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NON-DESTRUCTIVE TESTING AND CONDITION MONITORING A

TECHNIQUES FOR RENEWABLE ENERGY INDUSTRIAL ASSETS

Wind Turbine Inspection and Condition Monitoring
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The literature available on NDT and Condition Monitoring for Renewable Energy sources is

very fragmented. Most of the relevant literature sources on the subject can be found in the

form of conference and journal papers.

The number of wind turbines and their complexity have both increased in recent years.

Maintaining a high level of reliability for wind turbines as systems has become gradually

significantly more challenging. At the same time, maintenance costs have risen due to the size

and complexity of wind turbines even at subcomponent level. The most important faults in wind

turbines are those that result in the highest downtime and loss of productivity. There are some

studies that have considered specific faults affecting wind turbine operation. However, they

depend on the wind turbine model considered, the geographic and environmental changes, etc.
Wind Turbine Inspection and Condition Monitoring
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A
 Wind Turbine Inspection and Condition Monitoring
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Wind energy is also one of the most important renewable energy sources
exploited at a global scale with approximately 0.5T W of installed capacity as
of 2019. There is a need to optimize the operational and maintenance costs of
wind turbines in order to increase the competitiveness of this power
generation industry.

The main objective is to avoid the catastrophic failures.

Certain component faults can be particularly dangerous leading even to a
complete loss of the wind turbine. In order to avoid them, the main
inspections of wind turbine components are necessary.

An efficient way of reducing costs is through an evolution from corrective to

predictive maintenance procedures, for example based on condition
monitoring of critical turbine components.
 Wind Turbine Inspection and Condition Monitoring
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Condition monitoring systems allow early detection of health degradation of
the main components, for example gearbox, brake system, blade, tower,
facilitating a proactive response, minimizing downtime, and maximizing the
overall annual capacity production of wind farms.

A large number of recent research studies have focused on the field of wind
turbine remote condition monitoring due to the importance of operational
reliability.

The weather conditions determine the wind farm energy productivity with
time. Ice formation on blades is the environmental phenomenon that
generates more downtime in the wind energy industry.
 Wind Turbine Inspection and Condition Monitoring
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Wind turbine operation must stop production when ice is detected on the
blades for safety reasons. People, animals, devices, etc., close to the wind
farm can be put at risk due to the possibility of ice detaching from the blades
as they rotate at high speed. Moreover, abnormal vibration of the wind
turbine arising from the ice accumulation can cause failures. The resulting
downtime can lead to significant financial costs due to the lost production.
NDT techniques are therefore required in order to detect ice accumulation on
the blades.
 Wind Turbine Inspection and Condition Monitoring
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Gears are typically made from high Cr steel grades such as 4320, 4820, 9310, and
18CrNiMo7-6. These steel grades have low carbon and high chromium and molybdenum
content, to increase the maximum toughness of the material.
Wind turbine gearbox designs have been improving over the years resulting in the
continuous revision of the IEC-61400 international standard, which outlines the minimum
requirements for specification, design, and verification of gearboxes in wind turbines.
Despite these continuous improvements, several technical challenges remain that have
yet to be overcome, especially in the case of offshore wind farms.
Most common wind turbine gearbox failures, and different examples on how to detect
and prevent unexpected failures by using appropriate condition monitoring systems and
surface engineering treatment techniques, are well documented.
 Wind Turbine Inspection and Condition Monitoring
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Turbulence influences the amount of wind energy harvested
using wind turbine blades reducing the efficiency of the overall
electric power production of wind turbines.

This results to a lower level of competitiveness of this industry

in comparison with other energy sources such as fossil fuel-
based power generation. Turbulence effects can be further
enhanced by the characteristics of the wind turbine blade
surface itself, for example ice accumulation, impacting insects,
dirt, mud.
NDT techniques can be applied in order to monitor the blade
surface characteristics or condition. However, NDT is yet to be
widely employed for this particular purpose in the industry yet.
The application of ultrasonic waves for monitoring the presence
of dirt, mud, and other potential surface artefacts potentially
accumulating with time has been employed.
Wind Turbine Inspection and Condition Monitoring
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 Applications of Remotely Operated Vehicle in Wind Turbine
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The constant increase of renewable energy demand is leading
wind turbines to become very complex and sophisticated
devices.
These technological developments imply new methods and
tools to ensure the reliability of the systems.
For this purpose, non-destructive testing techniques are widely
employed in the field of wind turbine maintenance.
Implementation of a walking robot-based system that allows
non-destructive testing in difficult access areas of wind
turbines has been in great demand. Several applications of such
systems are shown in the picture. These applications can be
classified according to the type of sensor and the area to
inspect: Acoustic emission, visual inspection, guided wave
testing, noise analysis, or thermographic inspections are some
of the non-destructive testing techniques that can be aided.
 Condition Monitoring System for Solar Plants Based on
Thermography
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This part focuses on thermography techniques for the evaluation of solar panels.

