Externally gapped line arresters - First experience with the new IEC 60099-8 standard and Line study analysis

Surge arresters installed on a transmission line are termed Line Surge Arresters (LSA). These arresters are commonly used to address lightning- related phenomena with the intent to improve the overall reliability of transmission lines. In contrast to the purpose of station arrester installation LSAs task is not the protection of local insulation systems, like bushings, cable terminations, electrical machines etc. LSAs must prevent uncontrolled flashovers of transmission line insulators in order to prevent earth faults and short circuits “inside” of the system component “transmission line”. Thus, Line Surge Arresters can substantially improve the system reliability by reducing the earth, multi-phase and multi-circuit line outage rates. There are many ways to group LSAs, according to system voltage, the major problem on the line, housing types etc. But the most important is the difference between LSA without gap (non gapped line arresters, NGLAs) und externally gapped line arresters, the EGLAs. Both of these types are not new innovations. They have been well known for years. EGLAs have quite a long history, especially in East Asia. But the new IEC 60099-8 [1], which has been finally released at the beginning of the 2011, is the first global and specific EGLA-standard defining the right direction for proper testing and for correct operation coordination of externally gapped line arresters. This is an achievement, because there are significant differences when compared to the gapless arresters used as line surge arresters or standard substation arresters.