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Title: Upgrading a distribution system with d-facts devices : the impat on voltage profile, system losses and expected fault currents
Authors: Afzal, Suhail
Keywords: D-facts
Fault current constraints
Optimal power flow
Abstract: The continuous growth of demand and the dispersed nature of most new generation create a number of challenges for modern Power Systems like dynamic stability, line limit utilization, power sharing between different areas and reliability. Bus voltage magnitude is an important parameter for the quality of a power system and it is related to the flow of reactive power across the lines. Bus voltage magnitude is in direct relationship with the demand of reactive power. Decrease in bus voltages below the minimum threshold of nominal voltage range may cause voltage collapse and increase in bus voltage beyond the maximum threshold may lead to black out. The smaller the deviation of bus voltages from nominal, the more stable the power system will be. This research has been carried out with the goals of improving voltage profile of the system buses, decreasing system losses and limiting line fault currents. Distributed Flexible AC Transmission System Controllers (D-FACTS) are among those devices that can provide series compensation to the power system. To achieve the goals, Distributed Thyristor Controlled Series Capacitor Device (D-TCSC) has been utilized to provide series compensation to the network because of their simple structure, low cost, quick response and communication capability. Mathematical model of the device has been incorporated in the power flow equations by introducing new variables having lower and upper bounds based on the levels of capacitive and inductive compensations those can be provided by these series controllers. The Matpower/Matlab platform has been used for formulation of power flow equations and to calculate the gradients of equality and inequality nonlinear constraints. Objective function is formulated considering the total cost of power generation and the cost of these devices. Knitro optimizer has been utilized to find the optimal power flow solution. Further to this work, Fault Limit Constraint on a transmission line has also been incorporated in power flow as a new nonlinear constraint to find the optimal values for inductive compensation those satisfy the set fault constraint. The methodology has been tested on IEEE 06-Bus and 30-Bus power systems. In both cases, improvement in voltage profile has been observed. Reactive power line losses are reduced significantly whereas active power dissipation across the lines remained same causing decrease in total MVA generation of generating units. Some increase in line limit utilization of few lines has been observed; however, in general the average line utilization of the network has been reduced. Moreover, the set fault limit constraint has been respected with successful convergence to the optimal solution.
Abstract (translated): --
Appears in Collections:Τμήμα Ηλεκτρολ. Μηχαν. και Τεχνολ. Υπολογ. (ΔΕ)

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