Final Report Summary - PREWIND (Development of a Methodology for Preventive Maintenance of Wind turbines trough the use of Thermography)
The main objective of PREWIND was to develop a methodology for assuring the quality of wind turbines through the application of thermography. The methodology will be applicable to all wind turbines (onshore / offshore) by wind turbine operators, maintenance companies, manufacturing companies, insurance companies, etc.
The PREWIND methodology is expected to reduce the amount of large-failures that occur during the normal functioning of a wind turbine (e.g. damages to the rotor-blades due to vibration or oscillation, etc.), since they will be detected at an early stage, so that corrective actions can take place before the damages become critical. This means that by applying this methodology, the life time of the wind turbines can be extended and maintenance costs can be reduced. Furthermore, this methodology is not limited only to maintenance applications, thus it can be also applied for quality assurance during the manufacturing of the components or after the transport or assembling of the wind turbine before it is put into service.
Today, manufacturers of rotor blades take care of their production process following quality standards, etc.; however, there is no company capable of testing the final product adequately (at least in an automated way, the technology is not so developed yet). Nowadays, for the most companies manufacturing rotor blades, the final check of a rotor blade consists of a visual inspection by an expert, who with a 'screw-driver' knocks on the GRP material and out of the sound he perceives, he determines if the part is OK or not. This requires a highly trained ear, and lots of experience. It must be remarked then, that this commonly used method relays 100 % on a humans-factor and therefore is susceptible to errors.
Only a very small minority of manufacturers of blades have already discovered the advantages of thermography and apply (passive) thermography on recently manufactured blades. The heat generated by the chemical reaction of the used resins is monitored, and so the conclusions about the adhesion of the parts are deduced. It must be commented also, that once the heat generated by the chemical reaction is gone, no further tests can be performed using this method.
The method proposed in this project for non-destructive technologies (NDT) testing of the components does not have that time 'restriction'. Through the application of active thermography, the tests can be performed at any stage of the life on the rotor blades: after their manufacturing, prior to their installation or even after they have been working for some years. This was the big advantage of PREWIND towards the state of the art.
The project was structured into six work packages (WPs), as follows:
WP A - Definition of technological requirements
The objective of this work package is to specify the requirements of the PREWIND methodology in accordance with the end user's needs (SME partners and members of the associations). It is necessary to consider in this task usual failures / problems of wind turbines for the development of the working methodology in WP B, as well as quality control methods, international and national requirements for the manufacturing of wind turbines and quality standards.
Based on the research findings, one can conclude that:
- the safe and failure-free operation of wind turbines can only be achieved through an optimised preventive maintenance programme;
- an optimised preventive maintenance programme, is only possible through a good operation monitoring system;
- wind turbines can reach their estimated lifespan (and be for all involved parties an economical success), when fact 1 and 2 are fulfilled;
- the most critical parts to be taken care of for the better operation of a wind turbine, according to the information gathered in this document, are the electrical connections and electrical systems, as well as the rotor blades in third position.
WP B - Development of working methodology
The objective of this work package was to carry out analyses, planning, design, engineering and testing, activities necessary for the development of the working methodology of PREWIND and its components. The working methodology represents an essential part of the final PREWIND methodology, which includes the development of working procedures and their required templates.
WP C - Testing and evaluation of the working methodology
The objective of this work package was to test the PREWIND methodology in the field; both types of inspection: active and passive thermography. The results of these tests were analysed in the assessment of the field tests.
After performing the first series of tests on rotor blades, it became quite clear that the system could successfully identify defects such as delaminations, air cavities, etc. The difficulty was to evaluate the seriousness of the irregularities detected in a simple way (the consortium had no experience in this matter when the field tests began). So it became obvious that an 'evaluation catalogue' was to be compiled, containing as many examples as possible for all typical defects, so that the operator had references ('good' and 'bad' examples), to determine in an easy way the status of the inspected section. This simple but critical aspect had not been considered during the preparation of the proposal. For the consortium, it was already clear that the system could provide good and precise results; however, it would be very important to gather as much experience as possible (as many examples as possible), to be able to provide an accurate evaluation. So the consortium decided to prolong the field tests as much as possible (originally the field tests should last only 6 months, from month 19 to month 24) to gather as much testing material as only possible. At the end, the consortium managed to perform around 150 IR measurements (this represents around 200 000 IR images). And so the 'evaluation catalogue' could be compiled.
