Full-Scale Tests in Japan on 500-kV Transmission Line Insulation

The authors detail the outdoor switching-surge and impulse tests performed at Shiobara Laboratory to determine the insulation requirements of a 500-kV transmission system for the Tokyo Electric Power Company. Many kinds of insulator strings on single- and double-circuit configurations were thoroughly tested with the proximity effect at the tower window. The test for unbalanced insulation was conducted with the application of dc bias to the two insulator strings. The tests established a practical method for 500-kV line insulation design.