Preliminary Test of New Runners for the Turbines of Guri Hydropower Plant

8/18/2019 Preliminary Test of New Runners for the Turbines of Guri Hydropower Plant

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IAHR AIIHINTERNATIONAL SYMPOSIUM ON HYDRAULIC STRUCTURES

CIUDAD GUAYANA, VENEZUELA, OCTOBER 2006

PRELIMINARY TESTS OF NEW RUNNERS FOR THE TURBINES OF

GURI HYDROPOWER PLANT

Ing. Pedro Zambrano – CVG EDELCA–VENEZUELA – [email protected] Ing. Egda Calderón – CVG EDELCA–VENEZUELA – [email protected]

Ing. Antonio Márquez – CVG EDELCA–VENEZUELA – [email protected] Ing. Fidel Arzola – CVG EDELCA–VENEZUELA – [email protected]

ABSTRACT

With the objective to eliminate the cavitation of the runners, to increase the efficiency, toreduce the vibration, to repair or replace the worn components, and to put the turbines in “as new”

condition the processes for rehabilitations of Units 7, 8, 9 and 10 of Powerhouse I and Units 12, 15,16, 18 and 20 of Powerhouse II of Guri have been made. In both processes the Bid documentsincluded as a part of the technical evaluation, the realization of Competitive Model Tests with the

purpose of demonstrating that the hydraulic design of the Bidders fulfills the guaranteed values oftheir Bid and the requirements of the technical specifications, as well as determining the best

performance of each model. The present work shows the experience obtained during theaccomplishment of these competitive model tests, which were made in the Independent Laboratoryof ASTRÖ in Graz, Austria, for the case of the Units of the Powerhouse I and in the Independent

Laboratory of EPFL in Lausanne, Switzerland, for the case of the Units of the Powerhouse II. Inboth tests the efficiencies of the turbines, cavitation limits, hydraulic axial thrust and pressure

pulsations for each one of the operation conditions of the participant models were determined.

KEY WORDS: Hydraulic Turbine; Model Test; Hydraulic Laboratory

INTRODUCTION

The Hydroelectric Powerplant of Guri is the first of four hydroelectric stations built byEDELCA on the lower reaches of the Caroní river, which discharges into the Orinoco river, ineastern Venezuela. The Guri Project consists of two Powerhouses, each one integrated by ten unitswith Francis type turbines, that conform a total installed capacity of 10.000 MW, with a 162 m highdam, 85.400 million cubic meters in volume reservoir, and a spillway controlled by nine radial gateswith a total discharge capacity of 30.000 m3/s.

The Units 7 to 10 of Powerhouse No. 1 went into commercial operation between the years 1976 and1978. This Units were designed to operate with a nominal net head (net head for most frequentoperation) of 128 meters.

The Powerhouse No. 2 units went into commercial operation between 1984 and 1987, and wereconceived to operate with a nominal head of 130 m, with a rated and guarantee output of 610 MWfor each Unit.


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Nevertheless, during the first years of service the turbines operated under reduced heads, due tovarious reasons: low reservoir level during construction; late conclusion of the transmission lines;and design problems of the main power transformers limited the operation of the units.

Due to the different hydraulic conditions, appeared in the runners pronounced secondary flows thatcaused high intensity cavitation and excessive damages by cavitation pitting in the runners blades,which required massive and periodic repairs by welding, which in turn caused a distortion in the

profile of the blades and, in consequence, a loss of efficiency accompanied with high vibrations.

REHABILITATION SUBJECT

With the aim to increase the unit’s efficiency (and output for Powerhouse No. 2), eliminatecavitation, reduce vibration, replace the worn components, and moreover to get the turbines in an“as new condition”, EDELCA decided to initiate two bidding process, including model testing.

COMPETITIVES MODEL TEST

After the accomplishment of the established corresponding steps in each one of the Bids Documentsof CVG EDELCA, two manufacturers were qualified to participate in the competitive model tests,

to be carried out in an Independent Hydraulic Laboratory, in order to demonstrate that theirhydraulic designs fulfill with all the values guaranteed in their Bids and with the requirements of theTechnical Specifications, as well as to determine the best performance of each model, that servedlater in the bid evaluation.

