Structural health monitoring for wind turbines – Condition monitoring of foundation, tower and rotor blades

for damage detection at an early stage, life cycle prognosis and the optimization of wind farm operations

Regardless of location, a sustainable reduction of operating costs with a simultaneous increase in yields is gaining more and more relevance. Therefore, it is more important than ever to detect structural damage and icing at an early stage in order to avoid severe damage. Structural health monitoring (SHM) of the foundation, tower and rotor blade and conventional condition monitoring (CMS) on the drive train are becoming increasingly important in this context.

"The advancing state of the art offers new opportunities to sustainably increase yields", says Dr Carsten Ebert, Head of Wind Energy at Wölfel. "Our intelligent algorithms are based on the latest technological approaches and form the basis for data analysis and direct real-time optimization."

Wölfel is the European market leader in the field of structural monitoring of offshore wind farms and has, over decades built up a unique core competence in signal analysis. We offer comprehensive and individual support ranging from expert advice, delivery and installation of turnkey monitoring systems all the way through to data evaluation.

We record the real stresses affecting the system with our sensor systems and then extract the truly relevant technical statements from the flood of data. The integrated early warning systems can even reduce the number of inspections required by the authorities within the framework of recurring inspections (e.g. underwater inspections with diving robots).

Based on the detailed system condition analysis, you can plan ahead, optimize the operation of your wind turbines and extend their lifetime – the operation of your wind farm becomes more efficient and economical.

Our services

  • Development and design of turnkey monitoring systems, including coordination with authorities and certification companies
  • Provision of your plants with specially developed, robust measuring equipment with direct interface to the WT control system and SCADA system
  • Data acquisition and data analysis by intelligent algorithms and experienced specialist engineers
  • Visualization of results in a web portal, including warning and alarm system
  • Reporting of monitoring results with individual level of detail – for submission to authorities, for design validation and as a basis for lifetime optimization
  • Development of concepts for periodic inspections in which the necessary scope of testing is optimized by integrating monitoring results

SHM.Foundation® – Intelligent System for Early Detection of Tower and Foundation Damages and Optimized Lifetime Extension

Increased safety

Whether crack formation in the concrete, decoupling of the foundation and tower or a loosened foundation element – tower and foundation damage is a relevant risk factor. If they are not detected at an early stage, there is a risk of serious consequential damage, costly repairs and long downtimes.

Our SHM.Foundation monitoring system detects and monitors any damage that may occur reliably and efficiently. The continuous comparison of the current RMS values with the applicable standards – e.g. ISO 10816-21 and VDI 3834 – makes it possible to immediately identify problematic wind turbines (WTGs) under extreme load. The operator is alerted and can initiate appropriate countermeasures. If limit values are permanently exceeded, it indicates a faulty condition or faulty operation of the WTG.

Reduction of visual inspections and lifetime extension

Without a suitable monitoring system, damage can only be detected and monitored by regular visual inspections. These are usually complex and expensive. The monitoring of variables such as displacements, deformations, component stresses or frequencies is therefore unanimously recommended. In numerous offshore projects, however, only the monitoring of ten percent of all turbines has been established so far.

Since each wind turbine has individual characteristics and damage, we take a more comprehensive approach and recommend that all turbines in a wind farm be equipped with a system for monitoring the tower and foundation structure. In offshore wind farms, we generally equip ten percent of the turbines with the comprehensive SHM.Foundation individual system and 90 percent of the turbines with the cost-effective standard SHM.Foundation system. This combination makes it possible to switch from the previously used time-based inspections to condition-based inspection concepts.

Comprehensive monitoring is also useful for onshore wind farms. It enables operation to be optimized at all levels and thus reduces operating costs. An additional advantage is the exact statement about the total consumed lifetime. This means that the assessment of the continued operation of the plant is based on the fatigue loads that have actually occurred. In contrast to the evaluation with conventional methods, the entire potential for lifetime extension can be exploited.

Artificial intelligence (AI) enables even more precise results

Correlation with EOC/SCADA data compensates for the dependence of the damage indicators on operating conditions. In addition, extended compensation with AI methods can significantly increase the accuracy.

