Frequency scanning study of sub-synchronous resonance in power systems

This paper presents a frequency scanning analysis for detecting the potential of subsynchronous resonance (SSR) in induction generator based wind farms. Two types of induction generator: single-cage and double-cage based wind farms are considered. The wind farms are connected to modified IEEE First Benchmark and IEEE Second Benchmark System. Detailed positive sequence model of the study systems are developed and frequency scanning is carried out by calculating effective impedance looking from the rotor circuit of the induction generators. It is found that induction generator based wind farms are quite susceptible to SSR due to induction generator effect when they are connected to IEEE First Benchmark System. In this case, SSR may occur at realistic levels of series compensation if the wind farms employ double-cage induction generators. Incidentally, no SSR phenomenon is found in wind farms which are connected to IEEE Second Benchmark System. The frequency scanning results are compared and validated with eigenvalue analysis. Hence, frequency scanning technique can be successfully utilized for initial investigation of any potential for SSR in wind farms connected to a series compensated transmission line.