Due to the rapid increase of wind-power generators, it is difficult to operate power systems reliably as a small, isolated system such as the one on Jeju Island, which has about 600MW of peak load in 2009. Therefore, the maximum wind power penetration limit must be determined to guarantee the reliable operation of a power system. In the Jeju system, it is important to devise a cooperative operational scheme between variable generation sources because of the increase in renewable power generators, new combined cycle generators, and HVDC lines connected to the mainland system. An institutional, systematic, technical scheme for reliable operation of power system in Jeju in the long term is essential, considering current policies for renewable energy.