1 / 9 C. Heilmann, EWEA 2013 Annual Event, Vienna, 4 – 7 February 2013 REDUCING VIBRATION ISSUES AT SMALL VERTICAL-AXIS WIND TURBINES ON BUILDINGS Dr. Christoph Heilmann 1 (Presenter), Anke Grunwald 1, Michael Melsheimer 1, Prof. Dr. Jochen Twele 2, 3, Norman Pieniak 2, Jonathan Amme 3 1: BerlinWind GmbH 2: Reiner Lemoine Institut gGmbH 3: Hochschule für Technik und Wirtschaft – University of Applied Sciences

2 / 9 C. Heilmann, EWEA 2013 Annual Event, Vienna, 4 – 7 February 2013 REDUCING VIBRATION ISSUES AT SMALL VERTICAL-AXIS WIND TURBINES ON BUILDINGS Content  Investigated vertical-axis small wind turbine (SWT) and vibration measuring system  Potential vibrations systems at SWT and excitation  Campbell-diagram of excitation and natural frequencies  Measured vibration signals during operation  Evaluation of amplitudes produced by rotor speed and harmonics  Conclusions

3 / 9 C. Heilmann, EWEA 2013 Annual Event, Vienna, 4 – 7 February 2013 REDUCING VIBRATION ISSUES AT SMALL VERTICAL-AXIS WIND TURBINES ON BUILDINGS Investigated vertical-axis small wind turbine (SWT) Gravity foundations Minimast Rotor blades Generator, tower connection with dampers Blade holders Speed sensor Accelerometers Wind vane & cup anemometer Accelerometers Long braces Clamp Balustrade Short braces Foot braces Steel tower Strain gauges Elevator house End disk Accelerometers WEST NORTH Measuring system box  Power: 600 W  Rotor: 1.9 x 1.9 m  Hub height: 6 m  Tower support by long and short braces  Gravity foundation: 660 kg each  Gap between tower bottom and roof  Steel framework roof, 7 floor building  Mobile vibration measuring system with up to 17 sensors

4 / 9 C. Heilmann, EWEA 2013 Annual Event, Vienna, 4 – 7 February 2013 REDUCING VIBRATION ISSUES AT SMALL VERTICAL-AXIS WIND TURBINES ON BUILDINGS Vibration systems… 1.Blades + holders 2.Rotor + dampers 3.Top mass + minimast (MM) + tower 4.Long braces (LB) 5.Short braces (SB) 6.Foot bars 7.Gravity foundations 8.Building Blade-mast interaction producing harmonic excitation by 1*n, 3*n and 6*n …and excitation Wind v Mast Blade n Wake u w v

5 / 9 C. Heilmann, EWEA 2013 Annual Event, Vienna, 4 – 7 February 2013 REDUCING VIBRATION ISSUES AT SMALL VERTICAL-AXIS WIND TURBINES ON BUILDINGS SWT-Campbell-Diagram: Harmonic excitations and natural frequencies 15 Critical intersection points from harmonics with potential resonance hazard Bdg high: 12.0 Hz Tower 1 st : 10.5 Hz Bdg low 1 st : 7.9 Hz SB 1 st soft: 42 Hz LB 2 nd, SB 1 st : 47 Hz Tower 2 nd : 22 Hz Natural frequency (NF) from standstill tests Wind speed in m/s Natural or excitation frequency in Hz Wind 60 n20 n 6 n 3 n 1 n Rotor speed in rpm Blades+Holders: 7.5 Hz 20 n and 60 n from generator pole pair number

6 / 9 C. Heilmann, EWEA 2013 Annual Event, Vienna, 4 – 7 February 2013 REDUCING VIBRATION ISSUES AT SMALL VERTICAL-AXIS WIND TURBINES ON BUILDINGS Measured accelerations at SWT minimast and long brace Sensor color code: Horizontal at minimast: blue and red (at rectangles) Middle of long brace: green SWT with long braces and removed top dampers Measurement time: 40 min Wind speed: 3.5 to 5.0 m/s Rotor speed: 80 to 220 rpm If resonance occurs amplitudes exceed gravitational constant: 1000 mg = 1.0 g = 9.81 m/s² At long brace short-time ampli- tudes above 1500 mg = 1.5 g *) Unit: 1 mg = milli g = 9.81 * m/s² Detail Time in s Acceleration amplitude in mg *) Acceleration amplitude in mg *) Minimast 1 Long brace Minimast 2

7 / 9 C. Heilmann, EWEA 2013 Annual Event, Vienna, 4 – 7 February 2013 REDUCING VIBRATION ISSUES AT SMALL VERTICAL-AXIS WIND TURBINES ON BUILDINGS Sliding window vibration evaluation reveals resonances during SWT-operation *) Unit: 1 mg = 9.81 * m/s² NF = Natural frequency *) Tower: 1 st NF by 3 n LB: 1 st NF by 3 n SB: 1 st NF soft by 20 n Tower, 3 rd NF by 20 n Even more resonance issues from harmonics visible than expected! LB: 2 nd NF, SB: 1 st NF by 20 n Blades +holders, 1 st NF by 3 n Tower, 2 nd NF by 6 n MM1, 1 n LB, 1 n MM2, 1 n MM1, 3 n LB, 3 n MM2, 3 n MM1, 6 n LB, 6 n MM2, 6 n MM1, 20 n LB, 20 n MM2, 20 n MM1, 60 n LB, 60 n MM2, 60 n Sensor color code: Horizontal at minimast (MM): blue and red Middle of long brace (LB): green Rotor speed: 30 to 220 rpm Evaluation: Order analysis of sliding window ( 8 revolutions) Excitation frequency from rotor speed 1 n and harmonics 3 n, 6 n, 20 n, 60 n in Hz

8 / 9 C. Heilmann, EWEA 2013 Annual Event, Vienna, 4 – 7 February 2013 REDUCING VIBRATION ISSUES AT SMALL VERTICAL-AXIS WIND TURBINES ON BUILDINGS Conclusions  Dynamics of variable-speed vertical-axis SWT very complex  Harmonics produce resonance issues, despite sub-critical rotor speed  Additional vibration systems formed by SWT components may amplify vibration by their resonance  Total system of SWT and building relevant for resonance issues  SWT design including dynamic analysis imperative, professional manufacture, siting (including dynamics) and installation as well  Recommendations for the investigated SWT: - Fixing gravity foundations - Two-plane rotor balancing due to mass imbalance above limit - Removal of top dampers - Pre-tensioned guy wires instead of long braces  Development of compact load measuring system and sophisticated evaluation software for SWT vibration analysis in process

9 / 9 C. Heilmann, EWEA 2013 Annual Event, Vienna, 4 – 7 February 2013 REDUCING VIBRATION ISSUES AT SMALL VERTICAL-AXIS WIND TURBINES ON BUILDINGS Thank you for your attention! say… BerlinWind GmbH Reiner Lemoine Institut gGmbH Hochschule für Technik und Wirtschaft – University of Applied Sciences