Monitoring Of Concrete Bases Of Wind Turbines With Modern Inclinometers .

7, 1 0 ek 2 land e W , Fin g n i rk lsinki o Prof. Dr. B. Resnik G W in He I F e 017 h t t University of Applied Sciences Berlin, Germany) 2 a (Beuth , d 2 e nt - June e s Monitoring of concrete bases of wind turbines with Pre ay 29 M modern inclinometers: Approaches and experience 1. Wind energy - Current development 2. Condition monitoring vs. technical assessment 3. Application of inclination sensors (example) 4. Conclusions 1 FIG WORKING 29 – June 2 2017, Helsinki, Finland Resnik: MonitoringWEEK, of windMay turbines, FIG Working Week 2017, Helsinki

Wind energy - Current development Wind energy is the largest source of electricity production from renewable energy in Germany. Currently there are more than 24 000 wind turbines in use. Cumulative (MW) New installed (MW) 6.000 60.000 4.000 40.000 2.000 20.000 0 0 2000 2002 2004 2006 2008 New installed (MW) (Onshore) Source: www.wind-energie.de 2010 2012 2014 2016 Cumulative 14 – 17 years More than 10 000 of these wind turbines were built before 2003 and reach the limits of their planned lifespan over the next few years. Therefore, control of their bearing structures plays a particularly important role now. 2 Resnik: Monitoring of wind turbines, FIG Working Week 2017, Helsinki

Typical foundation defects in wind turbines Spalling outside Spalling inside Water intrusion Tower The increasing number of foundation defects in wind turbines shows that one of the main problems is the connection between the tower and the foundation. The damage symptoms are the cracks or spalling in the top of the foundation as well as the water intrusions inside the foundation. Circumferential cracks Foundation 3 Resnik: Monitoring of wind turbines, FIG Working Week 2017, Helsinki

Control of irregular movements of built-in parts Tower Irregular movements Measurements Built-in part Foundation The aim of the measurement is to control the irregular movements of the built-in part of the tower. Unfortunately, it is impossible to measure within the foundation. Measurements on its surface and at the tower provide the important information about the connection between both parts. 4 Resnik: Monitoring of wind turbines, FIG Working Week 2017, Helsinki

Technical assessment - Dynamic stress test (example) Inspection of a wind turbine is a periodic check of its important parts. In the case of bearing constructions this is as a rule a visual check. Special measurements such as dynamic stress test are only required for selected endangered constructions. The impulse generated at the rotor after an emergency stop is introduced into the tower and via the built-in part into the foundation. The corresponding deformations (for example the maximum swing) between both parts can be measured and interpreted. 5 1 Wind pressure A dynamic stress test: Working condition 2 Stopping the operation Standstill 3 Pressure Pull Built-in part Built-in part Maximum swing Resnik: Monitoring of wind turbines, FIG Working Week 2017, Helsinki Built-in part time

Condition monitoring - Detection of dynamic deformations Working condition Contrary to special dynamic stress test, the usual movements between the tower and the foundation (for example the average swing over the time interval) can be recorded and analyzed for a condition monitoring. Changing wind pressure Condition monitoring is the continuous measurement of different parameters of machines, in order to identify a developing fault. 1 Pull Oscillation 2 Oscillation Pressure Built-in part Built-in part Pull Average swing 6 3 Resnik: Monitoring of wind turbines, FIG Working Week 2017, Helsinki Built-in part time

Measuring systems for control of irregular movements Different measurement technologies for control of the connection between tower and foundation have been tested by myself in recent years. Distance measurements with vertical lasers Reflectors Measurements of coordinates with motorized tachymeter 7 Measurements of accelerations or inclinations Detectors Measurements of heights with rotary laser Resnik: Monitoring of wind turbines, FIG Working Week 2017, Helsinki

Measurement system based on inclination sensors (example) The here described system is based on several inclination sensors that are situated on the foundation inside the tower and are connected to a measurement computer. Tower Sensor T 0,50 m Sensor T Sensor FT Sensor F Sensor M Sensor FT ca. 50 Foundation Sensor F 0,10 m 0,50 m 1,40 m The choice of measurement locations is as important as the choice of measurement equipment. Example: Sensor T - the base of the tower, Sensor F - foundation, in the distance to tower, Sensor FT - foundation, near the tower, Sensor M - foundation, in the middle of the tower. 8 Resnik: Monitoring of wind turbines, FIG Working Week 2017, Helsinki

Concept of data analysis for Condition Monitoring It is known that the quality of monitoring is highly dependent on the applied processing algorithms. We have developed a special method for these purposes: 0 10 20 Time, min Measurements 9 30 0 10 Sensor 2 20 30 Ratio of standard deviations St. Dev. 1 Sensor 2 Sensor 1 St. Dev. 2 Sensor 1 Inclination Inclination Inclination Inclination The signal’s energy and therefore its amplitude decreases during its propagation in the foundation. The different defects cause more losses of energy. Therefore, the differences between standard deviations can be used for a check of its condition. Critical deviation 14 15 Time, day Time, min Filter and statistical analysis Long-term analysis Resnik: Monitoring of wind turbines, FIG Working Week 2017, Helsinki 16

Results of selected test measurements Tower Sensor FT Sensor F Sensor M 1. Based on the results it can be assumed that there are significant differences and considerable defects between Sensors F and FT. 2. Based on the results it can be assumed that there are no significant differences and defects between Sensors M and F. 10 standard deviations ca. 50 Foundation 0,4 0,3 Sensor FT Sensor F 0,2 Sensor M 0,1 0.0 1 4 7 10 13 Segment (one hour each) Resnik: Monitoring of wind turbines, FIG Working Week 2017, Helsinki

Conclusions - Many wind turbines will be reaching the limits of their planned lifespan in the next couple of years. The control of the foundation stability is more important for these turbines. - Several measurement technologies can be used to control the foundation. The measurements in different wind turbines in recent years showed a great potential of the presented method to identify defects with inclination sensors. Thank you very much for your attention! Please send me an email if you need further information: resnik@beuth-hochschule.de 11 Resnik: Monitoring of wind turbines, FIG Working Week 2017, Helsinki

2 Resnik: Monitoring of wind turbines, FIG Working Week 2017, Helsinki Wind energy - Current development Cumulative (MW) 20.000 40.000 60.000 0 Source: www.wind-energie.de 14 - 17 years Wind energy is the largest source of electricity production from renewable energy in Germany. Currently there are more than 24 000 wind turbines in use .