J. B. A. London

Offline Detection, Identification, and Correction of Branch Parameter Errors Based on Several Measurement Snapshots

This paper proposes a three-stage offline approach to detect, identify, and correct series and shunt branch parameter errors. In Stage 1 the branches suspected of having parameter errors are identified through an Identification Index (II). The II of a branch is the ratio between the number of measurements adjacent to that branch, whose normalized residuals are higher than a specified threshold value, and the total number of measurements adjacent to that branch. Using several measurement snapshots, in Stage 2 the suspicious parameters are estimated, in a simultaneous multiple-state-and-parameter estimation, via an augmented state and parameter estimator which increases the V-θ state vector for the inclusion of suspicious parameters. Stage 3 enables the validation of the estimation obtained in Stage 2, and is performed via a conventional weighted least squares estimator. Several simulation results (with IEEE bus systems) have demonstrated the reliability of the proposed approach to deal with single and multiple parameter errors in adjacent and non-adjacent branches, as well as in parallel transmission lines with series compensation. Finally the proposed approach is confirmed on tests performed on the Hydro-Québec TransÉnergie network.

Redundancy and Observability Analysis of Conventional and PMU Measurements

This letter shows that the <i>H</i> _Delta matrix can be used for redundancy and observability analysis of metering systems composed of PMU measurements and conventional measurements (power and voltage magnitude measurements). The <i>H</i> _Delta matrix is obtained via triangular factorization of the Jacobian matrix. Observability analysis and restoration is carried out during the triangular factorization of the Jacobian matrix, and the redundancy analysis is made exploring the <i>H</i> _Delta matrix structure. As a consequence, the <i>H</i> _Delta matrix can be used for metering system planning considering conventional and PMU measurements. These features of the <i>H</i> _Delta matrix will be outlined and illustrated by numerical examples.

Geometrical approaches for gross errors analysis in power systems state estimation

In this paper, a geometrical based approach is used to define the undetectability index (UI) that gives the distance of a measurement from the range of the jacobian matrix. The higher the value of this index the closer this measurement will be to the range of that matrix; the error in measurements with high UI is not reflected in their residues. A critical measurement has infinite UI, belongs to the range of the Jacobian matrix, and its error is totally masked. Using the UI, it is shown measurements not classified as leverage points, and having large masked gross errors in the state estimation process. As example to illustrate the way that UI index works, a two bus power system will be used; to test the index efficiency in identifying the measurements that have the gross errors masked by the state estimation process the IEEE-14 bus system will be used.

Network observability: identification of the measurements redundancy level

In this paper, a new method to identify the redundancy level of each measurement associated to an observable power system is proposed. The proposed method also identifies the critical measurements, and sets of measurements that removed at same time from the measurement set make the power system unobservable. The redundancy level is very important to operators in order to guide the search for adequate reinforcement of the available measurement set. The proposed method is based on the linear dependency relation of the rows of the Jacobian matrix. To determine this relation, a convenient exchange of basis in the state space is made. The exploration of sparsity techniques and some adaptations make the proposed method simple and fast. This method has been tested in the IEEE-14-bus system, and in two realistic systems of the Brazilian utilities (one of them is a 121-bus system from ELETROSUL, and the other is a 384-bus system from CHESF-Companhia Hidroeletrica do Sao Francisco).

Energy restoration in distribution systems using multi-objective evolutionary algorithm and an efficient data structure

This paper proposes a new strategy for solving the service restoration problem in large-scale Distribution Systems (DS). Due to the presence of various conflicting objective functions and constraints, the service restoration task is a multi-objective, multi-constraint optimization problem. As a consequence, finding feasible solutions is a hard task. The proposed strategy uses a new tree encoding, called Node-depth Encoding (NDE), and a modified version of the Non-Dominated Sorting Genetic Algorithm-II (NSGA-II). Using NDE and its operators the proposed strategy generates only radial configurations without disconnected areas reducing the running time necessary to find feasible solutions. On the other hand, the use of the modified version of the NSGA-II enables an efficient exploration of the search space. The efficiency of the proposed strategy is shown using a Brazilian DS, with 3,860 buses, 635 switches, 3 substations, 23 feeders, 2 transformers of 50MVA and 1 transformer of 25MVA.

