This paper proposes a new technique for the detection of inter-turn short circuit faults in the stator and rotor windings of doubly-fed induction generators. The proposed technique is based on the Fast Fourier Transform of the stator instantaneous reactive power. The effectiveness of the proposed diagnostic method to detect these faults is evaluated by extensive experimental tests that were performed for different generator operating conditions, namely for different values of the active and reactive power injected into the grid and different values of the rotor speed. The obtained results show that the proposed approach is appropriate for the identification and quantification of the faults under study.