Phasor Measurement Units (PMUs) are widely acknowledged as one of the most promising developments in the field of real-time monitoring of power systems. By aligning the time stamps of voltage and current phasor measurements that are consistent with Coordinated Universal Time (UTC), a coherent picture of the power system state can be achieved through either direct measurements or simple linear calculations. With the growing number of PMUs planned for installation in the near future, both utilities and research institutions are looking for the best solutions to the placement of units as well as to the applications that make the most of phasor measurements. This dissertation explores a method for optimal PMU placement as well as two applications of synchronized phasor measurements in state estimation. The pre-processing PMU placement method prepares the system data for placement optimization and reduces the size of the optimization problem. It is adaptive to most of the optimal placement methods and can save a large amount of computational effort. Depth of un-observability is one of the criteria to allow the most benefit out of a staged placement of the units. PMUs installed in the system provide synchronized phasor measurements that are highly beneficial to power system state estimations. Two related applications are proposed in the dissertation. First, a post-processing inclusion of phasor measurements in state estimators is introduced. This method avoids the revision of the existing estimators and is able to realize similar results as mixing phasor data with traditional SCADA with a linear afterwards step. The second application is a method to calibrate instrument transformers remotely using phasor measurements. Several scans of phasor measurements are used to accomplish estimating system states in conjunction with complex instrument transformer correction factors. Numerical simulation results are provided for evaluation of the calibration performance with respect to the number of scans and load conditions. Conducting theoretical and numerical analysis, the methods and algorithms developed in this dissertation are aimed to strategically place PMUs and to incorporate phasor measurements into state estimators effectively and extensively for better system state monitoring. Simulation results show that the proposed placement method facilitates approaching the exact optimal placement while keep the computational effort low. Simulation also shows that the use of phasor measurement with the proposed instrument transformer correction factors and proposed state estimation enhancement largely improves the quality of state estimations. / Ph. D.

The development of Smart Grid and an increased emphasis on Wide Area Measurement, Automation, Protection and Control (WAMPAC) has lead to the substantial increase in the development and use of Synchrophasor Systems. The Department of Energy having realized its importance in the Power System has encouraged its deployment through the Smart Grid Investment Grant. With many utilities beginning to implement a large number of PMUs over their respective power systems, Phasor Data Concentrators (PDCs) play a crucial part in accurately relaying data from the point of measurement to the operators at the control center. The current Synchrophasor standard, IEEE C37.118-2005 covers adequately the steady state characterization of PMUs but does not specify requirements for PDCs. Having recognized the need for such a standard for PDCs, the North American Synchrophasor Initiative (NASPI) has developed a guide outlining some of its objectives, functions and tests requirements. Virginia Tech has developed a PDC Test System under these guidelines and as per the requirements of the PJM Synchrophasor Systems Deployment Project. This thesis focuses on the testing tools developed and the procedures implemented in the Virginia Tech PDC Test System. / Master of Science

Phasor Measurement Units (PMUs) have been instrumental in building a reliable and robust Power System. Recent blackouts have increased the importance of PMUs and PMUs from various manufacturers are being installed in the in large quantities in the North American Grid. The interoperability and accuracy of these PMUs is important to obtain full benefit of the wide area monitoring systems. With the large number of installed PMUs it has become necessary to validate their performance and understand the limitations of each model. A test system was built by NIST in cooperation with NASPI to test for compliance to the existing IEEE C37.118 standard. This thesis presents the development of a Steady State Test System at Virginia Tech based on the NIST Steady State Testing system. The various issues that were faced during the process of development are discussed and the methodology implemented for solving these problems is described. This thesis also presents the additional benefits derived from the results obtained when different PMUs were tested using the Virginia Tech PMU Steady State Test System. / Master of Science

