40 International Journal of Science and Engineering Investigations vol. 9, issue 107, December 2020 ISSN: 2251-8843 Received on December 24, 2020 Compensation of Low Frequency AC Overhead Transmission Lines Using STATCOM Aamir Saleem 1 , Nasrullah Khan 2 , Anum Kalair 3 1,2 Department of Electrical and Computer Engineering, COMSATS University Islamabad, Pakistan ( 1 studyzone333@gmail.com, 2 nasrullahk@comsats.edu.pk) Abstract- Voltage instability is one of the major issue in HVAC power network operating at 50 Hz frequency due to limited power transfer capability and distance limit. The stable operation of power system must be kept within limits to increase the efficiency of power transmission system. In this research Low Frequency AC (LFAC) transmission system has been proposed as a new power transmission technology to reduce the losses of transmission network and controlling the reactive power using Flexible AC transmission device. A LFAC Transmission lines operates at 16.7Hz frequency for transmission of power from source to load and use two Frequency converters at source and load side. The normal operation of power system depends on the reactive power flowing through the power transmission lines, which can be adjusted by a flexible AC transmission device; Static synchronous compensator. LFAC transmission lines with STATCOM controller improve the Power system voltage stability under various disturbances and enhance the power transmission capability as compare to HVAC transmission. The simulations are done in Matlab Simulink 2017a .The Output of Matlab Simulink model shows that voltage will become Stable and reactive power is compensated for best performance for power system. Keywords-Low Frequency AC (LFAC) Transmission, Power System Analysis, Back to Back Frequency Converter, Static Synchronous Compensator (STATCOM) I. INTRODUCTION Power system is a multi-part system comprise of generators, transformers, transmission lines and diverse types of active and passive loads. Due to the increase in need of electrical power loading of HVAC transmission lines is increases and problem of voltage stability arises. Conventional HVAC transmission system with frequency 50 Hz is commonly used to transmit the power from generating station to consumer using three phase system [1]. The major drawback of HVAC transmission is that due to reactive components of transmission lines large reactive power is generated which raise the losses and reduce the power carrying capacity of power lines. High voltage AC transmission is well proven transmission system with high reliability and easy to transform voltage levels, but the cost of transmission increases noticeably as the distance expands, and stability problem [2]-[3]. So HVAC transmission is suitable for short distance power transmission. Due to limitations of HVAC, High Voltage DC (HVDC) transmission line operating at 0 Hz frequency is suggested as a new substitute technology for power transmission to long distance. HVDC is cost effective to transmit power over long distance. Due to zero frequency of transmission system reactive losses are removed and power carrying capacity of line is increased over long distance but the transmission cost increases for short and medium Distance [4]. In this paper LFAC system working at 16.7 Hz has been proposed as a substitute to HVDC and HVAC for the renewable energy sources and medium distance transmission in terms of reliability, economy and power loss. The idea of LFAC transmission system was first proposed by Funaki in [5].A low Frequency Transmission system reduces the losses of transmission lines, expands the power transfer capability and small amount of reactive power compensation required. Furthermore, HVAC transmission technology can be applied to LFAC framework straightforwardly excluding circuit breakers and transformers. LFAC transmission system combines the best of HVAC and HVDC to transmit power at a frequency, lesser than 50Hz with the advantages of high stability and power transfer capacity [6].The power electronic frequency converters are used in LFAC transmission system to decrease the frequency at generation side and also to convert low frequency to normal HVAC 50 Hz frequency at grid side shown in figure.1. Mainly, the frequency converter must be able regulate the frequency, voltage, reactive and real power, while working in abnormal conditions, While also operating under abnormal conditions [7]-[8]. For Reactive power compensation STATCOM is used along with low frequency transmission lines to increase the controllability, stability and power transmission ability of power system for best performance of existing power network [11]. Fixed synchronous compensator (STATCOM) is an emerging FACTS controller; connected in parallel to transmission lines deliver the necessary reactive power according to the requirement of power system for optimum performance. This device is attached mostly at center of the transmission lines through coupling transformer because voltage variations at center of transmission lines are more. This model uses the voltage source converter and STATCOM