Severe Contingencies Analysis in Portuguese Transmission System

Nowadays when utilities are faced with increasing requirements regarding quality of service, it is important to be aware that severe contingencies can happen, in an unpredictable way which far exceeds all the security principles used for planning and system operation. In any electricity transmission system, a security condition must be assured - either in steady or in transient state - otherwise the essential service provided to costumers could be severely jeopardized. Present day quality of service requirements that are imposed on the electrical utility companies force them to develop efficient processes to analyze and react to incidents that can happen in an unpredictable way and far exceed all the security principles used. The simulation and analysis of these scenarios allow us to minimize the risk of system unbalance and voltage collapse. The steady state simulations of the Portuguese transmission system were made in PSS/E software from Siemens Power Transmission Distribution, Inc., using savecases that represent pictures of the real system. The simulation results presented focus on aspects like energy not supplied, generation lost and topological changes resulting from an incident, which will affect mainly the power flow distribution within the grid elements that will remain in service (connected) and the voltage level in the system bus-bars. These results allow us to be better prepared to face these severe disturbances, defining procedures for emergency situation and training the control room operators.