Power system protection is important for service reliability and quality assurance. Various faults may occur due to natural and artificial calamity. To reduce the outage duration and promptly restore power services, fault section estimate has to be done effectively and accurately with fault alarms. Dispatchers study the changed statuses of protection devices from the Supervisory Control and Data Acquisition (SCADA) system to identify the fault. Single and multiple faults could coexist with the failed operation of relays and circuit breakers, or with the erroneous data communication. It needs a long time to process a large number of alarms under various conditions involving multiple faults and many uncertainties. To cope with the problem, an effective tool is helpful for the fault section estimation and alarm processing. Besides, power transformer plays a major role in a power system. For a better service quality, it is important to be routinely examined for detecting incipient faults inside transformers. Preventive techniques for early detection can find out the incipient faults and avoid outages. Power quality is another issue to considerable attentions from utilities and customers due to the popular uses of many sensitive electronic equipment. Harmonics, voltage swell, voltage sag, and, power interruption could downgrade the service quality. To ensure the power quality, detecting harmonic and voltage disturbances becomes important. A detection method with classification capability will be helpful for detecting disturbances. This dissertation developed various algorithm for detection including fault section detection, alarm processing, transformer fault diagnosis, and power quality detection. For a well-dispatched power system, the adaptive detection idea will be used, and the existing SCADA/EMS will be integrated without extra devices.

Power quality is a main subject to considerable attentions from utilities and customers owing to the popular uses of many non-linear electronic equipment in recent years. Harmonics, voltage swell, voltage sag, and, power interruption could downgrade the service quality. To ensure the power quality, detecting harmonic and voltage disturbances becomes an important issue. In other words, a detection method with classification capability will be helpful for detecting disturbances. The thesis proposed two models of power quality detection for power system disturbances using voltage-current(V-I) characteristics in the time domain with hybrid wavelets grey relational analysis (WGRA), and self-organizing feature map network (WSOM). Morlet wavelets are responsible for extracting features from voltages and currents. GRA and SOM were employed to identify the types of various disturbance patterns. Computer simulations have demonstrated the computational efficiency and accurate recognition capability for power quality detection and discrimination with an IEEE 14-Bus power system.

Voltage sag (dip), a sudden reduction of the voltage magnitude within a short duration in power system, is one of major concerns of power quality problems. The main reason of the increased concerns for voltage sag problems is that the losses caused by voltage sag events are high and not negligible. Reliability indices have been used for many years to quantify the effect of sustained interruptions on the electric power system. Power quality indices reflecting the severity of various power quality problems, such as flicker, harmonics, voltage swell and sag conditions, power factor, losses, electromagnetic interference, and other phenomena, are still under development. The representation and classification of voltage sags have been studied recently by standard-setting organizations. In order to find compatibility between service quality and the equipment adopted and a least cost solution for possible power quality problems, the concept of system disturbance level and equipment immunity level was proposed in IEC 61000-3-7 but without clear definitions. A novel voltage sag index based on fuzzy logic technique to quantify system disturbance and equipment immunity levels is proposed in this dissertation. This approach takes network vulnerability, equipment sensitivity and uncertainties in measuring voltage sags into account, thereby, providing meaningful information for both the utility and customers. Using the proposed method, the probabilistic distribution of system disturbances can be obtained from the single event indices of all events recorded and the probabilistic distribution of equipment sag immunity capability can be evaluated based on the device voltage sag tolerance curve. This dissertation also presents a novel framework for predicting the number of equipment disruptions due to voltage sags in a unit of time by using the disturbance and immunity levels concepts. In the proposed approach, the number of disruptions is computed by using the unreliability concept. The area of overlapping between the distributions of site disturbance and equipment immunity levels, which indicates the number of possible disruptions, is calculated based on interference theory and reliability computations. The presented methodology can be used as a planning tool to quantify the system disturbances and equipment sensitivity. It can also be used to perform cost analysis of the compatibility of equipment with an electric power system. To minimize the costs due to voltage sags, it is always a good strategy to maintain a minimum overlap between the equipment immunity level and site disturbance level to have satisfactory operation of the equipment. The tool achieved in this work can be used to perform such analyses.

