Apr 12 2017
The innovative radar scanner from Fraunhofer IAF enables defects in the material composition of the wind turbine blades to be detected with significantly greater accuracy. This cuts production and operating costs.
A steady increase has been observed in the share of wind energy in the electricity mix, and this increase is accompanied by a growing demand for high-quality and efficient wind turbines with the “Made in Germany” seal.
The rotor blades are considered to be centerpiece of a wind turbine, with their maintenance and production subject to rigorous testing procedures. It is now possible to detect the defects in the material composition of the wind turbine blades by using the innovative radar scanner from the Fraunhofer Institute for Applied Solid State Physics IAF. This detection can be carried out with greater accuracy and can be visualized in a cross-sectional view, thus saving costs in operation and production.
Wind power has now become a crucial part of an environmentally friendly power supply. About 50 gigawatts, equivalent to 12% of the total power in Germany, are produced by more than 28,000 wind turbines with an upward trend. The Global Wind Energy Council points out that the global wind power capacity will quadruple to 2,110 gigawatts by 2030 – constituting 20% of the global electricity supply.
For this reason, it is important for wind turbines to become more durable, reliable and efficient. Industry experts feel that weak points in blade production, for instance, could result in unplanned maintenance and operation costs amounting to several hundred thousand euros over the entire service life of the turbine. A material scanner for checking the quality of rotor blades has been developed by Fraunhofer IAF, in order to increase the reliability and efficiency of wind turbines. Radar-based technology will help in detecting the defects in the material composition of the wind turbine blades in a more detailed manner.
Identifying defects in composite plastics
The rotors are the key components of all wind turbines. Usually equipped with three blades, the rotors convert wind into rotational energy, and then into electricity. Similar to the wings on an aircraft, the blades are subjected to huge external loads and must be designed to be extremely robust.
Modern wind turbine blades are mostly made from glass fiber and carbon fiber reinforced plastics (GFRP/CFRP). This allows them to elastically absorb wind energy from strong gusts without breaking. For one blade, almost 100 sheets of glass fiber webbing are layered on top of each other. They are then shaped and glued together with epoxy resin. Quality control is crucial at this phase in the production process.
The difficulty lies in layering the glass fiber sheets flat before they are glued, without creating undulations and folds, and avoiding the formation of lumps of resin or sections of laminate which don’t set when applying the epoxy
Dr. Axel Hülsmann, coordinator of the radar project and group manager of sensor systems at the Fraunhofer IAF
It is possible to identify such defects, fractures or delaminations on a large-scale using infrared thermography.
Our material scanner enables defects to be identified with even greater accuracy, as depth resolution is also possible with radar technology – even in places where ultrasound methods fail.
Dr. Axel Hülsmann
Cross-sectional profiles with millimeter precision
A high frequency radar at the core of the material scanner works in the W band between 85 and 100 GHz with just very few watts of transmitting power. The transmitter and receiver signals are then processed with the help of specialized software, which also aids in visualizing the measurement results.
This enables us to generate a cross-sectional view of the blade, in which defects can be identified in the millimeter range, and makes our material scanner significantly more accurate than conventional methods.
Dr. Axel Hülsmann
The radar module is developed based on indium gallium arsenide semiconductor technology. This module is compact and extremely light because of its monolithically integrated construction. Varied functions and components are combined into a single chip. It measures 42 x 28 x 79 mm, almost the size of a pack of cigarettes, and weighs a mere 160 grams. This module has a low power consumption of about 5 watts and is fixed with an integrated microcontroller which gives out measurement signals through an internet interface.
Going forward, the frequency range of the module will be extended to 260 GHz into the so-called H band.
This will quadruple the bandwidth of the radar module from 15 GHz to over 60 GHz. Whilst the resolution of the rotor blade cross-section is already very high, our aim is to improve it even further.
Dr. Axel Hülsmann
Reduced downtime means lower maintenance costs
In the future, the Fraunhofer IAF material scanner will be used in the production of rotor blades and could also find a role in maintenance. Here, it could help to classify defects, such as those that are caused by the impact of birds.
Currently, the routine testing of rotor blades is mainly performed by hand: an expert knocks on the blade with a hammer and can tell from the tone whether there are any defects in that section. An automated solution, supplemented by our radar technology, could vastly reduce the downtime of wind turbines and thus save costs.
Dr. Axel Hülsmann
This is specifically true for the manual maintenance of offshore wind turbines, which is reached by boat, at times on rough seas. This indeed is a time-consuming process.
It is extremely complicated to integrate alternative testing technologies, such as ultrasound solutions, into maintenance procedures.
Water or gel has to be utilized as a coupling agent, as every air pocket between the sensor and measured part muffles the ultrasound signal to a considerable extent. Whilst this entails certain side effects, it is nonetheless possible when checking for defects during rotor blade production.
Applying water or gel to wind turbine blades which are 100 meters in the air is extremely complicated, because it allows for non-contact remote sensing. Radar is the optimal solution in this case.
Dr. Axel Hülsmann
The Fraunhofer IAF radar scanner can also play a vital role in the development of innovative material inspections in various other industries, for instance the aircraft industry. In newer aircraft such as the Airbus A350 or the Boeing 787 Dreamliner, the wings especially are built out of lightweight composite materials.
In the aircraft industry, as in the plastics industry, an accurate and rapid defect test during both production and maintenance can save costs and prevent damage caused by material fatigue.
Dr. Axel Hülsmann
Material scanner at the Hannover Messe 2017
The Fraunhofer IAF will be launching the material scanner ideal for testing wind turbine blades at the Baden-Württemberg shared booth at the Hannover Messe. This will be in hall 17, booth B76, between April 24 – April 28 2017. The displayed radar scanner will be performing tests of a variety of composite plastics, and will also demonstrate the potential for innovative radar technology.
Image Source: Tim Siegert, Fotolia.com