Given an increasing tendency towards distributed generation and alternative energy sources, the power grid must be more carefully monitored in order to ensure stability. Phasor Measurement Units (PMUs) provide very good observation of a small area of a network, but their relatively high cost prevents them from being deployed at every point. Therefore, to monitor an entire network, State Estimation is still required. By combining these two techniques, the accuracy and speed of power network monitoring can be improved. This thesis presents a method for achieving this goal from both hardware and computational perspectives. Practical considerations for PMU placement are discussed, such as instrument transformer calibration, and an algorithm is developed to apply this technique to any power system. The resulting method is termed reconfigurable monitoring - computationally isolated areas which may be grouped as necessary to allow for flexibility in power system monitoring. / Master of Science

We aim at expanding the horizon of existing research on cyberattacks against the time-syncrhonized devices such as PMUs and PDCs, along with corresponding countermeasures. We develop a PMU-PDC cybersecurity testbed at Virginia Tech Power and Energy Center (PEC) lab. The testbed is able to simulate real-world GPS-spoofing attack (GSA) and false data injection attack (FDIA) scenarios. Moreover, the testbed can incorporates cyberattack detection algorithm in pseudo real-time. After that, we propose three stealthy attack scenarios that exploit the vulnerabilities of time-synchronization for both PMU and PDC. The next part of this dissertation is the enhancement of Hankel-matrix based bad data detection model. The existing general Hankel-matrix based bad data detection model provide satisfactory performance. However, it fails in differentiating GPS-spoofing attack from FDIA. We propose an enhanced phase angle Hankel-matrix model that can conclusively identify GPS-spoofing attack. Furthermore, we reduce the computational burden for Hankel-matrix based bad data and cyberattack detection models. Finally, we verify the effectiveness of our enhanced Hankel-matrix model for proposed stealthy attack scenarios. / Doctor of Philosophy / Modern power systems incorporate numerous smart metering devices and communication channels to provide better resiliency against hazardous situations. One such metering device is Phasor Measurement Device (PMU), what provides GPS time-synchronized measurements to the system operator. The time-synchronized measurements are critical in ensuring the cyber and physical security of grids. However, like other smart devices, PMUs are susceptible to conventional cyberattacks. In addition to conventional cyberattacks, PMUs are also vulnerable to attacks against its time-synchronization. In this work, we dig deep into the realm of cyberattacks against time-synchronization of PMUs. We propose novel stealthy attacks against PMU time synchronization. Furthermore, we enhance existing attack detection model to conclusively identify such stealthy attacks and implemented the model in cybersecurity testbed that we developed at Virginia Tech.

Wind power generation influences on the quality of the power grid. Because wind velocity is consistently changing this change causes unstable wind power generation. Since more wind power is expected to be used in the future, it is crucial to study the influence of the wind penetration level on normalized-damping ratio and damped-resonant frequency. In this thesis three types of calculated data were used to analyze the effect of wind penetration level on the Texas power grid: the percentage of wind power generation in Texas, generator-unit trip damping coefficient, and damped-resonant frequency. The percentage of wind energy was calculated from wind data provided by the Electric Reliability Council of Texas. The damping coefficient and damped-resonant frequency values are the indicators of power system stability and were calculated from synchronized phase data from the Texas power grid. The synchronized phase measurements were collected from the University of Texas at Austin and the wind farm near the Mc-Donald observatory. The data analyzed in this paper were from September 2009 to February 2010. The wind data were correlated to the grid-stability indicators which allowed us to interpret the status of the power grid according to the wind penetration level. When the wind penetration level increased over 11 %, five generator trip events occurred with damping coefficient values ten times higher than those of the regular unit trips. Moreover, during those events, damped-resonant frequency values rose nearly four times higher than the frequency values of other events. The results of this study may lead us to the conclusion that simply increasing the capacity of wind power generation will cause the power system to become unstable, and this will result in low quality of electricity. Therefore, further study is needed to determine the optimum amount of wind power generation without causing instability in the power grid. / text

