Lifetime prognosis with SHM.Tower, our new solution developed in collaboration with our German partner WÖLFEL Group

SHM.Tower® – Our intelligent and cost-effective tower vibration
monitoring system. Valuable for a precise analysis of the lifetime
of your wind turbine for its further operation


Vibration monitoring and further operation


Every wind turbine has its own individual structural and vibrational behavior while being in operation. The vibration
load of wind turbines, especially that of the tower, can vary considerably depending on the location and operational
mode of the wind turbine. In the design phase, these loads are determined by means of wind classes which derive
the respective wind conditions from annual average values. Usually, data collected by neighboring meteorological
measuring stations are used during assessments regarding the lifetime extension of wind turbine towards the end of
their operational life. That means that both the design and the assessment for further operation of the wind turbines are
based on loads that may considerably deviate from the actual loads. Even two wind turbines in one and the same
wind farm may differ significantly in their vibration loads. This may also be due to different balancing conditions or
pitch angle errors.


Optimized operation

We recommend that the turbine settings should be optimized while taking the actual loads into account.
This is necessary because of the strong vibrations that occur in case of insufficient balancing or incorrect
pitch angles. The highest vibration amplitude values, which allow making direct statements about the global
vibration level, occur at the head of the tower, the ideal installation position for SHM.Tower.

Unbalance-related vibration amplitudes of two wind turbines in one
and the same wind farm


Remaining service life and further operation

To assess whether the operational life of a wind turbine can be extended, the remaining lifetime must be
determined as best as possible. This requires that the design loads are compared with the actual fatigue
loads. In this context, the full potential can only be exploited if the tower vibration data are collected using
measuring equipment.


 Potential for further operation identified by means of SHM.Tower



The solution: SHM.Tower


The SHM.Tower monitoring system has been developed for continuous measurement of the vibration loads
of wind turbine towers. Since it issues warnings if threshold values are exceeded, the system provides
considerable added value during ongoing operation. Wind turbines with excessive loads can be identified
instantly to initiate immediate countermeasures.

 Vibration amplitudes and limit values in the course of a day


During the entire life of the wind turbines, instantaneously evaluated and stored data provide valid statements
about the lifetime that has already elapsed. With SHM.Tower installed in the tower, the assessment
regarding lifetime extension of the wind turbine is based on actual fatigue loads rather than on mere
estimates. In particular, extreme loads are measured directly. Since SHM.Tower registers structural loads
using measuring equipment, the number of visual inspections can be reduced.


The system and particularly the software have been developed to meet the requirements of the industry
from the very beginning and have been tested in a multitude of wind turbines. The calculated lifetime
predictions have been verified and confirmed by validation measurements.


 SHM.Tower installed in the tower head


The SHM.Tower sensors and electronic components are accommodated in a compact housing and can
be easily installed in the head of the tower. In the energy self-sufficient operating mode, SHM.Tower
can register tower vibrations as early as during setup and without external power supply. In the operating
phase, data are collected even during power failures. The system continuously measures and stores any
fatigue loads.


Intelligent vibration monitoring

Using its integrated acceleration sensors, the SHM.Tower monitoring system constantly registers the
vibration status of the wind turbine. Since the system is installed in the head of the tower, the maximum
amplitudes of the tower vibrations can be measured in either horizontal direction and, if necessary, vertically as well.



Alarms and warnings

The integrated processor directly evaluates the measured raw data, which can then be directly
compared with the threshold values defined in ISO 10816-21 and VDI 3834. Any upward violation of
the threshold values cannot only be documented but also be transmitted to your monitoring system through
an Internet connection at any time as alarm or warning output.


Optimized wind turbine operating control system

The operating mode of the wind turbine can be analyzed at any time in combination with simultaneously
measured operating data, such as wind speed, rotorspeed, power, pitch angle or azimuth angle.
Acceleration data are output as averaged RMS values, allowing a precise analysis of the vibration load
and operating mode as daily, monthly and annual variations. Special events, such as strong wind and
its impact, can be identified and analyzed as time curves or frequency spectra.


