements from previouslymanufactured generators, and then evaluated. Basedon the comparisons and evaluation, the excellentcharacteristics and high reliability of this generatorhave been verified.

Table 1 Factory test results of 280 MVA air-cooled turbinegenerator

3. Technology for Enlargement in the Capacityof Indirectly Hydrogen-cooled Turbine Gener-ators

A 400 MVA-class indirectly hydrogen-cooled tur-bine generator in which Global VPI insulation systemis applied to the stator winding has been developed.As a representative example, Fig. 3 shows a cross-sectional view and Table 2 lists the ratings andspecifications of a 450 MVA generator.

In consideration of the economic reasons and FujiElectric’s proprietary technology and manufacturingfacilities, the following guidelines were adopted toduring development.(1) The maximum output of the generator to be

developed shall be limited by the capability ofGlobal VPI facility.

(2) The rotor and stator of the generator to bedeveloped shall adopt the same structure or thesame production method as an indirect air-cooledturbine generator.

(3) Newly installed manufacturing facilities such asautomatic brazing equipment for the rotor wind-

Table 2 Specifications of the 450 MVA indirectly hydrogen-cooled turbine generator

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

Output 280 MVA

Voltage 14.7 kV

Current 10,997 A

Power factor 0.9

Rotating speed 3,000 r/min

Frequency 50 Hz

Thermal class 155 (F class)

Coolant temperature 40°C

Excitation system Thyristor excitation

Standard IEC60034-3

Stator winding temperature rise ≤ 81 K

Rotor winding temperature rise ≤ 80 K

Short circuit ratio 0.52

Transient reactance 26.7 % unsaturated value

Sub-transient reactance 20.1 % unsaturated value

Efficiency 98.82 % conventional efficiency

Spe

cifi

cati

onF

acto

ry t

est

resu

lts

4500

12000

Stator frame

Stator RotorBearing

Main terminalVentilation fan Cushion plate

Output 450 MVA

Voltage 21 kV

Current 12,372 A

Power factor 0.85

Rotating speed 3,600 r/min

Frequency 60 Hz

Thermal class 155 (F class)

Coolant temperature 40°C

Coolant pressure 400 kPa (g)

Excitation system Thyristor excitation

Standard IEC60034-3


ing (to be described later) shall be used to themaximum extent possible.

3.1 ConstructionThe 400 MVA-class indirectly hydrogen-cooled tur-

bine generator differs from an air-cooled generator inthat the stator frame functions as a pressure vesseland bracket type bearings are used, since hydrogen isused as the coolant. The stator and rotor bothbasically adopt the same construction and manufactur-ing method as the air-cooled generator, however.

Moreover, similar to the air-cooled generator, thestator winding also utilizes a Global VPI insulationsystem, which is one of Fuji Electric’s principal technol-ogies. In order to realize this configuration, it wasnecessary to make the Global VPI insulation systemcompatible with high voltages. The relevant technicaldevelopment is described in detail in chapter 4.

After Global VPI processing, the completed statoris inserted into the cylindrical stator frame, which is apressure vessel, and secured via a spring plate to thestator frame. The spring plate, stator and stator frameare welded in the same manner as a large air-cooledgenerator.

The rotor winding utilizes the same radial flowdirect cooling as the air-cooled generator, but has athicker conductor due to the larger field current. Inthe case of the air-cooled generator, the ventilationhole for the conductor is formed with a punch-processin order to enhance the economic efficiency of theprocessing. In the case of the indirectly hydrogen-cooled turbine generator, that same punch processingcannot be used due to the deformation of the punch-outpart of the conductor, capacity of manufacturingfacilities, and other such factors. However, aftercareful investigation of many factors, including theclearance of the punching die and the sectional profileof the conductor, a punch process was realized for thisfabrication step.

3.2 Ventilation and coolingIn a large capacity air-cooled turbine generator,

ventilation is implemented using a “double flow”design. In this design, in order to achieve a uniformdistribution of the stator winding temperature, themiddle portion of the stator core is provided with astructure that flows a coolant gas from the outerdiameter to the inner diameter of the stator core. Onthe other hand, since hydrogen gas has a lower densityand larger thermal capacity, when the coolant gaspasses 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 hy-drogen-cooled turbine generator is implemented with a“single flow” design in which a coolant gas flows onlyfrom the inner diameter to the outer diameter of thestator core. In order to optimize the gas flow volumedistribution in the axial direction, the optimum thick-

ness and arrangement of the stator core block and theaxial arrangement of the rotor winding ventilation holewere determined using analytical techniques that hadbeen verified with the abovementioned 126 MVA proto-type generator.

3.3 Suppressing the vibration of a long rotorAs generator capacities increase, rotors are de-

signed to be longer in the axial direction. Consequent-ly however, mass unbalance and asymmetry in thestiffness of the rotor readily cause the shaft to vibrate.Thus, the issue of vibration must be given dueconsideration.

In order to verify double frequency vibrationcaused by asymmetry in the stiffness of the rotor, afactor which cannot be reduced by balancing the rotor,an impulse-force hammer test was performed as shownin Fig. 4 to compute the natural frequency in theprincipal axis direction of moment of inertia of area,and the asymmetry was compared with the calculationresults. The results of this analysis and comparisonwere reflected in the design of the compensation slit forthe rotor pole, which compensates asymmetry in thestiffness of the shaft.

4. Insulation Technology for the Stator Winding

Using its Global VPI insulation technology, whichhas been acquired over many years, and its world-leading Global VPI manufacturing equipment, FujiElectric has been appling Global VPI insulation tech-nology to turbine generators since 1993, and hassubsequently delivered approximately 100 units. Asthe capacities of the abovementioned indirectly hydro-gen-cooled turbine generators increase, the capabilityto withstand high voltages and provide stable insula-tion quality are required of Global VPI insulationtechnology. Accordingly, Fuji Electric has developed aGlobal VPI insulation system for 22 kV-class ratedturbine generators.

Fig.4 Impulse-force hammer test

Rotor

Impulse hammer


4.2 Development of 22 kV-class Global VPI insulation forturbine generatorsThe 22 kV-class Global VPI insulation for applica-

tion to 400 MVA-class hydrogen-cooled generators, thecoils are longer, the insulation is thicker and thewithstand voltage is higher than in previous statorcoil. Thus, Fuji Electric developed this technology byfocusing on the taping characteristics and impregna-tion characteristics of the main insulation layer andthe reliability of the end corona shield, and byevaluating the reliability of the Global VPI insulation.4.2.1 Analysis of the main insulation taping

The stator coil is insulated by winding a maininsulation tape of mica paper several times around thecoil. The insulation characteristics of this stator coilare influenced by the taping method and the thicknessand width of the tape. For an example, overlappingstate of the main insulation tape affects the breakdown voltage (BDV) value, so that it is required tostudy the taping method in order to achieve themaximum BVD value with the same layer numbers.In order to obtain the optimum condition for taping, ananalytical software program had been developed andapplied. In the operating voltage and withstandvoltage, the electric field was observed to concentrateat the corners of the cross-section of the stator coilinsulation. While taping, the number of overlappinglayers must not decrease at these locations. Figure 7shows the analysis results of taping with 22 kV-classinsulation. The number of overlapped tape layersincreases at the coil corners, and it was verified thatthe taping is regular. This result is reflected in thetaping process of the 22 kV coil.4.2.2 Temperature distribution of end corona shields

End corona shield zones are provided at the end ofthe stator to relieve the potential gradient from theend of the coil. The temperature distribution of theend corona shield zones was quantified with this22 kV-class insulation. Figure 8 shows the tempera-ture distribution of the end corona shield zone whilethe nominal operating voltage is applied. The maxi-mum temperature occurs near the edge of the slotcorona shield, and this is in agreement with the resultsof surface potential measurements. The maximumtemperature rise of 1.6 K was a small value, however.Even in withstand voltage tests, (2E+1, where E is therated voltage [kV]), no abnormalities such as flashoveror surface discharge were observed. Thus, it has beenverified that the end corona shield zones with 22 kV-class insulation provide sufficient functionality.4.2.3 Evaluation of insulation reliability

A straight bar model and full-scale model weremanufactured for the evaluation of insulation reliabili-ty. A heat cycle test and V- t test were performed withthe straight bar model, verifying that that insulationprovided stable performance in response to heat stressand a sufficient voltage endurance lifetime. Moreover,

Fig.6 Cross-sectional view of stator winding

Fig.5 Appearance of stator after Global VPI (280 MVA air-cooled generator)

4.1 Features of Global VPI insulation for turbine genera-torsGlobal VPI insulation system is advantageous

because the stator windings and the stator core areimpregnated and hardened together, thereby improv-ing the cooling performance of the stator windings andreliability against loosening of the windings, andrealizing less maintenance work. Figure 5 shows theappearance of a Global VPI insulated stator and Fig. 6shows the cross-section of the stator winding. ThisGlobal VPI insulation for turbine generators utilizesthe following insulation technologies in order to ensurethe reliability of the insulation.(1) Highly heat-resistant epoxy resin(2) Highly pregnable mica paper tape(3) Internal electric field relaxation layer providing

high voltage endurance and a long service life(4) Thermal stress relaxation layer providing high

heat cycle resistance

Core

Coil

Strand

Core

Thermal stress

relaxation layer

Main insulation

Internal electric field relaxation layer


5. Manufacturing Automation Technology

The market place demands turbine generators tohave short delivery times, low price and stable quality.In order to meet with these demands, Fuji Electric hasdeveloped and applied technology for the automationand mechanization of manufacturing processes. Aportion of this technology is introduced below. Previ-ously, generator manufacturing technology dependedlargely upon the skill of the manufacturing workers,but the introduction of automated and mechanizedmanufacturing processes has made if possible toachieve stable quality.

