Whole Number 176

Great Potential in the Coming Age,-Fuji Electric

,s Hydropower Equipment

Fuji Electric has provided any kind of turbines and

generators in the field of hydropower plant. Also the

company can meet all needs from distribution systems

to automated, total management and control systems

through integrated system design.

500MW Francisturbine-generator

Bulb-type turbine

Hydropowerplant simulator

200MW pumped storagepower plant

Pelton-type turbine

CONTENTS

Bulb Turbine/Generator for Minokawai Power Plant, 2The Kansai Electric Power Co., Inc.

26MW Pelton Turbine for Nikengoya Power Plant, 7Chubu Electric Power Co., Inc.

Recent Analysis Technologies for Hydropower Equipment 12

Vibration Analysis Technologies for High Head Pump-Turbine Runners 14

Application of Numerical Flow Analysis Technologies to 19Hydraulic Turbines and Pump-Turbines

Technologies to Modernize Existing Hydropower Plants 23

Cover Photo:With the rapid development of

computer technology, particularlythe price reduction and speed in-crease of workstations and personalcomputers, the serviceability ofsimulation technology is increasingin many fields.

Fuji Electric early developed itsown simulation software and hasutilized it for developing and de-signing various products.

The cover photo is an analysisexample of leakage flow around therunner of a bulb turbine, displayingvortex formation over the low pres-sure side of the blade surface usingthe three-dimensional viscous-flowanalysis software developed by FujiElectric.

Head Office : No.12-1, 1-chome, Yurakucho, Chiyoda-ku, Tokyo, Japan

Vol. 43 No. 1 FUJI ELECTRIC REVIEW2

Hiroshi OhtaMasataka SunagaTakanori Namiki

Bulb Turbine/Generator for Minokawai PowerPlant, The Kansai Electric Power Co., Inc.

1. Introduction

Recently in the field of hydro energy developmentboth in Japan and overseas, the benefits of using bulbturbine/generators at low head construction siteswhere the head is 25m or less have been reconsideredas a means to effectively develop domestic energysources. And in response, the planning & developmentof power plants equipped with bulb turbine/generatorsis underway.

Fuji Electric has manufactured and deliverednumerous large size and large capacity bulb turbine/generators ever since delivering the first large capacitybulb turbine/generator in Japan to the Akao PowerPlant of The Kansai Electric Power Co., Inc. in 1978.

The Kansai Electric Power’s Minokawai PowerPlant (Figs. 1 & 2) was recently put into its commercialoperation following an inspection by the Ministry ofTrade and begun Commerce. Fuji Electric delivered abulb turbine unit with a runner diameter of 5.55m, abulb generator with a stator frame external diameterof 7.0m, and a control system etc. to the MinokawaiPower Plant.

Table 1 shows the recent manufacturing history oflarge bulb turbine/generators.

As shown in Table 1, the turbine/generator for theMinokawai Power Plant ranks among the top group forboth runner diameter and power output. In addition,

it is also an advanced bulb turbine/generator thatutilizes numerous new technologies in design, manu-facture and installation. A summary of the newtechnology is introduced in the following report.

2. Project Summary

This project is located on the right bank of theImawatari Dam, situated approximately 800m down-stream of the point where the Kiso River and the HidaRiver merge, this project utilizes the abundant waterflow discharged from the Imawatari Dam. This damtype power plant provides a maximum power genera-tion of 23,400kW, has a maximum water consumptionof 220m3/s and an effective head of 12.36m.

As shown in Fig. 1, this is an urban type powerplant where the powerhouse is located in close proximi-ty to the consumers, which is rather rare for ahydropower plant.

Figures 3 and 4 illustrate, cross sections of theoverall power plant and the turbine/generator, respec-tively.

Equipment specifications are listed below.(1) Turbine

Max. power output : 24,200 kWEffective head : 12.36/12.16mWater consumption : 220 m3/sRated speed : 100 r/min

Fig.1 Vicinity of power plant Fig.2 External view of power plant after its completion

Hida RiverKiso River

Imawatari DamMinokawaiPower Plant

ImawatariPower Plant

Bulb Turbine/Generator for Minokawai Power Plant, The Kansai Electric Power Co., Inc. 3

Table 1 History of Fuji large bulb turbine/generators

Fig.3 Cross section of power plant

Fig.4 Cross section of turbine/generator

(2) GeneratorType : Vertical shaft, revolving magnetic field,

water-water heat exchanger, 3-phase syn-chronous generator (Fin cooling)

Max. power output : 26,000 kVARated voltage : 6.6 kVRated current : 2,274 ARated frequency : 60 HzRated speed : 100 r/minRated power factor : 0.9 (lag)Stator frame outer diameter : 7,000 mmExcitation method : Brushless excitation

3. Characteristics

3.1 Bulb support methodSince the bulb which houses the turbine and

generator is placed in a water passage, in addition tostatic loads such as hydraulic thrust force, deadweight, buoyancy, generator torque, etc., it receivesmechanical vibrations from the rotating part andhydraulic vibrations due to hydraulic pressure fluctua-tion. Therefore, for this project, a method to supportthe bulb with two vertical (upper & lower) stay vanesand an auxiliary supporting method, the anti-vibrationstay and casing support, are provided as illustrated inFig. 5 in an effort to increase the bulb’s naturalvibration frequency.

The upper stay vane is used as the passage forinspecting turbine bearings, shaft seals etc. The lowerstay vane, which also provides access to the turbinechamber, houses the oil and water drain pipes.

Also, a ladder had been provided in conventionalstay vanes to enter and exit the turbine chamber.However in this project a spiral staircase was installedfor reasons of safety and convenience and to improve

Item

Power plant

Akao, The Kansai Electric Power Co., Inc.

Sakuma #2, Power Development Co., Ltd.

16,800/ 16,000

Shingo #2, Tohoku Electric Power Co., Inc.

Main Canal Headworks, U.S.A.

Lower Mettur, India

New Martinsville, U.S.A.

Yamazato #2, Tohoku Electric Power Co., Inc.

Bailongtan, China

Chashma, Pakistan

Minokawai, The Kansai Electric Power Co., Inc.

1

1

2

1

8

2

1

6

8

1

17.40

22.45

15.50

12.80

7.53

6.40

15.93

9.70

13.80

12.16

5,100

5,000

4,485

5,350

6,250

7,300

4,750

6,400

6,300

5,550

36,000

40,900

17,000

27,370

18,333

21,620

24,100

33,684

26,000

26,000

6.6

6.6

6.6

6.9

6.6

6.6

6.6

10.5

11.0

6.6

60

50

50/60

60

50

60

50

50

50

60

Oct. 1978

Sept. 1984

Jul. 1982

Jul. 1986

Nov. 1987

Aug. 1988

Jun. 1992

Underconstruction

Beingdesigned

May 1995

34,000

40,600

26,800

17,200

20,040

23,700

33,000

23,700

24,200

125.0150.0

128.6

136.0

112.5

75.0

64.0

125.0

93.8

85.7

100.0

No. of units

Turbine output (kW) Head (m)

Speed(r/min)

Runnerdiameter

(mm)

Generatoroutput (kVA)

Voltage(kV)

Frequency(Hz)

Commercialoperation

Intakeportion44.7m

Power plant35.3m

Outlet46.6m

φ555

0

Specific speed : 685 m-kWRunner diameter : 5,550 mmMax. hydraulic pressure : 30 mMax. speed rise : 70%

Vol. 43 No. 1 FUJI ELECTRIC REVIEW4

Fig.5 Construction of bulb support

its maintainability.

3.2 Turbine runnerThe 4 blades of the turbine runner consist of 13%

chrome and 4% nickel stainless cast steel, and aremade movable so as to increase the partial loadefficiency. The servomotor, which operates the runnervane, is housed in the runner boss, and the pressurizedoil for operating the runner vane is supplied throughthe pressure oil distributing head located at the end ofthe generator shaft.

Normally, parts inside the runner boss such as thelink are lubricated by oil. For this project however, itwas decided to use water instead of oil for lubrication,since the construction site of this project is located atthe bottom of the Kiso River and the prevention ofriver pollution was a major concern.

This bulb turbine was the first in the world to havea servomotor housed inside a water-filled boss runner.Methods to defect leakage, of servomotor oil in therunner boss for example, were given special consider-ation.

Figure 6 shows a photograph of the completedrunner.

Fig.7 Ceramic seal system

Section A-A Section B-B

A B

A B

Fig.6 Complete turbine runner

Fig.8 Closed circulation method with water-water cooler

1

1

2

2

3

3

4

4

5

5

6

6

7

7

8

8

Sealing system coverWear indicatorCasing for packing boxSpring

Seal ringSeal packingMain shaftMain shaft seal

Heat exchange

Lubricationoil cooler

Flowrelay

Pressurizedoil cooler

Tap waterWatersupply tank

Water supplypump

M

M

N89-6388-108

Bulb Turbine/Generator for Minokawai Power Plant, The Kansai Electric Power Co., Inc. 5

Fig. 10 Construction of bulb’s internal monitoring systemFig. 9 Generator fan cooling method

Table 2 History of fin-cooled bulb turbine/generator

3.3 Main shaft sealing systemA ceramic seal system was used to seal the main

shaft. This ceramic seal system is a mechanical sealthat has ceramic overlays on the seat side of the mainshaft and uses resin packing for the seal packing. Theapplication of this system has benefits such as asimpler water supply system and improved friction/wear characteristics, compared to the conventionalsealing system which uses the carbon packing method.

Figure 7 shows the construction of the ceramicsealing system.

3.4 Water supply systemA closed-circulation method with a water-water

cooler was adapted for the water supply system for thepressurized oil and the lubrication oil. The closed-circulation method is, as illustrated in Fig. 8, a methodto exchange the heat of cooling water (circulation

ItemPower plant

Minokawai, The Kansai Electric Power Co., Inc.

Sakuma #2, Power Development Co., Ltd.

Pressure rise1.0 atmospheric

pressureMerced Main Canal, U.S.A.

Dawson, U.S.A.

Itado, Akita Prefecture

Yuda, Kyushu Electric PowerCo., Inc.

Oya, Fukushima Prefecture

Nibudani, Hokkai Hydropower Generation

1

1

2

1

1

1

1

1

26,000

2,830

17,000

4,660

2,040kW

5,750

3,470

3,060

6.6

4.16

6.6

4.16

6.6

6.6

6.6

6.6

Inductiongenerator

125150

100

180

120

375

150

214

250

No. of units Speed(r/min)

Generatoroutput (kVA)

Voltage(kV)

50

45

50

50

60

50

52

50

Temperature of coolingair at rib outlet (°C)

Remarks

Coolingfin

Motordrivenfan

water) at the pressurized oil and lubrication oil cooler,using a water-water cooler located at the top of thepowerhouse water intake. The cooling water isforcefully circulated by pump.

