Why high voltage keeps power lines from getting too hot

HostHave you ever been out for a walk on a really quiet day and heard that low, buzzing sizzle coming from those huge power lines overhead? It sounds like they're barely holding it together, like there's so much energy packed in there that it's trying to jump out.

GuestIt really does sound like a lot of strain. And in a way, it is. The big problem we face when moving power across the country is friction. You can think of any wire, even a really good one, like a long, narrow hallway. The electrons are like people trying to run through that hallway, but it's already crowded with atoms that make up the metal of the wire. Every time those electrons bump into an atom, they lose a little bit of energy as heat. We call that resistance. If we just tried to push the amount of power a whole city needs through a normal wire, it would get so hot that it would start to glow red. Eventually, the wire would sag down until it hit the ground, or it might even melt before the energy ever reached your house.

HostSo we have to find a way to get the power there without starting a fire. But if we need a lot of power for a whole city, do we not just have to send a ton of electrons? How do you avoid that friction if the volume has to be high?

GuestWell, we have two different knobs we can turn. Think of it like a garden hose. If you want to move a gallon of water every minute, you can use a giant, wide pipe and let the water just drift through slowly. Or, you can use a tiny nozzle and blast that same gallon of water through at crazy high pressure. In the world of electricity, we have flow—which we call current—and pressure—which we call voltage. Total power is just those two things timesed together. So we have a choice. To move a specific amount of power, we can use a high flow and low pressure approach, or a low flow and high pressure approach.

HostThis seems like a simple choice then. Why do we not just use the big wide pipe and keep the pressure low so it's safer?

GuestBecause of a very mean rule of physics. It turns out that heat isn't a fair player. While total power is just pressure times flow, the heat we lose to the air is tied to the square of the flow. This means if you double the amount of electron flow in a wire, you don't just get twice as much heat. You get four times the heat. If you triple the flow, you get nine times the heat. The heat loss speeds up way faster than the volume of flow does. Because of that, the only way to move energy across a whole state without losing it all as heat is to keep the flow of electrons as low as we possibly can. To make up for that tiny flow, we have to crank the pressure up to hundreds of thousands of volts.

HostOkay, but if the heat loss is that bad, does the high pressure not cause its own kind of trouble? I mean, I can't imagine plugging my phone into a wall that has that much pressure behind it.

GuestYou're right to be worried. We can't use that massive pressure inside a home because it would be way too dangerous. It would arc across rooms and destroy everything you own. So, the whole system relies on a handshake at both ends of the line. We use these machines called transformers that use magnetic fields to trade those values back and forth. At the power plant, a step-up transformer takes the high-flow electricity and trades it for high-pressure electricity for the long journey. Then, once the power reaches your neighborhood, a step-down transformer does the opposite. It trades that dangerous pressure back into a safer, higher-volume flow that your toaster and your computer are designed to handle.

HostSo the only reason we can have a power plant miles and miles away from where we actually live is because of this trade.

GuestThat's the heart of it. Without that trade, we would've to live right next door to the spinning blades and steam of a power plant. The wires would simply burn up before they could carry the energy very far.

HostThose giant power lines aren't just carrying electricity; they're holding back a massive amount of heat by pushing with all that pressure. The sizzle in the air is the sound of that trade-off keeping our world running while keeping the wires from melting into the grass.