In the presented paper, it is shown how the utilization of a systematic three-phase fundamental frequency analysis and three-phase frequency scan can become helpful tools in an electromagnetic transient study. The present methodology was applied to a study of real transmission system expansion, and it allowed for the identification of some rather severe cases which would be very hard to discover through the ordinary transient study procedure. (C) 2003 Elsevier B.V. All rights reserved.6941700143153