This research work is devoted to the analysis, design and development of the first medium power Current-Source Converter (CSC) based distribution-type Static Synchronous Compensator (D-STATCOM) with simplest converter topology and coupling transformer connection. The developed CSC-D-STATCOM includes a +/-750kVAr full-bridge CSC employing Selective Harmonic Elimination Method (SHEM), a 250kVAr low-pass input filter at 1kV voltage level, and a &amp / #916 / /Y connected coupling transformer for connection to medium-voltage load bus. The power stage of CSC is composed of series connection of natural air-cooled high-voltage IGCT switched at 500 Hz for the elimination of four lowest current harmonic components (5th, 7th, 11th, 13th), and optimized fast recovery high voltage diode in each leg. Reactive power control is achieved by applying the phase shift angle control at fixed modulation index, which is implemented digitally on a DSP microcontroller. The developed system has been implemented for compensation of rapidly varying reactive power demand of coal mining excavators in Turkish Coal Enterprises. The field test results have shown that the proposed CSC D-STATCOM serves as a technologically new full substitute of conventional Voltage-Source Converter based D-STATCOM having complex transformer connections in view of relatively fast response in reactive power compensation, very low total demand distortion factors, complying with the IEEE Std. 519-1992 even for the weakest power systems, and acceptable efficacy figures.

Electric Arc Furnace (EAF) modeling has been a common research area to date. This thesis work proposes a new field-data based EAF-specific model. The data used in developing the proposed model is obtained from field measurements of instantaneous voltages and currents of EAF the plants. This model presents the dynamic behavior of the EAF system including all its parts, which are the EAF transformer, the secondary circuit, the electrodes moving and the arc itself. It consists of a cascade connected variable-resistance and &ndash / inductance combination to represent the variation in time of the fundamental frequency, and a current source in parallel with it to inject the harmonics and interharmonics content of the EAF current. The proposed model is capable of representing both AC and DC EAFs, whose controllers&rsquo / set points are the impedance values seen from the low voltage (LV) side of the EAF transformer. The validity of the proposed model has been verified by comparing EMTDC/PSCAD simulations of the model with the field measurements. The results obtained have shown quite satisfactory correlation between the behavior of the proposed model and v the actual EAF operation. To show the advantages of the model while developing FACTS solutions for power quality (PQ) problem mitigation of a given busbar supplying single- or multi-EAF installations, various applications are presented.

<p>The thesis deals with the application of compensators andswitches based on power electronics in AC transmission anddistribution systems. The objective of the studieddevices/equipment is the power flow and voltage control intransmission systems and the mitigation of voltage sags andmomentary interruptions to critical loads in distributionsystems.</p><p>For validating the power electronics based devices/equipmentdescribed in the thesis, scaled models at a real-time simulatorhave been built. Simulation results of these models arepresented and discussed in the thesis.</p><p>The equipment studied in the thesis exploit the fast controlactions that can be taken by power electronics devices, whichare much faster than the speed of conventional equipment andprotection systems, based on electromechanical devices. In thisway, the power quality of distribution systems is improved,regarding duration and magnitude of voltage sags (dips) andmomentary interruptions, which are the most relevant types ofdisturbances in distribution systems.</p><p>The thesis presents some compensators based onforced-commutation voltage-source converters for correctingvoltage sags and swells to critical loads. The seriesconverter, usually denoted Dynamic Voltage Restorer (DVR), hasbeen proved suitable for the task of compensating voltage sagsin the supply network. The use of solid-state devices ascircuit breakers in distribution systems has also been studiedwith the objective of achieving fast interruption or limitationof fault currents. The location and practical aspects for theinstallation of these solid-state breakers are presented. Ithas beenshown that a configuration based on shunt and seriesconnected solid-state devices with controllable turn-offcapability can also provide voltage sag mitigation, without theneed of transformers and large energy storage elements.</p><p>The operation and control of two Flexible AC TransmissionSystem (FACTS) devices for voltage and power flow control intransmission systems, namely the Static Synchronous Compensator(STATCOM) and the Unified Power Flow Controller (UPFC),respectively, are also studied. A faster response compared totraditional equipment consisting of mechanically based/switchedelements is then achieved. This allows a more flexible controlof power flow and a secure loading of transmission lines tolevels nearer to their thermal limits. The behaviour of thesedevices during faults in the transmission system is alsopresented. Keywords: power electronics, power quality, voltagesags, voltage-source converters, Custom Power, FACTS, real-timesimulations, solid-state devices.</p>

