This paper carries out power system transient stability analysis in the presence of renewable energy sources (RESs), including wind farms and solar photovoltaic PV generators. The integration impact of RESs on power system time domain simulation and transient stability were analyzed using the Western System Coordinating Council (WSCC) IEEE 14 bus system. Through this work, we aimed to analyze and improve the transient stability of electrical networks by integrating renewable energy for a reduced Critical Clearing Time (CCT) when a fault appears. Therefore, it is important that the energy system can remain in a state of equilibrium functioning under normal operating conditions and can be able to reach an acceptable state of equilibrium after having been disturbed. For this, we studied the influence of the integration of renewable energy (wind turbines and PV generators) in an electrical network on the transient stability of the system. The standard test network (IEEE 14 buses) was employed for the simulation using PSAT software, which is a dedicated tool used for the static and dynamic analysis and control of electrical networks, and which runs under Matlab environment. Several scenarios that simulate transient stability are carried out in three periods: before, during, and after a three-phase short circuit fault.