The electric power systems operate nowadays close to the security limits. In order to protect the grid against severe contingencies and to increase the security, The aim of this research work includes to study the system performance under different operating conditions to analysis differences power system contingency, determines the voltage of the buses and determines the line flows by using power world simulator, So that we have built three system 5 bus, IEEE14 bus and IEEE 30 bus then analyze the data from the simulation to determine whether the systems secure or not secure.