The distance relays are used as the main protection in the first place and followed by transmission lines as backup protection. Traditional distance protection performs protection action by calculate the impedance seen from the relay location to fault location and compare it with predetermined protection areas. According to the ratio of voltage phasors to current in the traditional algorithm, there are some weaknesses. For example, conventional algorithms, detect the place of the high resistance single phase fault farther away from the actual location and may not work for faults that occurred at the end of the first area of the relay protection in long transmission lines.
To solve this problem, distance protection algorithm is provided in the double-feed network based on solving linear differential equation using one terminal data. This method is deduced in the R-L lumped transmission line model and not only detects faults inside and outside of protection areas , but also works pretty well and not makes mistakes in the faults with high resistance . When a fault occurs at the end of the first location relay, the fault distance is calculated greater than the actual fault distance, but less than estimated place in conventional relay. This will removed impact high-resistance for estimating place of fault greatly. For the correct operation of this algorithm, the main components and decaying DC in current and voltage signals are needed. this method is implemented on the IEEE 14 bus system, Resistance tolerance algorithm to the ratio of transient resistance, under the terms of power swing, load swing, fundamental system frequency swings and angle of the different error is investigated in PSCAD/EMTDC and MATLAB softwares and results show the more accurate function of the mentioned plan than the conventional algorithm.

In this study, an algorithm for detecting, classifying and locating faults in series compensated double circuit transmission lines has been investigated. Detection and classification algorithms are based on initial fault-induced current travelling waves (TWs) detected by the relay using the wavelet transform. In the fault detection algorithm, in order to detect short-circuit fault from other transients, another algorithm is proposed based on the difference between two consecutive cycles of the three-phase current signals. The algorithm for locating faults in one circuit is based on two-terminal unsynchronized voltage and current measurements. By solving current and voltage equations, depending on the distance variable with Newton- Raphson method, fault location and fault resistance are obtained. In order to increase accuracy, the mutual coupling between the parallel lines in the zero-sequence network is fully considered and the equivalent model of series compensated is not used. Also in this thesis a novel method for intercircuit faults detection, classification and location is proposed. Test signals are generated in PSCAD/EMTDC software and the algorithm is implemented in MATLAB. The results of the simulation confirm the performance of algorithms for different fault types in these lines.

 In order to improve the performance of single stage, multi-level AC/DC power factor correction converters with high DC link voltage, many studies have been done. This thesis investigates a three-level AC/DC isolated converter with high voltage DC link applications. This converter does the power factor correction and creation a three-level DC/DC in one step by sharing switches between two sides. Two controllers are used in this converter. The input controller does the task of power factor correction DC link voltage regulation and the output controller, controls the output voltage. With the proposed converter and switching scheme, input current shaping and output voltage regulation can be achieved simultaneously without applying additional switching actions in one step. In addition, the middle two switches are turned on under zero current (ZCS) in discontinuous conduction mode (DCM) operation, and the upper and bottom switches are turned on under zero voltage (ZVS). In this approach DC- link voltage is flexible and power factor can be modified by changing the DC-link voltage. In this thesis first operational modes of the converter are investigated then in order to achieve more power a three-phase converter with the same schematic, is introduced. Both of these two converters are simulated by Matlab-Simulink toolbox to prove the concept.

 C  onventional Distance Protection applies the positive-sequence impedance to protect a line against short-circuit faults. Series-Compensated lines may considerably change the positive-sequenc   e Impedance of the fault path and cause the Distance Relays to maloperate. In this thesis, to overcome this problem, the Mutual Impedance between Phases of a Transmission Line is used for the design of a new distance protection scheme. The voltages and currents of both ends of the line are applied to compute the mutual impedance between the relay and the fault point. The proposed scheme has a reliable performance in protection against single-phase and double-phase-to-ground faults and, therefore it can be used as a backup protection. Simulation results approve the efficiency of the proposed method in protection of series-compensated transmission lines.
Therefore, in this thesis, to overcome of communication conection between both ends, a grounded faults distance protection scheme based on measuring voltages and currents in relay local are proposed. The proposed scheme has a credible performance in protection for single and double phase to ground faults. Simulation results approve the efficiency of the proposed method in protection of series-compensated and conventional transmission lines.   

