The development of a novel rotor protection for large doubly-fed induction machines

This paper proposes a novel protection scheme for large doubly-fed induction motor generators (several hundreds of MVA), typically used in variable speed pump storage hydropower stations. The protection scheme makes use of non-conventional instrument transformers (NCITs) and low frequency injection to monitor the rotor currents, voltages and frequency under normal and faulty conditions. Two NCITs of different technology were investigated; the Rogowski coil and the optical sensor. The experimentation was validated using simulation and practical implementation on a low power representative test rig.