To determine the location to install the water-water cooler, hydraulic model tests were conducted atthe Technical Research Laboratory of The KansaiElectric Power Co., Inc., in order to confirm that thespecified flow velocity could be obtained.

With the application of this method, the watersupply system will be simplified. For example, com-pared to the conventional direct water supply system(a method of direct intake and use of river water ascooling water), the strainer is eliminated. In addition,the use of clear water (tap water) for the closed-circulation water has contributed to improved reliabili-ty of the water supply system, which is often problem-atic at hydropower generating facilities.

Control room

Speaker Recorder Monitor

CameraMicrophoneVibrometer

Vol. 43 No. 1 FUJI ELECTRIC REVIEW6

3.5 Generator cooling methodFin cooling was used to cool the generator. As

illustrated in Fig. 9, the fin cooling method is a methodin which steel cooling fins, attached to the stator frameand inner wall of the top nose of the bulb, are cooled byriver water that flows around the outside of the bulband cooled air is circulated inside the bulb with amotor-driven fan. The application of this method madeit possible to eliminate conventional air coolers, result-ing in easier maintenance.

Further, in the conventional air cooler, the area ofthe outer casing to be cooled needs to be increased asthe generator capacity increases, thereby limiting theapplicable power output. However, by changing thecoating of the bulb’s outer wall (river water side) fromconventional corrosion resistant paint to an aluminummetallic coating, in order to reduce heat resistance ofthe heat radiating area, fin cooling could be applied ona larger scale in this project.

Although this fin cooling method has been appliedto medium/small bulb generators, prior to this projectit had not been used in large capacity bulb generators.To date, this project is the largest capacity bulbgenerator in the world that uses the fin coolingmethod.

Table 2 shows the history of the fin-cooled bulbturbine/generator.

3.6 Control systemA total digital control system equipped with a

programmable controller is used to control the turbine/generators. With this total digital control system, themain unit sequence control function, governor function,automatic voltage control function and automatic syn-chronization control function are controlled by a singleprogrammable controller unit. Previously, separatecontrol systems had been utilized, however the realiza-tion of a programmable controller having high speedarithmetic operation made it possible to control allfunctions and thus to eliminate the control board.

3.7 Status monitoring systemA monitoring system in the control room was

introduced, in which movable and fixed type ITVsystems and microphones are installed in the turbineand generator chambers in order to externally monitorequipment status and to improve equipment maintain-ability.

Additional systems, such as a thermometer/hy-grometer, vibrometer, oxygen densitometer etc., areprovided to constantly monitor conditions inside the

bulb.Figure 10 illustrates the construction of the bulb’s

internal monitoring system.

3.8 Site installation procedureIn this project, outdoor gantry cranes were used to

install the equipment. Although use of outdoor gantrycranes for the installation of equipment may riskprolonging the work schedule due to inclement weath-er, this project was able to achieve a considerably shortinstallation period compared to the usual installationperiod for a bulb turbine, due to thorough preliminarypreparation for rainy weather, an efficient use of thesite assembly floor, and the application of new tech-niques to the turbine installation.

Explanations of the new techniques for turbineinstallation are given below.

To install the inner/outer casings and guide vanerings in a turbine, normally the inner/outer casings areassembled and installed, concrete is allowed to set, andthen the strain on the surface of the downstream sidecasing flange is corrected. Next the inner/outer guidevane rings are assembled and installed. However forthis project, the inner/outer casings and inner/outerguide vane rings of the turbine are simultaneouslyassembled and installed, followed by the application ofconcrete. As a result, the time necessary to correctstrain on the downstream side flange surface waseliminated, shortening the construction period by morethan 14 days.

This was the first time for Fuji Electric to use thistechnique, and a successful application of this tech-nique requires continuous monitoring, during applica-tion of the concrete, of the strain on casings and guidevane rings, the concrete temperature etc. from thestart to the completion of the concrete work. For thisproject, the inner/outer casings and guide vane ringswere safely installed without any indications of harm-ful strain due largely to the cooperation from relevantindividuals such as the civil contractor.

4. Conclusion

The characteristics and summary of the bulbturbine/generator for the Minokawai Power Plant weredescribed in this report.

The authors assume there will be increased de-mand in the future for developing and planning powerplants equipped with large size and capacity bulbturbines, and would be grateful if this report willbecome of reference, to whatever degree, for futuredevelopment/planning works.

26MW Pelton Turbine for Nikengoya Power Plant, Chubu Electric Power Co., Inc. 7

Masamichi MakinoHiromu HayamaTakashi Tozaki

26MW Pelton Turbine for Nikengoya PowerPlant, Chubu Electric Power Co., Inc.

Fig.1 Turbine/generator assembly

1. Introduction

Making hydropower plants more economical is themost important subject in promoting their develop-ment. Particularly in recent Japan, most of the largeand economical hydropower resources have alreadybeen developed, leaving the remaining hydropowerresources limited to either ultra low head or high headresources. Of the various turbines, Pelton turbines,which are used at high head resources, are ofteninstalled in secluded mountainous areas. Such hydro-power resources are becoming more remote every year.Therefore the construction and maintenance costs tendto be higher compared to those of existing hydropowerresources.

Under these circumstances, the Nikengoya PowerPlant with a 6-jet Pelton turbine began its commercialoperation in June of 1995. The main turbine/generatorspecifications for this power plant are shown in Table1. Also the turbine/generator assembly is shown inFig. 1.

This power plant is located in Japan’s centralmountainous area, at an elevation of over 1,400m,surrounded by numerous steep mountains. This reportintroduces the following new techniques adopted to

Table 1 Turbine/generator specifications for Nikengoya PowerPlant

Vertical shaft 6-jet Pelton turbine

283.6m

11.0m3/s

26,800kW

400r/min

Totally enclosed(Machine mounted heat exchanger type)

27,400kVA

11kV

1,439A

95% lag

60Hz

400r/min

Type

Net head

Discharge

Output

Rated speed

Type

Cooling

Output

Voltage

Current

Power factor

Frequency

Rated speed

3-phase verticalsynchronous generator

Turbine

Generator

overcome these unfavorable construction conditionsand to make the power plant more economical.(1) High specific speed design of 6-jet Pelton turbine(2) Elimination of bypass(3) Electrically powered deflector/needle operating

mechanism

2. High Specific Speed Design of 6-Jet PeltonTurbine

2.1 Background of high specific speed designLocated in a secluded mountainous area, this

power plant imposed extremely severe limits on trans-portation. Therefore, minimizing the size of theturbine/generator was the most important matter inplanning this power plant. In addition, since minimi-

Vol. 43 No. 1 FUJI ELECTRIC REVIEW8

Fig.2 Relative efficiency of conventional and new model

Fig.3 Bypass in run-of-river plant

zation of the turbine/generator not only lowers the costof equipment but also reduces the powerhouse size,construction costs of the power plant can also bereduced. Therefore, for this power plant, the turbine

was designed to have as high specific speed as possibleso as to make the equipment more compact, satisfy thetransportation limit, as well as to make the powerplant more economical.

The specific speed of a Pelton turbine is generallyexpressed with the following equation.

n √P/Zn s = ————— …………………………………… (1)H 5/4

Where, n s : Specific speed (m-kW)n : Speed (r/min)P : Turbine output (kW)Z : No. of jetsH : Net head (m)

As is clear from the definition of specific speed, it isnecessary to increase the number of jets and theturbine speed in order to increase the specific speed.However, it is well understood that when the numberof jets is increased to, for example 5 or 6 jets, aproblem with turbine performance – known as thefalaise effect – will occur. This effect has never been amatter of concern when the number of jets is less than4. For this reason, it is an international practice tolimit the specific speed of a 6-jet Pelton turbine toapprox. 20 m-kW or less.

The problems of this falaise effect have beenimproved and the result, as applied to this powerplant, is described below.

2.2 Falaise effectFigure 2 shows the relative efficiency of a conven-

tional model which exhibits the falaise effect, and of anew model with improved falaise effect. As this figureclearly shows, when the falaise effect occurs in a fullload region, it will lead to a considerable drop inturbine efficiency. In this region, power swings anderosion of the bucket’s inner surface will also occur.Therefore, the falaise effect must be eliminated fromthe actual turbine operation region.

The mechanism of this falaise effect occurrencewas analyzed by the observation of flow in model testand by numerical analysis. It was confirmed thatthere are 2 kinds of mechanisms for the occurrence ofthe falaise effect.2.2.1 Falaise effect due to jet interference inside bucket

Jet interference, already a known cause, occurswhen the next jet begins flowing into the bucket beforewater has completely flowed out of the bucket’s leadingedge, and these two jets violently collide in the bucket.As a result, a considerable hydraulic loss occurs insideof the bucket.2.2.2 Falaise effect due to jet interference outside bucket

This is a newly discovered type of jet interference,where water flow from a cut-out area, interferes withthe next jet which has not yet entered the bucket. As aresult, the jet becomes turbulent, scatters and loses itsenergy before flowing into the bucket.

Further, in this high specific speed design study, a

Fig.4 Deflector start-up characteristic at the field test

Relative discharge (%)

Rel

ativ

e ef

fici

ency

(%

)

Conventional model Falaise effect

New model

30 40 50 60 70 80 90 10080

85

90

95

100

Head tank Intake

Intake dam

Bypass

Power plant

Penstock Headrace tunnel

River

1 s

Needle servomotor stroke (Gr.B)

Needle servomotor stroke (Gr.C)

Deflector servomotor stroke

Speed

Needle servomotor stroke (Gr.A)

Penstock pressure

Generator output

Generator voltage

26MW Pelton Turbine for Nikengoya Power Plant, Chubu Electric Power Co., Inc. 9

comparative analysis was also made in the falaiseeffect region between the measured results of proto-type performance and those of the model test. Al-though several studies(1) have been made on theefficiency scale effect from model to prototype, so farthere is no established theory. We had the opportunityto examine the efficiency scale effect in a Peltonturbine from model to prototype including its relationto the falaise effect mechanism(2).