 In this thesis, a HVDC multi-terminal lines protection technique based on traveling wave and by synchronous measurements at each terminal, have been proposed. According to traveling waves theory, by the arrive time of initial fault-produced traveling waves, at each terminal and then calculating length of the line and the velocity of these waves at each line, faulty terminal and distance from the fault point to that terminal (faulty terminal) could be determined. In the following, a fault point detection method based on natural frequency of the traveling waves in multi-terminal VSC-HVDC lines, is proposed. In this method, by measuring the current signals at each terminal, and by determining the dominant frequency component and calculating the velocity of the waves at each line, the faulty terminal would be detected and the distance from the fault point to that terminal would be estimated. To verify the proposed method, an IEEE 9 bus standard system was simulated by PSCAD/EMTDC and the proposed algorithm was implemented using MATLAB. Simulation results show that the proposed method is satisfactory and with appropriate accuracy and speed is able to: discriminate between faults inside the protected region and external faults, determine the faulty terminal, and estimate the distance from the fault point to the determined terminal. Moreover, efficiency of this algorithm doesn’t depend on fault resistance, fault type and boundary conditions. The proposed algorithm was simulated on a star-connected 3 terminal VSC-HVDC system and results showed the appropriate operation of the proposed technique in fault point detection

Using a combined overhead transmission lines With underground power cable with considerations of safety and reliability in the distribution and transmission system in urban areas is expanding. Precise fault locating reduces time and costs related to the dispatched crews searching to find the fault location. improve the performance of the power system and identifies weak and vulnerable. Existing fault location methods, which are used to find location of fault in the overhead lines and underground cables, can be classified into two general categories impedance-based methods and traveling waves-based methods. Use of traveling waves-based algorithm is developed because they are more precise compare to impedance-based algorithms and are not influenced by source impedance, fault resistance and power flow. In the majority of traveling waves methods, fault generated high frequency transients are utilized to determine fault location. This thesis presents a traveling wave and support vector machines-Base fault location method for hybrid transmission Lines: an overhead line combined with an undergrounded cable. Discrete wavelet transformation is used to extract transient information frome the measured voltages. Support vector machine (SVM) classifers are utilized to classify the fault tyape, identify to the faulty-section and faulty-half. Bewley diagrams are observed for the traveling wave are used to locate the fault also the the wavelet coefficients of the aerial mode voltage are used to locate the fault. Suggested algorithmin compare to the double-ended algorithms has the advantage that does not need to communication equipments, and synchronization of data. In addition, because of using only voltage samples, it has require less equipment compare to the algorithms, which use both voltage and current samples. To evaluate proposed method, the 8 bus system is employed. The PSCAD/EMTDC is adopted for the test system simulation and MATLAB for algorithm implementation. The obtained results from many simulations under various fault conditions show that porposed algorithm can accurately locate faults.
 

This thesis presents a fault location method for three-terminal multisection nonhomogeneouse transmission lines using synchronized phasor measurment. The presented algorithm is extended from a two terminal fault location technique to an algorithm for three-terminal multisection nonhomogeneouse lines which combine overhead lines with underground power cables. The presented method is derived based on a distributed line model and no assumption is made. This method provides indication and location indices to recognize the faulty branch of a three-terminal multisection line and to locate the accurate faulted section/fault position in advance. The fault location algorithm can not only distinguish an exretnal/internal fault but it able to locate a fault on an overhead line or an underground cable as well. In follwing, the studied method is extended to fault location method for multiterminal multisection nonhomogeneouse lines and have the same advantages of studied method. Moreover, methods presented in this thesis, donʼt need to identify the type before locating a fault and also excludes iterative operations. To evaluate the studied method, the standard IEEE 9 bus system is employed and proposed method has been tested on four-terminal twelvesection transmission lines. The PSCAD/EMTDC is adopted for the test system simulation and MATLAB for the algorithm implementation. The obtained results from many simulations under various fault conditions show that the studied and proposed algorithms can accurately locate faults.