Thermography can be used to evaluate the condition of the photovoltaic system

very fast, and economically providing reliable inspection results.

The most important thermography techniques for solar plants are active and
passive techniques. Both the techniques has certain advantages and
disadvantages over each other in order to determine the condition or intensity of
damages of the panels.

The main advantages and disadvantages of using thermography technologies

depends on the main variables that should be considered during thermography
inspection.
 Condition Monitoring System for Solar Plants Based on
Thermography
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This part focuses on thermography techniques for the evaluation of solar panels.

Thermography can be used to evaluate the condition of the photovoltaic system

very fast, and economically providing reliable inspection results.

The most important thermography techniques for solar plants are discussed
herewith together with the governing principles. Active and passive techniques
are analyzed in order to determine the method that provides the best results.

The main advantages and disadvantages of using thermography technologies are

analyzed. In addition, the main variables that should be considered during
thermography inspection are considered. Finally, certain types of failures that
can be detected using thermography are evaluated through the different
thermographic patterns in obtained thermal images.
Condition Monitoring System for Solar Plants Based on
Thermography
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Finally, certain types of failures that can be detected using thermography are
evaluated through the different thermography patterns in obtained thermal
images.
 Remote Condition Monitoring for Solar Photovoltaic
Systems
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The development of newer and more ecofriendly energies is now more important in the world.
Solar energy has been growing considerably over the last years, and, for example, photovoltaic
solar farms size has increased, where the problems in operation and maintenance also has
raised. Automated inspection is being applied with emerging hardware and software
technologies such as computer vision, unmanned aerial vehicles, and thermal cameras.
Hydroelectric Power
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Normally a standard requirement to inspect all hydroelectric dams and power plants (HPP) in
every five to ten years, but the methods to be employed for such inspection are not well
defined.
Most of the work is currently done by autonomous scuba divers using visual and conventional
direct methods.

However, there is considerable pressure to reduce the use of diver deployment in such a
dangerous work environment.

Due to very low visibility the confidence in these surveys is relatively low with much time
required to accomplish an inspection.

In cases where extended monitoring of the presence of fish near turbines in turbid water is
necessary, an acoustic technique such as imaging sonar is needed to accomplish the desired
objectives.
 Hydroelectric Power
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The objectives for an HPP inspection can be summarized as follows:

1. Identification and location of specific targets, such as lost tools or parts that could inhibit or degrade
the operation of any component of the HPP.

2. Inspection of broad areas for maintenance, usually related to the civil structure (concrete) in
spillways and runoff channels with the objective of identifying structural problems indicated by
cracking, exposure of reinforcing bars, areas of concrete spalling (flaking), misalignment at joints, and
undermining and settlement of these structures.

3. General inspection and monitoring normally associated with critical operational issues such as
debris accumulation on water intake screens which may cause flow restriction.

4. Assessing environmental issues around inventory and monitoring biota and its relationship with the
generating process (i.e. assess the effectiveness of fish ladders or quantify fish injury/survival rates in
the hydro turbine passage).
Hydroelectric Power
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Hydroelectric power plant environments, normally associated with turbid waters, have
complex inspection needs and frequent requests for underwater inspection and maintenance
services.

Imaging sonar has proven to be effective with the performance of the sonar depending on the
proper combination of deployment (fixed mount, boat mount, ROV integration, and optional
rotator), orientation of the sonar (grazing angle, distance) and the settings of the sonar
(frequency).

When properly conducted, imaging sonar surveys could bring considerable advantages in
terms of safety, accuracy and costs in comparison with current methods of visual/scuba diving
inspections bringing innovative and cost-effective solutions for such strategic and complex
areas as Hydro power planning, construction and management.