5.1 Automatic brazing equipment for the rotor coilUntil now, the process of manufacturing a rotor

coil involved the manual brazing of a copper bar.Automatic brazing equipment has been newly devel-oped, however, and is shown in Fig. 11. This automaticbrazing equipment continuously brazes copper barswith a high-frequency brazing machine, and thenfinishes the copper bars to form spiral-shaped rotorcoils. In changing over the brazing work from amanual to an automated operation, the temperatureduring high-frequency heating and the timing for

Fig.7 Isolayer distribution over coil surface in 22 kV modelwith taping in both directions

Fig.9 Appearance of 22 kV full-scale model

the full-scale model shown in Fig. 9 was also manufac-tured in order to verify reliability of the insulation,including its method of manufacture. The full-scalemodel assumes a 450 MVA indirectly hydrogen-cooledturbine generator. The model core is 4.5 m in lengthand has 5 slots. The full-scale model is built with thesame configuration as an actual generator, i.e. with aninserted stator coil, a fastened coil end and Global VPIprocessing, and therefore a coil end support andsupport ring are attached to the stator core of the full-scale model so that after the vacuum pressure impreg-nation procedure, the stator coils and core can be curedwhile rotating.

After the initial withstand voltage (2E+1) test, 25iterations of a heat cycle test are then carried out withthe full-scale model. The tan δ vs. voltage characteris-tics during the heat cycle testing are shown in Fig. 10.Since the tan δ characteristics do not exhibit muchchange from their initial value to their value at the25th iteration of the thermal cycle test, the stability ofthe insulation performance was verified. Moreover,after the 25th heat cycle, an insulation breakdownvoltage test of the full-scale model was performed in anatmosphere of air, and the breakdown voltage wasverified to be at least three times greater than therated voltage (in air).

Fig.8 Surface temperature distribution on end corona shield in22 kV model

Fig.10 Tanδ - V characteristics of full-scale model duringthermal cycle testing

View from above

Side view

Main insulation layer

Length (mm)

Coil end portion

Dummy core

24.1 °C (Maximum temp.)

Slot corona shield

End corona shield

End of slot corona shield

Maximum temp. : 1.6 K

Stator core (segment core)

Stator coil

Rotating ring

0 5 10 15 20 25 30Voltage (kV)

5

4

3

2

1

0

InitialHeat-cycle : 160 °C×1 timeHeat-cycle : 160 °C×10 timesHeat-cycle : 160 °C×25 times

Without guard electrode

With guard electrode

tan

(

%)

δ


Fig.11 Automatic brazing equipment Fig.13 Automatic bending machine

Fig.12 Automatic transposing equipment

inserting the brazing filler metal were computed, andconditional settings for the automated machinery weredetermined based on such relationships as the materi-al strength and cross-sectional analysis of the brazedportion. Moreover, in the case of a rotor coil copper barof different dimensions, prior to manufacturing anactual generator, a brazed sample is fabricated and astrength test performed to verify whether the condi-tional settings are appropriate and to ensure goodquality.

5.2 Auto-transposing machineIn order to reduce loss in the stator coil, Roebel

transposition, in other words, strand transposition, isutilized. Previously, the tasks of strand cutting,forming, and transposing were performed manually foreach work process. An auto-transposing machine hasbeen newly developed, however, and is shown inFig. 12. This auto-transposing machine automates theseries of work processes from strand cutting, strippingof insulation from the strand ends, strand forming,transposing, and inserting of insulation material, tostrand bundling. When strand wire and insulating

material are input into the auto-transposing machine,the machine transposes the strands and outputs a coil.The auto-transposing machine is designed with aproprietary transposing mechanism to realize homoge-neity of the transposing.

5.3 Automatic bending machinePreviously, the end portion of the stator coil has

been formed by manually bending the coil, placing it ina shape, and then hardening it. An automatic bendingmachine has been newly developed, however, and isshown in Fig. 13. The automatic bending machine usesrobotic technology to automate all processes frombending the coil end portion into an involute shape andheat forming, to cutting the conductor at the coil end.Use of this automatic bending machine achieves uni-formity of the involute shape of the coil end andshorter lead-times.

5.4 Automatic process control for the Global VPI systemMoreover, in the Global VPI process, which is the

most important manufacturing technique, the impreg-nating resin used is controlled strictly and the impreg-nation and rotational hardening processes are regulat-ed automatically. Also, during the impregnationprocess, an impregnation monitoring system is utilizedto ensure that the resin has impregnated the insula-tion layer of the coil. Thus, the Global VPI process isimplemented under strict manufacturing process con-trol, aiming to realize automation and good stability ofthe quality.

6. Conclusion

The present status of Fuji Electric’s development ofturbine generators has been described.

Fuji Electric intends to continue to develop tech-nology to produce high quality and highly reliableturbine generators in response to market needs.

Copper bar

Brazing machine

Spiral-shaped rotor winding

Roebel transposition forming portion

Cutting portionTransposing portion

Stator coil end portion

Heat forming portion

Involute shape bending portion


Shigeto YamadaHiroshi Oyama

Small Capacity GeothermalBinary Power Generation System

1. Introduction

Japan is a volcanic country having abundantgeothermal resources. To date, Japan has 20 geother-mal power generation facilities, with a total installedcapacity of 550 MW. Most of these facilities are largecapacity geothermal power plants constructed by utili-ty power companies, but due to various circumstances,there are no further plans to build large capacityplants in the near future. The New Energy andIndustrial Technology Development Organization(NEDO) is continuing its program of GeothermalDevelopment Promotion Surveys, which since 2003have targeted the development of small and mediumcapacity resources. There are many high temperaturewells and steam discharge sites in Japan which are notutilized. Various studies are being carried out toexpand the usage of such geothermal energy sourcesthat are not currently utilized for domestic energygeneration. Efforts are underway to promote the useof natural resource-based energy systems, includinggeothermal energy, and this initiative is known asEIMY (energy in my yard).

In addition, RPS (renewable portfolio standard)legislation mandating the utilization of electricitygenerated from renewable energy has been enacted inmany countries. In Japan, the RPS became effective inApril 2003. The renewable energy required for use inaccordance with the RPS includes geothermal energy.Consequently, utilization of low temperature geother-mal resources for electricity generation, which was notconsidered previously, is now being planned.

For small scale or low temperature geothermalresources, it is sometimes more economical to use abinary power generation system having a lower boilingpoint medium than that of conventional geothermalsteam turbines.

In consideration of these circumstances, Fuji Elec-tric is developing a small capacity geothermal binarypower generation system.

2. Binary Power Generation System

Geothermal binary power generation systems uti-

lize a geothermal resource (steam or hot water) as aheating source to evaporate a low boiling point fluid,which drives a turbine. Such a system is called a“binary power generation system” because it uses twodifferent kinds of fluids, geothermal fluid and lowboiling point fluid. Figure 1 shows a conceptualschematic diagram of a geothermal binary powergeneration system. In Japan, binary systems wereexperimentally operated for 5 years beginning in 1993by NEDO (new energy and industrial technologydevelopment organization). During that experimentaloperation, hydrochlorofluorocarbon (HCFC) was usedas the low boiling point fluid, however, HCFC use mustbe abolished by 2020. There is a manufacturer abroadwho has commercialized a binary power generationsystem that uses hydrocarbons such as butane orpentane. Another system is the so-called “Kalinacycle” which uses a mixture of ammonia and water.

