I'm a bit confused as to how this works. I built a flamethrower and a couple of Tesla Arcs and hooked them to generators. However, a bit later the Defense rating for my settlement was back at 0 and when I went into the Workshop to view the defenses they had the Repair option available. I repeatedly repaired them but it only seemed to make a difference for a few seconds. I built another Tesla Arc and it added no Defense. All I could do was Repair it repeatedly. Does anyone understand how this works?