In a transmission network, optimal power flow (OPF) is considered as one of the most widely studied non-linear, non-convex and highly constrained problem. While solving the conventional OPF problem, power generation system mainly consists of fossil fuel thermal generators; however, with the increased energy demand, renewable energy sources like wind turbines, solar photovoltaic panels and hydro plants are also introduced. OPF problem is solved using traditional and heuristic approaches to attain the stated objectives that mainly include fuel cost reduction, power loss minimization and emission reduction. These objectives are either optimized individually or in combination where two or more objectives are optimized simultaneously to achieve multi-objective optimization. Further, this study gives an overview of how these economical, environmental and technical objectives are achieved.