The 60MW first phase, equipped with Vestas V112-3.3MW turbines, was commissioned in 2015.
The order includes a ten-year service contract together with online monitoring and preventive maintenance.
Installation and commissioning is planned for the fourth quarter of 2017.
"We have now experienced first-hand the high quality equipment and service that Vestas provides, and look forward to continued cooperation on this next project," said GS Yeongyang director Hwan Kim.