AC load flow based model for transmission expansion planning

•Linear DC load flow model adds new lines iteratively to solve TNEP problem.•Mixed integer linear DC model adds/deletes new lines maintaining the voltage loop equations.•AC load flow model considers the reactive power injection from the generators.•AC load flow model considers the system losses and bus voltage limits. This paper proposes an accurate model to solve the transmission network expansion planning (TNEP) problem. The TNEP problem is solved using a linear DC model, a mixed integer linear DC model, and the proposed accurate exact mixed integer non-linear AC model. A 19 bus system which is a part of the 220 kV Egyptian transmission network is used for the verification of the proposed load flow models. The proposed exact non-linear AC load flow based model that considered control of active and reactive power flow in the network and considered the power losses in the system yielded promising results when compared to DC load flow based linear and mixed integer linear models. It provided a planned network with least number of added lines and consecutively with the least cost.