This paper presents an algorithm for estimating the Total Harmonic Distortion (THD) in the electrical power grid nodes, which is based on a load flow analysis by frequency component. The aim of this algorithm is, on the one hand, to model the linear and non-linear loads which would be part of an electrical network and, on the other hand, to estimate the THD which would appear in the network nodes, in order to evaluate its effects and consequences, as well as to choose the best alternative for solving these problems. The proposed algorithm is able to show the grid’s buses in which the THD achieve a maximum, and could help to choose the most appropriate one to put the electronic devices up, as active power filters, optimizing the system design, permitting the reduction of the system losses and an increase of the energy transmission effectiveness into the grid.