Voltage Stability Indices Based on Active Power Transfer Using Synchronized Phasor Measurements

In recent years and in the foreseeable future, power demands generally around the world and particularly in North America will experience rapid increases due to the increase of customers\u27 requirements, while the development of transmission systems in North America is rather slow. Voltage stability assessment becomes one of the highest priorities to power utilities in North America. Voltage stability index is a feature for solving voltage stability problems. It is generated from the basic power flow equations and/or energy functions. The mathematical expression of a VSI is often written as a polynomial containing the systems real-time measurements such as voltage magnitudes, phase angles, bus injected power and branch power flow values, etc. In this thesis, the principle and derivation process of two voltage stability indices are presented. Relevant simulations are analyzed to demonstrate the VSIs\u27 functions as illustrating the system\u27s stability condition, estimating the systems operating states, determining system sensitive buses; and generator-sensitive buses and to help system apply voltage stability protection strategy. The thesis also discussed the application of VSIs with synchronized phasor measurement units, a precise system phasor measuring device using global positioning signal to obtain wide-area system measurements simultaneously. The effect of measurements errors on the computation of the VSI is studied and examined. Finally, a discussion of the future development of synchrophasors and VSI methods is given

PMU-Based ROCOF Measurements: Uncertainty Limits and Metrological Significance in Power System Applications

In modern power systems, the Rate-of-Change-of-Frequency (ROCOF) may be largely employed in Wide Area Monitoring, Protection and Control (WAMPAC) applications. However, a standard approach towards ROCOF measurements is still missing. In this paper, we investigate the feasibility of Phasor Measurement Units (PMUs) deployment in ROCOF-based applications, with a specific focus on Under-Frequency Load-Shedding (UFLS). For this analysis, we select three state-of-the-art window-based synchrophasor estimation algorithms and compare different signal models, ROCOF estimation techniques and window lengths in datasets inspired by real-world acquisitions. In this sense, we are able to carry out a sensitivity analysis of the behavior of a PMU-based UFLS control scheme. Based on the proposed results, PMUs prove to be accurate ROCOF meters, as long as the harmonic and inter-harmonic distortion within the measurement pass-bandwidth is scarce. In the presence of transient events, the synchrophasor model looses its appropriateness as the signal energy spreads over the entire spectrum and cannot be approximated as a sequence of narrow-band components. Finally, we validate the actual feasibility of PMU-based UFLS in a real-time simulated scenario where we compare two different ROCOF estimation techniques with a frequency-based control scheme and we show their impact on the successful grid restoration.Comment: Manuscript IM-18-20133R. Accepted for publication on IEEE Transactions on Instrumentation and Measurement (acceptance date: 9 March 2019

Methodology and Tools for Field Testing of Synchrophasor Systems

The electrical power grid, as one of today’s most critical infrastructures, requires constant monitoring by operators to be aware of and react to any threats to the system’s condition. With control centers typically located far away from substations and other physical grid equipment, field measurement data forms the basis for a vast majority of control decisions in power system operation. For that reason, it is imperative to ensure the highest level of data integrity as erroneous data may lead to inappropriate control actions with potentially devastating consequences. Performance of one of the most advanced monitoring systems, the synchrophasor system, is the focus of this thesis. This research will look at testing techniques used for performance assessment of synchrophasor system performance in the field. Existing methods will be reviewed and evaluated for deficiencies in capturing system performance regarding data quality. The focus of this work will be on improving synchrophasor data quality, by introducing new testing methodology that utilizes a nested testing approach for end-to-end testing in the field using a portable test set and associated software tools. The capability of such methods and these tools to fully characterize and evaluate the performance of synchrophasor systems in the field will be validated through implementation in a large-scale testbed. The purpose of this research is to specify, develop and implement a methodology and associated tools for field-testing of synchrophasor systems. To this day, there is no dedicated standard for field-testing of synchrophasor systems. This resulted in an inability to define widely accepted procedures to detect deterioration of system performance due to poor data quality and caused communication failures, unacceptable device and subsystem accuracy, or loss of calibration. This work will demonstrate how the new approach addresses the mentioned performance assessment gap. The feasibility of implementation of the proposed test procedures will be demonstrated using different test system configurations available in a large-scale testbed. The proposed method is fully leveraging the benefits of a portable device specifically developed for field-testing, which may be used for improvement of commissioning, maintenance and troubleshooting tests for existing installations. Use Cases resulting from this work will illustrate the practical benefits of the proposed methodology and associated tools

