ABSTRACT
This chapter aims to compare the specifications for extra high voltage and UHV transmission lines so as to ascertain which stress dominates the design. The burden of design innovation rests with lightning; the application of arresters to transmission lines has been initiated and will continue to evolve. The strike distance and insulator string length are each specified in the studies of lightning, switching surges, and contamination. The maximum value of the strike distance and insulator string length as obtained from each of these three study areas is the design specification. The alternate design criterion, the storm outage rate, combines both types of overvoltage, lightning and switching. Comparison of this criterion with the requirements of power frequency voltage illustrates the importance of the latter. Perhaps in the future, the overall design goal of designing the insulation only for the normal power frequency voltage will be achieved.