In countries such as the USA, Philippines, NewZealand and Iceland, binary power generation systemsare widely utilized for geothermal power generation atfacilities ranging in capacity from several hundreds ofkW to tens of thousands of kW. The binary powergeneration system by Ormat Industry, Inc. that usespentane is especially well known and has been deliv-ered to many geothermal countries. One of thosesystems has been delivered to Japan at the HachobaruGeothermal Power Station of Kyushu Electric PowerCo., Inc. as a pilot machine. Several published papers

Fig.1 Schematic diagram of binary power generation system

Evaporator

Geothermal steam or hot water

Productionwell

Fluid circulation pump

Turbine

Generator

CondenserRe-injection

well


describe small capacity geothermal binary power gen-eration systems of other manufacturers that are beingoperated in Europe. In Japan, there are no manufac-turers supplying geothermal binary power generatingsystems as commercial products, although there havebeen instances of experimental operation. Whenimporting a power generation system from overseas,the owners of the small capacity geothermal binarypower generation system may require technical sup-port from Japanese engineers to comply with Japan’svarious requirements such as documentation andinspections in accordance with the Electricity UtilitiesIndustry Law. There might also be some concernsregarding the after sales service of the importedsystem. In this regard, we consider it quite importantthat small scale geothermal binary power generationsystems be supplied by Japanese manufacturers.

The first geothermal power generation experimentwas successfully carried out in Italy in 1904(1), and theexperimental system reportedly used a steam enginedriven by steam obtained from pure water evaporatedby the geothermal steam. This system is one type of abinary power generation system.

A binary power generation system is driven by thevapor of fluid different from the heat source, and suchheat source is not necessarily a geothermal resource.In Minakami, Gunma, a binary power generationsystem has been constructed and operated utilizingsteam generated by an RDF (refuse derived fuel)boiler. A binary power generation system can be usedto generate electricity from various heat sources suchas industrial waste heat.

3. Development Through Experimental Opera-tion

Fuji Electric is proceeding with the development ofa geothermal binary power generation system, aimingat the Japanese market of small scale low temperaturegeothermal resources as well as geothermal resourcesthroughout the world which may be suitable for abinary system.

Binary power generation systems use the Rankinecycle and basically apply the technologies associatedwith thermal power generation systems. One of themost important issues is the selection of the mostappropriate and economical low boiling fluid, whicheffectively functions between the high heat source(geothermal resource) and the low heat source (atmo-sphere). Once a fluid is selected, the heat cycle can beplanned with a simpler heat balance calculation thanfor a conventional thermal power plant.

The other important issue is the selection ofoptimum design conditions so that the design is bothefficient and economical. It is also important to applyappropriate measures to prevent leakage of the fluid.Economical design is quite important for a smallcapacity system.

Fuji Electric plans the experimental operation of aprototype binary power generation system and intendsto develop a product series based on the results ofstudy and evaluation of the experimental operation.

4. Prototype System

4.1 Overview of prototype systemIn consideration of the targeted heat source (low

temperature geothermal resources) Fuji Electric decid-ed to use iso-pentane which effectively evaporates withsuch heat sources and condenses at atmosphericconditions. Although iso-pentane is a flammable gas,it can be safely used with proper design and handling.Moreover, since the similar hydrocarbon of butane isrecently being used as a cooling medium for home-userefrigerators, it is likely that the usage of hydrocarbonwill be easily accepted by future owners.

In order to facilitate proper evaluation of theresults from the experimental operation, the prototypesystem has been designed in consideration of thegeothermal resource temperature at the actual wellsite. It is expected that a mixture of geothermal steamand hot water will be used, and that the separated hotwater will be used for pre-heating and the separatedsteam will be used for evaporating at the pre-heaterand the evaporator respectively. Also, an air-cooledtype condenser is used because large amounts ofcooling water will not always be available at siteswhere the binary power generation system will beinstalled. The prototype system is designed with asimple cycle, that is, the pentane vapor evaporatedthrough the pre-heater and the evaporator drives theturbine, pentane vapor exhausted from the turbine iscondensed at the condenser, and the condensed pen-tane is pumped back to the pre-heater.

Figure 2 shows the main flow diagram of theprototype system, and Fig. 3 shows an overview of theprototype system.

In order to realize an economical system, theprototype system is designed with general productsand technologies, and does not require the develop-ment of any new equipment or materials.

4.2 Pre-heater and evaporatorBoth the pre-heater and evaporator use the geo-

thermal fluid as their heat source. In general, thegeothermal fluid contains calcium carbonate or silicawhich causes scaling, and therefore, the pre-heater andthe evaporator should be designed with a constructionthat enables easy periodic cleaning of the internalworks. For the prototype system, shell-and-tube typeheat exchangers are utilized, and the geothermal fluidflows on the tube side. Table 1 lists major features ofthe pre-heater and the evaporator.

4.3 Turbine and generatorIso-pentane is non-corrosive to metals, and there-


fore, a standard single-stage steam turbine is utilized.However, a dual mechanical seal system is applied atthe shaft seals to eliminate any leakage of iso-pentanefrom the shaft 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 andgoverning valve is unnecessary, and instead, a stan-

dard process stop valve and control valve which haveno fluid leakage can be used. The control valve is used

Fig.3 Overview of prototype system

Fig.2 Main flow diagram of prototype system

Table 1 Features of pre-heater and evaporator

Separator

Level header tank

Flash tank

Evaporator

Pre-heaterFluid measuring tank

Fluid circulating pump

TurbineInductiongenerator

Air-cooled condenser

Turbine

Oil cooling unit

Air-cooled condenser

Pre-heater

Evaporator

Induction generator

Item Major features

Pre-heater

Evaporator

Type Horizontal shell-and-tube type

Capacity 720 kW

TemperatureInlet / outlet

Iso-pentane : 36 / 84°C

Geothermal hot water : 130 / 100°C

Type Horizontal shell-and-tube type

Capacity 1,990 kW

TemperatureInlet / outlet

Iso-pentane : 84 / 105°C

Geothermal hot water : 130 / 130°C

Table 2 Features of turbine and generator

Item Major features

Turbine

Generator

Type Horizontal, single stage, impulse type

Output 220 kW (maximum)

Speed 1,800 min-1

Type Three phase induction type

Output 250 kW

Speed 1,800 min-1

Type of shaft seal Dual mechanical seal


Fig.4 Section of turbine considered as the primary option, and the prototypesystem also employs air-cooling with fin-tubes. Theair-cooled condenser is the largest component in thesystem and determines the dimensions of the system.When large amounts of water can be used for thepurpose of cooling, a water-cooled condenser may beused to achieve a smaller sized system.

5. Conclusion

The prototype system will be constructed withinthe fiscal year of 2005, and experimental operation willbe commenced thereafter. Fuji Electric intends toexpand the utilization of low temperature geothermalenergy in Japan and throughout the world by provid-ing economical and easy-to-operate binary power gen-eration systems, and anticipates that all forms ofrenewable energy and natural energy will be recog-nized as important energy sources. Furthermore, FujiElectric hopes that the expanded utilization of renew-able and clean geothermal energy will contribute topreservation of the global environment and will enablesociety to leave natural resources for our futuregenerations.

Reference(1) Geothermal Resources Council: Stories from a Heated

Earth. 1999.

1st blades 2nd blades

Nozzles

Main bearing

Shaft

Main bearing

to regulate the inlet pressure so as to maintain theevaporator outlet vapor pressure. The stop valvecloses immediately at the occurrence of an emergencyand stops the turbine and the generator.

Table 2 lists major features of the turbine and thegenerator. Figure 4 shows a cross-sectional view of theturbine.

4.4 Air-cooled condenserAs described above, the air-cooled condenser is


Yoshihiro SakaiKenji NakamuraKunio Shiokawa

Recent Technologies forGeothermal Steam Turbines

1. Introduction

Geothermal energy differs from fossil fuels such asoil, coal and natural gas in that it is a clean energy,having little impact on the environment and emitsalmost no carbon dioxide (CO2), nitrogen oxides (NOx)or sulfur oxides (SOx). Fuji Electric delivered Japan’sfirst practical geothermal power plant to the FujitaTourist Enterprises Co. at Hakone Kowaki-en, sincethen has gone on to deliver more than 50 geothermalplants in Japan and around the world. Fuji Electric iscounted as one of the leading manufacturers of geo-thermal power plants in the world.

Because geothermal steam is highly corrosive,when designing steam turbines for geothermal powergeneration, it is extremely important to realize andgive due consideration to the corrosion of materials.For this reason, Fuji Electric has carried out continu-ous corrosion testing onsite at the location of geother-mal power generation, and materials testing in alaboratory. The valuable data thus acquired wasreflected in the turbine design in order to realize highreliability. Moreover, Fuji Electric has also activelyworked to enhance the efficiency of geothermal steamturbines by applying recent blade row technology.

This paper introduces Fuji Electric’s recent tech-nologies for geothermal steam turbines.

