International Journal of Engineering Trends and Technology (IJETT) - Volume4 Issue7- July 2013 ISSN: 2231-5381 http://www.ijettjournal.org Page 3040 Impact of SVC and DG on Voltage Stability Constrained Available Transfer Capability A.N.Venkateswarlu 1 , Dr.S.S.Tulasi Ram 2 , Dr.P.Sangameswara Raju 3 1 Associated Professor, Vignan’s Lara Institute of Technology and Science, Guntur, AP, India 2 Professor, Jawaharlal Nehru Technological University, Hyderabad, AP, India 3 Professor, Sri Venkateswara University, Tirupati, AP, India Abstract— The transmission system loadability is mainly dependent on reactive power support in the system. The imbalance between reactive power generation and consumption in the system causes to voltage drooping in the entire system. This phenomenon will further increase under heavily loaded conditions as well as contingency conditions. In order to avoid blackouts due to lack of reactive power support, most of the current power systems are integrating the emerging technologies like Flexible Ac Transmission Systems (FACTS) devices and Distributed Generation (DG) systems. This paper is addressing the impact of Static Var Compensators (SVC) and Distributed Generation (DG) on Available Transfer Capability (ATC). Using repeated power flow (RPF), the Voltage Stability Constrained Available Transfer Capability (VSATC) has been improved. The case studies are performed on IEEE–14 bus test system and the results are validating the proposed approach for stability margin enhancement in real time applications. Keywords— Voltage Stability, VSATC, FACTS, DG, RPF I. INTRODUCTION Recent large-scale power system blackouts due to voltage instability, in the worldwide have given us a “wake-up” call on the need of reactive power reserve in the system. The literature on system blackouts due to voltage instability can be found in [1-3]. The investigation report on 2012 INDIA blackout [4] has been quoted as “In order to avoid frequent outages/opening of lines under over voltages and also providing voltage support under steady state and dynamic conditions, installation of adequate static and dynamic reactive power compensators should be planned” and “Intra-State transmission system needs to be planned and strengthened in a better way to avoid problems of frequent congestion”. This is an indication of the need of the ‘new technologies’ for the integration of the system. The deregulated and competitive energy market systems are also subjected to the increased economic inefficiency due to congestion. The remedial actions for congestion in the network can be found in [5-8]. The literature review has strongly pronounced the need of integration to technical as well as economical benefits of the system with FACTS devices and DG integration to the systems. The impact of FACTS devices on voltage instability in competitive energy market oriented systems can also be addressed in [9]. A novel approach for voltage stability enhancement with adequate corrective actions has been addressed in [10]. The SVC impact can be found on voltage collapse/instability in [11, 17], maximum loadability in [12, 15] and ATC in [13]. The economic schedule in liberalized market environment with DG can be found in [14]. The major advances due to DG systems can also be found in [16]. Keeping all these works in view, this paper has proposed a novel approach for voltage stability enhancement with distributed slack bus (DSB) concept in addition to the FACTS and DG applications at weak buses. This paper is organized as follows: Following the introduction (section I), distributed slack bus concept is explained briefly in Section II in which the evolution of voltage stability constrained available transfer capability is also presented using repeated power approach. The mathematical modelling of SVC and DG is given in Section III. Then, in section IV, different case studies are carried out and simulation results are discussed briefly. Finally, brief conclusions are made in the section V. II. DISTRIBUTED SLACK BUS CONCEPT The scheduling of generators while calculating voltage stability margin should be a considerable issue since the power flow in the network is mainly dependent on residual powers at each bus. The traditional approach to meet excessive load in the