Markos Asprou

Enhancement of hybrid state estimation using pseudo flow measurements

Synchronized measurement technology (SMT) is rapidly deployed in power systems, finding applications in many functions of the Supervisory Control and Data Acquisition System (SCADA). The incorporation of synchrophasors provided by the Phasor Measurement Units (PMUs), in the state estimation process has great impact on the state estimator accuracy improvement. In this paper, the incorporation of synchronized measurements in the state estimator (along with the existing conventional measurements) is examined. As a result, a hybrid state estimator that incorporates pseudo power flow measurements is presented. The performance of the estimator is assessed and compared to the conventional state estimator as well as to other hybrid state estimators proposed in the literature.

The Effect of Variable Weights in a WLS State Estimator Considering Instrument Transformer Uncertainties

The state estimator constitutes the cornerstone of the supervisory control and data acquisition system since it provides the power system operating situation in consecutive time intervals. Furthermore, the output of the state estimator is used by other tools responsible for the monitoring and control of the power system. Therefore, there is a need for the power system state estimator to be as accurate and reliable as possible. The main source of uncertainty that may deteriorate the accuracy of a weighted least squares (WLS) state estimator, provided that the network parameters are perfectly known, is the uncertainty that is encompassed in the measurements. It is well known that the measurement chain is not ideal and this information is passed to the state estimator through the measurement weights. In this paper, the effect of the measurement weights, which are calculated by considering both the standard uncertainties associated with the measurement devices and the instrument transformers, on the WLS state estimator is examined.

Dynamic IEEE Test Systems for Transient Analysis

Transient stability analysis is performed to assess the power systems condition after a severe contingency and is carried out using simulations. To adequately assess the systems transient stability, the correct dynamic models for the machines (i.e., generators, condensers, and motors) along with their dynamic parameters must be defined. The IEEE test systems contain the data required for steady-state studies. However, neither the dynamic model of the machines nor their specific parameters have been established for transient studies. As a result, there is a demand for test bed systems suitable for transient analysis. This paper defines dynamic machine models along with their parameters for each IEEE test bed system, thus producing full dynamic models for all test systems. It is important to mention that the parameters of the proposed dynamic models are based on typical data. The test systems are subjected to large disturbances, and a case study for each test system, which examines the frequency, angle, and voltage stability, is presented. Furthermore, the proposed dynamic IEEE test systems, implemented in PowerWorld, are available online.

Optimal PMU placement for improving hybrid state estimator accuracy

With the deployment of Synchronized Measurement Technology (SMT), many applications of the existing Supervisory Control and Data Acquisition (SCADA) system have been significantly improved. SMT may be used in many SCADA functions; one of its fundamental applications is in state estimation. The Phasor Measurement Unit (PMU) is the main component of the SMT, providing synchronized phasor measurements from the power system. It is therefore important to determine the optimal PMU locations for improving certain aspects related to state estimation. In this paper, the optimal PMU placement for improving state estimation accuracy is examined. The state estimator incorporates both conventional and synchronized measurements as the full deployment of PMUs in the power systems is neither affordable by electric utilities nowadays, nor practical. The concept of the hybrid state estimator as well as the proposed methodology for determining optimal PMU placements for improving its associated accuracy is presented in this paper. The hybrid state estimator is applied to the IEEE 14, 30, and 57 bus systems. The proposed PMU placement methodology is utilized to determine the optimal PMU placement in these systems. The accuracy of the conventional and hybrid state estimator when applied to IEEE 14, 30, and 57 bus system is also compared.

Measurement data aggregation for active distribution networks

Power Quality indicators are still conveyed into a classical paradigm of power systems where the steady state operation is governed by quasi-constant frequency. Moreover, distribution grids are considered as network structures with solely load behavior. The standards proposing power quality descriptors are built on models, which seem to limit the possibilities of achieving real time control targeting highly efficient energy transfer, at least in all-electric grids. In this paper the measurement data aggregation algorithms proposed in the well-known standard IEC 61000-4-30 are discussed based on an analysis performed on voltages and frequency measurements. Raw data are obtained from PMUs installed in various nodes of active distribution grids with reporting rate of 50 frames per second. New aggregation algorithms for frequency, rate of change of frequency and unbalance coefficient appear to be needed.

The use of a PMU-based state estimator for tracking power system dynamics

Monitoring of the power system states in real time, especially after the occurrence of a fault, can enhance the situational awareness of the power system operators. Although the state estimator is designed for monitoring steady state conditions of the power system, the advent of Synchronized Measurement Technology (SMT) can make the state estimator a helpful tool for monitoring the power system operating condition in quasi real time. In this paper, the use of a linear state estimator using only synchronized phasor measurements will be presented. The innovation lies in the use of the linear state estimator for the estimation of the states of the system in the presence of a fault. With the proper PMU placement, all system buses can be monitored accurately and the voltage/angle behavior can be tracked with precision.

The effect of parameter and measurement uncertainties on hybrid state estimation

State estimation constitutes the cornerstone of a Supervisory Control and Data Acquisition (SCADA) system, providing the operating situation of the power system in consecutive time intervals. With the incorporation of the Synchronized Measurement Technology (SMT) in the power system measurements layer, the state estimation is among the applications whose performance is improved considerably. In this paper, two sources of uncertainty that deteriorate the performance of a hybrid state estimator, that uses both synchronized phasor measurements and conventional measurements, are examined. Specifically, the measurement uncertainty and the uncertainty arising from the limited knowledge of the transmission line parameters are considered. These uncertainties are associated with the inputs of the hybrid state estimator and their effect on the overall accuracy of the process is investigated. The methodology is tested using the IEEE 14 and 118 bus systems.

A Two-Stage State Estimator for Dynamic Monitoring of Power Systems

Fault recorders can track the transients in the power system during a fault. However, they cannot provide a wide area picture of the power system operating condition. The provision to track the transients is of great interest for the power system operators. In this paper, a two-stage state estimator (SE), based on both conventional and phasor measurement unit (PMU) measurements, is presented. The estimator is able to track the dynamics of the power system states during a fault. The advantage of the proposed SE is that it does not require full power system observability by the PMU measurements. The two-stage SE was successfully tested on the IEEE 14 and 118 bus systems.

Estimation of transmission line parameters using PMU measurements

Transmission line parameters are affected by several factors, such as ambient temperature, mutual coupling of parallel lines, and erroneous transmission line length. Further, the several joints, especially at the line ends, cause additional changes in the calculated line parameters. These factors are rarely taken into consideration resulting to obsolete line parameter databases. The error that is encompassed in the values of the transmission line parameters can be up to 30% of their nominal value. In this paper, a methodology for estimating the actual parameters of transmission lines represented as a nominal pi model is proposed. In this methodology the PMU measurements at the one end of the line and the estimated states from a hybrid state estimator for the other end of the line are required. The proposed methodology is applied to the IEEE 14 bus system and the results are demonstrated in this paper.

The effect of time-delayed measurements on a PMU-based state estimator

The complete integration of the Synchronized Measurement Technology (SMT) in the power systems will bring about fundamental changes to the applications of the control center. One of the natural applications of the SMT is the state estimation. Although the state estimator is used for monitoring the steady state operating condition, it is envisioned that in the near future, a PMU-based state estimator will be able to monitor the dynamic behavior of the power system states. In such an application, the transfer delay of the PMU measurements should not be ignored. In this work, the effect of the PMU measurements transfer delay on the accuracy of a PMU-based state estimator is examined. Further, the optimal waiting time of the Phasor Data Concentrators (for sending information to the control center), and the time execution of a PMU-based state estimator for capturing accurately the state transients during fault conditions are also examined.