For the Powerhouse No. 1 process the Laboratory ASTRÖ (Anstalt für Strömungs-machinenGMBH) in Graz, Austria, was selected as an independent laboratory, in order to carry outcompetitive tests on the models of both qualified manufacturers.

For the Powerhouse No. 2 process the Laboratory EPFL (Laboratory for Hydraulic Machines of theEcole Polytechnique Fédérale de Lausanne), in Lausanne, Switzerland, was selected as anindependent laboratory, in order to carry out competitive tests on the models of both qualified

manufacturers.

GENERAL DESCRIPTION OF THE HYDRAULIC MACHINES LABORATORIES

The ASTRO laboratory contains two test rigs, the turbine test rig and the four quadrants test rig.The turbine test rig was used for the competitive model tests of Units 7, 8, 9 and 10 of Guri.

Figure 1.- Schematic diagram of the test rig - ASTRÖ Hydraulic Machines Laboratory


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On the other hand the EPFL laboratory contains three universal test rigs, denominated PF1, PF2 andPF3. The test rig PF2 was used for the competitive model tests of Units 12, 15, 16.18 and 20 ofGuri.

Both test rigs are equipped with high precision measuring instruments, so that they are adapted foracceptance and development tests, according to orders code IEC 60193.

These rigs are used in closed hydraulic circuit for the tests of efficiency and cavitation. The aircushion on the level of the water in the water discharge tank is connected to a pressurized airsupply, as well to a vacuum pump for pressure variation during the tests.

In general, with the equipment of these test rigs can reproduce the required conditions of generationfor the evaluation of the guarantees presented by the Bidders and of the global behavior of theirhydraulic turbine, respecting the hydraulic similarity between model and prototype.

Figure 2.- Schematic diagram of the test rig - EPFL Hydraulic Machines Laboratory

NORMATIVE FRAME OF THE COMPETITIVE MODEL TESTS PROCESS

The standards that regulated the competitive models tests processes were establishedaccording to following documents:Powerhouse I:

Biding document of the Contract N° 2.2.102.003.00 of CVG EDELCA (February 2002). Model Tests Procedure (January 2004). International Standard IEC Publication 60193, Second edition 1999-11.

Powerhouse II: Biding document of the Contract N° 1.1.102.012.01 of CVG EDELCA (June 2003). Model Tests Procedure (January 2005). International Standard IEC Publication 60193, Second edition 1999-11.

TEST The tests executed in both physical models and testified by CVG EDELCA and the

respective manufacturers, as much in the ASTRÖ Laboratory like in the EPFL Laboratory, includedthe following activities:

Calibrations


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Preliminary test Official test Calibration check Dimensional Check

CALIBRATIONS

The calibrations of the measuring instruments of the test rigs were made before and after carryingout the tests to each model with the purpose of guaranteeing that the measurements registeredduring the same ones were within the allowed rank of uncertainty with which they were consideredlike valid the obtained results of the tests. In case that differences greater had happened than thoseof the defined systematic uncertainty in the procedure, in several points between the twocalibrations, the affected tests had been repeated at laboratory cost. The calibrations include:

Flow measurement Specific Hydraulic Energy Manometer Main Torque Friction Torque Suction Head Manometer Axial Thrust Measurement Rotational Speed Measurement Dynamic Pressure Transducers

PRELIMINARY TEST

The preliminary tests consisted of measurements that the bidder made in the independentlaboratory in a way to verify the correct assembly of his model, in order to assure a smooth andstable operation. The preliminary test results were not used like official test results.

OFICIAL TEST

Each Bidder has the opportunity to testify the official tests of its model, to be executed in the

independent laboratory.

The official tests included axial hydraulic thrust, efficiency, cavitation, pressure and torquepulsations, with and without air admission, according to the established program.

Axial Hydraulic thrust

The axial hydraulic thrust tests were made for the speed factors of the model corresponding to thenet head for the prototype established in the tests procedure. The hydraulic thrust tests includedmeasurements from 20% to the guide vanes maximum opening in increases of 1 to 2° for each headof test.The model axial hydraulic thrust value turned to the corresponding prototype value, was comparedwith the guaranteed axial hydraulic thrust of the prototype like with the maximum indicatedacceptable value in the Technical specifications in agreement with the capacity of the existingbearing.