A power flow method computationally efficient for large-scale distribution systems

Due to several factors, conventional power flow does not present a good performance in solving distribution system power flow. Thus, the Backward and Forward Sweep method is the one more utilized in this kind of network, mainly in radial distribution system. In spite of there be several variants of this method, two more utilized are Current Summation Method and Power Summation Method. In this paper is proposed a data structure that guarantees better efficiency to these methods. It is known by Node-depth Encoding, and it can improve their performance. Mainly when they are utilized in large distribution networks and when is necessary to run the power flow many times. It will be presented results obtained by two methods well known at the literature and these methods with node-depth encoding. The results guarantee that it can be utilized in several applications, even though in larger distribution systems.

Method for meter and RTU placement for state estimation purposes

This paper presents a method that allows, in a straightforward manner, observability analysis and restoration, local measurements redundancy analysis, restoration and identification as well as increasing in the redundancy of critical remote terminal units (RTU). Consequently the method is a useful tool either to design a new measurement set or to upgrade an existing one. The proposed method allows the obtention of measurements placement plans that, besides making the system observable, maintain the observability when 1 or 2 measurements are lost, at same time, or even when an RTU is lost In order to do that, the proposed method analyzes the structure of the H/spl Delta/ matrix, obtained from a triangular factorization of the Jacobian matrix. To prove the efficiency of the proposed method, several tests were made using the IEEE-14-bus system and a 121-bus system from ELETROSUL, a Brazilian utility.

Node-depth Encoding and Evolutionary Algorithms applied to service restoration in distribution systems

Service restoration in distribution systems is usually formulated as a multi-objective and multi-constrained optimization problem. In order to improve the performance of Evolutionary Algorithms (EAs) applied in such problem, a new tree encoding, called Node-depth Encoding (NDE), has been successfully applied together with both a conventional EA and a modified version of the Non-Dominated Sorting Genetic Algorithm-II (NSGA-II). The objective of this paper is to verify what is the best choice to use to treat service restoration problem in large scale distribution systems? NDE with the conventional EA or NDE with the modified version of the NSGA-II. In order to do that, simulation results in two distribution systems are presented. One of these systems is the fairly large distribution system of Sao Carlos city in Brazil with 3,860 buses, 532 sectors, 509 normally closed sectionalizing switches, 123 normally open tie-switches, 3 substations, and 23 feeders.

Geometrical approach on masked gross errors for power systems state estimation

In this paper, a geometrical based-index, called undetectability index (UI), that quantifies the inability of the traditional normalized residue test to detect single gross errors is proposed. It is shown that the error in measurements with high UI is not reflected in their residues. This masking effect is due to the “proximity” of a measurement to the range of the Jacobian matrix associated with the power system measurement set. A critical measurement is the limit case of measurement with high UI, that is, it belongs to the range of the Jacobian matrix, has an infinite UI index, its error is totally masked and cannot be detected in the normalized residue test at all. The set of measurements with high UI contains the critical measurements and, in general, the leverage points, however there exist measurements with high UI that are neither critical nor leverage points and whose errors are masked by the normalized residue test. In other words, the proposed index presents a more comprehensive picture of the problem of single gross error detection in power system state estimation than critical measurements and leverage points. The index calculation is very simple and is performed using routines already available in the existing state estimation software. Two small examples are presented to show the way the index works to assess the quality of measurement sets in terms of single gross error detection. The IEEE-14 bus system is used to show the efficiency of the proposed index to identify measurements whose errors are masked by the estimation processing.

Recovering of masked errors in power systems state estimation and measurement gross error detection and identification proposition

In this paper, a topological/geometrical based approach is used to define an index, undetectability index (UI), which provides the distance of a measurement from the range space of the Jacobean matrix of the power system. The higher the value of this index, for a measurement, the closer it will be to the range space of that matrix, that is, the error in measurements with high UI is not reflected in their residuals, thus masking a possible gross error those measurements might have. Using the UI of a measurement, the possible gross error the state estimation process might mask is recovered; then the total gross error of that measurement is composed and used to the gross error detection and identification test. The gross error processing turns out to be very simple to implement, requiring only a few adaptations to the existing state estimation software. The IEEE-14 bus system is used to validate the proposed gross error detection and identification test.