Diagnostic Applications for Micro-Synchrophasor Measurements

This report articulates and justifies the preliminary selection of diagnostic applications for data from micro-synchrophasors (µPMUs) in electric power distribution systems that will be further studied and developed within the scope of the three-year ARPA-e award titled Micro-synchrophasors for Distribution Systems

Definition and assessment of reference values for PMU calibration in static and transient conditions

The calibration of Phasor Measurement Units (PMUs) consists of comparing Coordinated Universal Time (UTC) time-stamped phasors (synchrophasors) estimated by the PMU under test, against reference synchrophasors generated through a PMU calibrator. The IEEE Standard C37.118-2011 and its amendment (IEEE Std) describe compliance tests for static and dynamic conditions, and indicate the relative limits in terms of accuracy. In this context, the paper focuses on the definition and accuracy assessment of the reference synchrophasors in the test conditions dictated by the above IEEE Std. In the first part of the paper, we describe the characterization of a nonlinear least-squares (NL-LSQ) fitting algorithm used to determine the parameters of the reference synchrophasors. We analyse the uniqueness and robustness of the solution provided by the algorithm. We assess its accuracy within the whole range of static tests required by the IEEE Std. In the second part, we discuss the appropriateness of synchrophasor model to evaluate the PMU performance in step test conditions. We compare the proposed algorithm against two synchrophasor estimation algorithms. Finally, we propose a time domain process for the better evaluation of PMU performances in transient conditions

Measurement of dynamic voltage variation effect on instrument transformers for power grid applications

Within the framework of distribution and transmission grids, the knowledge of Instrument Transformers (ITs) behavior in distorted conditions is a topic of great interest. Its relevance stems from the ITs wide use in metering, protection, monitoring and control applications, where their role is to reduce voltage and current to levels compatible with measuring instrument inputs. In force standards require that the performance of measuring instruments is assessed under realistic conditions. On the contrary, performance tests of ITs are generally carried out only at rated conditions, so that their behavior under actual waveforms is not fully known. To cover this gap, a suitable setup for the traceable test of Voltage instrument Transformers (VTs) under a quite large set of static and time-varying test waveforms is developed. The paper, after a short description of the setup, shows the performance of two commercial VTs under some power quality events, that are amplitude and phase modulations and voltage dips

IEEE 1588 synchronization in distributed measurement systems for electric power networks

