A Per Unit Kind Formulation in Power System State Estimation

In Power systems state estimation, in general, measurements of very large and very small magnitudes exist at same time. This variety of measurement magnitudes brings significant numerical difficulties for the state estimation. This picture is even worse when the weights are attributed to those measurements. To solve that problem, in this paper a kind of per unit (p.u.) formulation for state estimation is proposed. This formulation requires a transformation on the measurement set where every measurement becomes of equal magnitude, equal to one p.u.. The gross error analysis is performed on this transformed measurement set avoiding, as a consequence, those numerical problems. The gross errors are detected, identified, and the measurements with errors are corrected using geometrical approaches formulation. After that, the inverse transformation is performed back, that is, going to the original measurement set. The geometrical formulation with two steps on the state estimation formulation is used. The IEEE-57 bus system and the 45-bus equivalent of the Southern part of Brazil are used to perform the tests.