Passive thermography:
The only suggestion that the consortium could make to a user, is to start the inspection at the bottom of the wind turbine and to work his way up (normally, due to safety procedures, the wind turbine has to be turned off when personnel is inside the nacelle). This way, the inspector could go up inspecting all electrical panels (with the turbine still running), and if he has to shut off the unit when reaching the nacelle, he still will have better temperature contrasts for the inspection than if the turns the wind turbine off before starting to climb (of course, safety comes always first, so if there are clear regulations forbidding to climb to the nacelle with the wind turbine in operation, those rules need to be followed).
Active thermography:
The only major comment to be made to the assessment of the 'active thermography' inspections is that at the beginning of the field test it was determined that it was necessary to create an evaluation catalogue. A centralised management of the information generated will be organised after the project is concluded, so that all the partners using the PREWIND method can share and benefit from a joined source of information. This will be a dynamic catalogue that will always be growing.
WP D - Development and implementation of the dissemination strategy
The objective of this WP was the development of a dissemination strategy for PREWIND. This work package ensured the dissemination of the project results by implementing this strategy, conduction of workshops, etc. Technical and scientific steps for preparing the methodology for its certification of the working methodology after the conclusion of the project were scheduled to take place as part of the dissemination strategy. In addition marketing tools and a publicity strategy were to be defined. This way the methodology will be available to a large number of SMEs.
WP E - Development of a training method
The objective of this WP was to develop a method for transmitting the know-how developed during the project to third parties (members of the IAGs, etc.), and to put that method into praxis.
The e-learning tool was oriented to wind turbine inspection technicians. It has been structured in modules that contain different chapters. Each chapter contains a didactic unit, with the necessary information about that topic. At the end of each chapter, there are different questions that must be answered in order to evaluate the learning about the topic.
The different modules developed are:
- thermography. It contains all information about thermography, that it is necessary to make any thermographic inspection. It does not focus on wind turbines or any other specific device.
- wind turbines thermography inspection. In this module it is developed the thermography of the different components to be inspected with the PREWIND method. It covers the different electrical and mechanical parts for passive thermography, and the rotor blades for active thermography.
- PREWIND methodology. This module covers the passive and active thermography PREWIND processes.
Besides dissemination, the participating associations (FGW, APPA, APREN, APER, IWEA and GEAL) were also committed to providing training on the PREWIND method to their members.
WP F - Project management
Several 'unofficial' meetings among the partners of the same country were organised in order to structure the development of the projects activities. Frequent meetings for example, among the German partners TTZ, Alphatherm and sometimes with the other RTD, Automation Technology, or with Reetec and Krypton, have taken place. The proximity of the location of these partners has facilitated the exchange of information, the facility of organising short informal meetings to discuss about the project's progress, etc. The communications between the coordinator and the partners did not show any difficulty, although the number of the partners in the consortium is high (16 partners of 7 different countries). Many times during the reporting period, information about the work to be performed, work effort foreseen for each contractor involved and time schedule (deadlines) were supplied to all the consortium by means of emails by the coordinator who controlled the work and collected the works material needed for the foreseen deliverables. All other information was distributed among the partners by means mechanisms such as email, fax, post or telephone. As it has been commented before, the consortium managed to successfully exchange two partners (ISES for APER and TEGOPI for ILIAKO).
After the finalisation of the project PREWIND the consortium can conclude the following:
- The consortium determined the main areas of interest to emphasise the efforts of study for the application of thermography for the improvement of the preventive maintenance of wind turbines: the rotor blades (active thermography), and the electrical components (passive thermography).
- The consortium managed to select the most suitable technology / components for the PREWIND method: type of camera, type of heat source, etc.
- The consortium managed to develop a method for the preventive maintenance of wind turbines using thermography.
Active thermography: the different tests carried out during the development of the project, proved that it is possible to inspect rotor blades while mounted on the wind turbine. The consortium was able to detect failures in the structure of the blades such as delaminations, areas with insufficient adhesion (glue) of the inner reinforcements of the blade, etc. up to a depth of about 12 mm (depending on measuring parameters).
