This work studies the consequences of a human-initiated targeted attack on the electric power system by simulating the detonation of a bomb at one or more substations in and around Washington DC. An AC power flow based transient analysis on a realistic power grid model of Eastern Interconnection is considered to study the cascading events. A detailed model of control and protection system in the power grid is considered to ensure the accurate representation of cascading outages. Particularly, the problem of identifying a set of k critical nodes, whose failure/attack leads to the maximum adverse impact on the power system has been analyzed in detail. It is observed that a greedy approach yields node sets with higher criticality than a degree-based approach, which has been suggested in many prior works. Furthermore, it is seen that the impact of a targeted attack exhibits a nonmonotonic behavior as a function of the target set size k. The consideration of hidden failures in the protective relays has revealed that the outage of certain lines/buses in the course of cascading events can save the power grid from a system collapse. Finally, a comparison with the DC steady state analysis of cascading events shows that a transient stability assessment is necessary to obtain the complete picture of cascading events in the aftermath of a targeted attack on the power grid. / M.S. / The modern day power system has been identified as a critical infrastructure providing crucial support to the economy of a country. Prior experience has shown that a small failure of a component in the power grid can lead to widespread cascading events and eventually result in a blackout. Such failures can be triggered by devastating damage due to a natural calamity or because of a targeted adversarial attack on certain points in the power system. Given limited budget to avoid widespread cascading failures in the network, an important problem would be to identify critical components in the power system. In this research an attempt has been made to replicate the actual power system conditions as accurately as possible to study the impact of a targeted adversarial attack on different points in the network. Three heuristics have been proposed to identify critical nodes in the network and their performance has been discussed. The case studies of cascading events have been performed on a synthetic power system network of Washington DC to achieve the actual system conditions of an operating power grid.

Wide-area disturbances are power outages occurring over large geographical regions that dramatically affect the power system reliability, causing interruptions of the electric supply to residential, commercial, and industrial users. Historically, wide-area disturbances have greatly affected societies. Virginia Tech directed a research project related to the causes of the major disturbances in electric power systems. Research results showed that the role of the power system's protection schemes in the wide-area disturbances is critical. Incorrect operations of power system's protection schemes have contributed to a spread of the disturbances. This research defined hidden failures of protection schemes and showed that these kinds of failures have contributed in the degradation of 70-80 percent of the wide-area disturbances. During a wide-area disturbance analysis, it was found that hidden failures in protection schemes caused the disconnection of power system elements in an incorrect and undesirable manner contributing to the disturbance degradation. This dissertation presents a methodology to assess and rank the effects of unwanted disconnections caused by hidden failures based on Regions of Vulnerability and index of severity in the protection schemes. The developed methodology for the evaluation of the Region of Vulnerability found that the indicator that most accurately reflects the relationship of the Region of Vulnerability with the single line diagram is kilometers. For the representation of the Region of Vulnerability in the power system, we found segments in the transmission line in which the occurrence of faults do make the relay to operate, producing the unwanted disconnection caused by hidden failure. The results in the test system show that the infeed currents restrain the Region of Vulnerability from spreading along power system elements. Finally the methodology to compute the index of severity is developed. The index of severity has the objective of ranking the protection schemes, considers the dynamics of the protection schemes, and evaluates the overall disturbance consequence under the static and dynamic perspectives. / Ph. D.

The differences between shipboard and land based power systems are explored to support the main focus of this work. A model was developed for simulating hidden failures on shipboard integrated propulsion plants, IPP. The model was then used to evaluate the segregation of the IPP high voltage, HV, buses in a similar fashion as a shipboard firemain. The HV buses were segregated when loss of propulsion power would put the ship as risk. This new treatment reduces the region of vulnerability by providing a high impedance boundary that limits the effects of a hidden failure of a current magnitude or differential based protective element, without the installation of any additional hardware or software. It is shown that this protection could be further improved through the use of a simple adaptive protection scheme that disarms unneeded protective elements in certain configurations. / Master of Science

