说明：  It is well established that fast acting exciter with high gain AVR can contribute to oscillatory instability in power system. This type of instability is characterized by low frequency (0.2 Hz to 2.0 Hz) oscillations. This type of instability can endanger system security and limit power transfer. In this paper Power System Stabilizers (PSS) are used to damp inter area mode of oscillation in two area power system. Simulations are carried out in MATLAB/Simulink environment for the two area system model with and without PSS to anal