Performance evaluation of a sub-harmonic protection relay using practical waveforms

Sub-synchronous resonance is a phenomenon in which electrical energy is exchanged between generators and transmission systems below the nominal power frequency (50/60Hz). It can be caused due to many reasons such as interaction of a series compensated transmission line with a synchronous generator, interaction of a generator with a power electronic controller in HVDC transmission system, interaction of a series compensated transmission system and a power electronic control system in a Type 3 wind turbine generator, etc.. This paper evaluates the performance of a sub-harmonic protection relay using practical waveforms captured by the digital fault recorders during sub-synchronous resonance events generated due to the interaction of series compensated transmission lines with Type 3 wind turbines.