That's so completely impractical I don't know where to begin. There are hundreds of thousands of substations in a modern country, and more transformers on top

That's so completely impractical I don't know where to begin. There are hundreds of thousands of substations in a modern country, and more transformers on top of that. And the bigger substations are huge. An urban 275kV substation could easily be 10 acres in size. "Wires" are also not especially cheap or easy to replace either, even at "low" voltages like under 33kV. It's not a few feet of twin and earth and an h-clip. And a couple of inches of steel will absolutely not stop small drones if they're designed from the ground up to be anti-materiel devices. Anduril are hawking these right now complete with their wierdly gleeful videos, and if they're the only ones in the world then short my secondary and call me a slagpile. And that's ignoring weapons anyway in use like those tungsten filled rockets that just shred everything in the area. They'd go right though both sides of your armoured switchgear.