Operation of large-scale power systems became more complicated in these days, especially when stability, safety and economic criteria for power system operation should be fulfilled. Stability of power system is becoming a one of the most severe problems in power system operation, mainly due to unpredictable circular power flows from renewable sources. Excitation systems of power generators can have positive influence to power system stability, especially by damping power oscillations. This can be provided by use of excitation system with power system stabilizer (PSS) included. Main goal of this paper is research of different models of excitation systems with various types of PSS, and their influence to transient stability of power system. This also includes investigation of different combinations of excitation system settings, focused on finding proper settings for improving transient stability of power system. For these purposes, an IEEE 39-bus power system model was used, which has been built using PSLF software. Paper shows different methods, which can be used for finding proper excitation system settings.