In the present research, a methodology was developed to determine the faults location in transmission lines, a hybrid model was developed that combines the advantages of the Relief algorithm with those of the Wavelet Transform in the presence of a contingency. For this, the information of the voltage and current synchrophasors obtained from the PMUs deployed in the power electrical system is used so as to minimize the number of them and to maximize the observability of the electrical system by means of a mixed mixed linear programming (MILP). The proposed method was tested in the 9 and 14 IEEE test systems against contingencies, finding the line with problems and the distance at which the fault occurs.