Pls provide context. I found some, but it might not be the same. Also, you've managed to cut/sever the sentence in a wrong place: It's about: harmonising grid rules and defining route-by-route electricity interconnection plans It means, IMO, that the interconnection is made from one route to another, or one route after another.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.