Design and Performance of Unbalanced Insulation in Double-Circuit Transmission Lines

This paper presents a practical design for unbalanced insulation of transmission lines and describes lightning performances on 70- and 140-kV lines. The basic practice of unbalanced insulation is to install one circuit at a higher insulation level than another circuit in order to eliminate double-circuit flashover. The effectiveness of this design was demonstrated by laboratory tests and field experiences. Double-circuit flashover should be considerably decreased when the unbalanced insulation line is properly designed.