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Integration of large wind farms may get constrained owing to the available transfer capacity of existing transmission networks. This transmission capacity may be enhanced by incorporating series compensation. However, series capacitors are known to cause subsynchronous resonance (SSR) oscillations in synchronous generators. In this study, the potential of SSR is investigated with series-compensated lines connected to wind farms based on single-cage self-excited induction generators. A small-signal mathematical model is developed for the prediction of SSR oscillations in such a wind farm for a study system similar to the IEEE First SSR benchmark system. Eigenvalue analysis is performed through MATLAB at various operating points. This is validated by detailed time-domain simulation through electromagnetic transient simulation software EMTDC/PSCAD for a three-phase-to-ground (LLLG) fault at the remote end of the compensated line. An equivalent circuit analysis is performed to examine the impact of a similar fault at the terminals of the wind farm. It is shown from detailed non-linear simulation that even at a realistic level of series compensation a three-phase fault at generator terminals for low levels of wind farm power generation may subject the generator shafts to potentially dangerous magnitudes.
Date of Publication: December 2011