Subsynchronous Impact of Series Compensation on Induction Generator Based Wind Farm

Series compensation of transmission networks is being increasingly considered for integration of large wind farms to transfer bulk power. This article presents an extensive analysis of the potential of subsynchronous resonance in wind farms connected to a series-compensated line. The impact of symmetrical faults at different locations in the network is studied in detail. An equivalent circuit model is presented to calculate the resonant speeds of the aggregated induction generator for varying power outputs and series compensation levels. This study is validated by electromagnetic transient simulations using PSCAD/EMTDC software. Two sets of results are presented: one for wind farms of different megawatt ratings, and the other for a wind farm with different megawatt outputs. Scenarios are described for a wind farm connected to a line with a realistic level of series compensation, when a symmetrical fault at the wind plant terminal may result in high shaft torques. Recurrence of such faults can potentially lead to generator shaft failure due to cyclic fatigue. To mitigate subsynchronous resonance, a static synchronous compensator (STATCOM) is proposed at the terminals of the wind farm. The STATCOM not only stabilizes the wind farm but also reduces the peak shaft torque, thereby obviating the potential of shaft damage due to subsynchronous resonance.