In this paper, a Two-Step Hybrid State Estimator based on classical SCADA and new phasor measurement unit inputs is presented. The first step is a linear state estimator that utilizes only synchrophasors. The second step is an iterative state estimator that combines conventional measurements with pseudo-measurements obtained from the first step. The developed hybrid model takes advantage of the high sampling frequency of the synchrophasors by running the first step state estimator several times between two consecutive runs of the second step state estimator. The methodology was tested on the IEEE 14 and 57 buses test systems and the real full Croatian transmission power system model. It was also compared with other hybrid models. The proposed formulation of the hybrid state estimator is comparable with other hybrid models in view of accuracy and convergence, and it offers enhanced filtering of measurement errors. Copyright © 2014 John Wiley & Sons, Ltd.

State estimation is one of the most important network management functions, responsible for determining the actual state of the power network based on the network model, available telemetry (analog measurements and digital device statuses) and pseudo measurements. Phasor measurement units (PMUs) provide valuable instantaneous information regarding power system stability and security, and thus have the potential to improve the reliability of the state estimator. Also, measured synchrophasors can be used for transmission line impedance estimation, which results in more accurate power system state estimation, in comparison with the traditional approach that uses catalogue values of the transmission line impedance.

In the paper the proposed algorithm for estimation of transmission line parameters is tested and evaluated. The proposed algorithm uses the weighted least square method with multiple scans of measurements derived from Phasor Measurement Units (PMUs). The network topology and loading conditions in the transmission network change continuously, which can influence the estimation of transmission line parameters with synchrophasor measurements. The case studies in the paper assess the influence of usage of multiple scans of synchrophasor measurements during sudden change of loading and network topology conditions. In the paper the presented algorithm is tested using simulated PMU measurements with and without introduced random errors. High number of measurement scans improves the transmission parameter estimation results but at the same time the calculation time of the algorithm increases. To obtain the optimal results, a compromise between the number of measurement scans and calculation time is needed.