Establishing Voltage Operation Standards for 70 kV Transmission Voltage

Preparations for grid integration of large-scale renewable energy sources, such as wind and solar farms, are being made worldwide. These sources require 154 kV transmission networks. However, such integration faces many practical difficulties, such as the economic viability of constructing transmission and distribution facilities against the potential revenue of the renewable energy and construction delays due to public complaints. Thus, the Korea Electric Power Corporation (KEPCO) introduced a 70 kV transmission voltage, an intermediate voltage between 22.9 and 154 kV, in August 2017. The 70 kV transmission and distribution equipment plan was included in the 10th Long-Term Transmission and Substation Facility Plan announced in April 2023 and is scheduled for full-scale implementation in October 2024. Voltage operation standards similar to those for existing transmission voltages of ≥ 154 kV are necessary for stable operation at 70 kV. Currently, voltage regulation targets and voltage maintenance standards are specified for 154, 345, and 765 kV in Articles 5 and 6 of the “Standard for maintaining reliability and electrical quality of power system.” Therefore, this study developed an analysis method and established voltage operation standards (drafts) for 70 kV through simulations under various conditions. The developed 70 kV voltage operation standards were presented to the Power System Reliability Council to be reflected in the Power System Reliability Notice. On April 25, 2023, these standards were included in Notice No. 2023-65 of the Ministry of Trade, Industry, and Energy, or the “Power System Reliability and Electrical Quality Maintenance Standards” for 70 kV voltage operation.