Fuzzy Logic based Stability Index Power System Voltage Stability Enhancement

Abstract

Abstract-This paper work aims the predication of steady state voltage stability conditions in a transmission network. The voltage stability is checked by formulating an (L) index and the corresponding uncertainties input parameters are efficiently modeled in terms of fuzzy sets by using triangular membership function. The proposed technique will be highly useful to ensure voltage security of power system by predicting the nearness of voltage collapse with respect to the existing load condition. This will in turn help us in determining the maximum load ability of the given system without causing voltage instability. The validity of the technique is tested on a sample 5-bus system and IEEE 14-bus system using software simulation. The results are provided for the feasibility of the technique includes fuzzy load flow solution for base and critical cases. This method can be applied both for off-line as well as on-line applications.Index Terms-Fuzzy logic, Power system enhancement, Stability index, Voltage Stability. I. INTRODUCTIONOne of the important operating requirements of a reliable power system is to maintain the voltage within the permissible ranges to ensure a high quality of customer service. In modern bulk power system, voltage instability would lead to blackout which is of major concern in planning and operation of power system. Voltage instability [1] is characterized by variation in voltage magnitude which gradually decreases to a sharp value accompanied with simultaneous decrease in power transfer to load end from the source. Prior to voltage instability , bus angle and frequency remain constant but after the occurrence of voltage instability the reactive power absorbed by the transmission line increases to such an extent that it becomes difficult to maintain the voltage magnitude within the limit .Hence it may be rightly said that voltage instability occur due to the inability of the system to supply reactive power to the load. It may also occur due to the network disturbance such as loss of an important transmission line, transformer or generator may also occur due to the line fault or bus fault, heavy HVDC power flow without adequate shunt capacitance and inverters [2]. In practice to over come the above problems, usually controlling devices such as tap changing transformers are employed. However they fail to get activated quickly enough to prevent voltage collapse. Most of the indices developed are system-based or based on bus orientation. There has not been much research in voltage stability assessment via line based voltage stability index. The existing technique is based on a line based voltage stability index which detects the critical lines for a specific load scenario for monitoring the system prior to experiencing line outage. The limitation of the above method is that it does not reach unity under various power factor operations of a transmission lines. Particularly, their index show very less value (much less than 1) for high power factor operation of a transmission line.A bacteria foraging...

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