abstract: Understanding the graphical structure of the electric power system is important in assessing reliability, robustness, and the risk of failure of operations of this criti- cal infrastructure network. Statistical graph models of complex networks yield much insight into the underlying processes that are supported by the network. Such gen- erative graph models are also capable of generating synthetic graphs representative of the real network. This is particularly important since the smaller number of tradi- tionally available test systems, such as the IEEE systems, have been largely deemed to be insucient for supporting large-scale simulation studies and commercial-grade algorithm development. Thus, there is a need for statistical generative models of electric power network that capture both topological and electrical properties of the network and are scalable. Generating synthetic network graphs that capture key topological and electrical characteristics of real-world electric power systems is important in aiding widespread and accurate analysis of these systems. Classical statistical models of graphs, such as small-world networks or Erd}os-Renyi graphs, are unable to generate synthetic graphs that accurately represent the topology of real electric power networks { networks characterized by highly dense local connectivity and clustering and sparse long-haul links. This thesis presents a parametrized model that captures the above-mentioned unique topological properties of electric power networks. Specically, a new Cluster- and-Connect model is introduced to generate synthetic graphs using these parameters. Using a uniform set of metrics proposed in the literature, the accuracy of the proposed model is evaluated by comparing the synthetic models generated for specic real electric network graphs. In addition to topological properties, the electrical properties are captured via line impedances that have been shown to be modeled reliably by well-studied heavy tailed distributions. The details of the research, results obtained and conclusions drawn are presented in this document. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2015

Transmission line is a crucial role in power transmission network which connects generating units to consumers. Some unpredicted failure events such as lightening or system faults can cause transmission line tripped, which may bring about a large interruption to the system and causes damage. When line outage happens, the power flow on the tripped line will be redistributed to the rest of lines in the system. It may cause risk of overload happens on other lines, and results in a cascading failure and system collapse. Reasonably, a single line outage will not affect all other lines in the system. Therefore, when a line outage happens, it is important for the system operator to have a preview of which lines will have serious impact and which lines will not, so that the operator can only focus on monitoring certain lines which will be seriously affected, rather than keeping monitoring the whole system. In this thesis, A Line Outage Distribution Factor (LODF) method is proposed and implemented in the IEEE 118 bus system to estimate active power flow redistribution after a line outage. After that, a definition of Thevenin electrical distance between two transmission lines is derived and applied to calculate electrical distances between the outage line and each line in the system. An exponential convergence tendency is found between maximum possible LODF predicted power flow variations and electrical distance, and an exponential regression method is applied to analyze this tendency. The contribution of this work is a rule has been found that starting from the outage line, the maximum possible active power flow variation on transmission lines exponentially decreases exponentially while the electrical distance increases. With only the information of system's normal operating condition and topological information, the maximum possible active power change on each lines caused by single line outage, and the margin of the impact of single line outage on power flow variations may propagate along electrical distance can be easily and quickly predicted. Ultimately, the goal of this work is to allow operators at the control center can concentrate on lines within a certain electrical distance instead of keeping monitoring the whole system when a line outage happens. / Master of Science

Continued increase in system load leading to a reduction in operating margins, as well as the tendency to move towards a deregulated grid with renewable energy sources has increased the vulnerability of the grid to blackouts. Advanced intelligent techniques are therefore required to design new monitoring schemes that enable smart grid operation in a secure and robust manner. As the grid is highly interconnected, monitoring of transmission and distribution systems is increasingly relying on digital communication. Conventional security assessment techniques are slow, hampering real-time decision making. Hence, there is a need to develop fast and accurate security monitoring techniques. Intelligent techniques that are capable of processing large amounts of captured data are finding increasing scope as essential enablers for the smart grid. The research work presented in this thesis has evolved from the need for enhanced monitoring in transmission and distribution grids. The potential of intelligent techniques for enhanced system monitoring has been demonstrated for disturbed scenarios in an integrated power system. In transmission grids, one of the challenging problems is network partitioning, also known as network area-decomposition. In this thesis, an approach based on relative electrical distance (RED) has been devised to construct zonal dynamic equivalents such that the dynamic characteristics of the original system are retained in the equivalent system within the desired accuracy. Identification of coherent generators is another key aspect in power system dynamics. In this thesis, a support vector clustering-based coherency identification technique is proposed for large interconnected multi-machine power systems. The clustering technique is based on coherency measure which is formulated using the generator rotor measurements. These rotor measurements can be obtained with the help of Phasor Measurement Units (PMUs). In distribution grids, accurate and fast fault identification of faults is a key challenge. Hence, an automated fault diagnosis technique based on multi class support vector machines (SVMs) has been developed in this thesis. The proposed fault location scheme is capable of accurately identify the fault type, location of faulted line section and the fault impedance in the distributed generation (DG) systems. The proposed approach is based on the three phase voltage and current measurements available at all the sources i.e. substation and at the connection points of DGs. An approach for voltage instability monitoring in 3-phase distribution systems has also been proposed in this thesis. The conventional single phase L-index measure has been extended to a 3-phase system to incorporate information pertaining to unbalance in the distribution system. All the approaches proposed in this thesis have been validated using standard IEEE test systems and also on practical Indian systems.

