Improved Sequence Network Model of Wind Turbine Generators for Short-Circuit Studies

Protective relay settings for wind turbine generators often depend on short-circuit calculations performed using sequence network circuits in rms-based protection software. Traditional assumptions made in deriving the sequence network representation of induction machines result in some error in short-circuit calculations, which could potentially cause incorrect relay settings. A more accurate sequence network model of induction machines is derived in this paper to aid in short-circuit calculations in induction-generator-based wind plants. A rigorous mathematical approach to defining the stator short-circuit current equations under general faults is described and validated with transient simulations. The sequence network model of the induction machine is derived from the closed-form mathematical solutions. An example short-circuit calculation is performed on a simple network in this paper, and found to have a marked improvement in accuracy from traditional sequence network calculation methods for unbalanced faults. Resonant effects of power factor correction capacitors are also described.