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EMTP based study of self-excitation phenomenon in an induction generator

A study of the application of an induction generator in power systems, conducted under Hydro-Quebec sponsorship, is presented in this paper. The phenomenon of self-excitation is investigated using the Electromagnetic Transients Program (EMTP). The results demonstrate that, if the induction generator is sufficiently compensated, it may become self-excited when disconnected from the power grid. High overvoltages then occur which can be dangerous for the insulation integrity of the nonutility generator (NUG) equipment, the local loads and, even worse, for the maintenance personnel. Taking into account the nonlinear aspect of the transformer, simulation results also demonstrate that, after islanding, ferroresonance will occur when the generator voltage level exceeds the saturation voltage level of the transformer. The wave shapes being extremely distorted, this could cause the protective devices to respond incorrectly.