The configuration of SHM.Foundation

Our monitoring systems are equipped with robust electronics of industrial standard. For monitoring, we only need a few, low-cost sensors in the easily accessible tower/TP area. Our Virtual Sensor concept based on a Digital Twin nevertheless provides you with information about the entire support structure. SHM.Foundation records the dynamic movement of the tower structure via an acceleration sensor in the tower. An inclination sensor at the base of the tower detects and monitors the global quasi-static inclination of the tower due to a damaged foundation.

The advantages of holistic monitoring with SHM.Foundation at a glance:

Optimized
lifetime extension

Reduction and optimization
of visual inspections

Preservation of
the asset value

Identification
of black sheep

Monitoring of
foundation damages


SHM.Foundation individual – An individually configurable system for the comprehensive monitoring of building ground, foundation and supporting structure in the offshore area

With the SHM.Foundation individual monitoring system, the structural behavior of your wind turbines and substations can be recorded, tracked and evaluated in compliance with the guidelines. The focus is on the detailed analysis of maximum and fatigue loads, the acting wind and wave loads, the structural condition and the resulting remaining lifetime, as well as the detection of corrosion and scouring.

The configuration of SHM.Foundation individual

Both the necessary hardware and the software for data analysis are individually configured to meet your project requirements. On the basis of our many years of experience, we advise you on the way to the system configuration that is individually suitable for you.

However, we do not only accompany you during conception, installation and commissioning, but throughout the entire monitoring process. Within the scope of signal analysis, we extract the information that is essential for you, compare the recorded stresses with design assumptions, calculate the lifetime consumption, prepare reports for approval authorities and identify optimization potential.


MIC.Foundation – Web portal for remote monitoring

The structural and SCADA data collected by our monitoring systems are processed directly in a Monitoring Intelligence Center. The results of the analysis and all important indicators are available to the user at any time in a clearly arranged form. You can see at a glance whether limit values are being adhered to, if and where a problem occurs, what may be the cause and what measures need to be taken to remedy the fault or prevent damage from progressing.

Event-controlled notifications and alarms can be configured individually. You do not receive standard evaluations, but an individual dashboard tailored to your requirements as well as concrete recommendations for optimization. In addition, automated reporting (optionally with expert evaluation) can be carried out, which also fulfills official requirements.

The security of the sensitive measurement data is always in the foreground. A computer center in Germany, a secure Internet connection and a three-tier user management system (administrator, editor, user) ensure that only authorized persons can view data and results and configure settings. If a data connection is nevertheless not desired or not possible due to the given conditions on site, all monitoring and data backup functions can also be outsourced to a central wind farm server.

Depending on the configuration, the following indicators can be visualized in MIC.Foundation:

  • Lifetime
  • Natural Frequencies
  • Corrosion
  • Moments, Loads and Stresses
  • Scour

Knowledge Library

Exploiting the potential of a wind farm in the best possible way – this is not only the overriding goal of manufacturers and operators, but is also essential with a view to achieving the fastest possible energy turnaround. In our white papers in the categories Increase yields, Optimize inspections and Extend service life, you can find out how you can sustainably increase the efficiency of your wind turbines.

Case Studies

Case Study "Structural Health Monitoring Offshore Wind Farm Arkona" 1.93 MB
Case Study "Structural Health Monitoring Offshore Wind Farm Arkona"

Arkona is the most efficient wind farm to date in the Baltic Sea: off the coast of the island of Rügen, 60 wind turbines are located on an area of 39 square kilometers and have a total output of 385 megawatts. An individual structural health monitoring concept developed by Wölfel is designed to ensure that the wind turbines feed into the grid as continuously and efficiently as possible, incur the lowest possible costs for operation and maintenance and meet the requirements of the authorities.

Articles

Technical Article "Probabilistic Approach for Detection of Scour on Monopile Substructures Using Measured SHM Data" 826.66 KB
Technical Article "Probabilistic Approach for Detection of Scour on Monopile Substructures Using Measured SHM Data"

Substructures of offshore wind turbines have to reliably withstand environmental conditions, operational and extreme loads during their design lifetime that may exceed the time period of 25 years. Within their lifetime, they may experience damage and structural changes. This study proposes a novel, data-driven approach for the quantification of probability of detection (POD) for the structural change due to scour on a monopile substructure. To achieve this aim, numerical analyses with finite elements are combined with real measured vibration data from an offshore wind farm.

