Abstract: The accelerated construction of UHV transmission lines by the state brings about, higher insulation performance requirements for the UHV transmission line towers. Based on an investigation of the research and application status of insulation towers, the paper proposes the structure pattern of insulation towers. By taking the insulated cross-arm tower as an example and with a reference to the 500 kV single circuit cup-type tower, the insulation level of the insulated cross-arm towers and the ordinary towers are calculated and the difference of their electrical performances are compared. The impacts of two factors, including reducing the number of insulators and shortening the length of insulated cross-arm, are analyzed on the electric performance of insulation towers. The results show that the towers with insulated cross-arms are superior over the common towers in terms of insulating margin under frequency voltage, switching overvoltage and lightning overvoltage. It can be concluded that number of insulators and the length of the insulated cross-arms may be reduced concurrently to achieve the unification of the safety and economy of insulation towers.

Key words: insulation tower, insulation configuration, the number of insulators, insulated cross-arm, insulation margin