1Presentation name | place or presenter | YYYY-MM-DD

Strain gauge measurementsof rotating parts with telemetryIGHEM 2012 – Trondheim, 2012-06-28/29

2Strain gauge measurements of rotating parts with telemetry | IGHEM 2012 - Trondheim | 2012-06-21

Strain gauge measurementsof rotating parts with telemetry

1. Introduction

2. Functionality of telemetry system

3. Configuration of data transmission

4. Strain gauge application

5. Measurement

6. Data Evaluation

7. Summary

8. References

3

Introduction

Modern design of hydraulic turbines aims to achieve very high levels of efficiency and structural integrity in the environment of highly variable loading conditions.

To combine those requirements, a profound knowledge of static and dynamic loads acting on hydraulic components is necessary.

The knowledge of dynamic loads is often derived from strain gauge measurements using telemetry systems.

With this technology it is possible to measure signals from the rotating (e.g. runner strains) and stationary (e.g. presure pulsations) system time synchronous.

Strain gauge measurements of rotating parts with telemetry | IGHEM 2012 - Trondheim | 2012-06-21

4

Functionality of telemetry system

Contact less data transmission of sensor signals (generally strain gauges) from the rotating system to a stationary receiver

• Amplification and conversion of sensor signals (voltage to frequency) to a subcarrier frequency

• Merging the channel specific subcarrier frequency

• Subcarrier mix modulated to main carrier frequency by HF-modulator

• Demodulation of HF-signal inside receiver to subcarrier mix

• Conversion from frequency to voltage signal

• Analog signal provided by analog amplifierStrain gauge measurements of rotating parts with telemetry | IGHEM 2012 - Trondheim | 2012-06-21

5

Configuration of data transmission

Data transmission through air

stationary antenna

rotating antenna

batteries and remote system

telemetry system

strain gauges

Strain gauge measurements of rotating parts with telemetry | IGHEM 2012 - Trondheim | 2012-06-21

6

Configuration of data transmission

Strain gauge measurements of rotating parts with telemetry | IGHEM 2012 - Trondheim | 2012-06-21

Data transmission through water

batteries and remote system

telemetry system

strain gauges

rotating antenna

stationary antenna

7

Application – steel patterns

In order to get the exact position for the strain gauge application, special tools are used. For exact position of the strain gauge sensor, steel templates are used. These are derived from the CAD-model of the Francis runner.

Strain gauge measurements of rotating parts with telemetry | IGHEM 2012 - Trondheim | 2012-06-21

8

Application – FARO-Arm

Another possibility to locate exact strain gauge positions is the usage of the FARO-Arm. This method of defining strain gauge positions on the prototype is used specially for Kaplan runners, where the usage of steel templates is not practicable.

Strain gauge measurements of rotating parts with telemetry | IGHEM 2012 - Trondheim | 2012-06-21

9

Application – strain gauge application

Strain gauge measurements of rotating parts with telemetry | IGHEM 2012 - Trondheim | 2012-06-21

Strain gauge are bond to the surface by using a modified alkyl cyanoacrylate compound

10

Application – protection layer

Strain gauge measurements of rotating parts with telemetry | IGHEM 2012 - Trondheim | 2012-06-21

Application of epoxy layer in order to protect the strain gauge wires against water irruption

Special surface treatment necessary in order to improve adhesion of the epoxy

Epoxy is shaped to minimize effects on hydraulic

For layouts working under high pressure (p > 3 bar) or special circumstances (e.g. high sand content), an additional local coating layer is applied

11

Data Evaluation – Start up procedure

Performing a strain gauge measurement by using a telemetry system offers the possibility of online assessment of recorded strain gauge data. Especially for transient load conditions, a fast and reliable online assessment of these load conditions is possible. They could be optimized in matters of time, dynamic loading and partial damage.

Strain gauge measurements of rotating parts with telemetry | IGHEM 2012 - Trondheim | 2012-06-21

Star

t up

1

Star

t up

2

Star

t up

3

Star

t up

4

12

Data Evaluation – Load rejection

Besides the start up procedure also the behaviour during load rejection can be observed and, if necessary, be adapted

Highest dynamic strain occur during load rejection

By adapting the distributor opening, significant improvements can be achieved

Strain gauge measurements of rotating parts with telemetry | IGHEM 2012 - Trondheim | 2012-06-21

13

Data Evaluation – Mean stress

• Measured mean stresses are normed to stresses at speed no load

• Plotted lines indicate the characteristic for crown (gray) and band (blue)

• Dots represent the calculated values from the Finite Element Analysis

Strain gauge measurements of rotating parts with telemetry | IGHEM 2012 - Trondheim | 2012-06-21

Deviations caused by:

• geometrical deviations

• deviations in loadingcondition

• strain gauge position

• flow disturbances

14

Data Evaluation – Dynamic stress

• Measured dynamic stresses are normed to stresses at speed no load

• Plotted lines indicate the characteristic for crown (gray) and band (blue)

• “Characteristic peak-to-peak” appr. 3% of highest peaks neglected

Strain gauge measurements of rotating parts with telemetry | IGHEM 2012 - Trondheim | 2012-06-21

15

Data Evaluation – Waterfall

• Load ramp with continous opening from 0-100% power

• This enables you to get a fast a clear overview of unit behaviour over the complete operating range and where deeper investigation is necessary.

Strain gauge measurements of rotating parts with telemetry | IGHEM 2012 - Trondheim | 2012-06-21

16

Data Evaluation – Partial Damage

• Partial damage calculation based on measured strain signals, load universe, material parameters and rainflow counting

• Partial damage is standardized to partial damage for Pmax

Strain gauge measurements of rotating parts with telemetry | IGHEM 2012 - Trondheim | 2012-06-21

• transient load conditionsare the main fatiguecontributor

• higher partial damage at runner band

17

Summary

• Performing strain gauge measurements using telemetry systems is state of the art

• Realization with almost no limitations of unit application and kind of runners

• Based on database of already performed strain gauge measurements, a calibrated procedure for predicting static and dynamic stresses has been developed and optimized

• This enables you to optimize runners with regard to static and dynamic stress as well as to fatigue behaviour

Strain gauge measurements of rotating parts with telemetry | IGHEM 2012 - Trondheim | 2012-06-21

18

References

Strain gauge measurements of rotating parts with telemetry | IGHEM 2012 - Trondheim | 2012-06-21

No. of realized and projected strain gauge measurements Francis runner Kaplan runner Pelton runner

Data transmission through air 6 - 2

Data transmission through water 3 projected n.a.

19Strain gauge measurements of rotating parts with telemetry | IGHEM 2012 - Trondheim | 2012-06-21