This paper proposes a novel approach for the transmission expansion planning (TEP) problem establishing a new mathematical DC model that allows a multistage planning considering within its formulation the calculation of technical losses of active power and the redesign and repowering of existing and added network elements. The model takes as a base the disjunctive model formulation which is then complemented with three main groups of constraints regarding the mentioned criteria. A study case is performed on a real electrical system existing in Lima, Peru where a flexible expansion plan is obtained, similar to real options valuation method, that contributes to maximize economic and technical efficiency of public and private investments in TEP.