<p>During the last decade, power quality has been recognised asa global problem. Among different types of power qualityproblems, voltage sags have been identified to be one of themost severe problems for different process industries. The mostcommon reason to voltage sags is lightning strikes in powerlines. Protection equipment, usually located at switchyards,disconnect faulted power lines as soon as possible, which isapproximately 100 ms. Thus, the duration of voltage sags areapproximately 100 ms. The sensitivity to voltage sags ofelectrical equipment in process industries can be observed asfor instance malfunction, automatic turnoff or damages.</p><p>This thesis gives an overview of three metals processes withfocus on the sensitivity to voltage sags and interruptions. Theinherent energy in the process is used to find the sensitivity.This energy may also be used to obtain "ride-through" for theprocesses. The three metals processes are a blast furnaceprocess, a hot rolling mill process and a cold rolling millprocess. The main attention in this thesis is paid to the blastfurnace process, which is powered by a line-operatedsynchronous machine.</p><p>The thesis shows that the protection equipment forelectrical machines can be adjusted to avoid unnecessaryshutdowns. It is also explained why there are high torque andcurrents during voltage sags as well as after voltage sags. Itis shown that the first peak torque and current during thevoltage sags is almost proportional to the voltage change, thatis the voltage magnitude before the voltage sag minus thevoltage magnitude during the voltage sag. The first peak torqueand current after the voltage sag depends sinusoidal-like onthe duration of the voltage sag and almost proportional to thevoltage change during the voltage sag. There is no fluxsaturation during voltage sags, however after voltage sagssaturation is very likely to occur. The thesis explains why andalso how the flux is changed during and after voltage sags.</p><p>The duration of voltage sags is in many cases set by theprotection equipment located in switchyards. It is shown thatthe durations of voltage sags can be changed to durations thatwill cause less peak torque and current after voltage sags forline-operated AC-machines. It is also shown how this istheoretically achieved.</p><p><b>Keywords:</b>Rolling mill, Blast furnace, Power Quality,Synchronous machine, Asynchronous machine, Voltage sag, Voltageinterruption, Ride-through, Process disturbances, Simulation,Modelling</p>

A model of the accurate harmonic allocation methods is developed to improve the current emission limits of IEEE Std.519. IEC 61000-3-6 and IEEE Std. 519 have by now been accepted as two well known standards for interconnecting the MV and HV-EHV customers to utility systems and widely adopted as standards to many power utilities. It is worth noting that the harmonic current emission limits of both standards have not been compared and justified with analytical proofs because there is still no explanation that discusses the origin of the emission limits in IEEE Std. 519, or the complex feature of IEC 61000-3-6. Two new novel methods of allocating the harmonic current emission limits for MV customers and HV-EHV customers have been proposed. Both methods have been developed in accordance with the principles of IEC 61000-3-6. Task II has compared and investgated the emission limits of both IEC 61000-3-6 and IEEE Std. 519. The difference, inconsistency and inaccuracy have been proven with the perspective of practical evaluations based on their own principles. The investigations focus on the specific numerical proofs of the resulting voltage distortions and the current emission limits in the MV and HV-EHV systems rather than on the philosophies. The proposed methods strongly support IEC 61000-3-6 and IEEE Std. 519, and add to their value; these methods could also help utilities allocate fairly and accurately harmonic emission limits to their MV and HV-EHV customers.

This thesis focuses on simulating, detecting, localizing and classifying the power quality disturbances using advanced signal processing techniques and neural networks. Primarily discrete wavelet and Fourier transforms are used for feature extraction, and classification is achieved by using neural network algorithms. The proposed feature vector consists of a combination of features computed using multi resolution analysis and discrete Fourier transform. The proposed feature vectors exploit the benefits of having both time and frequency domain information simultaneously. Two different classification algorithms based on Feed forward neural network and adaptive resonance theory neural networks are proposed for classification. This thesis demonstrates that the proposed methodology achieves a good computational and error classification efficiency rate.

Present day electrical equipment is rapidly becoming more and more sensitive to power quality problems, especially voltage sags. Various voltage sag correction devices are avaliable. This thesis analyzes a two-switch, single-phase electronic voltage regulator for correcting voltage sags. The theory of this voltage regulator has been investigated. An analytical method for sizing the energy storage capacitors has been established. The voltage regulator has been modeled and its steady-state and dynamic behavior has been studied by means of detailed computer simulations. A 220-V, 50-Hz, 1-kW rated regulator has been designed, simulated, and built. The results on the performance of voltage regulator and conclusions are also given.