Ferrimagnetic fiber optic sensor system for lightning detection on wind turbines

Due to EMI and isolation problems, current surges with amplitudes up to 200 kA, as they can appear in lightning strokes, are difficult to measure on wind turbines with state-of-the-art devices. Furthermore, fiber-optic magnetic field sensors achieve increasing acceptance and use in highpower applications for current monitoring due to their accuracy, bandwidth, dynamic range, and inherent isolation. Hence, the objective of this thesis was to develop a fiber-optic lightning detection system which is especially focused on wind turbine application. Different technologies and system setups were reviewed before a laboratory setup was realized. Extrinsic fiber-optic magnetic field sensors based on magnetic garnets were chosen for the distributed lightning current measurements. Tests demonstrated the feasibility of the final concept and identified limitations connected to sources of error. Finally, as fiber-optic components are still at high costs, further concepts were evaluated to combine the developed measurement system with other state-of-the-art fiber-optic sensors. These developments could enhance the system’s employment.