2.3 Reducing the falaise effectTo counteract the previously described mecha-

nisms, the following design was applied to this plant toreduce the falaise effect.2.3.1 Improved bucket configuration

The tendency of the jet output to flow toward theleading edge of bucket was controlled by improving thebucket wall slope and the shape of the cut-out area.2.3.2 Relatively larger bucket size

By selecting a relatively larger sized bucket, thetendency to flow toward the cut-out area of the bucketwas reduced.2.3.3 Increased number of buckets

By increasing the number of buckets, the time foreach bucket to receive the jet can be reduced.

With these design philosophies, a high specificspeed design (ns = 23.0m-kW) was successfullyachieved for the first time in the world.

3. Elimination of Bypass

3.1 Bypass in run-of-river plantAt run-of-river plant, river water flow into a power

plant through an intake dam and used as is for powergeneration. If the power plant is shut down or theamount of river water taken in becomes excessive, thebypass, as shown in Fig. 3, directly discharges suchexcess water from the head tank to the river, bypass-ing the power station. Therefore if this bypass can beeliminated, construction costs will be reduced by alarge percentage of the overall power plant construc-tion cost.

Since the elimination of a bypass will result inproblems such as a rise of the river water level due toclosing of the intake gate, pressurization of the head-race, etc., the installation of a bypass or similarsubstitute has been required at run-of-river plants by aJapanese statute. However, application of a Peltonturbine will make it possible to eliminate the bypass,as the above-mentioned problems can be avoided bydeflector discharge operation for long periods of timeand implementing start/stop controls with the deflec-tor.

3.2 Basic concept of bypass eliminationThe basic concepts for eliminating a bypass for a

Pelton turbine are as follows:(1) The intake gate shall be controlled such that the

rate at which the river water level rises is small.(2) The turbine will perform a full flow deflector

discharge operation.(3) When malfunctions of the transmission line are

not recovered within a specified time, and whenmalfunctions of the generating unit occur, theintake gate shall close.

(4) When malfunctions of the transmission line arerecovered within a specified time, the generatingunit shall automatically begin operation again inparallel.

3.3 Technical outline of bypass eliminationFor the previously mentioned basic concepts of

bypass elimination to be realized, the civil, electricaland mechanical equipment must take on new func-tions. An outline of bypass elimination techniqueswith regard to electrical and mechanical equipment isdescribed here.3.3.1 Deflector discharge operation over a long period of

timeDuring the deflector discharge operation, after

high speed jets directly hit the deflector, they sprayaround the deflectors, hitting the housing, nozzleprotection shield, etc. Therefore, after studying thestrength and rigidity of these parts, the plate thicknesswas increased by approximately twice the existingthickness of these parts.

To verify the reliability of a deflector duringdischarge, the most severe operating condition, inaddition to analytical studies on papers, the actualstress was measured beforehand on an identical proto-type turbine. These results were reflected in thedesign of this power plant.3.3.2 Start/stop controls by deflector

In conventional Pelton turbines, starting and stop-ping the generating unit was controlled by needles,and the deflector performed follow-up control. Howev-er, in the case of bypass elimination, needles will onlycontrol the head tank water level regulator and start/stop controls will be performed by the deflector. Toimplement such deflector control, the following studieswere made.(1) Reduction of hydraulic torsional moment of deflec-

torIn a 6-jet Pelton turbine with push-out deflectors,

when starting and stopping a units, a jet whichdeflected by an adjacent deflector will hit the rearsurface of a deflector. This causes the hydraulictorsional moment of the deflector to sharply increase.Therefore, models were tested to optimize the configu-ration, size and installation position of the protectingshield, so as to eliminate this collision between jet anddeflector rear surfaces. As a result, the hydraulictorsional moment of the deflector and the capacity ofthe deflector servomotor can be reduced.(2) Numerical analysis of deflector start operation

The optimization of a governor setting was made

Vol. 43 No. 1 FUJI ELECTRIC REVIEW10

by analyzing with a stability calculation program, thestable deflector start operation regardless of needleopening and nozzle combination.

From the result of the above studies, a stable start-up characteristic, as shown in Fig. 4, by a deflector wasobtained at the field test.3.3.3 Deflector and needle functions

There are two requirements for eliminating thebypass. First, the headrace tunnel should not bepressurized regardless of the type or severity ofaccident, and secondly, the water should not overflowfrom the head tank. Therefore, in case of a drop in orloss of power supply voltage during operation, thedeflector and needles must be able to securely carryout the following operations.(1) The deflector should be able to fully close and

switch to the deflector discharge operation inde-pendent of the electrical signals.

(2) Needles should maintain the current opening.These functions were added to the electrical servo-

motor described in the next section.

4. Electrically Powered Deflector/Needle Operat-ing Mechanism

4.1 Background of electrical powerIn convention hydropower plants, the oil pressure

servomotor was adapted as the operating mechanismfor the turbine. However, the oil pressure servomotorrequires auxiliary equipment such as oil pressuresupply equipment, oil pressure piping, etc. and aconsiderable amount of time was spent maintainingand inspecting this equipment. In particular, asPelton turbine construction sites have become increas-ingly remote in recent years, there is a strong demandfor reduced maintenance and inspection of this equip-ment.

Under these circumstances, the deflector/needleoperation mechanism of the 6-jet Pelton turbine forthis power plant was electrically powered for the firsttime in Japan, and the entire hydraulic oil pressuresystem was eliminated As a result, not only was theinitial equipment cost reduced but the maintenancecost, or in other words, the operating cost was alsoreduced.

4.2 Electrically powered deflector operating mechanismThe 6 deflectors are connected to a guide ring, via

the deflector shaft, by a slider block type linkagemechanism. The guide ring is connected to an electricservomotor and to a counter weight for emergencyclosure. A guide ring using a slider block is newlydeveloped, the application of which has resulted in thesimplification of the conventional complex linkagemechanism that utilized turnbuckles. Figure 5 is aphotograph of this deflector operating mechanism.

Specifications of the electric deflector servomotorare as follows:

Rated load : 156,900 NClosing and opening time : 15 sMaximum stroke : 250 mmMotor output : 11 kWMotor voltage : 200V ACMotor speed : 1,000 r/min

As mentioned in the section on bypass eliminationtechniques, the electric deflector servomotor is connect-ed to a counter weight for emergency closure so as tobe able to close the deflector independently of electricalsignals in case of a drop in or loss of power supplyvoltage. A photograph of this electric deflector servo-motor is shown in Fig. 6.

4.3 Electrically powered needle operating mechanismEach of the 6 needles is connected by a linkage

mechanism, via the needle shaft, to 6 electric needleservomotors that can be operated independently. Aspecial feature is the use of a slider block in the nozzlepipe to convert rotating motion of the needle shaft tolinear motion.

Fig.6 Electric deflector servomotor

Fig.5 Deflector operating mechanism

26MW Pelton Turbine for Nikengoya Power Plant, Chubu Electric Power Co., Inc. 11

The specifications of each electric needle servomo-tor are as follows:

Rated load : 58,800 NClosing and opening time : 30 sMaximum stroke : 205 mmMotor output : 1.5 kWMotor voltage : 200V ACMotor speed : 1,000 r/min

As stated in the section on bypass eliminationtechnique, since the electric servomotors must main-tain the current opening regardless of a drop or loss ofpower supply voltage, they are equipped with amagnetic brake. This type of magnetic brake is freewhen energized and brakes when released to operatesecurely under emergency conditions.

4.4 Power supply systemAn uninterruptible power unit is provided to

supply power to one electric deflector servomotor, 6electric needle servomotors and the magnetic brake.

This system supplies alternating current (200VAC), through a rectifier and inverter, as power at therated voltage and frequency. In case of a drop in ACvoltage or power outage, a battery will supply thepower. In addition, this system has a bypass circuit incase failures occur in the inverter. Should such afailure occur, the bypass circuit will be switched on

automatically to deliver the AC current directly andwithout interruption.

This system will provide each electric servomotorwith electrical backup functions, which in addition tomechanical backup functions (counter weight for emer-gency closure and magnetic brake) improve the overallreliability of the system.

5. Conclusion

The latest technologies applied to the vertical 6-jetPelton turbine of the Nikengoya Power Plant wereintroduced above. We expect that these new technolo-gies for the Pelton turbine will be efficiently adapted infuture plans for hydropower plants and that thesetechnologies will continue to develop.

We are most grateful to all the parties concernedwho advised and cooperated with us from the planning,design, and site installation phases through testing ofthis plant.

References:(1) H. Grein, et al.: Efficiency Scale Effects in Pelton

Turbine, IAHR Symposium (1986)(2) T. Kubota, et al.: Scale Effect on a 6-Nozzle Pelton

Turbine, 7th International Seminar Water EnergyPlants, Wien (1992)

Vol. 43 No. 1 FUJI ELECTRIC REVIEW12

Kentaro AkahaneRyoji Suzuki

Recent Analysis Technologies forHydropower Equipment

1. Introduction

Computers are being used at each stage of hydro-power equipment setup, from the receipt of a purchaseorder to onsite installation and testing.

The history of analysis technologies for hydropowerequipment began with the introduction of flow analysistechnology into runner design and has developed ascomputers have increased in speed and capacity. Thisanalysis has made the transition from the classicperformance improvement technique based on modeltests using the try and cut method to computer-aidedflow analysis and performance prediction technologies.Also, with the increase in the dimensions and head ofhydraulic turbines, a strength and vibration analysistechnique has been introduced. This technique con-tributes to the optimum construction design of hydrau-lic turbines. Presently, various numerical analysistechnologies are used at each stage of hydraulicturbine planning and design.

This paper outlines the analysis technologies com-monly used for hydropower equipment.

2. Flow Analysis Technologies

Flow analysis as a design tool for hydraulicturbines and reversible pump-turbines began in the1960s with two-dimensional, inviscid flow analysis,and continued in the 1970s with quasi-three-dimen-sional analysis. The quasi-three-dimensional methoddivides a flow passage into many rotating flow surfacesof axial symmetry and performs iterative calculations,repeating the flow analysis for each flow surface andmodifying the profile of the flow surface using eachanalysis result. Because this method requires only acomparatively small memory capacity and can becalculated quickly, it is still used as a simple designtool. However, this method is based on the approxima-tion that fluid flows on a rotating flow surface havingaxial symmetry, and is insufficient to describe thedetails of much more complicated flows in actualhydraulic turbines and reversible pump-turbines. Forexample, it is known that flow over the pressure

surface of high-specific-speed Francis runners used forlow head projects is approximately perpendicular tothe rotating flow surface, but this flow phenomenoncan not be described by the quasi-three-dimensionalmethod. In addition, because of recent demand forstable operation not only at the point of optimumefficiency and its vicinity but also over a wider range,the necessity to describe the internal flow at anoperating point far from the design point has in-creased. The quasi-three-dimensional method has poorconvergence in calculating these conditions, and littledetailed information about the flow can be obtainedfrom analysis with this method.

