This paper presents a modified formulation for transmission network augmentation planning (TNAP) with regards to the role of corona power loss. The proposed approach applies Peek’s law as a practical non-linear equation to calculate the impact of corona power loss. According to Peek’s law, the corona power loss is sensitive to the geometric mean distance (GMD) and the geometric mean radius (GMR) of bundle conductors as well as environmental issues (e.g. temperature, pressure, and contamination). The proposed model initially determines the corona power loss of each bundle conductor for every TNAP scenario and afterward uses its corresponding cost in the TNAP objective function. Hence, the TNAP problem is a mixed-integer linear programming (MILP) optimization problem minimizing the cost of investment as well as the cost of corona power loss. The proposed approach has been applied to a modified IEEE 24-bus reliability test system (RTS). Simulation results demonstrate the effectiveness of the GMD and GMR of bundle configurations on minimizing the cost of investment as well as the cost of corona power loss.