This paper proposes a transient stability analysis of interconnected multi-machine power system using ETAP (Electrical Transient Analysis Program)-software. During the operation of existing power systems, the network is gradually approaching their transmission limits, and these raise many stability problems that might cause severe consequences. Once the system is stressed, many undesirable phenomena arise, and these can cause damage to different parts of the system. The mathematical models developed and tested in this paper describe the dynamics of the multi-machine power system, including the interaction between aggregates and components. The study involved analyzes an IEEE 39-bus system that has 10-generators connected. This was done by applying different contingency scenarios and configurations. The ETAP software was used to carry out Transient Stability Analysis, Load Flow Analysis, and Optimal Power Flow Analysis. The results have shown that, during contingency analysis, the generators connected to the grid experienced changes in power input, and those which were closer to the fault location had a more significant power deviation. Numerical simulation has been compiled with all the components such as generators, transmission lines, transformers, and devices to achieve these studies. The stability of the system has been observed base on the simulation graphs.