Power systems must face new challenges in the current environment. The energy market liberalization and the increase in the loading level make the occurrence of instability phenomena leading to large blackouts more likely. Existing tools must be improved and new tools must be developed to avoid them. The aim of this thesis is the improvement of the voltage stability assessment efficiency. Two orientations are studied: the monitoring methods and the load modeling. The purpose of the monitoring methods is to evaluate the voltage stability using only measurements and without running simulations. The first approach considered is local. The parameters of the Thevenin equivalent seen from a load bus are assessed thanks to a stream of local voltage and current measurements. Several issues are investigated using measurements coming from complete time-domain simulations. The applicability of this approach is questioned. The second approach is global and uses measurements acquired by a Wide-Area Measurement System (WAMS). An original approach with a certain prediction capability is proposed, along with intuitive visualizations that allow to understand the deterioration process leading to the collapse. The load modeling quality is certainly the weak point of the voltage security assessment tools which run simulations to predict the stability of the power system depending on different evolutions. Appropriate load models with accurate parameters lead to a direct improvement of the prediction precision. An innovative procedure starting from data of long measurement campaigns is proposed to automatically evaluate the parameters of static and dynamic load models. Real measurements taken in the Belgian power system are used to validate this approach.

The development of an experimental synchrophasors network and application of synchrophasors for real-time transmission line parameter monitoring are presented in this thesis. In the laboratory setup, a power system is simulated in a RTDS real-time digital simulator, and the simulated voltages and currents are input to hardware phasor measurement units (PMUs) through the analog outputs of the simulator. Time synchronizing signals for the PMU devices are supplied from a common GPS clock. The real time data collected from PMUs are sent to a phasor data concentrator (PDC) through Ethernet using the TCP/IP protocol. A real-time transmission line parameter monitoring application program that uses the synchrophasor data provided by the PDC is implemented and validated. The experimental synchrophasor network developed in this thesis is expected to be used in research on synchrophasor applications as well as in graduate and undergraduate teaching.

The development of an experimental synchrophasors network and application of synchrophasors for real-time transmission line parameter monitoring are presented in this thesis. In the laboratory setup, a power system is simulated in a RTDS real-time digital simulator, and the simulated voltages and currents are input to hardware phasor measurement units (PMUs) through the analog outputs of the simulator. Time synchronizing signals for the PMU devices are supplied from a common GPS clock. The real time data collected from PMUs are sent to a phasor data concentrator (PDC) through Ethernet using the TCP/IP protocol. A real-time transmission line parameter monitoring application program that uses the synchrophasor data provided by the PDC is implemented and validated. The experimental synchrophasor network developed in this thesis is expected to be used in research on synchrophasor applications as well as in graduate and undergraduate teaching.

abstract: ABSTRACT This dissertation introduces a real-time topology monitoring scheme for power systems intended to provide enhanced situational awareness during major system disturbances. The topology monitoring scheme requires accurate real-time topology information to be effective. This scheme is supported by advances in transmission line outage detection based on data-mining phasor measurement unit (PMU) measurements. A network flow analysis scheme is proposed to track changes in user defined minimal cut sets within the system. This work introduces a new algorithm used to update a previous network flow solution after the loss of a single system branch. The proposed new algorithm provides a significantly decreased solution time that is desired in a real- time environment. This method of topology monitoring can provide system operators with visual indications of potential problems in the system caused by changes in topology. This work also presents a method of determining all singleton cut sets within a given network topology called the one line remaining (OLR) algorithm. During operation, if a singleton cut set exists, then the system cannot withstand the loss of any one line and still remain connected. The OLR algorithm activates after the loss of a transmission line and determines if any singleton cut sets were created. These cut sets are found using properties of power transfer distribution factors and minimal cut sets. The topology analysis algorithms proposed in this work are supported by line outage detection using PMU measurements aimed at providing accurate real-time topology information. This process uses a decision tree (DT) based data-mining approach to characterize a lost tie line in simulation. The trained DT is then used to analyze PMU measurements to detect line outages. The trained decision tree was applied to real PMU measurements to detect the loss of a 500 kV line and had no misclassifications. The work presented has the objective of enhancing situational awareness during significant system disturbances in real time. This dissertation presents all parts of the proposed topology monitoring scheme and justifies and validates the methodology using a real system event. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2015