Ph.D. Tezi Görüntüleme

      Maintenance and reliability for continues operation is very important problems in power systems. In order to remain continuity in operation the power outages must be minimized or prevented completely. The power outages are caused mainly by the faults that may occur unexpectedly anytime, anywhere in the power system. Therefore, the faults must be detected very quickly to start necessary actions as soon as possible and isolate the faulted parts of the system so that outages are prevented or made minimum. The reliability of a power system is based upon its continuity in operation, and the continuity depends on the protection against the faults. Thus, power systems protection against the faults and protection relays, which are used to detect faults, are very important research areas in electrical power systems.

      Line protection is more complicated compared to those of transformer, bus, generator and loads. In line protection, not only the detection of fault but also its type and location are important. Distance relays, which are based on the measurement of line impedance using voltage and current data, are frequently used in line protection. With the incredible development in computer technology and digital systems, electronic and microprocessor based protection relays have started replacing electromechanical types. Meantime, digital computers are also started being widely used in protection systems with their stable and reliable performances.

      In this study, a digital protection relay has been designed and tested in a laboratory environment using a prototype developed as a part of the thesis. The digital relay has been realized using fuzzy logic and neural-fuzzy systems instead of conventional digital approaches. This design requires less voltage and current readings to detect faults in power systems. First, the voltage and current signals are compared to yield the line impedance, then type and location of the fault are determined using either one of fuzzy logic and neural-fuzzy systems, which may called as intelligent systems.

      The relay proposed here is developed using conventional distance relay characteristics by adding some abilities such as to distinguish whether the fault is sub-transient, transient, or permanent, to determine either the fault is one of the types known as phase-to-phase, phase-to-neutral or balanced three phase. Besides it determines the distance of faulted point from the bus where the signals to the relay are measured. The prototype experimental setup consisting of both single and three phase systems is developed as a radial system and tested for all operating conditions with all methods proposed, and satisfactory results are obtained.

      The thesis consists of six chapters. A review of the related literature and general explanations of protection systems are given in the 1st chapter. The 1st chapter is an introductory chapter and also consists of the brief information on fuzzy logic, neural networks, and neural-fuzzy systems. The work done is given in chapter 2 as the results are depicted in chapter 3. A general discussion and results are given in chapters 4 and 5, respectively. Finally the suggestions for future work are discussed in chapter 6.

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