This document explores Hidden Failures in protection systems, which have been identified as key contributors in the degradation of Power System wide-area disturbances. The Hidden Failure Modes in which the protection systems may fail to operate correctly and their consequences are identified in a theoretical approach. This theoretical side has its practical counterpart since a number of Hidden Failure Modes are found in real wide-area disturbances. The original definition of Hidden Failure, which is a failure that remains undetected and is uncovered by another system event, is included as well as developments on Hidden Failure sequence of events and a methodology for Hidden Failure identification. This method is based on Protection Element Functionality Defects (PEFD), which are applicable to all the elements included in the protective chain. PEFD are classified in two main groups. Primary and Back-up protection schemes applied for Generators, Buses, Transformers and Transmission Lines are analyzed. The abnormal Power System conditions that each Power System element may have are enumerated. A catalogue of the relays or relay systems, in charge of detecting and stopping the continuous presence of the abnormal conditions is developed. Relay families organize this catalogue. The relaying schemes for five Special Protection Systems are described. Thirty-three Hidden Failures Modes are included based on the relaying implementation for Primary protection, Back-up protection and Special Protection Systems. These Hidden Failures Modes are based on PEFD-A. Hidden Failures related to PEFD-B are included in a general fashion. Wide-area disturbances based on NERC reports are analyzed and Hidden Failures are identified employing the developed methodology. The mechanisms in the disturbances are summarized and are applicable to Primary protection, Back-up protection and Special Protection Systems. Regions of Vulnerability and Areas of Consequence definitions are included and are identified for a Power System wide-area disturbance. For some protection schemes the term Condition of Vulnerability was developed. Regions of Vulnerability and Areas of Consequence will bring the initial steps towards the problem solution. Further research directions are oriented towards the development of a computer-based tool to track the regions of vulnerability in real time. / Master of Science

Transforming the aging electric grid to a smart grid is an active area of research in industry and the government. One of the main objectives of the smart grid is to improve the efficiency of power generation, transmission and distribution and also to improve the stability and the reliability of the grid. In order to achieve this, various processes involved in power generation, transmission, and distribution should be armed with advanced sensor technologies, computing, communication and networking capabilities to an unprecedented level. These high speed data transfer and computational abilities aid power system engineers to obtain wide area measurements, achieve better control of power system operations and improve the reliability of power supply and the efficiency of different power grid operations. In the process of making the grid smarter, problems existing in traditional grid applications can be identified and solutions have to be developed to fix the identified issues. In this dissertation, two problems that aid power system engineers to meet the above mentioned smart grid's objective are researched. One problem is related to the distribution-side smart grid and the other one is a part of the transmission-side smart grid. Advanced Metering Infrastructure (AMI) is one of the important distribution-side smart grid applications. AMI is a technology where smart meters are installed at customer site which gives the utilities the ability to monitor and collect information related to the amount of electricity, water, and gas consumed by the user. Many recent research studies suggested the use of 3G cellular CDMA2000 for AMI network as it provides an advanced and cost effective solution for smart grid communications. Taking into account both technical and non-technical factors such as extended lifetime, security, availability and control of the solution, Alliander, an electric utility in Netherlands deployed a private 3G CDMA2000 network for smart metering. Although 3G CDMA2000 satisfies the requirements of smart grid applications, an analysis on the use of the current state of the art 3G CDMA2000 for smart grid applications indicates that its usage results in high percentage of control overhead, high latency and high power consumption for data transfer. As a part of this dissertation, we proposed FLEX-MAC - a new Medium Access Control (MAC) protocol that reduces the latency and overhead in smart meter data collection when compared to 3G CDMA2000 MAC. As mentioned above the second problem studied in this dissertation is related to the transmission-side grid. Power grid transmission and sub-transmission lines are generally protected by distance relays. After a thorough analysis of U.S. historical blackouts, North American Electric Reliability Council (NERC) has concluded that the hidden failure induced tripping of distance relays is responsible for 70% of the U.S. blackouts. As a part of this dissertation, agent based distance relaying protection scheme is proposed to improve the robustness of distance relays to hidden failures and thus reduce the probability of blackouts. This dissertation has two major contributions. First, a hierarchically distributed non-intrusive Agent Aided Distance Relaying Protection Scheme (AADRPS) is proposed to improve the robustness of distance relays to hidden failures. The problem of adapting the proposed AADRPS to a larger power system network consisting of thousands of buses is modeled as an integer linear programming multiple facility location optimization problem. Distance relaying protection scheme is a real time system and has stringent timing requirements. Therefore, in order to verify if the proposed AADRPS meets the timing requirements or not and also to check for deadlocks, verification models based on UPPAAL real time model checker are provided in this dissertation. So, the entire framework consisting of AADRPS that aids in increasing the robustness of distance relays and reducing the possibility of blackouts, the multiple facility location optimization models and the UPPAAL real time model checker verification models form one of the major contributions of this dissertation. The second contribution is related to the MAC layer of AMI networks. In this dissertation, FLEX-MAC - a novel and flexible MAC protocol is proposed to reduce the overhead and latency in smart meter data collection. The novelty of the FLEX-MAC lies in its ability to change the mode of operation based on the type of the data being collected in a smart meter network. FLEX-MAC employs Frame and Channel Reserved (FCR) MAC or Frame Reserved and Random Channel (FRRC) MAC for scheduled data collection. Power outage data in an AMI network is considered as a random data . In a densely populated area, during an outage, a large number of smart meters attempt to report the outage, which significantly increases the Random Access CHannel (RACH) load. In order to reduce the RACH traffic during an outage, this dissertation proposes a Time Hierarchical Scheme (THS). Also, in order to minimize the total time to collect the power outage data, a Backward Recursive Dynamic Programming (BRDP) approach is proposed to adapt the transmission rate of smart meters reporting an outage. Both the Optimal Transmission Rate Adaption and Time Hierarchical Scheme form the basis of OTRA-THS MAC which is employed by FLEX-MAC for random data collection. Additionally, in this work, Markov chain models are presented for evaluating the performance of FCR and FRRC MACs in terms of average throughput and delay. Also, another Markov model is presented to find the mean time to absorption or mean time to collect power outage data of OTRA-TH MAC during an outage. / Ph. D.

