Registrations
DUNS: 400106873
Reg. in CCR & ORCA
NATO NCAGE: B6183
Reg. in Lux: B 32.016
Lux tax 1989 2406 173
EU VAT: LU 14308966
US EIN: 98-0497131

APPLICATION EXAMPLES
Uprating acceptable?
Identification of weak parts
Cavitation quality assessment
Runner improvement
Guide vanes improvement
Operation optimisation Francis
Operation optimisation Bulb
Cavitation as a diagnostic tool

METHODS
What is cavitation?
Physical background
How many sensors?
Raw cavitation data
Cavitation characteristics
Cavitation mechanisms
Spatial distribution
Calibration
How do we work?
Cavitation monitoring
Model vs. prototype

DOWNLOAD
Papers
Leaflets

CONTACTS

Letter to O&M Manager
(Click to read)

What is Korto?

Since 1996, our company has been providing highly specialised, leading-edge services and products to the hydropower industry.

Our staff is a highly specialised team of world-renowned experts from seven countries.

Our background lies in advanced proprietary methods and leading-edge research based on extensive full-scale experience.

Korto’s motto: Stay with the problem until it is solved.

Our Products

MULTIDIMENSIONAL CAVITATION MONITORING SYSTEMS

• Use
- Independent use
- As a cavitation channel of the plant monitor
• System configuration
- Typically 6 sensors per turbine
- One cavitation processor per turbine
- One control unit per plant (if used independently)
• Features
- High-sensitivity detection of deterioration effects
- Coverage of all cavitation segments
- Diagnostic functions
• Data
- True total cavitation intensity
- Assessment of spiral-case and distributor influence
- Runner-blade resolution
- Accumulated cavitation intensity
• Implementation
- Multidimensional algorithm
- FPGA/RT Technology
- Ethernet connection to plant/company network
• Options
- Operation data input
- Analog total cavitation intensity output
- Control unit
• Application
- Operation optimization
- Tracking changes, detection of incidents
- Predictive turbine maintenance

Cavitation sensors are installed in robust protection boxes on 6 or 8 guide-vane shafts or links.

Cavitation processor (gray box on the wall) is installed close to the distributor.

Cavitation processor Type 7391P (internal view).

Cavitation Monitoring System Type 7391 - Connections, Options

Details: download PDF 843 kB

Our Services

ON-SITE MULTIDIMENSIONAL DIAGNOSTIC CAVITATION TESTS

Please click to see PDF (596 kB).

A small vibro-acoustic laboratory is installed close to the distributor. Turbine operation is minimally disturbed.

Our Technique

We use our own multidimensional vibro-acoustic technique which:

• Identifies cavitation mechanisms
• Assesses the role of turbine parts in cavitation
• Yields data on the spatial distribution of cavitation
• Senses all cavitation segments in the turbine
• Delivers detailed turbine cavitation characteristics
• Detects adverse effects with high sensitivity

When Might You Need Us?

• Commissioning a turbine:
- Model predictions correct?
- Contract requirements met?
• Refurbishing or uprating a turbine:
- True state before and after refurbishment/upgrade
• Routine operation:
- Operation optimisation to achieve minimum erosion
- Maintenance optimisation in respect
- Control of ageing effects and incidents

Some Projects

EFFICIENCY AND CAVITATION IN CAM OPTIMISATION OF A KAPLAN TURBINE

The cam of the 28-MW Kaplan turbine at Kembs HPP of Electricité de France was optimised in a prototype test. Cavitation was also measured; the multidimensional method was applied. Two cam definitions were checked: one from the model test, and one optimised in the prototype test. The two cam definitions yield substantially differing efficiency values and cavitation intensity values:

Cavitation intensity vs. power for two cams: Black - optimised cam; Red - cam defined in the model test

Detailed analysis shows that strong cavitation appears only within a narrow circumferential interval behind the spiral casing:

Normalised cavitation intensity vs. angular position for different power values

This suggests it is possible to improve the turbine behaviour by changing the inclination and/or profile of the stay vanes in the critical circumferential interval.