SHM.Tower® – Intelligent and certified system for monitoring tower vibrations and maximizing lifetime extension

Vibration monitoring enables proactive optimization

Depending on the location and mode of operation of a wind turbine (WTG), the vibration stress – especially on the tower – varies greatly. The monitoring system SHM.Tower records these stresses via an integrated sensor. Due to the permanent comparison of the current RMS-values with the applicable standards – e.g. ISO 10816-21 and VDI 3834 – the condition of the turbine is always visible at first glance. Turbine settings and operating mode can be continuously and proactively optimized. The system issues warning messages if predefined threshold values are exceeded. WTGs with excessive loads are thus immediately identified and countermeasures can be initiated.

Reliable lifetime prognosis and optimized lifetime extension

Wind turbines are usually designed for a lifetime of 20 years. However, at the end of this design lifetime there is often a great potential for further operation. The decision on this is made within the scope of a lifetime extension report. So far, these are usually based on historical operating and wind data as well as turbulence reports. However, due to conservative load assumptions and insufficient consideration of the wind direction – and thus the distribution of lifetime consumption across the tower cross-section – the overall potential for a lifetime extension for as long as possible is often significantly underestimated.

SHM.Tower calculates the loads that actually occur and are distributed over the tower cross-section based on the accelerations measured in the tower and thus enables an exact statement to be made about the actual lifetime consumption. Even critical extreme conditions are directly recorded. Thus, the lifetime prognosis is no longer based on assumptions alone. The lifetime extension can be maximized and the entire yield potential can be tapped.

SHM.Tower was already certified as a Structural Health Monitoring System by Deutsche WindGuard in 2019. In 2020, the implemented load reconstruction methodology was also successfully assessed. It could be proven that SHM.Tower enables load measurement with a very high accuracy and is therefore very well suited for use in the context of lifetime extension reports:  

"After it was shown that the vibration profiles recorded with SHM.Tower very well represent the system dynamics relevant for fatigue, indeed valuable possibilities to assess the lifetime extension of modern WTGs opened up. On the one hand, the DELs derived from vibrations can be used to validate and optimize the dynamic calculation model in order to soften conservative safety factors. On the other hand, the measured load distribution in the tower cross-section can be used to reduce the determined damage to the foundation and tower. In real terms, this results in a significant extension of the service life horizon without any loss of forecasting reliability. We have proven this in the expert opinion procedure".

Frank Weise, Managing Director of WindGuard Certification GmbH

Use from the start or as retrofit

Sensors and electronics of SHM.Tower are built into a compact housing and allow for an easy installation in the tower head of the turbine. If the system is used right from the start, the operating status and the consumed lifetime are precisely recorded throughout all phases of use – thanks to the energy-autonomous mode even during construction and in the event of power failures. However, even if SHM.Tower is retrofitted, the system provides significantly improved lifetime assessments compared to conventional methods – even though the vibrations of the first years of operation are not recorded. Extrapolations enable the assessment over the entire service life.

After the initial lifetime extension report, you can optimally accompany the remaining service life of your WTG by continuously monitoring the vibration levels and tower loads.

The advantages of SHM.Tower at a glance:

Maximized
lifetime extension

Optimized
operation

Warning messages
when threshold values
are exceeded

Reliable asset
valuation

Identification of
black sheep

Functions:

Optimization of operation

  • Measurement of vibration stress and output of warning messages when threshold values are exceeded (ISO 10816-21/VDI 3834)
  • Frequency distribution of RMS values (e.g. annual cycle)
  • Wind farm monitoring to locate heavily loaded turbines
  • Monitoring of natural frequencies (tracking, long-term monitoring and trend analysis) to verify structural integrity
  • Unbalance indicator for aerodynamic unbalance and mass unbalance (for wind farm monitoring)

