Flaws in wind turbine blades detected with radar vision
Defects in wind turbine blades can now be more easily detected thanks to a new scanning method that uses radar to create a cross-sectional view.
According to industry experts, weak points in blade production can result in unplanned additional operation and maintenance costs for wind turbines amounting to several hundred thousand pounds over the entire service life of a turbine.
Wind power has become an indispensable part of an environmentally friendly power supply.
According to the Global Wind Energy Council, the global wind power capacity is predicted to quadruple to 2,110 gigawatts by 2030, constituting 20 per cent of the global electricity supply.
The new technique developed by a team at Fraunhofer Institute for Applied Solid State Physics should increase the efficiency, reliability and durability of wind turbine blades.
The rotors, which are usually equipped with three blades, are the central component of all wind turbines. They convert wind into rotational energy and then into electricity.
Much like the wings on an aircraft, the blades are subjected to enormous external loads and therefore must be designed to be extremely robust.
Modern wind turbine blades are mainly constructed from glass fibre and carbon fibre reinforced plastics so that they can elastically absorb the wind energy from strong gusts without breaking.
For a single blade, up to 100 sheets of glass-fibre webbing are layered on top of each other, shaped and then glued together with epoxy resin.
Quality control is essential at this stage in production: “The difficulty lies in layering the glass fibre 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,” said Dr. Axel Hülsmann, co-ordinator of the radar project.
These kinds of defects, as well as delaminations or fractures, can be identified 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,” Hülsmann said.
At the core of the material scanner is a high-frequency radar, which operates in the W band between 85 and 100GHz with only very few watts of transmitting power.
Specialised software is then used to process the transmitter and receiver signals and visualise the measurement results.
“This enables us to generate a cross-sectional view of the blade, in which defects can be identified in the millimetre range and makes our material scanner significantly more accurate than conventional methods,” Hülsmann explained.
The radar module is based on indium gallium arsenide semiconductor technology. It is extremely light and compact thanks to its monolithically integrated construction, in which different components and functions are integrated into a single chip. Measuring 42 x 28 x 79 mm, it is approximately the size of a pack of cigarettes and weighs just 160 grams.
It has a low power consumption of approximately five watts and is fitted with an integrated microcontroller which emits measurement signals via an internet interface.
Future improvements will see the module’s frequency range extended to 260GHz into the so-called H band. “This will quadruple the bandwidth of the radar module from 15GHz to over 60GHz. While the resolution of the rotor blade cross-section is already very high, our aim is to improve it even further,” says Hülsmann.
In January, a Spanish engineering consultancy demonstrated specially designed blades for small residential wind turbines with impressive energy efficiency for their size.