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Review of Under-voltage Load Shedding Schemes in Power System Operation DOI:10.12915/pe.2014.07.019

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A voltage collapse event is complex and localized in nature, but its effect is extensive. A vital effect of voltage collapse is total system collapse or blackouts, which will result in a significant loss to utility companies. Online monitoring of power system stability has thus become an important factor for electric power utilities. The final resort prevent the occurrence of a voltage collapse incident is the implementation of an undervoltage load shedding (UVLS) scheme. This paper focuses on the introduction of the UVLS scheme and presents an overview of the principles of the UVLS that are crucial to the design of such a protection scheme. This paper also presents the existing industrial practices and other research methods available to date. Streszczenie. W artykule opisano algorytm UVLS (Under Voltage Shedding Schemes) zastosowany do monitorowania stabilności systemu energetycznego I zapobiegania jego zapaściom. Artykuł jest przeglądem metod stosowanych w praktyce oraz prac badawczych w tej dziedzinie. (Metody UVLS w zastosowaniu do monitorowania stabilności systemu energetycznego I zapobiegania jego zapaściom) Keywords: voltage stability, voltage collapse, under voltage load shedding. Słowa kluczowe: doi:10.12915/pe.2014.07.19 Introduction Existing power systems are significantly more susceptible to voltage collapses today than many years ago because such systems are stressed because of the huge power transfers across grids. These transfers cause transmission lines to operate close to their limits. In addition, generation reserves are minimal, and reactive power is often insufficient to satisfy load demands. Thus, power systems have become more vulnerable to disturbances, outages, and instability. The disturbances that occur in power systems include faults, sudden loss of generation, and sudden rise in load demand [1]. All these disturbances vary in intensity and may cause the instability of the power system. For instance, whe[...]

Under Voltage Load Shedding Scheme Using Meta-heuristic Optimization Methods DOI:10.12915/pe.2014.11.43

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Load shedding has been extensively studied because of multiple power system failure occurrences worldwide. Reliable techniques are required to provide rapid and precise load shedding to avert voltage collapse in power networks. Meta-heuristic optimization approaches are currently the widely developed methods because of their robustness and flexibility in dealing with complex and non-linear systems. These methods include genetic algorithm, fuzzy logic control, particle swarm optimization, artificial neural network, ant colony optimization, big-bang big-crunch optimization, and many others. This study provides an overview of all the meta-heuristic methods implemented for under voltage load shedding in power systems. Streszczenie. Pozbywanie się obciążenia jest istotne z punktu widzenia możliwego zapadu systemu przesyłu energii. Do tego celu wykorzystuje się optymalizację meta-heurystyczną głównie dzięki odporności i szerokim możliwościom. W skład metody wchodzą: algorytm genetyczny, logika rozmyta, algorytmy mrówkowe, sieci neuronowe. W artykule dokonano przeglądu tych metod. Meta-heurystyczne metody optymalizacyjne wykorzystywane do szybkiego pozbywania się obciążenia sieci. Keywords: meta-heuristic optimization, under voltage load shedding, voltage collapse. Słowa kluczowe: optymalizacja mete-heurystyczna, zapad napięcia, pozbywanie się obciążeń doi:10.12915/pe.2014.11.43 Introduction The escalating number of voltage stability events around the world has attracted a great deal of concerns among the power utility operators. Substantial development has been made in the research on the implementation of the load shedding schemes over the past few decades [2-8]. Among different countermeasures for the prevention of the voltage instability, load shedding is the final remedy of defense when there is no other substitute to stop an impending voltage collapse [1]. However, inadequate load shedding has led to a high number of voltage collapse [...]

Study on P-V Curve and V-Q Curve of an Unbalanced Three- Phase System with Different Static Loads DOI:10.15199/48.2016.01.39

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P-V curve and V-Q curve (often term as Q-V curve) are widely used for planning and operation studies. The P-V curve and V-Q curve of an unbalanced three-phase system, unlike the balanced three-phase system, may not have similar loading margin (LM) and reactive power margin (RPM) on each phase. Therefore, DIgSILENT Programming Language (DPL) has been used to study the maximum loading point (MLP), critical point (CP), and also minimum reactive power point (MRPP) on each phase of an unbalanced three-phase system with different static loads. The tracing direction of P-V curve of each phase and the LM and RPM of each phase obtained from the P-V curve and V-Q curve for different static loads are also discussed. On top of that, continuation power flow (CPF) has become a common method to study the MLP. Hence, a simple 2-bus balanced three-phase system is used to validate the result obtained from the DIgSILENT with CPF method. Streszczenie. Krzywe P-V I V-Q w systemie trójfazowym niezrównoważonym mogą nie mieć tego samego marginesu obciążenia LM i marginesu mocy biernej RPM w każdej z faz. Zastosowano język programowania DIgSILENT do określenia maksymalnego punktu obciążenia MLP, punktu krytycznego CP i punktu minimalnej mocy biernej MRPP. Analiza krzywych P-W i V-Q w niezrównoważonym układzie trójfazowym o różnych obciążeniach statycznych Keywords: Continuation power flow (CPF), Critical point (CP), DIgSILENT, Loading margin (LM), Static load, V-Q curve. Słowa kluczowe: margines obciążenia LM system trójfazowego, krzywa V-Q, krzywa P-V Introduction Voltage stability problems have been recognized as the main causes for blackouts throughout the world in the recent past. The limited expansion of transmission and distribution system due to cost and environmental issues, and continuous increase in the load demand lead the existing power system operate near to voltage stability limit [1]. Hence, an accurate knowledge of how close the actual system&#[...]

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