An EU-funded project, TowerPower, is developing techniques to continuously monitor the structural condition of offshore wind turbines using non-destructive testing technology and wireless communication
Now entering its final year, the TowerPower project aims to develop a remote, real-time monitoring system to diagnosis the structural condition of offshore wind turbine structures. The organisations working on the project hope to enable windfarm operators to reduce maintenance costs by increasing the time between onsite inspections. More accurate and cost-effective monitoring will help wind turbine operators identify potential structural defects earlier and enable better planning and scheduling of maintenance activity.
Co-ordinated by Capenergies in France, TowerPower has brought together a number of companies and organisations, including Cylsolar in Spain and the Associazione Italiana Prove non Distruttive (AIPnD) in Italy, along with Kingston Computer Consultancy and Moniteye in the UK, Teknisk Data in Norway, WLB in Cyprus and Tecopy SA in Spain. Other participants include research centres such as CETIM in France, Innora in Greece and TWI in the UK.
Among the main ageing phenomena observed in turbine foundations are instances of fatigue cracking in the support towers, flange bolts becoming loose, higher than expected levels of vibration and degradation of the grouted joints between the pile and transition piece. Relying on a network of sensors, amplifying electronics and advanced signal processing algorithms, the participants in the TowerPower project are developing ways to determine the normal behavioural ‘signature’ of the structure and detect any deviation from this signature. The project is also making use of real-time wireless connectivity to enable the condition of structures to be monitored on land, saving time and money.
“To date, operators have struggled to optimise maintenance and inspection regimes,” says the TowerPower consortium, which hopes to offer them bespoke offshore solutions to the problem. “What made this project interesting is that it is focused on monitoring turbine structures offshore,” said project co-ordinator Dr Céline Auger, who works for Capenergies. “There are already a lot of monitoring solutions for the onshore market, but these are often not applicable to offshore windfarms.”
As she highlighted, the last decade has also seen risk-based inspection approaches applied in related industries, such as offshore oil and gas, and these have enabled operators to identify new strategies to inspect and control the deterioration in structures. The TowerPower project sought inspiration from some of these techniques in developing maintenance planning for offshore wind turbines. “We decided to apply some of these techniques to offshore wind turbines and focus specifically on inspecting the transition piece,” Dr Auger explained.
The project partners looked at ways to evaluate defects and tested two ultrasound-based techniques – acoustic emission and guided wave testing, both forms of non-destructive testing that are already widely used in other fields. These enabled researchers to evaluate the condition of large areas and volumes of material and detect the precise location of any defect.
“We are talking about 40–50 sensors per tower, with the data then aggregated and transmitted from the nacelle to a supervisor ashore,” Dr Auger explained. “We have already carried out a number of experiments on models and simulations in order to fine-tune the equipment. By the time the project is completed in 2017, we will have also taken into account environmental and weather conditions.” A number of tests offshore are also planned. These will help to monitor the impact of waves and the robustness of the processing unit, before the entire system is ready for testing on an offshore wind turbine.