Lifetime prognosis

  • Lifetime prognosis for each tower segment
  • Classification of stresses according to operating conditions
  • Lifetime consumption trend
  • Valid statements for the lifetime extension of the turbine (also in case of retrofit)

Performance

  • Energy self-sufficient monitoring function (recording up to 3 months without energy supply)
  • Connection to the Wölfel monitoring portal MIC.Tower
  • Interface for external sensors (three-channel sensors)
  • Frequency range: 0.1 – 10 Hz
  • Measuring range: ± 2 g

MIC.Tower – Web portal for remote monitoring

The structural and SCADA data collected by our monitoring systems are processed directly in a Monitoring Intelligence Center. The results of the analysis and all important indicators are available to the user at any time in a clearly arranged form. You can see at a glance whether limit values are being adhered to, if and where a problem occurs, what may be the cause and what measures need to be taken to remedy the fault or prevent damage from progressing.

Event-controlled notifications and alarms can be configured individually. You do not receive standard evaluations, but an individual dashboard tailored to your requirements as well as concrete recommendations for optimization. In addition, automated reporting (optionally with expert evaluation) can be carried out, which also fulfills official requirements.

The security of the sensitive measurement data is always in the foreground. A computer center in Germany, a secure Internet connection and a three-tier user management system (administrator, editor, user) ensure that only authorized persons can view data and results and configure settings. If a data connection is nevertheless not desired or not possible due to the given conditions on site, all monitoring and data backup functions can also be outsourced to a central wind farm server.

The following indicators are visualized in MIC.Tower:

  • Lifetime
  • Natural Frequencies
  • Rotor Imbalances
  • Moments, Loads and Stresses

Knowledge Library

Exploiting the potential of a wind farm in the best possible way – this is not only the overriding goal of manufacturers and operators, but is also essential with a view to achieving the fastest possible energy turnaround. In our white papers in the categories Increase yields, Optimize inspections and Extend service life, you can find out how you can sustainably increase the efficiency of your wind turbines.

SHM.Blade® – Intelligent system for the detection of structural damage, icing and aerodynamic imbalances on rotor blades

Rotor blades of wind turbines are exposed to extreme environmental conditions and high dynamic stresses. At the same time they have a decisive influence on the energy yield and thus on the economic efficiency of a wind turbine. Incipient damage must be detected at the earliest stage possible and distinguished from normal environmental and operational influences. Severe damage can be prevented by the repair measures, which are comparatively inexpensive at this early stage. Downtimes due to damage that is not detected or detected too late are avoided and the energy yield is increased. Periodic inspections are not sufficient for an early detection of damage. Continuous monitoring ensures a higher level of safety.

 

The solution from Wölfel: SHM.Blade for the detection of structural damage

SHM.Blade is a tried and tested system, certified by DNV GL, that can detect structural damage on rotor blades at an early stage. For this purpose, a reference condition is used which is determined individually for each rotor blade, fully automatically, immediately after the activation of SHM.Blade. The determination of the reference condition is a blade-specific learning phase which ensures the system's high sensitivity to damage – despite the mass and stiffness tolerances caused during production. When the learning phase is completed, the system continuously calculates condition indicators, which provide information on the current condition of the blade at any given time. By means of a two-level warning and alarm concept, the wind turbine control can react and subsequent damage can be avoided.

IDD.Blade® – Ice detection with automatic restart function

Especially at so-called "cold climate" locations further weather-related risks arise. Authorities demand that a wind turbine (WT) is stopped in case of icing to protect against ice shedding in the surrounding area. In addition, increased loads caused by icing have a significant impact on the lifetime of the WT.  The measurement of vibration behaviour has proven to be a safe and efficient method for ice detection.

With the IDD.Blade option, icing can be reliably detected.

  • Automatic ice detection
  • Automatic switch-off in case of icing
  • Automatic restart of the wind turbine when the blades are ice-free
    = Reduced risk of ice shedding  

    + Early detection of damage
    + Detection of aerodynamic imbalance

As the sensors in the rotor blades directly record the actual icing condition, the results are much more reliable than an assessment based on meteorological parameters. IDD.Blade reduces shutdown times to the times of actual icing.

