Master of Science

The growing usage of computer networks is requiring improvements in network technologies and management techniques so users will receive high quality service. As more individuals transmit data through a computer network, the quality of service received by the users begins to degrade. A major aspect of computer networks that is vital to quality of service is data routing. A more effective method for routing data through a computer network can assist with the new problems being encountered with today's growing networks. Effective routing algorithms use various techniques to determine the most appropriate route for transmitting data. Determining the best route through a wide area network (WAN), requires the routing algorithm to obtain information concerning all of the nodes, links, and devices present on the network. The most relevant routing information involves various measures that are often obtained in an imprecise or inaccurate manner, thus suggesting that fuzzy reasoning is a natural method to employ in an improved routing scheme. The neural network is deemed as a suitable accompaniment because it maintains the ability to learn in dynamic situations. Once the neural network is initially designed, any alterations in the computer routing environment can easily be learned by this adaptive artificial intelligence method. The capability to learn and adapt is essential in today's rapidly growing and changing computer networks. These techniques, fuzzy reasoning and neural networks, when combined together provide a very effective routing algorithm for computer networks. Computer simulation is employed to prove the new fuzzy routing algorithm outperforms the Shortest Path First (SPF) algorithm in most computer network situations. The benefits increase as the computer network migrates from a stable network to a more variable one. The advantages of applying this fuzzy routing algorithm are apparent when considering the dynamic nature of modern computer networks. / Ph. D.

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The power system has long been operated in a shroud of introspection. Only recently have dynamic, wide-area time synchronized grid measurements brought to light the complex relationships between large machines thousands of miles apart. These measurements are invaluable to understanding the health of the system in real time, for disturbances to the balance between generation and load are manifest in the propagation of electromechanical waves throughout the grid. The global perspective of wide-area measurements provides a platform from which the destructive effects of these disturbances can be avoided. Virginia Tech's distributed network of low voltage frequency monitors, FNET, is able to track these waves as they travel throughout the North American interconnected grids. In contrast to other wide-area measurement systems, the ability to easily measure frequency throughout the grid provides a way to identify, locate, and analyze disturbances with high dynamic accuracy. The unique statistical properties of wide-area measurements require robust tools in order to accurately understand the nature of these events. Expert systems and data conditioning can then be used to quantify the magnitude and location of these disturbances without requiring any knowledge of the system state or topology. Adaptive application of these robust methods form the basis for real-time situational awareness and control. While automated control of the power system rarely utilize wide-area measurements, global insight into grid behavior can only improve disturbance rejection. / Ph. D.

The goal of the proposed procedure in this dissertation is the implementation of phasor measurement unit (PMU) based instability detection for islanding prediction procedures using decision tree and neural network modeling. The islanding in the power system define as a separation of the coherent group of generators from the rest of the system due to contingencies, in the case that all generators are coherent together after introducing a fault, it is called stable or non-islanding. The main philosophy of islanding detection in the proposed methodology is to use decision trees and neural network data mining algorithms, performed off-line, to determine the PMU locations, detection parameters, and their triggering values for islanding detection. With the information obtained from accurate system models PMUs can be used online to predict system islanding with high reliability. The proposed approach is proved using a 4000 bus model of the California system. Before data mining was performed, a large number of islanding and non-islanding cases were created for the California model. PMUs data collection was simulated by collecting the voltage and current information in all 500 kV nodes in the system. More than 3000 cases were collected and classified by visual inspection as islanding and non-islanding cases. The proposed neural network and decision tree procedures captured the knowledge for the correct determination of system islanding with a small number of PMUs. / Ph. D.

Because of a move from Independent System Operators (ISOs) to Regional Transmission Operators (RTOs), a need for real-time wide-area system monitoring has arisen. The state estimator (SE) is the tool currently used in power systems for real-time monitoring. Because current SE techniques become operationally expensive on such large systems, it is beneficial to consider alternate methods for wide-area state estimation (WASE). In particular, hierarchal methods for WASE become beneficial for large systems because of their speed of operation and relatively low data volume. This study tests four hierarchal WASE methods - two taken from literature, and two developed by the author — and compares them with the use of an integrated wide-area estimator. Additionally, because of their accurate and readily available measurement capability, the inclusion of phasor measurement unit (PMU) data in the WASE methods is examined. For the purpose of realistically integrating an RTO WASE with current ISOs, the methods are constrained so that they do not require sensitive data, nor do they alter the operation of the ISOs SE in any way. The methods are tested for speed of operation, global and local accuracy, and robustness under bad data and data loss. / Master of Science

Verksamheten ombord på fartyg blir mer beroende av datakommunikation och många av arbetsuppgifterna ombord underlättas genom att besättningen kan nå information lagrad på annan plats. Fartygens bredbandsanslutning sker till största delen via satellitkommunikation där långa avstånd och begränsad datahastighet resulterar i att datakommunikationen blir ineffektiv. I denna studie undersöks vilken prestandaförbättring som utrustning för nätverksoptimering kan innebära för långsamma WAN-förbindelser via satellit. Undersökningen visade att det största problemet med anslutningar via satellit är den signalfördröjning som uppkommer vid långa sändningsavstånd. Detta medför att det blir prestandaproblem för datatrafiken och användare upplever anslutningen som långsam. För att åtgärda detta finns utrustning som hanterar datatrafiken och genom olika tekniker kan öka prestandan på anslutningen. För att undersöka hur stor prestandaförbättringen kan vara genomfördes ett antal olika experiment med utrustning för nätverksoptimering. Experimenten genomfördes genom att utvärdera filöverföringar med och utan nätverksoptimering. Resultaten visar att utrustningen för nätverksoptimering ger en stor prestandaförbättring vid filöverföringar. / Shipboard operations have become more reliant of data communication and many of the duties on board may be facilitated if the crew can access information stored elsewhere. The broadband connection between ship and shore is mostly done via satellite communication where long distances and limited data rate results in inefficient data communication. This study examines network optimization and the performance improvement this can have regarding slow WAN connections via satellite. The survey showed that the biggest issue with data communication via satellite is the signal delay caused by the long transmission distance which means that there will be performance degradation for data traffic and users will experience the data communication as slow. To solve this there is equipment that enhances the performance of the connection and handles the data communication by implementing various techniques. To investigate how much the performance improvement can be this study carried out a number of experiments with network optimization equipment.  The experiments evaluated file transfer with and without network optimization. The results show that the network optimization gives a major performance improvement regarding file transfer.

