Majlesi Journal of Electrical Engineering Vol. 6, No. 2, June 2012 1 Optimal placement of FACTS Devices to reduce Loss and improve Congestion in Transmission System using ABC Algorithm Hojat. Golafshani 1 , Hossein. Afrakhte 2 , Reza. Naghizadeh 3 1- Guilan University, Rasht, Iran. Email: hojat.golafshani@gmail.com 2- Guilan University, Rasht, Iran. Email: ho_afrakhte@guilan.ac.ir 3- Guilan University, Rasht, Iran. Email: naghizadeh.reza.n@ieee.org Received X X X Revised X X X Accepted X X X ABSTRACT: In this paper, Flexible AC Transmission Systems (FACTS) devices are used as a powerful tool for controlling power flow in power system to reduce active power losses and manage transmission lines congestion which are the main factors to restrict transmitted power in the network. Optimal location and size of these devices are specified by using artificial bee colony (ABC) algorithm which is one of the most effective method for solving optimization problems with the objective of minimizing active power losses and transmission lines congestion in order to relieve the line flow of the overloaded transmission lines and increase the loadability in transmission system. The proposed method is also able to improve voltage profile in the network. The effectiveness of proposed method is tested with IEEE 30-bus system and the test results are evaluated. KEYWORDS: Loss reduction, Congestion improvement, FACTS devices, Artificial bee colony. 1. INTRODUCTION Nowadays privatization and restructuring of the power industry have been had significant effect on all power systems around the world. Even by increasing consumption and demand of electric power, the amounts of transactions have been increased and one or more constraints of system are violated because of flowing the power in lines more than their allowed limits. In this circumstances the system is experiencing congestion. A congested system is not able to fulfill all the demands of the electric power consumption and in case of congestion in the system, prices will be increased in some areas and reduced in other and the overall situation of market will decline and removed from its natural state. Congestion management that is one of the most important tasks of system operators, means to take actions to control the transmission system so as to improve congestion effectively, various constraints are satisfied and also system security is guaranteed. Several methods to improve the congestion have been presented in [1]. In [2] a zonal model based on AC power flow is proposed and areas are selected based on transmission congestion distributed factors (TCDFs) and congestion is managed by rescheduling of active and reactive power of generators. In [3] rescheduling of generators method based on sensitivity analyze is used to improve congestion and reduce congestion costs using the optimal generators scheduling in form of optimal power flow and PSO algorithm is used as optimization algorithm. On the other side, because the transmission lines are not perfect electrical conductor and resistive power losses that appears in the form of heat energy along the transmission lines is about 10% of generated power, reducing total power loss is one of the most important concerns of power system operation [4]. The power loss can be decreased using optimal power flow (OPF) with power loss as an objective function. This problem is solved by satisfying different constraints related to power flow, control variables and state variables. In OPF different objective functions can be considered such as minimization of generation costs, voltage deviations, emissions and etc [5]. Generally, relieving congested lines and safe operation of power system so that the system is operated within thermal limits is achieved by controlling power flow fast and effectively and the use of flexible alternating current transmission systems (FACTS) has been always considered as a powerful