Via our web portal MIC.Blade, you have live access to all events at any time and will receive automatic alarms if defined threshold values are exceeded.

SHM.Blade for the detection of aerodynamic imbalances

Nearly 50 percent of all wind turbines have inadequately balanced rotors. In at least 30 percent of all cases, this is due to aerodynamic imbalance. This results in stronger vibrations, which lead to higher loads and thus to an increase in the consumed lifetime of the drive train, rotor blades, tower and foundation. The aerodynamic efficiency and thus also the generated electrical power of the wind turbine are therefore reduced. In addition, increased noise emissions can occur.

With the help of the imbalance indicator calculated by SHM.Blade, aerodynamic imbalances can be detected early and precisely. This ensures a vibration-optimized and component-protecting operation. A reduction in output is avoided and the risk of a shutdown of the turbine is reduced. The integrated pitch angle monitoring also allows for a lifetime extension of the drive train components and support structures.

MIC.Blade – Web portal for remote monitoring

The structural and SCADA data collected by our monitoring systems are processed directly in a Monitoring Intelligence Center. The results of the analysis and all important indicators are available to the user at any time in a clearly arranged form. You can see at a glance whether limit values are being adhered to, if and where a problem occurs, what may be the cause and what measures need to be taken to remedy the fault or prevent damage from progressing.

Event-controlled notifications and alarms can be configured individually. You do not receive standard evaluations, but an individual dashboard tailored to your requirements as well as concrete recommendations for optimization. In addition, automated reporting (optionally with expert evaluation) can be carried out, which also fulfills official requirements.

The security of the sensitive measurement data is always in the foreground. A computer center in Germany, a secure Internet connection and a three-tier user management system (administrator, editor, user) ensure that only authorized persons can view data and results and configure settings. If a data connection is nevertheless not desired or not possible due to the given conditions on site, all monitoring and data backup functions can also be outsourced to a central wind farm server.

The following indicators are visualized in MIC.Blade:

  • Ice Detection
  • Damage
  • Pitch Angle Monitoring
  • Rotor Imbalances
  • Dynamic Load Monitoring

Knowledge Library

Exploiting the potential of a wind farm in the best possible way – this is not only the overriding goal of manufacturers and operators, but is also essential with a view to achieving the fastest possible energy turnaround. In our white papers in the categories Increase yields, Optimize inspections and Extend service life, you can find out how you can sustainably increase the efficiency of your wind turbines.

Case Studies

Case Study "Ice detection with IDD.Blade – No loss of yield due to unnecessary downtime" 351.09 KB
Case Study "Ice detection with IDD.Blade – No loss of yield due to unnecessary downtime"

If ice forms on the rotor blades of a wind energy plant, it must be shut down in accordance with official regulations in order to protect the surroundings from ice being shed. Critical ice build-up must therefore be reliably detected using technical measures. A meteorological sensor for ice detection was installed in the Hamwiede wind farm from the very beginning. However, it became apparent already in the first winter that the shutdown due to ice was very imprecise. False alarms and unnecessary shutdowns became more frequent. The potential of the wind farm could therefore not be fully exploited in the particularly high-yield winter months. Discover in our case study how downtimes at the Hamwiede wind farm were significantly and reliably reduced with the help of IDD.Blade from Wölfel.

Rotor blade inspection by an officially appointed and sworn expert

During production: Third Party Inspection (TPI)

Precise and reliable production of rotor blades is essential for the quality of the blades and thus for the service life and the possible energy yield of a wind turbine. Due to the high level of manual labor in the production process, the rotor blades often have defects, which can develop into serious damage during operation. According to estimates by experts, approx. 4 out of 5 damages in the field are related to the production process. As independent experts we perform inspections during blade production directly at the manufacturer’s site on behalf of the operator and prepare a complete documentation of any deviations in quality.

Our TPI concept has proven itself in practice and has already been a great support for many operators. It consists of three complementary elements:

  1. General supervision of blade production within the scope of process audits
  2. Specific supervision of blade production for specific customer projects according to our witness point concept
  3. Factory Acceptance Test: The project rotor blades are thoroughly tested from the inside and outside, including the lightning protection system and all mounting parts.