Substations are joints in the power system that represent nodes that are vital to stable and reliable operation of the power system. They contrast the rest of the power system in that they are a dense combination of critical components causing all of them to be simultaneously vulnerable to one isolated incident: weather, attack, or other common failure modes. Undoubtedly, the loss of these vital links will have a severe impact to the to the power grid to varying degrees. This work creates a cascading model based on protection system misoperations to estimate system risk from loss-of-substation events in order to assess each substation's criticality. A continuation power flow method is utilized for estimating voltage collapse during cascades. Transient stability is included through the use of a supervised machine learning algorithm called random forests. These forests allow for fast, robust and accurate prediction of transient stability during loss-of-substation initiated cascades. Substation risk indices are incorporated into a preventative optimal power flow (OPF) to reduce the risk of critical substations. This risk-based dispatch represents an easily scalable, robust algorithm for reducing risk associated with substation losses. This new dispatch allows operators to operate at a higher cost operating point for short periods in which substations may likely be lost, such as large weather events, likely attacks, etc. and significantly reduce system risk associated with those losses. System risk is then studied considering the interaction of a power grid utility trying to protect their critical substations under a constrained budget and a potential attacker with insider information on critical substations. This is studied under a zero-sum game theoretic framework in which the utility is trying to confuse the attacker. A model is then developed to analyze how a utility may create a robust strategy of protection that cannot be heavily exploited while taking advantage of any mistakes potential attackers may make. / Ph. D. / Substations are key components to the continued and reliable operation of the power system. Their removal from the power system would severely hinder the system’s ability to transport power from power producers to end consumers. As larger weather events and potential threats to the power system are being considered, power system engineers to start considering the impact that losing substations would cause on the system. This work studies the impact on the system associated with losing substation and ranks them to find the most important ones. A probabilistic model is created based on incorrect operations in power system protection elements that historically have exacerbated large events in the power system. Mitigation of this impact is then studied through two preventative means: changing the operating condition of the current system and adding protection to the substations. This is in order to secure the system before potentially losing the operation of a substation. The operating point change is formulated as a new optimization problem that helps alleviate stress on the system close to the most critical substations found in the earlier model. Protection of these substations is analyzed through game-theoretic means where the utility tries to confuse any potential attackers on which substations actually have true, rigid protection on them. In doing so, on expectation, the damage done to the system may be reduced significantly.

One of the objectives of this study is to develop a methodology, together with a set of software programs that evaluate, in a power system, the risks of catastrophic failures caused by hidden failures in the hardware or software components of the protection system. The disturbance propagation mechanism is revealed by the analysis of the 1977 New York Blackout. The step-by-step process of estimating the relay hidden failure probability is presented. A Dynamic Event Tree for the risk-based analysis of system catastrophic failures is proposed. A reduced 179-bus WSCC sample system is studied and the simulation results obtained from California sub-system are analyzed. System weak links are identified in the case study. The issues relating to the load and generation uncertainties for the risk assessment of system vulnerabilities are addressed. A prototype system - the Hidden Failure Monitoring and Control System (HFMCS) - is proposed to mitigate the risk of power system catastrophic failures. Three main functional modules - Hidden Failure Monitoring, Hidden Failure Control and Misoperation Tracking Database - and their designs are presented. Hidden Failure Monitoring provides the basis that allows further control actions to be initiated. Hidden Failure Control is realized by using Adaptive Dependability/Security Protection, which can effectively stop possible relay involvement from triggering or propagating disturbance under stressed system conditions. As an integrated part of the HFMCS, a Misoperation Tracking Database is proposed to track the performance of automatic station equipment, hence providing automatic management of misoperation records for hidden failure analysis. / Ph. D.