Modern electric power systems can be considered as the consequence of the continuous technological evolution, often pushed by economical, political and social requirements. As an example, the main transformations in electric distribution systems arise from the diffusion of “Distributed Generation” (DG), i.e. small production plants, often supplied through renewable energy sources, whose presence has significant implications on both energy management (since “active networks” are needed to take into account bidirectional energy flows by means of innovative devices) and protection systems (since adaptive protections can be used to automatically reconfigure the network in the case of fault occurrence). In general, in both transmission and distribution networks, monitoring, control and protection tasks are usually performed by Intelligent Electronic Devices (IEDs), which can be, by their nature, connected to each other by suitable communication links. A famous example of this approach is represented by the series of Standard IEC 61850 (Communication Networks and Systems in Substations). These standards are related to networks and communication systems within the substation, but are used as a reference in all those circumstances in which an electrical system is managed through the use of IEDs communicating with each other (as in the case of active distribution networks). In this way, control and protection schemes practically become algorithms, whose correct behavior is determined firstly by the availability of data measured in strategic points of the network. The critical role of the above mentioned applications, which clearly emerges from their implications on safety, as well as from economical considerations, makes it of fundamental importance the evaluation of correctness and trustworthiness of the information on which such actions are based. Many of these applications implemented for control and protection purposes in electric power networks require the acquisition of information by Wide Area Monitoring System (WAMS) from strategic points of the system and need that the acquired data have an extremely accurate common time reference. Generally, amplitudes and phases of the positive sequence voltages are the quantities to be estimated in the network nodes. Because of the extension of power networks, suitable measurement devices should be used to ensure proper synchronization between the collected data. Thus, the key components of WAMSs are represented by Phasor Measurement Units (PMUs) designed to measure synchronized phasors (synchrophasors). Typical synchronization specifications for synchrophasors measurement are in the order of few microseconds. Such a tight synchronization requirements lead to the need of highly accurate clock settings, such as the ones bases on satellite systems. Currently, the Global Positioning System (GPS) is the only system to provide a time reference with sufficient availability and accuracy for most distributed monitoring and control applications in power systems. As an alternative, in situations where many devices are located in a geographically limited sub-area (e.g. a substation) of the system and are connected to each other by suitable communication networks (as described by the series of standard IEC 61850), it could be advantageous to distribute the time reference of a high accuracy clock to the devices through suitable network synchronization protocols. Between them, the PTP (Precision Time Protocol) defined in the Standard IEEE 1588 offers the best accuracy performance. It is worth mentioning that the Standard IEC 61850-9-2 practically indicates Ethernet as a preferred communication solution, thus offering an optimal support to implement 1588 synchronization in electric power plants. In this context, it should be recalled that the IEEE 1588 profile for power system applications (project PC37.238) is being developed under IEEE Power System Relaying Committee (PSRC) and Power System Substation Committee (PSSC). The scope covers all power system applications, including Synchrophasors. The group works in close coordination with TC57 WG10, which plans to adopt the PTP profile in the next revision of IEC 61850. In the first part of this thesis, the state of the art regarding power system evolution, IEEE Standard on synchrophasor measurements and synchronization system is presented. In particular, the problems related to the evolution of the power system along with some possible advantages due to the implementation of Phasor Measurement Units in Wide Area Monitoring Systems are introduced. After a general description of the architecture of a distributed measurement system based on PMUs, the new synchrophasors standard is analysed, highlighting the differences with previous versions, the requirements for the measurement of synchrophasors and the definition of synchrophasor under steady-state and dynamic conditions. Moreover, a summary of the possible synchronization solutions is introduced. For each solution, advantages and disadvantages are highlighted. In particular, satellite system and network based protocol are analysed in detail. In the second part of the thesis, a synchronization solution able to exploit the worldwide availability of the GPS and the possibility to disseminate the synchronization signal with high accuracy by means of the network synchronization protocol IEEE 1588 is proposed. This solution is used for the synchronization of PMUs. The objective of this work is to analyse the possibility to synchronize PMUs via PTP and to study the impact that such a synchronization solution has on the performance of measurement systems under both steady-state and anomalous operating conditions, as well as its effects on the applications that make use of their data. Two different versions of the PTP are used: the first one uses hardware-assisted time-stamp mechanism whereas the second one uses software-only time-stamp mechanism. Two experimental systems are characterized in detail with an accurate description of all the used hardware and software components, and their synchronization performances under different operative conditions are analysed. Finally, among all the sources which may contribute to the uncertainty introduced by PMUs, the last part of this thesis analyses the impact of the phasor estimation models on the accuracy of these devices, with particular attention to algorithms proposed in literature for the estimation of dynamic phasors and studies their performances under several different conditions

Synchrophasors: Multilevel Assessment and Data Quality Improvement for Enhanced System Reliability

