Fran ç ois Lafleur, IREQ: Research Institute of Hydro-Québec, Varennes, QC, Canada...

François Lafleur, IREQ: Research Institute of Hydro-Québec, Varennes,

QC, Canada

[email protected]

Vibratory detection system of cavitation erosion: historic and algorithm validation

Date: August 14th 2012

CAV 2012, Singapore

Groupe – Technologie

> INTRODUCTION> HISTORICAL REVIEW> NEW HARDWARE IMPLEMENTATION> PRESENT WORK

• CAVITATION INSPECTION RESULTS• TRANMISSIBILITY FUNCTION• CAVITATION MODEL VALIDATION

> CONCLUSION

Agenda


INTRODUCTION

> Cavitation erosion which results from repeated collapse of transient vapor cavities on solid surfaces is a constant problematic in hydraulic turbine runners and continues to enforce costly repair and loss of revenues.

> One way to gain information about the erosion status is to implement a cavitation detection system. Vibratory detection of cavitation in hydraulic turbine runners is a long time activity at Hydro-Québec (several power plants).

> The advancement in this field that will be described in this paper was pioneered by Paul Bourdon (researcher at IREQ)


> Slow evolution process> The utility ignores its

aggressiveness according to operating conditions

> The machine downtime for inspections is required, therefore ($)

> Costly repairs, loss of revenue (4-6 weeks or more) so its effect have to be minimized

Why to study cavitation erosion?


HISTORICAL REVIEW

> Several types of intervention were performed at different power plants and on prototypes for the characterization of cavitation to develop a vibratory algorithm of cavitations detection.

> Over the years, the system has been used in two principle ways :

•The evaluation of the cavitation signature vs. of operating conditions at several power plants (MSV (Mean Square Value in m2/s4)).•The continuous monitoring of the absolute cavitation erosion rate (in kg/10 000h) of 4 groups in a power plant.


Software modules and mathematical treatments

> The expertise and methodology were implemented in the form of a complete cavitation detection system including multichannel high speed acquisition hardware and used in conjunction with specific software modules.

> There are three mathematical treatments in the processes that are programmed within the various software modules:

• Datamax (data acquisition)• Cavimax (calculations of the aggressiveness)• Caviciel (continuous monitoring)


Algoritm of cavitation detection

> This system is based on vibration measurements analysis at the lower guide bearing and the algorithm is described in details in the work of Bourdon [1, 4].

> The measurement and analysis of the Mean Square Value (MSV) and its modulation at high frequency (generally 5 to 15 kHz) is the base of the cavitation erosion algorithm.

> There is three types of data analysis:• Data analysis I is basically the high speed data acquisition. • Data analysis II is the calculation of the relative aggressiveness

of cavitation vs. the operating conditions (cavitation signature) using the pertinent fraction of the modulated MSV (Mean Square Value in m2/s4) of acceleration.

• Data analysis III is use to evaluate the absolute cavitation erosion, by continuous monitoring, the knowledge of a vibratory transmissibility function between the blade and the guide bearing is necessary.


1) Measure the vibration signal at the lower guide bearing plus tachometer

2) mathematical treatments

Two methods of measuring the aggressiveness of cavitation:• Signatures of cavitation: measures (m/s2)2• Continuous measurements: absolute measurements kg or

kg/10,000h

3) Data analysis• Optimize the

operating procedure of hydraulic turbines

• Allow maintenance just in time

Detection system of the aggressiveness of cavitation

System configuration


Cavitation signature detection vs. operating conditions > Cavitation signature refers to relative aggressiveness of

cavitation vs. the operating conditions. > One or more accelerometers with mounting frequencies

of 45 kHz or higher are installed at the lower guide bearing.

> The data acquisition procedure includes several steps from 0% to 100% of guide vane opening. At every step there are 30 blocks of 6 seconds time data recording at a rate of 100ksample/seconds. A sensors verification step at 200ksample/seconds is also performed.

0

0,1

0,2

0,3

0,4

0,5

0,6

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0,9

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0 10 20 30 40 50 60 70 80 90 100

Guide vane opening (%)

Rela

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Groupe Working

Instantaneous erosion (Kg/10 000 hours)

Érosion cumulative (Kg)

Vibration

Continuous monitoring of the absolute cavitation erosion


Continuous monitoring of the absolute cavitation erosion

> The continuous monitoring of absolute cavitation erosion is performed using the CAVICIEL software module.

> This monitoring requires similar instrumentation than relative cavitation detection and the same information about the runner characteristics as well as the knowledge of a vibratory transmissibility function between the blade and the guide bearing.

> A series of 32 blocks of time at a sampling rate of 65536 samples/second are performed sequentially on the monitored group of the power plant.

> Continuous monitoring of 4 groups of high-power hydro-generators (> 300 MW) at the Robert Bourassa power plant since year 2000.


IMPROVEMENT TO THE CAVITATION DECTECTION SYSTEM

> In 2009, a new hardware version of the system was developed and installed.

> Optimization of the availability of the cavitation system.

> The reliability of the computer and the development of a fail proof reboot procedure and remote control of the system improved the availability of the system.

> Robert Bourassa power plant is approximately 1400 km from the IREQ research : remote control and access is one of the key parameter in the success on the monitoring.


PRESENT WORK

> The follow up of reliability of the new system

> Updating and documenting the methodology of cavitation damage inspection for the purpose of modeling the cavitation erosion.

> Perform the evaluation of damage on a regular basis (2 years) to be able to make adjustments to the model parameters.

