Paper Id: RTESC-13-250 1 Abstract— This paper presents impact of various Flexible AC Transmission System (FACTS) controllers with integrated wind farm, concept of voltage stability, main causes of voltage instability, classification of voltage stability, Wind farms, Wind Power Plants (WPP), classification of WPP. Various current techniques/methods for analysis of voltage instability caused by integrating large/small WPP in power systems have been studies through all over world. This paper also presents Wide Area Measurement Systems (WAMS) and Phasor Measurement Unit (PMU) based voltage stability analysis in deregulated market conditions. Authors strongly believe that this article will be very much useful to the researchers for finding out the relevant references in the field of voltage instability analysis and corrective action taken by implementing various FACTS controllers in power system environments when applied to the integrated wind farms. Index Terms— Voltage Stability, Voltage stability index, Voltage collapse, WAMS, PMU, WPP, Wind farms, FACTS controllers I. INTRODUCTION ith the ongoing deregulation of the electric utility industry. Numerous changes are continuously being introduced to a once predictable business. With electricity increasingly being considered as a commodity, transmission systems are being pushed closer to their stability and thermal limits. while the focus on the quality of power delivered is greater than ever. In addition, dynamic reactive power support is becoming more important, especially in urban areas where local (i.e. at the load) generation is being reduced or eliminated. In the deregulated utility environment, financial and market forces will demand a more optimal and profitable operation of the power system with respect to generation, transmission, and distribution. Now, more than ever, advanced technologies are paramount for the reliable and secure operation of power systems. Voltage stability assessment is one of the challenges for electrical utilities today. In the past, when the transmission Manuscript submitted december15, 2012; revised March 2, 2013. Satish kumar is Associate Professor with the Department of Electronics & instrumentation Engineering, Krishna Institute of Engineering & Technology (KIET), Muradnagar, Ghaziabad, U.P. India. Email: kumarsatish79@gmail.com Dr. N K Sharma is professor with the Department of Electrical Engineering, Krishna Institute of Engineering & Technology (KIET),Muradnagar, Ghaziabad ,U.P. India. Email: drnikhlesh@gmail.com Dr. Ashwani Kumar is Associate Professor with Department of Electrical Engineering, National Institute of Technology, Kurukshetra, Haryana, India. Email: ashwa_ks@yahoo.co.in systems were over designed and the most of the loads were simple in composition, voltage stability assessment represented a much easier problem. According to North American Electric Reliability Corporation (NERC) surveys [1], operating closer to the limits of the system, as well as limited construction of new transmission, significantly contributes to the technical challenges being faced by electric industry today. Major blackouts described in [2] have been related to voltage stability issues. The ability to transfer power from generation sources to loads during steady state conditions is a major aspect of voltage stability. Voltage stability analysis is performed for the following purpose [3]:  Ensuring that the power system meets the required Phase Voltage margins imposed by its relative criteria.  Identifying voltage stability limits on power transfers into selected load centers.  Identifying weak regions in the system and determining critical contingencies with respect to voltage stability. Power system stability has been recognized as an important problem for its secure operation since 1920s [4]-[5]. With continuous increase in power demand, and due to limited expansion of transmission systems, modern power system networks are being operated under highly stressed conditions. This has been imposed the threat of maintaining the required bus voltage, and thus the systems have been facing voltage instability problem [6]-[7].Due to increase in power demand, modern power system networks are being operated under highly stressed conditions. This has resulted into the difficulty in meeting reactive power requirement, especially under contingencies, and hence maintaining the bus voltage within acceptable limits. Voltage instability in the system, generally, occurs in the form of a progressive decay in voltage magnitude at some of the buses. A possible outcome of voltage instability is loss of load in an area, or tripping of transmission lines and other elements by their protective systems leading to cascaded outages and voltage collapse in the system [8]-[9]. So improvement of Voltage stability means the ability of a power system to maintain acceptable voltage at all buses in the system under normal conditions and after being subjected to a disturbance. The principal factors contributing to voltage collapse are the generator reactive power/voltage control limits, load characteristics, characteristics of reactive compensation devices, and the action of voltage control devices. Voltage instability in the power system occurs due to incapability of power system to supply loads under disturbances. Disturbances may be either Role of PMU & FACTS Controllers in Voltage Stability Analysis of Integrated Wind Farms Satish Kumar, Dr. N K Sharma and Dr. Ashwani Kumar W