Defects, Damage, and Repairs Subject to High-Cycle Fatigue: Examples from Wind Farm Tower Design

Wind farm towers are the steel lattice or tube towers serving as the support structures for large power-generating wind turbines. This paper presents a variety of wind farm tower problems encountered over two decades of practice in the wind energy industry. Wind towers are subject to turbine operational loads that cause very highcycle fatigue loading and can give rise to unusual tower problems requiring special repairs. Problems unique to wind towers include: structural damage or collapse from turbine overspeed (“runaway” condition); tower resonance with turbine operational frequencies; turbine fires; and excessive localized member vibrations. Further, wind towers can suffer from construction-related problems: fabrication and weld defects; design deviations; accidental dents and gouges during transport; construction errors during tower erection; and wind-induced vortex shedding oscillations. Each tower problem is discussed in terms of its cause, evaluation method, mitigation strategies, and repair options with special consideration for high-cycle fatigue.