Wind power is one of the most promising green energy sources, especially when produced in offshore power
plants. Corrective operations in wind turbines cause a considerable part of the maintenance costs of such plants.
One preventive action for reducing such operations is the periodic off-line control of oil samples from the wind
turbines. The time delay between sampling and availability of the results is a major disadvantage of this kind
of controlling. In-situ condition monitoring is a solution to this problem. In-situ monitoring allows real time
detection of random, time discrete events, thus enabling a better scheduling of preventive actions and reducing
costs and downtime.
Fluorescence spectroscopy is a complementary technique to absorption spectroscopy. Due to absorption of
UV or visible light, the electrons of specific molecules are excited from a ground electronic state to a vibrational
state of higher energy. By collision with other molecules, the excited electron looses a part of the acquired
energy and relaxes to a lower vibrational state. The remaining acquired energy is emitted during the electron's
transition to the ground state. The resulting frequency shift between excitation and emission energy, known as
Stokes shift, is unique and characteristic for each active molecule.
In this paper gear-oil condition monitoring based on fluorescence spectroscopy is proposed. Three typical
commercial gear-oils for wind turbines were studied. The spectra gained by UV excitation of the samples were
analyzed by means of partial least square (PLS) regression. Good prediction results were obtained for the total
acid number (TAN). The latter is a measure for the oil acidity and is considered to be a proxy variable for oil age.
Other parameters delivering information about gear-oil additive depletion and the related oil aging condition,
like phosphor, sulfur and molybdenum concentration, were also analyzed.
A major part of future renewable energy will be generated in offshore wind farms. The used turbines of the 5
MW class and beyond, often feature a planetary gear with 1000 liters lubricating oil or even more. Monitoring
the oil aging process provides early indication of necessary maintenance and oil change. Thus maintenance
is no longer time-scheduled but becomes wear dependent providing ecological and economical benefits. This
paper describes two approaches based on a linear variable filter (LVF) as dispersive element in a setup of a cost
effective infrared miniature spectrometer for oil condition monitoring purposes. Spectra and design criteria of a
static multi-element detector and a scanning single element detector system are compared and rated. Both LVF
miniature spectrometers are appropriately designed for the suggested measurements but have certain restrictions.
LVF multi-channel sensors combined with sophisticated multivariate data processing offer the possibility to use
the sensor for a broad range of lubricants just by a software update of the calibration set. An all-purpose oil
sensor may be obtained.
Linear variable filter (LVF) spectrometers represent an interesting group of low cost spectral monitoring systems
for procedural or condition monitoring systems. Such highly integrated, miniaturized spectral devices are
promising components for the design of rugged, portable and shock resistant monitoring systems. Among others,
detection of chemical substances and their corresponding concentrations in fluids is possible by analyzing the
characteristic absorption bands. Using this spectral device for lubricant condition monitoring a certain quality of
spectra is essential for revealing the change of their properties over lifetime. The focus of this work is to evaluate
the useability of a low cost chip-size wavelength interrogator having a 256 elements pyroelectric detector array
combined with a linear variable filter. Therefore, simulations were performed to specify the maximum resolution
and to compare it to real world measurement data in the petrochemical domain. The influence of a different
number of detector elements per array (e.g. 64 / 128) on the maximum spectral resolution is calculated and
compared to measured data. An ideal system design is presented and the limits of such interrogators with respect
to infrared spectral monitoring are indicated.
Wind turbine blades are made of composite materials and reach a length of more than 42 meters. Developments
for modern offshore turbines are working on about 60 meters long blades. Hence, with the increasing height
of the turbines and the remote locations of the structures, health monitoring systems are becoming more and
more important. Therefore, fiber-optic sensor systems are well-suited, as they are lightweight, immune against
electromagnetic interference (EMI), and as they can be multiplexed. Based on two separately existing concepts
for strain measurements and lightning detection on wind turbines, a fused system is presented. The strain
measurement system is based on a reflective fiber-Bragg-grating (FBG) network embedded in the composite
structure of the blade. For lightning detection, transmissive &fiber-optic magnetic field sensors based on the
Faraday effect are used to register the lightning parameters and estimate the impact point. Hence, an existing
lightning detection system will be augmented, due to the fusion, by the capability to measure strain, temperature
and vibration. Load, strain, temperature and impact detection information can be incorporated into the turbine's
monitoring or SCADA system and remote controlled by operators. Data analysis techniques allow dynamic
maintenance scheduling to become a reality, what is of special interest for the cost-effective maintenance of large
offshore or badly attainable onshore wind parks. To prove the feasibility of this sensor fusion on one optical
fiber, interferences between both sensor systems are investigated and evaluated.