2. Recent Materials Technology for GeothermalSteam Turbines

2.1 Corrosion testing in a modeled geothermal environ-mentIn order to increase the reliability of geothermal

steam turbines, it is important to assess the life ofmaterials under the conditions of the geothermalenvironment. Fuji Electric tests the corrosiveness ofgeothermal steam turbine materials and evaluatestheir applicability to even more severe environmentalconditions.

Assuming harsh conditions as the environment towhich a turbine is exposed, environmental conditionswere established for a concentrated corrosion test sothat the long-term usage condition of a turbine could

be modeled quickly. Table 1 lists the standard corro-sion test environment, Table 2 lists the various corro-sion tests performed in order to assess various stressconditions, and Fig. 1 shows the external appearance ofthe corrosion test equipment.

2.2 Use of new turbine materialsIn existing geothermal steam turbines, 13 % Cr

steel is used as the blade material and 1 % Cr steel isused as the rotor material. These materials are usedwidely and have a successful track record. However,we had developed and selected materials for both theblade and rotor in order to obtain even higher corro-sion resistance and reliability. Table 3 lists thechemical compositions of the developed and selected

Table 1 Standard environment for corrosion tests

Table 2 Contents of the corrosion test

Cl H2S SO42- pH Temp.

10,000 ppm 300 ppm 50 ppm 3.5 to 4.0 60°C

(1.8 %, as NaCl)

(H2S gas sealedat 0.2 L/min)

(Mixed as Na2SO4)

Corrosion testImmersed in a corrosive solution. Weight reduction is measured and corrosiveness is assessed.

Stress corrosion cracking (SCC) test

While applying a static stress, immersed in a corrosive solution and the time to failure is evaluated.

Corrosion fatigue testRepeatedly applied bending load while immersed in a corrosive solution, and number of ruptures are evaluated.

Corrosion fatigue test (mean stress loading)

Static mean stress and dynamic cyclic load are applied simultaneously, and the fatigue limit is obtained.

Blunt notched compact tension (BNCT) test

Static stress is loaded, and the amount of generated SCC cracking propagation is evaluated.

Double cantilever beam (DCB) test and Stress corrosion crack propagation (K1SCC) test

Pre-cracking is formed, and the susceptibility of propagation due to the concentration of stress at the tip of the cracking is evaluated (2 types of test are performed with different shaped test specimens)

Test Description


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

Fig.1 Corrosion cracking and corrosion fatigue test equipment

blade and rotor materials. New materials have higherchromium content than the existing materials, andthis contributes to their better resistance to corrosion.The new blade materials are also heat treated appro-priately in order to lower their susceptibility tocorrosion and cracking.

The corrosion test described in section 2.1 wasimplemented for the existing blade material and forthe new blade material, and the fatigue limit diagramobtained from the result of this testing is shown inFig. 2. The results verified that under the operationalstress conditions of the turbine, the new blade materi-als tolerated a higher stress amplitude, and exhibitedhigher corrosion resistance and reliability. This im-provement is believed to be due to the increasedchromium additive, which has the effect of suppressingthe formation of corrosion pitting that has a largeimpact on corrosion resistance and reliability.

Figure 3 shows the results of a stress corrosioncracking propagation test (K1SCC test) that was usedto evaluate the propagation of cracking at areas of

concentrated stress in both the existing material andthe new blade material. The crack propagationthreshold of the stress intensity factor (in units of MPa

m) was 10 MPa m (relative value of 0.17) for theexisting blade material and 60 MPa m (relative valueof 1.0) for the new material, thus demonstrating thesuperiority of this new material. On the other hand,Fig. 4 shows the results of corrosion fatigue testing

Fig.3 K1SCC test results

Fig.2 Fatigue limit diagram of existing and new materials

Blade material

Rotor material

MaterialChemical composition (%)

0.17 to0.22

C

Existing material (13 % Cr steel)

0.10 to0.50

Si

0.30 to0.80

13.0 to14.0≤0.030 ≤0.020

0.30 to0.80

≤0.05Developed material (16 % Cr 4 % Ni steel)

0.10 to0.35

0.30 to0.60

15.0 to16.0≤0.025 ≤0.005

4.2 to5.0

3.0 to3.7

0.20 to0.35

0.24 to0.34

Existing material (1 % Cr steel) ≤0.10 0.30 to

1.001.10 to

1.40≤0.007 ≤0.007 ≤0.0080.50 to

1.001.00 to

1.500.20 to

0.35

0.21 to0.23

Selected material (2 % Cr steel) ≤0.10 0.65 to

0.752.05 to

2.15≤0.007 ≤0.0070.70 to

0.800.80 to

0.900.25 to

0.350.60 to

0.70

0.26 to0.32

Selected material (3.5 % Ni steel) ≤0.07 ≤0.04 1.40 to

1.70≤0.007 ≤0.0073.40 to

3.600.30 to

0.45 ≤0.15 ≤0.010

Mn CrP S Ni Nb Mo V W AlCu

Plane bending test machine(Schenk plane bending)

Stress corrosion test machine(SCC)

Spring(static load)

Rotating motor(fluctuating load)

Test portion Test portion

Corrosive solution circulation tank (H2S, N2, NaCl, Na2SO4)

0.20 0.4 0.6 0.8 1

1

0.8

0.6

0.4

0.2

0

Mean stress (relative value)

Am

plit

ude

of

stre

ss

(rel

ativ

e va

lue)

Fatigue limit linefrom 13 % Cr steel test

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

Stress intensity factor (relative value)

13 % Cr steel16 % Cr 4 % Ni steel

Cra

ck p

ropa

gati

on s

peed

da

/ dt

(rel

ativ

e va

lue)

1.0

0.1

0.01

0.0010 1.0


Fig.4 Results of rotor corrosion test Fig.5 SCC test results (with and without shot peening)

performed on the rotor material. As in the case of theblade material, it can be seen that the application ofthe selected material (2 % Cr steel) resulted in higherresistance to corrosion.

2.3 Shot peening technologyAs described above, the application of newly devel-

oped materials was confirmed to achieve higher resis-tance to corrosion, but in order to support operation inan even more severe corrosive environment and underhigher stress, shot peening technology is also beingstudied and utilized. Shot peening generates compres-sive residual stress by impacting a blade or rotor areain which the generated stress is severe with a steel ballhaving a certain amount of energy.

Stress corrosion cracking tests were performed onthe shot-peened blade and rotor material, and Fig. 5shows results that verify their longer life. It can beseen that the time to failure is at least twice as long forshot-peened material compared to material that is notshot-peened. Based on these results, Fuji Electricbegan using shot peening as an effective measure toincrease the corrosion life of steam turbines.

2.4 Coating technologyBlade material is required to be resistant to both

corrosion and to erosion. Increasing the corrosionresistance generally requires that the material’s hard-ness be increased. However, when the hardness isincreased, the stress corrosion cracking characteristicsbecome poorer. Flame spray coating is considered tobe a method potentially capable of realizing resistanceto both corrosion and erosion simultaneously. Seventypes of materials were selected as candidates for theflame spray coating, their hardnesses were measured,and the corrosion test described in section 2.1 and ablast erosion test were performed for each. The resultsare listed in Table 4. These results show that the WC-CoCr material has excellent corrosion resistance anderosion resistance as a flame spray coating material.The flame spray coating conditions were optimized forthis material and the flame spray coating material and

Table 4 Results of coating test

application method were verified to be at a levelsuitable for practical application to steam turbines.

2.5 Welding repair technology for the rotorAs described above, various technologies have been

developed and selected in order to increase corrosionresistance. However, products that have already beendelivered contain existing materials and their corro-sion resistance is insufficient compared to the newproducts. In some geothermal steam turbines thathave been in operation for a long time, corrosion hascaused pitting and stress corrosion is causing cracks toappear. Accordingly, a repair technology was neededfor these already-delivered products.

In the case of a rotor, stress corrosion crackingoccurs at the bottom of the blade groove where theconcentration of stress is highest. If cracks occur inthis area, the propagation can be suppressed byshaving the area of occurrence so as to eliminate thecrack. However, if the crack grows larger, it will benecessary to shave the entire blade groove. At such atime, technologies for overlay welding and for reusingthe blade groove are required.