 Parallel transmission lines are extensively utilized in high-voltage (HV) transmission networks. Distance protection is commonly used as one of the main protections of parallel lines. However, the mutual impedance between parallel transmission lines can be as high as 50%–70% of the self-impedance for the zero-sequence coupling. When conventional distance relays based on one end sampling data from a single line are applied to parallel lines, its performance is affected by the mutual coupling between the lines, especially for cross-country faults. The protection zone of traditional distance relays without zero-sequence current compensation for parallel lines may vary from less than 50% up to far more than 100% of the total line length depending on the power system state. Moreover, a failure of distance relays caused by the cross-country faults may lead to three phase trips of both circuits. The impact of misoperations will be particularly serious under some conditions. A novel distance protection algorithm for the first-zone distance relay of parallel transmission lines is proposed for cross-country grounded faults. The algorithm calculates the fault impedance using one end sampling voltages and currents from a single line. The theoretical basis of the proposed algorithm is described in this thesis, which is based on the symmetrical component method for parallel lines. And an attempt is made to express the zero-sequence current of the adjacent parallel line at the relay location by the zero-sequence current of the concerned line in combination with the fault characteristics of the system model, by which the impact of the mutual coupling between the lines can be eliminated. And, thus, the distance algorithm for cross-country grounded faults is presented. The simulations show that the proposed algorithm can obtain the accurate fault reactance when cross-country bolted faults occur, which is superior to the existing distance protection algorithm based on one-end data from a single line. In this thesis, PSCAD/EMTDC software and MATLAB have been used for simulation.

In this thesis, a new power-based algorithm to discriminate between switching and internal fault conditions in power transformers is proposed and evaluated. First, the differential power signal is scrutinized and its intrinsic features during inrush conditions are introduced. Afterwards, a combined time-domain-based waveshape classification technique is proposed. This technique exploits the suggested features and provides two discriminative indices. Based on the values of these indices, inrush power signals are identified after only half a cycle. This method is founded upon some inherent low-frequency features of power waveforms and is independent of the magnitude of differential power. The approach is also unaffected by power system parameters, operating conditions, noise and transformer magnetizing curves. Simplicity of the suggested features and equations describe how the proposed method can help make it a practical solution for the inrush problem. Extensive simulations carried out in PSCAD/EMTDC and MATLAB softwares validate the merit of this technique for various conditions, such as current-transformer saturation applications.

In recent years, there has been a number of instances of bus-connected industrial generators which have experienced severe damage due to stator ground faults. In the distant past, the cost of failures of this sort wasprimarily the cost of repair. Today, however, the cost offailure is measured in broader terms, including the costsof lost production and replacement energy and, therefore,these costs are considerably greater than the repair costalone. These cost factors are also aggravated by largeunit ratings. This Thesisinvestigate industry concerns with excessivestator fault-point burning damage in conjunction withvarious industrial generator grounding and ground fault protectionpractices.also proposed a new method of grounding, called hybrid grounding, that offered the ability to limit damage while still providing the required level of ground fault current under all operating conditions. in the hybrid grounding scheme use both high-resistance (HRG) and low-resistance (LRG) grounding .This Thesis reports on the detailed design requirements for hybrid grounding. Finally, the results of switching transient studies that formed the basis for recommended overvoltage protection withuseing EMTP softwareWill be analysis .

Parallel transmission lines are widely used in power networks, in order to increase reliability and high power transmission systems. However, in terms of the protection, parallel transmission lines require special considerations compared to single circuit transmission lines. When the conventional distance relay for the protection of parallel lines is considered as independent circuit, mutual coupling between the two circuits affects on impedance of measurement by the relay. This leads to reduction or increase the range relay according to the characteristics of will be network. In this thesis a protection scheme for discrimination and classification of short-circuit faults in parallel circuit transmission lines is checked. Protection scheme is based on the initial fault-induced current travelling waves by using the wavelet transform. In the case of internal faults on any of the parallel circuits, the detected current travelling waves in the corresponding phases of the parallel circuits are different, whereas, for external faults, the initial current travelling waves are almost similar. This feature is used to discriminate between internal and external faults. In this scheme a fault-type classification algorithm is checked. It also covers inter-circuit faults, in which phases of both parallel circuits get involved in the fault. For determining the reflection coefficient traveling waves at any time, a fuzzy logic system It is suggested. The obtained simulation results on the IEEE 14 bus power system using the PSCAD/EMTDC software show that the proposed algorithm is able to discriminate the internal faults and to select the faulted phases very rapidly and reliably.

