Using tethered drones to investigate ESD in wind turbine blades during fair and thunderstorm weather

Elevated structures are submitted to the atmospheric potential which in fair weather can reach few tens of kilovolts for structures as high as modern wind turbines. In thunderstorm conditions, the potential of the lowest atmosphere below thunderstorms can be much higher submitting tall structures to very high potential differences. The effects of the atmospheric potential to tall structures will be the induction of electrostatic charge and, in case of ground-isolated structures such as some wind turbine blades, the acquiring of a potential. In this paper, we focus on the ESD produced by the fair and thunderstorm weather in vertical isolated wires and we apply the experiments and models to evaluate the ESD in wind turbines. We have found that a vertical isolated wire of 200 m can acquire potentials of about 10 kV and produce ESD of $\sim5$ A with time to peak of the order of 24 ns and electric charge of $1.5 \mu$ C. In the case of thunderstorms, we estimate that peak currents can reach several hundred of amperes being able to induce intense electromotive forces to electrical systems in wind turbine blades and nacelles.