Using recently introduced three-dimensional vis-cous flow analysis technologies, complex flow phenome-na in hydraulic turbines have become understood andthe accuracy of analysis in regions far from the designpoint has greatly improved. Many flow phenomena arebeing clarified, such as the flow separation occurring ina runner during high-head and low-head operation orthe channel vortex in partial load operation, theleakage flow from the blade tip clearance of a Kaplanturbine, and the reverse flow at the inlet of a reversiblepump-turbine during high-head pumping operation.This progress in analysis technologies has made itpossible to obtain more detailed information at thedesign stage than ever before.

On the other hand, the preparation of data foranalysis and those analysis calculations require muchmore time than the previous quasi-three-dimensionalanalysis. Therefore, quasi-three-dimensional analysisand three-dimensional viscous flow analysis are prop-erly used in combination at present.

The progress of flow analysis technologies hasimproved design accuracy and reliability. The previ-ous method in which performance was improved byrepeating model tests is gradually changing to amethod in which the optimum design obtained fromiterative flow analyses and then confirmed with amodel. However, to completely eliminate model tests,strict direct numerical simulation of Navier-Stokesequations must be easily performed on desktop com-puters and the accuracy and reliability of these resultsmust be recognized generally. These expectations are

Recent Analysis Technologies for Hydropower Equipment 13

unrealistic at the present time. It should be noted thatthe model test is an effective method to verify theresult of analysis. The flow analysis technologies arepowerful because they quantify elements previouslydependent on the designer’s perception and sense andpromote progress in design technology. These analysistechnologies will contribute to expanding the stableoperation region of hydropower equipment by shiftingthe range of instability or by controlling the strength ofthat phenomenon.

3. Strength Analysis Technologies

As described above, with the increase of computerspeed and capacity, the finite element method (FEM)which had been previously impractical because of itsenormous quantities of calculations became calculablein two-dimensions beginning from approximately 1970and in three-dimensions from the mid 1970s. Thistechnique also was applied to strength analysis of themain structures of hydraulic turbines and reversiblepump-turbines. First, it was mainly used for struc-tures having two-dimensions or axial symmetry withsimple shell elements and beam elements, and thengradually became used in complicated, large-scaleanalyses with three-dimensional solid elements. It hasbeen applied not only to simple supports or immovablerestraints but also to constraint conditions closer toactuality, such as multipoint constraint. Recently,FEM analysis has been easily performed with desktopengineering workstations or personal computers. Stat-ic and dynamic stress and displacement are moreprecisely calculated, greatly contributing to improvedequipment reliability, including fatigue strength.

It is important that each part of a high-headhydraulic turbine or reversible pump-turbine has thenecessary stiffness to endure high water pressure. TheFEM also handles nonlinear phenomenon such as therapid increase in bolt tensility caused by opening aflange fastened by large bolts. In contrast, low-headbulb turbines have a large thin plate structure and it isimportant to predict the precise amount of deformationunder manufacture, assembly, and installation. Ourmethod of onsite installation is based on the result ofanalyzing deformation during operation.

4. Vibration Analysis Technologies

Eigenvalue analysis with FEM is generally per-formed to eliminate resonance problems.

Reversible pump-turbines often have a high headand large capacity to improve economical efficiency.They also require high reliability. Because a high headincreases the exciting force of water pressure on theparts, an analysis of vibration in the water is neces-sary for the runner. A fluid reaction force proportionalto the acceleration of vibration acts on the runner in

the water and exerts the effect of additional mass,which lowers the natural frequency. The runner isalso influenced by the stationary head cover andbottom cover. Therefore, it is necessary to performfluid-structure-coupled vibration analysis that includesfluid around the runner and the stationary parts, andto ensure that the frequency of fluctuating stress issufficiently far away from the resonance frequency. Atpresent, verification is carried out both through analy-sis with software and the measurement of fluctuatingstress at an actual head testing facility.

On the other hand, low-head bulb turbines havelow stiffness and their natural frequency is low.Therefore, eigenvalue analysis is performed for thewhole model.

A special example is the verification of the effec-tiveness of a pump-turbine structure for reducingbuilding vibration. Vibration analysis of the buildingstructure of a certain high-head, pumped-storage pow-er station was performed. The analysis result agreedfavorably with onsite measured values.

5. Transient Phenomenon Analysis Technolo-gies

The analysis of transient phenomena in hydraulicturbines, especially the calculation of pressure rise(∆ P) and speed rise (∆ N) during load rejection, and therequired flywheel effect (GD2) that influence not onlythe preservation of the hydroelectric power plantbuilding and equipment but are also directly related tothe cost, is always carried out during estimation andplanning stage. In other words, a method of closingguide vanes to minimize the required GD2 whilemaintaining ∆ P and ∆ N within permissible toleranceis investigated. When a tailrace is formed by a longpressure tunnel, there is a possibility that pressureduring load rejection will drop to the vapor pressurelevel (known as the water column separation phenome-na) causing an abnormal pressure rise during thereattachment of water columns. Therefore, it isnecessary to simulate water pressure behavior. Inaddition, analysis may be necessary in a complexwaterway system such as where a penstock branch anda surge tank are combined to confirm stability of thegovernor control.

6. Conclusion

An outline of the history and recent analysistechnologies of Fuji Electric’s hydropower equipmenthas been presented. Other papers in this special issueintroduce “Vibration Analysis Technologies for HighHead Pump-Turbine Runners” and the “Application ofNumerical Flow Analysis Technologies to HydraulicTurbines and Pump-Turbines”. We would be gratefulif you would take the time to read them.

Vol. 43 No. 1 FUJI ELECTRIC REVIEW14

Ryoji SuzukiYutaka KimotoMasayoshi Sakata

Vibration Analysis Technologies forHigh Head Pump-Turbine Runners

Fig.1 Vibration modes of a disk with various diametrical nodes

k = 0 k = 1

k = 2 k = 3

1. Introduction

In the early 1970’s, the head exceeded 500 metersin pumped storage power plants in Japan. But for amore economical construction, a higher head waspursued. Recently, higher rotational speed and morecompact equipment have been adopted. Among themany technical subjects in the planning and design ofhigh head pump-turbines, the estimation of dynamicstress on the runners is most important in realizinghighly reliable runners. With higher speed and ahigher head, not only static stress on the runner butalso dynamic stress and its frequency increases. Thisis because the amplitude and frequency of the pressurepulsation around the runner increase. Therefore, inthe design stage, the technology for prediction ofdynamic stress acting on the runners is of majorimportance.

In accordance with these technical requirements,Fuji Electric has developed fluid-structure coupledvibration analysis technology and an actual headmodel test apparatus. In this paper, these develop-ments will be briefly described.

2. Vibration Characteristics of the Runner inWater

As the runner blades of a pump-turbine in generat-ing mode pass one by one through the wakes of theguide vanes, velocity and pressure around the bladesfluctuate periodically. In pumping mode, velocity andpressure around the blades also fluctuate as the bladesapproach and pass the guide vanes. Such pressurepulsation due to the interaction between stationaryand rotating cascades varies according to the combina-tion of the number of blades. This pressure pulsationgenerates a pressure field with diametrical nodessatisfying the equation;

n・Z G + k = m・Z R ………………………… (1)Where ZG and ZR are the number of guide vanes

and runner blades, respectively, and n and m areorders of excitation. The symbol k is the number ofdiametrical nodes which corresponds to the vibrationmode. This is illustrated in Fig. 1.

The frequency of pressure pulsation acting on therotating runner is;

fR = n・Z G・N / 60 …………………………… (2)Where N denotes the rotating speed of the runner

(r/min). Such a pressure field with diametrical nodesrotates with a speed of;

fPR = fR / k ……………………………………… (3)Where positive k corresponds to a progressive

wave, a wave rotating in the same direction as therunner, and negative k corresponds to a reverse wave,a wave moving in the opposite direction as the runner.

The frequency and the rotational speed of thepressure pulsation observed on the stationary partsare;

f S = m・Z R・N / 60 ………………………… (4)andfPS = fS / k ……………………………………… (5)

In addition, although there are infinite combina-tions of n, m and k satisfying equation (1), the specificmode of the pressure field which actually cause thevibration on the runners can be found. Taking intoaccount the response of the runner excited by such apressure pulsation, the following conditions can bedrawn:(1) Lower order excitation modes (smaller n) general-

ly cause a larger response on the runners.(2) Excitation modes with smaller k generally cause

larger response on the runners because they excite

Vibration Analysis Technologies for High Head Pump-Turbine Runners 15

Fig.2 Finite element analysis model of a pump-turbine runner

Table 1 Excitation mode on the runner (number of diametricalnodes)

6

7

8

9

10

- 4 / + 2

- 2 / + 5

- 8 / 0 / + 8

- 7 / + 2

- 6 / + 4

- 2 / + 4

- 6 / + 1

- 4 / + 4

- 2 / + 7

- 10 / 0 / + 10

- 6 / 0 / + 6

16ZG

ZR20 24

- 3 / + 4

- 8 / 0 / + 8

- 6 / + 3

- 4 / + 6

vibration with less diametrical nodes.(3) A pump-turbine runner consists of two disks

(crown and band) connected by blades, and thusresponds easily to the excitation by which thedisplacement at blade roots can always be zero.

The first and second conditions, specify modes withn = 1 and smaller |k|. From the third condition, it canbe concluded that the combination of two modes arespecified, of which the difference in k is equal to thenumber of runner blades. Table 1 lists the combina-tions of excitation modes for various numbers ofrunner blades and guide vanes which are obtained bysuch an investigation. For example, a pump-turbinewith 20 guide vanes and 6 runner blades is subject toexcitation with 2 and 4 diametrical nodes. In this case,the pressure pulsations with frequencies of 3 and 4times ZR × N are observed on the head cover.Excitation of the first order on the runner has afrequency of ZG × N in all cases.

When the resonance frequency of a pump-turbinerunner is numerically analyzed, the above-mentionedexcitation mode should be considered. Because thevibration caused on a runner by the interaction withguide vanes has a relatively high frequency, manynatural frequencies are obtained below the modes inquestion. The result should be evaluated, taking intoconsideration that the mode with the same number ofdiametrical nodes as the excitation mode is selectivelyamplified.

