The idea of optimal power flow (OPF) was introduced in the early 1960s as an extension of conventional economic dispatch to determine the optimal settings for control variables while respecting various constraints. The term is used as a generic name for a large series of related network optimization problems. The development of OPF in the last two decades has tracked progress closely in numerical optimization techniques and advances in computer technology. The model may also include other auxiliary generating units and representation of internal or external parts of the system are used in deciding the optimum state of the system. The trade-offs between reinforcements and control options are decided by carrying out OPF studies. It is clarified when a control option maximizes utilization of an existing asset , or when a control option is a cheaper alternative to installing new facilities.