Passive thermography: the consortium developed a procedure for the inspection (and documentation) of the electrical components of wind turbines, to enable the detection of failures at an early stage. For this type of inspection any regular IR-camera can be used.
The PREWIND methodology is expected to reduce the amount of large-failures that occur during the normal functioning of a wind turbine (e.g. damages to the rotor-blades due to vibration or oscillation, etc.), since they will be detected at an early stage, so that corrective actions can take place before the damages become critical. This means that by applying this methodology, the life time of the wind turbines can be extended and maintenance costs can be reduced. Furthermore, this methodology is not limited only to maintenance applications, thus it can be also applied for quality assurance during the manufacturing of the components or after the transport or assembling of the wind turbine before it is put into service.
Today, manufacturers of rotor blades take care of their production process following quality standards, etc.; however, there is no company capable of testing the final product adequately (at least in an automated way, the technology is not so developed yet). Nowadays, for the most companies manufacturing rotor blades, the final check of a rotor blade consists of a visual inspection by an expert, who with a 'screw-driver' knocks on the GRP material and out of the sound he perceives, he determines if the part is OK or not. This requires a highly trained ear, and lots of experience. It must be remarked then, that this commonly used method relays 100 % on a humans-factor and therefore is susceptible to errors.
Only a very small minority of manufacturers of blades have already discovered the advantages of thermography and apply (passive) thermography on recently manufactured blades. The heat generated by the chemical reaction of the used resins is monitored, and so the conclusions about the adhesion of the parts are deduced. It must be commented also, that once the heat generated by the chemical reaction is gone, no further tests can be performed using this method.
The method proposed in this project for non-destructive technologies (NDT) testing of the components does not have that time 'restriction'. Through the application of active thermography, the tests can be performed at any stage of the life on the rotor blades: after their manufacturing, prior to their installation or even after they have been working for some years. This was the big advantage of PREWIND towards the state of the art.
The project was structured into six work packages (WPs), as follows:
WP A - Definition of technological requirements
The objective of this work package is to specify the requirements of the PREWIND methodology in accordance with the end user's needs (SME partners and members of the associations). It is necessary to consider in this task usual failures / problems of wind turbines for the development of the working methodology in WP B, as well as quality control methods, international and national requirements for the manufacturing of wind turbines and quality standards.
Based on the research findings, one can conclude that:
- the safe and failure-free operation of wind turbines can only be achieved through an optimised preventive maintenance programme;
- an optimised preventive maintenance programme, is only possible through a good operation monitoring system;
- wind turbines can reach their estimated lifespan (and be for all involved parties an economical success), when fact 1 and 2 are fulfilled;
- the most critical parts to be taken care of for the better operation of a wind turbine, according to the information gathered in this document, are the electrical connections and electrical systems, as well as the rotor blades in third position.
WP B - Development of working methodology
The objective of this work package was to carry out analyses, planning, design, engineering and testing, activities necessary for the development of the working methodology of PREWIND and its components. The working methodology represents an essential part of the final PREWIND methodology, which includes the development of working procedures and their required templates.
WP C - Testing and evaluation of the working methodology
The objective of this work package was to test the PREWIND methodology in the field; both types of inspection: active and passive thermography. The results of these tests were analysed in the assessment of the field tests.
After performing the first series of tests on rotor blades, it became quite clear that the system could successfully identify defects such as delaminations, air cavities, etc. The difficulty was to evaluate the seriousness of the irregularities detected in a simple way (the consortium had no experience in this matter when the field tests began). So it became obvious that an 'evaluation catalogue' was to be compiled, containing as many examples as possible for all typical defects, so that the operator had references ('good' and 'bad' examples), to determine in an easy way the status of the inspected section. This simple but critical aspect had not been considered during the preparation of the proposal. For the consortium, it was already clear that the system could provide good and precise results; however, it would be very important to gather as much experience as possible (as many examples as possible), to be able to provide an accurate evaluation. So the consortium decided to prolong the field tests as much as possible (originally the field tests should last only 6 months, from month 19 to month 24) to gather as much testing material as only possible. At the end, the consortium managed to perform around 150 IR measurements (this represents around 200 000 IR images). And so the 'evaluation catalogue' could be compiled.
