Open Breaker Protection of EHV Systems

Although the use of line-entrance lightning arresters provides absolute protection for an open breaker condition, it represents a costly installation. No line entrance protection represents some risk of breaker damage. Line entrance rod gaps offer a compromise between these extremes. This paper discusses the probabilities of failures using these three alternatives and describes a procedure whereby the spacing of the line-entrance gap can be determined. Since this procedure depends on the particular configuration of the gap being used, test data are presented on one particular configuration used on a 345-kV system. Based on these data, recommended gap spacings for 345-and 500-kV systems are developed.