Application note WearSens® cmc102
Application:
Continuous, online, remote, condition monitoring of industrial gears in
wind turbine gearboxes to increase lifetime, reduce downtime and
‘demand-and wear-dependent’ regulation.
Method:
Highly sensitive oil sensor system
cmc Solution:
WearSens®
Figure 1: WearSens®
What it does:
The WearSens® oil sensor performs continuous condition monitoring of industrial gearboxes,
hydraulic systems and turbines as in wind turbine by evaluation of the system ‘oil-machine’.
WearSens® measures the conductivity , permittivity r and the temperature T. From these values,
wear additive consumption, oxidation and oil acidification in the oil are determined.
Customer:
Service providers for wind turbines, gearbox manufacturers, wind turbine manufacturers, turbine
test organizations, wind farm operators, asset protection providers, manufacturers and operators of
transmission and engine test stands.
Background:
In industrial gearboxes, especially in wind energy gearboxes, bearings often fail
early, long before their calculated L10 life. The damage begins as axial raceway
cracks and extends to branched crack systems with partial white etching cracks. The
cause of premature bearing failure is vibration-induced, mixed friction stress. [1]
Figure 2: Wind turbine
Details:
The sensor measures components of the specific complex impedance of the oils
with high precision. In particular, the electrical conductivity and permittivity.
Also, the oil temperature is measured to compensate for the strong
temperature dependence of the conductivity and permittivity measurements.
The temperature coefficient of the oil conductivity depends on the particular
pollutants and the aging state, so it is constantly changing and cannot be
assumed at any point. Therefore, a complex, adaptive, self-learning
Figure 3: Three-plate sensor
temperature compensation algorithm was developed.
Only from the temperature-compensated conductivity and dielectric constant can the rate of change
of the oil be accurately calculated. Thus changes in the oil, which affect the whole system, can be
detected much earlier than with other measurement systems and technologies. [2]
Maahantuonti ja myynti Suomessa:
Tiilenlyöjänkuja 9 B, FIN-01720 Vantaa
Tel. +358 29 006 230, [email protected], www.ytm.fi
Inhibitors and additives in the oil buffer away dirt, moisture and other carriers over minutes or
hours. The WearSens® system measures in seconds. Thus the high measurement speed enables a
continuous, online, remote monitoring and condition-based preventive maintenance of wind turbine
gearboxes. Also a dynamic, ‘demand-and wear-dependent’ regulation of the utilization of
transformers can be realized. The measurement of the dielectric constant also allows the
determination of the water (moisture) content of oil. From the temperature compensated
conductivity and dielectric constant, the loss factor tan can be calculated and from the
temperature compensated conductivity the acidification of oil can be determined.
The WearSens® sensor system enables the reduction of downtime, improved yield and an increase in
the overall life of wind turbine gearboxes. In Figure 4, the measured signal acquisition and
processing in WearSens ® is sketched with the fields of measurement signal acquisition,
measurement signal processing and signal output.
Figure 4: Data flow graph using WearSens®
Installation:
The following figure shows the installation of the sensor in the direction of the forced cooling of a
transformer. The sensor should be installed in a low vertical position and flow through from bottom
to top. When installing, make sure that the WearSens® sensor is before any built-in line filter.
Installation after the filter would not produce such a clear picture of what is happening. During
shutdown the WearSens® should remain completely filled with oil.
2
When installing, ensure that no air bubbles can form in the measuring chamber. The measurement
results are independent of flow rate.
Figure 5: Installation of WearSens® sensor in forced cooling line
Example:
Using a transmission test rig different load cycles and thereby speeds and torques were run, the
conductivity  dielectric constant r and the temperature of the transmission oil were measured.
During loading, the conductivity of the gear oil changes, in addition to the change caused by
temperature change, due to formation of wear particles, pollution products, broken oil molecules
and acids or oil soaps.
In Figure 6, the change of the electrical conductivity 40 against time is plotted using mean values
over 3 minutes. After switching to the higher load, the oil conductivity increases greatly. This is due
to high wear. The shrinkage (import) of the bearing is shown here by a reduction in the increase in
the conductivity. The high dynamic of the conductivity signal is indicative of continually fluctuating
pollution damage, and points to the formation of cracks and spalling. The jumps in the slope of the
electrical conductivity before switching off are an indication of the final bearing damage.
3
Figure 6: Rate of change of conductivity expressed as ∆40/∆t
After shutdown the oil conductivity drops sharply. This clearly shows the effect of the additives.
During periods of stress pollution products are produced more quickly than the additives can work.
After the shutdown of the test rig oil contamination does not increase, but the effect of the additives
continues.
Figure 7 shows the inner ring of the failed wheel bearing planets with highly peeled raceway after
completion of the test run.
Figure 7: Peeled inner ring raceway of the failed planetary cylindrical roller bearing
In Figure 8, the course of the wear of a machine without the use and with the use of WearSens®
(see, for example, the bench test described above) are shown. The damage is incurred at the time of
congestion and results in conventional monitoring systems to component failure. In the example of
the transmission test rig, conventional monitoring systems (vibration technology) responded only
after the onset of bearing damage and were too late to prevent the failure.
Using the WearSens® oil sensor system critical operating conditions are detected by changes in the
oil and damage avoided. By establishing allowable operating conditions using limits of oil
conductivity and permittivity and their gradients, both the life and the yield of wind turbines can be
optimized with a wear limit rule. The identification of critical damage states enables timely
corrective action long before irreversible damage or a gearbox failure.
4
Figure 8: Course in the wear with and without use of WearSens ®
Sensor:
The WearSens® sensor system consists of the sensor module and a communication
module. In the communication module, there is a web server with an HTML page for
presentation of the data. The measurement data can also be transferred to a web-based
monitoring system. An automated generation of e-mails, text messages, etc., in case of
alarm messages possible.
Figure 9: WearSens® Sensor system
What next?:
References:
[1]
[2]
Call cmc Instruments today for a quotation or to discuss your application in more detail.
Mauntz, M.; Gegner, J.; Klingauf, S.; Kuipers, U.: Kontinuierliche Überwachung des
Schmierölzustands und Begrenzung des Betriebsverschleißes von Wälzlagern mit einem neuen
Sensorsystem, 10. VDI-Fachtagung, Gleit- und Wälzlager, 23.04.2013-24.04.2013, Schweinfurt, VDI
Wissensforum GmbH, Düsseldorf, 2013, VDI-Berichte 2202, S. 283-296
Mauntz, M.; Gegner, J.; Klingauf, S.; Kuipers, U.: Early failure detection of gearbox components
based on the electrical response of the lubricating oil to chemical aging and contamination,
International Conference on Gears, 07.10.2013-09.10.2013, Munich, VDI Wissensforum GmbH,
Düsseldorf, 2013, VDI-Berichte 2013, S. 855-865
Maahantuonti ja myynti Suomessa:
Tiilenlyöjänkuja 9 B, FIN-01720 Vantaa
Tel. +358 29 006 230, [email protected], www.ytm.fi