Abstract—This paper reviews the optimization available transmission capability (ATC) of power systems using a device of FACTS named SSSC equipped with energy storage devices. So that, emplacement and improvement of parameters of SSSC will be illustrated. Thus, voltage magnitude constraints of network buses, line transient stability constraints and voltage breakdown constraints are considered. To help the calculations, a comprehensive program in DELPHI is provided, which is able to simulate and trace the parameters of SSSC has been installed on a specific line. Furthermore, the provided program is able to compute ATC, TTC and maximum value of their enhancement after using SSSC. Keywords—available transmission capability (ATC), total transmission capability (TTC), voltage constraints, stability constraints, FACTS, SSSC. I. INTRODUCTION BILITY of power systems in reliable firm transmission can be restricted by some system features like transmission line thermal limit, bus voltage magnitude and stability consideration. Available transmission capability is defined as the amount of power transmission which does not contravene the system limits [1]. Consequently, to acquire firm power transmission, it is essential to recognize the various network limits and maximum transferable power. There are several methods for ATC computations that should be selected appropriately depending on studied network. Spread using FACTS devices over real networks, the idea to use these devices in enhancing ATC made sense [2]. Although, in FACTS devices, parallel-connected devices effect on enhancing ATC properly by correcting bus voltages and injected reactive power [3], series-connected devices demonstrate extreme capability on intensifying ATC value for critical transmission lines by modifying line reactance and injected series voltage on lines [4]. So, SSSC appears to be an extra efficient and powerful series-connected device to enhance ATC. Sh. Javadi is with the Islamic Azad University, Central Tehran Branch, Iran (e-mail: sh.javadi@iauctb.ac.ir). A. Alijani is graduate student in Islamic Azad University, South Tehran Branch, Iran (corresponding author to provide e-mail: ali.alijani1984@gmail.com). A.H. Mazinan is with the Islamic Azad University, South Tehran Branch, Iran (e-mail: ah_mazinan@azad.ac.ir). In this paper, the repetitive power flow method will be concisely described at first and then, important constraints will be mentioned. Then, a model of simulating SSSC equipped with energy storage devices will be presented and enhancing method of SSSC to gain the maximum value of ATC will be defined. After that, the program has been provided in DELPHI, will be concisely described and expressed its features to computing ATC and TTC values and SSSC simulation. Finally, results of ATC calculations with and without SSSC application by the provided program will be analyzed. II. REPETITIVE POWER FLOW METHOD TO COMPUTE ATC In RPF method, to compute the power transmission capability between generating and consuming areas, it is increased the consuming load and is solved the load flow equations repetitively. The load Increasing will be permitted until the system restrictions will not be contravened [5]. Most important advantages of using RPF method are: TABLE I NOMENCLATURE Symbol Description QGi & PGi Reactive & Active generation power on bus i Q Di & P Di Reactive & Active load on bus i |Uj| & |Ui| Voltage magnitude on bus j & i B ij & G ij Real & Image part of Ybus i,j δij Line angel between buses i , j |U i | max Max of voltage magnitude on bus i |Ui|min Min of voltage magnitude on bus i S ij Reactive power on line between buses i & j N Number of buses N l Number of PQ buses M Number of transmission line NG Number of generator P º Gi Base active generated power relevant to generation area Q º Gi Base Reactive Load power relevant to load area P º Di Base active Load power relevant to load area P si Injected active power of SSSC on bus i Qsi Injected reactive power of SSSC on bus i P sj Injected active power of SSSC on bus j Qsj Injected reactive power of SSSC on bus i 1- To access P-V and V-Q curves for voltage stability studies [2], [4]; 2- Ease of regulating the control parameters; 3- High speed convergence [1]. The mathematic formula to compute ATC using RPF is Optimal SSSC Placement to ATC Enhancing in Power Systems Sh. Javadi, A. Alijani, A.H. Mazinan A World Academy of Science, Engineering and Technology International Journal of Energy and Power Engineering Vol:5, No:1, 2011 106 International Scholarly and Scientific Research & Innovation 5(1) 2011 ISNI:0000000091950263 Open Science Index, Energy and Power Engineering Vol:5, No:1, 2011 publications.waset.org/6757/pdf