Expandable sensor system

Optionally a 3-channel interface (4 … 20 mA) allows the connection of external sensors, such as
acceleration sensors, range sensors or strain gauges. These external sensors can be positioned in the wind
turbine as desired, for example to monitor strains or relative shifts between the base and the foundation of
the tower.



Lifetime prognosis with SHM.Tower


The integrated efficient processor evaluates measured data and monitors threshold values and, in addition,
runs comprehensive calculation algorithms. These algorithms calculate the fatigue loads in each tower
segment based on the vibration acceleration measured in the tower head. Due to the integrated algorithms,
the consumed lifetime of the turbine can be shown at any time for each tower segment. The reserves
for further operation can be optimally analyzed, especially before the design lifetime of 20 years is
reached. The integrated lifetime evaluation algorithms use a structural model of the tower which is adjusted
to your wind turbine in advance. The geometric data of the wind turbine and the material parameters are
used to create a customized tower model. This ensures exact calculation results.

Installation before setup or retrofitting

If SHM.Tower is installed when the wind turbine is set up, the operating condition and the consumed lifetime
are monitored during all life cycles of the turbine. Any extreme loads can be taken into account precisely.
Particularly single events, such as strong wind, which significantly influence the remaining lifetime of the
tower, are therefore included in the lifetime evaluation. This allows optimum utilization of the structure.


If retrofitted, SHM.Tower provides lifetime evaluations that are substantially better than the usual methods
used for assessing lifetime extensions, although no vibrations were measured during the first years of
operation. Extrapolations by means of the already measured loads allow evaluating the complete operating time of the wind turbine.



Individual lifetime evaluation in the wind farm

An individual lifetime evaluation of each wind turbine in a wind farm can be made when SHM.Tower
is installed. If reserves are sufficient, operation of individual wind turbines can be continued beyond the
end of their design lifetime. Since these reserves are documented and thus verifiable when a wind turbine
is sold, this provides considerable financial added value.


Monitoring Intelligence Center


SHM.Tower has been developed for fully automatic and autonomous operation on wind turbines. With
a direct interface to the turbine control system, the fatigue loads can be classified with respect to the
operating data. In addition, our systems can be connected to our web-based monitoring portal MIC.
Wind. This portal provides detailed information about the vibrations and the remaining lifetime of the tower.
Today, such remote monitoring of essential components is standard for profitable operation. On request,
all relevant data are transmitted and stored through the Internet.

All important indicators are available in graphical form on the web interface of Wölfel‘s monitoring
center MIC.Wind. Event-controlled messages and an automatic reporting feature ensure that any current
information is available at any time. If the customer does not want a data interface for safety reasons or if
a data interface is not available on site, all monitoring and data storage functions can be transferred to a
central wind farm server.


SHM.Tower specifications



Dimensions approx. 180 x150 x 90 (mm)
Weight approx. 2 kg
Temperature range -40°C to +55°C
Lightning protection Suitable for LPZ 1




Interfaces – hardware

Power 110 … 230 VAC
Ethernet (PoE) Suitable for Power over Ethernet
LED indicators Low battery charge; external
energy supply; storage overflow;
Digital out Alarm output (if necessary)



Measurement parameters

Measuring value Acceleration
Direction 2D (3D possible)
Measuring range ± 2 g
Frequency range 0,1 … 10 Hz
Noise ≤ 50 μg⁄√Hz
External sensor 3x (4 … 20 mA),
(optional) only with external
power supply



Interfaces – software

Modbus TCP, Transfer of operating data from
OPC UA the turbine control system
(e.g., wind speed, azimuth angle)
FTP Data transfer
MIC.Wind Results and configuration
Local web server Configuration and data transfer




Energy supply and data storage

Energy-self– ≥ 2 months
sufficient operation
and data
Battery Lithium battery, low
(no storage battery) self-discharge for up






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