Digital modeling of an induction generator

An induction generator mathematical model in the arbitrary reference frame is presented. With this model, short circuits, lines open at the terminals of an induction generator connected to an infinite bus are simulated. The transformed equations, especially the constraints for lines open for an induction generator with the neutral grounded through an impedance, are derived for the first time. The simulation results revealed some unknown transient characteristics of the small induction generator, such as the stator frequency following the rotor speed quickly during islanding, the nonfaulted phase current is larger than the faulted phase current for a line-to-line fault, and moderately large nonthree phase short circuit currents are sustained. These not only show that the conventional method for short circuit current calculation is not valid for small induction generators, but also suggest a scheme of protecting induction generators, including islanding, using only the local intelligence