This paper presents the solution to an optimal power flow problem for planning the daily operation of a transmission system in a co-simulation environment between PSCAD/EMTDC® and MATLAB® tools. This scheme is applied for a typical five-bus power system, proposed in the literature and to which the steady-state modeling is performed for the formulation of the multi-period OPF, with the MATPOWER® tool, which is open source and designed to work in the MATLAB® environment. This model defines typical load profiles of the commercial area to minimize the system's operating costs. The results show the integration between the two computational tools, presenting the operating points of the thermal generators as control variables according to the proposed demand curves. The results demonstrate the versatility to take advantage of the strengths of PSCAD® for the simulation of electromagnetic transients of electrical systems and the use of MATLAB® solvers for optimization problems.