Amir Pirouz Ghale; Majid Sanaye Pasand; Hamed Asadi
Abstract
Power system blackouts have become a serious problem for electric utilities especially in recent years. Different forms of system instability have emerged in recent blackouts, such as voltage instability and frequency instability. To counteract each form of system instability, special algorithms have ...
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Power system blackouts have become a serious problem for electric utilities especially in recent years. Different forms of system instability have emerged in recent blackouts, such as voltage instability and frequency instability. To counteract each form of system instability, special algorithms have been designed in the protection system, e.g. Under Frequency Load Shedding (UFLS) and Under Voltage Load Shedding (UVLS) schemes. One of the major weaknesses of these algorithms is that combination of different forms of instability is not considered in their design, while any one form of instability may not occur in its pure form. This is particularly true in highly stressed systems and for cascading events. This paper presents an adaptive algorithm to combine UVLS and UFLS schemes. The purpose of this method is to enhance the flexibility of under frequency relays and increase the security of power system during large disturbances by improving system voltage stability margins. In the proposed algorithm, loads with greater voltage decay are shed sooner. In this way, locations of load shedding become dependent to the location of disturbance and voltage stability margins of the system are enhanced. Indeed, load shedding is performed faster for severe events accompanying large voltage or frequency declines. Using this load shedding method, faster reactions could be obtained for major system failures. This way, system blackouts could be better controlled. Performance of the proposed method is compared with the conventional UFLS method. In this paper, dynamic model of the Khorasan HV network of Iran national grid is used for simulation. This network includes 75 high voltage 400 kV and 132 kV buses with about 2700 MW of generation. Performance of the schemes has been evaluated using dynamic simulations as well as the P-V curves, and reactive power margins for a number of events. Simulation results show that conventional UFLS algorithm will not necessarily result in acceptable voltage stability margins for the system following a disturbance. Meanwhile, the proposed algorithm improves voltage stability margins. The proposed algorithm is suitable for saving system stability after occurrence of major system disturbances.
Mehrdad Tarafdar Hagh; Seyyed Jalal Kazempour
Abstract
Although many mathematics-based and heuristic approaches have been recently developed on optimally allocation of TCSCs for lines overloads reduction and buses voltage stability enhancement during fault conditions, the works on the TCSCs efficiency to achieve the abovementioned goals are rare. This idea ...
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Although many mathematics-based and heuristic approaches have been recently developed on optimally allocation of TCSCs for lines overloads reduction and buses voltage stability enhancement during fault conditions, the works on the TCSCs efficiency to achieve the abovementioned goals are rare. This idea that TCSCs can surely enhance the system’s security must be comprehensively investigated. In this paper, after the optimal allocation of TCSCs, their efficiencies on lines overloads reduction and buses voltage stability enhancement during fault conditions are investigated using two new indices named “transmission index” and “voltage stability index”. The numerical results show TCSCs can remarkably enhance the buses voltage stability, but they can not significantly reduce the lines overloads. In addition, the impact of TCSCs installation on mitigation of load shedding aim to enhance the buses voltage stability is presented as a new work. The IEEE standard 14 and 30 buses systems are selected as case studies.
