On October 2002 the Interconnected North-Northeast Brazilian Power System experienced severe power and voltage oscillations in response to a sequence of line and load outages, triggered by a line-to-ground short-circuit in one 500 kV Northeast transmission line. Protective devices tripped out the links between these two systems, and as a result more lines and loads were tripped out. In the following days, the North power system operator detected abnormal operation conditions, such as voltage oscillations, apparently with no specific causes, indicating a high degree of vulnerability. In the years of 2003 and 2004, the adding of new transmission lines and generation units reinforced these interconnected systems. This paper investigates the 2002, 2003 and 2004 dynamic security of these power systems through large (time domain analysis) and small-signal (modal analysis) stability analysis using the October 2002 major disturbance as benchmark. It is also investigated the performance of the available FACTs devices as damping controllers. The dynamic oscillations for the 2003 and 2004 configurations are less severe in terms of amplitude and time duration as well, being damped out faster, resulting in the keeping of the system interconnectivity integrity. The results confirmed that the dynamic security state has been improved. © 2006 Elsevier Ltd. All rights reserved.