International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada / As testing requirements on the ranges require ever more sophisticated cross correlation of data from multiple data acquisition sources, it becomes increasingly advantageous to collect and disseminate this information in a more network oriented fashion. This allows any of the data collected at physically separated sites to be used simultaneously at multiple mission control or data reduction centers. This paper presents an approach that maximizes the use of legacy communication paths and data reduction systems to support an evolutionary migration toward the day when testing can take full advantage of commercial communication protocols and equipment such as OC-3, ATM, etc. One key element of this approach is the packetizing of data at each reception point to provide virtual circuit switching using packet routing. Based on the newly adopted IRIG/RCC 107-98 standard, the system may even be expanded all the way back to the actual sensors. The second key element is the use of the readily available time and timing pulses based on GPS to establish a uniform sampling interval that will allow the cross correlation of data received at different points spread over a wide area.

<p>Today’s electrical transmission & distribution systems, are facing a number of challenges related to changing environmental, technical and business factors. Among these factors are, increased environmental restrictions leading to higher share of production from renewable and uncontrollable sources as well as local environmental concerns regarding construction of new transmission and distribution lines. The re-regulation of the electricity market has created a dynamic environment in which multiple organizations have to coordinate and cooperate in the operation and control of the power system. Finally, the high rate of devel-opment within the ICT field is creating many new opportunities for power system opera-tion and control, thanks to introduction of new technologies for measurement, communi-cation and automation.</p><p>As a result of these factors, Wide Area Monitoring and Control (WAMC) systems have been proposed. WAMC systems utilize new ICT based technologies to offer more accurate and timely data on the state of the power system. WAMC systems utilize Phasor Measure-ment Units (PMUs) that have higher data rates and are time synchronised using, GPS satel-lites. This allows synchronized observation of the dynamics of the power system, making it possible to manage the system at a more efficient and responsive level and apply wide area control and protection schemes. The success WAMC systems, on the other hand, are largely dependent on the performance of the Information and Communication Technology (ICT) infrastructure that would support them.</p><p>This thesis investigates the requirements on, and suitability of the ICT systems that support WAMC systems. This was done by identifying WAMC applications and the elicitation of their requirements. Furthermore, a set of simulation projects were carried out to determine the communication system characteristics such as delay and the impact of this delay on the WAMC system.</p><p>This thesis has several contributions. First, it provides summary and analysis of WAMC application priorities and requirements in the Nordic region. Secondly it provides simula-tion based comparison and evaluation of communication paradigms for WAMC systems. The research documented in this thesis addresses these paradigms by providing a compari-son and evaluation through simulation. Thirdly, the thesis provides insight to the possible sources of delay in WAMC architecture and the impact of these delays on data quality specifically data incompleteness. This provides insight on what applications are important to practitioners and what is the expected performance of these applications, as seen from the power system control and operation point of view.</p>

Compared with conventional measurements from supervisory control and data acquisition (SCADA) system, phasor measurement units (PMUs) provide time-synchronized and direct measurements of phasors. The availability of synchronized phasor measurements can significantly improve power system protection and analysis. This dissertation is specifically committed to using synchronized measurements for estimation of fault locations in transmission systems. Transmission lines are prone to various short-circuit faults. Accurate fault location is critical for rapid power recovery. Chapter 2 proposes a new fault location method based on sparse wide area measurements. One distinguishing feature of this method is its applicability to both transposed and untransposed transmission lines. In addition, the method is developed based on sparse-wide area measurement that may be taken far away from the faulted line. Shunt capacitances of transmission lines are also fully considered by the algorithm. Moreover, when synchronized measurements from multiple buses are available, an optimal estimator can be used to make the most use of measurements, and to detect and identify potential bad measurements. Most of the existing fault location literatures discuss common shunt faults, including single line-to-ground faults, line-to-line faults, line-to-line-to-ground faults, and three-phase faults. However, in addition to common shunt faults, some complex faults may also occur in power systems. Among these complex faults, evolving fault and inter-circuit fault are two typical examples. Chapter 3 extends the method developed in Chapter 2 to deal with evolving faults. The proposed wide-area fault location methods are immune to fault type evolution, and are applicable to both transposed and untransposed lines. Chapter 4 discusses location of inter-circuit faults. Inter-circuit fault is a type of simultaneous fault, and it is the most common simultaneous fault type. Inter-circuit faults between each circuit in a double-circuit line is the most common inter-circuit fault. A fault location method for inter-circuit faults on double-circuit lines are developed and evaluated in Chapter 4. Chapter 5 puts forward a fault location algorithm, which does not require line parameters information, for series-compensated transmission lines. Two-end synchronized voltage and current measurements are utilized. The proposed method is independent of source impedance and fully considers shunt capacitances of transmission lines.