![]() ![]() The well-coordinated gap and varistor of an EGLA work in conjunction to turn the arrester on and off. 2: Protective characteristics of NGLAs versus EGLAs.ĬLICK TO ENLARGE CLICK TO ENLARGE Mode of Operation of EGLAs It also demonstrates that while EGLAs work well to eliminate insulator flashover, they cannot be expected to protect sensitive transformer insulation.įig. 2 contrasts the front-of-wave characteristics of EGLAs and NGLAs. Because it is being used only to eliminate insulator flashover, the front-of-wave sparkover of this type of arrester is not relevant and not an application issue. It is important to emphasize that the EGLA is being referred to in this article is a line arrester designed to be applied to eliminate insulator flashovers and not to protect sensitive oil-insulated equipment such as transformers. This type of EGLA is also an arrester recognized by the IEC community and has its own specific test standard. It is characterized by a larger gap section and smaller tolerance in gap dimension than the EGLAs that are discussed below. For systems above 230 kV, the IEC type EGLA does not need larger varistors to handle the energy associated with switching surges. This is achieved simply by increasing the gap spacing to a level that will not sparkover in the presence of switching surges. The IEC type EGLA differs in that it is designed to only protect lines from lightning. 1: Typical configuration of EGLA mounted on transmission line (in this case 115 kV).ĬLICK TO ENLARGE Surge protection with EGLA type arrester on lines in Japan 1, for example, has been applied in Japan, Europe and Mexico as an IEC certified device for many years.įig. It is these unique and repeatable characteristics that make the externally gapped MOV arrester the ultimate in distribution and transmission line protection. When highly non-linear metal oxide varistors (MOV) are connected in series with the age-old air gap, the combination takes on unique features not available in earlier designs of gapped arresters. In the presence of a surge, they sparkover and protect equipment on the line. It is therefore no accident that arrester designs over the years continue to make use of it and that there are currently millions of arresters in service that use the air gap to hold off line voltage until a surge appears. The reason for this long history is that air gaps have an excellent capability to withstand voltage and predictable breakdown at a very specific voltage level. The EGLA concept dates back to the earliest stages of surge protection on power lines, although in subsequent years it became an internal gap that performed the same function. This edited 2015 contribution by independent arrester expert, Jonathan Woodworth, discussed the basics of the externally gapped line arrester (EGLA) in order to increase knowledge and confidence in applying them for line protection. Nevertheless, it seems clear that another approach towards the goal of lightning proofing a line is necessary in order to eliminate all possible concerns by line designers. The NGLA has demonstrated that it is highly reliable and failures are comparatively few. The dominant design of transmission line arrester used over the past 20 years – the non-gapped type (NGLA) – has demonstrated that such concerns are generally not valid. Perhaps the most cited reasons for this are that the arresters themselves are seen as a potential factor in reduced reliability and could also require a lot of maintenance. However, for a number of reasons, most engineers involved in overhead line design have still not adopted this guaranteed strategy to improve lightning performance. Indeed, based on IEEE 1410 and IEEE 1243, installation of arresters on every phase of every tower of a shielded line will ensure no lightning induced insulator flashovers – essentially a line that is ‘lightning proof’. The goal of a lightning proof transmission line has been attainable since the early 1990s when the first polymeric-housed transmission line arresters became available. ![]()
0 Comments
Leave a Reply. |