OPTIMAL POWER FLOW POWER SYSTEMS OPERATION ACTIVE POWER DISPATCH NONLINEAR OPTIMIZATION NETWORK MODEL HYDROTHERMAL GENERATION SCHEDULING NETWORK FLOW SECURITY DC OPTIMAL POWER FLOW SECURITY CONSTRAINTS POWER FLOW CONTROLS LONG-TERM OPERATIONAL PLANNING POWER SYSTEMS HYDROTHERMAL INTERCONNECTED POWER SYSTEM POWER FLOW CONTROL POWER TRANSMISSION HYDROELECTRIC-THERMAL GENERATION LARGE-SCALE POWER SYSTEM