Enhanced Performance of Developed Two-Step (Hybrid/PMU) Linear State Estimator Model

Since the beginning in the 1960’s, the power system network has been growing larger and more complex; operators used to collect a set of incomplete and unsynchronized measurements and inserted them into a load flow calculation in an attempt to find the operating point of the system [1]. This was a very inexact approach and in most times led to divergence of the load flow equations. In 1970, Schweppe and Wildes suggested new methods of implementing state estimation in power systems [2]. Then the analysis of real time data received from Remote Terminal Units (RTU) in the Supervisory Control and Data Acquisition (SCADA) system is possible, more accurate and extensive but it was difficult to get the voltage phase angle because time reference is not synchronized. Synchronized Phasor Measurements (PMU) were launched in mid-1980s . These are digital metering devices used in conjunction with a timed GPS signal to provide synchronized phasor measurements at different locations in the power system. With GPS synchronization, measurements are synchronized regardless the large distances which may separate metering points and the magnitude and phase angle of voltages and currents are determined accurately [3]. In 1992, early prototypes of the PMU were built at Virginia Tech, and Macrodyne constructed the first PMU (model 1690). In the latter years, PMUs were continuously inserted in the monitoring and control of power systems. Consequently the PMU is used in distributed dynamic state estimator on the widest range. PMUs are used to measure voltages, current, angle and frequency, and can supply real-time information about the state of large portions of grids and allow one to obtain a true snapshot of the power system, making the technology for real-time supervision of power systems clearly at hand [4]. A model of new two-step hybrid state estimation using SCADA and PMU measurements is discussed in this paper. This model is implemented in Alexandria 22-bus system for enhancing the state estimation and gets better dynamic behavior. This paper is organized as follow: a review about the traditional state estimation, state estimator using PMU only, the hybrid SCADA/PMU and their algorithms is presented in section II. The new proposed two-step (hybrid/ PMU) is proposed in section III. Section IV shows the case study model structure used to simulate the proposed algorithm. The simulation results carried out on Alexandria 220kV power system are shown in section V, and are followed by conclusion in section VI.