3. Coupled Vibration Analysis in Water

3.1 Analysis method and calculation modelIt is a well-known fact that the natural frequency

of a structure in water generally varies from that inair. The natural frequency of a structure in extensivewater is reduced by around 20%. This reduction innatural frequency is caused by the added mass effect,which is due to the reaction force (pressure) from thewater adjacent to the structure. This reaction force isproportional to the acceleration of vibration.

In the case of a pump-turbine runner, there aresmall spaces between the crown and head cover andbetween the band and bottom cover. When the crownand the band vibrate, the water in these spaces mustmove peripherally or move out of the space through therunner seal and the outer periphery. The volume of

this water is determined by the displacement of thecrown and the band. Therefore, the reaction force fromwater, or the added mass effect, of the runner is muchlarger than in extensive water. Therefore, the naturalfrequency of pump-turbine runners in operation isreduced by around 50% that of air. Because thisreduction rate is affected by the mode shape ofvibration, the space between the head / bottom coversand the runner, the stiffness of the head cover, etc.,numerical analyses are necessary in order to quantita-tively predict the natural frequency in the designstage.

Vibration analysis of the runner is carried outusing the solver provided by MSC/NASTRAN, whichcalculates the added mass effect of fluid. As theboundary element method is used for the solution ofthe fluid property, the definition of the boundary isonly required for the modeling of the fluid region. Buta knowledge of the definition of the fluid boundary isnecessary. In addition, it takes a long time for thesolution of simultaneous equations. This is because afull matrix is produced for the fluid region due to theapplication of the boundary element method. As aresult, modeling knowledge has been accumulatedthrough the comparison between calculated and mea-sured vibration modes based on such systems as asimple disk in a vessel.

Figure 2 shows the analytical model of a pump-turbine runner. To take into account the effect of thegap between the runner and the head/bottom coversand the stiffness of the head cover, the model includesthe head and bottom covers.

3.2 Example of analysis resultsFigure 3 shows an example of the vibration mode

and stress distribution of a runner. Many naturalfrequencies with various vibration modes are obtainedby the fluid-structure coupled vibration analysis solverin MSC/NASTRAN. As mentioned above, the degree ofresponse is different for each mode because of thespecific mode of the pressure pulsation acting on therunner in operation.

Hence, the modal response analysis is carried out

Bottom cover

Runner

Head cover

Vol. 43 No. 1 FUJI ELECTRIC REVIEW16

Fig.4 Flow chart of mode synthesize method programFig.3 Vibration mode and stress distribution on the runner

Fig.5 Actual head model test stand

Cooling water

Flow meterStabilizing tank

Model turbine for powerrecovery

Model turbine for measure-ment

Speedincreaser

Mainmotor

by applying pressure pulsation on the runner, based onthe result of fluid-structure coupled vibration analysis,in order to predict the actual natural frequency. Then,the level and location of dynamic stress can bequantitatively estimated from the stress analysis ac-cording to the amplitude of vibration. Because theabsolute level of pressure pulsation as well as thedumping factor are difficult to directly calculate, thereliability of calculation is improved by feedback of themeasured data in the power plants and the actual headmodel test stand.

3.3 Fluid-structure coupled vibration analysis method bymode synthesize methodAs the fluid-structure coupled vibration solver in

MSC/NASTRAN applies the boundary element methodfor the fluid region, it has the advantage of easy meshgeneration. At the same time, its disadvantagesinduce long calculation time and structural modelinglimited by the shell elements. In order to eliminatesuch defects, a new fluid-structure coupled vibrationanalysis code was developed using the mode synthesizemethod.

This method is based on the governing equations ofunstable pressure distribution caused by small scalevibration of compressible fluid. The equation of motionfor structures are coupled with fluid elements byintroducing in the external force term the pressuregenerated by the vibration of the wall facing the fluidregion. If the simultaneous equations are solveddirectly, a very large matrix with a combination ofstructures and fluid regions is generated. Thus, thealgorithm shown in Fig. 4 is applied to reduce calcula-tion time.

By this method, the eigenvalue analysis of thestructures in air is carried out first. Then, the forceacting on the fluid is calculated using the mode ofvibration normal to the wall. Consequently, thepressure pulsation, generated by this external force,

acts on the structure. As this pressure pulsation isproportional to the acceleration of the wall, it isequivalent to the added mass on the boundary wall.These added mass components are calculated by themode synthesize method based on the vibration modeof the structure. These algorithms are iterated untilthe natural frequencies converge.

4. Dynamic Stress Measurement in Actual HeadModel Test Stand

4.1 Actual head model test standAs stated above, a pump-turbine runner rotating in

water forms a coupled vibration system due to itsinteraction with the surrounding water and structures.In order to simulate such a coupled vibration phenome-non using a model, the hydroelastic similarity lawmust be satisfied. In other words, the ratio of

Eigenvalue analysis of structures in air

Scaling of mode shapes

Generation of new mode shapes

End

Judgment of convergence of natural frequencies

Calculation of added mass by fluid from the mode shape

[ m]=p T[L]T[H G] -1[L] ∆ φ φΩ-

Supplement modal mass with added mass by fluid, and calculate

eigenvalue in modal coordinate system

∆[m]=[I]+[ m], Ω[K]=[ ]2

Yes

No

Vibration Analysis Technologies for High Head Pump-Turbine Runners 17

Fig.6 Actual head model test stand in operation

N89-6568-1

Fig.7 Measured stress amplitude on the runner in generatingmode

Fig.8 Measured stress amplitude on the runner in pumpingmode

Fig.9 Comparison between analyzed and measured stressamplitude (generating mode)

500 1,000 1,500 2,00000

10

20

30

40

50

Maximum stress amplitude 31MPa

Stress amplitude at rated speed 11MPa

Calculated value 1,073Hz

Calculated value

Measuredvalue

Res

onan

ce

freq

uen

cy1,

131H

z

Rat

ed s

peed

1,41

0Hz

Frequency of stress amplitude (Hz)

Str

ess

ampl

itu

de (

MP

a)

50

40

30

20

10

00 500 1,000 1,500 2,000

Maximum stress amplitude 17.7MPa

Stress amplitude at rated speed 5.3MPa

Res

onan

ce f

requ

ency

1,

131H

z

Rat

ed s

peed

1,4

10H

z

Frequency of stress amplitude (Hz)

Str

ess

ampl

itu

de (

MP

a)

50

40

30

20

10

00 500 1,000 1,500 2,000

Maximum stress amplitude 31.4MPa

Stress amplitude at rated speed 11.1MPa

Frequency of stress amplitude (Hz)

Rat

ed s

peed

1,

410H

z

Str

ess

ampl

itu

de (

MP

a) Res

onan

ce

freq

uen

cy

1,13

1Hz

hydraulic excitation frequency to the natural frequencyof the runner should be equal for both the prototypeand the model. In the case of a pump-turbine runner,this similarity can be satisfied by manufacturing themodel runner with the same material as the prototypeand by operating the model runner with the sameperipheral speed, or with the same head, as theprototype. Under such conditions, vibration observedin the model has a frequency in inverse proportion tothe scale ratio and the amplitude is nearly similar tothe prototype, if a small discrepancy in damping due tothe difference in the Reynolds number is overlooked.

The actual head model test stand is the facility forthe above-mentioned purpose and is outlined in Fig. 5.The torque generated by the main motor is transmittedto the model turbine through the speed increaser. Themaximum available speed of the model is more than7,000 r/min. In spite of the small scale model, a fewMW of input power is required for hundreds of metersof test head; thus, this facility is equipped with a pairof model turbines at both ends of the high speed shaft.When one of the models is operated in pumping mode,the other recovers the driving power through thegenerating mode operation. Figure 6 portrays themodel test facility in operation.

4.2 Example of measurement in actual head test standStress measurement was carried out in this test

stand with the model designed for a 400m classpumped storage power plant. The principal specifica-tions of the prototype are listed below.(1) Type : Reversible Francis pump-turbine(2) Net head : 400m(3) Max. output : 360MW(4) Speed : 360r/min(5) No. of runner blades : 6(6) No. of guide vanes : 20

The stress on the runner was measured by 12strain gauges, each of which was monitored simulta-neously by a 12 channel FM telemeter. Together withthe stress, operating conditions such as the rotatingspeed of the runner, discharge and static pressure at

the inlet and outlet of the model were also measured.Preceding the installation of the strain gauges, finiteelement analyses were carried out in order to deter-mine the location of maximum stress for the assumed

Vol. 43 No. 1 FUJI ELECTRIC REVIEW18

vibration mode.Figure 7 shows the amplitude of dynamic stress as

a function of frequency in generating mode, which ismeasured by changing the rotational speed continuous-ly. An obvious peak can be seen at 1,131Hz, and themaximum stress amplitude at the resonance point is31.4MPa. The frequency of hydraulic excitation of theprototype rotating with the rated speed of 360 r/mincorresponds to 1,410Hz on the model. Therefore, theprototype is operated at a frequency 20% different fromthe resonance frequency, where the stress amplitude is11.1MPa, or 1/3 of peak value.

Figure 8 shows the stress amplitude measuredduring pumping operation. An obvious peak exists at1,131Hz, the same as in the generating mode, but thelevel of the stress amplitude is about half that in thegenerating mode including the resonance point. Thisis because the hydraulic excitation due to the interac-tion between the guide vanes and runner blades is lessthan in generating mode.

From these measurements, it is confirmed that thelevel of the stress amplitude for the prototype’soperating conditions is sufficiently low compared withthe strength of the runner in both the generating andpumping modes.

4.3 Comparison of the results of coupled vibrationanalysisFigure 9 shows the results of the modal response

analysis in generating mode based on the fluid-structure coupled vibration analysis compared to mea-

surements taken during testing with the actual headmodel. The resonance frequency of the runner ob-tained by the analysis is 1,073Hz, while the measuredfrequency is 1,131Hz, as stated above. The error ofnumerical prediction is about 5%, and accuracy issufficient for practical use. In addition, simulatedstress amplitude as a function of frequency alsocoincides well with measurements. It is confirmedthat the stress amplitude acting on the runners can bepredicted in the design stage with sufficient accuracy,and that a design that avoids resonance is possible.

5. Conclusion

In this paper, an outline of recent developments inthe evaluation of vibration characteristics of pump-turbine runners in operation were reported. It wasshown that the characteristics of dynamic stress onpump-turbine runners in operation can be estimatedwith sufficient accuracy before the manufacturing ofprototypes. This was proven using both computeraided fluid-structure coupled vibration analysis tech-nology and actual head model test technology.

