MR supports the energy transition at key points – also with regard to the increasing general strain placed on grids. Experts from Power Quality have now installed the first high-frequency filter system in a wind farm for the range of up to 9 kHz. They broke new ground in all aspects, from conception to turnkey handover.

With the Offenbach an der Queich II wind farm, EnergieSüdpfalz and project developer juwi demonstrate how the energy transition works: decentralized, regional, and reliable. Six turbines have been generating clean power for 13,800 homes since 2014, and will continue to do so for at least 20 years. With substantial support from Reinhausen, the turbine operators overcame the last important hurdle in early 2017. Following the successful installation of an innovative high-frequency filter from MR, the wind farm was certified as being unproblematic for the grid of regional energy supplier Pfalzwerke. Dr. Thomas Schlegel, Head of Engineering at Power Quality, sums up the complex project with the words "It was a huge challenge".

At the Offenbach an der Queich II wind farm, six onshore wind turbines with a hub height of 139 meters and a rotor diameter of 120 meters generate 15.8 megawatts. They supply more than 40 million kilowatt hours of power a year. It became evident as early as the wind farm planning phase that measures would be needed to manage the harmonics to ensure reliable operation. This is because the modern wind energy systems deployed at Offenbach use IGBT-based inverter technology, which generates disruptive harmonic currents in a frequency range of up to 9 kHz. This leads to stipulated limit values being exceeded at the connection point to the grid operator by several hundred percent at certain frequencies. To avoid the resulting impairment of grid quality and in order to avoid the potential loss of the operating permit, it was necessary to limit the harmonics. "We were aware from the start that limit values would be infringed," says Thomas Schlegel from Power Quality. "Legislation, however, allows a time period for remedying such infringements. Therefore, our high-frequency filter system was retrofitted at a later date."

As a solution, Power Quality developed the first filter concept that lowers the harmonic level in the frequency range up to 9 kHz over a broad spectrum and significantly reduces individual harmonic frequencies. This was a comprehensive solution, from measurement and simulation up to installation and turnkey handover. During the course of the work, Power Quality broke new ground, not only with respect to the inductances and capacitances of the HF filter circuits themselves but also for other primary components such as circuit breakers, fuses, and special current and voltage transformers. All components of the filter circuit system were qualified for use at frequencies up to 9 kHz in coordination with the suppliers.

The filter circuit system is the first of its kind and was put into operation at the start of 2017. Since then, three filter circuits, installed in a concrete station, with tuning frequencies of 189/3,800/5,600 Hz and a total power of 2,800 kvar, ensure the performance promised at the outset. Michael Link, team leader of grid construction, planning & realization at juwi Energieprojekte GmbH, is completely satisfied. He says, "For us, it was very important to receive everything from a single source. Power Quality completed this very complex turnkey project with expertise as well as transparency for everyone involved." Thanks to this solution, unlimited operation of the wind farm is assured. "We have therefore already commissioned MR to also work on our next project."

MR solutions for onshore wind farms

Power Quality: Clean grids for reliable system operation