In the context of this article, it seems clear to me that GP has the right translation. The other figures say "each" in the same position, and it looks like there was one word that didn't get translated from the figure. The fact that this is all on a .nl domain and the author says this is a translation from a Dutch magazine article lends even more weight to the idea that the author wasn't talking about a particular type of transmission line.
i'm pretty confident both of you are correct. I know some Dutch and spotted that as well.
I did find it an interesting overlap that in the field of transmission lines (electricity lines specifically) there is literally a conductor size names elk :)
