Foreign object impact monitoring on wind turbine blade using FBGs

Although Fiber Bragg gratings (FBGs) have previously been employed for structural health monitoring of wind turbine blades, they were mainly used for measuring the vibration pattern and strain levels. No attempt has been made to monitor the occurrence and in particular to locate Foreign object impact (FOI) on blades. By using an improved energy modulation interrogation technique we showed that short duration impact signals arising from anywhere of a 23m blade from a Vestas V47-660kW turbine can be intercepted by FBGs installed near the hub. By means of the characteristic signature in the received impact signals, we were able to differentiate the approximate region of origins of the impact source. Finally, a signal origin backtracking scheme making use of the signal arrival time differences has been developed to allow the location of FOI to be evaluated from an array of three FBGs. Good location accuracy on the longitudinal coordinate of an impact event was achieved with the scheme over some region of the blade.