. This study presents a comprehensive framework for testing and evaluation of Phasor Measurement Units (PMUs) and synchrophasor systems under normal power system operating conditions, as well as during disturbances such as faults and transients. The proposed framework suggests a performance assessment to be conducted in three steps: (a) type testing: conducted in the synchrophasor calibration laboratory according to accepted industrial standards; (b) application testing: conducted to evaluate the performance of the PMUs under faults, transients, and other disturbances in power systems; (c) end-to-end system testing: conducted to assess the risk and quantify the impact of measurement errors on the applications of interest. The suggested calibration toolset (type testing) enables performance characterization of different design alternatives in a standalone PMU (e.g., length of phasor estimation windows, filtering windows, reporting rates, etc.). In conjunction with the standard performance requirements, this work defines new metrics for PMU performance evaluations under any static and dynamic conditions that may unfold in the grid. The new metrics offer a more realistic understanding of the overall PMU performance and help users choose the appropriate device/settings for the target applications. Furthermore, the proposed probabilistic techniques quantify the PMU accuracy to various test performance thresholds specified by corresponding IEEE standards, rather than having only the pass/fail test outcome, as well as the probability of specific failures to meet the standard requirements defined in terms of the phasor, frequency, and rate of change of frequency accuracy. Application testing analysis encompasses PMU performance evaluation under faults and other prevailing conditions, and offers a realistic assessment of the PMU measurement errors in real-world field scenarios and reveals additional performance characteristics that are crucial for the overall application evaluation. End-to-end system tests quantify the impact of synchrophasor estimation errors and their propagation from the PMU towards the end-use applications and evaluate the associated risk. In this work, extensive experimental results demonstrate the advantages of the proposed framework and its applicability is verified through two synchrophasor applications, namely: Fault Location and Modal Analysis. Finally, a data-driven technique (Principal Component Pursuit) is proposed for the correction and completion of the synchrophasor data blocks, and its application and effectiveness is validated in modal analyzes

Performance Improvement of Wide-Area-Monitoring-System (WAMS) and Applications Development

Wide area monitoring system (WAMS), as an application of situation awareness, provides essential information for power system monitoring, planning, operation, and control. To fully utilize WAMS in smart grid, it is important to investigate and improve its performance, and develop advanced applications based on the data from WAMS. In this dissertation, the work on improving the WAMS performance and developing advanced applications are introduced.To improve the performance of WAMS, the work includes investigation of the impacts of measurement error and the requirements of system based on WAMS, and the solutions. PMU is one of the main sensors for WAMS. The phasor and frequency estimation algorithms implemented highly influence the performance of PMUs, and therefore the WAMS. The algorithms of PMUs are reviewed in Chapter 2. To understand how the errors impact WAMS application, different applications are investigated in Chapter 3, and their requirements of accuracy are given. In chapter 4, the error model of PMUs are developed, regarding different parameters of input signals and PMU operation conditions. The factors influence of accuracy of PMUs are analyzed in Chapter 5, including both internal and external error sources. Specifically, the impacts of increase renewables are analyzed. Based on the analysis above, a novel PMU is developed in Chapter 6, including algorithm and realization. This PMU is able to provide high accurate and fast responding measurements during both steady and dynamic state. It is potential to improve the performance of WAMS. To improve the interoperability, the C37.118.2 based data communication protocol is curtailed and realized for single-phase distribution-level PMUs, which are presented in Chapter 7.WAMS-based applications are developed and introduced in Chapter 8-10. The first application is to use the spatial and temporal characterization of power system frequency for data authentication, location estimation and the detection of cyber-attack. The second application is to detect the GPS attack on the synchronized time interval. The third application is to detect the geomagnetically induced currents (GIC) resulted from GMD and EMP-E3. These applications, benefited from the novel PMU proposed in Chapter 6, can be used to enhance the security and robust of power system