State Estimlatjon with Phasor Measurements

The recent introduction of microprocessors into substations for protection and control makes it possible to measure positive sequence voltage phasors and positive sequence transmission line current phasors in real time. It is necessary to synchronize sampling clocks in various substations in order to put the phasors on a common reference. Techniques for synchronizing sampling along with a method for obtaining positive sequence phasors from samples are reviewed. Although it is possible to use these direct measurements in conventional state estimation algorithms, considerable advantage accrues if the state estimation is reformulated in terms of direct measurements of phasor voltages and currents. The resulting estimation algorithm involves an admittance like matrix with the sparsity of the admittance matrix. The new matrix is real rather than complex even for small X/R ratios for the lines. The algorithm requires no assumptions as to decoupling, flat voltage profiles, small resistance, etc. The algorithm converges in one step with the same amount of computation as one iteration of existing estimators. Examples are given for the IEEE 118 bus system.