The pumped storage power plants of the future willprobably increase in both head and speed. Though thetechnical requirements become increasingly severefrom the viewpoint of reliability for the vibration of therunners, we hope the technology presented here willcontribute to further developments in the world ofelectric power generation.

Application of Numerical Flow Analysis Technologies to Hydraulic Turbines and Pump-Turbines 19

Yi Qian

Application of Numerical Flow AnalysisTechnologies to Hydraulic Turbines andPump-Turbines

Fig.2 Discharge characteristics

Fig.1 Outline and computational results of the bulb turbine

1. Introduction

Numerical analysis technology has been widelydeveloped as an important tool in engineering designdue to the low cost and rapid development of ComputerTechnology (CT), especially in the Engineering Work-station (EWS) and Personal Computer (PC). Inaddition, the advancement of Computational FluidDynamics (CFD) technologies is also remarkable. Avariety of new analytical techniques and turbulentflow models have been proposed and are now beingapplied to complicated flow analysis. Recently, severalsimulations with separation and swirl have beenannounced one after another, thereby expanding therange of application. Moreover, computer graphics(CG) technology has developed remarkably in recentyears. This powerful drafting tool is used to visualize,in real time, analytical and data processing results onthe computer display.

In this paper, the author introduces applications ofthe latest flow analysis technologies(1) to the design ofhydraulic turbines and pump-turbines, and demon-strates the reliability and economy of the three-dimensional flow analysis technology.

2. Flow Analysis of Hydraulic Turbines andPump-Turbines

2.1 Bulb turbinesA bulb turbine comprised of sixteen guide vanes

and four runner blades is analyzed. The outline of thebulb turbine, which includes guide vanes, a runner anda draft tube, is shown in Fig. 1, and each operatingcondition is shown in Fig. 2. The optimum operatingcondition (on-cam) where cavitation at the runnerentrance does not occur is made standard a point ofcomputation (double circle). The computational do-main extends from the inlet of the guide vanes to thedraft tube exit, and the boundary conditions for theanalysis include only discharge rate and head. Toanalyze the flow of this bulb turbine, two technologiesare introduced.2.1.1 Interaction between the rotor and stator

The guide vanes are stationary, and the runner

blades are rotating. In fact, the flow patterns arethree-dimensional and unsteady flow. If the computa-tions are carried out by full, three-dimensional, un-steady flow, a very large computer and calculationcosts become necessary to analyze the interactionphenomenon of this unsteady flow. In order to avoidthese problems, previous researchers divided the com-putational area. That is, rotating and stationaryblades were independently calculated, the interfacebetween rotor and stator was disregarded. However, it

4,000

3,500

3,000

2,500

2,000

1,500120 140 160 180 200 220 240 260

1.2

1.11.051.0

0.95

0.9

0.8

/ oc=0.7

On-cam

Nd1.0

Runner vane open angle : / opt=1.33

Guide vane open angle : γ

Unit speed N11 (r/min)

Un

it d

isch

arge

Q11

(l/s

)

φφ

γ γ

φ

Vol. 43 No. 1 FUJI ELECTRIC REVIEW20

Fig.6 Outline and computational results of the pump-turbine

Fig.5 Cθ distribution by different passage forms upstream ofthe runner

Fig.4 Pressure distribution on the bulb turbine runner

Fig.3 Velocity and pressure distributions at the guide vanes’outlet

was confirmed that this divided calculation was differ-ent from the actual flow(3), and it was shown that thedifference in the flow velocity distribution at therunner inlet was especially large. To evaluate the timeaverage of a rotor-stator interaction correctly, theauthor proposed an approximate rotor-stator interac-tion analysis technique(2). In this technique, thecomputational memory was decreased so that thiscomputation could be carried out on a desktop EWS.Such techniques enable coupled analysis of the rotor-stator and use as a tool in hydraulic turbine design.2.1.2 Leakage flow analysis technology

Leakage flow exists in the gap between the fixeddischarge ring and rotating runner. When observingfrom the rotating runner, the leak flows from thepressure side of the blade tip gap toward the suctionside. A local attack angle near the tip side at theleading edge is larger due to the effect of this leakageflow than in the case of disregarding the gap influence.The leakage flow from the blade tip gap strongly

affects not only entrance cavitation performance butalso downstream flow. Therefore, it is necessary toanalyze the effects of leakage, taking the gap intoconsideration, to correctly evaluate the performance ofthe bulb turbine. As a result, the author developed theleakage flow analysis technique(2) which enables theleakage analysis of a very small gap.2.1.3 Computational results

Three-dimensional flow simulation in a bulb tur-bine can be accurately carried out by introduction ofthe flow analysis technologies described above. Figure1 shows the analytical results of a bulb turbine whichincludes guide vanes, a runner and a draft tube inoptimum operating condition. The length of vectorscorresponds to the magnitude of flow velocity. Figure 3shows the distribution of flow velocity and pressure atthe guide vanes’ exit. Here, the ordinate representsthe velocity components (C z, Cθ and C r) in the axial,circumferential, and radial directions, respectively.They are normalized by the runner’s peripheral speed,and the pressure coefficient Cp is normalized by thedynamic pressures of the runner’s peripheral speed.The pressure distributions on the pressure and suctionsurfaces of the runner blade at midspan are shown inFig. 4, with the three lines representing three on-cam0.3

0.2

0.1

0.0

-0.1

-0.20.4 0.6 0.8 1.0 1.2

Radius

Pre

ssu

re c

oeff

icie

nt

/ vel

ocit

y co

effi

cien

t

Cz

Cθ

Cp

C r

0.4

0.2

0.0

-0.20.0 0.2 0.4 0.6 0.8

Distance from blade inlet

Pre

ssu

re c

oeff

icie

nt

Midspan

Discharge ring

Type B

Type ABoss

Distance from runner vane center

Vel

ocit

y di

stri

buti

on (

Cθ)

0.6

0.5

0.4

0.3

0.2

0.1-0.2 0.2 0.6 1.0 1.4

Application of Numerical Flow Analysis Technologies to Hydraulic Turbines and Pump-Turbines 21

Fig.7 Velocity and pressure distributions at the inlet in lowdischarge pumping operation

Fig.8 Velocity vectors at partial discharge

Fig.9 Computational results for the low-pressure range

Fig.10 Erosion near the tip side on the suction surface ofactual runner

Fig.11 Tip leakage flow and vortex near tip side

operating conditions.In Fig. 5, the passage profile between the guide

vane and runner is changed and then the distributionsof circumferential velocity are compared from the bossto the discharge ring. It is understood that a differenceexists in the absolute velocity and the spanwise spreadof the velocity for both kinds of passages. Thedifference in velocity distribution directly affects therunner inlet flow condition. The best passage profile ofsuch on-cam conditions can be chosen by flow analysis.These computational results will be very important infurthering runner design.

2.2 Pump-turbinesThe pump-turbine operates the runner in either

the forward or reverse direction and performs pumpand turbine operations with one runner. Therefore,when the runner is designed, the performance of bothpump and turbine operations must be considered. Toimprove the balance between pump and turbine perfor-

mance, analysis of the flow of the pump-turbine in thedesign stage is much more important than the ordi-nary turbine runner.

Figure 6 shows the flow field in the blade-to-bladepassage at its most efficient pump operation. Thereduction of radial velocity can be found on thepressure surface. When the discharge is decreasedwith the guide vanes having the same opening, reverseflows are created at the leading edge of the runner.Efficiency and head suddenly changes, and vibration

0.6

0.4

0.2

0.0

-0.20.2 0.3 0.4 0.5 0.6

Radius

Pre

ssu

re c

oeff

icie

nt/

velo

city

coe

ffic

ien

t

Cθ

Cz

C r

Cp

(a) Pressure surface

(b) Suction surface

Tip

Boss

Centerline

Inlet

Cavitation erosion on suction surface

Erosion

Outlet

Low-pressure zone

Result of pressure calculation on suction surface

Vortex

Vol. 43 No. 1 FUJI ELECTRIC REVIEW22

and noise occur at the partial discharge operatingconditions. Figure 7 shows the velocity and pressuredistributions of the pump inlet in the case of reverseflow generating at the leading edge. The abscissa isthe radius, the left side is the crown, and the right sideis the band. Axial velocity C z starts decreasing frommidspan toward the band side and is negative near theband side. It is understood that Cθ increases steeply inthe same area. It is possible to say that reverse flowoccurs at the band side in this operating conditionwhen such results are analyzed. Figure 8 shows thevelocity vectors on the pressure and suction surfaces atthis operating condition. A strong reverse flow isobserved near the band side. Moreover, this reverseflow area expands from the pressure side toward thesuction side. It can be confirmed that efficiency andhead decrease due to reverse flow(3).

The performance and appearance of the flow of thepump-turbine model in the initial design stage areobtained by computational results. From these results,the initial design can be evaluated, and any redesignfor the next stage can be drawn. The accumulation ofsuch analytical information and the improvement inboth the analytical technologies and computationalenvironments will contribute to building a more reli-able tool for pump-turbine design.

2.3 Kaplan turbinesAn existing Kaplan turbine runner to be replaced

is also analyzed. The specific speed of this Kaplanturbine is nSQ = 156 (r/min, m3/s, m) at the maximumefficiency point. As in bulb turbines, there exists theleakage flow through the gap along the blade outerperiphery in Kaplan turbines. In high head machines,cavitation erosion can be generated due to this leak-age. The Kaplan turbine mentioned in this paper wasmanufactured in the 1960’s, with the discharge ringdesigned as a complete cylinder. Therefore, the gapexpands at the leading and tailing edges by anincrease in the runner opening. Figure 9 shows thepressure contours on the suction surface obtained bythe analysis. A narrow, low-pressure area can be seena little upstream of the runner’s center line near thetip side, and a high-pressure range exists adjacent tothis low-pressure range. Moreover, a low-pressurearea is also found along the leading edge. In thisturbine, extremely violent cavitation erosion was gen-erated in the suction surface of the blade tip side, asshown in Fig. 10. In particular, the heaviest erosionoccurs on the blade suction surface, where the gap isminimal in size. The dark color in this figure showsthat erosion is heavy. Although the low-pressurerange of the computational result appears a littleupstream in comparison with the actual erosion, theshapes of the two results are very similar.

In Fig. 11, the flow field near the tip side on thesuction surface is shown with the velocity vectors andstreamlines. It is understood that a thin, strong tip

vortex is formed near the center of the runner wherethe gap is narrow. Moreover, the high-pressure beltobserved in Fig. 9 is dependent on stagnant pressure.This in turn is a blade-to-blade secondary flow thatcollides with the blade suction surface at the inside ofthe tip vortex.

