Hydrovision paper kaplan runners predictive monitoring

July 19-22, 2011 ~ Sacramento Convention Center ~ Sacramento, CA USA

Kaplan Runners, discussing a case of internal mechanism fracture and proposal for

predictive monitoring

By Carlos Alberto Dias Costa, Duke Energy International, Brazil;

Renato J. Baccili Castilho, Duke Energy International, Brazil;

Wilson Takao, Alstom Power, Brazil and

Wanderley Silva, Alstom Power, Brazil

1. ABSTRACT

In 2007, a problem was identified on the Kaplan runner at one of the generating unit at Rosana

Power Plant.

The generating unit was approximately 15 years old with around 157,000 hours of operation.

The metallurgical analysis of the fractured parts (pins and spacers of the blade links) indicated

that the crack was caused by rupture due to fatigue on the pins of the blade links installed in the

Kaplan runner.

Before reassembling the machine, evaluations were made regarding the force applied on the

internal components of the drive mechanism of the Kaplan blades through finite element

simulations aiming to identify improvements in design of materials.

This paper will show the ratings listed in the preceding paragraph, the investigations undertaken

to identify the source of the problem after the breakdown of the generating unit, the verification

of static and dynamic behavior of structural parts of the drive mechanism of the Kaplan runner

with the unit in operation and the result of measurements taken to ensure operational reliability

after equipment returned to operation.

The authors will also present a predictive test to monitor and ensure the extension of the lifecycle

of Kaplan runner based on theoretical tests performed using finite elements, the dynamic tests

carried out by sensors installed on rotating parts and the calculation of remaining lifecycle of

internal components of the Kaplan runner.

The predictive test proposed can be performed with the generating unit in operation, with defined

periodicity and is supported by the theoretical and practical results of the analysis.

The proposed predictive monitoring can be expanded to several generating units in operation

with low initial investment.


2. INTRODUCTION

In January 2007, generating unit 01 at Rosana Power Plant was being put back into operation

when, after tests on the voltage regulator and reaching 15 MW power, abnormal noise and

vibration was detected and shutdown necessary.

Tests were conducted on command and control systems and verifications were performed on the

clearances of the bearings. As no abnormalities were identified, an inspection on the hydraulic

turbine was initiated.

During inspection, after drainage of the generating unit, one of the blades wasn’t responding to

the drive mechanism of the blades (open command) which resulted in the withdrawal of the

runner cap for more detailed verification.

After inspection with the runner cap lowered, the following abnormalities were observed:

Components of the drive mechanism of the blades were found in the runner cap: two

blade link spacers and part of the blade link pin that was torn out;

Drag of material on the internal surface of the runner hub due to probable contact between

the external blade links and runner hub;

Contact between blades and runner strap with no material tear;

Blade 01 had marks on the suction side of the blade due to the blows received from blade

05 (pressure side of the blade);

Blade 5 didn’t respond to opening and closing commands from the drive mechanism of

the blades.

Abnormalities mentioned above are shown in the following photos:

Figure 1-photo of drag of

material in the rotor hub

Figure 2-photo of contact

between blades and runner

strap

Figure 3-photo of marks left

on Blade 01 (suction side of

the blade) by blow received

from blade 05


In view of the complexity of the recovery services required and particulars of the project beyond

the difficulty to access the location (confined space), the best option was to perform a complete

disassembly of the rotating parts in order to carry out necessary repairs.

After complete disassembly of the rotating parts and Kaplan runner, the following additional

abnormalities were identified:

Two blade link pins were broken;

Two blade link pins were cracked;

Flange of the servomotor cylinder presented cracks at the fixation holes of eyebolts 4 and

5;

Spade lever 05 cracked.

Metallurgical analysis on the blade link pins (fractured components) indicated that the cause of

the incident was rupture due to fatigue. Accordingly and to investigate the source of the problem

and the possible occurrence on other generating units, the following investigations were held:

Metallurgical Analysis;

Modeling of the internal components of the Kaplan runner through finite element

method;

Measurement of dynamic behavior obtaining axis oscillation signals, electric power,

rotation, opening of distributor and runner blades, force applied on internal components

of the Kaplan runner, command signal for the rotor valve, upstream and downstream

level.

