International Journal of Engineering and Techniques - Volume 4 Issue 3, May - June 2018 ISSN: 2395-1303 http://www.ijetjournal.org Page 405 Mitigation of SSR in Series Compensated Power System Using a FACTS based Subsynchronous Damping Controller Mr.Gyan prakash Rai 1 ,Sneha Tibude 2 ,Radha Raman shaha 3 1 (M.Tech(IVth Sem IPS),AGPCE, RTMNU, Nagpur, India) 2 (Asst. Prof. EE Dept. AGPCE, RTMNU, Nagpur, India) 3 (HOD EE Dept. AGPCE, RTMNU, Nagpur, India) I. INTRODUCTION Due to re-structuring of the power market, use of new technologies and controls, aging of the power system infrastructures, operating in highly stressed conditions, stability of the power system becomes increasingly important. Currently, voltage stability, frequency stability, transient stability, inter -area oscillations are of great concern. As the interconnected power system becomes more complicated, more accurate system modeling is required to analyze various stability issues [11]. Capacitors are connected in series with the line conductors to compensate for the inductive reactance of the line. It reduces the transfer reactance between the buses with which the line is connected. Series compensation increases the maximum power that can be transmitted, & lowers the effective reactive power (I 2 X) loss. There are many methods proposed in literature for SSR mitigation [2][3][4][5][10][11] etc. This paper proposes that SSR can be mitigated with a proper gating pulse to TCSC. In order to detect this SSR; sub synchronous damping controller (SSDC) is designed in MATLAB SIMULINK software. SSDC observes these SSR phenomena and directs an appropriate signal to the TCSC automatically. Series capacitors can create an opposite interaction between the series compensated electrical system and the multi spring- mass mechanical system of the turbine-generators. This effect is called sub synchronous resonance (SSR). An IEEE committee report (1985) has defined SSR as “sub synchronous resonance is an electric power system condition where the electric network exchanges energy with a turbine generator at one or more of the natural frequencies of the combined system below the synchronous frequency of the system”. II. TYPES OF SSR INTERACTION There are three aspects of SSR which are best known as Induction Generator Effect, Torsional Interaction Effect and Transient Torque Effect. A. Induction Generator Effect This is purely an electrical phenomena. Three phase current at a frequency known as sub synchronous frequency can result due to fault or a nearby network disturbance. When the sub synchronous frequency currents flow through the generator RESEARCH ARTICLE OPEN ACCESS Abstract: Due to the continuous increase in the demand of electricity, we are left with two options; either to increase the installed generating capacity in proportion with the rise in demand or to use some other methods along with former; keeping the stability intact. In this regard series capacitive compensation comes at our rescue. Series capacitive compensation virtually reduces the length of transmission line by minimizing the line inductive reactance and enhances the power transmission capacity. However, in 1971 it was learned in one of the USA’s Mohave thermal power plant that series capacitors can create an adverse interaction between the series compensated electrical system and the spring-mass mechanical system of the turbine-generators. This effect is called sub synchronous resonance (SSR). Due to this torsional oscillation, the rotor shaft faces severe fatigue and can be damaged if a proper solution is not adopted to mitigate SSR. There are many methods proposed in literature for SSR mitigation.However this paper proposes that SSR can be mitigated with a proper gating pulse to TCSC. A Subsynchronous damping controller(SSDC) is proposed to be modeled for detecting SSR phenomena. SSDC observes this SSR phenomenon and directs an appropriate signal to the TCSC automatically. Thyristor controlled series capacitor (TCSC) which improves transmission line capability, can also be used in damping out Sub synchronous resonance (SSR) efficiently.All results are validated using simulations in MATLAB. Keywords: Sub synchronous damping controller (SSDC), Torsional Interaction, sub synchronous resonance(SSR), TCSC.