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Workshop for the WERAN Project - Interaction of Wind Turbines with Terrestrial Navigation and Radar


For the first time, measurements performed on systems for air navigation control and surveillance have shown that wind turbines (WT) may impose influences on the signal integrity of such systems. These results were found during a research project coordinated by the Physikalisch-Technische Bundesanstalt (PTB). The measurement instrumentation and methods used up to now have not been able to identify the interference caused by WT. The measurement results will be used to improve and harmonize the modeling and assessment of those interferences.

On December 6th and 7th, 2017, a workshop concerning interaction of wind turbines with terrestrial navigation such as very high frequency omnidirectional radio ranges (VOR) and radar systems was held at PTB. Representatives of the German air traffic control (DFS) were invited as well as representatives of the Federal Supervisory Authority for Air Navigation Services (BAF), of the German Meteorological Service (DWD), as well as representatives of the state authorizing departments, of the authorizing ministries, representatives of the Bundesverband Windenergie (BWE e.V.), of the Fördergesellschaft Wind und andere dezentrale Energien (FGW e.V.), of the Windagentur an Land (FA Wind e.V.), developers and other scientists.

First, the results of the research project WERAN – which is carried out by PTB as coordinator and its partners - were presented. On the second day, other scientist groups working on this topic had the possibility of presenting their results. In total, all interested groups were invited to discuss the current scientific findings and the presented results in detail. Next to expert questions, the economic situation was a point of discussion as the findings may impact the official permission of new wind turbine building applications. The BWE published the results of its member survey in 2015 which shows that around 1,600 WT with a total output of roughly 5 GW and amounting to an investment volume of more than 5 billion Euros could not be installed because of missing building permissions.

The research project WERAN focused on analyzing and quantifying the possible interaction of WT with conventional and doppler VOR as well as radar systems through the development of a state-of-the-art measurement instrumentation and measurement technique. At the same time the project partners developed a highly capable numerical simulation analysis methodology.

The comparison of measured and simulated data is one of the key elements of the project to quantify the interference of wind turbine installations with air navigation and surveillance. This is the reason why only parameters are considered to determine the possible interaction which can be obtained by measurements as well as by simulations. These are the electromagnetic fields in the airspace on-site. Now PTB and its partners are able to measure the signal contents in defined scenarios for real signals of all major terrestrial navigation/surveillance and radar systems as signal-in-space. On the one hand these can be unaffected signals and on the other hand as well signals measured behind a wind farm. The resolution of the high-end high-frequency measurement instrumentation is better by at least two orders of magnitude than e.g. the target figure to be considered of maximum angular errors at DVOR (Doppler Very High Frequency Omnidirectional Radio Range). The high frequency measurement instrumentation is mounted on an octocopter with precision navigation for the on-site investigations/measurements. In this way flight movements of the octocopter can be pre-defined in detail and can be retraced later on. The measuring data contains the recorded bandpass signal as well as information on location and time. They are synchronized and stored with a sufficiently high data rate. During the flights details of the measurement data can be observed in real time on a tablet computer. The operator can control the measurement unit during its operation, e.g. by switching frequencies using the tablet computer.

A comprehensive series of experiments has shown scientifically interesting results. For example, it was possible to measure signals of a DVOR in 8 km distance behind four big WT with a hub height of 140 m and 112 m rotor diameter during operation, during powering down, in standstill as well as during powering up the four WT. Investigations at a wind farm with eight rather small WT in a distance of 2.5 km to a DVOR showed a qualitative as well as a quantitative accordance of the angular errors of only a few tenth of degree in measurement and numeric simulation and even a good level of reproducibility. Thus, for the first time it was possible to proof the effect of WT on angular errors at DVOR with measurements. Until now, the conventional flight inspection has not been able to show proof of this interference.

The measurements at modern pulse compression radar systems of air traffic control and air defense showed how radar impulses on their way to their destination in airspace are influenced by WT. Through the record of every single pulse it was possible to determine even parameters as the horizontal beam width of the antenna diagram, the front-to-back ratio of the antenna, their side lobe suppression as well as the viewing height of the radar over ground.

During the remaining time of the project WERAN, more sites of WT near CVOR/DVOR will be investigated together with DFS in order to yield the most comprehensive data basis possible. During the upcoming investigations the operating parameters of WT such as orientation/direction of the nacelle, the orientation of the rotor blades, and operation and downtime of the WT will be adjusted as far as possible to obtain most detailed information of the impact on the signal-in-space.

Support was granted by the Federal Ministry of Economy and Energy based on a decision of the Parliament of the Federal Republic of Germany, FKZ: 0325644A-D.



Picture 1: Octocopter for on-site measurements of electromagnetic fields


Participants of the WERAN workshop

Picture 2: Participants of the WERAN workshop