© FEB 2020 | IRE Journals | Volume 3 Issue 8 | ISSN: 2456-8880 IRE 1701946 ICONIC RESEARCH AND ENGINEERING JOURNALS 147 Voltage Stability Improvement of Power Transmission System Using UPFC, a Case Study of 41-Bus Nigerian Power System Modelled In NEPLAN 1, 2 Department of Electrical Engineering Nnamdi Azikiwe University, Awka. 3 Department of Elect Elect Engineering Enugu State University of Science and Technology Abstract- This thesis deals with voltage stability improvement of power transmission system in Nigeria using UPFC (Unified Power Flow Controller). The UPFC model is an application of a power electronics device used to control the power flow and improve voltage stability of a system under static condition. Power flow solutions is developed in NEPLAN using Newton-Raphson iterative method and simulated on the existing 41-bus 330KV Nigerian composite power network. The simulated results were achieved without and with UPFC. The absence of UPFC is the normal state of the Network before intervention. At this state, voltage violations occurred at yola, new haven, makurdi, maiduguri, jos, gombe and damaturu bus stations with percentage bus voltage of 68.34%, 88.66%, 88.51%, 70.89%, 80.17%, 75.27%, 76.38% respectively. With the presence of UPFC in-between gombe and damaturu bus stations, the changes in voltage profile were very significant in yola, new haven, makurdi, maiduguri, jos, gombe and damaturu bus stations with percentage bus voltage of 104.44%, 93.68%, 93.59%, 93.73%, 91.61%, 100.00% and 98.47% respectively. The presence of UPFC in the network reveals a significant reduction in line losses. The active line loss on the network was significantly reduced (from 431.787MW to 278.406MW); about 21% reduction, while reactive line loss came down with 70% reduction (from 6035.725MVAR to 1827.334MVAR), thereby providing additional capacities for the consumers. In this way, the efficiency of the system is enhanced while the prolonged and frequent voltage collapses in the transmission network are minimized. Indexed Terms- Unified Power Flow Controller (UPFC), Voltage Collapse, NEPLAN, Load Flow. I. INTRODUCTION Human population growth matched by industrialization is in league to push electrical energy demand, subjecting the electric power system network configuration and operation to excessive stress. Alleviating this stress for reliable system operation is an enormous challenge. In meeting this challenge, innovations driven by economy, efficiency and chiefly, security for high level of operational and component reliability, have been made in the electric power sector with impacts that are both short and long termed. Flexible Alternating Current Transmission Systems (FACTS) was developed and deployed as a sustainable short term measure to control system operation by ensuring voltage stability and increasing transmission line transfer capacity and it is currently incorporated in the implementation of Electric Power System Smart Grids. FACTS technology offers flexibility and utilization which have the capability of making transmission and distribution of electricity more reliable and controllable. The UPFC is a second generation FACTS controller. It is the most promising device in the FACTS concept. It has the ability to adjust the three control parameters, i.e. the bus voltage, transmission line reactance and phase angle between two buses, either simultaneously or independently at its series connected output while maintaining reactive power support at its shunt connected input to enhance the useable transmission capacities of line and control the power flow. UPFC is also the most versatile FACTS controller that can be used to improve steady state stability, dynamic stability and transient stability. OGHENEOVO IBEBE OBUKOWHO 1 , ENGR. DR. J. C. ONUEGBU 2 , OKWUELU NNAEMEKA 3