1.0

0.5

0Am

plit

ude

of

stre

ss (

rela

tive

val

ue)

3.5 %Ni steel1 % Cr steel2 % Cr steel

1 % Cr steel

2 % Cr steel

3.5 % Ni steel

0.001 0.01 0.1 1.0Number of cycles to failure (relative value)

0.001 0.01 0.1 1.0

1.0

0.5

0

Str

ess

(rel

ativ

e va

lue)

Time to failure (relative value)

13 % Cr steel13 % Cr steel (shot peening)16 % Cr 4 % Ni steel16 % Cr 4 % Ni steel (shot peening)

Un-ruptured

No shot peening

With shot peening

Shot peening effect

CoNiCrAlY+ Al2O3 · TiO2

Coatingmaterial

Stresscorrosioncracking

(SCC)

Fatigue HardnessHv

Poor Poor Excellent Good 790

WC-10Co4Cr Excellent

Excellent Fair Fair Good 770

Excellent Excellent Excellent 1,100

CoCrMo Poor Fair Excellent

Poor Good 540

Good 650

Al-Zn Poor

Stellite No. 6B spraying

50 % Cr3C2-50 % NiCr

Fair Good 81075 % Cr3C2-25 % NiCr

Corrosionweight

reduction

Blasterosion(amount

of averagewear)

: Not tested


Fig.8 Efficiency of conventional and advanced reaction blades

After welding conditions were selected for the platematerial, welding was performed according to thedimensions of the turbine and then a mechanicalproperty test and a corrosion test were implemented.13 % Cr steel is used as the overlay material and thewelding was implemented as multi-layer tungsteninert gas (TIG) welding.

A test specimen was sampled at the weld location,and the results of its corrosion fatigue testing areshown in Fig. 6 and the sample’s overlay weldingmicrostructure is shown in Fig. 7. The microstructurehas zero defects. Excellent mechanical properties andcorrosion resistance were verified for the rotor hostmaterial, and this welding repair technology wasestablished for steam turbines.

As described above, a method has been establishedfor assessing corrosion, which largely impacts thereliability of geothermal steam turbines, and newmaterials, shot peening technology, coating technologyand repair technology have been developed and estab-lished. By using these materials and technologiesappropriately according to the geothermal conditionsand the generated stress, it is thought that higherreliability can be achieved.

In the future, Fuji Electric plans to advance theassessment and research of corrosion under geother-mal conditions and intends to evaluate techniques for

achieving even higher reliability and for assessing theresidual life.

3. New technologies of Improving the Efficiencyof Geothermal Steam Turbines

As a measure to improve the efficiency of geother-mal steam turbines, recent technologies based onexpertise acquired from the development of steamturbines for conventional thermal power generationare applied mainly to blade rows in order to realize asignificant improvement in efficiency.

3.1 Advanced reaction blades (high load and high efficien-cy reaction blades)Utilizing recent blade row design technology, high-

efficiency reaction blades capable of maintaining highefficiency while increasing the load per stage are usedin blade rows, with the exception of low-pressure bladerows, in geothermal steam turbines. For the samenumber of stages, the use of these reaction bladesincreases the efficiency by at least 1 % compared to theconventional reaction blades (see Fig. 8).

3.2 Improving the performance of low-pressure bladesBecause low-pressure blades in a geothermal

steam turbine account for a larger proportion of thetotal turbine load than in a conventional steamturbine, improving the performance of these low-pressure blades will have a greater effect on improvingthe performance of the total turbine than in the case ofa conventional steam turbine. Originally developed foruse with conventional steam turbines, a new series oflow-pressure blades having much higher performanceare being adjusted for use in an environment of highlycorrosive geothermal steam and are being applied toactual turbines.

Below, features of this new series of low-pressureblades will be described from the perspective of theirefficiency and the status of the compact-size high-efficiency low-pressure blades currently being devel-oped will also be discussed.

Fig.7 Microstructure of the overlay welding

Fig.6 Results of corrosion fatigue test of repair welded area

13 % Cr steel1 % Cr steelRepair welded area

0.001 0.01 0.1 1.0

1.0

0Am

plit

ude

of

stre

ss (

rela

tive

val

ue)

Number of cycles to failure (relative value)

13 % Cr steel

1 % Cr steelRepair welded area

Confirm health of microstructure

Welding 1st layer Final layer25 µm 25 µm

1.02

1.00

0.98

0.96

0.94

0.92

0.90

0.886.05.04.03.02.01.00

Rel

ativ

e ef

fici

ency

Loading factor

Conventionalreaction blades

Advanced reaction blades


proved by at least 2 % compared to the conventionalstationary blades.(3) Development of high efficiency, compact-size low-

pressure bladesThe technologies used to design the new series of

low-pressure blades for conventional large steam tur-bines were also applied to the design of 500 mm-and-shorter low-pressure blades, and a high-efficiencycompact-size low-pressure blade series that achievesdramatically higher performance is presently beingdeveloped (see Table 5).

This series is designed originally under consider-ation with use in geothermal steam turbines, and willalso be provided the following features as well as theitems adopted to enhance efficiency by using this newseries of low-pressure blades.(1) Highly reliable, rugged design for operation in a

corrosive environment(2) The blade root mounting area in all stages uses a

simple inverted T-shape(3) Redusing leakage loss from the blade tip with

shroud is in all stagesFigure 11 shows the blading plan for the largest

size blades (490 mm) in this series.

4. Example Applications of the Recent Technolo-gies

Introduced below are examples of actual geother-mal steam turbines to which the above-describedrecent technologies have been applied.

(1) Transonic profilesRecent advances in computational fluid dynamics

have made it possible to simulate accurately the flowwithin a blade row, and by optimizing the velocitydistribution within that blade row, a low-loss profilecan be realized (see Fig. 9). The new profile shape ischaracterized by a convergent-divergent profile (aprofile designed so that the flow path widens towardsthe end) that is adapted for transonic flow. The resultsof steam wind-tunnel testing confirmed that when theoutlet Mach number is large, use of the new profileshape reduces profile loss to less than 1/2 of the priorvalue.(2) Lean-radial stationary blades

Using a 3-dimensional time-marching method, var-ious profile shapes were compared while varying theflow pattern, and from the results of this comparison itcould be understood that a banana-shaped stationaryblade which leans toward the circumferential directionat its root and toward the radial direction at its tip, asshown in Fig. 10, was the optimal shape. By using thistype of lean-radial stationary blade, flow in the vicinityof the root, where separation is likely to occur, hasbeen improved dramatically. The results of a modelturbine test confirmed that stage efficiency was im-

Fig.9 Advanced low-pressure blade analysis example andsteam wind-tunnel test results

Fig.10 Results of efficiency test of lean-radial stationary bladesin a model turbine

Table 5 Development of high efficiency compact-size low-pressure blades

Fig.11 Blading plan for 490 mm low-pressure blades

1.2 1.4 1.6 1.8

5

4

3

2

1

0

Rel

ativ

e pr

ofil

e lo

ss

Mach number of blade row outlet

Advanced profile

Operating range

Conventional profile0.8

0.9

1.5

1.6

1.5

1.3

1.81.71.61.51.41.31.21.1

Drain slits

Trailingedge

Leadingedge

Lean-radial stationary blade Relative volumetric flow0.6 0.8 1.0 1.2 1.4 1.6

1.1

1.0

0.9

0.8

0.7

0.6

Rel

ativ

e st

age

effi

cien

cy Lean-radial stationary blade

Conventionalstationary blade

50 Hz-use (nominal exhaust area)

60 Hz-use (nominal exhaust area)

490 mm blade (2.5 m2) 410 mm blade (1.7 m2)




Fig.12 Cross-section of 64.7 MW geothermal steam turbine forDixie Valley geothermal power plant

Fig.13 Cross-section of 55 MW geothermal steam turbine forReykjanes geothermal power plant

4.1 64.7 MW geothermal steam turbine for the Dixie ValleyGeothermal Power PlantFigure 12 shows a cross-sectional view of the steam

turbine whose efficiency was upgraded at the DixieValley Geothermal Power Plant in the United States.This turbine was placed into service in 1988, and 15years later its internal components (rotor, blades,stationary blade holder, stationary blade rings, etc.)were upgraded using the latest technology in order toincrease efficiency of the turbine. The major recenttechnologies applied to this turbine are listed below.(1) New blade material is used in moving blades,

except in the last 2 stages(2) New series of high-efficiency 665 mm low-pressure

blades are used for the low-pressure blades (in thelast 3 stages)

(3) To increase reliability, shot peening is implement-ed in areas of concentrated stress at the blade rootand blade groove of low-pressure blades (in thelast 3 stages)

The efficiency upgrade enabled this plant to in-crease its maximum load significantly from the previ-ous value of 60.5 MW to 64.7 MW. After the upgrade,stable operation continued as before.

4.2 55 MW geothermal steam turbine for the ReykjanesGeothermal Power PlantFigure 13 shows a cross-sectional view of the steam

turbine currently being manufactured for the Reykjan-es Geothermal Power Plant in Iceland. The character-istic features of this turbine are a high inlet steampressure of 19 bar abs., and 2 × 14 blade stages, whichare more stages than in a normal geothermal steamturbine.

