International Journal of Engineering Research ISSN:2319-6890)(online),2347-5013(print) Volume No.5, Issue No.9, pp :768-771 1 September 2016 IJER@2016 doi : 10.17950/ijer/v5s9/909 Page 768 Voltage Sag Mitigation Using Static VAR Compensator S. Rashmi 1 , Dr. Venu Yarlagadda 2 Dept. of EEE,VNR Vignana Jyothi Institute of Engineering And Technology, Hyderabad rashmi.savulge@gmail.com 1 ,venuyar@gmail.com 2 Abstract: Voltage sag is defined as a decrease of RMS Voltage from 0.1 to 0.9 per unit (pu) for a duration of 0.5 cycles to 1 minute. Voltage sags are caused by short circuit faults on the system, transformer energizing, overloads and starting of large motors. In this paper voltage sag due to short circuit faults such as Line-to-ground, Line-to-Line, three Phase-to-ground faults are created in the power system network using MATLAB SIMULINK. This project deals with modeling and simulation of static var compensator(FC-TCR) in order to mitigate the voltage sag occurred due to short circuit faults. To implement Automatic control circuit of SVC using MATLAB SIMULINK and observe the simulation results with and without Automatic control circuit. Keywords: Power Quality, Voltage sag, Static Var Compensators(SVC), Fixed Capacitor(FC), Thyristor Controlled Reactor(TCR). I.INTRODUCTION Power Quality related issues are of most concern now a days. Wide use of electronics equipment such as information technology equipment, power electronics equipment viz. adjustable speed drives(ASD), Phase locked loops(PLL), Programmable logic controller (PLC) etc, change the nature of electric loads. These loads are major cause for power quality problems. The most severe power quality problems are voltage sags, interruptions, harmonics and flickering. Voltage sags are considered as one of the most important power quality problems, because they adversely affect the operation of the end user equipment. Voltage sag is defined as decrease in voltage from 0.1 to 0.9 per unit for short duration of time. Voltage sags are usually associated with system faults, energizing of transformers and starting of large induction motors. Figure 1 shows the voltage signal with sag. The faults in the system are more frequent. Voltage Sags are caused due to the faults in the system. A fault in the transmission line affects sensitive equipment up to hundreds of kilometers away from the fault. In this paper voltage sag due to short circuit faults are created using MATLAB/Simulink. Automatic control circuit of SVC is implemented in MATLAB/Simulink in order to mitigate these short circuit faults. Fig 1:Voltage Sag II.LINE FAULT SIMULINK MODEL The line fault model consists of 11KV 50 Hz three phase source block connected to transmission line. Transmission line is connected to a 11KV/415V delta/star transformer, feeding a 200MW resistive load. Both the Instantaneous and RMS waveforms are measured at 11KV and 415V bus. The line fault model developed in MATLAB/simulink is as shown in figure 2. Fig 2:Power System Fault Simulated in MATLAB/ Simulink A fault block is located at 415V bus(bus2). This line fault model is capable of simulating various line faults including single line to ground, double line to ground, line-to-line fault, three phase fault. III.SIMULATION RESULTS WITH OUT SVC Case 1:Line-to-Ground Fault Line-to-Ground Fault is created using three phase fault block. Fault is created in phase A. Fault is considered for a duration of 0.1 seconds(0.1-0.2). A 0.25 seconds Simulation time is set. Figure 3 shows the voltage and current waveforms with sag at bus 2(415V). The voltage of phase A drops, while the voltage of phase B and C remain at its prefault value. Fault due to line-to- ground is unsymmetrical in nature.