Flexible AC Transmission Systems (FACTS) controllers with its ability to directly control the power flow can offer great opportunities in modern power system, allowing better and safer operation of transmission network. In this paper, in order to find type, size and location of FACTS devices to install in power network a Dedicated Improved Particle Swarm Optimization (DIPSO) algorithm is proposed for decreasing the overall costs of power generation. Thyristor-Controlled Series Capacitor (TCSC) and Static VAr compensator (SVC) are two types of FACTS devices that have been considered to install in power network. The purpose of this study is reducing the power generation costs with considering different load levels and the costs of FACTS devices. The main bases of this paper are using of Optimal Power Flow (OPF) and DIPSO algorithm. The Net Present Value (NPV) method is used to economic analysis and power losses and maximum possibility load demand are considered to technical analysis of the results.