3. METALLURGICAL ANALYSIS

The two ruptured pins present similar metallurgical characteristics, manufactured in medium

carbon steel, type AISI/SAE 1040, without evidence of metallurgical problems that could

compromise their performance.

Conclusion was that both blade link pins ruptured due to FATIGUE. Rupture began at the radius

of resistant sections between the largest and the smallest diameter, and subcritical propagation

through practically the entire resistant section, indicating low load.


Figure 4 – Aspect of the ruptured

blade link pins

Figure 5 – Macroscopic and

Macrographic aspect of

ruptured Blade Link PIN #01. *

* The rupture started at the strain concentration point, which corresponds to the radius between

the smallest and largest diameters.

4. MODELLING THE INTERNAL COMPONENTS OF THE KAPLAN RUNNER

THROUGH FINITE ELEMENT METHOD

In order to load the finite element model, the stress verified on internal components of the

Kaplan runner is a result of the operation pressure when opening and closing the runner blades.

4.1. Calculations

4.1.1. Calculation Method

The calculations were made through finite element method - EF using ANSYS v10.0

software. The model was designed with Solid Type Elements (SOLID95). Existing

contacts in the mechanism were modeled by contact elements (CONTACT 174).

4.1.2. Load conditions and limits

Blade link, blade link pins and blade link spacers

Restrictions were imposed at the middle section of the blade link pin limiting axial

displacement.

The blade link restrictions were imposed on the mid longitudinal section limiting

transverse displacement (normal to the longitudinal section). The restrictions regarding

model offset towards the load were imposed on the blade link pin, spade lever side.


The load model, resulting from operation pressures in each case considered, was applied

on the blade link pin (eyebolt side) in the form of distributed load – normal pressure;

having equal value and resultant force from the initial load. The interface blade link and

the blade link pins and blade link spacers were developed through contact elements with a

0.17 static friction coefficient.

Figure 6 – Model of the

blade link, blade link pins

and blade link spacers

Figure 7 – Model of the

blade link pins

4.1.3. Load

Force applied on the mechanism results from the operation pressure of the servomotor

that actuates the runner and is defined by the relation:

Where:

FT- total force applied on servomotors

- operation pressure on the opening chamber

- operation pressure on the closing chamber

- projected area of the piston on the opening chamber side.

- projected area of the piston on the closing chamber side.

Dep - external diameter of the piston

- internal diameter of the piston on the opening chamber side.

- internal diameter of the piston on the closing chamber side.

The operation pressure on the opening and closing chamber was obtained through tests

using pressure sensors installed in existing pressure taps on the Kaplan head.

The values obtained during tests were used to feed the finite element model.


The tests to measure the pressure on the opening and closing chamber of the runner servo

motor were performed on generating unit 02. The highest pressure differential between

the chambers was chosen as operational condition, resulting in a greater load to be applied

on the model. In the case of generating unit 02, the operational condition chosen

comprises a power range of 80-88 MW for opening and 93-80 MW for closing, with the

values below:

Blades opening:

o Closing pressure =14.1 bar

o Opening pressure =36.0 bar

Blades closing:

o Closing pressure =30.6 bar

o Opening pressure =20.3 bar

4.1.4. Force on Mechanism:

The servomotor force was obtained by using the pressure data:

The force applied on each mechanism was obtained on the basis of total force developed

by servo motor and the number of runner blades. In this case, the force on each

mechanism corresponds to 1/5 of total force. Therefore:

F = 1,222 KN (blades opening)

F = 4,67 KN (blades closing)


4.2. Results

The following results were obtained after feeding the finite element model with the

results from the opening and closing chamber pressure metering tests:

Table 1 – Pressure and Frequency Values from the tests on GU02 used to input

(feed) FEA

Opening Chamber Closing Chamber ∆p

Opening 36.0 14.1 21.9

Closing 20.3 30.6 -10.3

Period Approximately every 2 minutes

Frequency 26.8 cycles/hour

Table 2 – Von Misses Stress σ [Mpa] – FEA (GU02)

Component Condition FEA (UG02)

Blade link Opening 19.6 (4.9)

Closing -7.6 (9.9)

Obs:

1- The values were obtained at the same points where the strain gauge was installed

(described on item 4.0);

2 – On the components that present more than one metering point, an average between

the values obtained was reached. The standard deviation is shown in parentheses.