Cavitation

The cavitation tests were made for the speed factors of the model corresponding to the net head forthe prototype established in the tests procedure, and in the number of required points to determine


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the values of the cavitation margin for the average weighed efficiency test points required in theTechnical specifications and to confirm the guaranteed cavitation limits.

During the cavitation tests the oxygen content dissolved in the water was measured constantly withthe intention of maintaining it within 2 to 5 ppm.

An expert in cavitation of the independent laboratory personnel made the visual observations,

documentation and evaluation (sketch and written documentation) of the cavitation behavior forboth models. The interpretation and official evaluation of the cavitation behavior of the expert incavitation were presented by sketch, drawings and written documentation.

The sigma break curves were done (σ - η). For each sigma break curve the behavior of thecavitation was observed at sigma plant, to check the presence of cavitation bubbles in the runner.

The critical sigma, for the determination of the cavitation margin for these Contracts, was sigma 1,according to defines IEC 60193, Clause 1.3.3.6,9, page 37. “The number of Thoma one (Sigma 1) isequal to the value of the Thoma number for which a fall of a point of percentage in efficiency isobtained compared with the efficiency to the Thoma zero number”, see Figure 3

The test report of the model showed the cavitation margin available ((sigma plant - sigma 1) x nethead) for each test head and power output, expressed in meters of water column between the downstream level corresponding to sigma the 1 and minimum down stream level corresponding to thecavitation limit. The cavitation margin must be equal or greater to the established one in the Bidingdocument for all the points within the continuous operation range of the turbine.

Figure 3.- Graphic definition of Sigma 1

For all the sigma plant values it took place sketch of the cavitation patterns and the runner vortex. Astroboscope and boroscope was settled in the model to allow the inlet cavitation observation in thecritical points of operation.

The cavitation occurrence in the pressure side and in the suction side, the formation anddisintegration of vortex at low load were located, analyzed and registered in terms of thecorresponding operation conditions.

Efficiency, power and flow

The efficiency tests of the turbine model were made with the speed factors of the modelcorresponding to the following net head for the prototype established in the tests procedure; and atthe minimum down stream levels (minimum sigma plant) corresponding to each one of the pointsincluded in the turbine efficiency, power output and flow guarantees. The tests to each net head


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included guide vanes openings from 20% to the maximum opening, made in the points required forthe preparation of the efficiency curves specified and hill diagram to be provided for the prototypeturbine.

In order to check the stability of the measurement, a test point near to the peak efficiency wasrepeated several times every day during the efficiency tests. The maximum deviation of the resultwas lower than ± 0.10% of the efficiency, in agreement with the Annex L of IEC 60193.

The water temperature of the model was maintained within ±1°C for each test of efficiency, and thevariation in the water temperature was maintained within ±2°C for the tests of all the models.

Pressure and torque fluctuations

The pressure pulsations tests were made for the speed factors of the model corresponding to theestablished prototype net head in the tests procedure. The pressure and torque pulsations in thecorresponding shaft were measured between a 20% guide vanes opening until the Maximumopening, in increases of 1° for each head of test.

The pressure and torque fluctuations were measured to determine their frequencies and amplitude.

The tests were made with the admission of variable amounts of air through cone of the runner, inorder to reduce the fluctuations.

The air admission tests were made for the speed factors of the model corresponding to theestablished prototype net head in the tests procedure, and the points selected according to theobtained results of the tests without air admission. The admission of the air was measured with ameasurer of volume (device of floating element) like a percentage of the water volume.

Dimensional check

Before beginning the installation of the model in the independent laboratory, the geometry of thetwo sections of measurement, upstream and down stream, as well as the gaps of the runner seals(length and radial gap of the seals) were checked.

After completing the model tests a detailed dimensional check of the new and modified componentsof the model was made (excepting the profiles of the runner), in the presence of CVG EDELCA andthe corresponding Bidder of each turbine model, to confirm that each model on scale will behomologous to the rehabilitated prototype and to confirm that the models of each Bidder weregeometrically within the limits of Code IEC 60193.