> Evaluation of the transmissibility function

> Validation of the cavitation erosion model


Filling method:

A filling method was developed over the year at IREQ using standard water based latex caulking tube.

A period of less than 4 hours is required to perform this inspection and the metal loss is available automatically using an analysis template.

CAVITATION INSPECTION RESULTS


Normalized IEC 60609 method :

> For this evaluation, the cavitation defects volume are evaluated by an approximation of the overall dimensions of the defect. A correction factor (usually 0.5 is applied) to the results.

> The time period to perform the IEC 60609 measurements is similar to the filling method but the analysis is longer.

> The over evaluation of the IEC method is of 1.70 in average from real cavitation defect volume from the filling method.


CAVITATION INSPECTION RESULTS

COMPARISON OF CAVITATION INSPECTION RESULTS

Filling method IEC 60609 method

Blade no.Volume of latex

caulk (cm3)equivalent weight of inox steel (kg) Blade no. equivalent weight of inox stell (kg)

1 147,9 1,18 1 1,66

2 66,5 0,53 2 1,14

3 88,1 0,71 3 1,25

4 88,1 0,71 4 1,30

5 327,4 2,62 5 5,07

6 44,9 0,36 6 0,47

7 147,9 1,18 7 2,69

8 236 1,89 8 3,32

9 307,5 2,46 9 2,64

10 41,5 0,33 10 0,46

11 58,2 0,47 11 1,21

Total 1553,9 12,45 Total 21,20

Estimated time since last repair (2007) of cavitation erosion damage: 18335 hours

Calculated Erosion rate (Filling method) 6.79 kg/10000hours Calculated Erosion rate (IEC 60609 method) 11.56 kg/10000hours


TRANMISSIBILITY FUNCTION

> Evaluation of the transmissibility function results between the blades and the lower guide bearing in different conditions were performed.

> The discrepancies of the between the use of the transmissibility function in water or in air are presently in evaluation.

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0 5000 10000 15000 20000 25000 30000

Frequency Hz

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Air Values order 40 Eau Values order 40

AVG Ratio air/water 5-15 kHz10.40


CAVITATION MODEL VALIDATION

> The cavitation model validation is based on the results of the next cavitation erosion visual inspection planned in 2013.

> Theses information will give the erosion rate in this period and will be compared with the cavitation system result.

> The enhanced reliability of the new system will allow having complete results over the same period.


CAVITATION MODEL VALIDATION

> A statistical model will also be study to find a relation between the operating conditions and the cavitation erosion.


CONCLUSION (1)

> A detection system gives more frequently updated information about the cavitation erosion of blades. This information can be used to optimize the power plant exploitation.

> A vibratory cavitation system was developed at Hydro-Québec. This system allows performing relative and absolute measurement of cavitation damage.

> The reliability of the initial system was not optimum due to computer and exploitation system failures. The new hardware version of the system is proven to be more reliable.


CONCLUSION (2)

> The validation of the cavitation erosion algorithm is based on visual inspection performed every 2 years.

> This work showed the efficiency of a filling method developed over the year at IREQ using standard water based latex caulking tube.

> This method is rapid and gives the exact volume of eroded material needed to validate the cavitation model over the time.

> Future work will focus on model validation, new approaches of absolute cavitation erosion estimation based on the used of the air transmissibility function and the uses of a statistical model.


REFERENCES (in the paper)

> [1] Bourdon, Paul, “Détection Vibratoire de l’érosion de cavitation des turbines Francis”, Ph. D. thesis, École Polytechnique de Lausanne, thesis no 2295 (2000), 406 pages.

> [2] Bourdon, P., Simoneau, R., Lavigne, P., “A vibratory Approch to the Detection of Erosive Cavitation”, ASME International Symposium on Cavitation and Erosion in fluid system, San Francisco, California, December 1989.

> [3] Bourdon, P., Simoneau, R., Avellan, F., “Hydraulic Turbine Cavitation Pitting Detection by Monitoring Runner Vibration”, Canadian Electrical Reseasch Projet 307 G 657 Report, June 1993, Montréal, Canada. (Available from CATI International).

> [4] IREQ internal reports, IREQ: 99-191C, 99-197C, 2000-129C, 2000-132C, 2001-039C, 2001-078C, 2011-0067.

> [5] Mossoba, Y., “Centrale Sept-Chutes: Expertise sur la Cavitation du Groupe 2 par la Detection Vibratoire”, Hydro-Québec internal report (APP 2010 1065), 2010.

> [6] Mossoba, Y., “On-Line Cavitation Monitoring”, Hydraulic Plant Interest Life Group (HPLIG), CEATI Report No. T062700-339, January 2009.

> [7] Tôn-Thât, L., “Experimental comparison of cavitation erosion rates of different steels used in hydraulic turbines”, 2010 IOP Conf. Ser.: Earth Environ. Sci. 12 012052.

> [8] Tôn-Thât, L., “Cavitation erosion behavior of high strength steels”, 2012 International Symposium on Cavitation, Singapore.

> [9] Simoneau, R., "Austenitic stainless steel with high cavitation erosion resistance," USA Patent US 4,751,046, 1988.

> [10] CEI/IEC 60609-1:2004, Internal Standard, Hydraulic turbines, storage pumpsand pump-turbines –Cavitation pitting evaluation –Part 1: Evaluation in reaction turbines, storage pumps and pump-turbines.

Fran ç ois Lafleur, IREQ: Research Institute of Hydro-Québec, Varennes, QC, Canada...

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