Figure 8 – Blade link

Longitudinal Stress – Opening

Figure 9 - Blade link

Longitudinal Stress – Closing


5. DYNAMIC BEHAVIOR MEASUREMENTS ON GENERATING UNIT

Measurements were performed with sensors installed on stationary and rotating parts. Static and

dynamic deformations were measured on the following four sets of servomotor cylinder

actuators: blade link, eyebolts, spade levers, blade link spacers and flanges of the cylinder.

The deformations on space levers, blade link spacers and eyebolts was measured using

unidirectional strain gauges, in other words, in a specific given direction. As for the spade levers

and the flange, the deformations were measured by three-directional strain gauge (strain rosettes),

in other words, in three directions on the surface plane.

Figure 10 - strain gauges

installed at the blade link

Deformation was also measured on the guide bearing support cone in order to obtain vertical

load. The pressure was measured in both chambers of the servo motor, spiral case, draft tube and

on the turbine head cover. Axis oscillation was measured by proximity sensors on the turbine and

generator guide bearing. Signs related to electric power, rotation, opening of distributor blades

and runner blades, command signal for the rotor valve, upstream and downstream levels were

measured concurrently with other signals.


5.1. Charts representing the pressure measurements of the chambers and blade link stress

The charts below were obtained after eight hours of operation with the generating unit at

80MW Power:

Figure 11 – Power and pressure of the opening and closing chambers

Figure 12 – Stress on Blade link 4


Figures 11 and 12 demonstrate that the stress on components is directly related to the

difference between the pressures of the opening and closing chambers.

With GU 01 under stable operating conditions (80MW), the pressure graphs clearly

demonstrated the presence of cycles with inversion of pressures in the chambers (opening

and closing) of the runner servomotor. There are 12 cycles in a 7 hours period.

5.2. Results

The following values were obtained during testing performed after returning Generating

Unit 01 to service:

Table 3 – Pressure Values and Frequency of Testing on GU01

Opening Chamber Closing Chamber ∆p

Opening 38.0 12.0 26.0

Closing 15.0 35.0 -20.0

Period Aproximately every 35 minutes

Frequency 1.71 cycles/hour

Table 4 - Von Misses stress σ [Mpa] – IPT (UG01)

Component Condition IPT (UG01)

Blade link Opening 26.4 (6.1)

Closing -10.0 (5.5)

Obs:

1 – For each type of component an average of all the values measured was calculated.

This is the value presented on the table. In parentheses is the standard deviation value.

6. BLADE LINK PIN USEFUL LIFE

Using the measurements taken on Unit 1, verification was performed to validate the lifecycle of

GU01 blade link pins by using the same finite element model.

The load on the blade link, blade link pins and equipment was set based on the medium stress

measured on the blade link as in table 4.


Based on the average value of stress and the cross-sectional area of the blade link, we can

determine the force acting on components, assuming that the average stress is constant

throughout this surface.

F = σ ⋅ A Transversal section area is:

Therefore, the force on the blade link pin is:

Opening: Fop = 26.4 *57,682 = 1,522,805N

Closing: Fclos = −10.0 *57,682 = −576,820N

Figure 13 – Von Mises stress

calculated - Opening

Figure 14 – Von Mises stress

calculated - Closing

Taking into account the load above, we can determine, by means of finite element model, the

matrix of the tensor of stress for the opening and closing conditions. Based on the difference

between the tensors, alternating stress is obtained (Salt). The remaining lifecycle of the blade link

pins under fatigue is then determined in accordance with the ASME code sec. VIII div. 2.

