Voltage stability monitoring and control studies in the Hellenic interconnected system (original) (raw)
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Abstract:[en] The Hellenic Interconnected System pre-sents a structural geographical imbalance between generation sites and load centers. This imbalance leads to bulk power transfers on long electrical distances leading to voltage stability problems. In order to improve the opera-tional practices aiming at improving the voltage security, an on-line Voltage Security Assessment tool has been installed at the National Control Center of the Hellenic Transmission System Operator that operates and controls the interconnected ...
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Application of Real-Time Voltage Security Assessment to the Hellenic Interconnected System
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Automatic load shedding schemes against voltage instability in the Hellenic system
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Based upon the experience gained from the 2004 blackout and the on-line Voltage Security Assessment operation that is in service since 2005, the Hellenic Transmission System Operator (HTSO) decided to automate the process of load shedding in the Hellenic Interconnected System, in order to reduce the risk of voltage collapse in the event of critical contingencies. Analytical description of the design and implementation of two individual load shedding schemes in the Hellenic System is presented in this paper. Analysis and simulation results that investigate and validate the efficiency of these protection schemes are included in the paper.
2006
Abstract:[en] Voltage instability is widely recognized as a significant threat of power system blackout. As far as real-time operation is concerned, there is a need for appropriate tools to identify dangerous contingencies and assess security margins. The Hellenic Interconnected System presents a structural geographical imbalance between the main generation site and the main load center. This imbalance leads to bulk power transfers over long distances leading to voltage stability problems in areas of the southern system during heavy load ...
Investigation of a local indicator of voltage emergency in the Hellenic interconnected system
2008
Abstract:[en] In this paper we evaluate the performance of a proposed local indicator of voltage emergency for a simulated unstable contingency of the Hellenic Intercon-nected System identified through the on-line VSA applica-tion for the summer peak of 2007. The effect of deadbands and tap range limits in delaying the emergency alarm issued is examined. The area mostly affected by the insta-bility is identified through the proposed algorithm and a simple load-shedding scheme sufficient to avert the collapse is suggested.
Voltage Stabilization in Power Systems
This paper investigates overall power system stability and stresses upon voltage stability by the impact of the load upon a power system security assessment. This is done according to two important aspects: the adopted direction for the load increment and the dynamic models used to represent its behaviour. The first aspect is tackled through an evaluation of contingencies, which is based on the system's load flow model for two load increment directions: the " traditional " approach, where the system active and reactive load demands are increased proportionally to the base case, and a second approach that regards the " worst case " , in which it is adopted the direction that gives the smallest " local " loading margin for the base case. The second aspect is tackled through a system multi-machine modelling that takes into account the impact of the generators, loads, Automatic Voltage Regulators (AVRs), Over Excitation Limiters (OXLs) and Load Tap Changers (LTCs) dynamic behaviour. The dynamic responses of the system are compared to the most critical contingencies previously obtained.