3. Conclusion

The development of three-dimensional analysistechnologies and the computational results of thehydraulic turbines and pump-turbines are introduced.More detailed information regarding flow through thehydraulic turbine and pump-turbine can be obtainednow than in the past by the advancement of the three-dimensional flow analysis technology. It is expected toachieve a wide but steady operating range by improv-ing the efficiency of hydraulic turbines and pump-turbines.

However, the CFD technologies which have beendeveloped are not perfect and have limitations in thefield of numerical techniques and turbulent models.When commercial software is used, there are manyinstances where the computational results greatlydiffer from the actual flow in the case of complicatedflow. Great care must be taken to recognize theseoccurrences. Therefore, the designer must performflow analysis after fully understanding the suitablerange of application for the computational code and theturbulent model. The hydraulic turbine's internal flowis a compound flow, as explained above, with separa-tion, cavitation, and a strong vortex. Selection of thebest computational techniques is necessary, in accor-dance with the various types and operating conditionsof the hydraulic turbine.

As a quantitative design tool, the improvement ofanalysis technologies and the improvement of analyti-cal accuracy and reliability is an important topic forthe future. The mission of the design tool is to pointthe way for design improvement by analyzing perfor-mance defects of the hydraulic turbine. We intend toadvance both utility and analytical technologies aim-ing at the achievement of the higher level CFDtechnology, by which the design can be completedthrough “Numeric experimentation” without relying onthe model test.

References:(1) Y. Qian, et al: Numerical Flow Simulation on Chan-

nel Vortex in Francis Runner, XVII IAHR Symposium,Beijing, (1994)

(2) Y. Qian, et al: 3-D Numerical Analysis of Bulb Tur-bine Runner Performance with and without Tip Clear-ance, FED-Vol.227, Numerical Simulation in Turbo-machinery ASME, (1995)

(3) Y. Qian, et al: Analysis of The Inlet Reverse Flows ina Pump Turbine using 3-D Viscous Numerical Tech-niques, XVIII IAHR, (1996)

Technologies to Modernize Existing Hydropower Plants 23

Takayuki OkunoYoshiaki ArakiMasaru Iijima

Technologies to Modernize ExistingHydropower Plants

1. Introduction

Japan’s hydropower plants occupy an importantposition as entirely domestic, clean energy sources andnew development of hydropower plants is promoted toensure a stable energy supply.

The history of hydropower plants in Japan is long(about 100 years) and Fuji Electric has suppliedhydropower equipment for nearly 60 years. Deterio-rated hydropower plants erected before the 1950s stillremain in large numbers.

Formerly, these plants that have been in operationfor a long time are restored to their initial conditionmainly by repairing only severely deteriorated parts.

However, there is a demand for reducing the laborinvolved in maintenance and inspection due to thetrend in unmanned hydropower plants. There are alsodemands for environmental protection measures toprevent pollution that are stricter than when theplants were originally built. Performance of the mainunit sometimes has to be reconsidered in response tochanges in the river flow and operating conditions.Also, the number of skilled engineers for maintenanceis insufficient. Because of these changes in theenvironment around existing hydropower plants, cus-tomer needs for repair and modernization are diversi-fied. Therefore, recent existing hydropower plantshave undergone integrated modernization by incorpo-rating measures for reduced labor, higher efficiency,environmental protection, improved performance of themain unit, equipment simplification, and improvedreliability.

This paper, based on recent technical trends tomeet current needs, introduces several characteristicexamples of modernization technologies for the equip-ment.

2. Trend of Modernization Technologies

A summary of the technologies used for moderniz-ing the equipment is shown in Table 1.

Amongst hydropower equipment, systems for cool-ing water and pressurized oil have the most complicat-ed configuration and require the most labor for mainte-

nance. Eliminating devices that use these systems willsimplify the equipment and increase reliability. There-fore, in the modernization of equipment, the applica-tion of technology to omit pressurized oil, air, andcooling water, the so-called “three-less” technology, isthe most important topic. Many new technologiesaimed at a wide range of applications have beendeveloped.

In consideration of the global movement for envi-ronmental protection which has become stricter, tech-nologies to prevent oil leakage into rivers and toeliminate toxic materials are the main focus of mod-ernization technologies.

With the goal to simplify equipment and provideadvanced functions, application of digital technology tocontrol equipment is increasing. The establishment ofdigital added value technologies such as automaticpatrol inspection systems to improve maintenanceefficiency will also be an important topic in the futureto improve the management techniques of powergenerating systems.

Table 1 mainly describes new technologies used forequipment modernization. In the future, it is antici-pated that there will be greater demands for enhancedtechnology to restore deteriorated equipment underthe existing restrictions.

3. Modernization Technologies

3.1 Modernization Technologies for hydraulic turbines3.1.1 Waterless cooling system

The water supply equipment at hydropower plantscontains many components, malfunctions most fre-quently, and thus requires much labor to maintain.

Therefore, the elimination of this water supplyequipment, known as waterless design, is a majortheme in the modernization of hydropower equipmentto reduce the incidence of malfunctions, simplifymaintenance, and shorten inspection time.(1) Use of air cooled oil-immersed turbine bearings

Many existing oil lubricated type hydraulic tur-bine-generators have used river water as the water forcooling.

Waterless cooling systems for turbine bearings

Vol. 43 No. 1 FUJI ELECTRIC REVIEW24

Fig.1 Outline of the mechanical seal

Table 1 Modernization technologies for hydropower equip-ment (summary)

Table 2 Record of air-cooled vertical hydraulic turbinebearings

User needs Turbines Generators Control

Red

uct

ion

of

mai

nte

nan

ce

Env

iron

men

tal

prot

ecti

onE

con

omic

al im

prov

emen

t

Waterless cooling

•

•

Waterless shaft seal Air-cooled bearing

•

•

•

Pipe-ventilated generators Air-cooled bearing Heat pipes

Oilless (grease-less)

•

•

•

Motor-operated servomotor Water-lubricated bearing Oilless bearings

•Electromagnetic braking

Airless

•Elimination of air compressors (bladder type oil pressure device)

•Electromagnetic braking

Extended life span, etc.

•

•

Wear resistant material to prevent cavitation (utilizing ceramic technology) Solid-state sensors

•

•

Brushless exciters Solid-state sensors

Prevention of oil leakage into rivers

•

•

•

Kaplan runner boss immersed in water Water-lubricated bearing Oilless bearings

Increase in annual power output

•Turbine runner efficiency improvement

Oil mist prevention

•Shaft seal device with magnetic fluid

Elimination of pollutants

•Non-asbestos brake lining

Reduction of size and weight

•Runaway speed machine (runaway speed machine design with specific generator GD2)

•Life expectancy diagnosis

Dig

ital

sol

id-s

tate

cir

cuit

s

Exp

ansi

on o

f to

tal d

igit

al c

ontr

ol s

yste

ms

Exp

ansi

on o

f to

tal

digi

tal c

ontr

ol s

yste

ms

Man

agem

ent

tech

niq

ue

impr

ovem

ent

Adv

ance

d fu

nct

ion

s

Pre

ven

tive

mai

nte

nan

ce

and

auto

mat

ic p

atro

l in

spec

tion

•

•

High specific speed runners Runaway speed machine (reduction of guide vane closing speed, increase of N by omitting the pressure regulator)

∆

Equipment simplifica-tion

•“Three-less” devices (waterless, oilless & airless)

•

•

Elimination of the spillway (deflector discharge, etc.) “Three-less” devices (waterless, oilless & airless)

Preventive mainte-nance

•Life expectancy diagnosis

•Condition monitoring sensor technologies

Condition monitoring

•Condition monitoring sensor technologies

User

Nipponkai P. Gen. Inc. Tohoku E. P. Co. Inc.

Chubu E. P. Co. Inc.

Chugoku E. P. Co. Inc. Hokkaido E. P. Co. Inc.

Tohoku E. P. Co. Inc.

KatagaiMinami-

mata

Ohzaso

Shichi-so

Shibaki-gawa No. 2

Shikari-betsu No. 2

Gassan

VP

VP

VF

VF

VF

VD

5,230

12,000

2,380

6,900

7,700

9,160

450

375

200

450

500

500

Fancooler

Fancooler

Aircooling

Aircooling

Aircooling

Fancooler

Oct.1989

Apr.1991

May1991

Mar.1992

Aug.1994

Under develop-ment

Newmachine

Newmachine

Newmachine

refur-bished

Existing,modified

Existing,modified

Newmachine

Plantname

Tur-binetype

Output(kW)

Speed(r/min)

Cool-ing

Startdate

Re-marks

Note (1) “Air cooling” in the Cooling column indicates anaturally cooled air cooling system.

(2) “Fan cooler” in the Cooling column indicates aseparately installed fan-cooled oil cooler system.

1

1

2

2

3

3

4

4

5

5

6

6

7

7

8

8

9

9

10

10

11

11

Main shaftSeat of the main shaftSeal ringSeal ring supportStopperSpring

Spring supportCasingWater pipeLabyrinthWear indicator

20 to 30mm

include natural air cooling, fan cooling with a separateoil-to-air heat exchanger, heat pipe cooling for horizon-tal machines, etc.

The application of heat pipe cooling is limited tolow power horizontal-shaft machines because of thecharacteristics of the working medium. Natural aircooling and fan cooling systems can be applied tovertical-shaft machines. The range of these applica-tions has been widened recently.

The natural air cooling system cools the lubricantby heat radiation from the external surface of the

Technologies to Modernize Existing Hydropower Plants 25

bearing oil tank and is an ideal system that needs noextra attachments such as a power source. Recently,this system has expanded its application range whileaccumulating the following features.

(a) Fins are attached to the external wall of theoil tank to raise heat radiation efficiency.

(b) Heat radiation is similarly improved by wid-ening the effective heat radiation area as wellas securing space around the oil tank.

(c) A low viscosity lubricant, VG46, is used toreduce heat generation in the bearings.

(d) Use of segment type bearings reduces heatgeneration.

(e) The guaranteed maximum bearing tempera-ture is raised from 65°C (former value) to75°C.

On the other hand, the fan cooling system coolsheated lubricant by drawing it into an air-cooled oilcooler equipped with an electric fan. This system has awider application range than the natural air coolingsystem as long as space to install the oil cooler withfan can be secured.