The points were analyzed with high intensity stress, and the maximum stress obtained was 174

MPa. Correcting this value for the modulus of elasticity:

The current material of blade link pins is ABNT 4340 steel, which is a high-alloy steel. From this

information, you can determine the number of cycles of the component using the Fig. 5-110.2.2

m –Curve design for fatigue on high alloy steels, ASME code sec. VIII div. 2, Appendix 5.


Figure 15 – extracted from the ASME sec. VIII, div. 2, appendix 5.

Using curve A in the figure above, it is possible to determine that at an alternating stress of 162

MPa the result is: N > 1,011 cycles or an Infinite lifecycle for the blade link pins from the Kaplan

runner analyzed.

7. CONCLUSIONS

Stress in the internal components of the Kaplan runner have direct relation to the difference

between the pressures of the opening and closing chambers of the servo motors that actuate the

runner, as well as their alternation.

From the pressure data, the force developed by servo motors can be obtained.

The force applied at each mechanism is obtained in function of total force developed by servo

motors and the number of blades on the runner.

The number of cycles (inversions of the opening and closing chamber pressures) and the pressure

difference between chambers (∆ p) is inversely proportional to the useful life of internal

components of the Kaplan runner.

In this way and based on the results of investigations above, the authors of this paper recommend

periodic monitoring of the pressure behavior of the opening and closing chambers of the Kaplan

runner servo motors, while maintaining generating unit on a fixed power for a minimum period


of eight hours, according to graph from Figure 11, to proceed with corrective actions on oil-

hydraulic power system in a anticipated manner in the case of deviations.

8. BIBLIOGRAPHICAL REFERENCES

[1] ZANUTO, J.C., RELATÓRIO TÉCNICO IPT N° 97 976-205 MEDIÇÕES DINÂMICAS

NO ROTOR KAPLAN DA UNIDADE GERADORA 01, DA UHE ROSANA

[2] ALSTOM RKV5168032 003-01 – Modelamento em elementos finitos: biela, pino e

distanciadores

[3] ALSTOM RKV5168032 004-01 – Modelamento em elementos finitos: alavanca, cilindro e

olhal

[4] ALSTOM RKV5168032 006-00 – Roda Kaplan – Análise do Mecanismo da Roda

[5] DUKE ENERGY Technical Report RT-ENG-050-07 – R2 – Análise da ocorrência na UG01

da usina Rosana

[6] TECMETAL Technical Report RT 335/2007 Rev.02 – Análise Metalúrgica de pinos da biela

da roda Kaplan. (Tecmetal)

[7] ALSTOM Relatório técnico Alstom RKV5168032-007-00 – Análise do mecanismo da roda

após ensaio embarcado

9. AUTHORS

Carlos Alberto Dias Costa was born in Casa Branca, São Paulo state, Brazil, on August 4, 1958.

He received his Electrical Engineering degree from Mackenzie University in 1984 and his MBA

degree from Fundação Dom Cabral. Currently he is the Operations Director for Duke Energy

International, Geração Paranapanema in Brazil. He is responsible for the operation and

maintenance of eight power plants with 2,307 MW installed capacity.

Renato José Baccili Castilho, was born in Ourinhos, São Paulo state, Brazil on February 13,

1971. He received his Electrical Engineering degree from Marilia University in 1997; his

Masters degree on Project Management from Fundação Getulio Vargas in 2004 and his MBA

degree from Fundação Dom Cabral in 2007. Currently he is Manager of Electromechanical

Maintenance Engineering at Duke Energy International in Brazil, responsible for maintenance of

eight power plants with 2,307MW installed capacity.


Wanderley Silva, was born in Araras, São Paulo state, Brazil, in 1953. He received his

Mechanical Engineering degree from the Universidade de Taubaté in 1981 and his

Specialization Degree from Alstom Technological Center in France in 1995. Currently he is

responsible for Alstom projects in Brazil and has 25 years of experience projecting hydro

turbines.

Wilson Takao, was born in Taubaté, São Paulo state, Brazil, in 1954. He received his

Mechanical Engineering degree from UNESP in 1977, has post-graduated from ITA-Aerospace

Technology and his Specialization degree on equipment from Petrobras. Currently he works as

an Alstom Specialist responsible for Santo Antonio Power Plant project.