The transition of the power sector from vertically integrated utility (VIU) to deregulated system has resulted in reshaping of generation, transmission and distribution components. Some of the objectives of restructuring are to ensure a secure and reliable supply of electricity, encourage competition in all segments, sustain future economic and technological growth, etc. There are many challenges that arise in fulfilling these objectives. The thesis addresses some of them related to planning and operational aspects of real and reactive power, covering the following areas: Real power tracing, loss allocation and pricing Reactive power tracing, loss allocation and pricing Power system generation expansion planning Power transfer capability in interregional grids Voltage stability enhancement by improving reactive power margins In deregulated power systems, it has become important to identify the generation and transmission entities responsible in meeting loads. This is done by tracing the power flows through the transmission network. Power tracing is required to assess the extent of network usage by the participants, so as to allocate the transmission losses and charges. Many loss allocation methods are presented in the literature. The loss allocation method implemented in this thesis is a circuit based method. For obtaining the generators contribution towards meeting system loads and transmission losses, an approach of relative electrical distance (RED) between the generation and the load buses, is presented. The method is used to trace both real and reactive power flows. In the case of real power, the generators are the only sources and loads are the only sinks. However, reactive sources and sinks are distributed all along the transmission system. The reactive power sources considered are generators, switchable VAR sources (shunt capacitor banks) and line charging susceptances; and the reactive sinks are shunt reactors and reactive inductive loads. While tracing their flows the actual sources or sinks are to be identified which is obtained after adding reactive injections and absorptions at each bus. If the net value is absorbing, the bus is a reactive sink and if the net value is injecting, the bus is a reactive source. The transmission line charge susceptances contribution to the system’s reactive flows; and its aid extended in reducing the reactive generation at the generator buses is also discussed. A reactive power optimization technique is applied to optimally adjust the reactive controller settings of transformer taps, generator excitations and switched capacitors, so that the available reactive resources can be fully utilized. In the thesis, a methodology for evaluation of real and reactive power load and loss sharing proportions; and cost allocation towards transmission utilization is presented. Due to the ever growing increase in demands; on one hand the existing transmission networks are getting overloaded at some locations and on the other hand, the available generation is becoming insufficient to cater to the additional demand. To handle this problem, generation and transmission expansions become inevitable. Hence, additional public sector units or independent power producers and transmission providers are to be brought in. However in a restructured system, generally there is no central planning for new generation capacity or transmission additions. The reason being, these investments need huge capital and long period of commitment. While making a generation investment decision, expectations concerning future electricity demand, spot market prices, variations of regulatory policies, etc., are the major considerations. The locations, capacities and timing of new power plants are basically at the generation companies’ own discretion. Also, generation companies do not have any obligation to ensure sufficient supply of electricity to meet present and future requirements. Hence, it is a matter of concern as to how adequate generation capacity can be secured in the long run. Optimal siting and sizing of these new generation locations is also an issue of concern. In this thesis a new index called as ‘Tindex’ is proposed, which identifies prospective new generation expansion locations. The index is formulated based on the transmission network information, and it helps in identifying the most suitable new generation expansion locations. To implement this methodology each of the load bus is treated as a generation bus, one at a time, and the maximum generation capacity that can be installed at the location is computed from the approach. This method ensures minimum transmission expansion. Interconnected power systems help in exchanging power from one area to other areas at times of power deficiency in their own area. To enable this, their tieline capability to transfer power has to be sufficient, which is determined using total transfer capability (TTC) computation. TTC is an important index in power markets with large volume of interarea power exchanges and wheeling transactions taking place on an hourly basis. In the thesis, the total transfer capability (TTC) of interconnected tielines, under normal and contingency conditions is evaluated. The contingency cases evaluated are single line contingency, tieline contingency and generator outage. The most critical lines in each zone are identified using Fuzzy set theory. Unified power flow controller (UPFC), a flexible AC transmission system (FACTS) device is incorporated to improve the power transfers under contingency conditions. The best locations for UPFC placement are identified by analysing the power flow results obtained after considering the contingencies. For each of the normal and contingency cases, a base case and a limiting case are formed and the TTC is evaluated. Limiting case is formed by increasing the load in small steps till a point after which bus voltages or line loadings start to violate their stability constraints. To improve the system conditions in the limiting case, reactive power optimization and UPFC installation is carried out. The results reflect the improvement in system conditions and total transfer capability margins. Availability of sufficient generator reactive margins is very essential to ensure system’s voltage stability, without which even minor disturbances may lead to catastrophe. The amount of reactive power margin available in a system determines its proximity to voltage instability under normal and emergency conditions. One way of improving the reactive margin of a synchronous generator, is to reduce the real power generation within its MVA ratings. However this real power reduction will affect the real power contract agreements formed while power trading. The real power contracts are not disturbed and the reactive power margins are improved by optimally adjusting the other available reactive controllers, namely, generator exciter, transformer taps and shunt compensators. To have further control on the reactive flows, UPFC device is incorporated at appropriate locations. The thesis discusses how reactive margins are computed and subsequently improved using a reactive power optimization technique and UPFC. Case studies are carried out on typical sample 6bus, 8bus, 10bus, 16bus, 20bus, IEEE 30bus, IEEE 39bus systems, and reallife equivalents of Indian southern grid 24bus, 72bus, 87bus and 205bus systems to illustrate the proposed approaches.