Marco Pau

Efficient Branch-Current-Based Distribution System State Estimation Including Synchronized Measurements

Deregulation and privatization actions are creating new problems of control, management and reliability, because of new players and new technologies spreading in distribution systems. Such new scenarios require more comprehensive and accurate knowledge of the system to make control actions efficient and reliable. In particular, attention must be paid to phase angles estimation to avoid critical situations. In this context, the use of phasor measurement units (PMUs) looks promising. This paper presents an efficient branch-current-based distribution systems state estimation. The estimator allows synchronized phasor measurements provided by PMUs to be included. In addition, the branch current state model is extended so that the knowledge of the voltage profile is significantly improved. The estimator is expressed both in polar and rectangular coordinates and a comparison between the obtainable accuracy and computational efficiency is presented. Furthermore, the possibility to treat radial and weakly meshed topology, also in presence of dispersed generation, is analyzed. The results obtained on different distribution networks are presented and discussed.

Effects of Measurements and Pseudomeasurements Correlation in Distribution System State Estimation

Distribution system state estimation (DSSE) is one of the key elements of the monitoring activity of an active distribution network, and is the basis for every control and management application. The DSSE relies on real measurements collected by the distributed measurement system and on other available information, mainly obtained from historical data that help in obtaining observability. This prior information is necessary to derive the so called pseudomeasurements. Accurate input data are fundamental for an accurate estimation, as well as knowledge on possible correlation in the measured and pseudomeasured data. A degree of correlation can exist in the measured data, due to measurement devices, and among power consumptions or generations of some particular nodes. This paper presents an exhaustive analysis on the influence of correlations on the quality of the estimation. The importance of including correlation in the weighted least square estimation approach is discussed using both traditional and synchronized measurements. Results obtained on a 95-bus distribution network are presented and discussed.

Postural sway modifications induced by backpack carriage in primary school children: a case study in Italy

The aim of this investigation is to assess modifications in sway parameters introduced by backpack carriage in Italian primary school children (6–10 years old, n = 447). Two 30-s trials (without and with backpack) were performed directly at a school on a regular school day to collect data on sway area, centre of pressure path length and maximum displacement range in antero–posterior and medio–lateral directions. The results show a significant load-induced increase in all sway parameters and the existence of a linear relationship between sway area and backpack weight. Since postural sway represents an effective indicator of balance abilities, the alterations observed suggest that backpack carriage originates balance impairment and thus may increase the risk of unintentional falls in children. Statement of Relevance: Loss of balance is among the primary causes of unintentional falls and postural sway represents an effective indicator of balance abilities. In this study, sway parameters were assessed in primary school children wearing backpacks. The differences that were observed show that backpack carriage potentially increases the risk of falls.

Electrical distribution system state estimation: measurement issues and challenges

The distribution grid is the infrastructure that transports electrical energy generated by large plants that are long distances away to the final user. A typical distribution grid consists of High-to-Medium Voltage (HV/MV) transformation centers; the MV grid; Medium-to-Low Voltage (MV/LV) transformation centers; and the LV grid, both three-phase and single-phase. Residential and commercial customers are mainly connected to the LV, while large industrial facilities are connected to the MV.

Effects of backpack carriage on foot-ground relationship in children during upright stance.

Although the scientific community widely recognizes that backpack carriage in primary school children represents a critical issue, its consequences in terms of postural alterations and possible onset of musculoskeletal pathologies are still not fully understood. In particular, little information is available on the way load carriage modifies the foot-ground relationship in terms of plantar pressure distribution. This issue is of particular relevance, because the presence of a load alters the physiological weightbearing functions and, when mechanical overloading is repeated in time, it can act as a co-factor in promoting foot discomfort or pain. On the basis of these considerations, this study analyzed plantar pressure maps of 359 children attending primary schools (6-10 years old) under static upright posture conditions, to assess the magnitude and features of effects originated by load carriage on the foot-ground relationship. The collected data showed that backpack introduces significant increases in overall contact area (up to 10%) and in the plantar pressure peaks in midfoot and forefoot regions (20-30%). A significant shift in the average position of the center of pressure towards the forefoot was also observed, as an indicator of the bodys attempt to restore the initial balance conditions threatened by the load. These results suggest that heavy loads, in the case of significant exposure times, may increase the risk of foot discomfort and act as a co-factor in the onset of foot structure alterations or pathologies.