The major recent technologies applied to thisturbine are listed below.(1) High-efficiency high-load reaction blades are used

in blade rows, except for the low-pressure blades(last 3 stages)

(2) 490 mm high-efficiency compact-size low-pressure

blades are used for the low-pressure blades (in thelast 3 stages)

(3) 2 % Cr rotor material, which has excellent corro-sion resistance, is used in the rotor

(4) New blade material is used in the moving bladesat the steam inlets (main steam, admission steam)

(5) To increase reliability, shot peening is implement-ed in areas of concentrated stress at the blade rootand blade groove of low-pressure blades (last 3stages)

This plant is scheduled to commence operation in2006.

5. Conclusion

Japan is a volcanic country with abundant geother-mal energy resources, but at present, geothermalpower generation only accounts for 0.2 % of Japan’stotal power generating capacity. Meanwhile, there areother countries such as the Philippines and Icelandwhere thermal power generation accounts for approxi-mately 15 % of their total power generating capacity.It is hoped that geothermal power generation usingdomestically produced geothermal energy will continueto be developed in the future. As a leading manufac-turer of geothermal power plants, Fuji Electric intendsto continue to work to increase the reliability andperformance of geothermal steam turbines.

References(1) Sakai, Y. et al. Geothermal Steam Turbines with High

Efficiency, High Reliability Blades. Geothermal Re-sources Council Transaction, Vol.24, 2000. p.521-526

(2) Sakai, Y. et al. SCC Growth Behavior of Materials forGeothermal Steam Turbines. Corrosion Engineering,Vol.53, 2004. p.175-185

(3) Sakai, Y. et al. Corrosion Resistance of Materials forGeothermal Steam Turbines. Proc. of InternationalConference on Power Engineering-03, Kobe, Japan.2003.

RotorCasing

Reactionblades

Low-pressure blades

Front bearingpedestal Rear bearing

pedestal

RotorCasing

Reactionblades

Low-pressure blades

Frontbearingpedestal

Rear bearingpedestal


Fig.1 View of reused thermal power generating unit

Masaki KatoSeiichi AsanoShousuke Fukuda

Recent Technology for Reusing AgedThermal Power Generating Units

1. Introduction

For the continuous operation in another 20 or moreyears from aged thermal power generating units thathave already been operated for 30 years, Fuji Electrichas replaced a two-cylinder reheat type turbine withsophisticated single-cylinder reheat type turbine, werereused the existing foundation and nearly all theauxiliary machinery as counter-measures of life prolon-gation of the plant.

By replacing a high-performance single-cylinderreheat type turbine in the limited space of an existingpower plant, renewing the insulation of power generat-ing equipment, renewing the high voltage powerconsole and control monitoring equipment, utilizing adigital-electrical governor instead of a mechanical-hydraulic governor, and by adopting an automaticturbine start-up system (ATS) and CRT operation,operability, reliability and maintainability have beenimproved dramatically.

Because this renewal technology can be applied atlow cost to aged thermal power generating units, whichare comprised approximately 70 % of the total numberof thermal power generating units supplied, thistechnology is expected to be in high demand as a wayto provide new solutions to meet customer needs.

This paper introduces power generating unit re-newal technology, which integrates sophisticated tech-nology with mostly reused equipment from an agedthermal power generating unit to solve the issuesconcerned with that aged unit, and also presents anexample application of the renewal technology. Fig. 1shows the full appearance of a reused power generat-ing unit.

2. Serious Issues Concerning Aged ThermalPower Generating Units

With the development of residual life assessmenttechnology, it has become possible to evaluate quanti-tatively the residual life of equipment, and statisticalresidual life and accident data have become publiclydisclosed. On the other hand, users have the followingconcerns regarding the continuous operation and ex-

tension of regular overhaul and maintenance, inspec-tion intervals for aged thermal power generating units,and we frequently hear about these serious belowconcerns.(1) Concern about aging of the entire unit and the

possible occurrence of trouble(2) Apprehension about damage caused by deteriora-

tion of the high-pressure high-temperature steamturbine materials

(3) Wear, corrosion and erosion occurring throughoutthe steam turbine

(4) Concern about the occurrence of accidents due topiping wear, narrowing of the pipe wall thickness,and pipe rupture

(5) Insulation degradation and life of the generatorand electrical equipment

(6) Incomplete maintenance due to a delay in discon-tinuing the use of obsolete equipment

(7) Deterioration in the reliability of control andprotection devices

(8) Incorrect operation due to a delay in improvingoperability

(9) Concern about the tendency toward increasedvibration with aging

(10) Loss due to a decrease in efficiency with aging(11) Starting power loss due to start-up time delay


3. Counter-measures of Life Prolongation for thePower Generating Units

The purpose of the counter-measures of life prolon-gation, basically repair, replace or renew deficientparts of aging facilities in order to make possible thefuture long-term continuous operation of the facilityand to eliminate user concerns. But it is alsoimportant to satisfy user needs by supporting theiroperating plans and to modernize the plants byapplying a wide range of new technologies. Figure 2shows an outline of the measures for plant longevitythat were implemented.

4. Application of Sophisticated Steam TurbineTechnology

In aged steam turbines that have been in opera-tion for more than 20 years, due to the many years ofoperation, high temperature creep damage and fatiguedamage to the materials can be observed. Suchsymptoms have typically been treated by replacing theaffected parts with new components.

The counter-measures for plant longevity are notsimply a return to the counter-measures against plantdeterioration which have been practiced thus far,

rather, these counter-measures employ the latest tech-nology to modify the configuration of a two-cylinderreheat type turbine into a single-cylinder reheat typeturbine while continuing to reuse the existing equip-ment to a large extent, in order to achieve a morecompact size, higher efficiency, lower start-up loss,improved operability and much lower maintenance costin a reused power generating unit.

4.1 Steam turbine specificationsSpecifications of this steam turbine are listed

below, and Fig. 3 shows a cross-sectional drawing of thesteam turbine.

Type: Single-cylinder reheatOutput: 85,000 kWMain steam pressure and temperature:

13.83 MPa/538°CReheat steam pressure and temperature:

3.13 MPa/538°CVacuum: 696 mmHgNumber of extraction stages: 5 stagesRotating speed: 3,600 r/min

4.2 Adoption of single-cylinder reheat steam turbinesIn recent years, steam turbine technology as

progressed toward larger machine capacities andsteam conditions of higher temperature and higherpressure. Turbines, which have conventionally beenconfigured from multiple cylinders, have become muchmore compact by transitioning from three-cylinder totwo-cylinder configurations, and then from two-cylin-der to single-cylinder configurations. The steamturbine also achieves a dramatically more compact sizeby using the existing two-cylinder configuration as ahigh-medium-low integrated single-cylinder configura-tion, without any modification to the existing founda-tion.

Fig.3 Steam turbine cross-section

Fig.2 Outline of work plan to increase plant longevity

Project coordination

Users operating plan

Reliability upgrading

No. of years of continuous useOperating format (DSS/WSS) Planned capital investmentDesired improvement in efficiencyDesired improvement in controllability Desired enhancement of monitoring functionDesired automationDesired shortening of regular inspection intervals

Adoption of integrated turbineAdoption of high-pressure control oil systemRenewal of generator insulationRenewal of high/low voltage cubicleRenewal of turbine and generator control systemAdoption of electronic protection device

Assessment ofpresent statusof equipment

Longevity work plan

Performanceupgrading

Official repair historyResidual life assessmentAssessment of operation dataVerification of current performance

Adoption of high performance reaction blades

Adoption of latest generation of low pressure blades

Functional upgrading

Adoption of digital control systemAdoption of automatic turbine start-up systemAdoption of CRT operation systemRenewal of computerTurbine performance life calculationTurbine start-up schedule calculationVoice announcement system, etc.

List up of work items

Evaluation of work items

Evaluation of costand work schedule

HP main steam control valve (MCV)

Outer casing (front part)

Outer casing (rear part)

Rear bearing pedestalStationary

blade ring

Electronic turning device

Roter

Stationary blade holder

Inner casing II

Inner casing I

Reheat steam inlet

Connection piping

Actuator for MCV



Table 1 Comparison of span and weight for reused andexisting steam turbines

Fig.4 Comparison of the reused and existing steam turbines

Table 1 and Fig. 4 compare the span and weight ofthe reused and existing steam turbines.

