Novel Differential Protection Technique for Doubly Fed Induction Machines

Doubly fed induction machines (DFIMs) typically work as a generator in wind turbine systems and as motor/generator in pumped-storage hydropower plants. Nowadays, they have an important role in the integration of renewable energies in power systems. This paper presents a new technique for differential protection of DFIMs, including the rotor. The proposed protection, which is based on the comparison of the vector components Id-Iq of the rotor and stator currents, can protect the whole induction machine during the internal faults. This protection considers the dynamic variation of the rotor frequency and the extremely low rotor frequency along the different operation points of the DFIM. The proposed method is validated using simulations on a 2-MW DFIM and the experimental results are obtained in a laboratory setup. The results show that the proposed differential protection effectively protects the entire induction machine during internal faults and does not trip in case of external faults.