Dissertation submitted in compliance with the requirements for Master's Degree in Technology: Electrical Engineering (Light Current), Durban Institute of Technology, 2002. / Modern society as a whole seems destined to have an ever-increasing demand for power for both industrial and domestic use, as continued population growth means that cities, suburbs and industrial areas become larger and denser. At the same time the trend toward increased productivity in all segments of industry is influencing the development and techniques employed at locating faults in power cables and networks to ensure only limited downtime and reduced direct and indirect costs associated with the location of faults / M

Fault location for series compensated lines cannot be addressed sufficiently by conventional solutions developed for traditional uncompensated lines. Line-parameters vary with loading and weather conditions, and therefore settings used for fault location are often erroneous. Line-parameter free solutions for fault location are therefore more reliable and accurate than conventional solutions that require such settings. Hence, line-parameter free fault location algorithms for single-circuit and double-circuit series compensated transmission lines were developed during the research project. Single-circuit lines and double-circuit lines both present unique challenges for fault location. They also vary in the number of available measurements that can be used to arrive at a solution for distance to fault. A third algorithm is presented that allows the extension of existing short line algorithms to the case of long lines. This is done by providing a method for incorporating the line shunt admittance into these existing algorithms. The aforementioned three bodies of research work, form the focus of this thesis. The algorithms are derived using two-terminal synchronised current and voltage sampled measurements. Of these, the algorithms for series compensated lines are also derived for asynchronous measurements. Phasors are obtained by carrying out a Fast Fourier Transform, and then appropriate calculations are performed for distance to fault. The thesis covers the mathematical derivations of the algorithms, involving the algebraic reduction of non-linear equations in numerous variables into a single expression for distance to fault. The results for a variety of simulation tests are shown subsequently and discussed. Various fault resistances, fault types, degrees of series compensation, line lengths, fault levels are considered in the tests carried out. The algorithms are largely found to be highly accurate under these various conditions, and where the algorithms perform to a lesser degree of accuracy are highlighted and discussed. Lastly, a detailed chapter discussing future work is also included in the thesis.

Power quality related problems cause large financial losses in the order of billions worldwide. The evaluation process aimed at determining effective remedial actions starts with the correct identification and characterization of power quality disturbances. Measurements performed in the electrical power network and the corresponding collection and process of data are the primary method of characterization of the phenomena. The ideal deployment of monitoring devices would entail a monitor installed at each node of the network so that the power quality throughout the system could be directly assessed. In reality, however, technical and mostly economical constraints limit the number of monitors a network operator can install in the system. Power quality at non-monitored sites, therefore, has to be estimated by extrapolating the data from monitored sites. Consequently, it is crucial to identify the sites that provide the most accurate picture of the system’s overall power quality. Unfortunately, no recommended practices or guidelines for determining the minimum number and the best locations for optimal power quality monitoring have been prescribed in standards or reports. This thesis investigates voltage sag monitoring as part of a larger power quality monitoring scheme. The aim is to develop a methodology for optimal monitor placement for fault location and sag estimation. The thesis, divided in four main parts, focuses on network sag performance estimation and optimal monitor placement for fault localization and sag estimation. The introductory part of the thesis gives an overview of power quality surveys conducted around the world in recent years with special emphasis on the monitor placement criteria used. It also summarizes the main methods for network sag performance estimation proposed to date. The main part of the thesis firstly reviews the most referred optimal monitor placement method for sag estimation proposed in academia, highlighting its limitations. Then a robust fault location algorithm is proposed to enhance this method and overcome the identified limitations. The enhanced method is thereafter used as the basis for the generalization of one of the leading methods for optimal monitor placement for fault location in the second part of the thesis. The formulation of its optimization problem is extended for application in large power networks by adapting the modeling approach for the sag monitor placement problem. To reduce the high computational and memory burden associated with finding the optimal fault location monitor program, the thesis introduces a less memory intensive heuristic search algorithm in the third part of the thesis. A series of custom objective functions are proposed to be used with this algorithm to find optimal fault location and sag monitoring programs aimed at estimating the most critical events for customers. In the final part of the thesis, the main concepts and techniques introduced in the first three sections are combined to develop a synergistic approach to optimal monitor placement for sag characterization based on fault location. The suitability of the new method for techno-economic assessment of voltage sags using strategically or conventionally deployed monitors is established.

No description available.

