As the world's population continues to grow, the demand for electricity is also increasing rapidly. Ensuring the quality of power supply, voltage stability, unity power factor, and minimizing power losses is essential for delivering power to every user end. In order to achieve this, compensation techniques are needed. This project focuses on Serial controllable Flexible AC Transmission Systems (FACTS) devices, such as Controllable Series Compensator (CSC) and Static Synchronous Series Compensator (SSSC), which have a significant impact on the voltage and power stability of an electric power system (EPS). The mathematical derivation of the voltage dependency of CSC and SSSC is extracted for the single-load infinitive-bus model (SLIB). New analytical equations are developed to compare the impact of CSC and SSSC on voltage stability in a five-bus system. The results of the analysis are expected to reveal that CSC has a crucial role to play in enhancing voltage stability, and its impact is greater than that of SSSC when considering equal CSC and SSSC MVA ratings. When it comes to voltage controllability, SSSC (Static synchronous series compensator) is superior to CSC (Controllable Series Compensator), especially in situations where there are having low voltages or having low loads.