The target for South Korea's domestic energy consumption is to increase the proportion of the total energy consumption supplied by renewable energy to 11% by 2030. Increasing renewable energy generation has become a natural trend, thereby making it an essential factor to be considered in research for the development of a smart grid. The power system of Jeju Island is connected to the mainland (the Korean Peninsula) through HVDC #1, with another line, HVDC #2, presently under construction. The purpose of the first HVDC construction was essentially to supply a portion of the power supply to the Jeju area. However, if the construction of HVDC #2 is completed, the role of the Jeju HVDC system in the Jeju power system will be changed significantly. If flexibility through the operation of an HVDC system is increased, more wind farms can be built on Jeju Island. In addition, depending on the operation of HVDC #1 and #2, the stability of the Jeju power system will be changed greatly. In this paper, the operation of the HVDC lines and its impacts are analyzed.