 

Transmission lines are often subjected to electrical faults. Since they are the vital links, improved reliability of transmission line protection is required. Distance relaying, either phase or ground type, is frequently applied to transmission lines as main protection. Performance of the conventional ground distance relaying manner is adversely affected by ground faults and also typical type, called a simultaneous open conductor and ground fault. This effect is more pronounced due to the considerable value of fault path resistance and direction and magnitude of power flow. This dissertation intends to provide a new comprehensive approach applied to digital ground distance relay to compensate the fault resistance on transmission line. Proposed one-ended fault location algorithm determines the distance between the intelligent electronic device (IED) and the location of the short-circuit fault by only solving a quadratic equation with complex coefficients. In order to do this, considered scheme utilizes minimum assumptions and input data requirements of local end. Fault detector which applied to fault detection unit (FDU) is based on the cumulative sum method, whose structure is adaptive with the current passing through the corresponding line. By using this compensated procedure, satisfactory performances have been approved over extensive simulation studies in different operating conditions. The proposed method which has been carried out on the IEEE 14 bus benchmark system model is executed in PSCAD/EMTDC and MATLAB software and the results show the accurate performance of mentioned configuration. 

 In this thesis, a busbar protection method is investigated based on the development of traveling wave theory. When the fault occurs on the busbar, the detected initial traveling waves on all connected lines will come from their back, which are defined as positive direction traveling waves. While a fault occurs on any one of these lines, the detected initial traveling waves on all healthy lines are positive direction traveling waves; however, the traveling wave direction on the faulted line is negative. Within a short duration of postfault, a criterion discriminating fault direction can be established according to the amplitude integral relationships between the positive direction traveling wave and the negative direction traveling wave. To evaluate the investigated method, the standard IEEE 14 bus system is employed. Simulation is implemented in PSCAD / EMTDC software. Simulation results show that the investigated method can rapidly and reliably discriminate the internal faults from external faults, and the protection performances are immune to fault resistances, fault inception angles, fault types, and current transformer saturation. In following, a new ungrounded fault location method for N-terminal transmission lines that uses time arrival of traveling wave signals and their polarity has been presented. The proposed algorithm first determines the type of faults (grounded or ungrounded) by calculating the magnitude of the ground mode wavelet coefficients of the main terminals. Next, by defining a new index, named distance, and by calculating the times of arrival of the first two TWs with contrary polarities, the faulted line section is identified. Finally the fault location is determined by taking the times arrival of the first two sequence aerial mode TWs at the nearest terminal to fault position. The proposed algorithm has been tested on five-terminal transmission lines using PSCAD/EMTDC software. The obtained results from many simulations under various fault conditions show that the proposed algorithm can accurately locate faults.

 Because of having responsibility to generate power, Synchronous generators are the most important part of the power systems and protection of them is necessary to maintain power generation, system stability and damage reduction to equipment due to occur any errors. Error of loss of excitation is considered for generator as a very harmful error. Until now, different methods have been proposed to detect this error But with all the progress, these protection has been slow and are more likely to malfunction. In this thesis, two new approaches to diagnose error of loss of excitation and protection against these errors will be presented. The first method proposes protection of loss of excitation based on fuzzy logic. This method is fed with apparent impedance and terminal voltage of the generator. In the fuzzy algorithm, these inputs are analyzed by considering membership functions and the written fuzzy rules. Finally, the algorithm to protect synchronous generator against the loss of excitation, makes a decision between cut, alarm and non-performance. The second method presents a new protection using voltage and the terminal current angle of generator. In this method, by considering the parameters and defining the threshold, error of loss of excitation and turbulence in the network are detected. At the time of turbulence in the network, in order to prevent incorrect operation of the proposed relay in the network, the relay is locked. During this time, the protection of loss of excitation based on fuzzy logic, works as the support protection in order to detect the possible loss of excitation occurring in the turbulence time and send cutting command. Both methods are simulated in errors and are able to show absolutely correct performance in diagnosis loss of excitation and non-performance in transient swing of power. The second method could diagnosis error in a very high speed compared to existing protections. In this thesis, DIgSILENT® Power Factory software and MATLAB have been used for simulation.