The fault location and reconfigurable designs of Ripple Carry (RC) adders and Carry Save (CS) multipliers are studied in this thesis. The proposed designs can locate a faulty cell and reconfigure the faulty array to tolerate the faulty cell. Laser programming technique is used for fault location and reconfiguration. The key idea employed in the proposed methods is to perform diagnosis and reconfiguration at the same time. Appropriate fuses are programmed to locate a faulty cell, and the programmed fuses are also used for reconfiguration. This leads to small area overhead, and hence, substantial improvement in yield. Experimental results show that the yield enhancement of reconfigurable RC adders and CS multipliers is substantial compared with that of original RC adders and CS multipliers, respectively. / Master of Science

Power outages usually lead to customer complaints and revenue losses. Consequently, fast and accurate fault location on electric lines is needed so that repair work can be carried out as fast as possible. Chapter 2 describes novel fault location algorithms for radial and non-radial ungrounded power distribution systems. For both types of systems, fault location approaches using line to neutral or line to line measurements are presented. It’s assumed that network structure and parameters are known, so that during-fault bus impedance matrix of the system can be derived. Functions of bus impedance matrix and available measurements at substation are formulated, from which the unknown fault location can be estimated. Evaluation studies on fault location accuracy and robustness of fault location methods to load variations and measurement errors has been performed. Most existing fault location methods rely on measurements obtained from meters installed in power systems. To get the most from a limited number of meters available, optimal meter placement methods are needed. Chapter 3 presents a novel optimal meter placement algorithm to keep the system observable in terms of fault location determination. The observability of a fault location in power systems is defined first. Then, fault location observability analysis of the whole system is performed to determine the least number of meters needed and their best locations to achieve fault location observability. Case studies on fault location observability with limited meters are presented. Optimal meter deployment results based on the studied system with equal and varying monitoring cost for meters are displayed. To enhance fault location accuracy, an optimal fault location estimator for power distribution systems with distributed generation (DG) is described in Chapter 4. Voltages and currents at locations with power generation are adopted to give the best estimation of variables including measurements, fault location and fault resistances. Chi-square test is employed to detect and identify bad measurement. Evaluation studies are carried out to validate the effectiveness of optimal fault location estimator. A set of measurements with one bad measurement is utilized to test if a bad data can be identified successfully by the presented method.

Thesis (MScEng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: This thesis describes the development of a GPS Based Time Stamping and Scheduling System for power system applications. These applications include Wide Area Measurements (WAMs) of electrical power system quantities and high-voltage transmission line fault location. The developed system employs a microcontrolIer and a GPS receiver to synchronise an onboard microsecond-accurate clock to a global time standard. The system is therefore able to provide an accurate GPS-synchronised time stamp of a received trigger signal for use in highvoltage transmission line fault location. The system is also able to generate a trigger signal at a pre-programmed time for initiation of data acquisition runs on electrical power systems. The system was constructed and tested in a laboratory environment. Although the system is designed to operate in stand-alone mode, a host computer software program was also developed for system control and data downloading. The software program was used to time stamp a number of trigger signals and data was downloaded to a host computer. Trigger signals were also generated at predefined times. The acquired data was validated and presented. In conclusion, the low system cost, relative to existing commercial systems, accuracy and programmability of the developed system makes it suitable for a wide variety of time-critical data acquisition applications. / AFRIKAANSE OPSOMMING: Hierdie tesis beskryf die ontwikkeling van 'n GPS gebaseerde tyd stempel en skedulerings sisteem met die oog op kragstelsel toepassings. Ingesluit by hierdie toepassings is wye area metings op elektriese kragstelsels, asook foutopsporing op hoogspanning transmissielyne. Die ontwikkelde sisteem gebruik 'n mikrobeheerder en 'n GPS ontvanger om 'n aanboord mikrosekonde-akkurate horlosie te sinkroniseer met 'n internasionale tyd standaard. Dus kan die ontwikkelde sisteem 'n akkurate GPS gesinkroniseerde tyd stempel aan 'n snellersein heg. Hierdie tyd stempel kan gebruik word in hoogspanning transmissielyn foutopsporing. Die sisteem kan ook 'n snellersein genereer op 'n vooraf geprogrammeerde tyd. Hierdie snellersein kan gebruik word om belangrike data van elektriese kragstelsels te versamel, deur gebruik te maak van bestaande dataversamelingstelsels. Die sisteem was ontwerp en getoets in laboratorium toestande. Alhoewel die stelselontwerp is om alleenstaande te funksioneer, is 'n beheer rekenaar gebruik om, met die hulp van ontwikkelde sagteware, die sisteem te beheer en data af te laai. 'n Tyd stempel is aan 'n aantal snellerseine geheg en hierdie data is afgelaai na 'n beheer rekenaar. Die sisteem is ook geprogrammeer om 'n aantal snellerseine te genereer op vooraf gedefinieerde tye. Die data wat uit hierdie toetse versamel is, is bespreek. In vergelyking met bestaande kommersiële stelsels is die ontwikkelde stelsel se lae koste, akkuraatheid en programmeerbaarheid eienskappe wat die stelsel geskik maak vir 'n wye verskeidenheid van tyd-kritieke dataversameling toepassings.

