Operational constraints cause an increase in complexity, operating cost, and environmental and socioeconomic impact on electrical systems; operational constraints can be due to power flow, voltage, or frequency deviations. These restrictions force the grid operator to perform unplanned actions. This article identifies the various Alternating Current Flexible Transmission Systems (FACTS) devices with their characteristics, attributes, and implementation methods to lessen operating constraints on isolated and relatively small transmission systems with frequent power flow limit violations and voltage deviations. The case study is carried out in the National Interconnected Electric System (SENI) of the Dominican Republic, where the Fast Stability Voltage Index is used as an indicator to see the impact of the implementation of FACT to mitigate the operational restrictions of the electric system. Simulations are performed in the PowerFactory DIgSILENT software to obtain the results when modeling the interconnected FACTS devices on the transmission lines. The use of FACTS reduces the loadability of transmission lines, which is an essential factor in the emergence of power flow control and voltage constraints in isolated power systems.