Summary form only given. The electricity markets are changing the power system operation. The increasing power exchanges make it necessary to operate the transmission grids closer and closer to security limits. A problem posed to power system engineers is therefore to find a suitable methodology to combine the results of both steady state and dynamic tools: this can reduce the overall computational effort and the difficulty in the interpretation of results. The paper presents a detailed comparison of the computations that can be performed through steady state and dynamic procedures regarding the power system security. In particular, the analysis of the loadability margins available on the corridor between the Italian power system and the UCTE (Union for the Coordination of the Transmission of Electricity) grids is carried out using both steady state and dynamic tools; the results are compared, pointing out also the security enhancement given by a hierarchical voltage control.