WLS distribution system state estimator based on voltages or branch-currents: Accuracy and performance comparison

This paper presents a comparison between the two main classes of Weighted Least Squares (WLS) state estimators used in distribution systems: state estimators based on node voltage state variables and estimators based on a state expressed in terms of branch-currents. In particular, the actual accuracy achieved for the estimated quantities by these estimators and their modified versions is analysed in details along with their performance, considering different types of real-time measurements (traditional or phasorial), different configurations of the measurement system and the impact of the network parameters uncertainty. Results obtained on two distribution networks with different scale, 18-bus and 95-bus, are presented and discussed.

Multiarea Distribution System State Estimation

This paper presents a new approach to the distribution system state estimation in wide-area networks. The main goal of this paper is to present a two-step procedure designed to accurately estimate the status of a large-scale distribution network, relying on a distributed measurement system in a multiarea framework. First of all, the network is divided into subareas, according to geographical and/or topological constraints and depending on the available measurement system. Then, in the first step of the estimation process, for each area, a dedicated estimator is used, exploiting all the measurement devices available on the field. In the second step, data provided by local estimators are further processed to refine the knowledge on the operating conditions of the network. To improve the accuracy of the estimation results, correlation arising in the first step estimations has to be suitably evaluated and considered during the second step. Performed analysis shows that existing correlations can be included in the estimation process with very low data exchange among areas, thus involving minimum communication costs. Both first and second steps can be performed in a decentralized way and with parallel processing, thus leading to reduced overall execution times. Test results, obtained on the 123-bus IEEE test network and proving the goodness of the proposed method, are presented and discussed.

Uncertainty of Voltage Profile in PMU-Based Distribution System State Estimation

Distribution system state estimation (DSSE) tools are required to estimate the real operating conditions of power distribution networks. The accuracy of the quantities estimated through DSSE plays a key role in the effectiveness of the management and control functions. This paper presents a comprehensive mathematical analysis aimed at highlighting the most important factors affecting the accuracy of the voltage profile obtained by means of weighted least squares estimators. The proposed analysis shows the way in which the uncertainty components of the voltage estimations depend on the measurement system available on the field. In particular, this paper considers synchrophasor measurements provided by phasor measurement units and hybrid measurement systems also presenting conventional devices. Tests performed on a 95-bus network prove the validity of the theoretical analysis and show the importance of the results also from a meter placement perspective, emphasizing the requirements needed to achieve specific accuracy targets.

Branch current state estimator for distribution system based on synchronized measurements

Throughout the last ages, the distribution systems have been undergoing more and more significant changes. These changes have a significant impact on the power system configuration creating new monitoring, management, and reliability issues. In particular, the smart grids, probably the future of the distribution systems, will present important management issues. Such scenario needs a knowledge of the system the more comprehensive and reliable. In this context, the use of Phaser Measurement Units (PMUs) looks promising. PMUs have proven highly useful for different applications concerning the power systems, and now they appear to be interesting also for applications in distribution systems. This paper presents an efficient branch currents estimator for distribution systems (BC-DSSE) based on PMUs measurements. The results obtained on a small (18-bus) distribution network will be presented and discussed.

Performance of three-phase WLS distribution system state estimation approaches

The roadmap towards the so-called Smart Grids calls for a clever and efficient management of the distribution systems. In this context, Distribution System State Estimation (DSSE) tools play a crucial role to acquire the knowledge about the effective operating conditions of the network and to enable the proper management and control functions operation. DSSE is usually performed by relying on a Weighted Least Squares (WLS) method. Different WLS formulations can be designed depending on the state variables used in the estimator. In this paper, an analysis concerning the two main classes of WLS approaches proposed for distribution systems is presented. Three-phase estimators with state variables based on both node voltages and branch currents have been considered. The performances in terms of accuracy, efficiency and numerical properties are analyzed and discussed. Results obtained on the 123 IEEE distribution network are presented and discussed.