Power system failures such as disturbances in generation, transmission lines, and other electrical equipment, may cause a large imbalance between power system supply and demand. Under certain conditions, disturbances such as in the interconnection network, the electric power system of a subsystem may be separated (island operation) by opening certain bays. To maintain the balance of the system, there is a mechanism called a defense scheme. This mechanism uses a conventional system protection mechanism, therefore the result able to overcome the problems. There is an advance mechanism in overcoming the problems of the electric power system called Adaptive Defense Scheme (ADS). This mechanism is dynamic, which means it able to read the loading and generation of a system in real time. In this study, the ADS PCS-992 Stability Controller implemented in Muarakarang subsystem has a crucial problem. The problem is island operation failure under certain disturbance conditions which causes blackouts in the subsystem. The total load saved with the island operation in scenario 1A is 1222 MW, scenario 1B is 1035 MW, and scenario 2A, 2B, 2C are 938 MW by installing ADS.