Ali Abur

Observability analysis and measurement placement for systems with PMUs

This paper is concerned about the analysis of network observability and phasor measurement unit (PMU) placement when using a mixed measurement set. The measurements will include conventional power flows and injections as well as phasor measurements for voltages and line currents provided by phasor measurement units. The observability analysis is followed by an optimal meter placement strategy for the PMUs.

Placement of PMUs to Enable Bad Data Detection in State Estimation

As the phasor measurement units (PMUs) start populating the substations, their benefits for different power system application functions are being debated. One of these functions is the bad data processing that is commonly integrated into the state estimation. Bad data detection is closely related to the measurement redundancy in that bad data appearing in critical measurements cannot be detected. Such measurements, however, can be transformed into redundant measurements by adding few PMUs at strategic locations. In this paper, it will be shown that with few extra PMUs, the bad data detection and identification capability of a given system can be drastically improved. Description of the placement algorithm is given, and case studies carried out on different size test systems are presented

Multi area state estimation using synchronized phasor measurements

This paper investigates the problem of state estimation in very large power systems, which may contain several control areas. An estimation approach which coordinates locally obtained decentralized estimates while improving bad data processing capability at the area boundaries is presented. Each area is held responsible for maintaining a sufficiently redundant measurement set to allow bad data processing among its internal measurements. It is assumed that synchronized phasor measurements from different area buses are available in addition to the conventional measurements provided by the substation remote terminal units. The estimator is implemented and tested using different measurement configurations for the IEEE 118-bus test system and the 4520-bus ERCOT system.

A Multilevel State Estimation Paradigm for Smart Grids

The main objective of this paper is to describe a multilevel framework that facilitates seamless integration of existing state estimators (SEs) that are designed to function at different levels of modeling hierarchy in order to accomplish very large-scale monitoring of interconnected power systems. This has been a major challenge for decades as power systems grew pretty much independently in different areas, which had to operate in an interconnected and synchronized fashion. The paper initially provides a brief historical perspective which also explains the existing state estimation paradigm. This is followed by a review of the recent technological and regulatory drivers that are responsible for the new developments in the energy management functions. The paper then shows that a common theoretical framework can be used to implement a hierarchical scheme by which even very large-scale power systems can be efficiently and accurately monitored. This is illustrated for substation level, transmission system level as well as for a level between different transmission system operators in a given power system. Finally, the paper describes the use and benefits of phasor measurements when incorporated at these different levels of the proposed infrastructure. Numerical examples are included to illustrate performance of the proposed multilevel schemes.

Experimental evaluation of EMTP-based current transformer models for protective relay transient study

This paper describes an EPRI study of current transformer (CT) digital models intended for protective relay transient performance analysis. Experimental evaluation of CT models implemented using the Electromagnetic Transient Program (EMTP) was carried out. Two relaying CTs with 600/5 and 2000/5 ratios were used in the study. Experiments in a high power laboratory were performed to obtain transient responses. Simulation of the CT response to the same transient events was set up using three different CT models. They were implemented based on the saturable transformer and nonlinear reactor models available in an EMTP. Comparison of laboratory and simulation results indicates that CT models developed based on the EMTP program give satisfactory results for most of the cases. It has also been discovered that in some instances EMTP models need further improvements. >

Travelling wave based fault location for teed circuits

This paper describes a fault location algorithm for three terminal lines using wavelet transform of the fault initiated transients. The results presented in are extended to the case of three terminal configuration and a new single ended procedure is developed for teed circuits. The algorithm gives accurate results for the case of three terminal lines including series compensated branch, mutual coupled line section and different values of fault resistances. The performance of the algorithm is tested on different scenarios by using ATP/EMTP program and MATLAB Wavelet Toolbox.

A direct numerical method for observability analysis

This paper presents an algebraic method that uses the triangular factors of singular, symmetric gain matrix to determine the observable islands of a measured power system. This is accomplished in a noniterative manner via the use of selected rows of the inverse factors. Implementation of the proposed method presents little additional effort, since sparse triangular factorization and forward/back substitution procedures common to existing state estimators, are the only required functions. The method is further extended for the choice of pseudo-measurements in order to merge the observable islands into a single observable system. Numerical examples are given to illustrate the details of the proposed methods.

Identifying the unknown circuit breaker statuses in power networks

This paper describes an approach by which the circuit breaker status errors can be detected and identified in the presence of analog measurement errors. This is accomplished by using the least absolute value (LAV) state estimation method and applying the previously suggested two stage estimation approach by A. Monticelli (see ibid., vol.8, no.3, p.1143-9, 1993). The ability of the LAV estimators to reject inconsistent measurements, is exploited in order to differentiate between circuit breaker status and analog measurement errors. The first stage of estimation uses a bus level network model as in conventional LAV estimators. Results of stage 1 are used to draw a set of suspect buses whose substation configurations may be erroneous. In the second stage, the identified buses are modeled in detail using the bus sections and the circuit breaker models while keeping the bus level network models for the rest of the system. The LAV estimation is repealed for the expanded system model and any remaining significant normalized residuals are flagged as bad analog measurements, while the correct topology is determined based on the estimated flows through the modeled circuit breakers in the substations. The proposed approach is implemented and tested. Simulation results for cases involving circuit breaker status and/or analog measurement errors are provided.

Robust Measurement Design by Placing Synchronized Phasor Measurements on Network Branches

This paper is concerned about optimal placement of synchronized phasor measurements that can monitor voltage and current phasors along network branches. Earlier investigations on placement of phasor measurement units (PMUs) have assumed that a PMU could be placed at a bus and would provide bus voltage phasor as well as current phasors along all branches incident to the bus. This study considers those PMUs which are designed to monitor a single branch by measuring the voltage and current phasors at one end of the monitored branch. It then determines the optimal location of such PMUs in order to make the entire network observable. The paper also addresses the reliability of the resulting measurement design by considering loss or failure of PMUs as well as contingencies involving line or transformer outages. Developed placement strategies are illustrated using IEEE test systems.

Integrated Use of Time-Frequency Wavelet Decompositions for Fault Location in Distribution Networks: Theory and Experimental Validation

The paper presents a procedure for fault location in distribution networks, based on the use of the integrated time-frequency wavelet decompositions of the voltage transients associated with the fault-originated travelling waves. The proposed analysis of time-frequency wavelet decompositions has been found to improve the identification accuracy of the frequencies associated to the characteristic patterns of a fault location with respect to a sole frequency-domain wavelet analysis. Several laboratory fault tests, carried out by means of a reduced-scale model of a distribution feeder, are used to illustrate the characteristics and assess the performances of the proposed improved procedure. The paper also illustrates the application of the proposed procedure to a transient, originated by a permanent phase-to-phase fault, measured in a real distribution network in which a post-test analysis has identified the faulted branch.