Passive thermography:
The only suggestion that the consortium could make to a user, is to start the inspection at the bottom of the wind turbine and to work his way up (normally, due to safety procedures, the wind turbine has to be turned off when personnel is inside the nacelle). This way, the inspector could go up inspecting all electrical panels (with the turbine still running), and if he has to shut off the unit when reaching the nacelle, he still will have better temperature contrasts for the inspection than if the turns the wind turbine off before starting to climb (of course, safety comes always first, so if there are clear regulations forbidding to climb to the nacelle with the wind turbine in operation, those rules need to be followed).
Active thermography:
The only major comment to be made to the assessment of the 'active thermography' inspections is that at the beginning of the field test it was determined that it was necessary to create an evaluation catalogue. A centralised management of the information generated will be organised after the project is concluded, so that all the partners using the PREWIND method can share and benefit from a joined source of information. This will be a dynamic catalogue that will always be growing.
WP D - Development and implementation of the dissemination strategy
The objective of this WP was the development of a dissemination strategy for PREWIND. This work package ensured the dissemination of the project results by implementing this strategy, conduction of workshops, etc. Technical and scientific steps for preparing the methodology for its certification of the working methodology after the conclusion of the project were scheduled to take place as part of the dissemination strategy. In addition marketing tools and a publicity strategy were to be defined. This way the methodology will be available to a large number of SMEs.
WP E - Development of a training method
The objective of this WP was to develop a method for transmitting the know-how developed during the project to third parties (members of the IAGs, etc.), and to put that method into praxis.
The e-learning tool was oriented to wind turbine inspection technicians. It has been structured in modules that contain different chapters. Each chapter contains a didactic unit, with the necessary information about that topic. At the end of each chapter, there are different questions that must be answered in order to evaluate the learning about the topic.
The different modules developed are:
- thermography. It contains all information about thermography, that it is necessary to make any thermographic inspection. It does not focus on wind turbines or any other specific device.
- wind turbines thermography inspection. In this module it is developed the thermography of the different components to be inspected with the PREWIND method. It covers the different electrical and mechanical parts for passive thermography, and the rotor blades for active thermography.
- PREWIND methodology. This module covers the passive and active thermography PREWIND processes.
Besides dissemination, the participating associations (FGW, APPA, APREN, APER, IWEA and GEAL) were also committed to providing training on the PREWIND method to their members.
WP F - Project management
Several 'unofficial' meetings among the partners of the same country were organised in order to structure the development of the projects activities. Frequent meetings for example, among the German partners TTZ, Alphatherm and sometimes with the other RTD, Automation Technology, or with Reetec and Krypton, have taken place. The proximity of the location of these partners has facilitated the exchange of information, the facility of organising short informal meetings to discuss about the project's progress, etc. The communications between the coordinator and the partners did not show any difficulty, although the number of the partners in the consortium is high (16 partners of 7 different countries). Many times during the reporting period, information about the work to be performed, work effort foreseen for each contractor involved and time schedule (deadlines) were supplied to all the consortium by means of emails by the coordinator who controlled the work and collected the works material needed for the foreseen deliverables. All other information was distributed among the partners by means mechanisms such as email, fax, post or telephone. As it has been commented before, the consortium managed to successfully exchange two partners (ISES for APER and TEGOPI for ILIAKO).
After the finalisation of the project PREWIND the consortium can conclude the following:
- The consortium determined the main areas of interest to emphasise the efforts of study for the application of thermography for the improvement of the preventive maintenance of wind turbines: the rotor blades (active thermography), and the electrical components (passive thermography).
- The consortium managed to select the most suitable technology / components for the PREWIND method: type of camera, type of heat source, etc.
- The consortium managed to develop a method for the preventive maintenance of wind turbines using thermography.
Active thermography: the different tests carried out during the development of the project, proved that it is possible to inspect rotor blades while mounted on the wind turbine. The consortium was able to detect failures in the structure of the blades such as delaminations, areas with insufficient adhesion (glue) of the inner reinforcements of the blade, etc. up to a depth of about 12 mm (depending on measuring parameters).
Passive thermography: the consortium developed a procedure for the inspection (and documentation) of the electrical components of wind turbines, to enable the detection of failures at an early stage. For this type of inspection any regular IR-camera can be used.