This work takes place in the context of distribution power system protection and tries to improve the detection and location of earth faults. The protection problem is vast and many ideas emerge every year to enhance the reliability of the grid. The author has focused his energy into the compensated and isolated network protection in the specific case of single phase earth fault. This PhD thesis is divided in two main parts that might be considered as independent. The first part studies the detection of single phase earth fault and the second analyzes the fault location of such fault.<p><p>Pragmatism was asked during these three years because a product development was necessary especially regarding the fault detection problem. The first part of the thesis took 18 months of research and development to obtain a prototype of transient protection able to detect single phase earth fault in compensated and isolated network. The sensitivity of the algorithm has been emphasized regarding the fault impedance and to detect earth fault up to 5 kOhm depending on the network characteristic. The fault location problem has been much more theoretical although the problem links to the accuracy of the algorithm and its robustness regarding wrong fault location indication has been strongly considered.<p><p>Compensated networks and in some conditions isolated networks are distribution from 12 kV up to 110 kV mostly used in East and North Europe but also in China. Others areas also work with such networks but they also have others systems and they do not use them on all the territory. These networks have the particularity to obtain very small fault current in case of single phase earth fault. Low current means the difference between a faulty and a sound feeder is not significant. Therefore classic overcurrent protection is completely useless to protect the network, forcing the development of more complex algorithm. A possibility to overcome the problem of the small fault current is to develop a transient protection. The transient occurring at the beginning of the fault has strong information to distinguish a faulty from a sound feeder. In this work I have chosen to use not only the transient but also the steady state to get the best sensitivity.<p><p>Then the fault location has been investigated but the small information coming from the faulty feeder is not sufficient to have a precise enough position of the fault. Therefore, active system has been suggested to be implemented in the grid to increase the faulty current and have enough power for a precise location. Different existing algorithms based on the steady state at the nominal frequency are compared using a tool developed during this work. Recommendations are then made depending on the topology, the network parameters, the measurements precision, etc. Due to the complexities of the problem, a simulator has been coded in Matlab .The user of a possible fault location must then use this tool to understand and see the future fault location precision that he could obtain from different algorithm on his network. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

a control, power quality and stability perspective. This is chiefly due to the future influence on power system behaviour resulting from the rapid cumulative growth of grid integrated wind power, and the improved control characteristics afforded by modern variable speed wind power generators. There is consequently strong motivation to enhance the inherent control robustness, power quality and fault-ride-through characteristics of modern wind power generators. By so doing, the attributes essential for power system operation regarding security of supply, reliability, and power quality can be assured. The work presented in this thesis employs a two-fold methodology in order to improve the inherent control, power quality and fault tolerance characteristics of a modern wind power generator based on a 2MW medium-voltage directly-driven permanently-excited architecture employing full-scale power conversion. Firstly, due to the complexity of modern wind power generators, accurate and complementary detailed non-linear (circuit orientated) and linear analytical (state-space based) wind generator models are developed. Collectively, these facilitate a wide range of detailed transient and smallsignal, control, stability and fault analysis studies. Ultimately, this facilitates the means by which advanced AC voltage controls are developed that significantly extend the wind power generator stable operating range for grid strength variations (grid impedance variation). Secondly, a supercapacitor based electrical energy storage system is designed and integrated within the developed wind generator models in order to facilitate the means by which fault-ridethrough characteristics and power quality can be improved. Fault-ride-through characteristics are ultimately improved by absorbing a proportion of generated power in the integrated storage system during grid-side faults. Power quality is ultimately improved by effectively buffering wind speed fluctuations in the integrated storage system so that a ‘smoothed’ version of the generated power results at the wind generator terminals.