In order to meet the target utilization rate of the STATCOM Station that is required by the customer during the warranty period, it is important to minimize the maintenance delay by injecting maintenance resources (spare parts, maintenance equipment, maintenance personnel, etc.) when a fault occurs. Spare parts, in particular, are relatively more expensive than other maintenance resources and require more time to supply. Therefore, it is necessary to always keep the appropriate number of spare parts in order to satisfy the target utilization rate. Recently, as more and more businesses have operated STATCOM stations in Korea and abroad, purchasing and storing of spare parts independently for each station seemed to raise unnecessary costs. There is a need to determine and manage the appropriate spare parts reserves to meet the target utilization rate of each STATCOM station. The purpose of this study is to determine the appropriate amount of spare parts to meet the annual target utilization rate (KEPCO requirements) of each operating site during the warranty period. To do this, we analyze the operation rate of STATCOM Station using BlockSim, a commercial RAM analysis simulation software, and determine the proper retention of the spare part using heuristic technique.