Hyundai Electric & Energy Systems completed the development of a high-voltage circuit breaker (HVCB) for the rating of 170 kV, 50 kA, and 60 Hz using CO2 and C4F7N. The HVCB, part of a Gas Insulated Switchgear (GIS) bay of the same voltage rating, is a three-pole operated in one tank encapsulated design that has fulfilled all the IEC 62271-100 tests. Its performance equals that of SF6 gas counterpart but shows a more than 99% reduction of the Global Warming Potential (GWP) of the gas mixture.