This paper focuses on the analysis of the electrical network loadability through the power flow model extended to consider the Secondary Voltage Control. Unlike the conventional power flow, the number of power flow variables is increased, keeping constant the number of equations. The application of Newton's method to solve this set of nonlinear equations requires the solution of an under-determined linear system at each iteration. This brings flexibility to obtain operational solutions taking into account performance indexes related to either the iterative process or the power system operation. This so-called extended power flow method has been computationally implemented and tests have been performed considering different loadability and initial solutions. The IEEE 118-bus test system is used to illustrate the application of the proposed methodology.