Increasing quality of power equipment and improved maintenance practices on the Korean transmission grid have helped reduce incidence of line problems. However, the majority of transmission lines in that country pass through forested areas where they are exposed to risk of failure caused by phenomena such as lightning, ice or snow and strong winds. Stability and provision of high quality electricity is deemed highly important by Korean power users and therefore great attention has been paid to countermeasures to deal with lightning which, according to operational data, accounts for up to 70% of sudden transmission line failures. Most transmission towers in Korea are sited in mountainous rocky terrain where tower footing resistance (TFR) is relatively high. To reduce failures due to lightning under these conditions, increased dielectric separation distance has been specified when designing towers. Similarly, engineering work has been done to reduce ground resistance of tower foundations and sub-structures. In addition, double shield wires and, in some cases, even triple shield wires have been installed. Moreover, different types of insulation have been applied on key multi-circuit transmission lines.
However, these methods have not been able to resolve all problem situations. While failures of transmission lines can be eliminated by protective systems, this solution can also lead to reduction in power quality due to instantaneous voltage drops. Especially, given high tower ground resistance, the situation is even more dangerous.
Attend the 2017 INMR WORLD CONGRESS in Barcelona-Sitges this November to hear a paper by LIM Hokyoung of Korea Electric Power Corp. (KEPCO). He will analyze statistics of failures due to lightning both before and after installation of arresters on 154 kV and 345 kV lines and present overall results for the country’s transmission grid.