With increasing load demand requires the development of systems work is necessary. On the other hand integrated generation and transfer systems considering economic and technical problems may seem difficult and hard. Distributed generation is the perfect choice with the added possibility distribution system to meet the load on the network is capable. DG added causes effects on protection system of distribution network, especially in the short-circuit. On short time with increasing short-circuit current coordination between protective devices will change. One of the most important protection scheme is coordination fuse-recloser. In this paper, a technique for eliminating the undesirable effect of inverter distributed generation (DG) on the coordination between the fuse-recloser on fuse saving scheme is presented. In the proposed scheme, the DG production is controlled by the voltage, thus increasing fault current is prevented by DG. Proposal to the location of DG and reactive power injection from DG is resistant. To simulate the strategies have been proposed the system IEEE 13-node and MATLAB / SIMULINK is used. In this way, no need to change the structure of protection and penetration level is not limited in normal conditions. The proposed scheme against other disturbances such as switching and starting induction motors is resistant.

One of the most common faults in the excitation system of synchronous generators is ground fault. Since the first ground fault doesn’t make any malfunctions in the generator, it can’t be detected by popular techniques. In this thesis, two techniques based on FFT for detecting ground faults in static excitation systems have been studied. The first technique can distinguish whether the fault occurs on the DC or AC side of the excitation system just when there is not another in excitation system. In second technique that has been proposed in this research, the ground fault occurred in the DC or AC side can be distinguished even though there is an open-circuit or short-circuit fault in the rectifier diodes. In addition to mentioned techniques, two techniques for locating the rotor winding ground fault in synchronous generators have been studied. In the first technique, the ground fault is located by measuring the components DC and AC of excitation voltage and the components DC and the AC of the ground impedance voltage between the ground and the neutral terminal of excitation transformer just in static excitation system. The second technique that has been proposed in this research is suitable for species of excitation systems. In this new technique, the fault can be located by measuring the input and output currents and voltage of the rotor winding. This technique has a simpler and more exact algorithm in compare to previous technique. Techniques of this thesis have been validated through computer simulations and experimental laboratory tests. Also a ground fault location device in synchronous generators rotor winding has been made based on proposed technique in this thesis.

An islanding situation occurs when part of a distribution system is disconnected from the utility system, but it remains energized due to distributed generators connected to the isolated subsystem. In this situation, the utilities have no control on voltage, frequency and loading of island that is known as unintentional islanding that could be fatally harmful to the line workers and power system facilities. Anti-islanding protection is an important technical requirement when interconnecting distributed generators. Anti-islanding techniques have to be reliable, which is measured by the terms dependability and security. However, most of them present technical limitations so that they are likely to fail in certain situations. Therefore, it is important to quantify and determine whether the scheme under study is adequate or not, that this research investigated these situations. So, the operation of over/under frequency and rate of change of frequency relays have been analyzed, the result of analytical studies have been compared with dynamical simulations, the nondetection zone concept in anti-islanding protection of distributed synchronous generators is introduced, the effects of different setting of these relays on performance curve are checked, the nondetection index of frequency relays is analyzed to assess the effectiveness of these relays and the impact of different systemically parameters as the amount of output power, the required time detection, delay setting and nominal capacity of distributed synchronous generators on nondetection index are analyzed to presented approach can assist distribution engineers to assess and set anti-islanding protection scheme.