Electric power systems (EPS) operate according to safety limits defined by the operation planning assessed through computer simulations. Therefore, the components of the electrical grid must be properly represented to ensure secure and economical operation. The technology of synchronized phasor measurement systems allows to obtain records of actual faults, which can be compared to simulation results to check their accuracy. Differences between records and computer simulations of the observed events have been verified in the current EPS. Such differences have also occurred in the Brazilian interconnected system (BIS), mainly related to frequency deviations, with the simulated response being less severe when compared to the observed performance. This may lead the BIS to operate under unsafe conditions, with risk of activating regional protection schemes for load shedding; a possible hasty and undesirable action. In this dissertation, the models of hydraulic and thermoelectric power plants and other parameters that can significantly influence the response of simulations are evaluated, with an emphasis on frequency performance. Disturbances that occurred in the BIS are reproduced using real-time cases, built from state estimator data, together with a collection of dynamic models. The simulation results are compared with the actual records obtained by PMUs (Phasor Measurement Units) installed in the BIS. Parameters such as hydropower head, response of speed regulators and dynamic and static modeling of loads are explored. Impacts and simulations of the multi-infeed phenomenon are also presented. The results show the need for improvements in the models and simulation input parameters of electromechanical transient studies of the BIS. There is a continuous need to observe the systemic and specific validation of models for planning and operation of the BIS.