The voltage stability of any power system is the ability of the system to maintain voltage within acceptable operational limits after being subjected to major disturbance. Various challenges can hinder voltage stability such as the high penetration levels of renewable energy resources (RES) due to their dynamics that differ from conventional generation. Also, dynamic loading, especially in industrial areas which can cause short-term voltage instability. Additionally, it's worth noting the routine behavior of voltage concerning loading conditions. During off-peak periods, voltage tends to rise, while during peak periods, it tends to drop. For instance, Oman power system is undergoing an expansion through the (Rabt) interconnection project that aims to connect the main interconnected system (northern region) with Dhofar system (southern region) through 400𝑘𝑉 system. Moreover, the power contribution from RES is expected to be around 20% by the year 2030 following the goal of Oman vision 2040, which is reflecting in reality through implementing RE projects such as Ibri solar and Manah solar independent power producers (IPPs). Despite the numerous benefits of the network interconnection between the north and the south and the RE projects implementation, they can disturb the voltage profile and stability of the system. Currently, conventional voltage control techniques are used to maintain the transmission system voltage profile in Oman such as tap changers and shunt inductors. The issue with the mentioned techniques is that they have slow response and limited functionalities. To overcome these issues, STATCOM, a type of FACTS device, is used to improve voltage profile due to its fast dynamic response and bidirectional flow of reactive power. This thesis proposes a particle swarm optimization (PSO) to optimally allocate STATCOMs in Oman power network of the year 2027 using DIgSILENT, with the objective of minimizing voltage deviation, real and reactive power losses. The optimal location of the STATCOM is found to be in Mahout 400𝑘𝑉 BB, Manah solar 400𝑘𝑉 BB, Ibri solar 3 400𝑘𝑉 BB, Misfah 400𝑘𝑉 BB, New Rustaq 400𝑘𝑉 BB, and Al Jefnin 400𝑘𝑉 BB. Moreover, the reactive power reserve (RPR) from solar power plants is also maximized in steady state model using PSO. The grid response in the presence of STATCOMs and PRP is evaluated during short-circuit faults and loss of generation events. The STATCOMs, in Manah solar 400𝑘𝑉 BB, Ibri solar 3 400𝑘𝑉 BB, Misfah 400𝑘𝑉, New Rustaq 400𝑘𝑉 and Al Jefnin 400𝑘𝑉 , effectively enhance the voltage profile in the areas near the fault during the large disturbances. The tests also indicate that higher STATCOM 𝑀𝑣𝑎𝑟 ratings are required as the severity of the disturbance increases. In addition, the contribution of the reactive power reserve from Manah and Ibri solar power plants prevent the voltage collapse at Manah solar 400𝑘𝑉 BB and the neighboring stations. Furthermore, the results show that an improved voltage profile and faster recovery can be achieved during three-phase fault events when the reactive power reserve from Manah and Ibri Solar, along with the STATCOMs at those corresponding buses, work together.