A new cam was installed and an anti-cavitation layer was applied on the endangered part of the runner. The result: the metal loss found earlier after 1500 hours is now found only after 8000 hours.

More info: info@korto.com or Mr. Philippe Gauvin, Electricité de France - CIH, philippe.gauvin@edf.fr or Mrs. Marie Delagarde, Electricité de France - DTG, marie.delagarde@edf.fr

CAVITATION MONITORING - FRANCE

Following the multidimensional cavitation test at Kembs 1 Kaplan unit of EDF, France, a broadened multidimensional cavitation monitor was left there. It consists of 20 cavitation sensors, remote-sensors unit, and the central processor.

20+4+4 cavitation sensors on Kembs 1

The aim of this hybrid installation - the cavitation monitor and the automatic cavitation-data acquisition system - is to deliver detailed cavitation data at various operation points which were not reached during the test.

Pascal Ratabouil of EDF installing the central processor

More info: info@korto.com or Mr. Philippe Gauvin, Electricité de France - CIH, philippe.gauvin@edf.fr or Mrs. Marie Delagarde, Electricité de France - DTG, marie.delagarde@edf.fr or Mr. Pascal Ratabouil, Electricité de France - GMH Est-EIS, pascal.ratabouil@edf.fr

CAVITATION IN A 650 MW FRANCIS TURBINE

Korto tested a 650-MW Francis turbine at the Third Powerplant of the USBR's Grand Coulee Dam, which is the largest electric power producing facility and the largest concrete structure in the USA.

Grand Coulee Dam has 6800 MW of installed generating capacity in its four hydropower plants.

The turbine global cavitation characteristics, which gives the erosion rate as a function of turbine power setting, are determined (black curve, below). Combined with the power setting statistics (blue), they yield an estimate of the contribution of each power setting to the erosion (red).
Such data can be used for operation optimisation and, if delivered by permanent monitoring, for maintenance optimisation.

Cavitation data (black and red) are compared to the turbine efficiency (violet). Power scale: 340-700 MW.

Quite uniform cavitation quality of the runner blades was found. The mean runner cavitation intensity behind different sections of the spiral casing is determined (below). This shows that the spiral casing is not optimal with respect to cavitation.

In this test three techniques for cavitation diagnostics and monitoring are compared:
(1) Simple: One sensor on a wicket gate link - simple data processing
(2) Simple: One sensor on the draft tube wall - simple data processing
(3) Multidimensional: Sensors on all wicket gate links - complex data processing. - This is Korto's approach to obtain the data shown above.

Blade-passage modulation amplitude vs. turbine power setting as measured in different sensor locations

In 24 positions of the sensor in (3) different estimates of the cavitation intensity were obtained. As a function of turbine power setting, they are presented in different colours above. The final result in (3), derived from all these data, incorporates contributions from all locations in the turbine and all cavitation mechanisms, while only one curve (black) is used as the final result in (1). Obviously, the results of the one-sensor techniques, thus also of (1) and (2), are quite arbitrary.
A further disadvantage of (2) is sensor's location. The sensor on the draft tube wall of the Francis turbine predominantly senses free vortices in the draft tube. Using its readings to estimate erosive rotor cavitation results in false conclusion:

Green...no cavitation, yellow...weak cavitation, red...strong cavitation

In (3), various special signal and data processing tools, such as "worms" shown below, are used to identify different cavitation mechanisms, determine the role of different turbine elements in cavitation processes, and derive un-biased estimates of cavitation intensity. None of this is possible with the simple methods.

Cavitation intensity (colour) vs. instantaneous runner angular position (horizontal) and power setting (vertical - 350 MW top, 700 MW bottom)

More info: info@korto.com or Mr. G. Michael Strombach, USBR Grand Coulee Dam, mstrombach@pn.usbr.gov