Put power lines underground?

I'm playing Cities Skyline on the PS4 right now.

Question: how can you put the power lines underground, is that possible or is it only possible with a mod?

I think you need such a high-mod. But actually, most of the lines fall away after a while anyway, you build tighter.

I only know that the lines are above ground. But with time, the city hangs together, so you do not need them anymore.