Abstract: The consequences of electric power outages impose studies of models that combine representations of the various components such as generators, loads, and networks in the power system. It is clear that the main role of the excitation system is supplying the field winding of the synchronous generator with the dc current for generation, as well as voltage and reactive power control to maintain a constant terminal voltage during the all loading conditions, and synchronous generator stability improvement. But addition of the excitation system with high response causes a large oscillation for the power system, because it is adding a negative damping torque. This makes a shift for the roots of motion equation from the negative part to the positive part. This paper discusses the effect of adding this type of excitation system on synchronous generator stability. A system having a synchronous generator connected to an infinity bus is discussed as case study during a sudden and continuous disturbance, and the simulation is done using MATLAB.

Keywords: Synchronous generator, stability, excitation, damping torque, oscillation.