During operation: Recurrent inspection – Onshore and Offshore

During operation, the high loads acting on the rotor blades lead to damage, with the problems typically originating in the manufacturing of the blade. Therefore, recurrent inspections during operation are essential to detecting possible damage of the rotor blades as early as possible and to ensure the highest possible blade quality.

  • Recurrent inspection on the wind turbine
  • External inspections of the rotor blade
  • Internal inspections including camera inspections
  • Lightning protection measurements
  • Further inspections as required (e.g. thermography)
  • Inspection before warranty expiration (generally after five years offshore, complete inspection of the blades including lightning protection system)
  • Supervision of repairs
  • Comprehensive documentation (incl. expert reports on the rotor blade, expert report on the damage detected)

Hartmut Höhns, Package Manager Quality Assurance at WindMW:

"The cooperation between WindMW and Wölfel Engineering GmbH + Co. KG, was – beside the professional working relationship – constructive, fruitful and always in a considerate manor at times. The availability and short reaction period of inspection capacities provided by Wölfel Engineering GmbH + Co. KG to the OWF Meerwind Süd/Ost project, was remarkable."

Our services for structural monitoring (SHM/CMS) and rotor blade inspection (TPI/WKP)

We have been working in the offshore wind energy industry for several years and have comprehensive expertise in the following fields:

  • Design of lifetime monitoring systems
  • Development and installation of measuring equipment
  • Data acquisition and data analysis for specific wind farms
  • Monitoring, monitoring center and reporting
  • Finite element modeling and simulation of the load-bearing behavior of structures
  • Automated data analysis and monitoring
  • Lifetime analysis and evaluation
  • Rotor blade inspection – from Third Party Inspections (TPI) up to periodic inspections
  • Combination of monitoring, maintenance and inspection.

Structural Health Monitoring Systems (SHMS) will reduce Levelized Cost of Energy (LCOE)

An inspection strategy, which is based on the deep knowledge of the structural integrity of your assets, enables and ensures the necessary cost reductions especially in offshore wind industry. The optimized evaluation process of the windfarm allows to switch from periodic to conditioned based inspections and further on extend the liftetime of your wind turbines:

Of the annual operating costs, approximately 4,500 euros per MW are spent on underwater and tower inspections. From our experience, these inspection costs can be reduced by 50 percent. Furthermore, the use of SHMS makes it possible to objectively achieve a lifetime extension of around 4-8 years. The investment costs are thus spread over a 20 percent longer period of use, which significantly reduces the levelized cost of energy (LCOE).

"A [...] route to reduce OPEX, and subsequently LCOE, is through the optimisation of the inspection and maintenance strategies. This optimisation is carried out by switching periodic or risk-based inspection regimes to a condition-based regime. In order to do so, periodic inspections can be postponed or directly taken out of the scope of works whenever the condition of the assets is proven to be appropriate. SHMS are currently the best approach to gain confidence in the assets’ integrity without actually deploying offshore."

(Source: Martinez-Luengo, M.; Shafiee, M.: Guidelines and Cost-Benefit Analysis of the Structural Health Monitoring Implementation in Offshore Wind Turbine Support Structures. Energies 2019, 12(6), 1176; https://doi.org/10.3390/en12061176)

In our interactive calculation tool, you will discover your individual potential for cost savings and lifetime extension by implementing SHMS. All incurred costs are included except unscheduled activities.

REDUCTION OF YOUR LEVELIZED COST OF ENERGY (LCOE) DUE TO SHMS

By moving the black dots you can calculate the reduction of your individual Levelized Cost of Energy (LCOE):

4.9 %*
WACC real
50 %
Potential reduction of inspection costs due to SHM

Please contact us personally

________

We would be pleased to support you in solving your problem concerning "Wind turbine vibrations" and advise you on questions regarding our system and service offerings in the areas of structural health monitoring, vibration reduction, sound and noise as well as structural design.

Dr.-Ing. Georg Enß

+49 40 524715-262
enss@woelfel.de
Formular

Timo Klaas

+49 40 524715265
klaas@woelfel.de
Formular

Dipl.-Ing. Bernd Wölfel