UNCERTAINTIES MEASUREMENT

For determination the individual uncertainties of the main parameters characterizing the hydraulic

performance were considered the following:

ASTRÖ:Flowa) Calibrating tank ± 0.04%b) Error in density of water, presumably ± 0.05%c) Calibration of Venturi tubes ± 0.15%

fQS

= + + =2 2 2b ca ± 0.163%


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Net Heada) Dead weight tester ± 0.022 %b) Calibration ± 0.100 %

HS2 2

f a b= + = ± 0.102 %Torque:a) Length of lever arm ± 0.02%b) Calibration of test weights ±0.01%c) Calibration of force measuring device ± 0.10 %

TSf a b c= + + =2 2 2

± 0.102 %

SpeedfnS

=± 0.02Density of water

=W

f ρ ± 0.05

According to the definition of the efficiency the systematic uncertainty of the efficiency iscomposed of the individual errors of flow, head, torque, speed and water density:

= f f f f f f W2nS2TS2HS2QS2S ρ η ++++= ± 0.224 %

According to IEC 60193 code the random uncertainty must be limited so that in the higherefficiency region does not exceed:

fRη = ± 0.10 %

This is the value that will be used in all of the measurement uncertainty calculations.

The total uncertainty of the measured efficiency hence is:

f f fTOT S Rη η η= + =

2 2

± 0.246 %

EPFL:Flowa) Calibrating tank ± 0,09%b) Error in density of water, presumably ± 0,05%c) Calibration of electromagnetic flow meter ± 0,1%

fQS

= + + =2 2 2b ca ± 0,14% (Q=0,2 -1,4m3 /s)

Specific Hydraulic Energya) Pressure gauge ± 0,08%

b) Calibration ± 0,1%HS

2 2f a b= + =± 0,13% (E=50 – 1000 J/kg)

Torque:a) Length of lever arm ± 0,03%b) Calibration of test weights ± 0,02%c) Calibration of force measuring device ± 0,1%

TSf a b c= + + =2 2 2 ± 0.106%

Rotational speed:


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fnS

= ± 0.01%

Density of Water:=

Wf ρ ± 0.05%

According to the definition of the efficiency the systematic uncertainty of the efficiency iscomposed of the individual errors of flow, head, torque, speed and water density:

= f f f f f f W2nS2TS2HS2QS2S ρ η ++++= ± 0.226 %According to IEC 60193 code the random uncertainty must be limited so that in the higherefficiency region does not exceed:

=ηRf ± 0.10 %

This is the value that will be used in all of the measurement uncertainty calculations.

The total uncertainty of the measured efficiency hence is:

f f fTOT S Rη η η= + =

2 2 ± 0.247 %

PERSONNEL

In addition to the participant personnel of each one of the laboratories and of the Bidder, the testscounted with the presence of external consulters and by CVG EDELCA the personnel of theMechanical Projects Department, Plant Guri Modernization Project and the Applied ResearchCenter.

CONCLUSIONS

In the present article have been shown relevant aspects of the experience of the technical missionsent by CVG EDELCA to testify and to lead the process of tests that was carried out in physical

models corresponding to the manufacturers selected by CVG EDELCA for the manufacture andprovision of new hydraulic components for the rehabilitation of Guri turbines.

In this process it allowed to the technical personnel of CVG EDELCA: To deeply know and evaluate the models of the runner proposed for the solution of the

problems that at the moment present the Francis type hydraulic turbines of GuriHydroelectric Complex.

To select the manufacturers who fulfilled in their proven design with the technicalrequirements of the guarantees specified by CVG EDELCA.

To evaluate before the manufacture of the new runners, its behavior in all the range ofoperation of the generation units.

To obtain experience testifying and leading of the process to be used in next model tests to

be developed by CVG EDELCA.

REFERENCES

[1] Procedimiento para Pruebas de Modelo (Enero 2004).[2] Procedimiento para Pruebas de Modelo (Enero 2005).[3] Norma Internacional IEC Publicación 60193, Segunda edición 1999-11.[4] Pliego de Licitación del Contrato No. 2.2.102.003.00 de CVG EDELCA.[5] Pliego de Licitación del Contrato No. 1.1.102.012.01 de CVG EDELCA.