Table 2 shows application examples of these aircooling systems.(2) Shaft seal device using ceramics

In conventional shaft seal devices, gland packingand carbon packing were widely used. These bothrequired complex water supply devices to remove dustand sand from the supply water. Other disadvantageswere that repeated tightening was necessary for glandpacking and carbon packing would rapidly wear in ashort time once abnormal wear occurred. The develop-ment of a shaft seal device which needs no clean watersupply, has higher reliability, and a long life span, ishoped for.

Application of the labyrinth seal with no slidingparts is worth investigating first. However, its appli-cation is limited to use with low tail water levels, andis therefore seldom used.

Recently, Fuji Electric has developed a mechanicalseal type shaft seal device which uses a ceramiccompound material for the sliding surface and aspecial synthetic resin for the seal material. This sealdevice was applied to a certain existing hydraulicturbine and was successful in yielding a low wear rateand stable performance. Figure 1 is an outline of thisdevice. Instead of a clean water supply, the mechani-cal seal type only requires a small quantity of riverwater at atmospheric pressure for cooling.

Fuji Electric is now promoting studies on thecombination of ceramic materials.3.1.2 Oilless (greaseless) Technologies(1) Water-lubricated bearings

Previously, grease-lubricated bearings were gener-ally used in Kaplan turbines. However, grease-lubricated bearings required a constant supply ofgrease for lubrication. Once used, the grease wouldflow out into the river. Recently to prevent pollution,

there has been a growing demand for greaselessbearings and a water-lubricated bearing was developedas a replacement.

Figure 2 shows an example of a water-lubricatedbearing structure.

The water-lubricated bearing uses water for thelubricant and glass fiber reinforced phenol resin woundin layers for the bearing surface material. Fuji Electricuses a hydrodynamic lubrication system. The hydrody-namic lubrication system efficiently uses the shaftrotation and water viscosity to form a wedge-shapedwater film between the shaft and bearing and supportsthe bearing load with this water film. Therefore, asthis system does not require a pressurized watersupply at the bearing surface (as used for hydrostaticbearings) it has the special feature of being a self-contained system.

Since unit No. 1 started operation in 1984, thenumber of Fuji Electric’s applications of this bearingsystem amounts to 15 existing modernized turbinesand to 20 when new turbines are included, all of whichcontinue satisfactory operation.(2) Application of the motor-operated servomotor

In conventional hydropower plants, guide vanes,inlet valves, and pressure regulators were generallyoperated by oil pressure. However, oil pressure devicesconsist of pipes, valves, and many other components,and as a result are prone to oil leakage. Various partswill be contaminated by an oil leak, and there is alsothe danger of fire in case pressurized oil is sprayed.For these reasons, this device was difficult to maintain.

In consideration of these problems, if the guidevane mechanism is made to operate electrically andthe oil pressure device is omitted, the station equip-ment will be much simplified, and the amount ofequipment to maintain as well as the required laborwill be greatly reduced.

In addition, the electrical operation of guide vanesmakes it possible to eliminate pressure regulators instations such equipped.

In this case, to limit the water pressure rise in thepenstock generated by the sudden closing of the guidevanes to values as in conventional devices, it isnecessary to close the guide vanes slowly. Accordingly,the hydraulic turbine generator shall tolerate a speedrise at load rejection up to the runaway speed of theprime mover, a so-called runaway speed machine.

However, the fatigue strength of the rotor compo-nents becomes a problem for the generator.

As long as steel plates produced under the presentmanufacturing technology and high quality control areused, fatigue strength is not a big problem. However,because most of the machines currently being refur-bished were manufactured during the postwar rehabil-itation period and are subject to repeated stress, it isdifficult to ensure their continuous use. Therefore it isnecessary to replace the main rotor parts in thesemachines.

Vol. 43 No. 1 FUJI ELECTRIC REVIEW26

Fuji Electric’s motor-operated servomotors havebeen used in applications since 1978. Currently 86units are in operation, including new installations.Figure 3 is a diagram to show the elements of amotorized power cylinder which converts the motor’srotational motion into linear motion of the outputshaft.

Fuji Electric formerly used a DC brushless system,but with the improvement of inverter technology, hasutilized an AC brushless system in applications with a

larger output. At present, an AC vector control systemis applied to rated outputs of 22kW or more.

The applicable range of motor-operated servomo-tors is not more than 20,000 kW for generator output,30 kW for motor output, and 295 kN for rated thrust.

In the repair of existing machines, however, some-times the installation of a motor-operated servomotoris restricted by space and each case must be consideredindividually.

Motor-operated servomotors have already beenapplied not only to Frencis turbines but also to operatePelton turbine needles and deflectors. Application tothe operation of Kaplan turbine runner vanes is nowunder development.

3.2 Modernization technologies for generators3.2.1 Shaft seal device with magnetic fluid

Fuji Electric prevents oil vapor leakage from theshaft seal of the bearing oil tank by partitioning theinside and outside of the oil tank with an air curtainusing the labyrinth system shown in Fig. 4 as astandard structure.

However, because the relation between pressureinside and outside of the oil tank and air pressuresealed in the labyrinth part can not be ideally regulat-ed, it is difficult to stop leakage completely.

– Runner –

Lower waterseal packing

Main shaftwater seal packing

Glass cloth + phenol resinCotton cloth + phenol resin

Bearinghousing

Bearingmetal

Water supply tomain bearing

Main shaft sleeve

– Main shaft –

Upper waterseal packing

Main shaft waterseal packing support

Bearing support

Thermometer

Upper cover

Natural drainage

Water supply tomain shaft waterseal packingDischarged water

D

Dφ

φ

Fig.2 Example of a water-lubricated bearing structure

Fig.3 Elements of a motor-driven servomotor system

Guide Vane

Guide vaneposition detector

Toothed disk(speed detection)

Electric governor panel

GOV(Sequencer)

(Speed control)

Servomotoramplifier(Motor control)

Powersupply panel

Power supplysystem(SPS)

200V AC 100V DC

200V ACSine wavePWM currentcontrol

Power cylinder(rotation to linear motion)

ServomotorM

Technologies to Modernize Existing Hydropower Plants 27

Fig.5 Shaft seal device using magnetic fluid

Fig.4 Labyrinth type shaft seal device Fig.6 Air flow when one unit is in operation

Labyrinth, rotating part

– Inside of the tank –

Labyrinth, fixed part

Air dischargepipe

Air feed pipeShaft

Shaft

Magnetic fluid

Pole piece

Permanent magnet

– Inside of the tank –

Discharge damper

Discharge duct

Dis-charge

Suction DischargeUnit No.1 Unit No.2

Connecting duct

(a) Side view of the generators

(b) Floor plan of the generators

Before hydropower plants were unmanned, it wasthought that oil leakage from the bearings was un-avoidable and would be monitored by the maintenancestaff, oil leaks were unimportant as long as there wasno undesirable effect. Now in unmanned plants, evenstains due to oil vapor are considered a problem.

Until now, all of the types of shaft seals have had aclearance between the shaft and oil mist cover.

The shaft seal device introduced here, as shown inFig. 5, completely fills this clearance with magneticfluid to stop oil vapor leakage.

The permanent magnet mounted on the inside ofthe oil mist cover forms a magnetic circuit through theclearance between the shaft and oil mist cover. Themagnetic force holds the magnetic fluid in its position.

However, for high shaft peripheral speeds, there isa problem in that the magnetic fluid is vaporized byfrictional heat or scattered by centrifugal force. There-fore, this device can not be applied to all machines.

Currently, one such device is being manufacturedfor application in a specific plant. It is desired to usethis device in applicable machines in the future in

order to reduce maintenance labor.3.2.2 Measure to maintain insulation resistance

In hydropower plants in which more than one pipe-ventilated generator is installed, the insulation resis-tance of the generator not in operation greatly dropsand when started, the field winding ground detectorrelay may activate.

The reason for this behavior is that the generatorin service takes in the room air and discharges itoutdoors. Simultaneously, the same quantity of out-side air is drawn into the generator room through thefresh air inlet. Because the building fresh air inlet isusually equipped with dust and insect filters, pressureinside the building is made a little negative by the flowresistance. As a result, the outside air flows backwardfrom the exhaust port of the generator not in opera-tion, and flows around the field windings and arma-ture windings into the generator room.

Therefore, when humidity is high, the windingsare directly exposed to moist outside air, and thedeteriorated, absorbent insulation cannot maintain theappropriate insulation resistance, resulting in activa-tion of the field winding ground detector relay. As ameasure to prevent insulation resistance from drop-ping, a space heater is provided, but this is noteffective when exposed to the flow of outside air.

This problem has been solved by connecting thedischarge ducts of several generators, providing motor-operated discharge dampers, and attaching openingregulators. Using Fig. 6, these measures are intro-duced below.

When both units No. 1 and No. 2 are in operation,air does not flow in the connecting duct. When unitNo. 2 stops, part of the discharge of unit No. 1 flows inthe connecting duct. By closing the discharge damper,that discharge is returned through the No. 2 generatorto the generator room.

As a result, although pressure inside the plant isnegative, the discharge of unit No. 2 does not havenegative pressure and therefore does not such inoutside air. Moreover, since the unit is filled with air

Vol. 43 No. 1 FUJI ELECTRIC REVIEW28

heated by unit No. 1, having low relative humidity, theinsulating material absorbs no moisture and theinsulation resistance can maintain the appropriatevalue. In addition, the amount of flow backward intothe room is related to the room temperature, and a risein room temperature raises the winding temperature.Therefore, by changing the opening of unit No. 1’sdischarge damper, the discharge quantity and flowbackward can be regulated to keep the room tempera-ture at a prescribed value. Further, in winter whenone unit is operated for a long period of time, not onlycan this system maintain the insulation resistance, but

can also heat the room air and solve the problem offrozen plant equipment.

4. Conclusion

This paper introduces several characteristic exam-ples of recent modernization technologies that FujiElectric is developing for existing hydropower plants.

In the future, customer needs for refurbishingexisting hydropower equipment will become more andmore diversified. It is hoped that the reader finds thispaper helpful in repairing deteriorated equipment.

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FUJI/GE PRIVATE LTD.171, Chin Swee Rd., #12-01/04 San Center,Singapore 169877, SINGAPORETEL : 533-0010 FAX : 533-0021

HOEI ELECTRONICS (S) PRIVATE LTD.51 Goldhill Plaza, #14-09/10 Newton Rd.,Singapore 368025, SINGAPORETEL : 251-8751 FAX : 251-0827

GE/FUJI ELECTRIC CO., LTD.Nicolaou Pentadromos Centre, Office 908,Block A, P. O. Box 123, Limassol 205, CYPRUSTEL : 5-362580 FAX : 5-365174

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