International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 2, Issue 12, December 2012) 708 Transient Stability Analysis of Power System With UPFC Using PSAT Rajesh Kr Ahuja, Mukul Chankaya Dept. of Electrical Engineering, YMCA University of Science &Technology, Faridabad (Haryana), India Abstract—UPFC is a versatile FACTS controller that can regulate the Power Flow through the Line by controlling its Series and shunt parameters. In shunt it is having STATCOM and in series SSSC are employed can independently control the Line Power Flow. Two Converters improves the flexibility and provide additional degree of freedom in Power System. With the application of UPFC, Transient stability of the system can be Improved. This Paper shows that how Transient Stability of the Inter Area system is Improved. The Mathematical Model of Transient Stability is also given in this Paper. Keywords—Power system, FACTS, Transient stability, Inter area power system. I. INTRODUCTION In recent years, energy, environment, deregulation of power utilities have delayed the construction of both generation facilities and new transmission lines. FACTS devices are available, which can help Power Engineers to deal with problems like Large Signal Stability and economic Factors that gives strong incentives to raise the Stability limit of the System, depending upon the diverse conditions. Facts devices can provide fast control of Active and Reactive power through Power system. Among the converter based FACTS devices Static Synchronous Compensator (STATCOM) and Unified Power Flow Controller (UPFC) are the popular FACTS devices. They play an important role, not only in increasing the amount of energy transported over the lines, but also in oscillatory and transient-stability enhancement, system reliability, and controllability over the power flow. Considering the practical application of the UPFC in power systems, it is of importance and interest to investigate the benefits as well as model of these devices for power system Transient Analysis. Unified Power Flow Controller (UPFC) is a power electronic based device that has capability of controlling the power flow through the line by controlling appropriate its series and shunt parameter. It has been reported that UPFC can improve transient stability of a system. II. PRINCIPLE OF UPFC One FACTS controller in particular, the Unified Power Flow Controller (UPFC), is capable of concurrently or selectively controlling transmission line power flows, voltage magnitudes and phase angles in a power system. Here in fig.1 given below UPFC is shown with both PWM and Phase Control strategy. The Unified Power Flow Controller (UPFC) concept was proposed by Gyugi in 1991. UPFC is an electrical device for providing fast-acting reactive power compensation on high-voltage electricity transmission networks. The UPFC is a combination of a Static Synchronous Compensator (STATCOM) and a Static Synchronous Series Compensator (SSSC) coupled via a common DC voltage link. The UPFC is made out of two voltage-source converters (VSC) with semiconductor devices having turn-off capability, sharing a common dc capacitor and connected to a power system through coupling transformers. The basic UPFC structure is depicted in Figure shown above. This figure represents control strategies (pulse-width modulation (PWM) and phase control). The reactive power is generated/absorbed independently by each converter and does not flow through the dc link. There are two basic control strategies that can be utilized to control the switching of the semiconductor switches in the converters, i.e., PWM and phase controls. GTO switches operate adequately at the “low” switching frequencies required in phase control, but present high losses at the “high” switching frequencies needed for PWM control.