4.3 Characteristics of single-cylinder reheat steamturbines

(1) Reuse of the existing foundation and auxiliaryequipment

One motivation for unit reuse is that the existinglow-pressure steam turbine foundation could be usedwithout any modification. The foundation concretewas assessed for deterioration and the strength of theturbine to be reused was analyzed, and the resultsshowed that it was possible to avoid the cost and laborinvolved in modifying the foundation. Additionally,the specifications of auxiliary plant equipment such asthe heater, de-aerator, condenser and turbine lubricat-ing oil system were reexamined for the purpose ofreusing the existing equipment.(2) Adoption of a throttle governing double-shell

structureThis plant is an oil-fired thermal power generating

plant, and because it was designed for daily start-and-stop (DSS) operation, a throttle governing system wasadopted, in which reaction blades were used in allstages, and without a control stage at the steam inlet.As a result of using this throttle governing system, thetemperature fluctuation due to changes in the load atthe cylinder under the most severe conditions has beenreduced, enabling high-speed start-up and a largerrange of allowable load changes. As a result, the start-up loss, an ongoing problem for existing plants, has

Fig.5 Steam turbine rotor

been reduced dramatically.(3) Analysis of shaft vibration and preventative mea-

suresAlong with the conversion to a single-cylinder

configuration, we used a computer to analyze vibrationover the length of the entire shaft coupled to theexisting generator. The analysis results showed anincrease in vibration of the exciter installed at the endof the generator. As a preventative measure, the fieldbalance of the exciter was reconsidered to achieve thesame level of vibration as was originally planned.Figure 5 shows the appearance of the steam turbinerotor.(4) Temperature distribution and stress analysis of

the entire turbineIn the structural conversion to a single-cylinder

reheat type turbine, the high pressure turbine steamoutlet (low temperature reheat part) and mediumpressure turbine steam inlet are combined within asingle casing, and as a result, the temperature devia-tion of the casing largely influences such factors asthermal stress, fatigue life and local deformation.Consequently, analysis of this temperature deviation isimportant.

For this reason, the temperature distribution andstress (finite element method) at the middle of theinterior of the reheat steam inlet were analyzedrepeatedly and an optimum design (design of thecasing and flange shape, wall thickness, etc.) for thesingle-cylinder reheat type turbine was achieved.Figure 6 shows the results of a temperature distribu-tion analysis performed at the reheat steam inlet.(5) Adoption of a separate-type oil system

The steam turbine was converted from a conven-tional common oil system (for both lubricating andcontrol oil) to a separate-type oil system. This controloil system achieves higher valve operating force andimproved controllability to realize a 14 MPa highpressure oil system, and is a new type of controlsystem, using a plunger-type control oil pump for theoperating oil, and using an electro-hydraulic actuator

Parameter

Axial span (mm) 8,300 12,980

Weight (t) 160 210

Single-cylinder type (reused)

Two-cylinder type (existing)

Two-cylinder type (existing turbine)

Single-cylinder type (reused turbine)


for the valve operation. Moreover, the low-pressurelubricating oil system has changed from a turbineshaft-driven main oil pump to an AC drive main oilpump and has been designed to allow the continueduse of existing lubricating oil system devices.(6) Adoption of a digital governor and a fully electron-

ic protection systemLabor savings, as typified by automatic start-up

and remote automation capabilities, and improvedcontrollability have been realized through the adoptionof a digital governor and a fully electronic protectionsystem.

Unlike the conventional protection system, thefully electronic protection system does not require oilpipes or mechanical apparatuses for detection, andthus realizes the advantages of a more compactdetection sensor design and greater freedom in theselection of an installation site. Fuji Electric leveragesthese advantages by adopting this protection system asstandard for all types of turbines, including the axialexhaust type turbine and the single-train type com-bined cycle generating plant.

5. Renewal Technology for Power GeneratingEquipment

The insulation for generator stator coil and othersused for a long period of time deteriorates due toelectrical stress, thermal stress, mechanical stress andcontamination, and comes to the limit of dielectricstrength (end point).

Accordingly, from the perspective of preventativemaintenance of the equipment, before the insulationcomes to the end point and causes a serious accident, itis important to renew that insulations systematically,based on the results of using methods such as non-destructive insulation diagnosis and physicochemicaldiagnosis to assess the level of degradation of theinsulation.

The work plan implemented for plant longevityestimated quantitatively the limit of dielectric strength

of the insulation from the statistically correlationbetween the generator stator coil breakdown voltage(BDV), calculated from non-destructive diagnosis data,and non-destructive data that had been accumulatedover many years, and then assessed the exact timingand scope of the insulation renewal so that theequipment could be reused for another 20 years ofcontinuous operation. This carried out example isdescribed below.

5.1 Specifications of the generatorThe generator has the following specifications.Year of manufacture: 1972Type: Horizontal-mount, cylindrical rotor,

fully-enclosed rotating field, internally-cooled

Output: 100,000 kVAVoltage: 13,800 VCurrent: 4,184 APower factor: 0.85Number of phases: 3Number of poles: 2Insulation class: B

5.2 Rewinding the generator statorBased on the results of a residual life diagnosis

which showed that the BDV value — an importantparameter for safe operation — had decreased, weperformed the renewal work of rewinding the coil.Since the insulation was class-B, we enhanced theinsulating performance by using class-F epoxy resinand vacuum impregnation insulation material, anddramatically reduced the time required for onsiterenewal work by upgrading the connecting method ofconductor to block connections. Figure 7 shows thegenerator stator coil during this renewal work.

5.3 Renewal of the retaining ring for the generator rotorAs a measure to prevent stress corrosion cracking

(SCC) of the retaining ring, we changed the material(18Mn18Cr) of the retaining ring. Additionally, weimproved the dropout prevention of the coil end spacerand renewed insulation below the retaining ring toenhance reliability. Figure 8 shows the retaining ringof the generator rotor during this renewal work.

5.4 Renewal of the brushless exciter windingBecause cracking and other types of degradation

were observed in the field winding lead, we rewoundthe rotor and stator coils of the exciter in order toimprove reliability.

5.5 Renewal of the main terminal bushingThe existing main terminal bushing used insula-

tion oil, but because we had previously experiencedleakage of this insulation oil and had been repairingcracks in the mounting flange, we decided to changethe main terminal bushing to an epoxy-molded type.

Fig.6 Temperature analysis of reheat inlet steam part (finiteelement method)

VALUE OPTION : ACTUAL

3.00E+02

2.25E+02

2.00E+02

1.75E+02

1.50E+02

1.25E+02

1.00E+02

7.50E+01

5.00E+01

2.50E+01

0.00E+00


Fig.7 Rewinding of generator stator

Fig.8 Renewal of retaining ring for generator rotor

5.6 Other improvementsIn addition, we improved the insulation to prevent

current in the shaft bearing and renewed the generatorstator pressurized through-terminal in order to en-hance the reliability of all generator equipment.

6. Improvement with Electronic Control Equip-ment Technology

Among a power company’s aged thermal powergenerating plants, the base plant is sometimes used asa load-adjusting plant and is operated to support dailyand weekly start-and-stop (DSS and WSS) operation.For this purpose, higher reliability, shorter start-uptime, and improved operability are required. In thework plan for plant longevity, in addition to imple-menting the previous measures for preventing degra-dation with age, it was also important to strengthenthe turbine generator monitoring function, to addequipment and to configure an interface to the existingreused components, in order to satisfy customer needsfor shorter start-up time and better operability of theturbine. The sophisticated digital control device and

Fig.9 Scope of automatic turbine start up system (for coldstart)

the integration with existing equipment in order tosatisfy these needs are described below.

6.1 Configuration of automation and monitoring functionsBy automating the various operations associated

with turbine start-up, which had previously beenperformed manually, and by strengthening the plantmonitoring function, the operator’s workload has beenreduced and start-up time shortened dramatically.(1) Automatic turbine start-up system

As can be seen in Fig. 9, the scope of the automaticturbine start-up system (ATS) is confined to the rangefrom the warming of the turbine main steam pipe untilapproximately 25 % of the rated output of the turbine,and thereafter, the load control switches to an auto-matic power control system (APC).(2) Automation of auxiliary steam pressure control

The auxiliary steam pressure of the existing tur-bine is used for turbine shaft sealing and ejectordriving, but such complicated switching operationsrequired a considerable amount of time. Accordingly,the manual operation and admission conditions for theauxiliary steam are now implemented by an automaticcontrol logic circuit, thereby achieving a drastic reduc-tion in turbine start-up time.(3) Automation of the existing turbine drain valve

operationThe existing turbine drain valve is driven by an

electric motor that operates automatically according tocommands from the ATS.(4) Strengthening the plant monitoring function

CRT operation (see Fig. 10) was introduced in orderto realize a comprehensive plant monitoring systemand to reduce the number of operations involved.Consequently, the operator’s workload decreased. Ad-ditionally, a voice announcement system enabled bythe unit computer was added and the human-machineinterface was improved.

Ste

am t

empe

ratu

re (

°C)

Boi

ler

ign

itio

n

Syn

chro

niz

atio

n

Rat

ed lo

ad

Scope of automatic turbine start up system (ATS)

Main steampressure8.93 MPa

Main/hot reheat steam temperature440°C

Main/hot reheat steam temperature538°C

Heat soak speed2,400 r/min

Rated speed3,600 r/min

Power change rate0.86 % /min

Rated load100 %

600

500

400

300

200

100

0

War

min

g of

tu

rbin

e m

ain

st

eam

pip

e

Ope

nin

g of

tu

rbin

em

ain

sto

p va

lve

Ste

amad

mis

sion

Init

ial l

oad

com

plet

ion

Load rise control withautomatic

powercontroller

(APC)

Main steampressure 13.83 MPa

Speed change rate500 r/min/min

Speed change rate200 r/min/min Initial load 10 %


Fig.11 System configuration, after renewal

Fig.10 Central operation room, after renewal

6.2 Configuration of the digital control systemFigure 11 shows the automation and monitoring

functions that were added and the interface to existingequipment. These added functions are configured witha digital controller. By using a digital controller thatis the same model as the boiler controller, the opera-tion monitoring system has been unified and replace-ment parts can now be shared. Additionally, all themain parts of controllers critical to plant control form aredundant system that instantaneously switches to astandby unit when an active control unit system goesdown, so as to continue operation without tripping theplant. These digital controllers and their interface to

existing equipment are described below.6.2.1 Addition of a digital electrical hydraulic governor

(D-EHG)The existing plant used a mechanical hydraulic

governor (MHG), but in order to link to the newlydesigned ATS, APC and other digital control systems,addition of the D-EHG was required.

The D-EHG has the following advantages.(a) Linear continuous control(b) Easy setting of the speed change rate(c) Turbine auto-accelerate and load-increase

functions6.2.2 Reconsideration and reconfiguration of existing

functions(1) Addition of a turbine auxiliary controller

The equipment for renewal includes a unit comput-er, and the system includes a computer I/O panel thatinputs and outputs many field device signals. Thebody of the unit computer is an independent panel. Byequipping the conventional computer I/O panel with adigital programmable controller for controlling turbineauxiliary equipment, a digital control system for bothturbine automation functions and computerI/O functions was realized. By installing this turbinedigital control system at the site from where theexisting computer I/O panel has been removed, allcomputer-related external cables can be reused.(2) Digitization of the turbine auxiliary closed loop

control

K.B

Turbine control Field excitation

Addition of equipment(Supplied by Fuji)

Engineeringwork station(Maintenance tool)

Unit computer

CPU

Turbine digital control system

Databasestation KB

AES Colorprinter

Engineering work station(Maintenance tool)

Local area network for control(FL-NET 100 Mbps)Automatic burner

control system

Automatic boilerauxiliary machine control system

Automatic power control system

Automatichydraulicgovernor

Instumentpanel

TurbinemotorvalvesO

CRT

Operatorconsole

Local area network for information (Ethernet 10 Mbps)

BTG (boiller/turbine/genarator)Supervisory instrumentation panel

Alarmdisplay

Recorder

Board operation panelOperationswitch for auxiliary machine

Supervisoryinstrumentationfor auxiliary

machine EHG

TR TR

Monochromeprinter

TR

Colorprinter

TR TR

Operator consolefor unit computer

C O C

CRT

Operatorconsole

CRT

Operatorconsole

HUB

TR

HUB

Switchingmodule

Switchingmodule

Switchingmodule

AVR

Databasestation

SW

SW

MPU×2

MPU×2

F120

ANN

MPU×2

MPU×2

MPU×2

MPU×2

Switching module

SW SW SW

SW

SW

SW SW

SW SW

SW

SW SW

SW SWSWSW

SW

SW

SW SW

SW SW

Automaticvoltageregulator

MPU×2

SW

SW

Interlock relay panel

Boiler interlock

relay panel

Turbineinterlock

relay panel

SSS

Cubicle forlocal

operationburner control

Cubicle forlocal


Cubicle forlocal


Cubicle forlocal


S

Cubicle formotor

operatedvalves

MMMM

Cubicle for BTG (boiller/turbine/genarator)auxiliary equipments

Renewal of equipment(Supplied by Fuji)

Conversion of equipment(Supplied by Fuji)

Addition and renewal of equipmentfor boiler control system (Supplied by other)


Fig.12 Turbine generator graphic

The existing turbine auxiliary closed loop controlused an analog programmable controller for each loop,but all these control functions have now been config-ured with a turbine digital control system. According-ly, what had been formerly board operations are nowconcentrated as CRT operations and the operator’sworkload has decreased. Due to the elimination of theanalog programmable controls, maintenance has be-come more efficient.6.2.3 Introduction of CRT operation

Plant information from the turbine auxiliary con-troller and other control equipment is transmitted asdigital signals to the CRT, and displayed. Figure 12shows an example display of the CRT graphics.

With the introduction of CRT operation, the dis-tinction between monitoring and operations with theexisting board were reconsidered, and board operationswere reduced. As an example, the necessary opera-tions for start-up and stopping are implemented fromthe CRT, and individual auxiliary devices are con-trolled as a board operation. An auto-mode has beenadded to the board, and selecting the auto-modeenables board operations to be reduced.6.2.4 Addition of voice announcement system enabled by

the unit computerLinked to the automated operation, a voice an-

nouncement system that provides pre-announcementsbefore a command is issued, post-announcements afteran operation is completed, and warning announce-ments in the case of plant trouble has been provided.

These voice announcements are linked to the informa-tion of CRT graphics.6.2.5 Improved reliability of data transmissions

A local area network (LAN) conforming to FL-netand connectable to an open loop dataway having high-speed transmission between digital controllers, highreliability, and a simple transmission interface wasused. This LAN has a maximum transmission speed of100 Mbps, is connected to both a digital automaticvoltage regulator and a digital controller which hadbeen delivered by the boiler manufacturer, and has aconfiguration that enables easy sharing of plant infor-mation. These communication networks are a mean ofimproving the reliability of the digital control system.The important control LAN relating to plant control isconfigured as a redundant system in order to improvereliability.

7. Conclusion

This paper introduced Fuji Electric’s recently im-plemented technology for reusing aged thermal powergenerating units and examples thereof. In order toreceive further continued use from these aged thermalpower generating units, Fuji Electric intends to contin-ue to supply reuse plans that combine existing unitswith sophisticated technology to transform those unitsinto modern thermal power units having excellentreliability and operability.

Turbine No.1 bearingTurbine

VibrationMetaltemperature

Turbine outer casing (upper)temperature

(Front) 341.7°C (Rear) 348.2°C

(Front) 341.6°C (Rear) 340.6°C(Front) 59.1°C (Rear) 55.1°C

Turbine outer casing (lower)temperature

Turbine thrust bearing metaltemperature

Turbine No.1 bearingdrain oil temperature 55.0°C

Turbine shaft position -0.02 mmTurbine decentering

Turbine No.2 bearingdrain oil temperature

65.1°C

Control of lube oil temperature Control of generator hydrogen temperature

Turbine bearing shaft vibration

(1) Turbine No.1 bearing shaft vibration

(2) Turbine No.2 bearing shaft vibration

81.0°C11 µmVibration

Metaltemperature

84.4°C10 µm

10 µm

Left 55.2°C Right 62.8°C85.0 MW5 µm

5 µm

3 µm 0 µm

0 µm

µm

Control fluid pressure 14.88 MPa

Lube oil pressure 0.195 MPa

Main steam inlet temperature 535.3°C

Main steam inlet pressure 13.83 MPa

Intermediate steam inlet temperature 539.5°C

Intermediate steam inlet pressure 3.375 MPa

Oil cooler inlet oil temperature 56.2°C

Oil cooler outlet oil temperature 45.0°C

Generator stator winding (U ph) temperature

79.8°C

Generator stator winding (V ph) temperature

80.2°C

Generator stator winding (W ph) temperature

78.5°C

Generator hydrogen pressure 0.19 MPa

Generator hydrogen purity 97.8 %

Generator No.1 bearing drain oiltemperature

59.6°C

Generator No.2 bearing drain oiltemperature

53.7°C

Exciter bearing drain oiltemperature

44.5°C

Left 54.6°C Right 60.2°C Left 50.2°C Right 46.9°C

Turbine No.2 bearing

Generator No.1 bearing

Generator No.2 bearing Exciter

Exciterbearing

G3,600 r/min

0

125

400

(1)11 µm

(2)

Generator bearing vibration

(1) Generator No.1 bearing shaft vibration

(2) Generator No.2 bearing shaft vibration

(1) Turbine casing expansion

(2) Turbine roter expansion

(3) Exiter bearing vibration

µm

0

40

200

(1)3 µm(2)

0 µm(3)

Turbine roter expansion

14.3 mm

mm

-5-3.2

+20

(1)2.0 mm

(2)

0

710

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